Performance of Adaptive Antennas in FH-GSM Using Conventional Beamforming

This paper presents the performance of adaptive antennas in a 1/3 reuse frequency hopping GSM network using conventional beamforming. It mainly focuses on C/I improvement for the purpose of capacity enhancement. The performance evaluation has been conducted by means of network computer simulations, where measured time-space radio channel impulse responses are applied for the desired user in the network. Measurements with an M = 8 element uniform linear array were conducted in the cities of Aarhus, Denmark, and Stockholm, Sweden. The simulated C/I improvement shows an almost 10* log(10)(M) behavior for low azimuth spread values. For large values of azimuth spread (relative to the antenna beamwidth), the performance gain is reduced significantly. For an azimuth spread of 10 degrees-12 degrees, which has been measured in urban macro-cellular environments, the C/I gain for M = 8 is reduced to approx. 5.5-7.5 dB (which should be compared to the theoretical value of 9 dB for a point source). The designed DoA algorithm is very robust to co-channel interference and only a small degradation in performance is observed for single element C/I down to approx. -8 dB. We conclude that the designed beamforming implementation facilitates a potential capacity gain of x3 in a 1/3 reuse FH-GSM network for an array size of M = 4-6.