Optimum Combining in Digital Mobile Radio with Cochannel Interference

TLDR

Thus, with cochannel interference, space diversity is used not only to combat Rayleigh fading of the desired signal but also to reduce the power of interfering signals at the receiver. This paper studies optimum signal combining for space diversity reception in cellular mobile radio systems. The authors analyze optimum combining by weighting and combining antenna signals to maximize output SINR, using analytical and simulation methods under Rayleigh fading, and describe implementation with LMS adaptive arrays. Results demonstrate that optimum combining outperforms maximal ratio combining, boosts output SINR by several decibels, and enables fewer base‑station antennas or higher channel capacity via greater frequency reuse.

Abstract

This paper studies optimum signal combining for space diversity reception in cellular mobile radio systems. With optimum combining, the signals received by the antennas are weighted and combined to maximize the output signal-to-interference-plus-noise ratio. Thus, with cochannel interference, space diversity is used not only to combat Rayleigh fading of the desired signal (as with maximal ratio combining) but also to reduce the power of interfering signals at the receiver. We use analytical and computer simulation techniques to determine the performance of optimum combining when the received desired and interfering signals are subject to Rayleigh fading. Results show that optimum combining is significantly better than maximal ratio combining even when the number of interferers is greater than the number of antennas. Results for typical cellular mobile radio systems show that optimum combining increases the output signalto-interference ratio at the receiver by several decibels. Thus, systems can require fewer base station antennas and/or achieve increased channel capacity through greater frequency reuse. We also describe techniques for implementing optimum combining with least mean square (LMS) adaptive arrays.