Power Control Algorithm of Ranging Process in IEEE Relay System

Transcription

1 Pwer Cntrl Algrithm f Ranging Prcess in IEEE Relay System D Hwan Lee and Hiryuki Mrikawa Department f Frntier Infrmatics The University f Tky Kmaba Megurku Tky Japan leedh@mlab.t.u-tyk.ac.jp Abstract Ranging prcess in IEEE system prvides a number f functinalities such as initial netwrk entry uplink synchrnizatin pwer adjustment and system crdinatin. As the intrductin f relay netwrk in IEEE systems a new transmissin pwer cntrl algrithm is necessary. Therefre this paper prpses a nvel ranging transmissin pwer cntrl algrithm which reduces the interference between MS- ranging (i.e. ranging between MS and ) and MS- ranging (i.e. ranging between MS and ). Cmputer simulatin results shw the perfrmance f ranging prcess in terms f ranging detectin success prbability and validate the efficiency f the prpsed transmissin pwer cntrl algrithm. These results will be beneficial as the guideline fr the design f IEEE relay system. Keywrds-cmpnent; IEEE ; Ranging; Relay; Transmissin pwer cntrl I. INTRODUCTION The standardizatin wrk f IEEE e bradband wireless access (BWA) system has been finished and its cmmercializatin has been nging [1 2]. IEEE e system is based n rthgnal frequency divisin multiple access (OFDMA) systems which have advantages due t spectral efficiency capability t cpe with inter symbl interference and rbustness in multipath prpagatin envirnment [3-5]. These advantages can be further imprved by adpting relay system [6]. Discussin n the enhancement f e system by adpting relay system is nging [7]. By the intrductin f relay system int IEEE system system thrughput imprvement and cverage extensin can be feasible with lw deplyment cst [8]. There exist several cntributins in the literature regarding IEEE relay system [9-12]. [9] prpsed a new frame structure and [10] studied n the system thrughput f IEEE relay system. [11] develped a new spectrum efficient channel allcatin algrithm and [12] prpsed an uplink data traffic scheduling algrithm. [13] prvided the fifth draft standard f multihp relay specificatin. This paper adpts fundamental system cnfiguratins frm [13] since it is the mst prmising candidate. Ranging prcess refers cntentin-based wireless randm access and prvides a number f functinalities such as initial netwrk entry uplink synchrnizatin pwer adjustment and system crdinatin [14-15]. The cnventinal ranging prcess f IEEE system has t be mdified and ptimized under the relay deplyed envirnment. Thus we prpse a new ranging pwer cntrl algrithm fr IEEE relay system and evaluate the perfrmance. This paper prvides fllwing cntributins: First a nvel transmissin pwer cntrl (TPC) algrithm f ranging prcess in IEEE relay system is prpsed. Secnd the perfrmance f ranging prcess in IEEE relay system is analyzed in terms f ranging detectin success prbability. The remainder f this paper rganized as fllw. Sectin Ⅱ prvides backgrund f IEEE e OFDMA system ranging prcess and IEEE relay system. Sectin Ⅲ describes the cnventinal and the prpsed TPC algrithms. Sectin Ⅳ gives perfrmance analysis f ranging prcess in IEEE relay system. Finally Sectin Ⅴ summarizes and cncludes this paper. II. BACKGROUND A. IEEE e OFDMA System Figure 1 depicts the frame structure f IEEE e OFDMA system with time divisin duplex (TDD) mde. Hrizntal and vertical axes refer the time dmain (OFDMA symbl) and the frequency dmain (subchannel) respectively. Dwnlink and uplink utilize the whle frequency band and are divided by transmit/receive transitin time gap (TTG/RTG). manages dwnlink and uplink channel resurces and bradcasts the scheduling infrmatin thrugh dwnlink map (DL-MAP) and uplink map (UL-MAP). Data traffics are transmitted thrugh DL/UL burst channel. One r multiple DL/UL bursts can be allcated t a single MS depending n the traffic rate. Hwever a DL/UL burst shuld be nly allcated t single MS t prevent interferences amng MSs. Ranging subchannel refers a part f uplink resurce which is allcated fr ranging prcess. Ranging subchannel is separated frm data channel and based n cntentin-riented randm access. Multiple MSs transmit their ranging signals thrugh ranging subchannel. Once cnducts ranging signal detectin successfully it allcates DL/UL burst t MS fr further cmmunicatin. B. Ranging Prcess Ranging prcess cnsists f initial handver (HO) peridic and bandwidth request ranging and it is carried ut by cntentin-based methd. Multiple MSs share cmmn channel (i.e. ranging subchannel) and transmit mutually exclusive ranging cdes simultaneusly. perfrms cntentin reslutin and uplink synchrnizatin by ranging cde identificatin and rund trip time () estimatin. Multiuser cntentin reslutin (i.e. ranging cde identificatin) and uplink time synchrnizatin (i.e. estimatin) are carried ut based n the peak detectin f /08/$ IEEE.

