Jae-Weon Cho

Statistical model of downlink interference for the performance evaluation of CDMA systems

A statistical model of the downlink interference for the analytical performance evaluation of code-division multiple-access (CDMA) systems is proposed. Based on Wilkinsons approximation, the statistical model of the relative other cell interference is developed in closed form. The best base station (BS) selection in the shadowed environment with a correlation is taken into consideration. We show that interference statistics obtained by the proposed analytical model agree with simulation results. It is also shown that the proposed analytical model can replace Monte Carlo simulation in outage analysis.

Downlink throughput and fairness analysis in multi-rate CDMA systems

This paper presents an analytical model and a method for the evaluation of the downlink throughput and fairness performance in multi-rate CDMA systems. We propose and use a model that can show the impact of self-interference to the received E/sub b//N/sub t/. The analytical method reflects the effect of lognormal shadowing, the best BS connection procedure, the bit rate granularity and the peak available bit rate limitation, and the limited number of spreading codes. A scheduling scheme for the fairness control is also developed and applied. The performance of packet channels for delay-tolerant service is evaluated in a 3GPP WCDMA system model. The system performance measures include asymptotic throughput, fairness performance factor, outage probability, and code shortage probability. From the analysis results, we can draw the downlink packet transmission control policy that can improve the system performance.

Coverage and capacity analysis for the multi-layer CDMA macro/indoor-picocells

This paper presents an analysis of coverage and capacity for the multi-layer CDMA cellular system. The multilayer CDMA system, that shares a common frequency band, consists of macrocells for outdoor users and picocells for indoor users. Though macrocells and picocells interfere with each other, the capacity of the whole system can be increased. We have analyzed the effect of mutual interference upon cell coverage, soft handover areas, and capacities. The parameters involved in the engineering of the system are discussed. The study results show that we can control the service coverage of indoor picocells with the system parameters set properly. It is also shown that the capacity of the whole system can be enhanced smoothly by deploying the indoor picocells within existing macrocells.

Tradeoff analysis of throughput and fairness on CDMA packet downlinks with location-dependent QoS

This work presents the quantitative tradeoff relation between system throughput and fairness on multirate code-division multiple-access (CDMA) downlinks. We develop and use an analytical model and a method for performance evaluation. The proposed model and method reflect the effects of multiplexing scheme, a limited data-rate set, log-normal shadowing, the best base station selection, and self-interference. System performance measures include asymptotic throughput, fairness performance factors, and outage probability . The performance of packet channels for delay-tolerant service is evaluated based on 3GPP wide-band code-division multiple-access (WCDMA) system model. Using the method developed, various algorithms for time resource assignment are applied and the system performance measures are derived and compared. We have derived the tradeoff between asymptotic throughput and fairness performance factors caused by the location-dependent carrier-to-interference ratio. The results show that we can control the tradeoff by applying various time resource-assignment schemes. It is also shown that the tradeoff in the system with the limited data-rate set can be improved by setting the number of simultaneous users properly.

Throughput comparison of CDM and TDM for downlink packet transmission in CDMA systems with a limited data rate set

Throughputs with code-division multiplexing (CDM) and time-division multiplexing (TDM) for downlink packet transmission are compared in multirate code-division multiple access (CDMA) systems. The authors propose and use a model that can show the impact of self-interference on the received bit energy per noise and interference power density (E/sub b//N/sub t/). The developed analytical method reflects the effect of a limited data rate set, shadowed radio paths, and a limited number of spreading codes. Performance measures include asymptotic throughput, outage probability, probability of the data rate being limited by the given rate set, and probability of the system throughput being limited by the available number of spreading codes. The system throughput of packet channels for delay-tolerant service is evaluated in a 3GPP WCDMA system model. The authors show that the throughput with CDM can be equal to that with TDM in a fully loaded system without the data rate limitation. It is also shown that CDM can outperform TDM with respect to the asymptotic throughput when one takes into account the self-interference, the limitation on the data rate set, and resource reallocation of users in outage.

Hierarchical cell deployment for high speed data CDMA systems

This paper presents hierarchical cell deployment strategies for high-speed data CDMA systems. The hierarchical cell structure has been considered as a method to improve the quality of service and increase the system capacity. We evaluate the performance of the hierarchical system with one embedded micro-cell. We show that the system capacity is dependent on the location of the micro-cell site and its transmission power. Then, two different deployment strategies for hierarchical systems with multiple micro-cells are proposed and compared. The analysis results show that the cell throughput can be maximized by co-locating micro and macro-cell site with different frequency bands. On the other hand, it is shown that both the fairness of the QoS and the cell throughput is improved by deploying a micro-cell at the edges of the macro-cell.

Traffic performance analysis of handover in GMPCS systems

This paper presents an analysis of handover process and its effect on the traffic performance in global mobile personal communications by satellite (GMPCS) systems. With the nongeostationary satellite used for the system, the handover scheme needs to be applied to make calls completed without any interruption. An analytical model is developed for the analysis of the handover process. We derive the mean number of handovers and handover delay with various satellite antenna patterns and different settings of handover parameter. A suitable traffic model of the whole system is also derived after due considerations of the handover process. The system performance measures include new call blocking probability, call dropping probability, and mean number of handovers per call. A computer simulation is developed and used. We also analyze the system performance with a number of handover priority schemes applied. Based on the study results, the handover parameters are selected to maximize the traffic performance. It is shown that we can improve the overall traffic performance of GMPCS system by setting handover parameters properly and using the handover priority scheme.

Traffic performance analysis of handover in GMPCS

This paper presents an analysis of the handover process and its effect upon the traffic performance in global mobile personal communications by satellite (GMPCS). With the non-geostationary satellite used for the system, the handover scheme needs to be applied to complete calls without any interruption. An analytical model has been developed for the analysis of the handover process. We have derived mean number of handovers and handover delay by using the developed model. A suitable traffic model of the whole system has also been derived after due considerations of the handover process. The system performance measures include new call blocking probability, call dropping probability and mean number of handovers per call. A computer simulation has been developed and used. We also analyzed the system performance with a number of handover priority schemes applied. Based on the study results, handover parameters have been selected to maximize the traffic performance. It is shown that we can make overall traffic performance of GMPCS system improved by setting handover parameters properly.

An efficient application scheme of adaptive antenna for multimedia CDMA communication systems

The adaptive array antenna has been studied and considered as a promising technique to enhance the spectrum efficiency of multimedia CDMA cellular mobile communication systems. It is a technique to control the multiple access interference (MAI) that limits the capacity of the systems. However, it is a very complex and expensive technology. We propose an application scheme to apply the technique efficiently to the system in the sense of cost and complexity. We derive an analytical formula of the system performance and use it to show that the system performance can be improved when the proposed scheme is applied.