Cochannel Interference in Cellular Fixed Broadband Access Systems with Directional Antennas

The Cellular Fixed Broadband Access System for LMCS (Local Multipoint Communication Services) is aiming to provide broadband services to fixed subscribers through wireless access. A representative LMCS scenario involves a cellular system design with the entire allocated bandwidth being used in each cell and with a highly directional antenna employed at the subscriber. The LMCS system designs rely on assumed information regarding radio propagation phenomena in the anticipated coverage areas. The research reported here, therefore, has the objective of verifying such information by theoretical modeling and simulation. Simulation and analysis have been used to study the effects of a number of factors on the system performance and interference characteristics of such a LMCS system. The investigated factors include beamwidth and gain ratio of directional antennas, sectorization of hub antennas, propagation exponent, lognormal shadowing, site diversity and transmitter power control. Both models of LOS (line of sight) and NLOS (non-line of sight) have been investigated in this work. The simulation results demonstrate that highly directional antennas at the subscribers can dramatically improve the system performance for both uplink and downlink. The system design with frequency reuse of one is examined, and it is confirmed that an outage of 0.9% for a NLOS system could be achieved by using narrow beam antennas of 3 degrees with site diversity and power control techniques employed. Under the condition of LOS available for the desired links, the outage can be expected to be as low as 0.3%.