Measuring the Closed-Loop Throughput of 2x2 HSDPA over TX Power and TX Antenna Spacing

Mobile network operators demand small base station antennas and high physical layer throughputs. In the downlink, high physical layer throughputs can be achieved by exploiting transmit diversity. Given that the correlation between different propagation paths reduces the achievable throughput, it is commonly conjectured that the greater the transmit antenna spacing, the better the radio link performance. The open question is, how much does the throughput of a communication system actually change over antenna spacing? We answer this question by closed-loop throughput measurements at 2.5GHz for standard compliant 2×2 HSDPA in a realistic, urban, outdoor scenario. The results are presented in terms of physical layer throughput over TX antenna spacing and TX power. We arrive at the somehow surprising conclusion that, for typical TX power values and typical antenna spacings, the throughput remains approximately independent with respect to the antenna spacing.