Internatonal Journal of Future Computer and Communcaton, Vol. 6, o. 3, September 2017 Study of Downln Rado Resource Allocaton Scheme wth Interference Coordnaton n LTE A etwor Yen-Wen Chen and Chen-Ju Chen Abstract Carrer Aggregaton (CA) s one of the most mportant technologes n the LTE-Advanced (LTE-A) system for better transmsson effcency. The basc dea of CA s to adopt more than one component carrer (CC) for user equpment (UE) to ncrease ts bandwdth. However, when UE adopts component carrers from other adjacent base statons, t wll cause the nterference and may decrease transmsson effcency especally for the cell edge UE. Therefore, solvng nterference wth carrer aggregaton s a crtcal ssue toward the effectve mprovement of system throughput. In ths paper, we propose a novel method to deal wth not only the nterference between pco staton and macro base staton, but also the nterference between base statons. In the proposed scheme, the rado nterference, channel condton of UE, and load balance are taen nto consderaton for proper CC selecton so as to mprove the cell-edge UE performance. The proposed scheme consders the nteracton and correlaton between Inter-cell Interference Coordnaton (ICIC) and enhanced Inter-cell Interference Coordnaton (eicic) to arrange the secondary CC for LTE-A UE. The smulaton results show that the proposed scheme can ncrease transmsson effcency especally for the edge UE. Index Terms Carrer aggregaton, component carrer, nter-cell nterference coordnaton, long term evoluton-advanced. I. ITRODUCTIO Recently, the fast deployment of moble multmeda servces pushes the hgh demand of bandwdth n wreless networs. The moble devce can access the rado channel through ether the unlcensed band, e.g. WF, or lcensed band, such as long term evoluton (LTE), for nternet connectons. Generally, the unlcensed band provdes easy and unrestrcted for users access, however, t s hard to mantan the effcent spectrum utlzaton due to the unmanageable accesses from users. On the contrarly, the lcensed band provdes the well-defned control protocol for the control node, e.g. the eodeb n LTE networ, to manage the rado resource. However, the rado nterference always happens unpredctably and t may decrease the spectrum effcency not only n the unlcensed band networs but also the lcensed band networs. In order to mnmze the rado nterference, especally for the manageable lcensed band, the negotaton mechansm s requred among nterference devces. In LTE, the nter cell nterference (ICI) s one of the most severe factors that downgrade the transmsson qualty and system throughput. To get over the ICI problem has become one of the most mportant ssues toward effectve transmsson n cellular networs. Recently, several studes were proposed for resource allocaton wth carrer aggregaton n LTE [1]-[3]. However, most of them only consdered the nterference between the pluraltes of pco statons and the assocated macro base staton. The nterference among macro base statons was not well dscussed. Generally, the pco statons are deployed over the cell edge area for the compensaton of poor rado condton of the assocated macro base staton, however, the neghbor macro base statons may ntroduce rado nterference to ths area. Thus t may not always a proper decson to choose the rado channel of ths small cell wthout consderng the nterference from the other statons. In order to provde bandwdth for users, 3GPP organzaton evolves the utlzaton of rado resource from tme dvson duplex (TDD) and frequency dvson duplex (FDD) to carrer aggregaton (CA) snce 3GPP release 10 as shown n Fg. 1 [4]. Comparng to the technologes of LTE and LTE-A, LTE-A provdes UE the capablty of aggregatng more than component carrer for hgher throughput. And, therefore, the nterference coordnaton ssue becomes more crtcal than that n LTE envronment. Because UE needs to select the CC, whch has better channel condton to t, however, t may nterfere wth the channel chosen by other UE. In ths paper, we study and propose the method to deal wth the nterference between base statons about the CC selecton by tang the load of CC and the channel condton of the UE receved n dfferent CCs nto consderaton so as to mprove the cell-edge UE performance. Manuscrpt receved February 5, 2017; revsed Aprl 4, 2017. Ths wor was supported n part by the Mnstry of Scence and Technology (MOST) (grant numbers: 105-2221-E-008-031-MY2, and 105-2221-E-008-030), Tawan. Yen-Wen Chen s wth the Department of Communcaton Engneerng, atonal Central Unversty, Tawan (e-mal: ywchen@ce.ncu.edu.tw). Chen-Ju Chen s wth the Department of Communcaton Engneerng, atonal Central Unversty, Tawan. She s also wth MedaTe Inc., Tawan (e-mal: jule081217@gmal.com). Fg. 1. The evoluton of 3GPP [4]. The rest of ths paper s organzed as follows. The followng secton provdes the related wors of our study do: 10.18178/jfcc.2017.6.3.500 110
