Estimating interfering channel gains of wireless backhaul links

Abstract

Disclosed are a transmitter device (1, T j ) and a receiver device (2, R k ) for a wireless backhaul network (7) of a mobile communication network, a radio resource management, RRM, device (3) for the mobile communication network, and methods (4, 5, 6) of operating said devices. The devices are configured to estimate cross-link channel gains in the wireless backhaul network (7) based on analog and digital signaling and performing cross-correlations. This avoids a scheduling of pilot transmissions in different time slots as well as additional processing functionalities at the baseband modules of the receiver devices (2, R k ).

Description

[0001]ESTIMATING INTERFERING CHANNEL GAINS OF WIRELESS BACKHAUL LINKS TECHNICAL FIELD The present disclosure relates generally to the field of mobile communication networks, and in particular to transmitter and receiver devices for a wireless backhaul network of a mobile communication network, a radio resource management (RRM) device for the mobile communication network, and methods of operating said devices. BACKGROUND ART In mobile communication networks, wireless (or mobile) backhaul networks are used to connect cell sites and a core network. For capacity reasons or to extend network coverage, wireless backhaul networks may comprise multiple closely spaced wireless point-to-point links with small angular separation, thus mutually interfering. A mutual interference of the closely spaced links may be addressed by optimized RRM schemes such as, but not limited to, an optimized allocation of transmit powers. Such schemes typically rely on the knowledge of both direct-link channel gains and cross-link channel gains. While the direct-link channel gains can be acquired by each receiver independently, the cross-link channel gains may be obtained by Time Division Multiple Access (TDMA)-, Space Division Multiple Access (SDMA)- or Code Division Multiple Access (CDMA)-based methods. In the TDMA-based method, each transmitter sends pilot signals in mutually orthogonal time slots, such that only one transmitter is active in a given time slot. Since TDMA calls for the use of orthogonal time windows for the estimation of the cross-link channel gains, transmissions of pilot symbols are not continuous but scheduled over different time slots, leading to higher latencies and lower spectral efficiencies. SDMA and CDMA can both solve this time-domain inefficiency. The SDMA-based method is based on the transmission of pilot sequences that overlap in both time and frequency. The cross-link channel gains can be derived as outputs of a shared baseband Multiple-Input Multiple-Output (MIMO) equalization block. However, SDMA requires a MIMO modem unit that is able to perform joint baseband processing of the signals received by the receivers. Thus, depending on the network topology, either a specialized MIMO processing unit in a separate device, or a heavy signaling exchange in a distributed architecture are needed. The CDMA-based method involves mutually orthogonal training sequences that overlap in time and frequency domain. The receivers estimate the cross-link channel gain by cross-correlating the received baseband signal with the training sequence used by the respective transmitter. Similarly to SDMA, the CDMA approach calls for a dedicated baseband modem unit at the respective receiver to perform the cross-correlation. SUMMARY It is an object to overcome the above-mentioned and other drawbacks. The foregoing and other objects are 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, a transmitter device for a wireless backhaul network of a mobile communication network is provided. The transmitter device comprises a wireless transmitter that is configured to transmit a wireless signal to a receiver device of the wireless backhaul network. A transmit power of the wireless signal is modulated with a predefined transmit power signature that extends over a plurality of time slots. The proposed analog signaling of transmit power signatures preserves a transmission continuity, so that network nodes do not need to schedule their transmissions over time. As used herein, a wireless transmitter may refer to a combination of an electric modulation circuit and an antenna that is configured to transmit a wireless signal. As used herein, a mobile communication network may refer to a cellular communication network, such as a 4th generation (4G) or 5th generation (5G) 3GPP network. As used herein, a transmit power signature may refer to a finite sequence of real numbers for modulation of a transmit power of a transmitter device. According to a second aspect, a receiver device for a wireless backhaul network of a mobile communication network is provided. The receiver device comprises a wireless receiver that is configured to receive a wireless signal from a transmitter device of the wireless backhaul network. A transmit power of the wireless signal is modulated with a predefined transmit power signature extending over a plurality of time slots. The receiver device further comprises a processor that is configured to determine a sequence of observables, one per each of the time slots, in accordance with a mean squared error of a symbol constellation of the received wireless signal within a respective time slot ^ of the plurality of time slots. The wireless receiver is further configured to send a deliverable to a radio resource management, RRM, device of the mobile communication network. The deliverable depends on the sequence of observables. The proposed digital signaling of deliverables (and / or observables) delegates stand-alone processing aspects to individual receiver devices and thereby avoids the introduction of additional and more complex baseband modem functionalities. As used herein, a wireless receiver may refer to a combination of an electric demodulation circuit and an antenna configured to receive a wireless signal. As used herein, a processor such as a central processing unit (CPU), digital signal processor (DSP), application-specific integrated circuit (ASIC) of field-programmable gate array (FPGA) may refer to a digital electric circuit that is configured to execute instructions of a computer program or to execute instructions implemented in circuitry of the processor. As used herein, modulation may refer to a procedure of varying a property of a carrier signal in accordance with a modulation signal that typically contains information to be transmitted. As used herein, a mean squared