Space sense random access with collision mitigation in uplink WLANs

Space sense random access (SSRA) with collision mitigation is proposed for TDD wireless local area networks (WLANs) with multiple antennas. Before transmitting a packet, the user performs space sense to detect the status of the channel. If the channel is idle, it then transmits a common training sequence for channel estimation. Multiple subslots are available for channel estimation and the user randomly selects one subslot to achieve the possible collision-free channel estimation. It is shown that SSRA removes the requirement of orthogonal training sequences while avoiding possible packet collision and further providing multipacket reception capability. Compared to the conventional slotted ALOHA scheme, SSRA can achieve much higher throughput, as verified by extensive simulation results.