2 OFDMA symbl number (time dmain) subchannel lgical number (frequency dmain) k k+ 1 k+ 3 k+ 5 k+ 7 k+ 9 k+ 11 k+ 13 k+ 15 k+ 18 k+ 21 k+ 24 k+ 27 k+ 28 Preamble DL-MAP FCH DL-burst #1 (UL-MAP) DL burst #5 Dwnlik DL burst #3 DL burst #4 DL burst #5 DL burst #6 TTG (transmit transitin gap) Ranging subchannel UL burst #1 UL burst #2 UL burst #3 UL burst #4 UL burst #5 Uplink RTG (receive transitin gap) Preamble DL-MAP FCH f MS 0 f MS 1 f MS M -1 Ranging subcarrier demapping N-pt FFT Remve CP & S/P RF & ADC estimatin with cde 0 estimatin with cde 1 estimatin with cde L -1 cde 0 cde 1 cde L-1 threshld threshld threshld multiple ranging detectin Fig. 1 Frame structure f IEEE e OFDMA system. received ranging signals by expliting the superir crrelatin prperty f raging cde. Well-knwn crrelatin prperty f ranging cdes is given as Eq. (1). Crrelatin f tw ranging cdes yields K (peak value) when tw cdes are identical and is crrectly estimated. On the ther hand it yields 1/K when tw cdes are nt identical r is incrrectly estimated. K 1 i= 0 n m Cm( i) Cn( i)exp{ j2 π ( fc + i f)( Δt t)} m K if m = n and t = Δt = 1/ Ktherwise. n m n where Cm () i Cn ( i ) t Δ t K f c and f are the m th user s ranging cde the n th crrelated ranging cde the m th user s the estimated fr ranging cde Cn ( i ) ranging cde length center frequency and subcarrier spacing respectively. Fig.2 shws a blck diagram f ranging prcess. Multiple MSs transmit ranging cdes simultaneusly. cnducts basic OFDMA signal prcessing including analgue-t-digital cnversin CP remval serial-t-parallel cnversin N-pint FFT and subcarrier demapping. Subsequently carries ut ranging cde identificatin and estimatin with all pssible ranging cde and value by the peal detectin. Since is unaware f transmitted ranging cdes it cnducts L parallel ranging detectin prcess fr whle L ranging cdes. Finally cmpares the imum value f each detectin blck with the threshld and determines apprpriate Cn ( i ) n and Δ t sets. Fr instance assuming three MSs transmit ranging cdes C 0 () i C () i and 3 C () 4 i amng ttal five ) (1) ranging cdes with and 0.5 (usec) respectively. Then utput matrix f ranging detectin will be given as Eq. (2). The imum and the reslutin f estimatin are assumed as 1.0 and 0.1 (usec) in this example. With utput matrix R is able t cnduct cde identificatin estimatin by the peak detectin. In the ideal channel all transmitted ranging cdes will be successfully identified and crrespnding s will be crrectly estimated. Hwever pssibilities f cde Fig. 2 Blck diagram f ranging prcess. identificatin r estimatin errr exist due t channel interferences and nise in the practical channel K K K K K K K K K K K K K K K K K K K K K K n R ( Cn Δ t) =. (2) K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K K C. IEEE Relay System In IEEE relay system the main purpse f the intrductin f is cverage extensin and thrughput enhancement. In cverage extensin case signal des nt reach MS due t lng distance r gemetrical bstacles. Thus delivers data packets in the middle f and MS t extend the cverage. In thrughput enhancement case is intrduced where signal strength is weak and lw MCS (mdulatin and cding scheme) level is adpted. enhances thrughput by maintaining signal strength strng and by allwing high MCS level adpted. In this paper -centric