Cdma2000 1X Capacity Decrease by Power Control Error in High Speed Train Environment

CDMA2000 1X CAPACITY DECREASE BY POWER CONTROL ERROR IN HIGH SPEED TRAIN ENVIRONMENT Simon Shin, Tae-Kyun Park, Byeung-Cheol Kim, and Yong-Ha Jeon Network R&D Center, SK Telecom, 9-1, Sunae-dong, Bundang-gu, Sungnam City, Gyunggi-do, South Korea Dongwoo Kim School of Electrical Engineering & Computer Science, Hanyang Univ. 1271 Sa-dong, Ansan, Kyungki-do 425-791, South Korea Keywords: CDMA2000 1X, Doppler shift, capacity, power control, Korea Train Express Abstract: CDMA2000 1X capacity was analysed in the high speed train environment. We calculated the power control error by Doppler shift and simulated bit error rate (BER) at the base station. We made the interference model and calculated the BER from lower bound of power control error variance. The reverse link BER was increased by high velocity although there was no coverage reduction. Capacity decrease was negligible in the pedestrian (5 km/h), urban vehicular(40 km/h), highway and railroad(100 km/h) environment. However, capacity was severely reduced in high speed train condition(300 km/h and 350 km/h). Cell-planning considering capacity as well as coverage is essential for successful cellular service in high speed train. 1 INTRODUCTION train with 300 km/h velocity. Received power, transmitted power, and pilot chip energy to Cellular mobile telephone and data communication interference ratio (Ec/Io) of mobile station were not correlated with the mobile velocity. We could serve services are very popular. Cellular service is usable in anywhere, even though tunnel, sea, and successfully the CDMA2000 1X in the KTX by underground places. Railroads and highways are existing cellular network. Experimental results confirm that coverage is not main service area of cellular service because many people move through them. Many countries adopts reduced by speed mobility. However, a few base the high speed train for transportation capability and station and frequency assignment (FA) is established in rural area. It makes the capacity shortage. One convenience for example TGV in France, ICE in Deutschland. Korea also constructs the Korea Train KTX train is composed of 20 cars and one car seats Express (KTX) between Seoul and Pusan. KTX 64 persons. It means more than 2000 calls can connect one base station when two opposite trains travels by 300 km/h speed and will be upgraded by 350 km/h speed. are in coverage of same base station. In the dense High speed mobility can damage pilot urban area, heavy traffic cell is split for dividing traffic. This method cannot be used for KTX acquisition, steady-state demodulation, code tracking, and power control. We experimented the because traffic cannot be split in one train. We must CDMA2000 1X service quality using channel increase the FA for capacity improvement. Adjacent cell uses same FA for smooth handoff. If one cell simulator in Test-bed network. There was no quality degradation such as MOS(mean of score), data increases the FA number, adjacent cells also throughput, call drop, and call fail. We got the same increase the FA number. Therefore we have to estimate the capacity of one FA for efficient network results in the KTX. Call origination, response, data download, and data upload was successful in the investment. 109 Shin S., Park T., Kim B. and Kim D. (2004). CDMA2000 1X CAPACITY DECREASE BY POWER CONTROL ERROR IN HIGH SPEED TRAIN ENVIRONMENT. In Proceedings of the First International Conference on E-Business and Telecommunication Networks, pages 109-113 DOI: 10.5220/0001398401090113 Copyright c SciTePress ICETE 2004 - WIRELESS COMMUNICATION SYSTEMS AND NETWORKS Velocity does not influence the coverage, but it variance of random variable measured by Watt- Si does not mean that capacity is not varied by velocity. unit are as follows. Network performance can be changed with user 1 number because CDMA is the system limited by βm + β 2σ 2 i 2 i E[Si ] = e interference. CDMA performance is influenced by 2.2 multi-user interference. CDMA capacity is limited 2βm +β 2σ 2 β 2σ 2 by Walsh code on the forward link and by cell i i i 2.3 Var(Si ) = e (e −1) loading on the reverse link. Cell loading is the received power increase by mobile station at the base station receiver. High cell loading increases the β is (ln10)/10 in equation 2.2 and 2.3. Received noise level at the base station receiver and it signal strength of user o is as equation 2.4. 