error may refer to an average of squared errors, such as the errors between actual and predicted symbol values in connection with a given symbol constellation of a received wireless signal. As used herein, a symbol constellation or constellation diagram may refer to a representation of actual values (i.e., samples) or predicted values of a digitally modulated signal in a complex plane. As used herein, observables may refer to processing results whose content depends on the circumstances, such as a location of the processing yielding the processing results. As used herein, radio resource management may refer to a functional entity of a mobile communication network that is responsible for efficient utilization of limited spectrum resources, also in relation to a wireless backhaul network of the mobile communication network. As used herein, a cross-link channel gain may refer to a channel gain that is effective between wireless transmitters and receivers of different point-to-point links, whereas a direct-link channel gain may refer to a channel gain that is effective between wireless transmitters and receivers of a same point-to-point link. According to a third aspect, a radio resource management, RRM, device for a mobile communication network is provided. The RRM device comprises a communication interface configured to receive a respective deliverable from a plurality of receiver devices of a wireless backhaul network of the mobile communication network. The respective deliverable depends on a sequence of observables. The RRM device further comprises a processor configured to estimate a cross-link channel gain between a first transmitter device of a plurality of transmitter devices of the wireless backhaul network and a second receiver device of the plurality of receiver devices in accordance with cross-correlations between the sequence of observables of the second receiver device and a predefined transmit power signature of the first transmitter device extending over a plurality of time slots. The proposed cross-link channel gain estimation technique based on relatively simple digital processing (i.e., cross-correlations) avoids the introduction of additional and more complex baseband modem functionalities. The knowledge of the cross-link channel gains, in turn, enables the application of convenient RRM schemes, with remarkable performance advantages. In a possible implementation form, the predefined transmit power signatures of the plurality of transmitter devices may be mutually orthogonal. In a possible implementation form, the predefined transmit power signatures of the plurality of transmitter devices may respectively have an impulsive autocorrelation function. In a possible implementation form, the predefined transmit power signatures of the plurality of transmitter devices may respectively have a zero-mean value. In a possible implementation form, the predefined transmit power signatures of the plurality of transmitter devices may start synchronously. In a possible implementation form, the predefined transmit power signatures of the plurality of transmitter devices may repeat following the lapse of the time slots. In a possible implementation form, the predefined transmit power signatures of the plurality of transmitter devices may repeat in accordance with a given repetition period. In a possible implementation form, the predefined transmit power signatures of the plurality of transmitter devices may respectively not exceed an absolute value of 3 dB, preferably not exceed an absolute value of 0,5 dB. In a possible implementation form, a duration of each of the time slots may exceed a symbol duration for carrying out symbol modulation or demodulation by at least a factor of 1, preferably by a factor of 1000, and more preferably by a factor of 1000000. In a possible implementation form, the respective observable of the sequence of observables may comprise: the mean squared error of the symbol constellation of the received wireless signal within the respective time slot, the received power level of the wireless signal within the respective time slot, and the average received overall noise and interference power level outside the time slots. In a possible implementation form, the processor of the receiver device or the RRM device may further be configured to calculate cross-correlations between the sequence of observables of the kth receiver device and the predefined transmit power signature of the jth transmitter device. In a possible implementation form, the deliverable may comprise one or more of: the sequence of observables, and the cross-correlations between the sequence of observables of the kth receiver device and the predefined transmit power signature of the jth transmitter device. In a possible implementation form, the estimated cross-link channel gain may comprise: a maximum value of the cross-correlations, the average received overall noise and interference power level of the kth receiver device, and the average transmit power of the wireless signal of the jth transmitter device. In a possible implementation form, the RRM device may comprise one of: none of the plurality of receiver devices, one or more of the pluralities of receiver devices, and the plurality of receiver devices. In a possible implementation form, the transmitter device may further be configured to provide the RRM device with its average transmit power. In a possible implementation form, the receiver device may further be configured to provide the RRM device with an estimate of the average transmit power of the corresponding transmitter device. In a possible implementation form, the RRM device may further be configured to allocate the average transmit powers of the plurality of transmitter devices. According to a fourth aspect, a method of operating a transmitter device for a wireless backhaul network of a mobile communication network is provided. The method comprises transmitting a wireless signal to a receiver device of the wireless backhaul network. A transmit power of the wireless signal is modulated with a predefined transmit power signature extending over a plurality of time slots. According to a fifth aspect, a method of operating a receiver device for a wireless backhaul network of a mobile communication network is provided. The method comprises receiving a wireless signal from a transmitter device of the wireless backhaul network. A transmit power of the wireless signal is modulated with a predefined transmit power signature extending over a plurality of time slots. The method further