WO2015096024A1

WO2015096024A1 - Method and apparatus for improving performance of cellular and d2d communications

Info

Publication number: WO2015096024A1
Application number: PCT/CN2013/090303
Authority: WO
Inventors: Ming Lei; Dalin Zhu; Chen Xu; Lingyang Song
Original assignee: Nec Corporation
Priority date: 2013-12-24
Filing date: 2013-12-24
Publication date: 2015-07-02

Abstract

Embodiments of the disclosure provide methods and apparatuses for improving performance of both cellular communication and D2D communication in a communication system. In a method according to embodiments of the present invention, a beamforming matrix for minimizing interference from the cellular communication to the D2D communication is determined, and a D2D transmit power is calculated based on the beamforming matrix to improve throughput of the communication system.

Description

METHOD AND APPARATUS FOR IMPROVING PERFORMANCE OF CELLULAR AND D2D COMMUNICATIONS

FIELD OF THE INVENTION

[0001] Embodiments of the present invention generally relate to communication techniques. More particularly, embodiments of the present invention relate to a method and apparatus for improving performance of both cellular communication and Device-to-Device (D2D) communication in a communication system.

BACKGROUND OF THE INVENTION

[0002] With the use of high-speed data service becoming more widespread, wireless communication users' demand for faster, more reliable, and better services is growing. To accommodate such a growing demand, research to provide more efficient and improved service is taking place. In other words, various methods of improving data transmission are being researched, and in particular, ways to improve use of frequency resources are being explored.

[0003] Due to the increasing demand for higher throughput, the tendency of offloading cellular network traffic has received enormous attention. Increasing demand of offloading cellular traffic has attracted attention from most industrial partners to the D2D communication. The aim of D2D communication is pursuing this track to allow mobile terminals to transmit data to each other without, or with limited help from the infrastructure.

[0004] Although D2D communication brings large benefits on system capacity, it may also cause undesirable interference to the primary cellular users due to the spectrum sharing. For example, in order to efficiently utilizing spectrum, same frequency band is allowed to be shared by both cellular users and D2D devices.

However, when the same subcarrier or frequency band is allocated for D2D communication and cellular communication at the same time, the interference to each other would highly degrade the communication quality for both of the cellular communication and the D2D communication.

[0005] In view of the foregoing problem, there is a need to improving performance of both the cellular communication and the D2D communication in a communication system.

SUMMARY OF THE INVENTION

[0006] To address or mitigate the above problem, embodiments of the present invention would propose to reduce the undesirable interference in a communication system comprising both the D2D communication and cellular communication and improve capacity of the communication system, such that the performance of both the cellular communication and the D2D communication is improved.

[0007] According to a first aspect of the present invention, embodiments of the invention provide a method for improving performance of both cellular communication and D2D communication in a communication system. The method may comprise steps of: determining a beamforming matrix for minimizing interference from the cellular communication to the D2D communication; and calculating a D2D transmit power based on the beamforming matrix, so as to improve throughput of the communication system.

[0008] According to a second aspect of the present invention, embodiments of the invention provide an apparatus for improving performance of both cellular communication and D2D communication in a communication system. The apparatus may comprise: a determiner configured to determine a beamforming matrix for minimizing interference from the cellular communication to the D2D communication; and a calculator configured to calculate a D2D transmit power based on the beamforming matrix, so as to improve throughput of the communication system.

[0009] The following benefits are expected with the invention. With the solution according to the present invention, undesirable interference from the cellular communication to the D2D communication is reduced and capacity of the communication system comprising both the cellular communication and the D2D communication is improved.

