WO2011136769A1

WO2011136769A1 - Method and apparatus for transmit power control in wireless networks based on monitoring multiple factors

Info

Publication number: WO2011136769A1
Application number: PCT/US2010/032875
Authority: WO
Inventors: Hang Liu; Hariharasudhan Viswanathan; Ishan Mandrekar; Mingquan Wu; Ramkumar Perumanam; Saurabh Mathur
Original assignee: Thomson Licensing
Priority date: 2010-04-29
Filing date: 2010-04-29
Publication date: 2011-11-03
Also published as: TW201220899A

Abstract

Described herein are a method and apparatus to determine transmit power including operating in a first mode until one of a first timer expires and a first mode switch message is received, operating in a second mode until one of a second timer expires and a second mode switch message is received, wherein in the first mode a transmit power is determined responsive to one of transmit power level instructions received from an associated access point and a maximum transmit power if no instructions have been received from the associated access point, and further wherein in the second mode the transmit power is a maximum of the transmit power level instructions received from the associated access point and a transmit power determined responsive to a frame transmission loss rate.

Description

METHOD AND APPARATUS FOR TRANSMIT POWER CONTROL IN WIRELESS NETWORKS BASED ON MONITORING MULTIPLE FACTORS

FIELD OF THE INVENTION The present invention relates to wireless networks and, in particular, to adjusting link transmit power control levels based on the results of monitoring multiple factors.

BACKGROUND OF THE INVENTION

In multicast and broadcast applications, data are transmitted from a server to multiple receivers over wired and/or wireless networks. A multicast system as used herein is a system in which a server transmits the same data to multiple receivers simultaneously, where the receivers form a subset of all the receivers up to and including all of the receivers. A broadcast system is a system in which a server transmits the same data to all of the receivers simultaneously. That is, a multicast system by definition can include a broadcast system.

A station can be any wireless device including but not limited to a computer, a laptop, a notebook computer, a personal digital assistant (PDA), a dual mode smart phone, user device, a client device, a mobile terminal and a mobile device. A station can be transmitter, a receiver or a transceiver. Data communicated between devices can be text, audio, video or multimedia or any other kind of data. Data is usually formatted into packets and or frames. That is, frames and packets are formats into which the data is packaged for transmission convenience. In the past several years, there has been a rapid growth of wireless network deployment in school campuses, shopping malls, hotels, airports, apartment buildings, and in homes. Emerging technology such as IEEE 802.11η radios make delivering multimedia contents over wireless networks possible. This increased deployment drives the technology deeper into our daily lives. Since the number of available wireless channels is limited, these channels have to be used or shared by multiple access points (APs) or base stations (BSs). In a dense deployment environment, for example in a multi-dwelling unit deployment with many APs in an apartment building or hotel, APs tend to interfere with each other. This impacts the throughput of overall wireless networks and thus, the quality of service for multimedia streaming applications.

A wireless (mobile) device associates and communicates only with its nearby AP. By properly controlling the transmit power of an AP and its associated mobile devices, the communications between the AP and the mobile devices can operate successfully, and the transmitted signal(s) by the AP or the mobile devices generate no or less interference with the communications between other APs and their associated mobile devices in the neighborhood (vicinity, surrounding area). The reuse distance of the same channel can be reduced. That is, the other AP and its associated mobile devices within a smaller (lesser) proximity (distance) can reuse the same channel to transmit simultaneously without interference. This principle allows many devices to communicate with their associated APs at the same time in a given area while using only a limited number of wireless channels (links).

The lower the transmit power, the less (smaller) spatial interval (distance) is needed to reuse the same channel without interference. Thus, the overall network capacity in a dense deployment is increased. For example, in a given area, with a cellular network, a smaller cell size with lower transmit power leads to the higher overall network capacity. The goal of controlling the transmit power of a wireless device (AP or mobile device) is that the device uses minimum transmit power while meeting the requirements for throughput and packet loss rate. Transmit power control helps reduce interference with other devices, improves channel reuse, and eventually increases the overall capacity of wireless networks. In addition, transmit power control helps conserve energy and improves battery life of mobile devices.

A transmitter (wireless device, station) can use low power to transmit data signals when the receiver is close to the transmitter and has good channel conditions. However, when the distance between a transmitter and a receiver is relatively large and the channel conditions are not good, the transmitter needs to increase power to transmit data in order to ensure the data are received correctly by the receiver and to maintain the link throughput. The challenge is how a transmitter determines and adapts (if the channel conditions change) it's transmit power to optimally transmit data signals to a receiver. In one prior art study, a transmit power control algorithm was proposed to reduce interference and increase capacity in IEEE 802.11 wireless networks. It adapted the transmit power based on the packet loss rate. However, it needed certain samples to obtain an accurate packet loss rate, leading to a long measurement time and slow response to a channel condition changes. In addition, it is difficult to accurately adapt the transmit power based only upon the packet loss rate. In another prior art study, the transmit power control was performed only based on received signal strength. This approach may cause hidden node and asymmetric channel access problems.

SUMMARY OF THE INVENTION The present invention is directed to an adaptive algorithm for per-link transmit power control (TPC) in wireless networks, especially for IEEE 802.11 wireless local area networks (WLANs) in a densely deployed environment. It opportunistically reduces the transmission power to mitigate interference, improve channel reuse and overall network capacity while meeting the requirements for throughput and frame (packet) loss rate. Unlike previous transmit power control solutions, the method of the present invention leverages both the Received Signal Strength Indicator (RSSI) measurements as well as Frame Loss Rate (FLR) measurements to determine the optimal transmit power required for transmitting to a station. In particular, the method of the present invention tackles the classic hidden terminal problem and asymmetric channel access problem that are usually exacerbated by transmit power changes. No unrealistic assumptions are made in the design of the method and the solution does not need any modification to the existing media access control protocol. The TPC method of the present invention is complementary to any link rate adaptation algorithm since it can mitigate any adverse impact of transmit power change to the rate control. These attributes makes the method of the present invention readily and incrementally deployable. Described herein is a transmit power control method that optimizes the transmitter power in order to reduce the interference, improve channel reuse and overall network capacity as well as conserving energy while meeting the requirements for throughput and packet (frame) loss rate. The method of the present invention cognitively adjusts the transmit power based on active monitoring of several parameters (factors) including received signal strength at the receiver and the frame (packet) loss rate.

Described herein are a method and apparatus to determine transmit power including operating in a first mode until one of a first timer expires and a first mode switch message is received, operating in a second mode until one of a second timer expires and a second mode switch message is received, wherein in the first mode a transmit power is determined responsive to one of transmit power level instructions received from an associated access point and a maximum transmit power if no instructions have been received from the associated access point, and further wherein in the second mode the transmit power is a maximum of the transmit power level instructions received from the associated access point and a transmit power determined responsive to a frame transmission loss rate. Also described herein are a method and apparatus for responding to a transmit power measurement report request including receiving the transmit power measurement request, measuring a received signal strength, estimating a downlink margin and sending a transmit power measure report responsive to the transmit power measurement request including the measured received signal strength and the estimated downlink margin.

Also described herein are a method and apparatus for determining a transmit power including operating in a first mode until one of a first timer expires and a first mode switch message is received, and operating in a second mode until one of a second timer expires and a second mode switch message is received, and wherein in the first mode a downlink transmit power is one of a maximum transmit power and a downlink transmit power determined responsive to a received signal strength, and further wherein in the second mode the downlink transmit power is determined responsive to one of a frame transmission loss rate and the received signal strength, and further wherein in the second mode one of an aggregate downlink transmit power for all associated clients and a per link downlink transmit power is determined for each associated client.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. The drawings include the following figures briefly described below:

Fig. la shows an exemplary deployment scenario. Fig. lb shows another deployment scenario in which content is delivered over a wireless home network.

Fig. lc summarizes the interaction between two transmitters (Tx) - receiver (Rx) links.

Fig. 2a is a flowchart of the transmit power control (TPC) measurement operation from the perspective of the AP. Fig. 2b is a flowchart of the TPC measurement operation from the perspective of the client.

Fig. 3a and Fig. 3b together are a flowchart of the procedure of the AP (aggregate) transmit power control (TPC) (operational mode 2), in accordance with an exemplary embodiment of the present invention. Fig. 3b and Fig. 3c together are a flowchart of the procedure of the AP transmit power control (TPC) (operational mode 1), using the information of the link quality (received signal strength and link margin) report from the client, in accordance with an exemplary embodiment of the present invention.

Fig. 3d is a flowchart of the AP transmit power control procedure operating in mode 1 and mode 2 in a time sharing fashion in accordance with an exemplary embodiment of the present invention.

Fig. 4a and Fig. 4b together are a flowchart of AP transmit power control (TPC) procedure (operational mode 2), when the AP has the information on per link frame (packet) loss rate and the link quality (received signal strength and link quality) in accordance with an exemplary embodiment of the present invention. Fig. 5a is a flowchart of client transmit power control (TPC) procedure (operational mode 2), in accordance with an exemplary embodiment of the present invention.

Fig. 5b is a flowchart of client transmit power control procedure operating in mode 1, in accordance with an exemplary embodiment of the present invention. Fig. 5c is a flowchart of client transmit power control procedure operating in mode 1 and mode 2 in a time sharing fashion in accordance with an exemplary embodiment of the present invention.

Fig. 6 is a flowchart of client transmit power control (TPC) procedure (operational mode 2), when the client maintains a window of uplink transmission status in accordance with an exemplary embodiment of the present invention.

Fig. 7 is a block diagram of an exemplary implementation of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described using an IEEE 802.11 wireless local area network (WLAN). However, the present invention can be used in other wireless networks.

