EURASIP Journal on Wireless Communications and Networking

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1 EURASIP Journal on Wreless Communcatons and Networkng Ths Provsonal PDF corresponds to the artcle as t appeared upon acceptance. Fully formatted PDF and full text (TM) versons wll be made avalable soon. Dstrbuted user selecton scheme for uplnk multuser MIMO systems n a multcell envronment EURASIP Journal on Wreless Communcatons and Networkng 2012, 2012:202 do: / Byong Ok ee (byongok.lee@samsung.com) Oh-Soon Shn (osshn@ssu.ac.kr) Kwang Bok ee (klee@snu.ac.kr) ISSN Artcle type Research Submsson date 4 February 2012 Acceptance date 12 May 2012 Publcaton date 21 June 2012 Artcle UR Ths peer-revewed artcle was publshed mmedately upon acceptance. It can be downloaded, prnted and dstrbuted freely for any purposes (see copyrght notce below). For nformaton about publshng your research n EURASIP WCN go to For nformaton about other SprngerOpen publcatons go to ee et al. ; lcensee Sprnger. Ths s an open access artcle dstrbuted under the terms of the Creatve Commons Attrbuton cense ( whch permts unrestrcted use, dstrbuton, and reproducton n any medum, provded the orgnal work s properly cted.

2 Dstrbuted user selecton scheme for uplnk multuser MIMO systems n a multcell envronment Byong Ok ee 1 Emal: byongok.lee@samsung.com Oh-Soon Shn 2* * Correspondng author Emal: osshn@ssu.ac.kr Kwang Bok ee 3 Emal: klee@snu.ac.kr 1 Modem System ab, Samsung Electroncs, Suwon , South Korea Abstract 2 School of Electronc Engneerng, Soongsl Unversty, Seoul , South Korea 3 School of Electrcal Engneerng & Computer Scence, Seoul Natonal Unversty, Seoul , South Korea We propose an nterference-aware user selecton scheme for uplnk multuser multple-nput multple-output systems n a multcell envronment. The proposed scheme works n a dstrbuted manner. Each moble staton determnes ts transmt beamformng vector based on the locally avalable channel state nformaton, and nforms the assocated base staton (BS) of the amount of potental nterference caused to adjacent cells along wth the resultng beamformng vector. Then, the BS selects a set of users to be served smultaneously wth consderaton of ntercell nterference. The user selecton scheme s devsed ether to maxmze the sum rate or to acheve proportonal farness among users. For each case, we derve an optmal user selecton crteron and propose a suboptmal dstrbuted user selecton algorthm wth low complexty. Smulaton results confrm that the proposed scheme offers sgnfcant throughput enhancement due to reducton of the ntercell nterference n a multcell envronment. Introducton Multuser multple-nput multple-output (MU-MIMO) s wdely accepted as a key technology for enablng hgh-speed wreless access. In the uplnk MU-MIMO systems, multple moble statons (MSs) are allowed to smultaneously transmt ther sgnals to the base staton (BS) to ncrease the system capacty. Under ths scenaro, the system performance may depend on the set of transmttng users and ther transmt beamformng vectors [1-3]. In [1], a general framework for transmt beamformng and user selecton was developed based upon general convex utlty functons. In [2], successve user selecton algorthms were proposed along wth optmzaton of transmt beamformng vectors. In [3], varous low-complexty beamformng and user selecton schemes were proposed. All these