resurce allcatin and link adaptatin are assumed fr bth cases. schedules resurce allcatin fr all links including - -MS and -MS links and bradcasts channel allcatin infrmatin thrugh DL-MAP (dwnlink map) and UL-MAP (uplink map) messages. cnveys bradcast message t MS and delivers data packets between and MS. MS cmmunicates with r accrding t DL-MAP and UL-MAP. III. PROPOSED RANGING TRANSMISSION POWER CONTORL ALGORITHM IN IEEE RELAY SYSTEM A. Prblem Statement f the Cnventinal Ranging Transmissin Pwer Cntrl Algrtihm This subsectin describes the prblem statement f the cnventinal TPC algrithm in IEEE relay system. Cnventinal TPC f ranging prcess is cnducted based n

3 (a) Cnventinal TPC algrithm (single cell). (b) Cnventinal TPC algrithm (relay system) (c) Prpsed TPC algrithm (relay system). Fig. 3 Transmissin pwer distributin f the cnventinal and the prpsed TPC algrithm. pen-lp pwer cntrl expliting the reciprcity f dwnlink and uplink channel. Channel cherence time f IEEE e OFDMA system which perates n the 2.5 GHz with the mbility supprt up t 60 km/h is apprximated as 3.6 msec [3]. It is reasnable t determine that dwnlink and uplink channel are reciprcal because bradcast signal slts and ranging signal slts are apart less than 3 msec [1-2]. Figure 3(a) shws the transmissin pwer distributin f the cnventinal TPC algrithm in a single cell which is given as Eq. (3). XY-plane shws the distance frm and Z-axis shws the ranging transmissin pwer. P = EIP P + _ EIRP S (3) TX _ IR _ MAX X IR MS where P TX _ IR _ MAX EIPXP IR _ EIRP and S AB are the imum transmissin pwer the imum equivalent istrpic received pwer (btained frm the DCD) transmissin pwer (btained frm the DCD) and measured received signal strength f A at B respectively. Each MS adjusts ranging transmissin pwer accrding t the difference between the riginal transmissin pwer and the received signal strength. Basically it is based n the distance between and each MS. Ranging transmissin pwer increases as the distance between and MS increases. Figure 3(b) shws the transmissin pwer distributin when the cnventinal TPC algrithm is adpted in relay system. Since the cnventinal TPC algrithm is based n the path lss which is highly relies n the distance between and MS r and MS transmissin pwer f MS- ranging is set t relatively lwer than that f MS- ranging. As cnfirmed by Fig. 3(b) MS- ranging signal gets severe interference frm MS- ranging signal. B. Transmsissin Pwer Cntrl Algrithm This subsectin prvides a nvel ranging TPC algrithm fr IEEE relay system. The basic cncept f the prpsed ranging TPC algrithm is increase the MS- ranging pwer t vercme the interference f MS- ranging. Figure 3(c) shws the transmissin pwer distributin f the prpsed ranging TPC algrithm when tw exist. MS- ranging transmissin pwer is dynamically adjusted depending n the lcatin f t suppress the interference frm MS- ranging. Suggested algrithm is given as belw. PTX _ IR _ MAX = EIPX PIR + _ EIRP S MS if S MS thres EIPXP IR + _ EIRP S MS if S MS < thres (4) and S MS thres MSTX _ MAX therwise. where MS TX _ MAX is imum transmissin pwer f MS and thres and thres are predefined threshld defined as belw. thres = EIPX PIR + _ EIRP MSTX _ MAX (5) thres = EIPX PIR + _ EIRP MSTX _ MAX. Basically MS- ranging is set t have the higher pririty than MS- ranging. Therefre