In the past few years, there has been a rapid increase in Wireless Local Area Network (WLAN) deployment in school campuses, shopping malls, hotels, airports, apartment buildings and homes. Emerging technology such as IEEE 802.11η, which is becoming increasingly affordable, making delivering multimedia content over wireless networks possible and this drives the technology further into our daily lives. As the number of available wireless channels is limited (3 non-overlapping channels in 2.4GHz unlicensed spectrum and up to 24 non- overlapping channels in 5GHz unlicensed spectrum), the available channels have to be used or shared by multiple WLANs including Access Points (APs) and numerous STAtions (STAs). For example, in a Multi-Dwelling Unit (MDU) like an apartment building or hotel with densely deployed WLANs, the transmissions in different cells tend to interfere with each other. This will adversely impact the aggregate wireless network throughput and, thus, the quality of the experience for applications such as multimedia streaming. Fig. la shows an exemplary deployment scenario. A satellite TV-IP (internet protocol) gateway, a Gigabit Ethernet backbone and IEEE 802.11 APs are used to distribute High Definition (HD) video to wireless Set Top Boxes (STBs) in a building, such as a hotel or apartment building. Multiple APs and STAs in the vicinity result in heavy inter-cell interference. Off-the-shelf APs come with default factory settings that end users rarely change. Hence, there is a need for an automatic operation parameter adaptation method such as transmit power control to adapt to the operating environment and optimize overall network performance.

Fig. lb shows another deployment scenario in which content is delivered over a wireless home network. In this case, the gateway receives content (data including but not limited to audio, video and multimedia data) via the internet or any other source. The gateway has channel selection and power control processes and methods. The methods include the ability to perform link measurements in order to effect transmit power control and channel selection. The gateway may be a master set top box.

Transmit power control (TPC) aims to use the minimum transmit power possible to achieve successful transmission while meeting a data rate requirement. The design of an efficient TPC algorithm is challenging since it has to take different network topologies, deployment scenarios, and interference effects of multiple APs in the area into account, such as hidden nodes and channel access asymmetry between two links operating on the same channel.

To explain these effects, Fig. lc summarizes the interaction between two transmitters (Tx) - receiver (Rx) links. In Fig.lc, a solid arrow -> from Tx to Rx indicates that the Rx is in the communication range of Tx. A dashed arrow ( >) from Tx2 to Txl indicates that Txl can carrier sense Tx2 (i.e., Txl is in Tx2's interference range). When the TPC method of the present invention is applied to a link it can result in any of the scenarios presented in Fig.lc. Scenario (a) represents the best case where the application of TPC has resulted in complete spatial reuse, i.e. Txl can transmit to Rxl while Tx2 transmits to Rx2. Scenario (b) represents no gain as far as spatial reuse is concerned but it is a wise choice to operate in the lowest possible transmit power if the target data rate can be sustained. The links Txl -Rxl and Tx2-Rx2 share the same channel. Scenario (c) represents the channel access asymmetry. Txl -> Rxl link is starved since Tx2 cannot sense Txl's transmissions and always perceives a clear channel and transmits to Rx2. Txl then always senses the channel is busy and cannot transmit. Scenario (d) also results in channel access asymmetry but the problem manifests itself in the form of packet losses at Rxl because Tx2 transmits during Txl's transmission. Scenario (e) represents the classic hidden terminal problem. The transmitters Txl and Tx2 are not in each other's carrier sensing range, but the receiver Rxl is in the interference range of both Txl and Tx2. While Tx2 is transmitting, Txl may sense a clear channel and transmit to Rxl. The transmissions from Txl and Tx2 collide at Rxl and Rxl cannot receive the packet(s) correctly. In Scenario (f), Txl and Tx2 are hidden nodes to both Rxl and Rx2, and then packet losses may occur at Rxl and Rx2 due to simultaneous transmissions by both Txl and Tx2. The prior art has failed to account for scenarios (c), (d), (e) and (f) since the methods of the prior art rely on only one trigger, either the received signal strength (RSSI) measurements or frame (packet) loss rate (FLR) measurements of frame loss rate (FLR) measurement. As a matter of fact, those previous transmit power control methods tended to aggravate the hidden node and asymmetric channel access problems in scenarios (c), (d), (e) and (f). If the control power solution is only based on RSSI measurements, the hidden terminal problem and asymmetric channel access problems cannot be diagnosed and there would be performance degradation due to frame (packet) losses. Solutions based on frame (packet) loss rate measurements alone are non-trivial as the minimum number of samples required to accurately deduce the channel conditions is a critical design choice and also frame (packet) loss rate measurements take a great deal of time to converge.

In the present invention, an adaptive per-link TPC solution based on both RSSI measurements and FLR measurements is described. The method of the present invention handles all the above scenarios and solves the hidden node and asymmetric channel access issues. It quickly converges to the optimal transmit power at which to operate. In addition, the TPC method of the present invention is complementary to any rate control algorithm since it can mitigate any adverse impact of transmit power change to the rate control.

In the present invention, to determine the transmit power, an AP requests each of its associated wireless clients (stations (STAs), mobile devices) to measure its received signal strength, reporting the received signal strength (RSSI) and/or its estimated link margin as well as the client's current transmit power. The link margin is the difference between the received (available) channel signal-to-noise ratio (SNR) or RSSI and the channel SNR or RSSI required for reliable communications (meeting the packet loss rate and link transmission data rate requirements). The AP periodically sends transmit power control (TPC) measurement request message to its associated clients in multicast or to each of its associated clients in unicast. In addition, once a new client is associated, the AP issues a request to the new client. The requested client receiving such a request measures its received signal power, estimates the link margin for the downlink, and reports the received signal strength and/or the estimated link margin and its transmit power to the AP by sending a TPC measurement report message. Here the downlink is the transmission link from the AP to the client, and the uplink is the transmission link from the client to the AP. The link margin estimation is described below. The AP and clients also periodically measure the packet (frame) transmission loss on the downlink and uplink respectively.

Based on the received signal strength or link margin measurement reported by the clients (stations) and/or the frame (packet) loss measurement, the AP determines its desired downlink transmit power. The transmit power will meet the throughput and packet loss rate requirements while generating the least interference to other devices in the neighborhood. The AP also determines the transmit power of its associated clients and instructs the clients to use the determined power for uplink transmission. Fig. 2a is a flowchart of the transmit power control (TPC) measurement operation from the perspective of the AP. At the 205 the TPC measurement timer Tm is set. It should be noted that for all timers used herein in the exemplary embodiments that either up timers or down timer could be used. At 210 a test is performed to determine if the timer has expired. If the timer has not expired then at 215 a test is performed to determine if a new client (station) has associated with the AP. If a new client has not associated with the AP then processing proceeds to 210. If a new client has associated with the AP then at 220 a TPC measurement request is sent (forwarded) to the newly associated client. Processing then proceeds to 210. If the timer has expired then at 225 the AP sends TPC measurement requests to all of its associated clients. It is assumed that the AP has associated clients. Fig. 2b is a flowchart of the TPC measurement operation from the perspective of the client. At 230 the client receives a TPC measurement request. This measurement request may be received because the timer in the AP expired or because this client is newly associated with an AP. At 235 the client (station, terminal) measures its downlink received signal strength. At 240 the client (station, terminal) estimates its downlink margin. At 245 the client sends the results (downlink margin and downlink received signal strength) to the AP with which it is associated. It is assumed that the client has already associated with an AP.

The TPC method of the present invention is used to control the transmit power to be as low as possible while maintaining a target data rate Ri and a target packet (frame) loss rate. In an exemplary embodiment, the target data rate is set to be the highest data rate supported by both the transmitter and receiver. The reason for this is that the airtime will be the smallest to transmit a frame using the highest data rate so that the time that a transmitter interferes other devices is minimized. The target packet loss rate can be set to be the same values as that for determining the receiver sensitivity for the target data rate, or a value small enough to ensure the quality of service. The receiver sensitivity is the minimum received signal power (strength) required for a targeted link data rate and a targeted packet loss rate. It is possible to select other values of the target data rate and/or the target packet loss rate in different ways.

In order to guarantee the target data rate for a client i, the targeted downlink received power P_ri is equal to t arg etP_ri = S_ti + D (1) where ¾ is the receiver sensitivity for the target data rate and D is the margin above the receiver sensitivity to compensate for the channel condition fluctuation. D is a configurable parameter. Note that the units in the above equation and the following equations, unless specified, are decibels.

If the path loss is L„ the targeted transmit power is etP_ti = L_{i +} S_ti + D = I_{i +} D (2) where /,· is defined as /, = L_i + S_ti .

The link margin Mi(j) in the j^'th TPC report from client i (receiver, station) is

M_i {j) = P_ri {j) - S_ti (3)

Note that P_ri(j) is the j^'th sample value of the received signal power measured at the receiver, that is, the value of the received signal power measured when the j^'th TPC request is received. The j^'th sample of /,· is then

/,· (j) = U (j) + S_ti = P_ti (j) - P_ri (j) + S_ti = P_ti (j) -M (j) (4) where P_ti(j) is the actual transmit power of the j^'th TPC request.

It is possible that the values of target data rate can be selected by the AP or station in different ways. The target data rate can be determined by the AP that notifies the stations. One method to notify the station regarding the targeted data rate is to include the target data rate value in a control message such as the TPC request. Another method is to transmit the TPC request at the target data rate. If the target data rate is the rate at which the TPC request is sent, the value of link margin M (that is, the receiver sensitivity to calculate M in eq (3)) is the one for the data rate at which the TPC request is transmitted. The value of M (that is a function of the receiver sensitivity) should be calculated according to the targeted data rate (that is, the receiver sensitivity to calculate M is the receiver sensitivity for the targeted data rate). In the alternative, the target data rate can be configured, e.g. it can be set to be the maximum data rate supported by both the transmitter and the receiver. A linear estimation method is used by the present invention to calculate /, avelt (j) = ax avelt (j - 1) + (1 - a)I_t (j) (5)

AI_i (j) =\ I_i (j) - aveI_i (j) \ (6) var /,· (j) = βχ var /,· (j - 1) + (1 - β)Μ_ί (j) (7) where avel_l ( j) represents the smoothed link quality l_i (path loss plus receiver sensitivity) after the jth TPC measurement report from receiver i, i.e. the estimator of the average, var 7, (7) is the smoothed mean deviation of link quality /, . Δ/, ^') =1 /,· ( ) - ave/,- ^') I is the difference between the jth measured value just obtained and the current estimation of the average. Both avel^ j) and var /,· ( ) are used to calculate the estimated value of /, . The estimated value of /, is equal to

I_i (j) = avel_i (j) + q x var l_i (j) (8) where a , β , and q are configurable parameters.

