WO2014110806A1

WO2014110806A1 - Channel reservation and synchronous transmission

Info

Publication number: WO2014110806A1
Application number: PCT/CN2013/070711
Authority: WO
Inventors: Wei Zou; Zhenhong Li; Haifeng Wang; Shi Chen; Xianjun FENG
Original assignee: Broadcom Corporation
Priority date: 2013-01-18
Filing date: 2013-01-18
Publication date: 2014-07-24

Abstract

Embodiments of the invention provide that in response to determining that the wireless local area network node (WLAN node) is an exposed node while having data to transmit to a peer WLAN node, the WLAN node that so determined transmits to the peer WLAN node a modified clear-to-send (CTS') message on a channel while the channel is reserved for a primary WLAN node pair. These embodiments further provide for transmitting data to the peer WLAN node only in response to receiving a clear-to-send CTS message from the peer WLAN node in reply to the transmitted modified CTS' message.

Description

CHANNEL RESERVATION AND SYNCHRONOUS TRANSMISSION

TECHNICAL FIELD:

[0001 ] The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to radio resource management in wireless networks which in the examples herein comprise multiple devices and synchronous transmission of the devices over a network.

BACKGROUND:

[0002] The volume of wireless traffic and the number of wireless devices engaging in such traffic continues to increase. Cellular network operators are exploring many options to deal with this increased traffic given there is a finite amount of available bandwidth.

[0003] In wireless local area network (WLAN) systems, a request to send/clear to send (RTS/CTS) handshake is utilized to reserve the unlicensed channel for transmission, as shown in Figure 1. The RTS/CTS exchange is part of what is known as a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) mechanism. The data source sends a request to send (RTS) addressed to the intended destination and, if the sender receives from the destination a CTS frame after a short inter-frame space (SIFS), the source will send a DATA frame to the destination. Finally, the destination will send an acknowledgment (ACK) frame to confirm its successful reception of the DATA fame. Other stations will update their network allocation vector (NAV) to the end of ACK frame after hearing either or both of the RTS/CTS frames, which carry the NAV information. Hence, these other stations will keep silent until the end of the NAV. In this technique, collision can only happen at the relatively short RTS frame, leading to a much smaller resource waste compared with the case where collision happens at the long DATA frame when an RTS/CTS handshake is not utilized. It should be noted that a DATA frame can be as long as 20 milliseconds while the general length of distributed inter-frame space (DIFS), SIFS, RTS, CTS and ACK frame is in the tens of microseconds. [0004] Figure 2 shows a problem referred to as the exposed-node problem, where STA3 cannot send data to STA4 due to the reception of the RTS frame transmitted from STA1 to STA2 because that RTS frame will disable transmission by STA3 in the reserved NAV period. STA1, STA2, STA3 and STA4 represent wireless local area network nodes (WLAN nodes), or other electronic communication devices. The intersecting ovals of range 1 and range 2 represent the coverage area for transmissions from STA1 and STA2, respectively. Since STA3 is only within the oval surrounding STA1 it only receives transmissions from STA1 and not STA2. Hence, even though it is possible to transmit data from STA3 (the exposed node) to STA4 concurrently without affecting the primary data transmission from STA1 to STA2, STA3 will not do so due to the NAV it learned from STA 1 ' s RTS .

[0005] It should be noted that a STA can find itself an exposed node by monitoring the reception status of RTS and CTS frames from the primary pair (i.e., STA1 and STA2 in the Figure 2 example). For example, when STA3 finds that it can decode the RTS frame (from the primary pair) successfully, it will continue to monitor the channel. If no CTS frame is received at STA3 before the detection of a DATA frame, STA3 will consider itself an exposed node.

SUMMARY:

[0006] In a first exemplary aspect of the invention there is a method for controlling a wireless local area network node (WLAN node). In this aspect the method comprises: in response to determining that the WLAN node is an exposed node while having data to transmit to a peer WLAN node, transmitting to the peer WLAN node a modified clear-to-send (CTS') message on a channel while the channel is reserved for a primary WLAN node pair. The method further comprises transmitting data to the peer WLAN node only in response to receiving a clear-to-send CTS message from the peer WLAN node in reply to the transmitted modified CTS' message.

