Performance comparisons of adaptive antenna arrays with fixed multibeam systems for IS-136 systems

We present uplink simulation results comparing four-element adaptive arrays with a six-sector antenna system and a fixed multibeam (four 30° beam with two-branch diversity per beam in each 1200 sector) antenna system using an IS-136 TDMA modulation format and slot structure. The results consist of the capacity improvement (i.e., frequency reuse reduction) of these antenna systems over the baseline antenna system using the, simulated bit error rate (BER) as the basis of comparison. The baseline antenna system was assumed to be a typical three-sector antenna system employing two-branch spatial diversity in each sector. Simulations were run for two different cell sizes, two Doppler spread values, and multiple reuse scenarios. The results show that substantial interference suppression gains can be obtained in an interference-dominated system using adaptive antennas. This improvement allows a reduction in the frequency reuse pattern from seven to three. In contrast a simple six-sector system is found to be limited to a frequency reuse of four. The fixed multibeam antenna can achieve similar reuse patterns but with poorer performance and requires twice as many antenna elements. It is noted that the simulation results presented here are for the uplink only, similar downlink gains must be supported in order to achieve the overall capacity improvement