• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.42 no.11
• /
• pp.87-92
• /
• 2005

This paper analyzes the performance for an improved multistage parallel interference cancellation (PIC) technique with a reverse-link synchronous transmission technique (RLSTT) for DS-CDMA system in a frequency-selective Rayleigh fading channel with an imperfect power control scheme. The performance degradation due to power control error (PCE), which is approximated by a log-normally distributed random variable, is estimated as a function of the standard deviation of the PCE. The uncoded bit error performance is evaluated in order to estimate the system capacity. Comparing with the conventional one-stage PIC system, we show achievable gain around $60\%$ by the RLSTT even in the presence of PCE. We conclude that the capacity can be further improved via RLSTT, which alleviates the detrimental effects of the PCE

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.8A
• /
• pp.868-878
• /
• 2004

In this paper, we analyse feasibility of Zone-based Power Control (ZPC) scheme introduced for CDMA forward link(1) in the reverse link. To operate ZPC scheme in the CDMA systems the maximum power level that can be allocated to each traffic channel should be determined. Because all the service channels share the whole power resource in the forward lint a specific mechanism that determines Maximum power resource to each traffic channel is required to operate ZPC scheme in the forward link. However, ZPC scheme can be easily adopted to the reverse link, because of the fact that the whole power resource of service terminal is only confined to its traffic channel. In other words, we need not to determine the maximum power resource to be allocated in the reverse traffic channel. Simulation results show that ZPC scheme adopted to the reverse link yields a significant performance improvement compared with the conventional TPC(IS-95 TPC) scheme in terms of the power consumption and the traffic capacity of Portables, especially with the increasing number of high-rate data traffics. With the proposed scheme, not only be extended the service coverage of high-rate data traffic to the entire cell service coverage, but also the QoS of low-rate traffic can keep going through the service time, especially, in the situation that the incoming interference is much larger.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.1
• /
• pp.33-39
• /
• 2002

In mobile communication systems, there are areas where signal coverage is not adequately accomplished by base stations. These areas may be underground parking zones, underground stores, tunnels, and insides of buildings, etc. In these areas, repeaters are broadly used as an economical solution. However, the capacity is decreased as the number of repeaters increases because the noise power that flows to a base station in the reverse link is proportional to the number of repeaters. The reduction of capacity in the reverse link is no longer negligible in the case that several tens or hundreds repeaters are connected to a base station. In this paper, we propose c repeater that is switched off automatically when there is no active user within its coverage. With the switching repeater, we can reduce the unnecessary noise level enhancement when there is no active user within the repeaters coverage. The reverse link capacity of a DS/CDMA system with AOS repeater is analyzed mathematically and compared with that without switching repeater. From the numerical results, noticeable improvement with the switching repeaters is shown.

• The Journal of the Acoustical Society of Korea
• /
• v.14 no.1
• /
• pp.48-55
• /
• 1995

The capacity of a digital cellular CDMA system is evaluated by computer simulation for reverse link (mobile-to-base) with 37 hexagonal cells including 3 rings from a center cell. It is assumed that the channels have shadow fading and the system is ideally power controlled. In this paper the capacity of CBMA system is evaluated for various propagation exponents, voice activity factors and neighboring cell traffics. The following results are obtained. The capacity of CDMA system is increased according to the increase of the propagation exponents and the decrease of the voice activity factors. Its capacity is about 15 and 5 times larger thari that of analog cellular FM/FDMA and digital cellular TDMA for $\gamma=4$ respectively, and is very sensitive to the neighboring cell traffics.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.7A
• /
• pp.996-1004
• /
• 1999

In this paper, we evaluate the performance of reverse link synchronous CDMA with orthogonal spreading and Rake combining, and compare this to that of an asynchronous transmission under Rayleigh multipath fading environments. The link performance is evaluated in terms of average bit error rate (BER) and capacity, assuming ideal BPSK data modulation. The focus of this paper is on the impact that the multipath intensity profile (MIP) shape and number of taps in Rake receiver have on the performance of synchronous transmission. The results show the reverse link synchronous transmission can always achieve smaller BER than the asynchronous transmission even if inter-path interference exists.

