Field experiments on optimum number of antennas for adaptive antenna array-beam forming transmitter in W-CDMA forward link

The paper experimentally clarifies the optimum number of antennas, J, in an adaptive antenna array-beam forming (AAA-BF) transmitter from the viewpoint of the achievable minimum transmission power of the base transceiver station (BTS) for the target user equipment (UE), thereby bringing about the maximum link capacity in the W-CDMA forward link. Field experiments are conducted employing high-elevation BTS array antennas associated with a 120-degree sectored-cell configuration assuming approximately 500-1000 m between the BTS and UE, considering key techniques such as pilot channel-assisted coherent RAKE combining, fast transmission power control (TPC) based on the received signal-power-to-interference-power ratio (SIR) measurement, and convolutional channel coding. Field experimental results elucidate that the angle spread among paths affects the optimum J value from the tradeoff between the improvements by increasing the antenna gain and degradation due to the received signal power loss. Consequently, we clarify that the optimum number of array antennas from the point of view of the multipath interference (MPI) (including own and other physical channels) suppression effect is approximately 10-12 in an actual measured angle spread of 2-5 degrees for the high-elevation array antenna configuration.