The new desired transmit power for client / then equals

When the AP transmit data packets (frames) to client i or a destination i, it uses the transmit power equal to P_ti = I_t + D . That is, the transmit power is controlled per client or per destination address or per wireless link. Different transmit power values are used for different clients (receivers or destination addresses).

In an alternative embodiment of the present invention, the AP does not change it's transmit power per client. The AP determines its transmit power based on the worst client. It selects a transmit power value to ensure that the downlink received signal strength at its worst client is high enough for this client to successfully decode the received frames that are transmitted at the target data rate. If multiple clients are associated with an AP, the AP's transmit power is

P, = max{P_ft. } (10)

i

When an AP boots up, the initial value of its transmit power is the maximum supported (permitted) power, that is,

P, (0) = max P (11)

When a new client powers up and associates with the AP, the AP uses the maximum supported (permitted) transmit power for this client as its initial value. P_ri (0) = max P (12)

Furthermore, when a new client associates with the AP, the AP issues a TPC request for this new client after its association process is complete (see Fig. 2a).

To react to sudden deterioration of link (channel) quality or link (channel) disconnection, for example, if a client moved away or there was increased frame (packet) loss caused by receiver side interference, the AP also monitors the loss count (rate) of the packets (frames) that it transmitted to its clients and adjusts the transmit power based on the packet (frame) loss rate.

In one exemplary embodiment, the AP periodically determines its frame (packet) loss rate (FLR) for its downlink transmissions to a client. If the FLR(fc) for a client k during a time interval (say x seconds) is greater than a high threshold HFT(fc), i.e. FLR(fc) > HFT(fc), the AP increases its transmit power to the client by a value P_d. If the current AP transmit power for the transmission from the AP to client k is P_tk, the new transmit power for the AP transmission to client k is the smaller value of P_tk + P_d and the maximum transmit power supported (permitted) by AP, max P, i.e. the new transmit power is P_tk = min{ P_tk + P_d, max PJ (13)

Since the change to the transmit power at the AP is made to account for sudden deterioration of the link quality, the AP continues to monitor the FLR(fc) periodically and adjusts the transmit power at the AP as described above until the frame (packet) loss rate is below the low threshold LFT(fc), i.e. FLR(fc) < LFT(fc). If the FLR(fc) is less than LFT(fc) for a particular time interval (for example, y seconds), the AP decreases its transmit power to client k by the value P_d and the new transmit power for AP transmission to client k is the maximum of P_tk - P_d and the minimum transmit power supported by AP, min P, i.e. the new transmit power is

Ptk = max{ Ptk - Pd, min PJ (14) and the AP continues to monitor FLR(fc). As a precautionary mechanism to avoid repetitive switching between two power levels (FLR(fc) < LFT(fc) and FLR(fc) > HFT(fc)) in the continued presence of interference or client movement or channel condition fluctuation, a transition probability (less than 1) may be assigned for transition from a higher power level to a lower power level when FLR(fc) < LFT(fc). HFT(fc), LFT(fc), P^, x and y are configurable design parameters. It is possible that the AP does not record the frame (packet) loss rate statistics for each of its associated client individually. In an alternative embodiment, the AP does not change its transmit power to a client responsive to the frame (packet) loss rate for the transmission to this particular client. The AP determines its transmit power based on the aggregate FLR.

The AP periodically determines its frame (packet) loss rate (FLR) for its downlink transmissions to all of its associated clients. If the FLR during a time interval (for example, x seconds) is greater than a high threshold HFT, i.e. FLR > HFT, the AP increases its transmit power to each of its associated client by a value P_d. If the current AP transmit power for the transmission from the AP to client k is P_&, the new transmit power for the AP transmission to client k is the smaller value of P_tk + P_d and the maximum transmit power supported (permitted) by AP, max P, i.e. new transmit power is

P_tk = min{ P_tk + P_d, max PJ (13a)

Since the change to the transmit power at the AP is made to account for sudden deterioration of the link quality, the AP continues to monitor the FLR periodically and adjusts the transmit power at the AP as mentioned above until the packet (frame) loss rate is below the low threshold LFT, i.e. FLR < LFT. If the FLR is less than LFT for a particular time interval (for example, y seconds), the AP decreases its transmit power to each of its associated clients by the value P_d and the new transmit power for AP transmission to client k is the greater of P_tk - P_d and the minimum transmit power supported by AP, min P, i.e. the new transmit power

Ptk = max{ Ptk - Pd, min PJ (14a) The AP continues to monitor FLR. As a precautionary mechanism, to avoid repetitive switching between two power levels (one with FLR < LFT and the other with FLR > HFT) in the continued presence of interference or client movement or channel condition fluctuation, a transition probability (less than 1) may be assigned for transition from a higher power level to a lower power level when FLR<LFT. HFT, LFT P_d, x and y are the configurable design parameters.

An exemplary embodiment supports two modes of operation at the AP. In mode 1 the AP operates at the transmit power determined by the measurement reports of received signal strength (RSSI) and link margin measurements obtained from each of its individual clients only in a TPC power adjustment interval (timer Tt_>), that is

Model _ P_t (k) = P_& , (15) where P_tk = I_k + D is determined using equation (9). If the link quality suddenly deteriorates and the RSSI and link margin measurement reports from a client k are lost for a particular time interval (expiration timer T_e), the AP uses the maximum transmit power, max P for transmission to this client.

In mode 2 the AP periodically monitors the FLR for each of its clients individually (using adjustment timer T_a) , FLR(fc) for client k, or the aggregate frame loss rate (FLR) for its downlink transmissions to all of its associated clients. The AP uses the greater of transmission powers determined by the measurement reports from each of its clients and the power calculated as a result of FLR measurement, that is,

Mode2_P_t(£) = max{ P_tk , P_tk}, (16) where P_tk = I_k + D is determined by equation (9) and Ptk is determined by equations (13) and

(14) if the packet loss for each client (station) is monitored or equations (13a) and (14a) if the aggregate packet loss for all the clients (stations) is monitored.

An AP may use one of the modes to determine its transmit power. Alternatively, an AP may operate in the two modes in a time-sharing fashion. That is, an AP switches to mode 2 after it operates in mode 1 for a time period Tl . An AP switches from mode 1 to mode 2 after it operates in mode 1 for a time period Tl or receives a model to mode 2 switch message from one of its neighboring APs. When an AP switches from mode 1 to mode 2, the AP broadcasts (multicasts, propagates) a mode switch message to indicate its mode change to its neighboring APs and its associated clients to advise them that it is now operating in mode 2 . The AP also updates (resets) its timer T2. Similarly, an AP switches to mode 1 and multicast (broadcast, propagate) a mode switch message to its neighbors after it operates in mode 2 for a time period T2 or receives a mode 2 to mode 1 switch message from one of its neighboring APs. An AP updates (resets) its timer Tl and broadcasts (multicasts, propagates) the mode switch message to its neighboring APs and its associated clients to advise them that it is now operating in mode 1. In this way, the operating mode of the APs in a neighborhood (vicinity) is a loosely synchronized.

By operating in the two modes in a time-sharing fashion, the method of the present invention can effectively handle hidden node and asymmetric channel access issues as described below.

In a first example, consider API operating in mode 1 TPC and using a low transmit power based only on link quality (received signal strength and link margin) measurement reports from the clients, but another AP, AP2 does not perform power control at all and always uses high power. AP2 is referred to as the non-cooperative interferer. AP2 interferes with its transmissions, but API does not interfere with AP2's transmissions, which results in asymmetric channel access condition. API is hidden with respect to AP2. By switching to mode 2, API increases its transmit power if its frame (packet) loss rate is high due to either collision or unfairness of asymmetric channel bandwidth sharing. If the share of the channel capacity (bandwidth) obtained by API is unfair and less than its traffic load due to the low transmit power API uses, its frame (packet) loss rate will increase. In mode 2, API increases its transmit power to get its fair share of channel bandwidth.

In a second example, packet (frame) loss may be caused by either congestion or link transmission errors. When the packet loss is due to link transmission errors, it is desirable to increase the transmit power. On the other hand, if the packet loss is due to congestion, increasing the transmit power will not help and may aggravate the congestion problem because of the interference. For example, consider two pairs of APs and stations (AP -> STA1 and AP2 -> STA2). Both the pairs operate in mode 2 TPC, and they use low transmission power according to the TPC and hence do not interfere with each other. If AP2 increases its transmission power to react to sudden movement of STA2, it causes the transmission power of API to increase because of frame (packet) losses at STA1 due to packet interference and collisions due to interference from AP2. The two pairs start interfering with each other and even worse, the aggregate traffic load may be heavy, leading to congestion. If only TPC mode 2 is used, the transmission power of API and AP2 will not decrease due to continued interference with each other and packet loss even if STA2 returns closer to AP2. By switching to mode 1 synchronously, the two APs will decrease their respective transmit power based on the link quality measurement reports from their associated clients. Hence, the APs and their associated clients (stations) will not interfere with each other anymore. If the traffic on each AP is less than the channel capacity, the congestion condition is removed. Also, later on when the APs switch to mode 2 from mode 1, the APs will not interfere with each other anymore, the packet loss rate remains low and they will not increase their transmission power.