[0007] In a second exemplary aspect of the invention there is an apparatus for controlling a wireless local area network node (WLAN node). In this aspect the apparatus comprises a processing system, and the processing system comprises at least one processor and a memory storing a set of computer instructions. The processing system is configured to cause the apparatus at least to: in response to determining that the WLAN node is an exposed node while having data to transmit to a peer WLAN node, transmitting to the peer WLAN node a modified clear-to-send (CTS') message on a channel while the channel is reserved for a primary WLAN node pair. The processing system is configured to further cause the apparatus to transmitting data to the peer WLAN node only in response to receiving a clear-to-send CTS message from the peer WLAN node in reply to the transmitted modified CTS' message. [0008] In a third exemplary aspect of the invention there is a computer readable memory tangibly storing a set of computer executable instructions for controlling a wireless local area network node (WLAN node). In this aspect the set of computer executable instructions comprises: code for in response to determining that the WLAN node is an exposed node while having data to transmit to a peer WLAN node, transmitting to the peer WLAN node a modified clear-to-send (CTS') message on a channel while the channel is reserved for a primary WLAN node pair. The computer executable instructions further comprises code for transmitting data to the peer WLAN node only in response to receiving a clear-to-send CTS message from the peer WLAN node in reply to the transmitted modified CTS's message.

[0009] These and other aspects are detailed below with more particularity.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0010] Figure 1 is a prior art signaling diagram that illustrates resource reservation by RTS/CTS handshake in a WLAN.

[001 1 ] Figure 2 is a high level schematic of a radio network environment that illustrates an example of the exposed node problem.

[0012] Figure 3 is similar to Figure 2 but with additional STAs, and illustrating an example of collisions between simultaneous transmissions at neighboring exposed nodes. [0013] Figure 4 is a high level signaling diagram illustrating an example procedure for channel reservation signaling exchange by synchronous transmission and receiving in the secondary pair according to certain embodiments of these teachings. [0014] Figure 5 is a block diagram illustrating an example of frame control field of the modified CTS' frame according to certain embodiments of these teachings.

[0015] Figure 6 is a high level signaling diagram illustrating an example of the concurrent transmission implementation when fragmented transmissions are applied in the primary pair according to certain embodiments of these teachings.

[0016] Figure 7 is a logic flow diagram that illustrates a method for controlling a wireless local area network node (WLAN node), and a result of execution by an apparatus of a set of computer program instructions embodied on a computer readable memory for operating or otherwise controlling such a WLAN node, in accordance with certain exemplary embodiments of these teachings.

[0017] Figure 8 is a simplified block diagram of multiple user equipments (UE's), and a WLAN AP which are exemplary electronic devices suitable for use in practicing the exemplary embodiments of these teachings.

DETAILED DESCRIPTION:

[0018] The examples detailed herein are in the context of the WLAN radio access technology, also known as the IEEE 802.xx family of radio standards. But that is only to provide a practical context to describing the inventive concepts; these teachings may be utilized with other types of radio access technologies (RATs) such as for example Universal Terrestrial Radio Access Network (UTRAN) or evolved UTRAN (E-UTRAN, sometimes referred to as long term evolution or LTE) that might be developed to use a channel reservation mechanism among peers, whether in the licensed or in the licensed exempt radio bands.

[0019] In a WLAN system, the exposed-node problem can be partially solved by opportunistic synchronous transmission at the exposed node shown in Figure 3, where STA3 can send a DATA frame to its destination opportunistically after STA3 finds itself an exposed node. The transmission coverage area for STA1 and STA2 are represented by range 1 and range 2, respectively. Typically in WLAN systems the wireless local area network node (WLAN node) is referred to as a station or STA and the (non-STA) access node is referred to as an access point or AP. [0020] However, when another exposed node exists near to STA3 (e.g. STA5 in Figure 3), its transmission (which is also synchronous to STAl's transmission as STA3) will interfere with STA3's transmission and nothing will be received at STA4 even when the unlicensed channel is idle at STA4 except their transmissions. Hence, this kind of transmission collision results in wasted radio resources. Because the exposed node STA3 and STA5 can hear the primary transmission (e.g. the transmission from STA1 to STA2 in Figure 3), it cannot perform any channel sensing before its own opportunistic transmissions. Hence, the collision probability is very large once there are two or more exposed stations nearby. [0021 ] Moreover, when STA4 is receiving status, some other WLAN device (who does not hear the transmission of STA3) can consider the channel idle and occupy the channel, e.g. WLAN API in Figure 3 may transmit a frame to one of its associated STAs. This will lead to external interference at STA4, and the opportunistic transmission at the secondary pair (e.g. STA3 and STA4 in Figure 3) will also fail. [0022] Below is detailed a channel reservation mechanism by concurrent transmissions at the exposed node, and in these examples it is for WLAN devices. Further below are detailed, a synchronous transmission method of DATA fragment frames at the exposed node when the fragmented transmissions are applied in the primary WLAN pair. [0023] The following concepts of these teachings are detailed further in the detailed explanation below. There is a slotted period designated for the transmission of a modified CTS frame (referred to as CTS') to express the channel reservation request at the exposed node. Another CTS frame (shown as CTS2 in Figures 4 and 6) is sent from the peer STA simultaneously with the primary ACK frame as the peer' s response to the modified CTS' frame, if a CTS' frame from the exposed node is received successfully. When fragmented transmissions are detected in the primary pair, some extra DATA fragment frames can be sent concurrently in the secondary pair after a short delay. As a result, synchronous transmission at the exposed node can be realized smoothly without collision, and the interferences from nearby WLAN devices can also be suppressed.