[0010] Other features and advantages of the embodiments of the present invention will also be apparent from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the invention are presented in the sense of examples and their advantages are explained in greater detail below, with reference to the accompanying drawings, where

[0012] FIG. 1 illustrates a schematic diagram of a communication system 100 comprising both the cellular communication and the D2D communication;

[0013] FIG. 2 illustrates a flow chart of a method 200 for improving performance of both the cellular communication and the D2D communication in a communication system according to embodiments of the invention;

[0014] FIG. 3 illustrates a flow chart of a method 300 for improving performance of both the cellular communication and the D2D communication in a communication system according to embodiments of the invention;

[0015] FIG. 4 illustrates a block diagram of an apparatus 400 for improving performance of both the cellular communication and the D2D communication in a communication system according to embodiments of the invention; and

[0016] FIG. 5 illustrates a schematic diagram of a system model of the communication system 500 comprising both the cellular communication and the D2D communication according to embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0017] Embodiments of the invention will be described thoroughly hereinafter with reference to the accompanying drawings. It will be apparent to those skilled in the art that the invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments and specific details set forth herein. Like numbers refer to like elements throughout the specification.

[0018] The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, the usage of the phrases "certain embodiments," "some embodiments," or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, appearances of the phrases "in certain embodiments," "in some embodiments," "in other embodiments," or other similar language, throughout this specification do not necessarily all refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0019] In the context of the disclosure, the term "user equipment" or "UE" may refer to a terminal, a Mobile Terminal (MT), a Subscriber Station (SS), a Portable Subscriber Station (PSS), Mobile Station (MS), or an Access Terminal (AT), and some or all of the functions of the UE, the terminal, the MT, the SS, the PSS, the MS, or the AT may be included. According to embodiments of the present invention, a cellular user may be a UE in cellular communication with a BS, and such a cellular user may be called as "cellular UE". Additionally, a D2D device (e.g., a D2D transmitter or a D2D receiver) may also be a UE.

[0020] The term "base station" or "BS" may refer to a node B (NodeB), an evolved NodeB (eNodeB), a Base Transceiver Station (BTS), an Access Point (AP), a Radio Access Station (RAS), or a Mobile Multihop Relay (MMR)-BS, and some or all of the functions of the BS, the NodeB, the eNodeB, the BTS, the AP, the RAS, or the MMR-BS may be included. According to embodiments of the present invention, the BS may serve one or more UEs in cellular communication.

[0021] The term "beamforming matrix" may refer to a precoding matrix for using in the process of beamforming.

[0022] Reference is first made to FIG. 1 , which illustrates a schematic diagram of a communication system 100 comprising both the cellular communication and the D2D communication.

[0023] The communication system 100 illustratively comprises a BS (e.g., eNB 110), a cellular UE (e.g., UEc¹ 120), a D2D transmitter (e.g., UEd¹ 130), and a D2D receiver (e.g., UE 140). The cellular UE 120 is being served by the eNB 110 in cellular communication, specifically, the eNB 110 is transmitting data to the cellular UE 120 in downlink; and the D2D transmitter UEd¹ 130 and a D2D receiver UEd² 140 are in D2D communication, specifically, the D2D transmitter is transmitting data to the D2D receiver.

[0024] As can be seen from FIG. 1 , during the D2D communication, especially when the eNB 110 is transmitting data to the cellular UE 120, the D2D receiver 140 may suffer the interference from the cellular communication. At the same time, when the D2D transmitter 130 is transmitting data to the D2D receiver 140, the cellular UE 120 may also suffer the interference from the D2D communication.

[0025] Embodiments of the present invention may be applied in various communication systems, including but not limited to a Long Term Evolution Advanced (LTE-A) system. Given the rapid development in communications, there will of course also be future type wireless communication technologies and systems with which the present invention may be embodied. It should not be seen as limiting the scope of the invention to only the aforementioned system.

[0026] For better understanding, the following embodiments of the present disclosure are described based on the communication system 100 shown in Fig. 1. As can be appreciated by those skilled in the art, the present disclosure is not limited to the specific arrangement shown in FIG.1.

[0027] To reduce interference from the cellular communication to the D2D communication and improve throughput of the communication system, embodiments of the present invention propose solutions. Reference is first made to FIG. 2, which illustrates a flow chart of a method 200 for improving performance of both the cellular communication and the D2D communication in a communication system according to embodiments of the invention. The communication system may be, but not limited to, the system as shown in FIG. 1. In accordance with embodiments of the present invention, the method 200 may be carried out by a BS (e.g., eNB 110 of FIG. 1) or some other suitable device, or may be carried out by an apparatus comprised in the BS or some other suitable device.