Fig. 3a and Fig. 3b together are a flowchart of the procedure of the AP (aggregate) transmit power control (TPC) (operational mode 2), in accordance with an exemplary embodiment of the present invention. Figs. 3a and 3b operate as independent threads or processes but data generated (created) or updated by either operational thread or process is available to and may be used by the other operational thread or process. At 305 the AP sets two frame (packet) loss rate thresholds (HFT and LFT) and sets the frame (packet) loss rate measurement timers (Up_timer and Down_timer). Both of the FLR measurement timers are timers that count down in this exemplary embodiment but they could just as easily and readily be timers that count up. At 310 a test is performed to determine if a TPC report has been received. If a TPC report has been received then at 315 the AP estimates the uplink path (link, channel) loss for client k. At 320 the AP stores the downlink margin (received in the TPC report) and the uplink path (link, channel) loss in a database (in memory, a buffer or any other storage media) for client k. At 325 the AP estimates the desired (target) downlink transmit power for transmission to client k. At 330 the AP estimates the target (desired) uplink transmit power for transmissions from client k. This is used by the operational thread depicted in Fig. 3b (395) and is set for client k and sent to client k associated with this AP. Processing proceeds to 310. If a TPC report has not been received then at 335 the AP determines the frame (packet) transmission loss rate for downlink transmissions (FLR). A test is performed at 340 to determine if the FLR is greater than or equal to the high frame loss rate threshold (HFT). If the FLR is less than the high frame loss rate threshold (HFT) then at 360 a test is performed to determine if the FLR is less than or equal to the low frame loss rate threshold (LFT). If the FLR is less than or equal to the low frame loss rate threshold (LFT) then at 365 the Up_timer is reset. A test is performed at 370 to determine if the Down_timer has expired. If the Down_timer has not expired, then processing proceeds to 310. If the Down_timer has expired then at 375 the AP estimates the transmit power for transmission to each client k to be P_{PLR ¾} = max ¾ - P min PJ. The AP also sets an update flag and resets both the Up_timer and the Down_timer. Processing then proceeds to 310. If the FLR is greater than the low frame loss rate threshold (LFT) then at 380 the AP resets both the Up_timer and the Down_timer. Processing proceeds to 310. If the FLR is greater than or equal to the high frame loss rate threshold (HFT) then at 345 the AP resets the Down_timer. At 350 a test is performed to determine if the Up_timer has expired. If the Up_timer has not expired, then processing proceeds to 310. If the Up_timer has expired then at 355 the AP estimates the transmit power for transmission to each client k to be PP R k = min {P_tk + Pd, max PJ. The AP also sets an update flag and resets both the Up_timer and the Down_timer. Processing then proceeds to 310. The above described method is used in conjunction with Fig. 3b.

Referring again to Fig. 3b, at 385 the AP sets the TPC power adjustment timer T_a. At 390 a test is performed to determine if the TPC power adjustment timer T_a has expired or if the update flag is set. If either the TPC adjustment timer T_a has expired or if the update flag is not set then processing proceeds to 390. If the TPC adjustment timer T_a has expired or if the update flag is set then at 395 the AP sets the downlink transmit power for transmission to each client k to P& = max (PRSSI k, PPLR kj and sends the estimated uplink transmit power to client k and resets the update flag. At 301 a test is performed to determine if the TPC power adjustment timer T_a has expired. If the TPC power adjustment timer T_a has expired then processing proceeds to 390. If the TPC power adjustment timer T_a has not expired then processing proceeds to 385.

Fig. 3b and 3c together are a flowchart of the procedure of the AP transmit power control (TPC) (operational mode 1), using the information of the link quality (received signal strength and link margin) report from the client, in accordance with an exemplary embodiment of the present invention. Figs. 3b and 3c operate as independent threads or processes but data generated (created) or updated by either operational thread or process is available to and may be used by the other operational thread or process. At 306 the AP sets a TPC power adjustment timer T and also sets a TPC expiration (expiry) timer T_e. At 311 a test is performed to determine if a TPC report has been received. If a TPC report has been received then at 316 the AP estimates the uplink path (link, channel) loss for client k. At 321 the AP stores the downlink margin (received in the TPC report) and the uplink path (link, channel) loss in a database (in memory, a buffer or any other storage media) for client k. At 326 the AP estimates the desired (target) downlink transmit power for transmission to client k. At 331 the AP estimates the target (desired) uplink transmit power for transmissions from client k. This is used by the operational thread depicted in Fig. 3b (395) and is sent to client k associated with this AP. Processing proceeds to 311. If a TPC report has not been received then at 336 a test is performed to determine if the TPC power adjustment timer T has expired and if all TPC reports from client k have been lost for the expiration (expiry) time period T_e (interval). If the TPC power adjustment timer T_b has expired and if all TPC reports from client k have been lost for the expiration (expiry) time period T_e (interval) then at 341 the AP sets the transmit power for transmission to client k to P_& = max P and resets the expiration (expiry) timer. If the TPC power adjustment timer T_b has not expired or if all TPC reports from client k have not been lost for the expiration (expiry) time period T_e (interval) then at 346 a test is performed to determine if TPC power adjustment timer T_b has expired. If TPC power adjustment timer T_b has not expired then processing proceeds to 311. If TPC power adjustment timer T_b has expired then at 351 the AP sets the transmit power for transmission to client k to P_tk = Pussi_k and resets TPC power adjustment timer T_b.

Fig 3d is a flowchart of the AP transmit power control procedure operating in mode 1 and mode 2 in a time sharing fashion in accordance with an exemplary embodiment of the present invention. At 356 the AP is assumed to be operating in mode 1 and the AP sets the mode 1 operational timer Tl . At 361 a test is performed to determine if timer Tl has expired or the AP has received a mode 1 to mode 2 switch message (from a neighboring AP). If either timer Tl has expired or the AP has received a mode 1 to mode 2 switch message (from a neighboring AP) then at 366 the AP switches to TPC mode 2 operation and sets the TPC mode 2 operational timer T2 and propagates (broadcasts, multicasts) a mode 1 to mode 2 switch message to its neighboring APs and its associated clients. A test is performed at 371 to determine if timer T2 has expired or the AP has received a mode 2 to mode 1 switch message. If neither timer T2 has expired nor has the AP received a mode 2 to mode 1 switch message then at 376 a test is performed to determine if the AP has received a mode 1 to mode 2 switch message. If the AP has not received a mode 1 to mode 2 switch message, then processing proceeds to 371. If the AP has received a mode 1 to mode 2 switch message, then at 381 the AP resets the TPC mode 2 operational timer T2. Processing then proceeds to 371. If either timer T2 has expired or the AP has received a mode 2 to mode 1 switch message, then at 396 the AP switches to TPC mode 1 operation and sets TPC mode 1 operational timer Tl and propagates (broadcasts, multicasts) a mode 2 to mode 1 switch message to its neighboring APs and its associated clients. Processing proceeds to 361. If neither timer Tl has expired nor the AP has received a mode 1 to mode 2 switch message (from a neighboring AP) then at 386 a test is performed to determine if the AP has received a mode 2 to mode 1 switch message. If the AP has not received a mode 2 to mode 1 switch message, then processing proceeds to 361. If the AP has received a mode 2 to mode 1 switch message, then at 391 the AP resets the TPC mode 1 operational timer Tl. Processing then proceeds to 361.

In another exemplary embodiment, in the mode 2 operation, the AP performs the frame (packet) loss rate measurement for its transmission to each of its associated client individually, i.e. the AP maintains the information on per link frame (packet) loss rate. Specifically, to measure the packet loss rate, the AP maintains a window of transmission status for N_kt frames that were most recently transmitted to its associated clients k (k=l, 2, ...). If for client k, the frame (packet) loss rate FLR_k = N_ke I N_kt > HFT , the AP adjusts its transmit power for its transmission to client k, where N_ke is the number of lost or retransmitted frames out of the last N frames transmitted to client k by the AP. If the current AP transmit power to client k is P_tk, the new transmit power for the AP transmission to client k is the smaller value of P_tk + P_d, where P_d is a configurable design parameter, and the maximum power supported (permitted) by AP, max P, i.e.

Ptk = min{ Ptk + Pd, max PJ. (17)

Since the change to the transmit power at the AP is made to account for sudden deterioration of the link quality, the AP continues to monitor the FL¾ periodically with a timer T_c and adjusts the transmit power as mentioned above until the frame (packet) loss rate is below the low threshold LFT, i.e. FLR_k < LFT. If the FLR_k is less than LFT the AP decreases its transmit power to client k by the value Pd and the new transmit power for AP transmission to client k is the greater of P_& - Pd and the minimum transmit power supported by AP, min P, i.e. new transmit power is

P_tk = max{ P_tk - Pd, min PJ (18)

The AP continues to monitor FLR_k.

As a precautionary mechanism to avoid repetitive switching between two power levels (FLR_k < LFT and FLR_k > HFT) in the continuous presence of interference or client movement, a transition probability (less than 1) may be assigned for transition from a higher power level to a lower power level when FLR_k < LFT. Nk_t , HFT, LFT, Pd and y are all configurable design parameters.

Fig. 4a and Fig. 4b together are a flowchart of AP transmit power control (TPC) procedure (operational mode 2), when the AP has the information on per link frame (packet) loss rate and the link quality (received signal strength and link quality) in accordance with an exemplary embodiment of the present invention. Figs. 4a and 4b operate as independent threads or processes but data generated (created) or updated by either operational thread or process is available to and may be used by the other operational thread or process. At 405 the AP sets two frame (packet) loss rate thresholds (HFT and LFT) and sets the frame (packet) transmission loss rate (FLRk) and sets the frame (packet) loss rate measurement window Nk_t , and initializes two counters Nt=0, Nk_e= for a client k. It should be noted that while in this exemplary embodiment that the counters are up counters, they could just as easily be down counters. At 410 a test is performed to determine if a TPC report has been received. If a TPC report has been received then at 415 the AP estimates the uplink path (link, channel) loss for client k. At 420 the AP stores the downlink margin (received in the TPC report) and the uplink path (link, channel) loss in a database (in memory, a buffer or any other storage media) for client k. At 425 the AP estimates the desired (target) downlink transmit power for transmission to client k. At 430 the AP estimates the target (desired) uplink transmit power for transmissions from client k. This is used by the operational thread depicted in Fig. 4b (480) and is sent to client k associated with this AP. Processing proceeds to 410. If a TPC report has not been received then at 435 a test is performed to determine if there is a frame (packet) to transmit to client k. If there is not a frame (packet) to transmit to client k, then processing proceeds to 410. If there is a frame (packet) to transmit to client k, then at 440 the AP updates the transmission status for client k, adjusts Nk and adjusts Nke if the transmission to client k failed. At 445 a test is performed to determine if Nk is greater than or equal to Nkt- If Nk is less than Nkt then processing proceeds to 410. If Nk is greater than or equal to Nkt then at 447 the AP determines the frame (packet) transmission loss rate for client k FLR_k = Nke Nkt- At 450 a test is performed to determine if the frame (packet) transmission loss rate is greater than or equal to the high frame transmission loss rate threshold (HFT). If the frame (packet) transmission loss rate is less than the high frame transmission loss rate threshold (HFT) then at 455 a test is performed to determine if the frame (packet) transmission loss rate is less than or equal to the low frame transmission loss rate threshold (LFT). If the frame (packet) transmission loss rate is greater than the low frame transmission loss rate threshold (LFT) then at 458, the AP resets both Nke and Nk and processing proceeds to 410. If the frame (packet) transmission loss rate is less than or equal to the low frame transmission loss rate threshold (LFT) then at 460 the AP estimates the transmit power for transmission to each client k to be PPLR k = max (Ptk - Pd, min PJ. The AP also sets an update flag and resets both Nke and Nk. Processing then proceeds to 410. If the frame (packet) transmission loss rate is greater than or equal to the high frame transmission loss rate threshold (HFT) then at 465 the AP estimates the transmit power for transmission to each client k to be PPLR ¾ = min {P_tk + P_d, max PJ. The AP also sets an update flag and resets both Nke and Nk. The above described method is used in conjunction with Fig. 4b.