3 works, however, have dealt wth only a sngle cell envronment where the ntercell nterference does not exst. Intercell nterference s one of the most crtcal factors that lmt the performance of cellular systems, especally for low-frequency reuse factor. There have been several works on MIMO that account for the ntercell nterference n a multcell envronment [4-7]. In [4], t was reported that the performance of spatal multplexng MIMO scheme s sgnfcantly degraded n an nterference-lmted multcell envronment. In [5], an optmal MIMO transmsson strategy was studed when the channel state nformaton (CSI) s not avalable at the transmtter. For the case when the CSI s avalable at the transmtter, a centralzed precodng scheme that maxmzes the total sum rate was proposed n [6]. In [7], a precodng scheme was proposed to maxmze the total sum rate n a dstrbuted manner. owever, these works have been based on a sngle user MIMO system where only one MS s served at a tme. MU- MIMO systems were only recently nvestgated n a multcell envronment [8-10]. In [8], downlnk multcell MU-MIMO systems were dscussed from the aspects of tradeoffs, overhead, and nterference control. In [9], schedulng schemes were developed for the downlnk multcell MIMO systems. Uplnk MU-MIMO systems were analyzed n [10] n the case that the adjacent BS s are allowed to cooperate. In ths artcle, we develop an nterference-aware user selecton scheme for uplnk MU-MIMO systems n a multcell envronment. The scheme comprses of two steps and works n a dstrbuted manner. In the frst step, each MS determnes ts transmt beamformng vector. By utlzng the prevous result on the nterference-aware beamformng proposed n [7], we can effectvely reduce the nterference caused to adjacent cells. In the second step, each BS selects a set of users to be served smultaneously to realze multuser dversty wth consderaton of nterference caused to adjacent cells as well as the desred lnk performance. The user selecton scheme s developed so to maxmze the sum rate or to acheve proportonal farness among users. For each objectve, we derve an optmal user selecton crteron and propose a suboptmal dstrbuted user selecton algorthm wth low complexty. Smulaton results are provded to show the throughput enhancement of the proposed scheme. The rest of ths artcle s organzed as follows. Secton 2 descrbes the system model. In Secton 3, we explan dstrbuted beamformng schemes. In Secton 4, we propose an uplnk user selecton algorthm based on the beamformng vectors. Smulaton results are presented n Secton 5, and conclusons are drawn n Secton 6. We defne here some notaton used throughout ths artcle. We use boldface captal letters and boldface small letters to denote matrces and vectors, respectvely, ( ) T and ( ) to denote transpose and conjugate transpose, respectvely, det( ) to denote determnant of a matrx, tr( ) to denote trace of a matrx, ( ) 1 to denote matrx nverson, to denote Eucldean norm of a vector, I N to denote the N N dentty matrx. System model We consder the uplnk of an MU-MIMO system comprsed of cells where there are K users n each cell. Each MS and each BS are equpped wth N t transmt antennas and N r receve antennas, respectvely. The kth MS n the th cell s assumed to communcate wth the BS n the th cell by usng a transmt beamformng vector w k.

4 The receved sgnal vector y at the BS n the th cell can be expressed as, x, j, j j xj ks j1, j ksj y w w n, (1) where S denotes the set of selected users to be smultaneously served n the th cell. We assume that the maxmum number of selected users per cell s N r. x denotes the nput symbol transmtted from the kth MS n the th cell,, denotes an N r N t channel matrx between the kth MS n the jth cell and the BS n the th cell. We assume a flat fadng channel j n both tme and frequency. The elements of, and x k are assumed to be ndependent and dentcally dstrbuted (..d.) crcularly symmetrc complex Gaussan random varables wth zero mean and unt varance. In (1), n denotes the addtve whte Gaussan nose j (AWGN) vector at the BS n the th cell wth each element havng unt varance, denotes the sgnal-to-nose rato (SNR) of the kth MS n the th cell, and, denotes the nterference-to-nose rato (INR) for the nterference that the kth MS n the jth cell causes to the BS n the th cell. We assume that each BS performs a lnear mnmum mean-square error (MMSE) detecton to suppress the resdual nterference and detect the desred sgnal. The MMSE combnng vector g used n recevng the kth MS s sgnal n the th cell s expressed as j 1 g w K (2) ( k) ( k) ( k) ( k) (, k), NI, ( k, ) where K NI denotes the covarance matrx of the nose plus receved nterference sgnal whch s gven as (, k ) ( k ') ( k ') ( k ') ( k ') ( k ') ( k ') ( k ') ( k ') ( k ') ( k ') NI Nr,,, j, j j, j j k ' S, k ' k j1, j k ' Sj K I w w w w. (3) In (3), the frst term s due to the AWGN, and the second and thrd terms represent the ntracell nterference and ntercell nterference, respectvely. The post processng SINR of the kth MS s sgnal n the th cell s represented as 1, NI, ( k) ( k) ( k) ( k) (, k) ( k) ( k) ( k) SINR. w K w (4) Then, the achevable rate of the kth MS n the th cell s calculated as r log(1 SINR ). (5) ( k) ( k) Snce the achevable rate s affected by the ntercell nterference, the optmal desgn for transmt beamformng and user selecton needs a system-wde centralzed optmzaton, whch requres a lot of feedback and huge sgnalng overhead among cells, makng the