[0028] After the method 200 starts, at step S201, a beamforming matrix for minimizing interference from the cellular communication to the D2D communication is determined.

[0029] In accordance with embodiments of the present invention, channel state information of channels from a BS to a cellular UE and from the BS to a D2D receiver may be obtained, and then the beamforming matrix may be determined based on the channel state information.

[0030] According to embodiments of the present invention, the beamforming matrix may be determined based on the channel state information in several ways. For example, the beamforming matrix may be calculated based on the channel state information according to a predetermined beamforming criterion. The predetermined beamforming criterion may be maximizing Signal-to-Leakage-plus-Noise Ratio (SLNR) criterion, Zero-forcing (ZF) criterion, Block Diagonalization (BD) criterion, Minimum Mean Square Error (MMSE) criterion, and/or the like.

[0031] In an embodiment, the beamforming matrix is calculated based on the channel state information according to the maximizing SLNR criterion, such that the leakage from the cellular communication to the D2D communication is minimized. Details may be found in embodiments in connection with FIG. 3.

[0032] At step S202, a D2D transmit power is calculated based on the beamforming matrix, so as to improve throughput of the communication system.

[0033] In accordance with embodiments of the present invention, the D2D transmitter may transmit detection signals to the D2D receiver and the cellular UE. In this way, the D2D receiver may determine, based on the detection signals, channel state information about the channel from the D2D transmitter to the D2D receiver, which also refers to as data channel state information. Likewise, the cellular UE may determine, based on the detection signals, channel state information about the channel from the D2D transmitter to the cellular UE, which also refers to as interference channel state information. To calculate the D2D transmit power, first, the interference channel state information may be received from the cellular UE and the data channel state information may be received from the D2D receiver; then, a system sum rate may be derived based on the interference channel state information, the data channel state information and the beamforming matrix, e.g., determined at step S201; and finally, the D2D transmit power may be determined by maximizing the system sum rate. Details of the embodiments may be found in embodiments in connection with FIG. 3.

[0034] According to embodiments of the present application, optionally, the method 200 may further comprising step of judging whether the D2D transmit power is applicable, and sending information about the D2D transmit power to a D2D transmitter if the D2D transmit power is applicable. In some embodiments, the BS may judge whether the D2D transmit power calculated at step S202 goes beyond the capability of the D2D transmitter, for example, a range of values predefined for the D2D transmit power. If the calculated D2D transmit power is in the range, the BS may notify the D2D transmitter to performing transmission by using the calculated D2D transmit power, e.g., by sending information about the D2D transmit power to the D2D transmitter. Otherwise, the BS may cancel the link of the D2D communication. It is to be noted that the judging and sending steps are optional, and should not be construed as limitation on the scope of any disclosure or of what may be claimed.

[0035] FIG. 3 illustrates a flow chart of a method 300 for improving performance of both the cellular communication and the D2D communication in a communication system according to embodiments of the invention. The method 300 may be considered as an embodiment of the method 200 described above with reference to Fig. 2. In the following description of method 300, the beamforming matrix is determined by minimizing interference from the cellular communication to the D2D communication; meanwhile, the D2D transmit power is calculated by maximizing the system sum rate. As such, the interference is reduced and the throughput of the communication system is increased. However, it is noted that this is only for the purpose of illustrating the principles of the present invention, rather than limiting the scope thereof.

[0036] At step S301, channel state information of channels from a BS to a cellular UE and from the BS to a D2D receiver is obtained.

[0037] FIG. 5 illustrates a schematic diagram 500 of a system model of a communication system comprising both the cellular communication and the D2D communication according to embodiments of the invention. The communication system may be, for example, the communication system 100 of FIG. 1, or other suitable communication system.

[0038] As shown in FIG. 5, the BS (eNB) 510 is equipped with two antennas

(Txl and Tx2). There are one cellular UE (UE_c ¹) 520 and one D2D pair, i.e., a D2D transmitter (UEd¹) 530 and a D2D receiver (UE/) 540. Generally, channel state information (CSI) refers to channel properties of a communication link. The channel state information may be estimated at a receiver, e.g., the cellular UE 520 or the D2D receiver 540, and fed back to the transmitter, e.g., eNB 510. In this way, the eNB 510 may obtain the channel state information of channels from a BS to a cellular UE and from the BS to a D2D receiver. Specifically, in embodiments of FIG. 5, the channel state information may be as follows:

wherein hn and hn denote the channel state information of the channel from the two antennas of the eNB 510 to the cellular UE 520, respectively; and i2i and denote the channel state information of the channel from the two antennas of the eNB 510 to the D2D receiver 540, respectively.

