WO2014117377A1

WO2014117377A1 - Method and apparatus for resource allocation for device-to-device communication

Info

Publication number: WO2014117377A1
Application number: PCT/CN2013/071233
Authority: WO
Inventors: Dalin Zhu; Ming Lei; Chen Xu; Lingyang Song
Original assignee: Nec(China) Co., Ltd.
Priority date: 2013-01-31
Filing date: 2013-01-31
Publication date: 2014-08-07
Also published as: CN105144811A

Abstract

The present invention relates to method and apparatus for resource allocation for device-to-device communication. According to an embodiment of the present invention, a method for resource allocation for device-to-device communication in a cellular system comprising a number C of cellular UE and a number D of D2D UE pairs, which are divided into ND2D packages, comprising : a) for cellular spectrum resources occupied by a cellular UE c, determining transmit power for a D2D package by maximizing a respective utility function, wherein the D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources; b) repeatedly performing step a) for each of said number N of D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; c) calculating values of the utility functions based on the determined transmit power for all of said N D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; d) sorting the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs. The embodiments of the present invention further relate to corresponding base station, user equipment and computer program product.

Description

METHOD AND APPARATUS FOR RESOURCE ALLOCATION FOR

DEVICE-TO-DEVICE COMMUNICATION

TECHNICAL FIELD

The present invention generally relates to a wireless communication system, particularly to a method and apparatus for resource allocation for device-to-device (D2D) communication .

DESCRIPTION OF THE RELATED ART

Nowadays, the demand of high-speed data services to wireless bandwidths grows rapidly, which has promoted various technology developments. Device-to -Device (D2D) , a local area communication form, has been proposed to be an underlay to the cellular network aiming to improve spectrum efficiency and system sum rate. In a D2D link, user equipments (UEs) are allowed to communicate with each other by a direct connection instead of through the base station (BS) . D2D UEs share the same subcarrier resources with the traditional cellular UEs while the setup process is controlled by the network. For its potential to resource reuse and system capacity improvement, D2D communication is considered to be a key feature of the next generation wireless network, and attracts much attention .

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. To utilize D2D technology efficiently, proper resource allocation has to be applied to improve system performance with the interference being limited.

It is desired to provide an improved solution of resource allocation for D2D communication.

SUMMARY OF THE INVENTION

To solve the problems in the prior art, one or more method and apparatus embodiments according to the present invention aim to provide an improved solution of resource allocation for D2D communication.

According to an aspect of the present invention, an embodiment of the present invention provides a method for resource allocation for D2D communication in a cellular system. The cellular system comprises a number C of cellular user equipments (UEs) and a number D of D2D UE pairs, which are divided into N D2D packages. The method comprises: a) for cellular spectrum resources occupied by a cellular UE c, determining transmit power for a D2D package ^« by maximizing a respective utility function wherein the D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources and wherein the utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; b) repeatedly performing step a) for each of the number N of D2D packages against the cellular spectrum resources occupied by each of the number C of cellular UEs; c) calculating values of the utility functions based on the determined transmit power for all of the N D2D packages against the cellular spectrum resources occupied by each of the number C of cellular UEs; d) sorting the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs.

According to another aspect of the present invention, an embodiment of the present invention provides an apparatus for resource allocation for device-to-device (D2D) communication in a cellular system. The cellular system comprises a number C of cellular user equipments (UEs) and a number D of D2D UE pairs, which are divided into W D2D packages. The apparatus comprises: a) means for determining, for cellular spectrum resources occupied by a cellular UE c, transmit power for a D2D package by maximizing a respective utility function

