New phase adjustment and channel estimation methods for RF combining applicable in mobile terminals

Abstract

Antenna diversity is able to alleviate multipath fading in a wireless communications system. Traditionally, multiple down-conversion chains have to be used in order to implement antenna receive diversity, making it difficult for implementation in mobile terminals, where the physical size, power consumption and implementation cost are three major limiting factors. RF combining, which combines the received signals at RF level, is well applicable for mobile terminals as it requires only one down-conversion chain. This paper investigates RF combining techniques for improving downlink performance by applying a two-element array at the mobile terminal. A new phase adjustment algorithm is suggested in order to combine the RF signals while minimizing noise effect. Also, a new channel estimation method based on the suggested phase adjustment algorithm is proposed, and further applied to systems with transmit diversity. Computer simulations have shown that with the new channel estimation method together with the new phase adjustment algorithm, the RF combining techniques can improve the BER performance considerably, especially for fast fading environment.