WO2021093969A1

WO2021093969A1 - Techniques for power control in microwave backhaul systems

Info

Publication number: WO2021093969A1
Application number: PCT/EP2019/081503
Authority: WO
Inventors: Jonathan Gambini
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2019-11-15
Filing date: 2019-11-15
Publication date: 2021-05-20
Also published as: CN114731591A

Abstract

A power control device for controlling transmit powers of a Microwave Backhaul network of a Microwave Backhaul system includes a plurality of Microwave Backhaul networks. For the Microwave Backhaul network the power control device acquires for each of a plurality of microwave links of the Microwave Backhaul network, information on a channel status of the respective microwave link over a specific number of time slots; determines, for each microwave link, a throughput over the respective microwave link for the specific number of time slots based on the information on the channel status of each microwave link and a time information indicating that the throughput over the respective microwave link is above a link-specific threshold; and determines, for each microwave link, a transmit power for each time slot, upon determining that the time information is below a given threshold for at least one microwave link.

Description

TECHNIQUES FOR POWER CONTROL IN MICROWAVE BACKHAUL

SYSTEMS

TECHNICAL FIELD

The present disclosure relates to techniques for power control in Microwave Backhaul systems, in particular to techniques for adaptive power control for Microwave Backhaul networks. BACKGROUND

In traditional Microwave Backhaul networks 100 providing connectivity to MacroCell Base Stations, star topologies are realized as shown in Figure 1. A plurality of leaf nodes 101, 102, 103, 104 is connected via respective links 111, 112, 113, 114 to a hub node 110. Such Microwave Backhaul networks 100 are managed by: assigning to the pair of links j and k orthogonal frequency channels if their angular separation ajk 121 is below a given threshold angle an; and assigning to the pair of links j and k the same frequency channel if their angular separation ajk 121 is above said threshold angle an. Threshold angle an typically depends on: the radiation pattern (or, equivalently, the interference rejection capability) of the antennas mounted at the leaf nodes 101, 102, 103, 104 and at the Hub Node 110; and the target available throughputs to be guaranteed over the different links 111, 112, 113, 114 (exemplary throughput requirements for a Microwave Backhaul link can be 1 Gbit/s with 99.9% availability and 250 Mbit/s with 99.995% availability). In the vast majority of the Microwave Backhaul systems in operation that provide transport of backhaul information among MacroCell Base Stations, transmit power at time slot A over any /th link is selected as a function of the channel status CS.(A) at time slot l related to the

/th link only, as depicted in the Microwave Backhaul network 200 shown in Fig. 2. With reference to the star-based deployment sketched in Fig. 2, in the following the power transmitted from any y^'th leaf node will be referred to as /th uplink transmit power 221, 222, 223, 224 and the power transmitted from the Hub Node to any /th leaf node will be referred to as y^'th downlink transmit power (not shown in Fig. 2). When utilizing the Microwave Backhaul network 200 shown in Fig. 2, the following limitations occur:

LIMIT 1) The selection of the transmit power to be used over a given link does not account for the interference that is possibly produced over all the other links of the network. The use of the prior art transmit power management policy can generate high interference levels over some network links, so that the requirement on the threshold angle an between adjacent links sharing the same frequency channel becomes stricter (an increases). The immediate DISADVANTAGE of this is that if an increases the area spectral efficiency decreases.

LIMIT 2) The selection of the transmit power to be used on a given link at a given time slot A only depends on the channel status at time slot A and does not account for the channel statuses over a wider time span, that have a major impact in determining the available throughputs that can be guaranteed over the said link. Therefore, the selection of the transmit powers according to the prior art transmit power management policy does not optimize the available throughputs that can be guaranteed over the different links. As a consequence, the value of threshold angle an is not optimized as well (notice that threshold angle an plays a crucial role in determining the available throughputs that can be guaranteed over the different links), and this can lead to a decrease of the area spectral efficiency.

SUMMARY

It is an object of the invention to provide techniques for solving the above described problems of Microwave Backhaul networks, i.e. to improve throughput for a Microwave Backhaul system, in particular for a Microwave Backhaul system including a plurality of Microwave Backhaul networks.

This object is achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, the invention relates to a power control device for controlling transmit powers of at least one Microwave Backhaul network of a Microwave Backhaul system including a plurality of Microwave Backhaul networks, wherein the power control device is configured to perform for at least one Microwave Backhaul network the following: acquire, for each of a plurality of microwave links of the at least one Microwave Backhaul network, information on a channel status ( CS_n(t-a )) of the respective microwave link over a specific number ( T) of time slots ( t-a ); determine, for each microwave link, a throughput Thn(t-a )) over the respective microwave link for the specific number (T) of time slots (t-a) based on the information on the channel status ( CS_n(t-a )) of each microwave link of the at least one Microwave Backhaul network, and a time information (b_h) indicating that the throughput ( Th_n(t-a )) over the respective microwave link is above a given link-specific threshold ( Thmin ); and determine, for each microwave link, a transmit power for the respective microwave link for each time slot, upon determining that the time information (fhi) is below a given threshold (p,rm ) for at least one microwave link.

Such a power control device results in a requirement relaxation: the dynamic joint optimal selection of uplink (and downlink) transmit powers at each time slot leads to a reduction of the required threshold angle an between adjacent links sharing the same frequency channel, for fixed antenna patterns and target available throughputs. Reducing the threshold angle an leads to an increase of the area spectral efficiency.

In an exemplary implementation form of the power control device, the information on the channel status ( CS_n(t-a )) of the respective microwave link depends on information on the channel status of each microwave link within the at least one Microwave Backhaul network itself and information on the channel status of each interfering microwave link from or to another Microwave Backhaul network.

This provides the technical advantage that the transmit powers can be optimally adjusted even for a Microwave Backhaul system being including multiple Microwave Backhaul networks, since the interfering microwave links are incorporated in the optimality criterion.

In an exemplary implementation form of the power control device, the transmit powers are determined by maximizing a minimum Signal-to-Interference-plus-Noise Ratio, SINR, that is related to a generic time slot and a generic microwave link. This provides the technical advantage that the maximization result, and hence the optimal transmit powers, are valid for generic time slots and generic microwave links.

In an exemplary implementation form of the power control device, the transmit powers are determined by maximizing a sum throughput of the plurality of microwave links of the at least one Microwave Backhaul network over the specific number ( T) of time slots under the constraint that each microwave link provides a throughput greater than or equal to the given link-specific threshold, Thmin, for a time information greater than or equal to the given threshold, pmin.

This provides the technical advantage that the requirements of Microwave Backhaul systems which require a minimum throughput for a minimum percentage of time over a given link can be fulfilled.