[0024] Figure 3 is a schematic diagram illustrating an example of collisions between simultaneous transmissions at neighboring exposed nodes. In Figure 3 STA1 sends an RTS to STA2. The intersecting ovals surrounding STA1 and STA2 represent each area/range of transmission where signals can be received. Since STA3 and STA5 are outside STA2's range, they only receive the RTS sent from STA1 and do not receive the CTS sent from STA2. Potential interference at STA4 comes from two sources: one is the simultaneous transmission by another exposed node near to STA3 (e.g., STA5); the other is WLAN transmissions from a remote WLAN device who does not hear the transmission of STA3. In order to overcome these two kinds of interferences, a novel channel reservation mechanism at the exposed node of WLAN devices is detailed herein.

[0025] Firstly, a slotted period is defined in the primary DATA frame after a STA finds itself an exposed node. This slotted time period should finish at the end of the primary DATA frame. In any of the designated slots, a modified CTS frame (referred to as CTS' frame in the following) can be sent from the exposed node. Based on the new slotted design, the following process can be applied to reserve the channel for synchronous transmission and reception among a secondary WLAN pair after a STA in that secondary pair finds itself an exposed node: The exposed node (e.g., STA3 in Figure 3) selects one slot in the slotted period randomly, and sends a modified CTS' frame in that slot (as shown in Figure 4). The slot size is large enough to accommodate one CTS' frame, whose size is from 24μ& to 44μ8 in one non-limiting embodiment (assuming we use the same size as specified for the CTS by IEEE 802.11a/g). The transmitted CTS' frame will disable the transmissions of the other WLAN devices near to the exposed node. It should be noted that each exposed node can only send one CTS' frame at the beginning of one slot. This is different from the frame transmission method in the traditional CSMA/CA mechanism. If the peer STA of the exposed node (e.g., STA4) cannot receive the CTS' frame successfully, the whole process shown at Figure 4 stops. [0026] If one or multiple CTS' frames are received correctly at the peer STA (e.g., STA4) in different slots due to the transmissions by different exposed nodes, the first received CTS' frame will be considered as the valid one. If the peer STA is the destination of the valid CTS' frame, then the peer STA of the exposed node (e.g., STA4) will monitor the unlicensed channel at the beginning of the ACK frame when it is allowed to transmit. If the channel is idle, it will send another CTS frame (shown as CTS2 in Figure 4) and the NAV information in this CTS2 frame will disable the transmissions of the other WLAN devices near to STA4. If the channel is busy, no CTS2 is transmitted and the whole process stops. If STA3 receives a CTS2 frame successfully, the following DATA frame and ACK response will be transmitted between this secondary pair (STA3 and STA4) as shown at Figure 4; otherwise, the whole process stops.