U<^.-→^■·>^. _f wherein the D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources and wherein the utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; b) means for instructing means a) to repeatedly perform for each of the number N of D2D packages against the cellular spectrum resources occupied by each of the number C of cellular UEs; c) means for calculating values of the utility functions based on the determined transmit power for all of the N D2D packages against the cellular spectrum resources occupied by each of the number C of cellular UEs; d) means for sorting the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs. According to further aspect of the present invention, an embodiment of the present invention provides an apparatus for resource allocation for device-to-device (D2D) communication in a cellular system. The cellular system comprises a number C of cellular user equipments (UEs) and a number D of D2D UE pairs, which are divided into W D2D packages. The apparatus comprises: at least one processor and at least one memory including compute program code, the memory and the computer program code configured to cause the apparatus at least to: a) determine, for cellular spectrum resources occupied by a cellular UE c, transmit power for a D2D package by maximizing a respective utility function wherein the D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources and wherein the utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; b) repeatedly perform step a) for each of the number Wof D2D packages against the cellular spectrum resources occupied by each of the number C of cellular UEs; c) calculate values of the utility functions based on the determined transmit power for all of the N D2D packages against the cellular spectrum resources occupied by each of the number C of cellular UEs; d) sort the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs.

BRIEF DESCRIPTION OF THE DRAWINGS

Inventive features regarded as the characteristics of the present invention are set forth in the appended claims. However, the present invention, its implementation mode, other objectives, features and advantages will be better understood through reading the following detailed description on the exemplary embodiments with reference to the accompanying drawings, where in the drawings:

Fig. l schematically illustrates an example of a cellular system in which embodiments according to an embodiment of the present invention can be implemented;

Fig.2 schematically illustrates a flow chart of a method for resource allocation for D2D communication according to an embodiment of the present invention;

Fig.3 schematically illustrates a flow chart of a process for evaluating transmit power for all possible D2D pairs with respect to cellular spectrum resources occupied by a cellular UE c according to one embodiment of the present invention;

Fig.4 schematically illustrates a flow chart of a process for cellular spectrum resource allocation for D2D communication according to one embodiment of the present invention;

Fig.5 schematically illustrates a block diagram of a base station according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, many specific details are illustrated so as to understand the present invention more comprehensively. However, it is apparent to the skilled in the art that implementation of the present invention may not have these details . Additionally, it should be understood that the present invention is not limited to the particular embodiments as introduced here . On the contrary, any arbitrary combination of the following features and elements may be considered to implement and practice the present invention, regardless of whether they involve different embodiments. Thus, the following aspects, features, embodiments and advantages are only for illustrative purposes, and should not be understood as elements or limitations of the appended claims, unless otherwise explicitly specified in the claims.

Embodiments of the present invention relate to resource allocation techniques for D2D communication in a cellular system. To optimize the system performance over the resource sharing of both D2D and cellular communication modes, a joint spectrum resource and transmit power allocation scheme is proposed based on the maximizing the system sum rate.

Fig. 1 schematically illustrates an example of a cellular system in which embodiments according to an embodiment of the present invention can be implemented.

Referring to Fig.l, a cellular system 100 as shown consists of a base station (BS) 110, a number C of cellular user equipments (UEs) (only UE_C shown in Fig. 1 as an example) and a number D of D2D UE pairs (only one pair d of UE_d,i and UE_df2 shown in Fig. 1 as examples) . As shown in Fig. 2, the D2D UE pairs such as the pair d of UE_d,i, UE_d,2 have direct data signal transmissions, while the traditional cellular UEs such as UE_C transmit data signals to the BS 110. Each UE may be equipped with a single omnidirectional antenna and uniformly distributed in the cell. The two UEs in the D2D pair d satisfy the distance constraint of D2D communication, and at the same time they also have communicating demands. The BS 110 can be configured as the control center of the radio resource for both cellular and D2D communications. A scenario is considered without loss any generality where uplink resource of cellular communication is shared with D2D communication. Assuming UE_dfi is the D2D transmitter sharing the same cellular spectrum resources with UE_C, UE_{df 2} as the D2D receiver receives interference from UE_C . At the same time, the BS 100 is exposed to interference from UE_d,i . In the practical system, more than one D2D pairs reusing the same subcarrier may bring better performance on system sum rate. Thus, it may be assumed that any resource blocks occupied by the cellular UE_C can be reassigned to multiple D2D pairs. In that case, interference between different D2D pairs cannot be ignored. For the entire system, assume the total number of cellular orthogonal subchannels is C, and the number of D2D pairs that send communicating requests is D. Define as a set of D2D pairs sharing the same subcarriers which can be called a package. The total D pairs can be divided into N such packages i^¹' . in an implementation, the N D2D packages may correspond to all non-empty subsets of the number D of D2D UE pairs, where N = 2^D-1. Thus, if subcarriers used by cellular UE_C (c = 1,2, ..., C) are assigned to the nth

