Optimal versus suboptimal combining with imperfect channel knowledge

Optimal combining and suboptimal combining-techniques are investigated for multipath Rayleigh fading channel with additive white Gaussian noise where only imperfect channel knowledge is available at the receiver. The exact bit error performance using optimal combining is derived, whereas the upper bound and lower bound of bit error rate of suboptimal combining are obtained via similar derivation. Numerical results presented for certain channels and estimation models show that when SNR increases, suboptimal combining methods can be used instead of optimal ones in order to reduce the complexity without much performance degradation.