[0027] Figure 4 diagrams the above process in detail, where the transmission frames are shown as shaded vertical bars. For clarity of the signaling the SIFS between frames is not particularly illustrated in Figure 4 but is assumed present. By applying this approach, a channel can be reserved successfully by a secondary WLAN node pair (STA3 and STA4) during the NAV period of WLAN transmissions among a primary WLAN node pair (STA1 and STA2). Hence, the unlicensed channel can be utilized more efficiently. [0028] It should be noted that the process following the CTS' frame is different from that following a conventional CTS frame. For example, in the Figure 4 example STA4 needs to start monitoring the slotted period only after it recognizes a correct CTS' frame. Then, STA4 needs to decide whether to respond with a CTS2 frame or not at the beginning the next ACK frame. If the destination address of the first received CTS' frame is STA4's MAC address, it will respond with a CTS2 frame and continue the process as described above and as shown at Figure 4; otherwise, the whole process stops and nothing will be sent among the secondary pair. Therefore, the CTS' frame is differentiated from a conventional CTS frame according to these teachings, in a manner that still allows it to be recognized by other WLAN devices as a frame that reserves the channel (i.e. other WLAN devices will still consider it as a CTS frame and keep silent based on the NAV information in it).

[0029] One solution to realize this is shown in Figure 5, where the 'More Frag' bit in the 'frame control' field of a conventional CTS frame is set to value T in the CTS' frame. It should be noted that the 'More Frag' bit is always '0' in conventional CTS frames. By monitoring the 'More Frag' bit in the received CTS frame, STA4 can then recognize the special CTS' frames and process it with the corresponding actions. While at other WLAN devices, CTS' will still be considered as a normal CTS frame and its 'Duration' will be used to update the NAV of the unlicensed channel. For the frame CTS2 frame, it can be as same as a conventional CTS frame since STA3 already knows its status after transmitting the CTS' frame and the CTS2 frame here is only used for channel reservation at STA4.

[0030] In the above description with respect to Figure 4, it is assumed that the primary pair of WLAN devices is not transmitting the DATA frame in fragmented mode. When the fragmented transmissions are applied, the above mentioned mechanism can be further enhanced to realize the concurrent transmissions among the secondary pair by the exposed node. Hence the unlicensed channel can be reused at the secondary pair and a much larger system capacity is achievable. [0031 ] One exemplary process for this is detailed at Figure 6. After STA3 finds itself an exposed node, it continues to monitor the physical layer convergence procedure (PLCP) header of the first fragment frame between the primary pair. If the 'duration/length' field is longer than NAV indicated in previous RTS/CTS frames (between STAland STA2), it can be judged by other nodes/STAs that the primary pair of STA1 and STA2 is using fragmented transmission mode. Then, after the CTS'-CTS2 handshake between the secondary pair STA3 and STA4, the exposed node STA3 will postpone its DATA frame (the first data fragment between the secondary pair) and monitor the PLCP header of the second-in-time fragment frame between the primary pair STA1 and STA2 (i.e. 'Fragl' as shown in Figure 6) in order to get the information of the next NAV ('NAV3' as shown in Figure 6). After that, the exposed node (STA3 in Figure 6) will send its first fragment (with the updated NAV information in it) synchronously to the primary pair.

[0032] The same procedures continue until the last fragment by the primary pair, where the exposed node will find that the NAV in PLCP header is as same as that in the previous primary pair's fragment. The exposed node can then know that this is the last fragment from the primary pair and control its own transmissions correspondingly. In the entire transmission process, the ACK frames within primary pair and within the secondary pair are synchronized. By applying the techniques shown at Figure 6, concurrent transmissions at the secondary pair can be performed smoothly even when the primary pair is using fragmented data transmissions. Hence, a much larger system capacity can be potentially realized.

[0033] Embodiments of these teachings provide the technical effect of enabling the unlicensed-band channel to be reserved successfully by an exposed node before the NAV of the primary pair ends, and the unlicesed-band channel can thus be utilized more efficiently. Collision between exposed nodes are avoided since only the first CTS' frame will be considered as the valid CTS' frame; and only when the STA's MAC address is the same as the destination MAC adderss of the valid CTS' frame will that STA respond with CTS2 frame and continue the process. Concurrent transmissions from an exposed node can be performed successfully even when fragmented transmissions are utilized by the primary pair, leading to a much higher spectrum effeciency.

