Performance of TD-CDMA systems during crossed slots

Many multimedia services of the next generation mobile telecommunication systems have an asymmetric traffic distribution between uplink and downlink. The combination of the Time Division Duplex (TDD) with the Time Division Multiple Access (TDMA) technique in the Universal Mobile Telecommunications System (UNITS) allows an asymmetric use of radio resources due to the flexible allocation of time slots. To conserve this flexibility, the uplink and downlink slot distribution is prefered to be different in cells due to the different rates of asymmetry. Hence, crossed slots, where a set of cells are active in downlink and another set are active in uplink, must be allowed. In crossed slots, intermobile and inter-base station interferences appear. Intermobile interference is very difficult to measure and may induce very high outage probability when two close mobiles are active in opposite link directions during the same slot. In this paper, a simplified optimum power control is used to study the performance of a TD-CDMA system during a crossed slot. Simulation results has shown that the system performance may be better in crossed slots than in uplink slots for some mobile distributions.