comprises determining a sequence of observables, one per each of the time slots, in accordance with a mean squared error of a symbol constellation of the received wireless signal within the respective time slot ^ of the plurality of time slots. The method further comprises sending a deliverable to a radio resource management, RRM, device of the mobile communication network. The deliverable depends on the sequence of observables. According to a sixth aspect, a method of operating a radio resource management, RRM, device for a mobile communication network is provided. The method comprises receiving a respective deliverable from a plurality of receiver devices of wireless backhaul networks of the mobile communication network. The respective deliverable depends on a sequence of observables. The method further comprises estimating a cross-link channel gain between a jth transmitter device of a plurality of transmitter devices of the wireless backhaul network and a kth receiver device of the plurality of receiver devices in accordance with cross-correlations between the sequence of observables of the kth receiver device and a predefined transmit power signature of the jth transmitter device extending over a plurality of time slots. According to a seventh aspect, a computer program is provided, comprising a program code for performing the method of the fourth, fifth or sixth aspect when executed on a computer. The disclosed devices and methods enable an estimation of the gain of all the interfering channels affecting each point-to-point wireless link of a wireless backhaul network without scheduling the transmissions of the involved network nodes in different time slots according to state-of-the-art multiple access schemes that would instead lead either to inefficient radio resource utilization or to the implementation of specific and complex baseband processing modules. Instead, the methods can be implemented in the existing network nodes through cost- efficient software-only upgrades that do not require their physical replacement. This increases spectral efficiency, decreases system complexity as well as expenses on the side of the mobile network operators, and reduces a time-to-market. BRIEF DESCRIPTION OF DRAWINGS The above-described aspects and implementations will now be explained with reference to the accompanying drawings, in which the same or similar reference numerals designate the same or similar elements. The drawings may be at least partly schematic, and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and purpose become apparent to those skilled in the art. FIG.1 illustrates schematically a wireless backhaul network in accordance with the present disclosure; FIG.2 illustrates schematically a modulation of transmit powers of wireless signals of the wireless backhaul network in accordance with the present disclosure; FIG.3 illustrates exemplary transmit power signatures in accordance with the present disclosure; FIGs.4 – 6 illustrate schematically various scheduling options for the modulation of the transmit powers of the wireless signals of the wireless backhaul network in accordance with the present disclosure; FIGs.7 – 8 illustrate schematically various localization options for the RRM device in accordance with the present disclosure; FIGs.9 – 11 illustrate schematically various disclosure options for average transmit powers of the wireless signals of the wireless backhaul network to the RRM device in accordance with the present disclosure; and FIGs.12 – 14 illustrate schematically flow charts of methods in accordance with the present disclosure of operating the transmitter, receiver and RRM devices. DETAILED DESCRIPTIONS OF DRAWINGS In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and which show, by way of illustration, specific aspects of implementations of the present disclosure or specific aspects in which implementations of the present disclosure may be used. It is understood that implementations of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. 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. For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding apparatus or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary implementations and / or aspects described herein may be combined with each other, unless specifically noted otherwise. FIG.1 illustrates schematically a wireless backhaul network 7 in accordance with the present disclosure. The wireless backhaul links belonging to the wireless backhaul network 7 may form part of a mobile communication network. In accordance with FIG.1, the wireless backhaul network 7 may comprise a plurality of closely spaced point-to-point links that experience mutual interference, indicated as inclined dashed arrows. The respective point-to-point link comprises a transmitter device 1, ^^(wherein ^ = 1,2, … , ^) and a corresponding receiver device 2, ^^(wherein ^ = 1,2, … , ^), both indicated as circles. In other words, the wireless backhaul network 7 may comprise a plurality of transmitter devices 1, ^^and a plurality of receiver devices 2, ^^. The respective transmitter device 1, ^^of the plurality of transmitter devices 1, ^^comprises a wireless transmitter 11 configured to transmit a wireless signal (being indicated as horizontal solid arrow) to the corresponding receiver device 2, ^^of the plurality of receiver devices 2, ^^. The respective receiver device 2, ^^of the plurality of receiver devices 2, ^^comprises a wireless receiver 21 configured to receive the wireless signal from the corresponding transmitter device 1, Tj of the plurality of transmitter devices 1, ^^. The respective receiver device 2, ^^further comprises a processor 22 whose functioning will be explained in more detail below. The wireless receiver 21 of the respective receiver device 2, ^^is further configured to send a deliverable (i.e., a processing result whose content depends on the circumstances explained in more detail below) to a radio resource management (RRM) device 3 for the wireless backhaul network 7 of the mobile communication network. The RRM device 3 may serve a plurality of wireless backhaul networks 7, including the wireless backhaul network 7 depicted in FIG.1. The RRM device 3 comprises a communication interface 31, being configured to receive the deliverables of the plurality of receiver devices 2, ^^. The communication interface 31 may comprise a wireless interface or a wire-line interface. The RRM device 3 further comprises a processor 32 whose functioning will also be explained in more detail below. FIG.2 