IEEE 802.16 Capacity Enhancement Using an Adaptive TDD Split

In urban areas, users have become more and more accustomed to the availability of broadband access. However, in rural and suburban areas, it is often too expensive for network providers to serve every user with traditional wired broadband access such as DSL or cable modem. In such areas, WiMAX (worldwide interoperability for microwave access) networks based on the IEEE 802.16 standard are the most promising solution. In this paper, we focus on the performance of the IEEE 802.16 time division duplex (TDD) mode in rural areas with only one cell. When using TDD, the duration of the downlink and uplink subframe can be set individually, which is called adaptive time division duplex (ATDD). However, the ratio between downlink and uplink is normally set to a fixed value. We will show the performance of different fixed downlink/uplink ratios for several traffic models. Furthermore, we propose an algorithm for an adaptive downlink/uplink boundary in dependence on the current traffic load in the cell. The results show an enormous performance gain compared to the fixed settings.