Adaptive antennas in IS-136 systems

Performance of an IS-136 cellular system is evaluated to determine the capacity enhancement and the communication quality improvement that can be achieved with base station multibeam adaptive antennas. Using adaptive antennas to receive and transmit in narrow beams, improves the C/I in both uplink and downlink, since interference is rejected in the uplink and less downlink interference is spread. System performance is evaluated by means of system level simulations focused on the downlink C/I distribution. Beamforming on a carrier basis and on a time slot basis are studied corresponding to IS-136 Rev. A and potential Rev. B mobile stations, respectively. The main conclusion is that introducing low complexity adaptive antenna systems can give gains sufficient for a 4/12 re-use within the existing IS-136 specification. In comparison, a 7/21 frequency re-use plan is required for acceptable quality with conventional sector antenna technology. If the beamforming gain is utilized to maximize the amount of served traffic, system capacity can be enhanced by more than 100% with preserved or increased communication quality