Internatonal Journal of Future Computer and Communcaton, Vol. 6, o. 3, September 2017 ssue. The ntegrated scheme for Inter-cell Interference Coordnaton (ICIC) and enhanced Inter-cell Interference Coordnaton (eicic) are proposed n secton III. The smulaton results are llustrated wth dscusson n secton IV. And, the fnal secton concludes our wors. II. RELATED WORKS The ICIC and eicic mechansms were provded to reduce the nterferences between macro base statons and between macro base staton and pco staton, respectvely. In LTE, ebs exchange nformaton to each other through the X2 nterface for management purpose. Thus eb can negotate wth other ebs for rado resource utlzaton accordng to the receved Relatve arrowband Tx Power (RTP), and send the Hgh-Interference Indcator (HII), and Overload Indcator (OI) to/from ts neghbor ebs as reference when performng resource allocaton as well as handover [5]. For the ICIC schemes, the proposed scheme n [6] deals wth the ICIC ssue based on Harmony Search (HS). Accordng to ther procedure, ebs perform decentralzed arbtraton to mute RBs by referrng to the average nterference weght calculated by each eb. In [7], the author suggested to assgn conflcted RBs by comparng the traffc load of two adjacent macro base statons. Its concept s to let eb, whch has heaver traffc load, have hgher probablty to obtan the conflcted RB. However, the mpact of channel condton was not well consdered. In order to ncrease overall throughput, the reuse of valuable spectrum s one of the convncble solutons towards ths objectve. Thus pco statons or remote rado head (RRH) unts can be deployed over the cell edge of the macro staton. Due to the low transmsson power of the pco staton, there s no nterference among pco statons and the spectrum can then be reused. However, the nterference ssue between the macro base staton and ts assocated small statons exsts. And the framewor of eicic was proposed n 3GPP release 10. The basc concept of eicic s that eb adopts the almost blan sub-frames (ABS) so that pco statons can utlze those sub-frames wthout nterference from the base staton. Although macro base staton wll decrease ts throughput, several pco statons can reuse these sub-frames and, therefore, the overall throughput ncreases. As shown n Fg. 2, the macro base staton mutes the sub-frames 2 and n-2 so that pco base statons 1 and 2 can utlzes these two sub-frames wthout nterference from macro base staton.. addton to the LTE-sm smulator, three schedulng algorthms, ncludng general mult-band schedulng, basc mult-band schedulng, and enhanced mult-band schedulng, were proposed to arrange the resource by usng weght factor [8]. In [9], the logarthmc utlty functon and the sgmodal-le utlty functon were desgned to allocate the resource bloc (RB) of CC n a proportonal farness manner. Addtonally, the mprovement of the throughput for cell edge users was dscussed n [10]-[12]. In [10], the authors proposed the user assocaton algorthm to decde whether UE s n the cell edge or not. Then the greedy bnary carrer selecton algorthm was appled for CC selecton. In [11], the nterferences of control channel and data channel were analyzed separately, and the prce based algorthm was desgned to determne the transmsson power so that the nterference can be mnmzed. In addton to nterference aware scheduler, the requrements of qualty of servces (QoS) for dfferent traffc types, e.g. data and vdeo, were taen nto consderaton n [12]. The nterference can be subdvded nto frequency doman and tme doman. In [13], the dynamc Q-learnng and satsfacton based learnng approaches were proposed for the decsons of bas, transmsson power, and prmary CC. The above proposed schemes focus on the negotaton between the macro base staton and the pco base statons, the nterference from other neghbor macro base statons s not well dscussed. Therefore, t s the man research objectve of ths paper. III. THE PROPOSED ITEGRATED ICIC AD EICIC SCHEME The LTE-A UE shall have a fxed prmary CC (PCC) for the connecton management and control sgnalng and may choose