Diversity selection combining and non-linear equalization in DQPSK indoor radio systems

In this work we evaluate the performance of an indoor radio system with π/4-DQPSK modulation in frequency selective fading channels. For a theoretical analysis of the system, a simplified two-ray channel model has been adopted; each ray has a log-normal distribution. Moreover, in order to enhance system performance, impaired by fading and intersymbol interference, diversity reception in combination with a novel non-linear equalizer has been proposed. For typical in-building environments it is seen that space diversity may improve performance up to 5 dB at BER 10-3. However, for strong multipath components non-linear intersymbol interference is the predominant disturbance and performance can only be enhanced by the non-linear equalizer. These considerations can be easily extended to more complex channel models, although system performance can only be evaluated by computer simulations