In an exemplary implementation form of the power control device, the transmit powers are determined under the constraint to comply with given transmit power dynamic ranges and/or given output transmit power levels of the Microwave Backhaul system.

This provides the technical advantage that the requirements of dynamic ranges and output levels for transmit powers can be fulfilled.

In an exemplary implementation form of the power control device, the power control device is configured to: adjust the Microwave Backhaul system to employ the transmit powers determined for each microwave link of the plurality of microwave links of the at least one Microwave Backhaul network.

This provides the technical advantage that the whole Microwave Backhaul system can be optimally designed and run based on the determined optimal transmit powers.

In an exemplary implementation form of the power control device, the power control device is configured to: determine the transmit power separately in both communication directions of each microwave link of the plurality of microwave links of the at least one Microwave Backhaul network. This provides the technical advantage that a more precise adjustment of the transmit powers can be achieved when determining the transmit powers separately for both communication directions, e.g. uplink and downlink. In an exemplary implementation form of the power control device, the power control device is configured to: determine, for each microwave link, the transmit power for the respective microwave link in an iterative manner time slot by time slot; and recompute the time information (//,,) that the throughput (Thn(t-a)) over the respective microwave link is above the given link-specific threshold ( Thmin ) after each time slot iteration.

This provides the technical advantage that a processing complexity for solving the optimization problem is decreased when using an iterative mechanism, since the whole algorithm can be distributed over the various iterations. Further, while a first iteration can deliver a rough result, each further iteration can provide a more precise result.

In an exemplary implementation form of the power control device, the power control device is configured to: determine, for each microwave link, the throughput, Thn(t-a), over the respective microwave link for the specific number ( T) of time slots based on a Signal-to- Interference-plus-Noise Ratio (SINRn(t-a)) of the respective microwave link at a respective time slot, wherein the Signal-to-Interference-plus-Noise Ratio (SINRn(t-a)) of the respective microwave link at a respective time slot (t-a) is based on the information on the channel status (CSn(t-a)) of each microwave link of the at least one Microwave Backhaul network at the respective time slot (t-a). This provides the technical advantage of decreasing the computational complexity for computing the throughputs, as the Signal-to-Interference-plus-Noise Ratios are usually available for the power control device.

In an exemplary implementation form of the power control device, the power control device is configured to: determine, for each microwave link, the Signal-to-Interference-plus-Noise Ratio (SINRn(t-a)) of the respective microwave link at the respective time slot (t-a) based on the following relation:

where q_h(ί — α) represents an overall attenuation occurring between a transmit device of the «th microwave link and a receive device of the «th microwave link at time slot t — α, P_n(t — α ) represents the transmit power employed over the «th microwave link at time slot t — α, 0_k(t — α ) represents an overall attenuation occurring between a generic k th transmit device belonging to the Microwave Backhaul system and the receive device of the «th microwave link at time slot t — α, g_h®h accounts for the overall gain due to the antenna radiation pattern of the transmit device of the «th microwave link and the antenna radiation pattern of the receive device of the «th microwave link, y_fe®n accounts for the overall gain due to the antenna radiation pattern of the k th transmit device and the antenna radiation pattern of the receive device of the «th microwave link, and P_n0iSe represents a measure of the receive noise power.

This provides the technical advantage that computational complexity for computing the Signal-to-Interference-plus-Noise Ratios is low, since it can be determined by simple multiplication and addition operations.

In an exemplary implementation form of the power control device, the power control device is configured to: create a channel status to optimal power, CS2P, table which comprises for each microwave link and at each time slot the acquired information on the channel status (CSn(t-a)) of the respective microwave link at the respective time slot and the associated optimal transmit power.

This provides the technical advantage that the CS2P table can be used to easily lookup for the desired information on the association between the channel statuses and the optimal transmit powers to be employed in the Microwave Backhaul system. The CS2P table can be predetermined and pre-stored in the Microwave Backhaul system.

In an exemplary implementation form of the power control device, the power control device is configured to: update the CS2P table with new information on the channel statuses ( CS_n(t - a)) and the associated optimal transmit powers based on a predefined periodicity. This provides the technical advantage that changes in the Microwave Backhaul system, e.g. addition of new backhaul networks or removal of existing backhaul networks, can be easily mapped to the CS2P table.

In an exemplary implementation form of the power control device, the power control device is configured to: derive the information on the channel status (CSn(t-a)) of the microwave links in an initialization phase from a memory accessible by the power control device, wherein the memory stores information acquired from available databases containing attenuation statistics for a given geographic area or from existing standard recommendations, in particular ITU recommendations, or from information acquired before the Microwave Backhaul system is deployed in field.

This provides the technical advantage of avoiding latencies to derive the required channel statuses of the links in the Microwave Backhaul network for the specific number ( T) of time slots, since this information is available from the memory.

In an exemplary implementation form of the power control device, the power control device is located as a central entity in one of the Microwave Backhaul networks; or distributed as a plurality of distributed entities over the whole Microwave Backhaul system.

This provides the technical advantage of high design flexibility. Depending on the actual requirements of the network elements, the power control device can be implemented in any of the network elements, for instance in such a network element that provides the necessary resources for the processing tasks of the power control device.

According to a second aspect, the invention relates to a method for controlling transmit powers of at least one Microwave Backhaul network of a Microwave Backhaul system including a plurality of Microwave Backhaul networks, wherein the method comprises: performing for at least one Microwave Backhaul network the following: acquiring, for each of a plurality of microwave links of the at least one Microwave Backhaul network, information on a channel status (CSn(t-a)) of the respective microwave link over a specific number (T) of time slots (t-a); determining, for each microwave link, a throughput ( Th_n(t - a)) over the respective microwave link for the specific number (T) of time slots (t-a) based on the information on the channel status (CSn(t-a)) of each microwave link of the at least one Microwave Backhaul network, and a time information (b_h) indicating that the throughput (Thn(t-a)) over the respective microwave link is above a given link-specific threshold ( Thmin ); and determining, for each microwave link, a transmit power for the respective microwave link for each time slot, upon determining that the time information (b_h ) is below a given threshold (p_min) for at least one microwave link.

Such a method for controlling transmit powers results in a requirement relaxation: the dynamic joint optimal selection of uplink (and downlink) transmit powers at each time slot leads to a reduction of the required threshold angle an between adjacent links sharing the same frequency channel, for fixed antenna patterns and target available throughputs. Reducing the threshold angle an leads to an increase of the area spectral efficiency.

According to a third aspect, the invention relates to a computer program product including computer executable code or computer executable instructions that, when executed, causes at least one computer to execute the method according to the third or fourth aspect. Such a computer program product may include a non-transient readable storage medium storing program code thereon for use by a processor, the program code comprising instructions for performing the methods or the computing blocks as described hereinafter.

