We previously proposed a next generation cellular system for IMT-2000 based on wideband DS-CDMA with TDD scheme and have evaluated its performance by computer simulation, laboratory and field experiments. This paper presents the design concept of TDD-mode operation on wideband DS-CDMA systems. These systems employ almost the same techniques with a little difference as FDD-mode. We also present the schemes of the TDD-mode specific techniques such as fast cell search, transmission diversity and transmitter power control and show the evaluation results of them are effective. Performance can be improved by use of enhanced techniques such as interference cancellation and adaptive antenna array diversity.

This paper compares the BER performance of two types of pilot channel-based coherent Rake combining achievable by the use of weighted multi-slot averaging (WMSA) channel estimation filter in DS-CDMA transmission links. One is for the time-multiplexed pilot channel and the other is for the parallel pilot channel. The WMSA channel estimation filter weights and averages the received pilot over a period of several slots to improve the BER performance. We propose the WMSA channel estimation filters for time-multiplexed pilot and parallel pilot structures. Achievable BER performance under frequency-selective fading environments is computer simulated. The simulation results show that almost same BER performance can be achieved for both pilot channel structures when the same energy is allocated to the pilot.

This paper reviews Dynamic Channel Allocation (DCA) in TDMA cellular systems. The emphasis is on distributed DCA, which features decentralized control and adaptability to interference. Performance measures are discussed not only from a theoretical viewpoint but also from a practical viewpoint. Major techniques to enhance the capacity of cellular systems are channel segregation, reuse-partitioning, and transmitter power control. In addition to the performance of conventional cellular systems, differing performance in microcellular systems and multi-layer cellular systems is also discussed.

We compared--for the same propagation conditions and parameters--the performances of distributed dynamic channel assignment (DDCA) strategies and the performance of fixed channel assignment (FCA). This comparison quantitatively showed the effects of DDCA strategies in increasing spectrum efficiency. It also showed that using DDCA with transmitter power control (TPC) increases the system capacity to 3 4 times what it is with FCA and to 1.4 1.8 times what it is when using DDCA without TPC. We also evaluated the blocking rate and the interference probability for the inside of a cell and found that these are generally much higher close to the cell border than they are near the base station.

Four imperfections encountered in transmitter power control (TPC) for direct sequence code division multiple access (DS/CDMA) cellular mobile communications systems, faulty TPC, finite dynamic range, restricted site diversity, and non-uniform user distribution, are investigated where account is taken of the effect of the propagation constant on the traffic capacity. Computer simulation schemes for traffic capacity estimation under these TPC imperfections are presented. Traffic capacity estimates are produced for a representative DS/CDMA cellular mobile communications system.