(n = 1,2, ..., N) D2D package , the signal to interference plus noise ratio (SINR) at the BS corresponding to channel c is

B _ P<: }'^l2<:B

^{/ →l} ∑ ¾+A¾

d^ 1 ) and the SINR at the receiver of D2D pair d (d ε ¾ can be obtained by y ₌ ¾

d'ev_7i-{d} 2 ) where P_c, Pa and Pa_' represent the transmit power of cellular user c, D2D transmitter d, d^' , respectively. h±_j

{ c ,B , d, d' } ) is the channel response from equipment i to j. No accounts for the noise power at each receiver.

For the D2D underlay system as illustrated in Fig. 1, the channel sum rate involves the communicating rates of cellular and D2D links. Thus, the sum rate of the entire system can be expressed as

According to embodiments of the present invention, the sum rate of the system is considered as the central optimization problem. As D2D pairs reuse the spectrum resources such as subcarriers of cellular UEs, the co-channel interference should be restricted. The transmitting signals experience varying degrees of fading which depend on transmit power and spatial distance. Therefore, embodiments of the present invention provide solutions of joint spectrum resource and power allocation for D2D communication to optimize the system performance.

With reference to Figs. 2-7, various embodiments of the present invention will be described in details.

Fig.2 schematically illustrates a flow chart of a method for resource allocation for D2D communication according to an embodiment of the present invention.

In step S210, for cellular spectrum resources occupied by a cellular UE c, transmit power for a D2D package ^u« is determined by maximizing a respective utility function

U_→n _ The utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package

Based on equations 1) and 2), when the cellular spectrum resources occupied by the cellular UE c is assigned to the D2D package , the sum rate can be expressed as

In the condition that the cellular spectrum resources occupied by the cellular UE c is assigned to no package, the channel rate can be expressed as: i ... = l g₂ 1 + '^{' '}

No j ₅₎

Accordingly, in an embodiment of the present invention, the channel sum rate gain of channel c for package v_c→n = imix (r_<:→_n - r_c→0, 0) 6)

The gain is considered as being non-negative, which means, if the packages bring much interference leading to lower channel sum rates, they are of no value for the channel.

Cellular channels that obtain rate gains need to pay for the cost due to additional power consumption for D2D communication. Thus, the cost factor of package D_n for the spectrum resource occupied by the cellular UE c may be expressed as

Where Pa represents the transmit power of the D2D UE pair d; λ represents a unit price of transmit power which can be announced by the BS .

The utility function in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package can be expressed as

=(r_(;→„-r_(:→0)⁺-A P_fJ- dev_7i Q ) where where (·)⁺ denotes a operation max(*,0) . Based on equation (8) , for a certain given package , the utility of the cellular spectrum resources occupied by the cellular UE c depends on the power i¾ (d £= ) . That means, it should be evaluated the optimal channel sum rate gain of the spectrum resource occupied by the cellular UE c for each package by calculating the optimal transmit power of D2D UE pairs that maximize its utility. The optimal transmit power can be expressed as

{¾ = aig max U_→n

- {P,,}:d€V_7i s.t. F "^'≤ P,i≤ P^'"'"- Vd V_n c {1, 2, ... , D\

The constraint function gives the power range. Here, ^r is fixed maximum power while ^r<i is a lower bound that guarantees the channel rate ¹ <i of D2D UE pair d without interference .