The entities described in this disclosure may include a processor to process the respective functionalities. A processor as described in this disclosure may comprise hardware and software. The hardware may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or general- purpose processors. In one embodiment, the processor comprises one or more processor cores and a non-transitory memory connected to the one or more processor cores. The non- transitory memory may carry executable program code which, when executed by the one or more processor cores, causes the apparatus to perform the operations or methods described herein.

DEFINITIONS In the following sections, the following terms, abbreviations and notations will be used:

Backhaul network:

In a hierarchical telecommunications network, the backhaul portion of the network comprises the intermediate links between the core network, or backbone network, and the small subnetworks at the Edge of the network.

Angular separation:

The angular separation or angular distance between two point objects, as viewed from a location different from either of these objects, is the angle between the two directions originating from the observer and pointing toward these two objects.

Time slot:

A time slot is defined as a generic limited period of time.

Channel Status:

A channel status CSjfi) at time slot l related to the /th link is defined as an indicator of the quality of said /th link in both uplink (from the /th leaf node to the Hub Node) and downlink (from the Hub Node to the y^'th leaf node) directions during the time span of a given time slot l. As an example, but not limited to, it can include a measure of the attenuation (in both directions) experienced over the y^'th wireless link during time slot l, together with a measure of the interference level or pattern produced by other transmit devices deployed in the Microwave Backhaul system. It can also include the antenna gains over said y^'th link.

CS: Channel Status

CS2P: Channel Status to Power (table)

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, in which: Fig. 1 shows a schematic diagram illustrating a Microwave Backhaul network 100;

Fig. 2 shows a schematic diagram illustrating a Microwave Backhaul network 200 for uplink direction;

Fig. 3 a shows a schematic diagram illustrating a Microwave Backhaul network 300 for uplink direction and a power control device 310 according to the disclosure;

Fig. 3b shows an example of a Channel Statuses To Optimal Powers (CS2P) Table 300b according to the disclosure;

Fig. 4a shows an exemplary histogram 401 of throughputs over a first link of a Microwave Backhaul network;

Fig. 4b shows an exemplary histogram 402 of throughputs over an N-th link of a Microwave Backhaul network;

Fig. 5 shows a schematic diagram 500 illustrating a constrained maximization of throughput functions according to the disclosure;

Fig. 6 shows a flowchart of a method 600 for controlling transmit powers of a Microwave Backhaul network according to the disclosure;

Fig. 7 shows a schematic diagram illustrating a Microwave Backhaul system 700 comprising two Microwave Backhaul networks according to the disclosure;

Fig. 8 shows a schematic diagram illustrating a network scenario 800 with two hubs and six leaves according to the disclosure;

Fig. 9a-d show schematic diagrams illustrating further random network scenarios 900a, 900b, 900c, 900d with two hubs and six leaves according to the disclosure; Fig. 10 shows a performance diagram 1000 illustrating performance of network scenarios with and without power control according to the disclosure; and

Fig. 11 shows a schematic diagram illustrating a method 1100 for controlling transmit powers of a Microwave Backhaul system according to the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A solution according to the disclosure as described hereinafter and in the summary section introduces a novel scheme of Adaptive Power Control for Microwave Backhaul networks that selects each /th uplink (and downlink) transmit power P_j (A) at time slot A as a joint function of the channel statuses CS_n(t-a ) related to all the links « = 1, 2, ..., A of the network measured over a specific time span of T time slots (a = 0, 1, 2, ..., T-l), where said time span of T time slots does not necessarily include time slot A (see below with respect to Figure 3). The presented scheme is adaptive as transmit powers Pi (A), P₂ (A), ... , P_W(A) to be used over the N links can be changed at each time slot l. Transmit powers Pi (A), P₂(A), ... , P_/v(A) at each time slot A are selected with the goal of maximizing the overall throughput of the N links under the constraint of guaranteeing the required set of available throughputs at each of the N links (that are typical requirements in Microwave Backhaul systems).

A benefit of this scheme lies in the requirement relaxation: the dynamic joint optimal selection of uplink (and downlink) transmit powers Pi (A), P₂(A), ... , P_W(A) at each time slot A leads to a reduction of the required threshold angle an between adjacent links sharing the same frequency channel, for fixed antenna patterns and target available throughputs. Reducing the threshold angle an leads to an increase of the area spectral efficiency.

The disclosed scheme represents an adaptive power control mechanism for Microwave Backhaul networks which is including the following five operations: 1) Initial Data Acquisition

2) Data Analysis

3) Transmit Power Optimization Procedure 4) Dynamic Transmit Power Control

5) Update of Optimum Transmit Power Allocations

These five operations will be detailed in the following sections of the disclosure. A flowchart of the presented scheme is shown in Figure 6 (for steps 1-4).

In the following detailed description, reference is made to the accompanying drawings, which form a part thereof, and in which is shown by way of illustration specific aspects in which the disclosure may be practiced. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

It is understood that comments made in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

The described devices may include integrated circuits and/or passives and may be manufactured according to various technologies. For example, the circuits may be designed as logic integrated circuits, analog integrated circuits, mixed signal integrated circuits, optical circuits, memory circuits and/or integrated passives.

The devices and systems described herein may include processors or processing devices or processing circuitries, memories and transceivers, i.e. transmitters and/or receivers. In the following description, the term “processor” or “processing device” describes any device that can be utilized for processing specific tasks (or blocks or steps). A processor or processing device can be a single processor or a multi-core processor or can include a set of processors or can include means for processing. A processor or processing device can process software or firmware or applications etc. Fig. 1 shows a schematic diagram illustrating a Microwave Backhaul network 100. Such traditional Microwave Backhaul network 100 provides connectivity to MacroCell Base Stations. A plurality of leaf nodes 101, 102, 103, 104 is connected in a star topology via respective links 111, 112, 113, 114 to a hub node 110. As described above, such Microwave Backhaul network 100 is managed as follows: assigning to the pair of links j and k orthogonal frequency channels if their angular separation cijk 121 is below a given threshold angle an; and assigning to the pair of links j and k the same frequency channel if their angular separation ajk 121 is above said threshold angle an. The threshold angle an typically depends on the radiation pattern (or, equivalently, the interference rejection capability) of the antennas mounted at the leaf nodes 101, 102, 103, 104 and at the Hub Node 110 and the target available throughputs to be guaranteed over the different links 111, 112, 113, 114 (exemplary throughput requirements for a Microwave Backhaul link can be 1 Gbit/s with 99.9% availability and 250 Mbit/s with 99.995% availability).