Referring again to Fig. 4b, at 470 the AP sets the TPC power adjustment timer T_c. At 475 a test is performed to determine if the TPC power adjustment timer T_c has expired or if the update flag is set. If either the TPC adjustment timer T_c has expired or if the update flag is not set then processing proceeds to 475. If the TPC adjustment timer T_c has expired or if the update flag is set, then at 480 the AP sets the downlink transmit power for transmission to each client k to P_tk = max (Pussi_h PPLR _kl and sends the estimated uplink transmit power to client k and resets the update flag. At 485 a test is performed to determine if the TPC power adjustment timer T_c has expired. If the TPC power adjustment timer T_c has expired then processing proceeds to 475. If the TPC power adjustment timer T_c has not expired then processing proceeds to 470.

The AP can also control the transmit power of its associated clients. The target data rate and the target packet loss rate for uplink may be different from those for the downlink. As an exemplary embodiment, the highest supported data rate is used as the target uplink data rate, and the target packet loss rate is set to be the same value used to determine the receiver sensitivity for the target data rate, or a value small enough to ensure the quality of service. It is possible to select other values of the target data rate and/or the target packet loss rate in different ways.

Note that the quality of uplink and downlink may not be symmetric. For a client i, to guarantee the target uplink data rate without packet loss, the targeted received power P_uri at the AP is equal to t a g etP_uri = S_uri + U (19) where S_uti is the AP receiving sensitivity for the target data rate and U is the uplink margin over the receiver sensitivity. U is a configurable design parameter. If the path loss for the uplink is L_ui, the targeted client transmit power is then t arg etP_uti = L_ui + S_uti + U (20)

The AP can estimate the path loss L_ui based on the actual client transmit power P_uti in the TPC report and the actual received power P_uri at the AP.

L_uti ⁼ ^uti ^~ Puri (21) Once again, a linear estimation method is used to calculate the uplink path loss L_ui. aveLut (j) = OX aveL_ui (j - 1) + (1 - o)L_ui (j) (22) AL_ui (j) =\ L_ui (j) - aveL_ui (j) \ (23) var L_ui (j) = cox var L_ui (j - 1) + (1 - co)AL_ui (j) (24) The estimated value of L_Mi from the j^'th TPC report is equal to i (J) = we i (J) + ^c X var L_ui (j) (25) where σ , a , and c are the configurable design parameters. The new uplink transmit power is equal to P_uti = L_ui + S_uti + U (26)

The AP can instruct the client to use the new transmit power by sending a message to the client. The message can be sent in a beacon or some other frames (e.g. management or control frames).

In an alternative embodiment, the AP may want all the clients to use the same transmit power for uplink. The AP then determines the uplink transmit power based on the worst client. If multiple clients are associated with an AP, the uplink transmit power is

^_f = max{P_Hfi } (27)

l

When a client boots up, its initial power can be the maximum supported power by this client P_u-sup_Ported- Alternatively, it can be the maximum allowed (permitted) transmit power specified in the AP beacons or probe responses P_u-aiiowed, or the smaller value of the maximum supported power and the maximum allowed transmit power, that is, pu_t (0) = min{max P_u__{SUV ported} , max P_u__allowed } (28)

The new client (just booting up) will use this maximum power for association and transmission until it successfully receives the AP's instruction to change its transmit power. When a new client associates with an AP, the AP issues a TPC request for this new client after its association process. After receiving the TPC report from this client, the AP determines and adapts the uplink and downlink transmit power. The updated uplink transmit power is sent to the client using a management (control) message or advertised in the beacons to instruct the client to use the updated (new) transmit power value for uplink transmission. To react to sudden deterioration of link quality or link loss, for example, if a client moved away or frame (packet) loss caused by receiver side interference at the AP, the client also monitors its frame (packet) loss rate and adjusts the transmit power based on the packet loss rate.

In one exemplary embodiment, a client periodically determines its frame (packet) loss rate (FLRc) for its uplink transmissions to its associated AP. If the FLRc during a time interval (for example, x seconds) is greater than a threshold HFTc, FLRc > HFTc, the client adjusts its uplink transmit power. If the current uplink transmit power for client k is P_utk, the new transmit power for the client k uplink transmission to the AP is the lesser of P_utk+P_ud and the allowed (supported, permitted) maximum uplink power of the client, max P_uk, i.e. new transmit power is P_utk = min{ P_utk+Pud, max P_uk J (29)

Since the change to the transmit power at the client is made to account for sudden deterioration of the link quality, the client continues to monitor the FLRc periodically and adjusts its transmit power as described above until the frame (packet) loss rate is below the threshold LFTc, i.e. FLRc < LFTc. If the FLRc is less than LFTc for a particular time interval (for example, y seconds), the client decreases its uplink transmit power by the value P_U(1 and the new transmit power for uplink transmission at client k is the greater value of P_utk - P_ud and the minimum transmit power supported by client, min P_uk, i.e. new transmit power is

P_utk = max{ P_utk - Pud, min P_uk I (30) and the client continues to monitor FLRc. As a precautionary mechanism to avoid repetitive switching between two power levels one with FLRc < LFTc and the other with FLRc > HFTc, a transition probability (less than 1) may be assigned for transition from a higher power level to a lower power level when FLR^ < LFTc. HFTc, LFTc, P_ud, x and y are the configurable design tuning parameters.

Similar to the AP, the client can support two modes of operation. In the first mode the client chooses to operate at the transmit power determined for it by the AP that is based on the received signal strength measurement only. That is,

Model _ P_ut {k) = P_utk , (31) where P_utk is the transmit power that the AP determines for the station k to use according to the received signal strength measurement, i.e. equation (26) if per link transmit power control is used or (27) if per cell transmit power control is used. In mode 1, if the downlink quality suddenly deteriorates and the messages containing the power setting decision from the AP are lost for a particular time interval, the client uses the allowed (supported, permitted) maximum transmit power, max P_uk for its uplink transmission.

In the second mode the client periodically monitors the FLRc for all its uplink transmissions and uses the maximum of transmission powers determined by the power setting decision by the AP and the power calculated as a result of FLRc measurement for its uplink transmissions. That is, the transmit power in mode 2 is set to be

Mode2_P k) = max{ P_u& , P_utkJ, (32) where P_utk is determined by equation (26) or (27) and P_utk is determined by equations (29) and (30)

The client may use one of the modes to determine the transmit power. Alternatively the client may operate in the two modes in a time-sharing fashion. That is, the client switches to mode 2 after it operates in mode 1 for a time period T3 or it receives a mode 1 to mode 2 switch message from the AP. Similarly, it switches to mode 1 after it operates in mode 2 for a time period T4 or receives a mode 2 to mode 1 switch message from the AP. If the client receives a mode 1 to mode 2 switch message from the AP and it is already operating in mode 2, it reset its timer T4. Similarly, if the client receives a mode 2 to mode 1 switch message from the AP and it is already operating in mode 1, it reset its timer T3.

Fig. 5a is a flowchart of client transmit power control (TPC) procedure (operational mode 2), in accordance with an exemplary embodiment of the present invention. At 505 this client sets two frame (packet) loss rate thresholds (HFTc and LFTc) and sets the frame (packet) loss rate measurement timers (Up_timer and Down_timer). Both of the FLR measurement timers are timers that count down in this exemplary embodiment but they could just as easily and readily be timers that count up. At 510 a test is performed to determine if a TPC setting has been received from this client's associated AP. If a TPC setting has been received then at 515 this client determines the uplink transmit power (PRSSI uk) based on the instructions from this client's associated AP and sets the uplink transmission power to P_utk = max{ PRSSI _uk, PPLR _UIJ- Processing then proceeds to 510. If a TPC setting has not been received then at 520 this client determines the frame (packet) transmission loss rate for uplink transmissions (FLRc). A test is performed at 525 to determine if the FLRc is greater than or equal to the high frame loss rate threshold (HFT). If the FLRc is less than the high frame loss rate threshold (HFT) then at 530 a test is performed to determine if the FLRc is less than or equal to the low frame loss rate threshold (LFT). If the FLRc is greater than the low frame loss rate threshold (LFT) then at 535 this client resets both the Up_timer and the Down_timer. Processing then proceeds to 510. If the FLRc is less than or equal to the low frame loss rate threshold (LFT) then at 540 the Up_timer is reset. A test is performed at 545 to determine if the Down_timer has expired. If the Down_timer has not expired, then processing proceeds to 510. If the Down_timer has expired then at 550 this client estimates the uplink transmit power for transmission to the AP to be PP R _uk = max {P_Mk - Pd, min Puki- The client also resets both the Up_timer and the Down_timer. At 555 this client sets the transmit uplink transmission power to P_utk = max{ PRSSI uk, PPLR _UIJ- If the FLRc is greater than or equal to the high frame loss rate threshold (HFT) then at 560 this client resets the Up_timer. A test is performed at 565 to determine if the Up_timer has expired. If the Up_timer has not expired, then processing proceeds to 510. If the Up_timer has expired then at 570 this client estimates the uplink transmit power for transmission to its associated AP to be P_PLR = min {P_utk + Pd, max P_ukJ- This client also resets both the Up_timer and the Down_timer. Processing then proceeds to 555. The above described method is used in conjunction with Fig. 5b.