illustrates schematically a modulation of transmit powers ^^^^ ^ ^^(^)of wireless signals of the wireless backhaul network 7 in accordance with the present disclosure. As set out in FIG.2, the transmit powers ^^^^ ^ ^^(^) of the wireless signals (i.e., of the plurality of transmitter devices 1, ^^) are modulated with predefined transmit power signatures 8, that extend over a plurality of W time slots (where ^ = 1,2, … , ^ denotes the respective timeslot). FIG.3 illustrates exemplary transmit power signatures ^^,^^(^) in accordance with the present disclosure. The following conditions may apply (note that the transmit power signatures may be expressed in terms of linear or logarithmic scales, depending on mathematical convenience): First, the predefined transmit power signatures ^^(^)of the plurality of transmitter devices 1, ^^may be mutually orthogonal: Second, the predefined transmit power signatures ^^(^) of the plurality of transmitter devices 1, ^^may respectively have an impulsive auto-correlation function (where the ⋆ operator denotes a cross-correlation): Third, the predefined transmit power signatures ^^,^^(^)of the plurality of transmitter devices 1, ^^may respectively have a zero-mean value:∑^ ^^^^^,^^(^) = 0. Fourth, the predefined transmit power signatures ^^(^)of the plurality of transmitter devices 1, ^^may respectively not exceed an absolute value of 3 dB, preferably not exceed an absolute value of 0,5 dB: ^^^,^^(^)^ ≤ 3 ^^ (or ^^^,^^(^)^ ≤ 0,5 ^^) In other words, the transmitter devices 1, ^^change their respective transmit powers with small absolute deviations. Additionally, a duration ^ of each of the ^ time slots may exceed a symbol duration ^^^^^for carrying out symbol modulation or demodulation by at least a factor of 1, preferably by a factor of 1000, and more preferably by a factor of 1000000: ^ ≫ ^^^^^In accordance with FIG.3, the processor 22 of the respective receiver device 2, ^^is configured to determine a sequence of W observables 9, ^^,^^(^), ^ = 1,2, … , ^, i.e., one per each of the W time slots of the predefined transmit power signatures 8, ^^(^), in accordance with a mean squared error ^^^^,^^(^) of a symbol constellation of the received wireless signal within a respective time slot ^ of the plurality of W time slots. More specifically, the respective observable 9, ^^.^^(^)of the sequence of W observables 9, ^^.^^(^)may comprise: the mean squared error ^^^^,^^(^) of the symbol constellation of the received wireless signal within the respective time slot ^, the received power level ^^^,^^^(^) of the wireless signal within the respective time slot ^, and the average received overall (or background) noise and interference power level ^ ^^^ ^,^^outside the W time slots: ^ ^^^ ^,^^= 10 ∙ ^^^^^{^^^^^}, Note that an equivalent computation in terms of a linear scale involves multiplication instead of addition and division instead of subtraction. The mean squared error ^^^^(^)measures the average of squared errors. In other words, the differences between the actual values ^^of the symbols of the received wireless signal and the predicted values ^^^of the given symbol constellation are squared and averaged: The received power level ^^^^(^)of the received wireless signal within the respective time slot ^ can be estimated / measured according to known state-of-the-art methods, and is based on the direct-link channel gain ℎ^(^, ^)between transmitter device 1, ^^and receiver device 2, ^^of a same point-to-point link. The average received overall noise and interference power level ^ ^^^ ^,^^can be estimated / measured when none of the transmitter devices 1, ^^in the network performs the disclosed modulation technique. One of the processor 22 of the receiver device 2, ^^or the processor 32 of the RRM device 3 may further be configured to calculate cross-correlations ⋆ ^^,^^(^) between the sequence of W observables 9, ^ th ^,^^(^)of the k receiver device 2, ^^and the predefined transmit power signature 8, ^^,^^(^),^ = 1,2, … , ^ of the jth transmitter device 1, ^^. If the processor 32 of the RRM device 3 has this cross-correlation processing capability, then the above-mentioned deliverable of the receiver device 2, ^^comprises the sequence of W observables 9, ^^,^^(^)only. If the processor 22 of the receiver device 2, ^^has this cross-correlation processing capability, then the above-mentioned deliverable of the receiver device 2, ^^may alternatively or additionally comprise the cross-correlations ⋆ ^^,^^(^)^ between the sequence of W observables 9, ^^,^^(^)of the kth receiver device 2, ^^and the predefined transmit power signature 8, ^^,^^(^),^ = 1,2, … , ^ of the jth transmitter device 1, ^^. In any case, the deliverable for the RRM device 3 depends on the sequence of W observables 9, ^^,^^(^). The processor 32 of the RRM device 3 is further configured to estimate a cross-link channel gain ℎ^(^, ^,^ ≠ ^) between a first transmitter device 1, ^^of the plurality of transmitter devices 1, ^^, ^ = 1,2, … , ^ of the wireless backhaul network 7 and a second receiver device 2, ^^of the plurality of receiver devices 2, ^^, ^ = 1,2, … , ^ in accordance with the cross-correlations ^^^,^^(^)⋆ ^^,^^(^)^ between the sequence of W observables 9, ^^,^^(^)of the second receiver device 2, ^^and the predefined transmit power signature 8, ^^,^^(^), ^ = 1,2, … , ^ of the first transmitter device 1, ^^extending over the plurality of W time slots. The estimated cross-link channel gain ℎ^(^, ^,^ ≠ ^) may comprise a maximum value ^^^{.}of the cross-correlations ^^^,^^(^)⋆ ^^,^^(^)^ , the average received overall noise and interference power level ^^^^ th ^ of the k receiver device 2, ^^, and the average transmit power ^^^^ of the wireless signal o th ^ f the j transmitter device 1, ^^. Note that the estimated cross-link channel gain ℎ^(^, ^,^ ≠ ^) in terms of a linear scale resembles an inverted signal-to-noise ratio. Note that an equivalent computation in terms of a logarithmic scale involves subtraction instead of division. FIGs. 4 – 6 illustrate schematically various scheduling options for the modulation of the transmit powers ^^^^ ^ ^^(^) of the wireless signals of the wireless backhaul network 7 in accordance with the present disclosure. In accordance with FIGs.4 – 6, the predefined transmit power signatures ^^(^)of the plurality of transmitter devices 1, ^^respectively extend over a plurality of W time slots, each having duration ^. In accordance with FIG. 4, the predefined transmit power signatures ^^(^)may start synchronously: ^^,^= ^^,^= ^^,^= ⋯ = ^^In accordance with