Fig. 2 shows a schematic diagram illustrating a Microwave Backhaul network 200 for uplink direction. The network structure is the same as that of the Microwave Backhaul network 100 shown inFigure 1. A plurality of leaf nodes 101, 102, 103, 104 is connected in a star topology via respective links 111, 112, 113, 114 to a hub node 110. Figure 2 describes the uplink case where uplink transmit powers are considered.

Transmit power at time slot A over any y^'th link 221, 222, 223, 224 is selected as a function of the channel status CS(A) at time slot l related to the /th link only. The power transmitted from any /th leaf node is denoted as the /th uplink transmit power. Note that, in a downlink direction (not shown in Fig. 2), the power transmitted from the Hub Node to any /th leaf node will be referred to as y^'th downlink transmit power. Hence, the Microwave Backhaul network 200 experiences the limitations as described above.

Fig. 3 a shows a schematic diagram illustrating a Microwave Backhaul network 300 for uplink direction and a power control device 310 according to the disclosure. The network structure is the same as that of the Microwave Backhaul networks 100, 200 shown in Figures 1 and 2. A plurality of leaf nodes 101, 102, 103, 104 is connected in a star topology via respective links 111, 112, 113, 114 to a Hub Node 110. Figure 3 describes the uplink case where uplink transmit powers are considered.

A power control device 310 is used to control the transmit powers 320 of the Microwave Backhaul network 300. The power control device 310 can be used to control the transmit powers 320 of a single Microwave Backhaul network 300 as shown in Fig. 3a. Additionally, the power control device 310 can be used to control the transmit powers of at least one Microwave Backhaul network of a Microwave Backhaul system including a plurality of Microwave Backhaul networks, e.g. as shown in the network scenarios of Figures 7 to 9.

The power control device 310 is configured to perform for at least one Microwave Backhaul network, e.g. network 300 shown in Fig. 3a, the following steps: 1) acquire, for each of a plurality of microwave links 111, 112, 113, 114 of the at least one Microwave Backhaul network 300, information on a channel status CSn(t-a) of the respective microwave link over a specific number T of time slots (t-a); 2) determine, for each microwave link 111, 112, 113, 114, a throughput Thn(t-a) over the respective microwave link for the specific number T of time slots (t-a) based on the information on the channel status CSn(t-a) of each microwave link 111, 112, 113, 114 of the at least one Microwave Backhaul network 300, and a time information b_h indicating that the throughput Thn(t-a) over the respective microwave link 111, 112, 113, 114 is above a given link-specific threshold Thmm; and 3) determine, for each microwave link 111, 112, 113, 114, a transmit power 320 for the respective microwave link 111, 112, 113, 114 for each time slot, upon determining that the time information b_h is below a given threshold p_min for at least one microwave link 111, 112, 113, 114. These steps are described in more detail in the following sections.

The information on the channel status CSn(t-a) of the respective microwave link 111, 112, 113, 114 may depend on information on the channel status of each microwave link 111, 112, 113, 114 within the at least one Microwave Backhaul network 300 itself and information on the channel status of each interfering microwave link from or to another Microwave Backhaul network 801, e.g. as shown in Fig. 8. The transmit power 320 may be determined by maximizing a minimum Signal-to- Interference-plus-Noise Ratio, SINR, that is related to a generic time slot and a generic microwave link, e.g. as described below.

The transmit power 320 may be determined by maximizing 501 a sum throughput of the plurality of microwave links 111, 112, 113, 114 of the at least one Microwave Backhaul network 300 over a specific number D < T time slots under the constraint 502 that each microwave link 111, 112, 113, 114 provides a throughput greater than or equal to the given link-specific threshold, Thmin, for a time information greater than or equal to the given threshold, p_mm, e.g. as described below with respect to Fig. 5.

The transmit power 320 may be determined under the constraint to comply with given transmit power dynamic ranges and/or given output transmit power levels of the Microwave Backhaul system 800.

The power control device 310 may be configured to adjust the Microwave Backhaul system 800 to employ the transmit powers 320 determined for each microwave link of the plurality of microwave links 111, 112, 113, 114 ofthe at least one Microwave Backhaul network 300.

The power control device 310 may be configured to determine the transmit power 320 separately in both communication directions of each microwave link of the plurality of microwave links 111, 112, 113, 114 of the at least one Microwave Backhaul network 300.

The power control device 310 may be configured to: determine, for each microwave link, the transmit power 320 for the respective microwave link in an iterative manner time slot by time slot; and recompute the time information (b_h) that the throughput (Thn(t-a)) over the respective microwave link is above the given link-specific threshold (Thmin) after each time slot iteration, e.g. as described below.

The power control device 310 may be configured to determine, for each microwave link 111, 112, 113, 114, the throughput, Thn(t-a), over the respective microwave link for the specific number T of time slots based on a Signal-to-Interference-plus-Noise Ratio SINRn(t-a) ofthe respective microwave link at a respective time slot, wherein the Signal-to-Interference-plus- Noise Ratio SINRn(t-a) of the respective microwave link at a respective time slot t-a is based on the information on the channel status CSn(t-a) of each microwave link 111, 112, 113, 114 of the at least one Microwave Backhaul network 300 at the respective time slot (t-a).

The power control device 310 may be configured to determine, for each microwave link 111, 112, 113, 114, the Signal-to-Interference-plus-Noise Ratio SINRn(t-a) of the respective microwave link at the respective time slot t-a based on the following relation:

where θ_n(t — α) represents an overall attenuation occurring between a transmit device of the «th microwave link and a receive device of the «th microwave link at time slot t — α, P_n(t — α) represents the transmit power employed over the «th microwave link at time slot t — α, θ_k(t — α) represents an overall attenuation occurring between a generic k th transmit device belonging to the Microwave Backhaul system and the receive device of the «th microwave link at time slot t — α, γ_n→n accounts for the overall gain due to the antenna radiation pattern of the transmit device of the «th microwave link and the antenna radiation pattern of the receive device of the «th microwave link, γ_k→n accounts for the overall gain due to the antenna radiation pattern of the kth transmit device and the antenna radiation pattern of the receive device of the «th microwave link, and P_n0iSe represents a measure of the receive noise power, e.g. as described below.

The power control device 310 may be configured to create a channel status to optimal power, CS2P, table which comprises for each microwave link 111, 112, 113, 114 and at each time slot the acquired information on the channel status CSn(t-a) of the respective microwave link at the respective time slot and the associated transmit power 320.