[0039] At step S302, the beamforming matrix is determined based on the channel state information.

[0040] According to embodiments of the present invention, the beamforming matrix may be determined by calculating the beamforming matrix based on the channel state information according to a predetermined beamforming criterion. As discussed above, the predetermined beamforming criterion may be maximizing SLN criterion, ZF criterion, BD criterion, MMSE criterion, and/or the like. In an embodiment, the beamforming matrix is calculated based on the channel state information according to the SLNR criterion. Specifically, the beamforming matrix may be calculated by:

wherein W is the beamforming matrix, which satisfies W^W = 1 ;

h_c represents channel state information of the data channel of the cellular UE,

h_d represents channel state information of the interference channel of the D2D receiver, and h_d = (h_n h₂₂f ;

N₀ is variance of thermal noise;

P_B is the transmit power from the eNB;

max(-) is an operation of maximizing; and

(^■)^H is a conjugate transpose operation.

[0041] Based on the above SLNR criterion, the beamforming matrix may be expressed as follows:

wherein H = h_c h_d ) ; and

[0042] Since the beamforming matrix W is determined according to the SLNR criterion, the leakage from the cellular communication to the D2D communication is minimized. As such, the interference from the BS to the D2D receiver is efficiently reduced.

[0043] At step S303, interference channel state information is received from a cellular UE.

[0044] In accordance with embodiments of the present invention, the D2D transmitter may transmit detection signals to the D2D receiver and the cellular UE. In this way, the cellular UE may determine, based on the detection signals, interference channel state information about the channel from the D2D transmitter to the cellular UE. In other words, the interference channel state information may be determined at the cellular UE based on detection signals transmitted from a D2D transmitter. To calculate the D2D transmit power, the BS may receive the interference channel state information from the cellular UE.

[0045] At step S304, data channel state information is received from a D2D receiver.

[0046] Based on the detection signals transmitted from the D2D transmitter, the D2D receiver may determine data channel state information about the channel from the D2D transmitter to the D2D receiver. In other words, the data channel state information may be determined at the D2D receiver based on the detection signals transmitted from the D2D transmitter. To calculate the D2D transmit power, the BS may further receive the data channel state information from the D2D receiver.

[0047] At step S305, a system sum rate is derived based on the interference channel state information, the data channel state information and the beamforming matrix.

[0048] According to embodiments of the present invention, assuming that the interference channel state information is denoted as hdc and the data channel state information is denoted as hdd . based on hdc , hdd and the beamforming matrix \\ , the system sum rate (denoted as "R") may be derived as follows: = log₂ 1 + (4)

wherein h_c represents channel state information of the data channel of the cellular UE and h_c = (h_n h_2l J ;

h_d represents channel state information of the interference channel of the D2D receiver and h_d = {h_n h₂₂ J ;

N₀ is variance of thermal noise;

P_B is the transmit power from the eNB;

P_d is the transmit power from the D2D transmitter, i.e., the D2D transmit power;

max(-) is an operation of maximizing; and

(^■)^H is a conjugate transpose operation.

[0049] At step S306, the D2D transmit power is determined by maximizing the system sum rate.

[0050] In accordance with embodiments of the present invention, the D2D transmit power may be determined in several ways. According to one embodiment, a cellular Signal-to-Interference-plus-Noise Ratio (SINR) of the cellular communication and a D2D SINR of the D2D communication may be derived based on the interference channel state information, the data channel state information and the beamforming matrix; then, an upper limit and a lower limit of the D2D transmit power may be determined based on the cellular SINR, a cellular SINR minimum threshold, the D2D SINR and a D2D SINR minimum threshold; and finally, a target D2D transmit power may be selected from a range from the lower limit to the upper limit, to maximize the system sum rate.

