Interference mitigation in TDD fixed broadband wireless access using channel assignment and antenna arrays

In time division duplex (TDD) fixed broadband wireless access networks, co-channel interference that arises from the correlation of downlink and uplink signals in different sectors may considerably degrade the spectral efficiency. To overcome the complexity and costs of complete frame-TDD boundary synchronization in the network, a combined channel assignment (CA) and antenna array (AA) approach is proposed to mitigate interference. First a rotated-interleaved CA (RICA) scheme is applied, which exploits sector antenna directivity to reject the majority of interferers by receiving them through the antenna side and back lobes. Combined with RICA, an AA system is used in the base station side to further reduce intersector interference during both transmission and reception phases. For the worst-case interference scenario an unsynchronized TDD scheme, the proposed methodology achieves a 51.5% improvement in the average channel capacity while it considerably improves the uplink availability. An advantage of this approach is that it considers only low-complexity AA system configurations, thereby optimizing the corresponding cost