FIG. 5, the predefined transmit power signatures ^^(^)may start asynchronously: In accordance with FIGs.4 – 6, the predefined transmit power signatures ^^(^)may repeat in accordance with a given repetition period ^^^^, resulting in a recurrent (and potentially intermittent) modulation of the transmit powers ^^^^ ^ ^^(^)of the wireless signals of the wireless backhaul network 7. In accordance with FIG. 6, the predefined transmit power signatures ^^(^) may repeat following the lapse of the W time slots. In other words, the duration ^ ∙ ^ of the plurality of W time slots may correspond to the given repetition period ^^^^, resulting in a continuous modulation of the transmit powers ^^^^ ^ ^^(^)of the wireless signals of the wireless backhaul network 7. FIGs. 7 – 8 illustrate schematically various localization options for the RRM device 3 in accordance with the present disclosure. In accordance with FIG. 7, the RRM device 3 may comprise one or more of the pluralities of receiver devices 2, ^^, and the plurality of receiver devices 2, ^^., resulting in a partially lumped implementation of the RRM device 3 and the one or more of the pluralities of receiver devices 2, ^^. An external signaling of the deliverables of the remaining standalone receiver devices 2, ^^to the RRM device 3 still applies. In accordance with FIG.8, the RRM device 3 may comprise the plurality of receiver devices 2, ^^, resulting in a fully lumped implementation of the RRM device 3 and the plurality of receiver devices 2, ^^. As such, no external signaling of any deliverables to the RRM device 3 applies. In accordance with FIG. 1, the RRM device 3 may comprise none of the plurality of receiver devices 2, ^^at all, resulting in standalone implementations of the RRM device 3 and the plurality of receiver devices 2, ^^, wherein a comprehensive external signaling of the deliverables to the RRM device 3 applies. FIGs. 9 – 11 illustrate schematically various disclosure options for average transmit powers ^^^^ ^ of the wireless signals of the wireless backhaul network 7 to the RRM device 3 in accordance with the present disclosure. The average transmit powers ^^^^ ^ serve as input for the estimation of the cross-link channel gain ℎ^(^, ^,^ ≠ ^) by the RRM device 3. The RRM unit is assumed to know the average transmit powers ^ ^ employed by the plurality of transmitter devices 1, ^^,^ = 1,2, … , ^. This information is maintained by conventional RRM devices. However, different implementations for disclosing this knowledge to the RRM device 3 will be discussed in the following. In accordance with FIG.9, the RRM device 3 may be configured to allocate the average transmit powers ^^^^ ^ , ^ = 1,2, … , ^ of the plurality of transmitter devices 1, ^^,^ = 1,2, … , ^. In other words, the RRM device 3 may already have access to the average transmit power ^^^^ ^ of the respective transmitter device 1, ^^because it actually allocated and saved the respective value. In accordance with FIG.10, the respective receiver device 2, ^^may be configured to provide the RRM device 3 with an estimate of the average transmit power ^^^^ ^ of the corresponding transmitter device 1, ^^, j=k. For example, channel sounding techniques may be used to estimate the average transmit powers . In accordance with FIG.11, the respective transmitter device 1, ^^may be configured to provide the RRM device 3 with its average transmit power ^^^^ ^ . FIGs. 12 – 14 illustrate schematically flow charts of methods 4, 5, 6 in accordance with the present disclosure of operating the transmitter, receiver and RRM devices 1, 2, 3. The method 4 of operating a transmitter device 1, ^^,^ = 1,2, … , ^ for a wireless backhaul network 7 of a mobile communication network is depicted in FIG.12. The method 4 comprises a step of transmitting 41 a wireless signal to a receiver device 2, ^^of the wireless backhaul network 7. A transmit power ^^^^ ^ ^^(^)of the wireless signal is modulated with a predefined transmit power signature 8, ^^(^),^ = 1,2, … , ^ extending over a plurality of W time slots. The method 4 may be performed by the transmitter device 1, ^^of the first aspect or any of its implementations. The method 5 of operating a receiver device 2, ^^,^ = 1,2, … , ^ for a wireless backhaul network 7 of a mobile communication network is depicted in FIG.13. The method 5 comprises a step of receiving 51 the wireless signal from a (corresponding) transmitter device 1, T of the wireless backh ^^^ j aul network 7. A transmit power ^^^^(^)of the wireless signal is modulated with a predefined transmit power signature 8, , ^ = 1,2, … , ^ extending over a plurality of W time slots. The method 5 may be performed by the receiver device 2, ^^of the second aspect or any of its implementations. The method 5 further comprises a step of determining 52 a sequence of W observables 9, ^^.^^(^),^ = 1,2, … , ^, one per each of the W time slots, in accordance with a mean squared error ^^^^,^^(^) of a symbol constellation of the received wireless signal within the respective time slot ^ of the plurality of W time slots. The method 5 further comprises a step of sending 53 a deliverable to a radio resource management, RRM, device of the mobile communication network. The deliverable depends on the sequence of W observables 9, ^^,^^(^). The method 6 of operating a radio resource management, RRM, device 3 for a mobile communication network is depicted in FIG.14. The method 6 comprises a step of receiving 63 a respective deliverable from a plurality of receiver devices 2, ^^, ^ = 1,2, … , ^ of a wireless backhaul network 7 of the mobile communication network. The respective deliverable depends on a sequence of W observables The method 6 further comprises a step of estimating 64 a cross-link channel gain ℎ^(^, ^,^ ≠ ^) between a jth transmitter device 1, ^^of a plurality of transmitter devices 1, ^^,^ = 1,2, … , ^ of the wireless backhaul network 7 and a kth receiver device 2, ^^of the plurality of receiver devices 2, ^^in accordance with a cross-correlation ^^,^^(^)^ between the sequence of W observables 9, = 1,2, … , ^ of the kth receiver device 2, ^^and a predefined transmit power signature 8, ^^,^^(^) of the jth transmitter device 1, ^^extending over a plurality of W time slots. The method 6 may be performed by the RRM device 3 of the third aspect or any of its implementations. The present disclosure has been described in conjunction with various implementations as examples. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation. A computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Claims

