On the performance of flexible UL-DL switching point in TDD wireless networks

An advantage of Time Division Duplex (TDD) wireless networks over Frequency Division Duplex (FDD) is that the UL-DL switching point may be flexibly adapted to asymmetric traffic loads. This enables more efficient spectrum use, but on the other hand may lead to harmful cross-link interference between cells. As a result, the net gain (or loss) from flexible TDD depends on the traffic characteristics and network scenario. In this paper we address the problem in local area packet data networks where high fluctuation in short term traffic loads is expected. We show through analysis and system level simulations that in such a scenario a significant gain in effective user throughput (TP) may be achieved under low traffic loads. At high load the gain vanishes due to saturated queues implying full bandwidth usage. We also study the impact of interference-awareness at the scheduler. It is found out that the range of traffic loads over which there is gain from flexible TDD is significantly extended by interference-awareness as compared to a conventional scheduler.