According to an embodiment of the present invention, the transmit power for the D2D package ⁿ is determined with respect to each D2D UE pairs comprised in the D2D package -^" in an iterative manner.

If package is unpacked, the contribution of each D2D link on cellular channel rate can be formulated as the channel sum rate gain of the spectrum resource occupied by the cellular UE c (c G {1,2,..., C} ) for D2D UE pair d in , which can be expressed as

where (·)⁺ denotes a operation max(*,0) And the utility function of the spectrum resource occupied by the cellular UE c owing to the D2D UE pair d in can be written as

11)

Then for each D2D UE pair d in the D2D package

optimal transmit power ^ can be expressed as

Pi = (λ, {Ρ,ΐ'}) , Vd€ V_n

.t. !>;;'- < P_d < /"""'. ^'id e V_n c {1, 2, ... , £>} 12)

An exemplary process for evaluating transmit power for all possible D2D pairs in ^^« with respect to cellular spectrum resources occupied by a cellular UE c will be described in detail with reference to Fig. 3.

Step S210 is repeatedly performed for each of the number N of D2D packages against the cellular spectrum resources occupied by each of the number C of cellular UEs.

In step S220, values of the utility functions are calculated based on the determined transmit power for all of the J\i D2D packages - · · , _ag_{a ns} the cellular spectrum resources occupied by each of said number C of cellular UEs. According to an embodiment of the present invention, the values of the utility functions may be calculated according to equation 8 ) .

In step S230, the calculated values of the utility functions are sorted in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs. An exemplary process for step S230 will be discussed in detail with reference to Fig. 4.

Fig.3 schematically illustrates a flow chart of a process for evaluating transmit power for all possible D2D pairs with respect to cellular spectrum resources occupied by a cellular UE c according to one embodiment of the present invention.

In step S300, in the 1st round ( t=0) , for all the D2D UE pairs in the D2D package , the initial power ^^'(^(>) ^{= (}-' , the initial value of the utility function ^{1 ■} "^' ~ . The initial unit price λ. _Qf transmit power.

In step S310, in a round t (denoting a round index), transmit power of a D2D UE pair d comprised in the D2D package is calculated by

P_d(t) = ai- niiix U*_→(il. ₎ (A, {P_d, (t-1)}) ₁₃₎ where ^d' ≠ ^d'^{d! G V}" .

Step S310 are performed repeatedly until the transmit power of all D2D UE pairs has been updated at the round t .

In step S320, the value of the utility function

^< - ^«) - " i s calculated. In step S330, the transmit power of the D2D package and an optimal unit price of the transmit power is

Tj*—¹ Tj^f T) determined depending on whether <:->(^■, ) > <:→(^■>^■,"^■) , 3i G ^U" is satisfied .

If

- ^U→(.^·,«), ^Vi€ , then set the round index t = t + l, λ = λ + Δλ^, _and return to step S310.

If ^J<:→(i,n) > _<:→(i,n _r 3; _{e f} then stop the process for evaluating transmit power, determine the transmit power of the D2D package and set '→-„. = λ ^_ Αλ. _

Based on equation 11), the increase in the unit price λ. of the transmit power eventually results to the utility function decline. For a range of transmit power, the optimal value of P_d that maximizes the utility function with the unit price ^ increasing can not provides a continuous improvement of the utility function. That is, the iterative process of a channel evaluating its channel sum rate gain for a package is convergence.

The exemplary iterative method as shown in Fig. 3 has been discussed as a noncooperative power control game with pricing in C. U. Saraydar, N. B. Mandayam, and D. J. Goodman, "Efficient power control via pricing in wireless data networks ," IEEE Trans . on Commun . , vol. 50, no. 2, pp. 291-303, Feb. 2002, which are incorporated by reference herein in their entirety. Applying the determined transmit power for D2D UE pairs in each package, the spectrum resource occupied by a cellular UE can get its optimal channel sum rate gain for the packages, and then give the best strategy in the whole resource allocation . Fig.4 schematically illustrates a flow chart of a process for cellular spectrum resource allocation for D2D communication according to one embodiment of the present invention .

