Transmit antenna beamforming for the Advanced Mobile Phone System

Adaptive antenna arrays at the base station in cellular radio can be used in both a receive and transmit mode to improve system performance. While the receive problem is well-studied, methods for transmit beamforming have only recently become available. We propose a "closed loop" transmit beamforming method for the Advanced Mobile Phone System (AMPS) which uses feedback from the base to the mobile to aid the base in adapting its beampatterns. This method does not require modification or exchange of the handsets. Preliminary results show the's method is able to track spatial channel variations if either the angle spread or Doppler spread is low.