Fig. 5b is a flowchart of the client transmit power control procedure operating in mode 1, in accordance with an exemplary embodiment of the present invention. At 575 this client sets a TPC expiration (expiry) timer T_ue. At 580 a test is performed to determine if this client has received a TPC setting from its associated AP. If this client has received a TPC setting from its associated AP then at 585 this client determines the uplink transmit power (PRSSI uk) based on the instructions this client received from its associated AP. At 590 this client sets the transmit power for its uplink transmissions (to its associated AP) to P_utk = PRSSI uk- Processing then proceeds to 580. If this client has not received a TPC setting from its associated AP then at 501 a test is performed to determine if the TPC expiration (expiry) timer has expired and if all TPC settings from this client's associated AP have been lost for the TPC expiration (expiry) time period (for the duration of the TPC expiration (expiry) timer T_ue). If the TPC expiration (expiry) timer has not expired or if all TPC settings from this client's associated AP have not been lost for the TPC expiration (expiry) time period (for the duration of the TPC expiration (expiry) timer T_ue) then processing proceeds to 580. If the TPC expiration (expiry) timer has expired and if all TPC settings from this client's associated AP have been lost for the TPC expiration (expiry) time period (for the duration of the TPC expiration (expiry) timer T_ue) then at 506 this client sets the transmit power for uplink transmission (to its associated AP) to P_utk = max P_uk- Processing then proceeds to 580.

Fig. 5c is a flowchart of the client transmit power control procedure operating in mode 1 and mode 2 in a time sharing fashion in accordance with an exemplary embodiment of the present invention. At 511 this client is assumed to be operating in mode 1 and this client sets the mode 1 operational timer T3. At 516 a test is performed to determine if timer T3 has expired or this client has received a mode 1 to mode 2 switch message (from its associated AP). If either timer T3 has expired or the AP has received a mode 1 to mode 2 switch message (from its associated AP) then at 521 this client switches to TPC mode 2 operation and sets the TPC mode 2 operational timer T4 and sends a mode 1 to mode 2 switch message to its neighboring APs and its associated clients. A test is performed at 526 to determine if timer T4 has expired or this client has received a mode 2 to mode 1 switch message. If neither timer T4 has expired nor has this client received a mode 2 to mode 1 switch message then at 531 a test is performed to determine if this client has received a mode 1 to mode 2 switch message. If this client has not received a mode 1 to mode 2 switch message, then processing proceeds to 526. If the AP has received a mode 1 to mode 2 switch message, then at 536 this client resets the TPC mode 2 operational timer T4. Processing then proceeds to 526. If either timer T4 has expired or this client has received a mode 2 to mode 1 switch message, then at 551 this client switches to TPC mode 1 operation and sets TPC mode 1 operational timer T4 and propagates (broadcasts, multicasts) a mode 2 to mode 1 switch message to its neighboring APs and its associated clients. Processing proceeds to 516. If neither timer T3 has expired nor the AP has received a mode 1 to mode 2 switch message (from its associated AP) then at 541 a test is performed to determine if this client has received a mode 2 to mode 1 switch message. If this client has not received a mode 2 to mode 1 switch message, then processing proceeds to 516. If this client has received a mode 2 to mode 1 switch message, then at 546 this client resets the TPC mode 1 operational timer T3. Processing then proceeds to 516. In another exemplary embodiment, in mode 2, to compute the frame (packet) loss rate, the client k maintains a window of transmission status for N_uk_t frames that were most recently transmitted to its associated AP. If the uplink frame loss rate for client k,

FLRc_k = N_uke I N _ukt > HFTc (33) the client k adjusts its uplink transmit power, where N_uk_e is the number of lost or retransmitted frames out of the last N_uk_t frames transmitted from client k to the AP. If the current uplink transmit power for client k is P_utk, the new transmit power for the client k uplink transmission to the AP is the lesser of P_utk+Pud and the allowed (supported, permitted) maximum uplink power of the client, max P_uk, i.e.

P_utk = min{ P_Mk+Pud, max P_uk I (34) Since the change to the transmit power at the client is made to account for sudden deterioration of the link quality, the client continues to monitor the FLR¾ periodically and adjusts its transmit power as described above until the frame (packet) loss rate is below the low threshold LFTc, i.e. FLRc_k < LFTc. If the FLRc_k is less than LFTc, the client decreases its uplink transmit power by the value P_ud and the new transmit power for uplink transmission at client k is the greater value of P_utk - Pud and the supported minimum transmit power of the client, min P_uh i.e. new transmit power is

Putk = max{ P_Mk - Pud, min P_uk } (35) and the client (station, node, peer) continues to monitor FLRc_k. As a precautionary mechanism to avoid repetitive switching between two power levels (FLRc_k <HFTc and FLRc_k > LFTc), a value of transition probability (less than 1) may be assigned for transition from a higher power level to a lower power level when FLR_k < LFTc. HFTc, LFTc, P_ud and y are the configurable design parameters. Fig. 6 is a flowchart of client transmit power control (TPC) procedure (operational mode 2), when the client maintains a window of uplink transmission status in accordance with an exemplary embodiment of the present invention. At 605 this client sets two frame (packet) loss rate thresholds (HFTc and LFTc) and sets the frame (packet) transmission loss rate FLR¾ and sets the TPC transmission measurement window N_ukt- At 610 a test is performed to determine if a TPC setting has been received from this client's associated AP. If a TPC setting has been received then at 615 this client determines the uplink transmit power (PRSSI uk) based on the instructions from this client's associated AP and sets the uplink transmission power to P_utk = maxfPRssi uk, PpLR ukJ- Processing then proceeds to 610. If a TPC setting has not been received then at 620 a test is performed to determine if this client has a frame to transmit to its associated AP. If this client has no frame to transmit to its associated AP then processing proceeds to 610. If this client has a frame to transmit to its associated AP then at 625 this client updates the transmission status, adjusts N_uk and adjusts N_uke if the transmission to client k failed. At 630 a test is performed to determine if N_uk is greater than or equal to N_ukt- If N_uk is less than N_ukt then processing proceeds to 610. If N_uk is greater than or equal to N_uk_t then at 635 this client determines the frame (packet) transmission loss rate FLR¾ = N_uke/N_uk_t. At 640 a test is performed to determine if the frame (packet) transmission loss rate is greater than or equal to the high frame transmission loss rate threshold (HFT). If the frame (packet) transmission loss rate is less than the high frame transmission loss rate threshold (HFT) then at 645 a test is performed to determine if the frame (packet) transmission loss rate is less than or equal to the low frame transmission loss rate threshold (LFT). If the frame (packet) transmission loss rate is greater than the low frame transmission loss rate threshold (LFT) then at 650 this client resets both the Up_timer and the Down_timer. Processing proceeds to 610. If the frame (packet) transmission loss rate is less than or equal to the low frame transmission loss rate threshold (LFT) then at 655 this client estimates the uplink transmit power for transmissions to its associated AP to be PP R _uk = max (Putk - Pud, min P_uk}- The AP also resets both N_uk and N_uke- At 660 this client sets the transmit power for uplink transmissions to P_utk = max{ PRSSI uk, Pput uiJ- Processing then proceeds to 610. If the frame (packet) transmission loss rate is greater than or equal to the high frame transmission loss rate threshold (HFT) then at 665 this client estimates the uplink transmit power for transmissions to its associated AP to be P_{P R u}k = min {P_utk + P_ud, max P_ukj- The AP also resets both N_uk and Nuk_e- Processing then proceeds to 660.

In an alternative embodiment, the AP periodically determines its frame (packet) loss rate (FLR) for its downlink transmissions to its associated clients. If the FLR during a time interval is greater than a threshold HFT, i.e. FLR > HFT, the AP adjusts its transmit power to each of its associated client as described above. In the meantime, the AP also increases the uplink transmit power of each of its associated client and sends the instruction (beacon, control, management) messages regarding the new uplink transmit power to the clients. If the current uplink transmit power for client k is P_utk, the new transmit power for the client k uplink transmission to the AP is the lesser value of P_utk+Pud and the allowed (permitted, supported) maximum uplink power of the client, max P_uk, i.e. new P_Mk = min{P_utk+P_ud, max P_uk}- - Similarly, the AP also determines the uplink transmit power of each of its associated clients and sends the instruction (control, beacon, management) messages regarding the new uplink transmit power to the clients when its FLR is below the low threshold LFT, i.e. FLR < LFT. The new uplink transmit power for client k is the greater one of P_utk - P_ud and the minimum transmit power supported by client , min P_uk_, i.e. the new uplink transmit power is P_utk = max{ P_utk - P_ud, min P_uk J

In another exemplary embodiment, the AP performs the frame (packet) loss rate measurement for its transmission to each of its associated client individually, i.e. the AP maintains the information on per link frame (packet) loss rate. Specifically, the AP maintains a window of transmission status for Nk_t frames that were most recently transmitted to its associated client k (k=l, 2, ...). If for client k, the frame loss rate FLRk = N_ke I N_kt > HF_T , as described above, the AP adjust its transmit power to client k, where Nk_e is the number of lost or retransmitted frames out of the last Nk_t frames transmitted to client k by the AP. In the meanwhile, the AP also increases the uplink transmit power of client k and sends the messages regarding the new uplink transmit power to client k to instruct client k to use the new transmit power for uplink transmission. If the current uplink transmit power for client k is P_utk, the new transmit power for uplink transmission from client k to AP is the lesser value of P_utk+P_ud and the allowed (permitted, supported) maximum power of client k, max P_uk, i.e. new P_utk = min{P_utk+Pud, max P_ukJ- Similarly the AP also determines the uplink transmit power of client k and sends the instruction (beacon, management, control) message regarding the new uplink transmit power to the client k when its FLR for client k is below the low threshold LFT, i.e. FLR_k < LFT