As shown in the exemplary process of Fig. 4, step S230 of Fig. 2 may comprise steps as follows.

In step S410, at a round τ (denoting a round index), the utility function U_→n with a maximum value greater than zero, which indicates a case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package , can be collected.

In step S420, the cellular spectrum resources occupied by the cellular UE c is allocated to the D2D package ^^« together with the determined transmit power of the D2D package according to for example the process as shown in Fig. 3.

In step S430, the cellular spectrum resources occupied by the cellular UE c and D2D packages comprising any D2D UE pair which is also comprised in the D2D package are excluded to avoid further allocation.

Steps S410, S420 and S430 are performed repeatedly until cellular spectrum resources occupied by all the number C of cellular UEs have been allocated to the D2D packages or all the number D of D2D UE pairs have been allocated with cellular spectrum resources.

According to an embodiment of the present invention, considering the cost factor for D2D communication again, there may also exist a cost on control signals transferring and information feedback during the access process. In general, when the channel obtains more D2D pairs, it has to pay more for the signaling overhead. Therefore, the cost factor may

o be further associated with additional signaling overhead ^d for the D2D communication, where d denotes a D2D UE pair in the D2D package ^^« . In this embodiment of the present invention, the cost factor may be further expressed as

P_(:→„ - A∑ P_d+∑ ¾

The utility function in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ^^« can be expressed as

where (·)⁺ denotes a operation max(*,0) . Therefore, the values of the utility functions may be calculated in step S220 according to equation 15) .

According to an embodiment of the present invention, the additional signaling overhead ^{1 d} may be announced by the base station and used as an iterative argument to determine the values of the utility functions. In such embodiment of the present invention, the process for cellular spectrum resource allocation for D2D communication as shown in Fig. 4 may further comprises steps as follows. In Step S440, the additional signaling overhead ^{1 d} for the D2D communication to update the cost factor of the utility functions is adjusted. For example, in the first round, i.e.,

O

T=0, an initial additional signaling overhead ^d and a step value ^ can be announced by the base station. If cellular spectrum resources occupied by all the number

C of cellular UEs have been allocated to the D2D packages or all the number D of D2D UE pairs have been allocated with cellular spectrum resources, the allocation is concluded; else set S_d ^T+l = S_d ^T -δ , τ = τ + 1 and the process goes back to step S220 to calculate the values of the utility functions based on the updated cost factor of the utility functions according to equation 15) .

The processing according to one or more embodiments of the present invention has been depicted in detail with reference to Figs. 2-4. It should be noted that the above depiction is only exemplary, not intended for limiting the present invention. In other embodiments of the present invention, this method may have more, or less, or different steps, and numbering the steps is only for making the depiction more concise and much clearer, but not for stringently limiting the sequence between each steps; while the sequence of steps may be different from the depiction. For example, in some embodiments, the above one or more optional steps may be omitted. Specific embodiment of each step may be different from the depiction. All these variations fall within the spirit and scope of the present invention.

Fig.5 schematically shows a simplified block diagram of a base station according to an embodiment of the present invention .

The base station 500 is adapted for communication with user equipments in the cellular system which supports both cellular and D2D communication. As discussed previously, the base station 500 can be configured as the control center of the radio resource for both cellular and D2D communications.

The base station 500 includes a data processor (DP) 510, a memory (MEM) 520 coupled to/embedded in the DP 510, and suitable RF transmitter TX/receiver RX module 540 coupling antenna array 550 to the DP 510. The RF TX/RX module 540 is for bidirectional wireless communications with at least one UE. The MEM 520 stores a program (PROG) 530.