MS perfrms MS- ranging when S MS surpasses thres regardless f S and thres. Only when MS- ranging is MS infeasible and S MS surpasses thres MS cnducts MS- ranging. If bth MS- and MS- ranging are infeasible MS transmits ranging signal t with the imum transmissin pwer. Furthermre each shuld set EIPXP IR in rder t minimize interferences between MS- and MS- ranging. We prpse EIPXP IR t be set as Eq. (6). EIPXP IR = EIPXP IR + _ EIRP S Plss( r) (6) where Plss ( r ) is a path lss calculatin functin with the variable r (the cverage f ) and it will be given in the fllwing sectin. Eq. (6) can be interpreted as fllw: MS- ranging transmissin pwer is adjusted fr received MS- ranging signal pwer at and MS- ranging signal pwer at t be maintained equivalent regardless f the lcatin f.

4 Table 1. System parameters f IEEE relay system. Parameter Value Parameter Value Cell radius () 1 Km Frame size 5 ms Cell radius () 100 m Nise figure 5 db Career frequency 2.5 GHz Max transmissin pwer 46 dbm Ttal bandwidth 10 MHz Max transmissin pwer 36 dbm Subcarrier spacing KHz Max MS transmissin pwer 23 dbm Ttal number f sub-carriers 1024 EIPXP IR -116 dbm Number f ranging sub-carriers 144 Path lss mdel Fading mdel Rayleigh fading mdel [17] (Urban Micrcell & Macrcell) Lg nrmal shadwing standard deviatin Mdified COST 231 Hata mdel [18] 8 db IV. PERFORMANCE EVALUATION A. Simulatin Parameters Simulatin parameters are chsen frm [1 2] [17] and details are given in Table 3. We mdified Matlab simulatin pen surce f 3GPP spatial channel mdel [16] fr IEEE relay system. Cell radius f and are set t 1 Km and 100 m. Career frequency f 2.5 GHz with ttal bandwidth 10 MHz mdel is cnsidered. Ttal number f sub-carrier and number f ranging subcarrier are 1024 and 144 which indicates that ranging cde length K in Eq. (1) equals t 144. Mdified COST 231 Hata path lss mdel [18] is adpted. Fr the realistic analysis path lss mdel includes Urban Macrcell and Urban Micrcell scenari with bth LOS (line f sight) and NLOS (nn line f sight) cases simultaneusly as belw. Plss Urban Micr ( r) r 300 m Plss ( r) = (7) Plss Urban Macr ( r) r > 300 m. where r is the distance between MS and r MS and. Plss Urban Micr () r and Plss Urban Macr () r are path lss mdel f Urban Macrcell and Urban Micrcell scenari. Prbability f LOS in an Urban Micr cell is given as belw [17]. 1 r < 15 m PLOS ( r) = (8) ( 1 ( lg ) 1/3 10 ( r)) r > 15 m. We assume that all channel f Urban Macrcell mdel are NLOS. Rayleigh fading channel mdel with 20 tabs and lg nrmal shadwing with 8 db standard deviatin mdel are als adpted. Transmissin pwer f and MS are set t 46 dbm 36 dbm and 23 dbm respectively. Nise figure at and is set t 5 db and EIPXP IR is set t -116 dbm. The difference between the actual and the estimatin less m n than 1.6 usec (i.e. t Δ t < 1.6 usec) is set t be ranging detectin success. B. Cmparisn Between the Cnventinal and the Prpsed Ranging TPC Algrithm Figure 4 shws the cmparisn f MS- ranging between the cnventinal and the prpsed ranging TPC algrithm in terms f the lcatin f. X-axis refers the distance between and and Y-axis indicates ranging detectin success prbabilities (RDSP) at. The distance between and is set frm 200 m t 900 m. Tw MSs are deplyed: the first MS is set t be randmly lcated within the cverage and cnducts