[0051] Again, assuming that the interference channel state information is denoted as hdc and the data channel state information is denoted as hdd , the cellular SINR (denoted as "SINR ") may be derived as follows: SINR. =^■ (5)

P ¹ dh^Hdc + ^T N ^{J V} 0

wherein the same or similar symbols have the same or similar meaning as above.

[0052] At the same time, the D2D SINR (denoted as "SINR_D") may be derived as follows:

P ¹ dhⁿdc (6)

+ N

wherein the same or similar symbols have the same or similar meaning as above.

[0053] Then, the upper limit and a lower limit of the D2D transmit power may be determined based on the cellular SINR, a cellular SINR minimum threshold, the D2D SINR and a D2D SINR minimum threshold. According to an embodiment, the cellular SINR is not less than the cellular SINR minimum threshold and the D2D SINR is not less than the D2D SINR minimum threshold. As such, the following equations (7) and (8) may be derived:

SINR_R > (?)

SINR_D = - ¹ P dh^Hdc

(8)

+ N

wherein fi_c is the cellular SINR minimum threshold, which indicates the minimum value of the cellular SINR; and

fi_d is the D2D SINR minimum threshold, which indicates the minimum value of the D2D SINR.

[0054] In view of equations (7) and (8), the upper limit and a lower limit of the D2D transmit ower may be determined as follows:

+ N₀ ≤ P_d≤ min P_h N₀ ,P_m, (9)

wherein P_f the lower limit; - ^No ^{is the u}PP^{er limit}; ^and

P_ma_x is the maximum transmit power that a UE supports. [0055] Next, a D2D transmit power (PJ) may be selected from the range from the lower limit to the upper limit, as indicated by equation (9). According to embodiments of the present invention, the criterion for selecting a target D2D transmit power may be maximizing the system sum rate, as indicated by equation (4). In other words, the target D2D transmit power is to be found according to the following:

subject to P_l

[0056] Since the target D2D transmit power maximizes the system sum rate, the system throughput may be efficiently increased when the D2D transmitter transmits D2D data by using the target D2D transmit power.

[0057] Reference is now made to FIG. 4, which illustrates a block diagram of an apparatus 400 for improving performance of both the cellular communication and the D2D communication in a communication system according to embodiments of the invention. The apparatus 400 may be implemented at a BS (for example, eNB 110 of FIG. 1) or some other suitable devices.

[0058] According to embodiments of the present invention, the apparatus 400 comprises: a determiner 410 configured to determine a beamforming matrix for minimizing interference from the cellular communication to the D2D communication; and a calculator 420 configured to calculate a D2D transmit power based on the beamforming matrix, so as to improve throughput of the communication system.

[0059] According to embodiments of the present invention, the determiner 410 comprises: an obtaining unit configured to obtain channel state information of channels from a base station (BS) to a cellular user equipment (UE) and from the BS to a D2D receiver; and a matrix determining unit configured to determine the beamforming matrix based on the channel state information.

[0060] According to embodiments of the present invention, the determining unit comprises: a matrix calculating unit configured to calculate the beamforming matrix based on the channel state information according to a predetermined beamforming criterion, wherein the predetermined beamforming criterion is one of: maximizing Signal-to-Leakage-plus-Noise Ratio (SLNR) criterion, Zero-forcing (ZF) criterion, Block Diagonalization (BD) criterion, and Minimum Mean Square Error (MMSE) criterion.

[0061] According to embodiments of the present invention, the calculator 420 comprises: a first receiving unit configured to receive interference channel state information from a cellular user equipment (UE), wherein the interference channel state information is determined at the cellular UE based on detection signals transmitted from a D2D transmitter; a second receiving unit configured to receive data channel state information from a D2D receiver, wherein the data channel state information is determined at the D2D receiver based on the detection signals transmitted from the D2D transmitter; a sum rate deriving unit configured to derive a system sum rate based on the interference channel state information, the data channel state information and the beamforming matrix; and a power determining unit configured to determine the D2D transmit power by maximizing the system sum rate.

