Adaptive time slot allocation strategy in WCDMA/TDD system

Abstract

Time Division Duplex (TDD) system is getting more attention for the third generation mobile radio systems designed for asymmetric multimedia service between links. As both uplink and downlink are allocated in time domain, it is possible to change the duplex switching point and move capacity from uplink to downlink, or vice versa, depending on the capacity requirement between links. In this thesis, we consider multiple service classes with traffic unbalance between uplink and downlink in WCDMA/TDD system. First, we evaluate the system performance using Markov analysis and computer simulation for single-cell model. The overall capacity of TDD system is maximized when time slot allocation is managed with respect to the level of traffic asymmetry. Second, a time slot allocation strategy based on mobile position is proposed in multiple-cell environment, where each cell has a significantly different level of traffic asymmetry from each other. Our strategy reduces the effect of inter-cell interference. The concept of service area is introduced to find out the threshold for time slot allocation in advance, where service area is defined as the area that can be served with a given outage probability. Simulation results reveal the proposed time slot allocation strategy outperforms the conventional same time slot allocation in system throughput and blocking probability.