CLAIMS 1. A transmitter device (1, ^^,^ = 1,2, … ,for a wireless backhaul network (7) of a mobile communication network, the transmitter device (1, ^^) comprising: a wireless transmitter (11) configured to ^ transmit a wireless signal to a receiver device (2, ^^) of the wireless backhaul network (7), wherein a transmit power (^^^^ ^ ^^(^)) of the wireless signal is modulated with a predefined transmit power signature (8, ^^(^), ^ = 1,2, … , ^) that extends over a plurality of W time slots.

2. A receiver device (2, ^^,^ = 1,2, … ,for a wireless backhaul network (7) of a mobile communication network, the receiver device (2, ^^) comprising: a wireless receiver (21) configured to ^ receive a wireless signal from a transmitter device (1, Tj) of the wireless backhaul network (7), a transmit power (^^^^ ^ ^^(^)) of the wireless signal being modulated with a predefined transmit power signature (8, ^^(^), ^ = 1,2, … , ^) extending over a plurality of W time slots; and a processor (22) configured to ^ determine a sequence of W observables (9, ^^,^^(^) , ^ = 1,2, … , ^ ), the sequence comprising one respective observable for each of the W time slots, in accordance with a mean squared error (^^^^,^^(^)) of a symbol constellation of the received wireless signal within a respective time slot ^ of the plurality of W time slots; wherein the wireless receiver (21) is further configured to ^ send a deliverable to a radio resource management, RRM, device (3) of the mobile communication network, the deliverable depending on the sequence of W observables (9,3. A radio resource management, RRM, device (3) for a mobile communication network, comprising: a communication interface (31) configured to^ receive a respective deliverable from a plurality of receiver devices (2, ^^,^ = 1,2, … , ^) of a wireless backhaul network (7) of the mobile communication network, the respective deliverable depending on a sequence of W observables (9, ^^,^^(^)); a processor (32) configured to ^ estimate a cross-link channel gain (ℎ^(^, ^),^ ≠ ^) between a first transmitter device (1, ^^) of a plurality of transmitter devices (1, ^^,^ = 1,2, … , ^) of the wireless backhaul network (7) and a second receiver device (2, ^^, ^ = 1,2, … , ^) of the plurality of receiver devices (2, ^^) in accordance with cross-correlations (^^^,^^(^)⋆ ^^,^^(^)^) between the sequence of W observables (9, ^^,^^(^)) of the second receiver device (2, ^^) and a predefined transmit power signature (8, ^^,^^(^),^ = 1,2, … , ^) of the first transmitter device (1, ^^) extending over a plurality of W time slots.