5 algorthm mpractcal. Instead of a centralzed approach, we take a dstrbuted approach for determnng transmt beamformng vectors and the correspondng set of users, as llustrated n Fgure 1. In the frst step, each MS determnes ts transmt beamformng vector based on the locally avalable CSI and calculates the amount of potental nterference caused to adjacent cells. Then, each MS nforms the assocated BS of the amount of nterference to adjacent cells along wth the determned beamformng vector. In the second step, each BS selects a set of users to be smultaneously served based on the nformaton receved from MSs. The BS then broadcasts the ndces of selected users wth approprate modulaton and codng schemes level. Fnally, the selected users transmt ther own data to the BS. It must be noted that the proposed approach based on the local CSI wll provde a more practcal soluton than the centralzed optmzaton from the vewpont of feedback overhead and computatonal complexty, although t may not guarantee the optmalty. We explan detals of the transmt beamformng and user selecton scheme n the followng two sectons. Fgure 1 The proposed approach for dstrbuted transmt beamformng and user selecton Transmt beamformng In ths secton, we explan transmt beamformng schemes that were proposed n [7] for the case of sngle user MIMO n a multcell envronment. We assume that each MS ndependently determnes ts transmt beamformng vector based on the locally avalable CSI. ( k, ) ( k, ) We defne the desred channel D and nterference generatng channel GI for the kth MS n the th cell as (6) (, k ) D k k,, ( k, ) GI ( k) ( k) 1, 1, ( k) ( k) 1, 1, ( k) ( k) 1, 1, ( k) ( k),,. (7) ( k, ) (, k ) (, k ) We assume that the kth MS can obtan D and GI GI by explotng the channel recprocty. Ths s possble for tme dvson duplex systems. For example, the MS n the th cell can estmate ( k, ) D through downlnk sgnal that comes from the BS n the th cell. (, k ) (, k ) Smlarly, the MS can determne GI GI by estmatng the covarance matrx of aggregate nterference sgnals that come from adjacent cells durng the downlnk perod. Based on the above assumptons, we ntroduce two dstrbuted transmt beamformng schemes proposed n [7]: MAX-SNR beamformng and MAX-SGINR beamformng.

6 MAX-SNR beamformng The MAX-SNR beamformng vector s constructed to maxmze the desred sgnal power wthout consderaton on the ntercell nterference. The MAX-SNR beamformng vector of the kth MS n the th cell can be expressed as w arg max w s.t. w 1. (, k ) 2 2 SNR D w (8) The soluton of (8) can be obtaned as the egenvector correspondng to the largest egenvalue of (, k ) (, k ) D D. MAX-SGINR beamformng The MAX-SGINR beamformng vector s determned consderng not only the desred sgnal power, but also the ntercell nterference caused to adjacent cells. The metrc called sgnal to generated nterference plus nose rato (SGINR) at the kth MS n the th cell s defned as w SGINR, (, k ) 2 D (, k ) 2 1 GI w (9) where the numerator corresponds to the desred sgnal power and the denomnator represents the nose plus nterference caused to adjacent cells by the kth MS n the th cell. The MAX- SGINR beamformng vector maxmzes the SGINR at each MS as w w arg max s.t. 1. (, k ) 2 ( k) D ( k) 2 SGINR w (, k ) 2 w 1 GI w (10) The soluton of (10) can be obtaned as the egenvector correspondng to the largest egenvalue of 1 N t I (, k ) (, k ) (, k ) (, k ) GI GI D D. The MAX-SGINR beamformng effectvely reduces the nterference to adjacent cells whle mantanng the desred sgnal power. It s shown n [7] that the MAX-SGINR beamformng approxmately maxmzes the total sum rate for multple-nput sngle-output systems n a two-cell envronment. After determnng a transmt beamformng vector, each MS calculates the amount of nterference caused to adjacent cells as w, (11) (, k ) 2 GI where denotes the amount of nterference caused to adjacent cell by the kth MS n the th cell. Note that assocated BS of depends on the transmt beamformng vector. Each MS nforms the w and for user selecton.