The power control device 310 may be configured to update the CS2P table with new information on the channel statuses CSn(t-a) and the associated transmit powers based on a predefined periodicity. The power control device 310 may be configured to derive the information on the channel status CSn(t-a) of the microwave links 111, 112, 113, 114 in an initialization phase from a memory accessible by the power control device 310, e.g. as described below, wherein the memory stores information acquired from available databases containing attenuation statistics for a given geographic area or from existing standard recommendations, in particular ITU recommendations, or from information acquired before the Microwave Backhaul system 800 is deployed in field.

The power control device 310 may be located as a central entity, e.g. in hub node 110, in one of the Microwave Backhaul networks 300, 801; or distributed as a plurality of distributed entities, e.g. in leaf nodes 111, 112, 113, 114, over the whole Microwave Backhaul system 800, e.g. as shown below with respect to Fig. 8.

Hence, the power control device 310 represents an apparatus for performing the disclosed scheme, that is, an adaptive power control scheme for Microwave Backhaul networks, which is including the five main operations: 1) Initial Data Acquisition; 2) Data Analysis; 3) Transmit Power Optimization Procedure; 4) Dynamic Transmit Power Control; 5) Update Of Optimum Transmit Power Allocations. These five operations will be detailed in the following part of this disclosure. A flowchart of the presented scheme in terms of the steps of a method is shown below with respect to Figure 6 (for steps 1-4).

First operation: Initial Data Acquisition

The Hub Node 110 may be equipped with a control unit, i.e. the power control device 310 depicted in Fig. 3 a, adapted to acquire information on the uplink and downlink channel statuses CS_n(t — α) of the links 111, 112, 113, 114 to whom it has been configured to provide backhaul connectivity (n = 1, 2, ..., N) over a time span of T time slots (a = 0, 1, 2, ..., T-l). Said control unit can be implemented in a centralized fashion (e.g., located at the Hub Node 110 only) or in a distributed fashion (distributed over the whole system).

According to an embodiment, in the initialization phase the information on the uplink and downlink channel statuses is available at the control unit. These pieces of information may be derived from available databases (e.g., publicly accessible or proprietary databases) containing attenuation statistics for a given geographic area or from existing ITU recommendations (for example, the ITU-R 530). Said initial information on the uplink and downlink channel statuses may be acquired before the apparatus is deployed in field and stored in appropriate memory support connected to the control unit. Alternatively, operations 1-3 may be performed off-line and the results of the Transmit Power Optimization Procedure (namely the CS2P Table that is outcome of the Third operation, see below) can be directly stored in an appropriate memory support that may be connected to said control unit (as initial transmit power allocations). Channel status CS_n(t — a ) can represent the attenuation that is experienced over the «th link at time slot t-a. The acquired information on CS_n(t — a ) related to said T time slots and N links (« = 1, 2, ..., N and a = 0, 1, 2, ..., T-l ) may be collected and stored in an appropriate memory, being the time span of T time slots sufficiently large to properly characterize the statistical behavior of the status of the different links.

Second operation: Data Analysis

From the set of acquired measurements CS_n(t — α) (« = 1, 2, 3, ..., N and a = 0, 1, 2, ..., T- 1 ) and the transmit power levels P_n(t — a) used over each «th link at each time slot t-a, the control unit can compute the Signal-to-Interference-plus-Noise-Ratio SINR_n(t — α ) experienced over each «th link at each time slot t-a (« = 1, 2, 3, ..., N and a = 0, 1, 2, ..., T- I). This can be defined as

where 9_n(t — a ) represents an overall attenuation occurring between a transmit device of the «th microwave link and a receive device of the «th microwave link at time slot t — α, P_n(t — a ) represents the transmit power employed over the «th microwave link at time slot t — α, 0_k(t — α) represents an overall attenuation occurring between a generic k th transmit device belonging to the Microwave Backhaul system and the receive device of the «th microwave link at time slot t — a, g_h®h accounts for the overall gain due to the antenna radiation pattern of the transmit device of the «th microwave link and the antenna radiation pattern of the receive device of the «th microwave link, y_fe®n accounts for the overall gain due to the antenna radiation pattern of the /cth transmit device and the antenna radiation pattern of the receive device of the nth microwave link, and P_n0iSe represents a measure of the receive noise power.

In an implementation, the initial uplink transmit powers may be set by the control unit (e.g., in hub node 110) and may be communicated to the leaf nodes 101, 102, 103, 104 through a proper proprietary control channel. In an alternative implementation, the initial uplink transmit powers may be selected by each leaf node 101, 102, 103, 104 independently and then each leaf node can communicate the value of its initial uplink transmit power to the control unit through a proper proprietary control channel.

The control unit can use the derived set of SINRs to derive the corresponding set of throughputs supported over the N links and over the T time slots as

for uplink and downlink (a = 0, 1, 2, ..., T-l and n = 1, 2, 3, ..., N), where BW is the system bandwidth and w() is a convenient function mapping a SINR into a corresponding spectral efficiency measured in [bit/s/Hz] (as an example, it can be the well known Shannon formula defined as w(c ) = log₂( 1 + x) ).

Microwave Backhaul systems typically require that a minimum throughput Thmin is guaranteed for a minimum percentage of time p_mm over a given link. For example, it can be required that each link in a given Microwave Backhaul network experiences a throughput that is greater or equal to 77? min = 250 Mbit/s for 99.995% of time (in this case, p,vm = 0.99995).

In order to verify that these requirements on the per-link available throughputs are met, the control unit may then compute the histogram of the throughputs Th_n(t — α) delivered over each nth link (over the time span of T time slots). The control unit may estimate the percentage of time b_h that the backhaul throughput delivered over each nth link keeps above the minimum throughput Th_min as

where t_n represents the number of times the throughput experienced over the nth link is greater than or equal to the threshold Th_min (see below with respect to Fig. 4a/b). If all link percentages β₁, β₂, β₃,..., β_N are above p_min, no further action is required. If at least one link percentage out of β₁, β₂, β₃,..., β_N is below p_min, the Transmit Power Optimization Procedure is performed. Said Transmit Power Optimization Procedure is detailed in the following operation (Third operation or step 3).

Third operation: Transmit Power Optimization Procedure

The control unit may first identify a subset D = (b, , d₂, ... , d_B] oi the T time slots (D < T) where at least one of the throughputs experienced over the N links is below Thmin. In mathematical notation:

The control unit may then select the transmit power values P₁(δ_ί), P₂(δ_ί), ..., R_N(δ_ί) to be used over the N links 111, 112, 113, 114 for each time slot to

maximize the overall throughput of the N links over the said D time slots while guaranteeing that each nth link provides a throughput greater than or equal to Th_min for a percentage of time

Notice that percentages of time over each nth link and system

throughputs depend on said new transmit power allocation. This dependence is further

outlined in Figure 5 illustrating the optimization scheme in mathematical notation. The goal is to maximize 501 the sum throughput over the D time slots and N links 111, 112, 113, 114 under the constraints 502 on minimum available throughput over each link 111, 112, 113, 114 for pmin percentage of time.