4. The transmitter device (1, ^^) of claim 1, or the receiver device (2, ^^) of claim 2, or the RRM device (3) of claim 3, wherein the predefined transmit power signatures (^^(^)) of the plurality of transmitter devices (1, ^^) are mutually orthogonal.

5. The transmitter device (1, ^^) of claim 1 or 4, or the receiver device (2, ^^) of claim 2 or 4, or the RRM device (3) of claim 3 or 4, wherein the predefined transmit power signatures (^^(^)) of the plurality of transmitter devices (1, ^^) respectively have an impulsive autocorrelation function.

6. The transmitter device (1, ^^) of any one of the claims 1 or 4 – 5, or the receiver device (2, ^^) of any one of the claims 2 or 4 – 5, or the RRM device (3) of any one of the claims 3 – 5, wherein the predefined transmit power signatures (^^(^)) of the plurality of transmitter devices (1, ^^)have a zero-mean value, respectively.

7. The transmitter device (1, ^^) of any one of the claims 1 or 4 – 6, or the receiver device (2, ^^) of any one of the claims 2 or 4 – 6, or the RRM device (3) of any one of the claims 3 – 6, wherein the predefined transmit power signatures (^^(^)) of the plurality of transmitter devices (1, ^^) start synchronously.

8. The transmitter device (1, ^^) of any one of the claims 1 or 4 – 7, or the receiver device (2, ^^) of any one of the claims 2 or 4 – 7, or the RRM device (3) of any one of the claims 3 – 7, wherein the predefined transmit power signatures (^^(^)) of the plurality of transmitter devices (1, ^^) repeating following the lapse of the W time slots.

9. The transmitter device (1, ^^) of any one of the claims 1 or 4 – 8, or the receiver device (2, ^^) of any one of the claims 2 or 4 – 8, or the RRM device (3) of any one of the claims 3 – 8, wherein the predefined transmit power signatures (^^(^)) of the plurality of transmitter devices (1, ^^) repeat in accordance with a given repetition period10. The transmitter device (1, ^^) of any one of the claims 1 or 4 – 9, or the receiver device (2, ^^) of any one of the claims 2 or 4 – 9, or the RRM device (3) of any one of the claims 3 – 9, wherein the predefined transmit power signatures (^^,^^(^)) of the plurality of transmitter devices (1, ^^)do not exceed an absolute value of 3 dB.

11. The transmitter device (1, ^^) of any one of the claims 1 or 4 – 10, or the receiver device (2, ^^) of any one of the claims 2 or 4 – 10, or the RRM device (3) of any one of the claims 3 – 10, wherein a duration (^) of each of the ^ time slots exceeds a symbol duration (^^^^^) for carrying out symbol modulation or demodulation by a factor of at least 1.

12. The receiver device (2, ^^) of any one of the claims 2 or 4 – 11, or the RRM device (3) of any one of the claims 3 – 11, wherein the respective observable (9,(^)) of the sequence of W observables (9, ^^.^^(^), ^ = 1,2, … , ^) comprises: ^ the mean squared errorof the symbol constellation of the received wireless signal within the respective time slot ^, ^ the received power levelthe wireless signal within the respective time slot ^, and ^ the average received overall noise and interference power level (^ ^^^ ^,^^) outside the W time slots.