7 User selecton In ths secton, we develop user selecton schemes wth two dfferent objectves: sum rate maxmzaton, and proportonal farness (PF). For each objectve, we frst derve an optmal user selecton crteron and then propose a suboptmal dstrbuted algorthm wth low complexty. Sum rate maxmzaton We begn wth a conventonal user selecton algorthm for sum rate maxmzaton, whch was proposed for a sngle cell envronment. In ths case, each BS selects users to maxmze only the sum rate of ts own cell as S CONV arg max r for 1, 2,,. S ks (12) owever, ths soluton s not optmal n a multcell envronment due to the ntercell nterference. In order to maxmze the total sum rate of the cells, we modfy the formulaton of (12) as ( opt1, opt2,, opt) arg max r. ( S 1, S 2,.. S ) 1 k S S S S (13) The soluton of (13) can only be obtaned through centralzed optmzaton among cells, whch requres perfect CSI, a lot of sgnalng overhead among cells, and very hgh computatonal complexty. As a more practcal soluton, we propose a suboptmal dstrbuted user selecton algorthm wth low complexty. The algorthm s descrbed as n the followng steps. Step 1. Intalzaton: S {}. knew arg max C( k) Step 2. k. Step 3. If Ck ( new ) 0, then S S { knew} and go back to the Step 2; otherwse termnate the algorthm. Each BS ndependently selects users to be served by usng the above algorthm. In Step 1, the set S of selected users s ntalzed. In Step 2, the BS chooses one user among the users not n S so as to maxmze the amount of the change n the total sum rate. Note that Ck denotes the amount of the change n the total sum rate when the kth user s added to S. In Step 3, f the addton of the selected user n Step 2 ncreases the total sum rate, then the BS adds the user to S and goes back to Step 2. Otherwse, the algorthm termnates and the fnal set of selected users s gven by S. The most challengng part of the above algorthm s to calculate Ck wthout sharng nformaton among neghborng cells. We can splt Ck nto two components as

8 C( k) C ( k) C ( k), (14) gan loss where C ( k) gan denotes the sum rate ncrement n the th cell by addng the kth user to S, and C ( k) loss denotes the sum rate decrement n adjacent cells by addng the kth user to S due to the ncreased nterference. The BS can easly calculate C ( k) gan as C k r r ( k') ( k') gan. k ' S{ k} k ' S (15) owever, t s dffcult to calculate C ( k) loss n the dstrbuted manner, snce C ( k) loss s dependent on the set of selected users n adjacent cells. Instead of drectly calculatng C ( k) loss, we propose to estmate C ( k) loss based on whch s fed back from the kth MS represents the amount of nterference caused to adjacent cells n the th cell. Note that by selectng the kth user n the th cell. The man dea s to estmate C ( k) loss by calculatng the sum rate decrement n the th cell to whch the BS belongs, wth addtonal nterference wth the power k. Then the estmated sum rate decrement C ( k) loss n adjacent cell can be expressed as C k r r ( k ') ( k ') loss ( ), k ' S{ k} k ' S{ k} (16) ( k) ( k) where r ( ) denotes the achevable rate of the k th user n the th cell wth addtonal nterference of the power k, and t can be calculated as ( k) ( k k ) r ( ) log 1 SINR ( ), (17) where 1, NI, ( k) ( k) (, k ) ( k) SINR w K w, (18) N K ( ) 1 I w w j1, j k S j w w (, k) r k k k k k NI Nr,, ks, kk ( k) ( k) ( k) ( k) ( k), j, j j, j j. (19) From (15) and (16), the estmated Ck can be obtaned as C k C k C k r r ( k ') ( k ') gan loss ( ). k ' S{ k} k ' S (20)