The optimization problem illustrated in Fig. 5 is complex, due to its non-convex nature. Different heuristics can be used to find convenient transmit power allocation strategies that are able to satisfy the target throughput requirements.

One exemplary low-complexity method for finding optimal transmit powers is described by the following pseudocode. Compute initial link percentages β₁, β₂, β₃,..., β_N Select current time slot

While at least one link percentage among β₁, β₂, β₃,..., β_N is below p_min

1) Select transmit powers P₁(δ_ί), P₂(δ_ί), ..., R_N(δ_ί) by solving the max-min SINR optimization problem P 1 (see description in the following) related to time slot δ_ί

2) Recompute link percentages b_h ( n = 1, N) using the Data Analysis Procedure (see step 2 above)

3) 5_;=b_i+1

End

The max-min SINR optimization problem PI related to a generic time slot d_{ is formulated as the optimal choice of the transmit powers P₁(δ_ί), P₂(δ_ί), ..., R_N(δ_ί) that maximize the minimum SINR of the Microwave Backhaul network at the given time slot δ_ί . In mathematical notation:

where Signal-to-interference-plus-noise-ratios S//VR_n(b ;) (n = 1, 2, .. N) at the given time slot δ_ί have been previously defined.

Said throughput maximization problem can be further constrained to comply with the available transmit power dynamic ranges or the available output transmit power levels of the system. At the end of this optimization, the N optimized transmit power values 320 at each time slot δ_ί (i = 1, 2,..., D) are associated with the set of N channel statuses measured at said time slot δ_ί, producing the Channel Statuses To Optimal Powers (CS2P) Table as shown in Figure 3b.

The Channel Statuses To Optimal Powers (CS2P) Table as shown in Figure 3b may have a size D x 2Nx W bytes, where W is the size, in bytes, of one binary string required to represent each entry of the CS2P T able and, as previously stated, N is the number of links and D is the number of time slots where at least one of the throughputs experienced over the N links is belOW Thmin. In one exemplary implementation with the following typical values:

T= 10⁸ time slots,

- D = T/10⁴ = 10⁴time slots (e.g., for p_min = 0.9999),

- N= 30 links (for dense scenarios), - W= 2 bytes, the CS2P Table would occupy a size of 1.2 Mbyte.

Fourth operation: Dynamic Transmit Power Control

During subsequent system operation, at a given time slot l, if the measured channel statuses CS_n(λ) over the N links (^'« = 1 , 2, ..., N) arc equal, with a pre-defmed tolerance e, to the combination of channel statuses at row k of the CS2P Table, then the control unit may configure the Microwave Backhaul system to employ the combination of transmit powers specified at row k of the CS2P Table. For example, if

then transmit powers should be employed over the N links for time slot 2.

If, conversely, no matching is found between

the N measured channel statuses at time slot l and the combinations listed in the CS2P Table, a predefined default value for the N transmit powers may be applied.

In case of uplink transmissions, the optimum uplink transmit power value to be employed may be communicated to each leaf node 101, 102, 103, 104 through a proprietary control channel.

Fifth operation: Update Of Optimum Transmit Power Allocations The Hub Node 110 may be equipped with a control unit (i.e. the power control device 310 shown in Fig. 3a) adapted to measure on a regular time basis the uplink and downlink channel statuses CS_n(t — a) of the links 111, 112, 113, 114 to whom it has been configured to provide backhaul connectivity (n = 1, 2, ..., N) over a time span of T time slots (a = 0, 1, 2, ..., T-l ).

The measurements on CS_n(t — a) related to said T time slots and N links (n = 1, 2, ..., N and a = 0, 1, 2, ..., T-l ) may be collected and stored in an appropriate memory, being the time span of T time slots sufficiently large to properly characterize the statistical behavior of the status of the different links.

This set of measurements may be used according to the same procedure described before (operations 1 to 3 or steps 1-3 respectively) for updating the transmit power values and channel status values in the CS2P Table. The Update Of Optimum Transmit Power Allocations step can be executed with a predefined periodicity. In case of a newly added leaf node the CS2P Table may be recomputed according to the disclosed scheme.

Figures 4a and 4b show exemplary histograms 401, 402 of throughputs over a first link and over an A-th link of a Microwave Backhaul network.

The power control device 310 as described above with respect to Fig. 3a may compute the histogram 401, 402 of the throughputs Th_n(t — α ) delivered over each nth link (over the time span of T time slots). The power control device 310 may estimate the percentage of time b_h that the backhaul throughput delivered over each nth link keeps above the minimum throughput Th_min as

where t_n represents the number of times the throughput experienced over the nth link is greater than or equal to the threshold Th_min (Figure 4a shows an example for t, , while Figure 4b shows an example for t_N). If all link percentages β₁, β₂, β₃,..., β_N are above p_min, no further action is required. If at least one link percentage out of β₁, β₂, β₃,..., β_N is below p_min, the Transmit Power Optimization Procedure is performed, e.g. according to the description above with respect to Fig. 3a.

Fig. 5 shows a schematic diagram 500 illustrating a maximization of a throughput function according to the disclosure.

The power control device 310 shown in Fig. 3a may select the transmit power values P₁(δ_ί), P₂(δ_ί), ..., R_N(δ_ί) to be used over the N links 111, 112, 113, 114 for each time slot δ_ί £ D (i = 1, 2,..., D) to maximize the overall throughput of the N links over the said D time slots while guaranteeing that each nth link provides a throughput greater than or equal to Th_min for a percentage of time Notice that percentages of time over each

nth link and system throughputs depend on said new transmit power allocation. This

dependence is illustrated in Figure 5 depicting the optimization scheme in mathematical notation. The goal is to maximize the sum throughput 501 over the D time slots and N links 111, 112, 113, 114 under the constraints 502 on minimum available throughput over each link 111, 112, 113, 114 for p_min percentage of time.

The optimization problem illustrated in Fig. 5 is complex, due to its non-convex nature. Different heuristics can be used to find convenient transmit power allocation strategies that are able to satisfy the target throughput requirements. One exemplary allocation strategy was described above with respect to Fig. 3 a.

Fig. 6 shows a flowchart of a method 600 for controlling transmit powers of a Microwave Backhaul network according to the disclosure.