The PROG 530 is assumed to include program instructions that, when executed by the DP 510, enable the base station 500 to operate in accordance with the exemplary embodiments of this invention, as discussed herein with the operating procedure as shown in Figs. 2, 3 and 4.

The MEM 520 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one MEM is shown in the base station 500, there may be several physically distinct memory units in the base station 500.

The DP 510 performs any required calculation as described with reference to Figs.2, 3 and 4. The DP 510 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, DSPs and processors based on multi-core processor architecture, as non-limiting examples . According to an embodiment of the present invention, the base station 500 comprises a) means (not shown in Fig. 5) for determining, for a cellular spectrum resources occupied by a cellular UE c, transmit power for a D2D package by maximizing a respective utility function ^^J<→n , wherein the D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources. The utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package .

The base station 500 further comprises b) means (not shown in Fig. 5) for instructing means a) to repeatedly perform for each of the number N of D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs.

The base station 500 further comprises c) means (not shown in Fig. 5) for calculating values of the utility functions based on the determined transmit power for all of said N D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs.

The base station 500 further comprises d) means (not shown in Fig. 5) for sorting the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs.

It can be appreciated that the functionalities of means a), b),c) and d) can be implemented by one or more suitable modules of the base station 500 as described above. 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 invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block and signaling diagrams, 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 .

As such, it should be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules. As well known in the art, the design of integrated circuits is by and large a highly automated process .

The present invention may also be embodied in the computer program product which comprises all features capable of implementing the method as depicted herein and may implement the method when loaded to the computer system.

The present invention has been specifically illustrated and explained with reference to the preferred embodiments. The skilled in the art should understand various changes thereto in form and details may be made without departing from the spirit and scope of the present invention.

Claims

WHAT IS CLAIMED

1. A method for resource allocation for device-to-device (D2D) communication in a cellular system comprising a number C of cellular user equipments (UEs) and a number D of D2D UE pairs, which are divided into N D2D packages, comprising: a) for cellular spectrum resources occupied by a cellular

UE c, determining transmit power for a D2D package by maximizing a respective utility function wherein the D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources and wherein the utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; b) repeatedly performing step a) for each of said number N of D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; c) calculating values of the utility functions based on the determined transmit power for all of said N D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; d) sorting the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs.

2. The method according to Claim 1, wherein in step a), the transmit power for the D2D package ^u« is determined with respect to each D2D UE pairs comprised in the D2D package T m an iterative manner.

3. The method according to Claim 2, wherein step a) comprises : e) in a round t, calculating transmit power of a D2D

UE pair d comprised in the D2D package by

P_d(t) = nifix U*_→(d!ft) (A, [P_d, {t-l)})_r where ≠ '^-^' , ^ denotes a unit price of transmit power announced by a base station; f ) repeatedly performing step e) until the transmit power of all D2D UE pairs has been updated at the round t; g) calculating the value of the utility function ^_→(i,„₎. i€D_n; h) determining the transmit power of the D2D package -^" and a optimal unit price of the transmit power depending on whether <;→(»)> <^:→(^■>^■,"^■) _r 3 e ^un is satisfied.

4. The method according to Claim 1, wherein said cost factor is further associated with additional signaling overhead for the D2D communication.

5. The method according to any of Claims 1-4, wherein step d) comprises: i) collecting the utility function U_→n with a maximum value, which indicates a case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; j) allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package together with the determined transmit power of the D2D package ^u« ·, k) excluding the cellular spectrum resources occupied by the cellular UE c and D2D packages comprising any D2D UE pair which is also comprised in the D2D package , to avoid further allocation;

1) repeatedly performing steps i) , j) and k) until cellular spectrum resources occupied by all the number C of cellular UEs have been allocated to the D2D packages or all the number D of D2D UE pairs have been allocated with cellular spectrum resources .

6. The method according to Claim 5, wherein step d) further comprises: adjusting the additional signaling overhead for the D2D communication to update the cost factor of the utility functions ; returning to perform step c) to calculate the values of the utility functions based on the updated cost factor of the utility functions.