other secondary CC (SCC) to ncrease bandwdth. As each UE may have dfferent channel condton n dfferent CC and the bandwdth of each CC s lmted, therefore, the selecton of SCC s complex and crtcal for spectrum effcency and system throughput. In addton to the channel condton, the nterference shall also be properly consdered so that the spectrum can be effectvely utlzed. Bascally, ICIC and eicic negotate the spectrum n the frequency doman among macro base statons and n the tme doman between macro base staton and pco base staton, respectvely, as shown n the followng Fg. 3. Fg. 3. ICIC and eicic. Fg. 2. The ABS of macro base staton for eicic. The CA s appled to ncrease the bandwdth n LTE-A system. Several researches dscussed the allocaton and schedulng of CC to maxmze system throughput [8], [9]. In Bascally, UE shall select PCC at the connecton establsh stage and PCC s fxed durng the connecton duraton and most control sgnals between UE and eb go through PCC. UE shall report ts channel condtons, such as channel qualty ndcator (CQI) and RTP, of the feasble ebs to ts management eb through PCC. The SCC can be flexbly adjusted accordng to the receved channel condtons. The 111
Internatonal Journal of Future Computer and Communcaton, Vol. 6, o. 3, September 2017 management eb shall decde the handover, modulaton and codng scheme (MCS), the selecton of SCC, etc., through PCC. The proposed scheme s subdvded nto the SCC selecton phase and the resource allocaton phase as descrbed n the followng. The selecton of PCC for each LTE-A UE s bascally accordng to the sgnal to nose rato, however, the nterference from other CC s consdered as shown n equaton (1). n equaton (1) denotes the receved SIR value of the u-th UE from the CC of eb c. The hgher value of means the more sutable for the u-th UE selects the CC of eb c as ts CC. where P u c, (1), means the receved power of the u-th UE from the CC of eb c. The proposed scheme wll always assgn the CC of eb c to the u-th UE as ts PCC for the hghest value of each UE f the bandwdth of CC s affordable. It s noted that, at ths stage, eb only allocates one RB of the PCC for each UE. If the requred bandwdth of UE s not satsfed, the proposed scheme wll choose the sutable CC, whch may be ts PCC or the other CC, for further bandwdth allocaton. The procedure eeps allocaton untl ether the bandwdth s satsfed or there s no bandwdth left n the CC. It s noted that the number of CC of UE s lmted and ths s the constrant durng the bandwdth allocaton. For example, f each UE can accommodate two CCs, then one CC shall be PCC and t can only have one SCC. Once ts SCC s decded, t can only be allocated wth bandwdth from these two CC. The basc flow of the proposed scheme s provded n the followng Fg. 4. by more than one macro cell, then we need to decde whch macro eb shall mute some sub-frames so that the pco cell can have better transmsson performance. In the proposed scheme, we apply the weghtng functon to decde whch macro cell shall mute. The basc concept of the weghtng functon W of macro cell refers the numbers of UEs that can be served by one macro cell, two macro cells, or pco cell to maxmze the system utlzaton as shown n equaton (2). where 1,0 1 x 1 2,1 R 0 W (2) m, n means the number of UE, whch under macro cell, that can be covered by m macro cells and n pco cells, and R denotes the number of resdual RBs of the -th CC of the macro cell. In the proposed scheme, UE can be located at the locaton, where s covered by ether one, two, or three macro base statons. And the proposed scheme assumes that the pco cell s deployed over the cell edge, however, except the area covered by three macro base statons as shown n Fg. 5. As the weghtng functon s desgned to determne whch macro base staton shall mute for eicic, therefore, we only compare the numbers of UEs that are only served by one macro base staton and are located at the coverage of two macro base statons and the pco base staton n equaton (2). Thus, 0 1 and, 1 2 of equaton (2) denote the numbers of UEs for the above deployment assumpton. Fg. 5. Deployment of macro base cells and pco cells. Fg. 4. The basc operaton flow of the proposed scheme. In Fg. 4, the selecton of one RB from ether PCC or SCC also refers to the value calculated n equaton (1). Thus, f the orgnal assgned CC of the PCC has the hghest value, the allocated RB wll come from the orgnal PCC f t stll has RB left, otherwse the other CC wll be selected as the SCC of ths UE. If the selected CC comes from pco cell, then the proposed scheme wll perform eicic at tme doman. In the proposed scheme, as the pco eb s always deployed over the cell edge of the macro cell and t may be nterfered 112