MS- ranging. The secnd MS is set t be lcated ut f the cverage and cnducts MS- ranging. T investigate the effect f the distance between and the interfering MS (i.e. the secnd MS) the distance between the secnd MS and the -cell edge is set t 0 ~ 50 m 50 ~ 100 m and 100 ~ 150m respectively. There exist several pints t be analyzed in this simulatin. First RDSP f the cnventinal TPC algrithm decreases as the distance between and increases which reveals the prblem f the cnventinal ranging TPC algrithm as stated in at Sectin Ⅲ. Secnd RDSP f the prpsed TPC algrithm shws almst similar results regardless f the distance between and. It indicates that the interference f MS- ranging at is effectively vercme by the prpsed TPC algrithm and the prpsed TPC algrithm is able t be adpted regardless f the lcatin f. Third RDSP f the cnventinal TPC algrithm shws the wrse perfrmance as the distance between and the interfering MS (i.e. the secnd MS) becmes clser. It is expectable result because the received signal strength f the interfering signal (i.e. MS- ranging signal) is getting strnger as the distance between and the interfering MS becmes clser. Thus the perfrmance f MS- ranging prcess varies depending n the lcatin f the interfering MS when the cnventinal TPC algrithm is adpted which makes the perfrmance f ranging prcess t be unreliable. Frth RDSP f the prpsed TPC algrithm shws similar results regardless f the distance between and the interfering MS which prvides reliability in the system design. Figure 5 shws the cmparisn f MS- ranging between the cnventinal TPC algrithm and the prpsed ranging TPC algrithm in terms f the number f MSs. X-axis and Y-axis indicate the number f MSs and RDSP respectively. 5 s are set t be randmly lcated in a cell and multiple MSs are als set t be randmly lcated in a cell. The prbability that an MS belngs t any is Nte that the number f MSs des nt mean the number f MSs in the cverage but means the whle number f MSs in a cell. In Fig. 5 RDSP f the prpsed TPC algrithm shws almst similar result while that f the cnventinal TPC algrithm decreases as the number f MSs increases. It validates that MS-

5 Ranging detectin success prbability Prpsed TPC algrithm adpted 0-50m (Prpsed TPC) m(Prpsed TPC) Cnventinal TPC m(Prpsed TPC) algrithm adpted 0-50m(Cnventinal TPC) m(Cnventinal TPC) m(Cnventinal TPC) Distance between and Fig. 4 Cmparisn between the cnventinal and the prpsed ranging TPC algrithm in terms f the lcatin f (MS- ranging). Ranging detetin success prbability Prpsed TPC Cnventinal TPC Number f MSs Fig. 5 Cmparisn between the cnventinal and the prpsed ranging TPC algrithm in terms f the number f MSs (MS- ranging). Ranging detectin success prbability Prpsed TPC Cnventinal TPC Number f MSs Fig. 6 Cmparisn between the cnventinal and the prpsed ranging TPC algrithm in terms f the number f MSs (MS- ranging). ranging with the prpsed TPC algrithm vercme the effect f interference caused by MS- ranging signals. Figure 6 shws the cmparisn f MS- ranging between the cnventinal TPC algrithm and the prpsed ranging TPC algrithm in terms f the number f MSs. Simulatin setting is identical with that f Fig. 5. RDSP f bth cnventinal and prpsed TPC algrithm shw almst identical results in this case. It indicates that MS- ranging signal with the prpsed algrithm des nt