7. The method according to any of Claims 1-6, wherein the N D2D packages correspond to all non-empty subsets of the number D of D2D UE pairs, where N = 2^D-1.

8. An apparatus for resource allocation for device-to-device (D2D) communication in a cellular system comprising a number C of cellular user equipments (UEs) and a number D of D2D UE pairs, which are divided into ΝΌ2Ό packages, comprising : a) means for determining, for cellular spectrum resources occupied by a cellular UE c, transmit power for a D2D package " by maximizing a respective utility function ^w<:→"_r wherein the D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources and wherein the utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; b) means for instructing means a) to repeatedly perform for each of said number N of D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; c) means for calculating values of the utility functions based on the determined transmit power for all of said N D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; d) means for sorting the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs.

9. The apparatus according to Claim 8, wherein means a) is configured to determine the transmit power i¾ for the D2D package with respect to each D2D UE pairs comprised in the D2D package in an iterative manner.

10. The method according to Claim 9, wherein means a) comprises: e) means for calculating, in a round t, transmit power of a D2D UE pair d comprised in the D2D package ^^« by p_d (t) = ai-gmax U*_→(d>n) (A, [P_d, (t - 1)}) ^ where ≠ '^^' ^e , A. denotes a unit price of transmit power announced by a base station; f) means for instructing means e) to repeatedly perform until the transmit power of all D2D UE pairs has been updated in the round t; g) means for calculating the value of the utility function ^_→(i,„₎. i€D_n; h) means for determining the transmit power of the D2D package ^u« and a optimal unit price <^:→ri of the transmit power depending on whether <;→(>»> . <^;→0» , 3 e ^Un is satisfied.

11. The apparatus according to Claim 8, wherein said cost factor is further associated with additional signaling overhead for the D2D communication.

12. The apparatus according to any of Claims 8-11, wherein means d) comprises: i) means for collecting the utility function U_→n with a maximum value, which indicates a case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; j) means for allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package together with the determined transmit power of the D2D package ^u" ; k) means for excluding the cellular spectrum resources occupied by the cellular UE c and D2D packages comprising any D2D UE pair which is also comprised in the D2D package , to avoid further allocation;

1) means for instructing means i) , j) and k) to repeatedly perform until cellular spectrum resources occupied by all the number C of cellular UEs have been allocated to the D2D packages or all the number D of D2D UE pairs have been allocated with cellular spectrum resources.

13. The apparatus according to Claim 12, wherein means d) further comprises: means for adjusting the additional signaling overhead for the D2D communication to change the cost factor of the utility functions ; means for instructing means c) to calculate the values of the utility functions based on the updated cost factor of the utility functions.

14. The apparatus according to any of Claims 8-13, wherein the N D2D packages correspond to all non-empty subsets of the number D of D2D UE pairs, where N = 2^D-1.

15. An apparatus for resource allocation for device-to-device (D2D) communication in a cellular system comprising a number C of cellular user equipments (UEs) and a number D of D2D UE pairs, which are divided into ΝΌ2Ό packages, comprising : at least one processor and at least one memory including compute program code, the memory and the computer program code configured to cause the apparatus at least to: a) determine, for a cellular spectrum resources occupied by a cellular UE c, transmit power for a D2D package ^u« by maximizing a respective utility function wherein the

D2D package comprises one or more D2D UE pairs operable to share the cellular spectrum resources and wherein the utility function denotes a difference between a channel sum rate gain and a cost factor associated with at least additional transmit power consumption for the D2D communication in case of allocating the cellular spectrum resources occupied by the cellular UE c to the D2D package ; b) repeatedly perform step a) for each of said number N of D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; c) calculate values of the utility functions based on the determined transmit power for all of said N D2D packages against the cellular spectrum resources occupied by each of said number C of cellular UEs; d) sort the calculated values of the utility functions in descending order to determine cellular spectrum resource allocation for the plurality of D2D UE pairs.