Effect of transmit antenna pattern on RAKE reception in multipath fading channels

In cellular radio systems, one can take advantage of multi-beam antennas at the cell-site to increase the system capacity and improve the quality of service. The antenna pattern may have an effect on the channel's characteristics in the multipath propagation environments. On the one hand, the use of a sectorized antenna pattern tends to reduce the multipath diversity since a portion of multipath components are suppressed to a certain extent. On the other hand, sometimes the multipath fading can be mitigated for the same reason. This paper investigates the effect of the antenna pattern on the mobile RAKE receiver. We have observed that a higher SNR is required for RAKE reception in a multipath fading environment to guarantee an acceptable bit-error-rate performance and at a given BER, the excess SNR requirements depend on the beamwidth and sidelobe levels of the sectorized antenna, as well as the characteristics of the propagation environment. In a multipath scenario, although the adjacent beams have a relatively high correlation in the channel's impulse response, the RAKE receiver at the mobile can take advantage of the soft-handoff from beam to beam to greatly improve the RAKE reception in fast fading channels. Simulation results are provided in this paper.