[0034] The new CTS' frame has to be recognzied at STAs so that the new-defined signaling process can be followed even by those STAs not participating but only remaining silent. Hence, WLAN STAs may need to be enhanced to implement certain embodments of these teachings, but it is anticipated that most if not all of such adaptations can be implemented simply by software upgrade. [0035] Figure 7 presents a summary of the above teachings for controlling and/or for operating a wireless local area network node (WLAN node) such as for example one capable of operating in a WLAN network. At block 704, in response to determining that the WLAN node is an exposed node while having data to transmit to a peer WLAN node, the WLAN node that did the determining transmits to the peer WLAN node a modified clear-to-send (CTS') message on a channel while the channel is reserved for a primary WLAN pair; and it transmits data to the peer WLAN node only in response to receiving a clear-to-send CTS message from the peer WLAN node in reply to the transmitted modified CTS' message. This is shown by example in Figure 6 at STA3. [0036] Some of the non-limiting implementations detailed above are also summarized in Figure 7 following block 704. Block 706 of Figure 7 specifies one embodiment in which all of the said transmissions occur in license exempt radio spectrum. In addition, another non-limiting embodiment has those transmissions in the licensed band, for example if WLAN technology is applied to the licensed/cellular band. Block 708 further specifies determining that the WLAN node is an exposed node comprises detecting that a first WLAN node of the primary WLAN node pair transmitted a request- to- send (RTS) message and data without detecting that a second WLAN node of the primary WLAN node pair sent a CTS message in reply to the RTS message prior to the data. This is shown by example in Figure 6 wherein STA3 receives the RTS message from STA1, but does not receive the CTS message from STA2.

[0037] Block 710 in Figure 7 specifies wherein the modified clear- to-send CTS' message is transmitted to the peer WLAN node in a slot that is randomly selected from a slotted period defined by time period information comprised in the request- to- send (RTS) message. Block 712 specifies that the modified clear-to-send CTS' message is distinguished from the clear-to-send (CTS) message by only a single bit value in a frame control field. Block 714 specifies wherein the CTS message is received from the peer WLAN node at the expiration of a time period when the channel is reserved for the primary WLAN node pair, wherein the time period is synchronized with transmissions of the primary WLAN node pair.

[0038] Block 716 in Figure 7 specifies further in response to determining that the primary WLAN node pair are communicating data in a fragmented mode, imposing a listening period after a period of time when the channel is reserved for the primary WLAN node pair when transmitting the data to the peer WLAN node in response to receiving the clear-to-send CTS message. An additional step can be added wherein during the imposed listening period, monitor a header of a data fragment sent between the primary WLAN node pair to determine a network allocation vector. Furthermore, these steps can be executed by a WLAN node which is operating as a station in a wireless local area network (WLAN). Additionally, these steps can also be executed by a WLAN node which is operating as an access point in a WLAN.

[0039] The logic diagram of Figure 7 may be considered to illustrate the operation of a method, and a result of execution of a computer program stored in a computer readable memory, and a specific manner in which components of an electronic device are configured to cause that electronic device to operate, whether such an electronic device is the WLAN node, a UE or some other portable electronic device. The various blocks shown in Figure 7 may also be considered as a plurality of coupled logic circuit elements constructed to carry out the associated function(s), or specific result of strings of computer program code or instructions stored in a memory.

[0040] Such blocks and the functions they represent are non-limiting examples, and may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention. [0041 ] Such circuit/circuitry embodiments include any of the following: (a) hardware- only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) combinations of circuits and software (and/or firmware), such as: (i) a combination of processor(s) or (ii) portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a user equipment/UE, to perform the various functions summarized at Figure 7 and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" also covers, for example, a baseband integrated circuit or applications processor integrated circuit for a wireless local area network node (WLAN node), a user equipment UE or for a network access node/eNB or a similar integrated circuit in a server or other network device which operates according to these teachings.

[0042] Reference is now made to Figure 8 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing the exemplary embodiments of this invention. In Figure 8 a user equipment (UE) 24 is adapted for communication over a wireless link 25 with an apparatus, such as a mobile terminal or UE 22. The UE 22 may be any electronic device or user equipment for communication over any wireless network, such as a WLAN. In the above examples the STA WLAN node was a UE. [0043] The UE 24 includes processing means such as at least one data processor (DP) 24A, storing means such as at least one computer-readable memory (MEM) 24B storing at least one computer program (PROG) 24C, communication means such as a transmitter TX 24D and a receiver RX 24E for bidirectional wireless communications with the UE 22 over the WLAN. All of these wireless communications are via one or more antennas 24F. Also stored in the MEM 24B at reference number 24G are CTS' and CTS2 frame processing which enable the UE 24 to use the messages it receives from the UE 22 to configure itself for WLAN communications according to embodiments above. Those embodiments are described in further detail above.