9 The proposed algorthm requres at most KN r computatons of Ck per cell, snce users are successvely selected. Proportonal farness The proportonal farness (PF) schedulng effectvely provdes a trade-off between the average throughput and farness among users [11]. The conventonal PF schedulng was orgnally proposed for a sngle cell envronment. In ths case, each BS selects users as CONV K argmax log( R ) for 1, 2,,, S k 1 S (21) where that R denotes the average throughput estmate of the kth user n the th cell. We assume R s calculated as R 1 ( k) 1 ( k) 1 R ( t 1) r ( t), f served at t T c Tc ( t) 1 1 R ( 1), f not served at t t T c (22) where T c s the tme constant of the averagng wndow. The soluton of (21), however, does not guarantee the system-wde PF due to the ntercell nterference. We consder an optmal user selecton crteron for the system-wde PF, whch can be expressed as opt1 opt2 opt 1 ( S1, S2,.. S ) ( S, S,, S ) arg max U, (23) where U 1 s the system-wde PF utlty functon expressed as U 1 K log( R ). 1 k1 (24) As n (13), the optmal soluton of (23) needs centralzed optmzaton among cells. ere, we also propose a suboptmal dstrbuted algorthm. Instead of U 1 n (23), we use another utlty functon U 2 gven as U 1 r ks T 1 c R (25) As provded n the Appendx, the optmzaton problem (23) remans the same even though U 1 s replaced wth U 2. The use of U 2 enables the user selecton algorthm to work n a dstrbuted fashon wth low computatonal complexty. Based on the newly defned utlty functon U 2, the proposed algorthm works as follows.

10 Step 1. Intalzaton: S {}. knew argmax U 2( k) Step 2. k. Step 3. If U2 ( knew ) 0, then S S { knew} and go back to the Step 2, otherwse termnate the algorthm. Note that the above algorthm s the same as the dstrbuted algorthm developed n Secton 4.1, except that Ck s replaced by U ( k) 2, whch denotes the amount of the change n U 2 when the kth user s added to S. As n (14), U ( k) 2 can be expressed as U ( k) U ( k) U ( k), (26) 2 2gan 2loss where U ( k) 2gan denotes the ncrement of U 2 n the th cell by addng the kth user to S, whch can be expressed as ( k') ( k') 1 r 1 r U2gan ( k) 1 1. ( k') ( k') k ' S { } 1 ' 1 k Tc R k S T c R (27) U ( k) 2loss n (26) denotes the decrement of U 2 n adjacent cells by addng the kth user to S due to the ncreased nterference. ke the approach used for the total sum rate maxmzaton, we propose to estmate U ( k) 2loss as ( k ') ( k') ( k) 1 r 1 rj ( ) U2loss ( k) 1 1. ( k') ( k') k ' { } 1 ' { } 1 k Tc R k k Tc R S S (28) Then, by usng (27) and (28), the estmaton of U ( k) 2 can be found as ( k ') ( k ') 1 rj ( ) 1 r j U2 ( k) 1 1. ( k') ( k') k ' { } 1 ' 1 k Tc R k T c R S S (29) Ths algorthm also requres at most KN r computatons of U ( k) 2 per cell. Smulaton results In ths secton, we evaluate the performance of the transmt beamformng and user selecton algorthms dscussed n Sectons 3 and 4 usng computer smulatons. We consder a wraparound hexagonal model wth seven cells as shown n Fgure 2. There are K users per cell who are assumed to be unformly dstrbuted over the cell. Each channel between the MS and