• Korean Management Science Review
• /
• v.16 no.1
• /
• pp.39-50
• /
• 1999

This paper proposes a new call admission control method to enhance the reverse link capacity of a cell with heavy traffic in the CDMA PCS system under the uneven traffic load between cells. Since the capacity of a cell in the CDMA system is restricted by the total interference caused by terminals in the own cell and the adjacent cells, we can enhance the capacity of a cell by reducing the interference from other cells if possible. Our power control method allows that the signal powers received in base stations with heavy traffic be larger than those received in base stations with light traffic in order to make the interference due to other cells in the cells with heavy traffic relatively small. In the previous study, it was assumed that the signal power received by each base station in the CDMA PCS system is same when the call admission control algorithm is implemented. We could show that the reverse link capacity of a cell in the CDMA PCS system can be increased about 20% under our call admission control method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.4
• /
• pp.313-322
• /
• 2003

In this paper, the reverse link performance of imperfect power controlled cdma2000 cellular system that using array at a base station is analyzed, when MCGM beamforming algorithm and power control error is considered in shadowing. The blocking probability of the cdma2000 cellular system based on array parameters, E$\_$b//N$\_$0/ and interference statistics is calculated, and then the system capacity is calculated at a specific blocking probability. When the blocking probability is set 1 %, PCE(power control error) is 2 dB, M=2, 4, 8, 10, the capacity of cdma2000 is increased 2.3 ∼ 2.5 times higher than IS-95.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.23 no.4
• /
• pp.901-913
• /
• 1998

This paper presents a new analytical approach for the evaluation of the reverse link interference in a CDMA cellular system with unequal cell loading. In particular, the dynamic nature of the reverse link power control has been taken into account in the proposed approach so that a realistic effect of unequal cell loading, including the shadowing and soft handoff, on system capacity may be precisely captured. This is aspect that has not beensuccessfully formmulated and rarely attempted tosolve in any previous analytical approach. Our computational result shows that as the loading of every tier of surrounding cells is doubled, the subscriber capacity of the reference cell can be reduced as much as 27% of that obtained in the case that the effect of power control is not appropriately modeled.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.22 no.5
• /
• pp.1075-1082
• /
• 1997

In this paper, we propose a channel assignment scheme for reducing call blocking rate in a base station(BS) of DS-CDMA cellular systems. The proposed scheme can e applied to the case where the capacity of reverse radio link is enough, but not are the available traffic channels performing the digital modulation and demodulation functions between a mobile station and the base station. The proposed scheme takes advantage of the feature of soft handoff in which a mobile station keeps its communication link even if one of the two communication links is released. The scheme estimates the mean and variance of the received power level measured at the base station before assigning a traffic channel for a new call request. The BS makes decision based on the estimated balues whether the new call request will be accepted or not. If it is decided that the capacity of reverse radio link is enough, but all traffic channels are not available, then the BS increases the soft handoff parameter T_DROP to release the traffic channels of mobile stations loactedin soft handoff area. The BS assigns the released traffic channel to anew call or a handoff call. The performance of the proposed channel assignment scheme is evaluated by computer simulation. The results show that the call blocking rate for new calls and handoff calls is reduced.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.22 no.7
• /
• pp.1448-1458
• /
• 1997

In this paper the reverse link of the GLOBALSTAR-the representative CDMA LEO satellite system and LEO mobile satellite channel are developed by the SPW software simulation tool. And the performance of the system is evaluated. GLOBALSTAR is designed to give cellular-type service to hand-held user terminals through a constellation of 48 LEO satellites in circular orbites with 1414 Km altitude. Since LEO mobile satellite system communicates with mobile unit, it is suffered from severe multipath fading and shadowing. The fast mobility of LEO satellites makes the channel condition time vering. So, the LEO mobile satellite channel is different from land mobile channels. In this unique LEO satellite channel, it is shown that the performance of the GLOBALSTAR reverse link is varied according to the elevational angle, but this variation is overcome by satellite path diversity.