[0044] The UE 22 also includes processing means such as at least one data processor (DP) 22A, storing means such as at least one computer-readable memory (MEM) 22B storing at least one computer program (PROG) 22C, and communication means such as a transmitter TX 22D and a receiver RX 22E for bidirectional wireless communications with the UE 20 on the WLAN via one or more antennas 22F. The UE 22 stores at block 22G CTS' and CTS2 frame processing to configure itself for WLAN communications according to the embodiments above.

[0045] Also at Figure 8 is shown a WLAN AP 26 as a specific implementation of the access node operating on the WLAN. The WLAN AP 26 includes processing means such as at least one data processor (DP) 26A, storing means such as at least one computer-readable memory (MEM) 26B storing at least one computer program (PROG) 26C, and communication means such as a transmitter TX 26D and a receiver RX 26E for bidirectional wireless communications with the UE 20, UE 22 and UE 24 via one or more antennas 26F. The WLAN AP 26 stores at block 26G its own CTS' and CTS2 frame processing for configuring the WLAN according to the various embodiments detailed above.

[0046] While not particularly illustrated for the UE or STA's, those devices are also assumed to include as part of their wireless communicating means a modem and/or a chipset which may or may not be built-in onto an RF front end chip within those devices which also operates according to the WLAN as set forth above.

[0047] At least one of the PROGs 24C in the UE 24 is assumed to include a set of program instructions that, when executed by the associated DP 24A, enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above. The UE 24 also has software stored in its MEM 24B to implement certain aspects of these teachings such as CTS' and CTS2 frame processing. Further, the WLAN AP 26 may also have implementing software to put into effect the teachings herein as detailed above. In these regards the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 24B, 24B which is executable by the DP 24A of the UE 24 and/or by the DP 22A of the UE 22, and/or by the DP 26A of the WLAN AP 26; or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware) in any one or more of these devices 20, 22, 24. Electronic devices implementing these aspects of the invention need not be the entire devices as depicted at Figure 8 or may be one or more components of same such as the above described tangibly stored software, hardware, firmware and DP, or a system on a chip SOC or an application specific integrated circuit ASIC. [0048] In general, the various embodiments of the UE 20, UE 22, and UE 24 or a WLAN node can include, but are not limited to personal portable digital devices having wireless communication capabilities, including but not limited to cellular telephones, navigation devices, laptop/palmtop/tablet computers, digital cameras and music devices, and Internet appliances.

[0049] Various embodiments of the computer readable MEMs 20B, 22B, 24B, 26B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 20 A, 22A, 24A, 26 A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.

[0050] Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. While the exemplary embodiments have been described above in the context of the WLAN systems, as noted above the exemplary embodiments of this invention are not limited for use with only this particular type of wireless radio access technology networks.

[0051 ] Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

WHAT IS CLAIMED IS:

1. A method for controlling a wireless local area network node (WLAN node) comprising:

in response to determining that the WLAN node is an exposed node while having data to transmit to a peer WLAN node, transmitting to the peer WLAN node a modified clear-to-send (CTS') message on a channel while the channel is reserved for a primary WLAN node pair; and

transmitting data to the peer WLAN node only in response to receiving a clear-to-send CTS message from the peer WLAN node in reply to the transmitted modified CTS' message.

2. The method according to claim 1, wherein all of the said transmissions occur in license exempt radio spectrum.

3. The method according to claims 1 or 2, wherein determining that the WLAN node is an exposed node comprises detecting that a first WLAN node of the primary WLAN node pair transmitted a request- to- send (RTS) message and data without detecting that a second WLAN node of the primary WLAN node pair sent a CTS message in reply to the RTS message prior to the data.

4. The method according to any of claims 1-3, wherein the modified clear-to-send CTS' message is transmitted to the peer WLAN node in a slot that is randomly selected from a slotted period defined by time period information comprised in the request- to- send (RTS) message.

5. The method according to any of claims 1-4, wherein the modified clear- to- send CTS' message is distinguished from the clear-to-send (CTS) message by only a single bit value in a frame control field.

6. The method according to any of claims 1-5, wherein the CTS message is received from the peer WLAN node at the expiration of a time period when the channel is reserved for the primary WLAN node pair, wherein the time period is synchronized with transmissions of the primary WLAN node pair.

7. The method according to any of claims 1-6, the method further comprising: in response to determining that the primary WLAN node pair are communicating data in a fragmented mode, imposing a listening period after a period of time when the channel is reserved for the primary WLAN node pair when transmitting the data to the peer WLAN node in response to receiving the clear-to-send CTS message.