[0062] According to embodiments of the present invention, the power determining unit comprises: a Signal-to-Interference-plus-Noise Ratio (SINR) deriving unit configured to derive a cellular SINR of the cellular communication and a D2D SINR of the D2D communication based on the interference channel state information, the data channel state information and the beamforming matrix; a limit determining unit configured to determine an upper limit and a lower limit of the D2D transmit power based on the cellular SINR, a cellular SINR minimum threshold, the D2D SINR and a D2D SINR minimum threshold; and a selecting unit configured to select a target D2D transmit power from a range from the lower limit to the upper limit, to maximize the system sum rate.

[0063] According to embodiments of the present invention, the cellular SINR is not less than the cellular SINR minimum threshold and the D2D SINR is not less than the D2D SINR minimum threshold.

[0064] According to embodiments of the present invention, the apparatus 400 may further comprise a judging unit and a sending unit. The judging unit may be configured to judge whether the D2D transmit power is applicable. The sending unit may be configured to send information about the D2D transmit power to a D2D transmitter, if the D2D transmit power is applicable. [0065] It is noted that the apparatus 400 may be configured to implement functionalities as described with reference to FIGs. 2 and 3. Therefore, the features discussed with respect to any of methods 200 and 300 may apply to the corresponding components of the apparatus 400. It is further noted that the components of the apparatus 400 may be embodied in hardware, software, firmware, and/or any combination thereof. For example, the components of the apparatus 400 may be respectively implemented by a circuit, a processor or any other appropriate selection device. Those skilled in the art will appreciate that the aforesaid examples are only for illustration not limitation.

[0066] In some embodiment of the present disclosure, the apparatus 400 comprises at least one processor. The at least one processor suitable for use with embodiments of the present disclosure may include, by way of example, both general and special purpose processors already known or developed in the future. The apparatus 400 further comprises at least one memory. The at least one memory may include, for example, semiconductor memory devices, e.g., RAM, ROM, EPROM, EEPROM, and flash memory devices. The at least one memory may be used to store program of computer executable instructions. The program can be written in any high-level and/or low-level compilable or interpretable programming languages. In accordance with embodiments, the computer executable instructions may be configured, with the at least one processor, to cause the apparatus 400 to at least perform according to any of methods 200 and 300 as discussed above.

[0067] Based on the above description, the skilled in the art would appreciate that the present disclosure may be embodied in an apparatus, a method, or a computer program product. In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the exemplary embodiments of this disclosure may be illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0068] The various blocks shown in FIGs. 2-3 may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). At least some aspects of the exemplary embodiments of the disclosures may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this disclosure may be realized in an apparatus that is embodied as an integrated circuit, FPGA or ASIC that is configurable to operate in accordance with the exemplary embodiments of the present disclosure.

[0069] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any disclosure or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular disclosures. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0070] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. [0071] Various modifications, adaptations to the foregoing exemplary embodiments of this disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. Any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this disclosure. Furthermore, other embodiments of the disclosures set forth herein will come to mind to one skilled in the art to which these embodiments of the disclosure pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings.

[0072] Therefore, it is to be understood that the embodiments of the disclosure are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

WHAT IS CLAIMED IS:

1. A method for improving performance of both cellular communication and Device-to-Device (D2D) communication in a communication system, comprising:

determining a beamforming matrix for minimizing interference from the cellular communication to the D2D communication; and

calculating a D2D transmit power based on the beamforming matrix, so as to improve throughput of the communication system.

2. The method of Claim 1 , wherein determining a beamforming matrix for minimizing interference from the cellular communication to the D2D communication comprises:

obtaining channel state information of channels from a base station (BS) to a cellular user equipment (UE) and from the BS to a D2D receiver; and

determining the beamforming matrix based on the channel state information.

3. The method of Claim 2, wherein determining the beamforming matrix based on the channel state information comprises:

calculating the beamforming matrix based on the channel state information according to a predetermined beamforming criterion,

wherein the predetermined beamforming criterion is one of: maximizing Signal-to-Leakage-plus-Noise Ratio (SLNR) criterion, Zero-forcing (ZF) criterion, Block Diagonalization (BD) criterion, and Minimum Mean Square Error (MMSE) criterion.