13. The receiver device (2, ^^) of any one of the claims 2 or 4 – 12, or the RRM device (3) of any one of the claims 3 – 12, wherein the processor (22, 32) is further configured to: ^ calculate cross-correlations(^)) between the sequence of W observables (9, ^^,^^(^)) of the kth receiver device (2, ^^) and the predefined transmit power signature (8, ^^,^^(^),^ = 1,2, … , ^) of the jth transmitter device (1, ^^).

14. The receiver device (2, ^^) of claim 13, or the RRM device (3) of claim 13, wherein the deliverable comprises one or more of: ^ the sequence of W observables (9, ^^,^^(^)), and ^ the cross-correlations (^^^,^^(^)⋆ ^^,^^(^)^) between the sequence of W observables (9, ^^,^^(^)) of the kth receiver device (2, ^^) and the predefined transmit power signature (8, ^^,^^(^),^ = 1,2, … , ^) of the jth transmitter device (1, ^^).

15. The RRM device (3) of any one of the claims 3 – 14, wherein the estimated cross-link channel gain (ℎ^(^, ^),^ ≠ ^) comprises: ^ a maximum value of the cross-correlations (^^^^^^,^^(^)⋆ ^^,^^(^)^), ^ the average received overall noise and interference power level (^^^^ th ^ ) of the k receiver device (2, ^^), and ^ the average transmit power ^^^^ th ^ of the wireless signal of the j transmitter device (1, ^^).

16. The RRM device (3) of any one of the claims 3 – 15, comprising one of: ^ none of the plurality of receiver devices (2, ^^), ^ one or more of the pluralities of receiver devices (2, ^^), and ^ the plurality of receiver devices (2, ^^).

17. The transmitter device (1, ^^) of any one of the claims 1 or 4 – 11, further configured to: ^ provide the RRM device (3) with its average transmit power (^^^^ ^ ).

18. The receiver device (2, ^^) of any one of the claims 2 or 4 – 14, further configured to:^ provide the RRM device (3) with an estimate of the average transmit power (^^^^ ^ ) of the corresponding transmitter device (1, ^^, j=k).

19. The RRM device (3) of any one of the claims 3 – 16, further configured to: ^ allocate the average transmit powers (^^^^ ^ , ^ = 1,2, … , ^) of the plurality of transmitter devices (1, ^^,^ = 1,2,20. A method (4) of operating a transmitter device (1, ^^,^ = 1,2, … , ^) for a wireless backhaul network (7) of a mobile communication network, the method (4) comprising: ^ transmitting (41) a wireless signal to a receiver device (2, ^^) of the wireless backhaul network (7), wherein a transmit power (^^^^ ^ ^^(^)) of the wireless signal is modulated with a predefined transmit power signature (8,, ^ = 1,2, … ,that extends over a plurality of W time slots.

21. A method (5) of operating a receiver device (2, ^^,^ = 1,2, … ,for a wireless backhaul network (7) of a mobile communication network, the method (5) comprising: ^ receiving (51) a wireless signal from a transmitter device (1, Tj) of the wireless backhaul network (7), a transmit power (^^^^ ^ ^^(^)) of the wireless signal being modulated with a predefined transmit power signature (8,= 1,2, … , ^) that extends over a plurality of W time slots; ^ determining (52) a sequence of W observables (9, ^^.^^(^),^ = 1,2, … , ^), the sequence of W observables comprising one respective observable for each of the W time slots, in accordance with a mean squared error (^^^^,^^(^)) of a symbol constellation of the received wireless signal within the respective time slot ^ of the plurality of W time slots; and ^ sending (53) a deliverable to a radio resource management, RRM, device of the mobile communication network, the deliverable depending on the sequence of W observables (9,22. A method (6) of operating a radio resource management, RRM, device (3) for a mobile communication network, the method (6) comprising^ receiving (63) a respective deliverable from a plurality of receiver devices (2, ^^,^ = 1,2, … , ^) of a wireless backhaul network (7) of the mobile communication network, the respective deliverable depending on a sequence of W observables (9, ^^,^^(^)); and ^ estimating (64) a cross-link channel gain (ℎ^(^, ^),^ ≠ ^) between a jth transmitter device (1, ^^) of a plurality of transmitter devices (1, ^^,^ = 1,2, … , ^ ) of the wireless backhaul network (7) and a kth receiver device (2, ^^) of the plurality of receiver devices (2, ^^) in accordance with cross-correlationsbetween the sequence of W observables (9, ^ th ^,^^(^), ^ = 1,2, … , ^) of the k receiver device (2, ^^) and a predefined transmit power signature (8, ^^,^^(^)) of the jth transmitter device (1, ^^) that extends over a plurality of W time slots.

23. A computer program comprising a program code for performing the method (4) of claim 20 or the method (5) of claim 21 or the method (6) of claim 22 when executed on a computer.

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