8. The method according to claim 7, the method further comprising:

during the imposed listening period, monitor a header of a data fragment sent between the primary WLAN node pair to determine a network allocation vector.

9. The method according to any of claims 1-8, wherein the method is executed by the WLAN node which is operating as a station in a wireless local area network (WLAN).

10. An apparatus for controlling a wireless local area network node (WLAN node), the apparatus comprising a processing system which comprises at least one processor and a memory storing a set of computer instructions, the processing system configured to cause the apparatus to at least:

11. The apparatus according to claim 10, wherein all of the said transmissions occur in license exempt radio spectrum.

12. The apparatus according to claims 10 or 11, wherein determining that the WLAN node is an exposed node comprises detecting that a first WLAN node of the primary WLAN node pair transmitted a request-to-send (RTS) message and data without detecting that a second WLAN node of the primary WLAN node pair sent a CTS message in reply to the RTS message prior to the data.

13. The apparatus according to claims 10-12, wherein the modified clear-to-send CTS' message is transmitted to the peer WLAN node in a slot that is randomly selected from a slotted period defined by a time period information comprised in the request-to-send (RTS) message.

14. The apparatus according to claims 10-13, wherein the modified clear-to-send CTS' message is distinguished from the clear-to-send (CTS) message by only a single bit value in a frame control field.

15. The apparatus according to claims 10-14, wherein the CTS message is received from the peer WLAN node at the expiration of a time period when the channel is reserved for the primary WLAN node pair, wherein the time period is synchronized with transmissions of the primary WLAN node pair.

16. The apparatus according to claims 10-15, wherein the processing system is configured to in response to determining that the primary WLAN node pair are communicating data in a fragmented mode, imposing a listening period after a period of time when the channel is reserved for the primary WLAN node pair when transmitting the data to the peer WLAN node in response to receiving the clear-to-send CTS message.

17. The apparatus according to claim 16, wherein the processing system is configured to during the imposed listening period, monitor a header of a data fragment sent between the primary WLAN node pair to determine a network allocation vector.

18. The apparatus according to claims 10-17, wherein the WLAN node is operating as a station in a wireless local area network (WLAN).

19. A computer readable memory tangibly storing a set of computer executable instructions for controlling a wireless local area network node (WLAN node), the set of computer executable instructions comprising:

code for in response to determining that the WLAN node is an exposed node while having data to transmit to a peer WLAN node, transmitting to the peer WLAN node a modified clear-to-send (CTS') message on a channel while the channel is reserved for a primary WLAN node pair; and

code for transmitting data to the peer WLAN node only in response to receiving a clear-to-send CTS message from the peer WLAN node in reply to the transmitted modified CTS' message.

20. The computer readable memory according to claim 19, wherein all of the said transmissions occur in license exempt radio spectrum.

21. The computer readable memory according claims 19 or 20, wherein determining that the WLAN node is an exposed node comprises detecting that a first WLAN node of the primary WLAN node pair transmitted a request- to- send (RTS) message and data without detecting that a second WLAN node of the primary WLAN node pair sent a CTS message in reply to the RTS message prior to the data.

22. The computer readable memory according to claims 19-21, wherein the modified clear-to-send CTS' message is transmitted to the peer WLAN node in slot that is randomly selected from a slotted period defined by time period information comprised in the request- to- send (RTS) message.

23. The computer readable memory according to claims 19-22, wherein the modified clear-to-send CTS' message is distinguished from the clear-to-send (CTS) message by only a single bit value in a frame control field.

24. The computer readable memory according to claims 19-23, wherein the CTS message is received from the peer WLAN node at the expiration of a time period when the channel is reserved for the primary WLAN node pair, wherein the time period is synchronized with transmissions of the primary WLAN node pair.

25. The computer readable memory according to claims 19-24, wherein the set of computer executable instructions further comprising:

code for in response to determining that the primary WLAN node pair are communicating data in a fragmented mode, imposing a listening period after a period of time when the channel is reserved for the primary WLAN node pair when transmitting the data to the peer WLAN node in response to receiving the clear- to- send CTS message.

26. The computer readable memory according to claim 25, wherein the set of computer executable instructions further comprising:

code for during the imposed listening period, monitor a header of a data fragment sent between the primary WLAN node pair to determine a network allocation vector.

27. The computer readable memory according to claims 19-26, wherein the WLAN node is operating as a station in a wireless local area network (WLAN).