INVESTIGATION OF VEHICULAR USERS FAIRNESS IN CDMA-HDR NETWORKS

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1 21 22 September 2007, BULGARIA 119 Proceedngs of the Internatonal Conference on Informaton Technologes (InfoTech-2007) 21 st 22 nd September 2007, Bulgara vol. 2 INVESTIGATION OF VEHICULAR USERS FAIRNESS IN CDMA-HDR NETWORKS Valentn P. Hrstov South West Unversty- Blagoevgrad e-mal(s): v_hrstov@ax.swu.bg Bulgara Abstract: The purpose of present paper s to show the advantages of usng more accurate estmaton of the SINR, and ts mpact on farness n CDMA-HDR (Code Dvson Multple Access- Hgh Data Rate) networks. The smulaton results obtaned wth an avalable onlne smulator evdence for rasng vehcular users farness through more accurate estmaton of the SINR combned wth H-ARQ. Key words: Cellular Data Networks, Farness, SINR estmaton, and Smulatons. 1. INTRODUCTION Improvng throughput and farness n Code Dvson Multple Access- Hgh Data Rate- CDMA-HDR networks s a problem of present nterest. In these networks, tme s dvded nto many tme slots and each wreless termnal-wt s transmttng packets to a base staton-bs. These Cellular Data Networks- CDNs combne the advantages of both technques- TDMA and CDMA. Ths combnaton s well suted to the bursty nature of packet data, as well as has the advantage of beng able to have frequency reuse n every sector (fg.1). The CDNs as CDMA systems are nterference lmted,.e. ther capacty can be ncreased by reducng the mnmum requred (for stable recepton of data at the recever) energy of sgnal wth a gven Sgnal to Interference and Nose Rato-SINR. Sgnal to Interference and Nose Rato-SINR s a functon of several factors such as path loss, shadowng, fadng, nose, and ntercell nterference.

2 120 PROCEEDINGS of the Internatonal Conference InfoTech-2007 The WT measures the SINR of the receved sgnal through the plot channel and sends feedback to the BS; based on the feedback from the WT, the BS adjusts ts transmtted power level. Mhatre et al. study the mpact of network load n the neghborng sectors on the nter-cell nterference n a cellular data network [5]. The observaton s that sgnal receved by a WT over the forward lnk (and used by the WT to predct SINR) contans nterference from the neghborng base statons,.e. estmaton of SINR s no accurately. Moreover, t results n data throughput decrease. In spte of ntal conservatve SINR estmaton, Hybrd Automatc Repeat Request- H-ARQ overcomes the problem partally, because, H-ARQ adjusts to network loadng n the adjacent sectors [1]. The purpose of present paper s to show the advantages of usng more accurate estmaton of the SINR 2. FAIRNESS IN CDMA-HDR NETWORKS 2.1. Background The sgnal receved by a WT over the forward lnk n a cellular data network contans nterference from the neghborng base statons. In Fg. 1 s depcted WT n sector0 of cell C receve nter-cell nterference from sector 1 of cell C and sector 2 of cell C. Also, t s shown that the SINR s functon of sgnal ampltude-a, wdth of pulse- Tc (chp), the channel gan from the base staton of the nterferng sector to the termnal- G, and the probablty that a tme slot on the forward lnk of -th sector s busy - ρ. C C C Sector 0 Interferng sectors - 1 and 2 Fg. 1. Inter-cell nterference example.

3 21 22 September 2007, BULGARIA 121 Nowadays, n the actual mplementaton of CDMA-HDR [5], the BSs are GPSsynchronzed and all the BSs transmt ther plot sgnal at the same tme. Hence, the SINR measured by the termnals contans the worst case nter-cell nterference, snce the nterferng sgnals are transmtted constantly durng the measurement phase: 2 2 G0 A TC SINR = (1) A TC(G1 + G2 ) + 2N 0 3 The SINR gven by (1), s a functon of G, and gven by: 2 G.W n ξ / 10 2 = cd. 10 (2) In (2), the frst term n the product s determnstc (for a fxed WT locaton), and corresponds to path loss, whle the second term s a random varable correspondng to lognormal shadowng loss. Here, ξ s a Gaussan random varable wth mean 0, and varance σ G. Shadowng s correlated over each tme slot dependng on the speed of the WT as per Gudmundson model [6]. Last term- Raylegh fadng s accounted through W. However, If the termnal has the nformaton about the network loads n all the sectors that are n ts actve set, t can calculate the actual SINR : 2 2 G0 A TC SINR = (3) A TC(G1ρ1 + G2ρ2 ) + 2N 0 3 Thus, usng more accurate estmaton of the SINR, WTs wll be able to mprove data throughput and even farness Farness The classcal ndex of farness dsplays level of satsfacton of each user/wt, respectvely far sharng of the network resources (e.g. data throughput- X), and s gven by: 2 ( X ) n 2 Farness = X (4) / Below n present paper, f Farness =1 ths corresponds to qute farness sharng of the data throughput between users, and f Farness =0 then ths s absolutely opposte stuatons [7]. The performance metrc s based on data throughput (X).

