Antenna selection and deployment strategies for indoor wireless communication systems

Effective antenna selection and deployment strategies are important for reducing co-channel interference in indoor wireless systems. Low-cost solutions are essential, and strategies that utilise simple (passive) antennas (such as directional patches) are advantageous from this perspective. However, performance is always an issue and the improvements achievable through clever antenna deployment (both placement and orientation) need to be quantified. An experimental investigation of indoor propagation comparing the performance of directional and omni-directional antennas is reported. In the case study of a voice-based indoor communication system employing DS-CDMA radio access technique with BPSK modulation, the outage probability for base stations fitted with directional antennas was observed to change in the -54% to +66% range relative to the omni-directional case. The effective change in the distribution of carrier-to-interference ratios by the use of directional antennas is well established in outdoor micro cellular deployment scenarios; however, the magnitude of the influence is quantified for an indoor environment in this case study. It is also shown that obstacles in the environment can amplify the effectiveness of the antenna deployment by acting as physical cell boundaries that restrict interference. External interference has been shown to cause a significant degradation to the performance of an indoor system when the carrier-to-external-interference ratio. This performance degradation can be minimised by appropriate deployment of directional antennas at the base stations, although the optimum antenna orientations depends on the strength of external interference.