The method 600 represents the first four operations of the disclosed scheme, e.g. according to the description above with respect to Figure 3. The first operation “Initial Data Acquisition” includes step 601. The second operation “Data Analysis” includes steps 602, 603 and 604. The third operation “Transmit Power Optimization Procedure” includes step 605. The fourth operation “Dynamic Transmit Power Control” includes steps 606, 607, 608 and 609. The method 600 starts with step 601: “Acquire CS_n(t — α) of the N links (n = 1, 2, N ) over a time span of T time slots (a = 0, 1, 2, T-l)”. Step 602 follows: “Estimate the throughputs over the N links for the T time slots”. Step 603 follows : “Estimate the percentage of time b_h that the throughput of each nth link is above threshold Th_rnin". If, in step 604, b_h-Pmin is true for all the N links (n = 1, 2, N), method 600 jumps to step 606, otherwise step 605 is performed: “Solve the constrained throughput maximization problem (see Fig. 5) and build a table associating a combination of channel statuses over the N links to a combination of optimal transmit powers over the N links (CS2P table)”. Step 606 follows: “During subsequent system operation, measure channel statuses CS_n(A) at each time slot A (n = 1, 2, ..., N )”. If, in step 607, measured channel statuses at time slot A appear in CS2P table, go to step 608: “Employ the corresponding N optimal transmit powers as indicated in CS2P table at time slot A”. Otherwise, go to step 609: “A predefined default value for the N transmit powers is applied at time slot A”.

Fig. 7 shows a schematic diagram illustrating a Microwave Backhaul system 700 comprising two Microwave Backhaul networks according to the disclosure.

The scheme described above with respect to Fig. 3 a can also be applied to a Microwave Backhaul system 700 comprising two Microwave Backhaul networks as shown in Fig. 7. This Microwave Backhaul system 700 is including an exemplary number of two star-shaped backhaul subsystems 711, 712 operating over the same frequency channel, each subsystem 711, 712 comprising a Hub Node 710, 720 and multiple leaf nodes 701, 702, 703, 704, 705.

According to the disclosed Adaptive Power Control scheme for Microwave Backhaul networks, the uplink and downlink transmit powers over each link may be selected according to the same procedure described above that leverages the knowledge of the uplink and downlink channel statuses of all the network links, measured over an appropriate time span.

Fig. 8 shows a schematic diagram illustrating a network scenario 800 with two hubs 110, 820 and six leaves 101, 102, 103, 104, 805, 806 according to the disclosure.

The network scenario 800 represents a Microwave Backhaul system 800 comprising two

Microwave Backhaul networks, e.g. a first Microwave Backhaul network 300 according to the description above with respect to Figure 3 and a second Microwave Backhaul network 801 including one hub node 820 and two leaf nodes 805, 806. Each of the star-shaped backhaul subsystems 300, 801 may operate over the same frequency channel.

Numerical simulations have been made on the specific network scenario shown in Fig. 8. The use of the disclosed Adaptive Power Control Method for Microwave Backhaul networks enables to achieve the target performance (throughput greater than 3.5 Gbit/s for 99.5% of time and throughput greater than 500 Mbit/s for 99.995% of time) over all the radio links. Prior art transmit power management would guarantee this target performance over only 33% of the network links.

Fig. 9a-d show schematic diagrams illustrating further random network scenarios 900a, 900b, 900c, 900d with two hubs and six leaves operating over the same frequency channel according to the disclosure.

Numerical simulations have been made on 50 network scenarios as shown in Fig. 9a-d, each characterized by 2 Hub Nodes and 6 Leaf Nodes. The network scenario of Figure 9b is a special case in which a first hub 930 is connected to six leaf nodes while a second hub (not shown) has no leaves. Performance of these network scenarios is shown in Figure 10. The use of the disclosed Adaptive Power Control Method for Microwave Backhaul networks enables to gain 15 dB, 1009, in the interference rejection capability at Hub Nodes with respect to the prior art transmit power management approach.

Fig. 10 shows a performance diagram 1000 illustrating performance of network scenarios with and without power control according to the disclosure. The X axis depicts interference rejection capability at central Hub sites in dB; the Y axis depicts percentage of links matching the target performance.

The performance diagram 1000 shows that nearly 100% of the links are matching the target performance when applying adaptive network power control 1001 according to the disclosure. In particular, a throughput greater than 3.5 Gbit/s can be achieved with 99.5% availability and a throughput greater than 500 Mbit/s can be achieved with 99.995% availability. In contrast, without using adaptive network power control 1002 according to the disclosure much less of the links are matching this target performance as it can be seen from the figure. A gain 1009 of about 15 dB can be realized for interference rejection capability at the hub nodes.

When applying adaptive network power control according to the disclosure, the following benefits can be achieved: (7) the disclosed Adaptive Power Control Method is effective in increasing the number of co-channel links (i.e., links sharing the same frequency channel) by enhancing the link availabilities; (77) the disclosed Adaptive Power Control Method enables high gains (>10 dB) in interference mitigation of co-channel links at the hub nodes.

The method 1100 can be applied for controlling transmit powers of at least one Microwave Backhaul network of a Microwave Backhaul system including a plurality of Microwave Backhaul networks, e.g. as described above with respect to Fig. 3a.

The method 1100 comprises: performing for at least one Microwave Backhaul network the following: acquiring 1101, for each of a plurality of microwave links of the at least one Microwave Backhaul network, information on a channel status CSn(t-a) of the respective microwave link over a specific number T of time slots (t-a), e.g. as described above with respect to Fig. 3a; determining 1102, for each microwave link, a throughput Th_n(t-a) over the respective microwave link for the specific number T of time slots t-a based on the information on the channel status CSn(t-a) of each microwave link of the at least one Microwave Backhaul network, and a time informationf_>„ indicating that the throughput Thn(t-a) over the respective microwave link is above a given link-specific threshold Thmm, e.g. as described above with respect to Fig. 3a; and determining 1103, for each microwave link, a transmit power for the respective microwave link for each time slot, upon determining that the time informationf_>„ is below a given threshold p_mm for at least one microwave link, e.g. as described above with respect to Fig. 3a.

The present disclosure also supports a computer program product including computer executable code or computer executable instructions that, when executed, causes at least one computer to execute the performing and computing steps described herein, in particular the methods and procedures described above. Such a computer program product may include a readable non-transitory storage medium storing program code thereon for use by a computer. The program code may perform the processing and computing steps described herein, in particular, the methods and procedures described above.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms “coupled” and “connected”, along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.

Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A power control device (310) for controlling transmit powers (320) of at least one Microwave Backhaul network (300) of a Microwave Backhaul system (800) including a plurality of Microwave Backhaul networks (300, 801), wherein the power control device (310) is configured to perform for at least one Microwave Backhaul network (300) the following: acquire, for each of a plurality of microwave links (111, 112, 113, 114) ofthe at least one Microwave Backhaul network (300), information on a channel status (CSn(t-a)) of the respective microwave link over a specific number ( T) of time slots ( t-a ); determine, for each microwave link (111, 112, 113, 114), a throughput (Th_n(t-α)) over the respective microwave link for the specific number (T) of time slots (t-a) based on the information on the channel status (CSn(t-a)) of each microwave link (111, 112, 113, 114) of the at least one Microwave Backhaul network (300), and a time information (b_h) indicating that the throughput (Thn(t-a)) over the respective microwave link (111, 112, 113, 114) is above a given link-specific threshold ( Thmin ); and determine, for each microwave link (111, 112, 113, 114), a transmit power (320) for the respective microwave link (111, 112, 113, 114) for each time slot, upon determining that the time information (β_n) is below a given threshold ( p_min ) for at least one microwave link (111, 112, 113, 114).

2. The power control device (310) of claim 1, wherein the information on the channel status (CSn(t-a)) ofthe respective microwave link (111, 112, 113, 114) depends on information on the channel status of each microwave link (111, 112, 113, 114) within the at least one Microwave Backhaul network (300) itself and information on the channel status of each interfering microwave link from or to another Microwave Backhaul network (801).

3. The power control device (310) of claim 1 or 2, wherein the transmit power (320) is determined by maximizing a minimum Signal- to-Interference-plus-Noise Ratio, SINR, that is related to a generic time slot and a generic microwave link.

4. The power control device (310) of one of the preceding claims, wherein the transmit power (320) is determined by maximizing (501) a sum throughput of the plurality of microwave links (111, 112, 113, 114) of the at least one Microwave Backhaul network (300) over the specific number ( T) of time slots under the constraint (502) that each microwave link (111, 112, 113, 114) provides a throughput greater than or equal to the given link-specific threshold, Thmin, for a time information greater than or equal to the given threshold, pmin.

5. The power control device (310) of claim 4, wherein the transmit power (320) is determined under the constraint to comply with given transmit power dynamic ranges and/or given output transmit power levels of the Microwave Backhaul system (800).

6. The power control device (310) of one of the preceding claims, configured to: adjust the Microwave Backhaul system (800) to employ the transmit powers (320) determined for each microwave link of the plurality of microwave links (111, 112, 113, 114) of the at least one Microwave Backhaul network (300).

7. The power control device (310) of one of the preceding claims, configured to: determine the transmit power (320) separately in both communication directions of each microwave link of the plurality of microwave links (111, 112, 113, 114) of the at least one Microwave Backhaul network (300).

8. The power control device (310) of one of the preceding claims, configured to: determine, for each microwave link, the transmit power (320) for the respective microwave link in an iterative manner time slot by time slot; and recompute the time information (/_>,,) that the throughput (Thn(t-a)) over the respective microwave link is above the given link-specific threshold ( Thmm ) after each time slot iteration.

9. The power control device (310) of one of the preceding claims, configured to: determine, for each microwave link (111, 112, 113, 114), the throughput, Thn(t-a), over the respective microwave link for the specific number ( T) of time slots based on a Signal-to-Interference-plus-Noise Ratio (SINRn(t-a)) of the respective microwave link at a respective time slot, wherein the Signal-to-Interference-plus-Noise Ratio (SINR n(t-a)) of the respective microwave link at a respective time slot ( t-a ) is based on the information on the channel status (CSn(t-a)) of each microwave link (111, 112, 113, 114) of the at least one Microwave Backhaul network (300) at the respective time slot (t-a).

10. The power control device (310) of claim 9, configured to: determine, for each microwave link (111, 112, 113, 114), the Signal-to-Interference- plus-Noise Ratio ( SINR n(t-a)) of the respective microwave link at the respective time slot (t-a) based on the following relation:

where θ_n(t — a) represents an overall attenuation occurring between a transmit device of the nth microwave link and a receive device of the «th microwave link at time slot t — a , P_n(t — a) represents the transmit power employed over the «th microwave link at time slot t — a, θ_k(t — a) represents an overall attenuation occurring between a generic k th transmit device belonging to the at least one Microwave Backhaul network and the receive device of the «th microwave link at time slot t — a, g_h®h accounts for the overall gain due to the antenna radiation pattern of the transmit device of the «th microwave link and the antenna radiation pattern of the receive device of the «th microwave link, y_k®n accounts for the overall gain due to the antenna radiation pattern of the k th transmit device and the antenna radiation pattern of the receive device of the nth microwave link, and P_n0iSe represents a measure of the receive noise power.

11. The power control device (310) of one of the preceding claims, configured to: create a channel status to optimal power, CS2P, table which comprises for each microwave link (111, 112, 113, 114) and at each time slot the acquired information on the channel status (CSn(t-a)) of the respective microwave link at the respective time slot and the associated transmit power (320).

12. The power control device (310) of claim 11, configured to: update the CS2P table with new information on the channel statuses (CSn(t-a)) and the associated transmit powers based on a predefined periodicity.

13. The power control device (310) of one of the preceding claims, configured to: derive the information on the channel status (CSn(t-a)) of the microwave links (111, 112, 113, 114) in an initialization phase from a memory accessible by the power control device (310), wherein the memory stores information acquired from available databases containing attenuation statistics for a given geographic area or from existing standard recommendations, in particular ITU recommendations, or from information acquired before the Microwave Backhaul system (800) is deployed in field.

14. The power control device (310) of one of the preceding claims, located as a central entity (110) in one of the Microwave Backhaul networks (300, 801); or distributed as a plurality of distributed entities (110, 111, 112, 113, 114) over the whole Microwave Backhaul system (800).

15. A method (1100) for controlling transmit powers of at least one Microwave Backhaul network of a Microwave Backhaul system including a plurality of Microwave Backhaul networks, wherein the method comprises: performing for at least one Microwave Backhaul network the following: acquiring (1101), for each of a plurality of microwave links of the at least one Microwave Backhaul network, information on a channel status ( CS_n(t-a )) of the respective microwave link over a specific number ( T) of time slots (t-a); determining (1102), for each microwave link, a throughput (Thn(t-a)) over the respective microwave link for the specific number (T) of time slots (t-a) based on the information on the channel status (CSn(t-a)) of each microwave link of the at least one Microwave Backhaul network, and a time information (fin) indicating that the throughput (Thn(t-a)) over the respective microwave link is above a given link-specific threshold ( Thmm ); and determining (1103), for each microwave link, a transmit power for the respective microwave link for each time slot, upon determining that the time information (fin) is below a given threshold (p,rm ) for at least one microwave link.

16. A computer program product including program code for performing the method according to any one of claim 15, when the program code is run by a processor.