Internatonal Journal of Future Computer and Communcaton, Vol. 6, o. 3, September 2017 The hgher value of W means that the macro base staton need eep more RBs to be allocated for the UE whch can only be served by t because of the smaller values of 2, 1 and R. The proposed CC selecton and resource allocaton algorthm s llustrated as follows. IV. EXPERIMETAL SIMULATIOS In order to nvestgate the performance of the proposed scheme, exhaustve smulatons were performed. The archtecture that conssts of three macro base statons and three pco base statons s appled durng the smulatons. Each base staton was assumed to have two CC and the maxmum number of CC can be aggregated by each UE was also assumed to be 2. The cell edge area means the ntersecton between macro cells. And the wdest dstance of the cell edge s 200m. The TDD wth confguraton 5 confguraton was adopted and 8 ms of each frame was reserved for downln transmsson. Therefore, there are 800 RBs (or 272 RBGs) to be utlzed. The other smulaton parameters are gven n the followng Table I. TABLE I: SIMULATIO PARAMETERS Carrer bandwdth 10MHz umber of cell Macro cell:3 Pco cell:3 ISD/cell radus Macro cell:500m;pco cell:40m Carrer frequency 10MHz @ 1.8GHz umber of RB 50 Sze of RBG 3 umber of RBG 17 BS transmt power Macro cell:46 dbm Pco cell:30 dbm Antenna heght 15m Macro cell: 40(1-0.004H)log(R)-18log(H)+21log(F)+80 Path loss model [14] db (R[m]) Pco cell: 140.7+21log(F/2000)+36.7log(R) db (R[m]) UE bandwdth requrements 3 Mbps ABS rato 0/8,1/8,3/8,5/8 Ths paper focuses on the sutable CC selecton and the harmonc coordnaton of ICIC and eicic, therefore, we compare the results of 6 smulaton scenaros as follows: Scenaro 1 (proposed): ICIC and eicic Scenaro 2 (w/o ICIC): nether ICIC nor eicic Scenaro 3 (w/o eicic): only ICIC Scenaro 4 (fx mutng 2,3): ICIC and eicic, fx mutng by eb 2 and eb 3 (.e. W s not appled) Scenaro 5 (fx mutng 1,3): ICIC and eicic, fx mutng by eb 1 and eb 3 Scenaro 6 (fx mutng 1,2): ICIC and eicic, fx mutng by eb 1 and eb 2 The smulaton results of the average throughputs of all UEs and the cell edge UEs are shown n Fg. 6 and 7, respectvely. It shows that the results of scenaro 2 (w/o ICIC) s the worst. Thus the average throughput manly depends on whether ICIC s appled or not. The mnmum bandwdth requrement of each UE s assumed to be 3 Mbps, we compare the dssatfcaton ratos,.e. the rato of UE that can not receve 3 Mbps, of the sx scenaros n Fg. 8. It ndcates that the scenaro 2 has the lower dssatsfacton rato when the number of UEs exceeds 80. The man reason s that the coverage of the overlapng area between macro base statons and the pco cell s relatvely much smaller than that of the macro cell (40m v.s. 500m n radus) and the UEs are unformally dstrbuted over the area. The ICIC mechansm s utlzed to tradeoff the utlzaton of RB at the cell edge. Although the scenaro 2 does not tae care of the UE n the cell edge, t can satsfy most UEs. Fg. 6. The average overall throughput. Fg. 7. The average cell edge throughput. Fg. 8. Comparson of dssatfcaton ratos. The above smulatons assume that the UE s unformly dstrbuted over the smulaton area. In order to examne the performance when the dstrbuton of UE s nonunform, we put 20%, 50%, and 80% of UEs to be located n the cell edge to see ther performance of throughput. We compare the smulaton results of the scenaro 1 and scenaro 3 (.e. ICIC only) to examne the effectveness of eicic. Fg. 9 presents the average throughputs of cell edge UEs, respectvely. It clearly llustrate that the proposed scheme (scenaro 1) acheves hgher throughput for cell edge UEs n the unbalance UE dstrbuton condton especally when the 113
