Centralized wireless MAC protocols using slotted ALOHA and dynamic TDD transmission

ALOHA scheme with dynamic Time Division Duplexed (TDD) transmission is designed and analyzed. A centralized (i.e., star) network is adopted as the topology of a cell which consists of a base station and a number of mobile clients. In dynamic TDD transmission mode, a channel is time-shared for downlink and uplink transmissions under the dynamic access control of the base station. We first propose two MAC protocols (called TDD1 and TDD2) depending on how downlink and uplink transmissions are multiplexed. We then analyze throughput and average delay of TDD1 and an alternative ALOHA scheme using Frequency Division Duplexed (FDD) transmission. Finally, we evaluate the performance of these schemes, and compare TDD1 (calculations), TDD2 (simulations), and FDD (calculations). TDD schemes are found to always work as good as, or better than, FDD. TDD2 is observed to outperform TDD1 with respect to the downlink delay in the presence of light uplink and heavy downlink traffic loads while they work almost the same in other cases.