4. The method of Claim 1 , wherein calculating a D2D transmit power based on the beamforming matrix comprises:

receiving interference channel state information from a cellular user equipment (UE), wherein the interference channel state information is determined at the cellular UE based on detection signals transmitted from a D2D transmitter;

receiving data channel state information from a D2D receiver, wherein the data channel state information is determined at the D2D receiver based on the detection signals transmitted from the D2D transmitter;

deriving a system sum rate based on the interference channel state information, the data channel state information and the beamforming matrix; and

determining the D2D transmit power by maximizing the system sum rate.

5. The method of Claim 4, wherein determining the D2D transmit power by maximizing the system sum rate comprises:

deriving a cellular Signal-to-Interference-plus-Noise Ratio (SINR) of the cellular communication and a D2D SINR of the D2D communication based on the interference channel state information, the data channel state information and the beamforming matrix;

determining an upper limit and a lower limit of the D2D transmit power based on the cellular SINR, a cellular SINR minimum threshold, the D2D SINR and a D2D SINR minimum threshold; and

selecting a target D2D transmit power from a range from the lower limit to the upper limit, to maximize the system sum rate.

6. The method of Claim 5, wherein the cellular SINR is not less than the cellular SINR minimum threshold and the D2D SINR is not less than the D2D SINR minimum threshold.

7. The method of Claim 1, further comprising:

judging whether the D2D transmit power is applicable; and

if the D2D transmit power is applicable, sending information about the D2D transmit power to a D2D transmitter.

8. An apparatus for improving performance of both cellular communication and Device-to-Device (D2D) communication in a communication system, comprising: a determiner configured to determine a beamforming matrix for minimizing interference from the cellular communication to the D2D communication; and

a calculator configured to calculate a D2D transmit power based on the beamforming matrix, so as to improve throughput of the communication system.

9. The apparatus of Claim 8, wherein the determiner comprises:

an obtaining unit configured to obtain channel state information of channels from a base station (BS) to a cellular user equipment (UE) and from the BS to a D2D receiver; and

a matrix determining unit configured to determine the beamforming matrix based on the channel state information.

10. The apparatus of Claim 9, wherein the determining unit comprises:

a matrix calculating unit configured to calculate the beamforming matrix based on the channel state information according to a predetermined beamforming criterion, wherein the predetermined beamforming criterion is one of: maximizing Signal-to-Leakage-plus-Noise Ratio (SLNR) criterion, Zero-forcing (ZF) criterion, Block Diagonalization (BD) criterion, and Minimum Mean Square Error (MMSE) criterion.

11. The apparatus of Claim 8, wherein the calculator comprises:

a first receiving unit configured to receive interference channel state information from a cellular user equipment (UE), wherein the interference channel state information is determined at the cellular UE based on detection signals transmitted from a D2D transmitter;

a second receiving unit configured to receive data channel state information from a D2D receiver, wherein the data channel state information is determined at the D2D receiver based on the detection signals transmitted from the D2D transmitter;

a sum rate deriving unit configured to derive a system sum rate based on the interference channel state information, the data channel state information and the beamforming matrix; and

a power determining unit configured to determine the D2D transmit power by maximizing the system sum rate.

12. The apparatus of Claim 11, wherein the power determining unit comprises: a Signal-to-Interference-plus-Noise Ratio (SINR) deriving unit configured to derive a cellular SINR of the cellular communication and a D2D SINR of the D2D communication based on the interference channel state information, the data channel state information and the beamforming matrix;

a limit determining unit configured to determine an upper limit and a lower limit of the D2D transmit power based on the cellular SINR, a cellular SINR minimum threshold, the D2D SINR and a D2D SINR minimum threshold; and

a selecting unit configured to select a target D2D transmit power from a range from the lower limit to the upper limit, to maximize the system sum rate.

13. The apparatus of Claim 12, wherein the cellular SINR is not less than the cellular SINR minimum threshold and the D2D SINR is not less than the D2D SINR minimum threshold.

14. The apparatus of Claim 8, further comprising:

a judging unit configured to judge whether the D2D transmit power is applicable; and

a sending unit configured to send information about the D2D transmit power to a D2D transmitter, if the D2D transmit power is applicable.