The new uplink transmit power for client k is the greater one of P_utk - P_uci and the minimum transmit power supported by client , min P_uk_, i.e. the new uplink transmit power P_utk = max{ P_utk - Pud, min P_uk }■

Fig. 7 is a block diagram of an exemplary implementation of the present invention. Since a wireless device (station, node, gateway, AP, base station) can be a transmitter, a receiver or a transceiver, a single block diagram is used showing a wireless communication module 725 having a radio transmitter/receiver 735. That is, the radio transmitter/receiver 735 can be a transmitter, a receiver or a transceiver. The present invention includes a host computing system 705 and a communication module (wireless) 725. The host processing system 705 can be a general-purpose computer or a specific -purpose computing system. The host computing system 705 can include a central processing unit (CPU) 710, a memory 715 and an input/output (I/O) interface 720. The wireless communication module can include a media access control (MAC) and baseband processor 730, radio transmitter/receiver 735, and one or more antennas. An antenna transmits and receives the radio signals. The radio transmitter/receiver 735 performs radio signal processing. The MAC and baseband processor 730 performs MAC control and data framing, modulation/demodulation, coding/decoding for the transmission/receiving. At least one embodiment of the present invention can be implemented as a routine in the host computing system 705 or wireless communication module 725 to process the transmission and receiving of data and control signal. That is, the block diagram of Fig. 7 may be implemented as hardware, software, firmware, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a reduced instruction set computer (RISC) or any combination thereof. Further, the exemplary processes illustrated in the various flowcharts and text above are operationally implemented in either the host processing system 705 or the wireless communication module 725 or a combination of the host processing system 705 and the communication module 725. The block diagram thus fully enables the various methods/processes to be practiced in hardware, software, firmware, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a reduced instruction set computer (RISC) or any combination thereof.

Specifically, when the apparatus shown in Fig. 7 is operating as a client (station, end device) then the client may operate in either the CPU of the host computing system 705 or the MAC and baseband processor of the wireless communication module 725 or a combination of both the CPU of the host computing system and the MAC and baseband processor of the wireless communication module and determines transmit power for the client. The CPU of the host computing system and/or the MAC and baseband processor of the wireless communication module include means for operating in a first mode until one of a first timer expires and a first mode switch message is received and means for operating in a second mode until one of a second timer expires and a second mode switch message is received, wherein in the first mode a transmit power is determined responsive to one of transmit power level instructions received from an associated access point and a maximum transmit power if no instructions have been received from the associated access point, and further wherein in the second mode the transmit power is a maximum of the transmit power level instructions received from the associated access point and a transmit power determined responsive to a frame transmission loss rate. The client can operate in either the first mode or the second mode or switch between the two modes of operation. The CPU of the host computing system and/or the MAC and baseband processor of the wireless communication module include means for switching between the means for operating in the first mode of operation and the means for operating in the second mode, wherein switching between the first mode and the second mode is optional and further includes means for setting the first timer, means for determining if one of the first timer has expired and the first mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)), means for switching to the second mode and means for setting the second timer and means for multicasting the first mode switch message responsive to the first means for determining (the actual means for multicasting uses the radio transmitter/receiver of the wireless communication module (735)), means for determining if one of the second timer has expired and the second mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)), means for determining if the first mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)), means for setting the second timer responsive to the third means for determining, means for switching to the first mode and means for setting the first timer and means for multicasting the second mode switch message responsive to the second means for determining (the actual means for multicasting uses the radio transmitter/receiver of the wireless communication module (735)), means for determining if the second mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)) responsive to the first means for determining and means for setting the first timer responsive to the fourth means for determining. Further, when operating in the second mode, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 include means for setting a first frame loss threshold and a second frame loss threshold, means for determining if the transmit power level instructions has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)) from the associated access point, means for determining the frame transmission loss rate for uplink transmissions responsive to the fifth means for determining, means for comparing the frame transmission loss rate for uplink transmissions to the first frame loss threshold, means for estimating the transmit power responsive to the first means for comparing, means for comparing the frame transmission loss rate for uplink transmissions to the second frame loss threshold, means for estimating the transmit power responsive to the second means for comparing, means for setting the transmit power responsive to the estimated transmit power, means for determining the transmit power responsive to the sixth means for determining and responsive to the received transmit power level instructions and means for setting the transmit power responsive to the seventh means for determining and responsive to the estimated transmit power. Further, when operating in the first mode the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 include means for setting a third timer, means for determining if the transmit power instructions has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)) from the associated access point, means for determining the transmit power responsive to the fifth means for determining and responsive to the received transmit power level instructions, means for setting the transmit power responsive to the sixth means for determining, means for determining if the third timer has expired and all estimated transmit power settings have been lost during a pendency of the third timer and means for setting the transmit power responsive to the seventh means for determining.

Further, in an alternative embodiment when operating in the second mode the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module include means for setting a first frame loss threshold and a second frame loss threshold, means for setting a frame loss rate measurement window, means for initializing a first counter and a second counter, means for determining if the transmit power level instructions has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)) from the associated access point, means for determining if there is data for transmission to the associated access point responsive to the fifth means for determining, means for adjusting the first counter responsive to the sixth means for determining, means for adjusting the second counter if the data transmission to the associated access point failed, means for comparing the first counter to the frame loss rate measurement window, means for determining the frame transmission loss rate responsive to results of the first means for comparing, means for comparing the frame transmission loss rate to the first frame loss threshold, means for estimating the transmit power to the associated access point responsive to results of the second means for comparing, means for clearing the first counter and the second counter, means for comparing the frame transmission loss rate to the second frame loss threshold responsive to the second means for comparing, means for estimating the transmit power to the associated access point responsive to results of the third means for comparing, means for clearing the first counter and the second counter means for setting the transmit power responsive to the estimated transmit power, means for determining the transmit power responsive to the fifth means for determining and responsive to the received transmit power level instructions and means for setting the transmit power responsive to the sixth means for determining and responsive to the estimated transmit power. Further, the client receives a request for a transmit power measurement report from its associated access point via the radio transmitter/receiver of the wireless communication module 735 and upon receipt of such a request, processes the request in the APU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 which include means for receiving the transmit power measurement request, means for measuring a received signal strength, means for estimating a downlink margin and means for sending a transmit power measure report responsive to the transmit power measurement request including the measured received signal strength and the estimated downlink margin to the client's associated access point (the actual sending (transmitting) uses the radio transmitter/receiver of the wireless communication module (735)).

Specifically, when the apparatus shown in Fig. 7 is operating as an access point then the access point (AP) may operate in either the CPU of the host computing system 705 or the MAC and baseband processor of the wireless communication module 725 or a combination of both the CPU of the host computing system and the MAC and baseband processor of the wireless communication module and determines downlink transmit power for the AP and the uplink transmit power for the client (station, end device). The CPU of the host computing system and/or the MAC and baseband processor of the wireless communication module include means for operating in a first mode until one of a first timer expires and a first mode switch message is received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)) and means for operating in a second mode until one of a second timer expires and a second mode switch message is received, and wherein in the first mode a downlink transmit power is one of a maximum transmit power and a downlink transmit power determined responsive to a received signal strength, and further wherein in the second mode the downlink transmit power is determined responsive to one of a frame transmission loss rate and the received signal strength, and further wherein in the second mode one of an aggregate downlink transmit power for all associated clients and a per link downlink transmit power is determined for each associated client. The CPU of the host computing system and/or the MAC and baseband processor of the wireless communication module include means for switching between the means for operating in the first mode of operation and the means for operating in the second mode, wherein switching between the first mode of operation and the second mode of operation is optional and further wherein the switching means includes means for setting the first timer, means for determining if one of the first timer has expired and the first mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)), means for switching to the second mode and setting the second timer and multicasting (the actual multicasting uses the radio transmitter/receiver of the wireless communication module (735)) the first mode switch message responsive to the first determination, means for determining if one of the second timer has expired and a second mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)), means for determining if the first mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)), means for setting the second timer responsive to the third means for determining, means for switching to the first mode and setting the first timer and multicasting (the actual multicasting uses the radio transmitter/receiver of the wireless communication module (735)) the second mode switch message responsive to the second means for determining, means for determining if the second mode switch message has been received (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)) responsive to the first means for determining and means for setting the first timer responsive to the fourth means for determining.

Further when the AP operates in the first mode of operation and the second mode of operation, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 include means for receiving a transmit power measurement report (the actual receiving uses the radio transmitter/receiver of the wireless communication module (735)), means for estimating an uplink path loss for an associated client responsive to data in the received transmit power measurement report, means for storing the estimated uplink path loss and a downlink margin received in the transmit power measurement report, means for estimating a target downlink transmit power for transmissions to the associated client and means for estimating a target uplink transmit power for transmissions from the associated client. Further when the AP operates in the second mode of operation, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 include means for setting a first frame loss threshold and a second frame loss threshold, means for determining the frame transmission loss rate for downlink transmissions, means for comparing the frame transmission loss rate to the first frame loss threshold, means for estimating the downlink transmit power to the associated client responsive to results of the first means for comparing, means for setting a flag, means for comparing the frame transmission loss rate to the second frame loss threshold, means for estimating the downlink transmit power to the associated client responsive to results of the second means for comparing and means for setting the flag. When operating in the second mode of operation, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 also include means for setting a third timer, means for determining if one of the third timer has expired and the flag is set, means for setting the downlink transmit power for the associated client responsive to the sixth means for determining and responsive to the estimated downlink transmit power to the associated client and responsive to the estimated target downlink transmit power, means for transmitting (the actual transmitting uses the radio transmitter/receiver of the wireless communication module (735)) the estimated uplink transmit power to the associated client and means for clearing the flag.

