A novel interference-resolving algorithm to support asymmetric services in TDD-CDMA systems with directional antennas

Abstract

This paper presents a new cross-slot interference-resolving algorithm for supporting unbalance traffic between downlink and uplink in TDD-CDMA systems. To avoid cross-slot interference between downlink and uplink, traditional algorithms typically require a global control on the transmission direction in each time slot among all cells. Obviously, this requirement significantly limits one of the key advantages in the TDD system -- enabling different rate asymmetry. We observe that the tri-sector cellular architecture possesses additional orthogonality inherently due to the directivity of directional antenna, which can provide an additional degree of freedom in allocating radio resource (i.e., time slots). Thus we propose a new distributed slot allocation algorithm based on the tri-sector cellular architecture. The advantage of the proposed algorithm is to enable a TDD-CDMA system to provide asymmetric services with different rates of asymmetry in all cells, thereby having more flexibility in handling uniform traffic patterns.