Low-Complexity Antenna Diversity Receivers for Mobile Wireless Applications

Abstract

This paper describes low-complexity diversity receiver techniques suitable for handsets and other wireless mobile applications. The techniques are illustrated using two branches of diversity feeding a parameter-combining RF circuit at the front-end, followed by a single digital receiver chain. A baseband processing algorithm is used to adjust the front-end combining parameters, allowing the receiver to adaptively choose among three different diversity techniques. The method as presented is primarily targeted for indoor environments where handset movement is slow and delay spread is small. We present algorithms for efficient co-phasing and equal-gain combining as well as a novel cochannel interference-reduction algorithm. These are implemented in a system simulation at 900 MHz which conforms to the PACS standard. Link performance for selection diversity (SD), equal-gain combining (EGC), and interference-reduction combining (IRC) is presented. The algorithm's performance is compared with optimal combining parameters, and its performance as a function of Doppler frequency is enhanced. The results show that EGC and IRC yield a signal-to-noise improvement of 1 dB and a signal-to-interference improvement of 4 to 5.5 dB respectively, compared with SD. The receiver also lowers the irreducible word error rate due to multipath delay spread for Doppler shifts of 6 Hz and below. Finally, algorithm behavior is characterized and discussed.