Internatonal Journal of Future Computer and Communcaton, Vol. 6, o. 3, September 2017 number of UEs s gettng more. Fg. 9. The average cell edge throughput for unbalance number of UE. The smulaton results of 100 UEs by applyng dfferent ABS rato are gven n Fg. 10. The results clearly ndcate that the cell edge throughput can be sgnfcantly mproved f cell edge UE s dense and the hgher ABS rato s appled. Fg. 10. The average cell edge throughput of dfferent ABS rato. Accordng to the above smulaton results, the performance s affected by nterference coordnaton mechansm and UE dstrbuton. We summarze the pros and cons of the polctes dscussed n the paper n the followng the followng Table II. TABLE II: PROS AD COS OF DIFFERET ITERFERECE POLICIES Pros: sgnfcant mprovement on edge UE throughput and ICIC+eICIC the other UEs can stll mantan n acceptable level Cons: helpless when most UEs are located n macro cell Pros: beneft to overall throughput for banance and w/o ICIC undense UE dstrbuton Cons: unfar and lower throughput when load s heaver Pros: better performance when less UE n pco cell w/o eicic Cons: unable to mtgate the load of macro-eb Fxed Pros: beneft to cell edge UE mutng Cons: poor utlzaton of RB n macro cells V. COCLUSIOS In ths paper, we propose the ntegrated nterference coordnaton scheme for proper rado resource allocaton n LTE-A networ. The performance of the proposed scheme s evaluated through exhaustve smulatons. In addton to the smulaton results, we analyze the effectveness of the coordnaton polces, whch nclude ICIC, eicic, and ABS rato. The results llustrate that the proposed scheme can effectvely utlze rado resource so as to mprove the throughput of cell edge UE. However, the ABS rato shall be carefully adjusted accordng to the number and dstrbuton of UE. And the dynamc ABS adjustment scheme wll be one of our future research drectons. REFERECES [1] 3GPP TS 36.101 (v12.5.0 Release12), Evolved unversal terrestral rado access (E-UTRA); User equpment (UE) rado transmsson and recepton, ovember 2014. [2] 3gpp. [Onlne]. Avalable: (June 2013). http://www.3gpp.org/technologes/eywords-acronyms/101-carrer-ag gregaton-explaned [3] G.-X. Yuan et al., Carrer aggregaton for LTE-advanced moble communcaton systems, IEEE Communcaton Magazne, vol. 48, no. 2, pp. 88-93, February 2010. [4] A. Brydon. (March 2014). Evoluton of LTE-advanced carrer aggregaton. [Onlne]. Avalable: http://www.unwrednsght.com/2014/lte-carrer-aggregaton-evoluto n [5] 3GPP TS 36.213 (v12.5.0 Release 12), Evolved unversal terrestral rado access (E-UTRA); physcal layer procedures, March 2015. [6] S. S. Khalfa et al., Inter-cell nterference coordnaton for hghly moble users n lte-advanced systems, Vehcular Technology Conference (VTC Sprng), pp. 1-5, June 2013. [7] S.-J. Wang et al., A decentralzed downln dynamc ICIC method for mult-cell OFDMA system, n Proc. Internatonal Conference on Wreless Communcatons and Sgnal Processng (WCSP), pp. 1-5, ovember 2011. [8] D. Robalo et al., Extendng the LTE-sm smulator wth mult-band schedulng algorthms for carrer aggregaton n LTE-advanced scenaros, n Proc. IEEE 81st Vehcular Technology Conference (VTC Sprng), pp.1-6, May 2015. [9] H. Shajaah et al., Utlty proportonal farness resource allocaton wth carrer aggregaton n 4G-LTE, n Proc. IEEE Mltary Communcaton Conference, pp. 412-417, ovember 2013. [10] C.-Y. Sun et al., Component carrer selecton and nterference coordnaton for carrer aggregaton system n heterogeneous networs, n Proc. IEEE 14th Internatonal Conference on Communcaton Technology (ICCT), pp. 402-407, ovember 2012. [11] H.-L. Jang et al., Carrer aggregaton based nterference coordnaton for lte-a macro-pco Hetet, n Proc. IEEE 77th Vehcular Technology Conference (VTC Sprng), pp. 1-6, June 2013. [12] Z. Lman et al., Interference-aware resource schedulng n lte hetnets wth carrer aggregaton support, n Proc. IEEE Internatonal Conference on Communcaton (ICC), pp. 3137-3142, June 2015. [13] M. Smse et al., Learnng based frequency- and tme-doman nter-cell nterference coordnaton n Hetets, n Proc. eee transacton on vehcular technology, vol. 64, no. 10, pp. 4589-4602, October 2015. [14] H. Wang et al., Upln nter-ste carrer aggregaton between macro and small cells n heterogeneous networs, n Proc. IEEE 80th Vehcular Technology Conference (VTC Fall), pp.1-5, September 2014. Yen-Wen Chen receved the Ph.D. degree from the Electronc Engneerng, atonal Tawan Unversty of Scence and Technology (TUST) n 1997. He wored at Chunghua Telecommuncaton Laboratores Tawan durng 1983 to 1998. Currently, he s a professor of the department of Communcaton Engneerng, atonal Central Unversty, Tawan. Hs research nterests nclude broadband moble networs, QoS management, networ applcatons, cloud servces, and software defned networng (SD). Dr. Chen s a member of the IEEE communcaton socety. Chen-Ju Chen receved the BS and MS degrees from the Department of Communcaton Engneerng, atonal Central Unversty, Tawan. And, currently, she s the research engneer of MedaTe Inc., Tawan. 114