11 BS s assumed to experence an ndependent long-term fadng comprsed of the path loss and log-normal shadow fadng. Correspondngly, and, j Fgure 2 Wrap-around hexagonal model wth seven cells n (1) can be expressed as s, 10 d, P 10, s, j 10, j d, j Pj 10, (30) where d, j s the dstance between the BS n the th cell and the kth MS n the jth cell, α s the path loss exponent, and s k, s a zero-mean Gaussan random varable that stands for the shadow fadng. It s assumed that the long-term power control perfectly compensates for the long-term fadng so that a gven target SNR s satsfed at the BS. In the followng smulaton, the path loss exponent, log standard devaton of the shadow fadng, and the target SNR are set to 3.7, 8 db, and 10 db, respectvely. We frst consder user selecton for the sum rate maxmzaton. Fgures 3 and 4 depct the average achevable sum rate per cell versus the number of users for N t = N r = 2 and N t = N r = 4, respectvely. The performance of the centralzed user selecton derved from an exhaustve search s plotted together as an upper bound. owever, the results are provded only up to eght users due to very hgh computatonal complexty. It s shown that the MAX-SGINR beamformng outperforms the MAX-SNR beamformng, and the proposed user selecton scheme outperforms the conventonal one. It must be noted that the proposed user selecton gan ncreases wth the number of users, and that the gan s more dstngushed than the beamformng gan. For the case of K = 16 and N t = N r = 2, for example, the proposed user selecton scheme s shown to provde as much as 2.72 bps/z mprovement over the conventonal user selecton scheme, when the MAX-SGINR beamformng s adopted. Under the same condtons, the gan of the MAX-SGINR beamformng over the MAX-SNR beamformng s 0.65 bps/z, when the proposed user selecton scheme s appled. Fgure 5 depcts the average amount of generated nterference per cell for N t = N r = 2. It s shown that the proposed user selecton scheme consderably reduces the generated nterference especally for a large number of users. Fgure 3 The average achevable sum rate per cell versus the number of users for N t = N r = 2 Fgure 4 The average achevable sum rate per cell versus the number of users for N t = N r = 4 Fgure 5 The average amount of generated nterference per cell versus the number of users for N t = N r = 2 Now we consder the case of the PF utlty. Fgures 6 and 7 depct the system-wde PF utlty U 1 and the average achevable sum rate per cell, respectvely, versus tme for K = 16, N t = N r = 2, and T c = 200 slots. As n the case of the sum rate maxmzaton, the MAX-SGINR beamformng outperforms the MAX-SNR beamformng, and the proposed user selecton scheme outperforms the conventonal one. The results n Fgure 6 also mply that the

12 proposed scheme mproves the farness among users as compared to the conventonal scheme. Correspondngly, the proposed user selecton scheme wth the MAX-SGINR beamformng provdes the best performance. Fgure 6 The system-wde PF utlty versus tme for K = 16 and N t = N r = 2 Fgure 7 The average achevable sum rate per cell versus tme for K = 16 and N t = N r = 2 Concluson In ths artcle, we have developed an nterference-aware dstrbuted user selecton scheme for uplnk MU-MIMO systems n a multcell envronment. Multple transmt antennas at each MS are utlzed for transmt beamformng to reduce the nterference caused to adjacent cells. Multple receve antennas at each BS are utlzed for recevng the sgnals from the selected users and suppressng ntercell nterference. We have derved system-wde optmal user selecton crtera and proposed dstrbuted user selecton algorthms wth low complexty. Smulaton results have shown that the proposed user selecton scheme provdes sgnfcant performance mprovement n a multcell envronment. Appendx ( S, S,.. S ) arg max U opt1 opt2 opt 1 ( S1, S2,.. S ) K arg maxlog R ( t) ( S1, S2,.. S ) 1 k1 ( k) ( k) arg max log R ( t) log R ( t) ( S1, S2,.. S ) 1 ks 1 ks 1 1 k ( k) 1 ( k) arg max log 1 R ( t 1) r 1 R ( t 1) ( 1, 2,.. ) 1 k T c T S S S c 1 k T S S c 1 1 r log1 R ( t1) log1 1 ks 1 1 ( 1) Tc ks T c R t arg max ( 1, 2,.. ) S S S 1 1 R ( t1) 1 k T S c K 1 1 r arg max log 1 R ( t1) log 1 ( k) ( 1, 2,.. ) 1 k1 Tc 1 k T 1 ( 1) c R t S S S S 1 r 1 ( 1) arg maxlog1 ( S 1, S k 2,.. S ) 1 k T c R t S arg max1 ( S 1, S k 2,.. S ) 1 k T c R t S ( S1, S2,.. S ) 2 arg max U. 1 r 1 ( 1)