Further when the AP operates in the first mode of operation, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 include means for setting a third timer and a fourth timer, means for determining if one of the fourth timer has expired and all transmit power measurement reports of the associated client have been lost during a pendency of the fourth timer, means for setting the downlink transmit power to the associated client responsive to the first means for determining and setting the fourth timer, means for determining if the third timer has expired responsive to the first means for determining and means for setting the downlink transmit power to the associated client responsive to the second means for determining and setting the third timer. When operating in the first mode of operation, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 also include means for setting a fifth timer, means for determining if one of the fifth timer has expired and a flag is set, means for setting the downlink transmit power for the associated client responsive to the third means for determining and responsive to the estimated downlink transmit power to the associated client and responsive to the estimated target downlink transmit power, means for transmitting (the actual transmitting uses the radio transmitter/receiver of the wireless communication module (735)) the estimated uplink transmit power to the associated client and means for clearing the flag.

Further in an alternative embodiment when operating in the second mode of operation, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 include means for setting a first frame loss threshold and a second frame loss threshold, means for setting a frame loss rate measurement window, means for initializing a first counter and a second counter, means for determining if there is data to transmit to the associated client and transmitting the data (the actual transmitting uses the radio transmitter/receiver of the wireless communication module (735)), means for adjusting the first counter responsive to the first means for determining, means for adjusting the second counter if the data transmission to the associated client failed, means for comparing the first counter to the frame loss rate measurement window, means for determining the frame transmission loss rate responsive to results of the first means for comparing, means for comparing the frame transmission loss rate to the first frame loss threshold, means for estimating the downlink transmit power to the associated client responsive to results of the second means for comparing, means for setting a flag, means for comparing the frame transmission loss rate to the second frame loss threshold, means for estimating the downlink transmit power to the associated client responsive to results of the third means for comparing and means for setting the flag. Further when operating in the alternative embodiment of the second mode of operation, the CPU of the host computing system 705 and/or the MAC and baseband processor of the wireless communication module 735 also include means for determining if one of the third timer has expired and the flag is set, means for setting the downlink transmit power for the associated client responsive to the third means for determining and responsive to the estimated downlink transmit power to the associated client and responsive to the estimated target downlink transmit power, means for transmitting (the actual transmitting uses the radio transmitter/receiver of the wireless communication module (735)) the estimated uplink transmit power to the associated client and means for clearing the flag. It is to be understood that the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. Preferably, the present invention is implemented as a combination of hardware and software. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage device. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random access memory (RAM), and input/output (I/O) interface(s). The computer platform also includes an operating system and microinstruction code. The various processes and functions described herein may either be part of the microinstruction code or part of the application program (or a combination thereof), which is executed via the operating system. In addition, various other peripheral devices may be connected to the computer platform such as an additional data storage device and a printing device.

It is to be further understood that, because some of the constituent system components and methods steps depicted in the accompanying figures are preferably implemented in software, the actual connections between the system components (or the process steps) may differ depending upon the manner in which the present invention is programmed. Given the teachings herein, one of ordinary skill in the related art will be able to contemplate these and similar implementations or configurations of the present invention.

Claims

A method to determine transmit power, said method comprising: operating in a first mode until one of a first timer expires and a first mode switch message is received; operating in a second mode until one of a second timer expires and a second mode switch message is received, wherein in said first mode a transmit power is determined responsive to one of transmit power level instructions received from an associated access point and a maximum transmit power if no instructions have been received from said associated access point, and further wherein in said second mode said transmit power is a maximum of said transmit power level instructions received from said associated access point and a transmit power determined responsive to a frame transmission loss rate.

The method according to claim 1, wherein switching between said first mode of operation and said second mode of operation is optional and further comprises: setting said first timer; determining if one of said first timer has expired and said first mode switch message has been received; switching to said second mode and setting said second timer and multicasting said first mode switch message responsive to said first determination; determining if one of said second timer has expired and said second mode switch message has been received; determining if said first mode switch message has been received; setting said second timer responsive to said third determination; switching to said first mode and setting said first timer and multicasting said second mode switch message responsive to said second determination; determining if said second mode switch message has been received responsive to said first determination; and setting said first timer responsive to said fourth determination.

3. The method according to claim 1, wherein said second mode of operation further comprises: setting a first frame loss threshold and a second frame loss threshold; determining if said transmit power level instructions has been received from said associated access point; determining said frame transmission loss rate for uplink transmissions responsive to said fifth determination; comparing said frame transmission loss rate for uplink transmissions to said first frame loss threshold; estimating said transmit power responsive to said first comparison; comparing said frame transmission loss rate for uplink transmissions to said second frame loss threshold; estimating said transmit power responsive to said second comparison; setting said transmit power responsive to said estimated transmit power; determining said transmit power responsive to said sixth determination and responsive to said received transmit power level instructions; and setting said transmit power responsive to said seventh determination and responsive to said estimated transmit power.

4. The method according to claim 1, wherein said first mode of operation further comprises: setting a third timer; determining if said transmit power instructions has been received from said associated access point; determining said transmit power responsive to said fifth determination and responsive to said received transmit power level instructions; setting said transmit power responsive to said sixth determination; determining if said third timer has expired and all estimated transmit power settings have been lost during a pendency of said third timer; and setting said transmit power responsive to said seventh determination.

5. The method according to claim 1, wherein said second mode of operation further comprises: setting a first frame loss threshold and a second frame loss threshold; setting a frame loss rate measurement window; initializing a first counter and a second counter; determining if said transmit power level instructions has been received from said associated access point; determining if there is data for transmission to said associated access point responsive to said fifth determination; adjusting said first counter responsive to said sixth determination; adjusting said second counter if said data transmission to said associated access point failed; comparing said first counter to said frame loss rate measurement window; determining said frame transmission loss rate responsive to results of said first comparison; comparing said frame transmission loss rate to said first frame loss threshold; estimating said transmit power to said associated access point responsive to results of said second comparison; clearing said first counter and said second counter; comparing said frame transmission loss rate to said second frame loss threshold responsive to said second comparison; estimating said transmit power to said associated access point responsive to results of said third comparison; clearing said first counter and said second counter; setting said transmit power responsive to said estimated transmit power; determining said transmit power responsive to said fifth determination and responsive to said received transmit power level instructions; and setting said transmit power responsive to said sixth determination and responsive to said estimated transmit power.

An apparatus to determine transmit power comprising: means for operating in a first mode until one of a first timer expires and a first mode switch message is received; means for operating in a second mode until one of a second timer expires and a second mode switch message is received, wherein in said first mode a transmit power is determined responsive to one of transmit power level instructions received from an associated access point and a maximum transmit power if no instructions have been received from said associated access point, and further wherein in said second mode said transmit power is a maximum of said transmit power level instructions received from said associated access point and a transmit power determined responsive to a frame transmission loss rate.

The apparatus according to claim 6, wherein switching between said means for operating in said first mode of operation and said means for operating in said second mode is optional and further comprises: means for setting said first timer; means for determining if one of said first timer has expired and said first mode switch message has been received; means for switching to said second mode and means for setting said second timer and means for multicasting said first mode switch message responsive to said first means for determining; means for determining if one of said second timer has expired and said second mode switch message has been received; means for determining if said first mode switch message has been received; means for setting said second timer responsive to said third means for determining; means for switching to said first mode and means for setting said first timer and means for multicasting said second mode switch message responsive to said second means for determining; means for determining if said second mode switch message has been received responsive to said first means for determining; and means for setting said first timer responsive to said fourth means for determining.

8. The apparatus according to claim 6, wherein said second mode of operation further comprises: means for setting a first frame loss threshold and a second frame loss threshold; means for determining if said transmit power level instructions has been received from said associated access point; means for determining said frame transmission loss rate for uplink transmissions responsive to said fifth means for determining; means for comparing said frame transmission loss rate for uplink transmissions to said first frame loss threshold; means for estimating said transmit power responsive to said first means for comparing; means for comparing said frame transmission loss rate for uplink transmissions to said second frame loss threshold; means for estimating said transmit power responsive to said second means for comparing; means for setting said transmit power responsive to said estimated transmit power; means for determining said transmit power responsive to said sixth means for determining and responsive to said received transmit power level instructions; and means for setting said transmit power responsive to said seventh means for determining and responsive to said estimated transmit power.

9. The apparatus according to claim 6, wherein said first mode of operation further comprises: means for setting a third timer; means for determining if said transmit power instructions has been received from said associated access point; means for determining said transmit power responsive to said fifth means for determining and responsive to said received transmit power level instructions; means for setting said transmit power responsive to said sixth means for determining; means for determining if said third timer has expired and all estimated transmit power settings have been lost during a pendency of said third timer; and means for setting said transmit power responsive to said seventh means for determining.

10. The apparatus according to claim 6, wherein said second mode of operation further comprises: means for setting a first frame loss threshold and a second frame loss threshold; means for setting a frame loss rate measurement window; means for initializing a first counter and a second counter; means for determining if said transmit power level instructions has been received from said associated access point; means for determining if there is data for transmission to said associated access point responsive to said fifth means for determining; means for adjusting said first counter responsive to said sixth means for determining; means for adjusting said second counter if said data transmission to said associated access point failed; means for comparing said first counter to said frame loss rate measurement window; means for determining said frame transmission loss rate responsive to results of said first means for comparing; means for comparing said frame transmission loss rate to said first frame loss threshold; means for estimating said transmit power to said associated access point responsive to results of said second means for comparing; means for clearing said first counter and said second counter; means for comparing said frame transmission loss rate to said second frame loss threshold responsive to said second means for comparing; means for estimating said transmit power to said associated access point responsive to results of said third means for comparing; means for clearing said first counter and said second counter; means for setting said transmit power responsive to said estimated transmit power; means for determining said transmit power responsive to said fifth means for determining and responsive to said received transmit power level instructions; and means for setting said transmit power responsive to said sixth means for determining and responsive to said estimated transmit power.

11. A method, said method comprising: receiving a transmit power measurement request; measuring a received signal strength; estimating a downlink margin; and sending a transmit power measure report responsive to said transmit power measurement request including said measured received signal strength and said estimated downlink margin.

12. An apparatus comprising: means for receiving a transmit power measurement request; means for measuring a received signal strength; means for estimating a downlink margin; and means for sending a transmit power measure report responsive to said transmit power measurement request including said measured received signal strength and said estimated downlink margin.