4 122 PROCEEDINGS of the Internatonal Conference InfoTech-2007 It s expected that more accurate ntal estmaton of the SINR and H-ARQ can mprove throughput and farness. In next secton t wll be verfed through smulatons whether these mprove the farness. 3. SIMULATION RESULTS We present smulaton results of farness when three WTs are served over the forward lnk, as run two sets of smulatons. In the frst set, all WTs use (1) n order to estmate SINR, and H-ARQ for early packet termnaton (Prmary Scheme), whle n the second set, all WTs use (3) to estmate SINR, and also use H-ARQ (Secondary. scheme ). Carrer frequency, fo 2000 MHz Log-normal Shadowng varance, σ G 10 db Shadow correlaton dstance 20.0 m Nose spectral densty, No -174 dbm/hz A, ampltude of transmt waveform (base staton 5.48 transmt power of 15W) Chp duraton, T c (1.25 Mcps) 0.8 us Radus of the sector, R 1 Km Ro for 90% cell coverage 0.95R = 0.95 Km Mscellaneous gans: antenna gans, body loss, 15.2 db cable loss Vehcular path loss n db, 10log 10 (cd n ) 21log 10 (f 0 ) log 10 (d) (f 0 n MHz, d n Km) Fracton of mult-path power captured by the recever (vehcular WT) Table 1. Smulaton parameters are lsted n Table I, and have been taken from [5]. Each smulaton s run for 20,000 tme slots, and 600 ndependent smulatons are run to gather WT throughputs wthn 90% confdence nterval. The WT locaton s selected so that the termnal s equdstant from the two nterferng base statons. The locatons from the servng base staton of WTs are selected to be 0.4R0, 0.7R0 and R0. The cell radus R s 1 Km. In all our smulatons, although the tme-varyng shadowng and fadng, t s assumed that the WT locaton remans unchanged durng the course of the smulaton. In all the smulatons, for smplcty, t s assumed that the network loads n both the nterferng sectors are the same,.e., ρ1 = ρ2, and vared ρ to study the farness of Prmary (ρ1 = ρ2 =1) and Secondary Schemes (ρ1 = ρ2 = ρ) for dfferent network loads n the nterferng sectors.

5 21 22 September 2007, BULGARIA 123 Table 2. ρ X1 X2 X3 Farness The tables 2 and 3 present (for vehcular model) the throughput (kbps) receved by each WT as a functon of the network load under the both schemes. Table 2 gves the ndexes of throughput and farness for standard CDMA-HDR networks (Prmary Scheme). In columns ttled as X1, X2, and X3 are presented end to end throughput for WTs 1, 2, and 3. In the last column s calculated the ndexes of farness usng (4). Smulaton results for Secondary Scheme are gven n table 3. Note that as the nterferng network load decreases, both the schemes result n hgher throughput for WTs 2 and 3. Ths s because both the schemes are desgned to mprove the throughput of a WT when the nter-cell nterference s lower. However ths beneft s especally more pronounced for WTs located near the cell boundary (WTs 2 and 3). Table 3 ρ X1 X2 X3 Farness Near the cell boundary the throughput degrades more rapdly, due to a lower path loss exponent,.e. more serous. ntercell nterference. In fg. 2 s compared the farness of prmary scheme (squares), and secondary scheme (dots) for the vehcular users (See table 2, and table 3). Farness of Prmary Scheme s worse then Secondary Scheme. Ths can be explaned by the observervaton that the Secondary Scheme benefts the WTs located far from the servng base staton, as well as penalzng more nearly-located WTs, partcularly for hgher load on the forward lnk ρ= One can compare throughput receved by WS1 n tables 2 and 3, and see that unlke Prmary Scheme, where the throughput of WT 1 ncreases wth decreasng network load, n Secondary Scheme, the throughput of WT 1 decreases wth decreasng network load. As has

6 124 PROCEEDINGS of the Internatonal Conference InfoTech-2007 been shown, the mechansm of the Secondary Scheme (descrbed above) s better than standard CDMA-HDR nto account throughput and farness. Fg. 2. Farness of Prmary and Secondary Schemes. 4. CONCLUSION Ths paper shows the advantages of usng more accurate estmaton of the SINR combned wth H-ARQ n Cellular Data Networks, as well as presents some smulaton results obtaned wth an avalable onlne smulator [4]. REFERENCES 1 Kwon et al. (2005), Power Controlled H-ARQ n cdma2000 1xEV-DV, IEEE Communcatons Magazne, Vol. Aprl 2005, pp Lee K. and Samuel C.(2006), Analyss of a Delay-Constraned Hybrd ARQ Wreless System, IEEE Transactons on Communcatons, Vol. 54, No. 11, November 2006, pp Mhatre V. et al. (2006), Impact of Network Load on Forward Lnk Inter-Cell Interference n Cellular Data Networks, IEEE Transactons on Wreless Communcatons, Vol. 5, No. 12, December 2006, pp Mhatre V., and C. Rosenberg, A smulator for CDMA-HDR data networks wth Hybrd-ARQ and opportunstc schedulng functonalty. Onlne avalable: 5. Осипов Е.А. (2006), Проблемы реализации надежной передачи данных в самоорганизующихся и сенсорных сетях, ISSN сп. Электросвязь, 6, 2006, с