2.4 degrades the bit energy to noise ratio (Eb/Nt). Low So = ε o (dB) Eb/Nt increases the transmitted power of mobile station by power control and high transmitted power In equation 2.4, it is assumed has a log-normal ε o degrades Eb/Nt repeatedly. CDMA2000 1X uses the distribution with variance 2 . σ e (dB) fast power control for corresponding to variable Received power from other cell users must be radio channel. High velocity of mobile causes the considered to analyse multi-cell environment. power control error due to Doppler shift and fast Interference from other cell is represented by in-cell radio channel environment variation. This paper interference. If there are K users in the each cell and analysed the capacity decrease by power control average propagation loss ratio of in-cell and other error. Section 2 will derive the calculation of power cell is g, other cell interference is gK. Standard control error and Section 3 will show the simulation deviation of received signal is the control function of results. base station transmitted power because of fading. Total interference considering both in-cell and other cell interference is as equation 2.5 2 POWER CONTROL ERROR K gK 2.5 SIMULATION I = ∑ S ei + ∑ S oi i=1 i=1 2.1 Interference Model S ei is signal power of in-cell user i with standard deviation . is signal power of other cell user i σ ei Soi We starts making interference model by followed with standard deviation . Therefore, expected σ oi assumption. value and variance of I is as follows - User o who is analysis target has the appropriate received signal strength 0 dB. K gK - There are K+1 users including target user o. 2.6 E[I] = ∑ E[Sei ] + ∑ E[Soi ] - K+1 users are served in same cell. i=1 i=1 - K+1 users are riding the KTX. K gK 2.7 - There is no other user who is not riding KTX in Var(I) = ∑Var(Sei ) + ∑Var(Soi ) the analysed cell. That is to say, all of users in i=1 i=1 the analysed cell are riding KTX. - Other cell user K interference is assumed in-cell Probability density function (PDF) of I can be user gK. approximated by log-normal random variable ξ , - There is no error in the power control procedure because I is sum of independent log-normal random of the other cell user. variables. Expected value and variance of ξ is as follows Received signal in base station from interference 1 user i is as follows: m + σ 2 K 2 K 2.8 E[ξ ] = e + Si = mi ε i (dB) 2.1 2 2 Var(ξ) = e2mK +σ K (eσ K −1) 2.9 is the signal strength without power control error. mi ε i is the random variable due to power control error It is assumed power control error variance of in-cell and has log-normal distribution with 0 dB expected 2 2 users and other cell is σ e and σ o , respectively. value and 2 dB variance. Expected value and σ i Expected value and variance of I is defined with 110 CDMA2000 1X CAPACITY DECREASE BY POWER CONTROL ERROR IN HIGH SPEED TRAIN ENVIRONMENT expected value and variance of ξ using Wilkinson’s ∞ Method. γ 2.19 Pe = Q(e )g(γ )dγ ∫0 1 1 1 2 2 2 2 2 βm+ β σ e βm+ β σ o mK + σ K Ke 2 + gKe 2 = e 2 2.10 Equation 2.19 is approximated to equation 2.20 using the expansion of central difference. 2 2 2 2 2 2 2 2 2 2 Ke 2 βm+ β σ e (e β σ e − 1)+ gKe 2 βm+ β σ o (e β σ o − 1)= e 2mK +σ K (eσ K − 1) 2 m 1 m + 3σ 1 m − 3σ 2.11 γ γ γ γ γ 2.20 Pe ≈ Q(e )+ Q(e )+ Q(e ) 3 6 6 We get mk and σ k from equation 2.10 and 2.11. ⎡ ⎤ 2.3 Variance of Power Control Error ⎢ 2 2 2 2 2 2 2 2 ⎥ β σ e β σ e β σ o β σ o 2.12 2 ⎢e ()e −1 + ge (e −1)⎥ σ K = ln⎢ 2 +1⎥ Each base station controls the received power from 1 2 2 1 2 2 ⎢ ⎛ β σ e β σ o ⎞ ⎥ mobile station in cellular CDMA network. There is K⎜e 2 + ge 2 ⎟ ⎢ ⎜ ⎟ ⎥ four main error factor when tracking the received ⎣ ⎝ ⎠ ⎦ power. They are the quantum(σ q), decoding(σ d), 1 1 β 2σ 2 β 2σ 2 ⎛ e o ⎞ 1 2 measurement( ), and propagation delay( ) error. m = ln K + ln⎜e 2 + ge 2 ⎟ − σ 2.13 σ m σ p K ⎜ ⎟ 2 K ⎝ ⎠ Generally, σ m and σ p is much larger than σ q and σ d. If error factor is statistically independent, 2.2 Mean BER Calculation 2 2 2 2 2 2.21 σ e = σ m + σ p + σ q + σ d Bit energy to interference ratio of BPSK having bandwidth W is given by equation 2.14.

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