13 Competng nterests The authors declare that they have no competng nterests. Acknowledgment Ths work was supported n part by the Natonal Research Foundaton of Korea (NRF) grant funded by the Korea government (MEST) (No ), and n part by the KCC (Korea Communcatons Commsson), Korea, under the R&D program supervsed by the KCA (Korea Communcatons Agency) (KCA ). References 1. KN au, Analytcal framework for multuser uplnk MIMO space-tme schedulng desgn wth convex utlty functons. IEEE Trans. Wrel. Commun. 3(9), (2004) 2. Y ara, Brunel, K Oshma, Uplnk spatal schedulng wth adaptve transmt beamformng n multuser MIMO systems, n Proceedng of IEEE Internatonal Symposum on Personal, Indoor and Moble Rado Communcatons, elsnk, Fnland, September do: /pimrc S Serbetl, A Yener, Beamformng and schedulng strateges for tme slotted multuser MIMO systems, n Proceedng of Aslomar Conference on Sgnals, Systems, and Computers, Pacfc Grove, CA USA, 1st edn., 2004, pp S Catreux, PF Dressen, J Greensten, Smulaton results for an nterference-lmted multple-nput multple-output cellular system. IEEE Commun. ett. 4(11), (2000) 5. RS Blum, MIMO capacty wth nterference. IEEE J. Sel. Areas Commun. 21(6), (2003) 6. S Ye, RS Blum, Optmzed sgnalng for MIMO nterference systems wth feedback. IEEE Trans. Sgnal Process. 51(11), (2003) 7. BO ee, W Je, OS Shn, KB ee, A novel uplnk MIMO transmsson scheme n a multcell envronment. IEEE Trans. Wrel. Commun. 8(10), (2009) 8. SA Ramprashad, C Papadopoulos, A Benjebbour, Y Kshyama, N Jndal, G Care, Cooperatve cellular networks usng mult-user MIMO: tradeoffs, overheads, and nterference control across archtectures. IEEE Commun. Mag. 49(5), (2011) 9. M Kobayash, M Debbah, J Belfore, Outage effcent strateges for network MIMO wth partal CSIT, n Proceedng of IEEE Internatonal Symposum on Informaton Theory (Seoul, Korea, 2009), pp do: /isit J oyds, M Kobayash, M Debbah, Optmal channel tranng n uplnk network MIMO systems. IEEE Trans. Sgnal Process. 59(6), (2011)

14 11. A Jalal, R Padovan, R Pankaj, Data throughput of CDMA-DR a hgh effcency-hgh data rate personal communcaton wreless system, n Proceedng of IEEE Vehcular Technology Conference-Sprng (Tokyo, Japan, 2000), pp vol. 3 Query Q1: Artcle structure: Journal standard nstructon regardng artcle structure requres the secton "Introducton; Man text; Conclusons; Methods" for artcle type "Research". owever, "Man text and Methods" secton was not provded. Please supply the requred secton. Otherwse, kndly advse us on how to proceed.

15 Fgure 1

16 Fgure 2

17 Average achevable rate (bps/z) centralzed user selecton wth MAX-SGINR BF proposed user selecton wth MAX-SGINR BF proposed user selecton wth MAX-SNR BF conventonal user selecton wth MAX-SGINR BF conventonal user selecton wth MAX-SNR BF conventonal user selecton wthout BF Fgure Number of users

18 Average achevable rate (bps/z) centralzed user selecton wth MAX-SGINR BF proposed user selecton wth MAX-SGINR BF proposed user selecton wth MAX-SNR BF conventonal user selecton wth MAX-SGINR BF conventonal user selecton wth MAX-SNR BF conventonal user selecton wthout BF Fgure Number of users

19 Average amount of generated nterference (db) Fgure proposed user selecton wth MAX-SGINR BF proposed user selecton wth MAX-SNR BF conventonal user selecton wth MAX-SGINR BF conventonal user selecton wth MAX-SNR BF conventonal user selecton wthout BF Number of users

20 The System-wde PF Utlty proposed user selecton conventonal user selecton proprosed user selecton MAX-SGINR BF proprosed user selecton wth MAX-SNR BF conventonal user selecton wth MAX-SGINR BF conventonal user selecton wth MAX-SNR BF conventonal user selecton wthout BF Fgure Tme

21 Average Achevable Rate (bps/z) proprosed user selecton MAX-SGINR BF proprosed user selecton wth MAX-SNR BF conventonal user selecton wth MAX-SGINR BF conventonal user selecton wth MAX-SNR BF conventonal user selecton wthout BF proposed user selecton conventonal user selecton Fgure Tme