A space-division time-division multiple access scheme for high throughput provisioning in WLANs

Directional antennas may dramatically increase the capacity of a wireless LAN by allowing several stations to simultaneously communicate. Since deployment of directive/smart antennas on the customer's terminals is awkward (for technological, cost, robustness, and convenience reasons) it is of interest to deploy advanced antenna solutions only at the access point. When omnidirectional transmissions are used at the mobile stations, the asynchronous nature of the 802.11 MAC handshake structurally limits the possibility to exploit spatial reuse. Significant throughput enhancements can be achieved only at the expense of redesigning (part of) the 802.11 MAC protocol: mainly a form of synchronization is required. This paper addresses this problem and proposes a novel solution, devised to operate in the above scenario. The system operation is based on the joint usage of space division and time division multiple access techniques. A synchronous time-division structure avoids unwanted interference among different antenna coverage regions. Backward compatibility with legacy IEEE 802.11 terminals is also accounted for.