give severe interference t MS- ranging. These results validate that the perfrmance f MS- ranging can be enhanced by the prpsed ranging TPC algrithm while nt degrading the perfrmance f MS- ranging. V. CONCLUSIONS This paper prpses a nvel ranging TPC algrithm in IEEE relays system cnsidering the received signal strength f bth and t reduce the interference between MS- ranging and MS- ranging. Cmputer simulatins are cnducted t analyze the perfrmance f the prpsed TCP algrithm. Simulatin results validate the efficiency f the prpsed TPC algrithm. These results will be beneficial as the guideline fr the design f IEEE relays system. REFERENCES [1] IEEE LAN/MAN Standards Cmmittee IEEE Standard fr lcal and metrplitan area netwrks part 16: Air interface fr fixed bradband wireless access systems IEEE Std TM [2] IEEE LAN/MAN Standards Cmmittee IEEE Standard fr lcal and metrplitan area netwrks Part 16: Air interface fr fixed and mbile bradband wireless access systems amendment 2: Physical and medium access cntrl layers fr cmbined fixed and mbile peratin in licensed bands and crrigendum 1 IEEE Std e-2005 and IEEE Std /Cr [3] R. Nee and R. Prasad OFDM Wireless Multimedia Cmmunicatins Artech Huse [4] L. J. Cimini Analysis and simulatins f a digital mbile channel using rthgnal frequency divisin multiplexing IEEE Trans. Cmmun vl. 33 n. 7 pp Jul [5] T. Keller and L. Hanz Adaptive multicarrier mdulatin: A cnvenient framewrk fr time-frequency prcessing in wireless cmmunicatins Prc. IEEE vl. 88 n. 5. pp May [6] R. Pabst et al. Relay-based deplyment cncepts fr wireless and mbile bradband radi IEEE Cmmun. Mag. vl. 42 n. 9 pp Sep [7] IEEE s Relay Task Grup [nline] [8] B. Can M. Prtalski H. Lebretn S. Frattasi and H. Suraweera. Implementatin Issues fr OFDM-based multihp cellular netwrks IEEE Cmmun. Mag. vl. 45 n. 9 pp Sep [9] Z. Ta A. Li K.H. Te and J. Zhang Frame structure design fr IEEE j mbile multihp relay (MMR) netwrks in Prc. IEEE Glbal Telecmmunicatins Cnference 2007 pp Nv [10] Y.Q. Bian A.R. Nix Y. Sun and P. Strauch Perfrmance evaluatin f mbile WiMAX with MIMO and relay extensins in Prc. IEEE Wireless Cmmunicatins and Netwrking Cnference 2007 pp Mar [11] E. Liu D. Wang J. Liu G. Shen and S. Jin Perfrmance evaluatin f bandwidth allcatin in j mbile multi-hp relay netwrks in Prc. IEEE 65 th Vehicular Technlgy Cnference 2007 pp Apr [12] O. J and D. Ch Traffic adaptive uplink scheduling scheme fr relay statin in IEEE based multi-hp system in Prc. IEEE 65 th Vehicular Technlgy Cnference 2007 pp Sep [13] IEEE LAN/MAN Standards Cmmittee Draft Amendment t IEEE Standard fr lcal and metrplitan area netwrks part 16: Air interface fr fixed and mbile bradband wireless access systems: Multihp relay specificatin IEEE P802.16j/D5 May [14] X. Fu Y. Li and H. Minn A new ranging methd fr OFDMA systems IEEE Trans. Wireless Cmmun. vl. 6 n. 2 pp Feb [15] D.H. Lee and H. Mrikawa Perfrmance analysis f ranging prcess in IEEE e systems in Prc. IEEE 3 rd Internatinal Cnference n Wireless and Mbile Cmputing Netwrking and Cmmunicatin Oct [16] J. Sal et al. MATLAB implementatin f the 3GPP spatial channel mdel (3GPP TR ) [nline]. Available: [17] R. Srinivasan et al. Draft IEEE m evaluatin methdlgy IEEE m-07/037r1. [18] Digital mbile radi twards future generatin systems COST Actin 231 Final Reprt EUR