OPTIMUM DIVERSITY COMBINING AND EQUALIZATION IN DIGITAL DATA-TRANSMISSION WITH APPLICATIONS TO CELLULAR MOBILE RADIO .2. NUMERICAL RESULTS

In Part I we presented a comprehensive theory for Nth-order space diversity reception combined with various equalization techniques in digital data transmission over frequency-selective fading channels. The theory was applied to optimize system parameters and to predict performance for QAM data transmission operating over the following model for the mobile radio channel: The diversity paths are statistically independent and each is characterized by the sum of two delayed and independently Rayleigh-fading beams. For this model we provided estimates of average attainable error rates and outage probabilities as functions of system parameters. Here we study the probability distributions of the data rates that can be supported by the optimum receiver structures as well as the distribution of the Shannon capacity. The dependence among the important system parameters are exhibited graphically for several illustrative examples including QPSK. At low outage probabilities, < 10(-2), and at typical operating SNR's, 15-25 dB, the Shannon capacity with optimal dual diversity reception is about 2 b/s/Hz higher than without diversity. The optimized uncoded systems are typically 1-2 b/s/Hz lower than the Shannon limit but dual diversity, even in the uncoded systems, provides a gain of about 2 b/s/Hz in data rate efficiency. Alternatively, at typical operations of QPSK with 1.5 b/s/Hz, two orders-of-magnitude in outage probability can be gained by diversity reception. When we compare the uncoded average probability of error for the optimized MSE systems, we find at most an order-of-magnitude difference among the different equalizers investigated except for the zero-forcing equalizer whose performance is drastically inferior to the others. Again, dual diversity can provide two-orders-of-magnitude improvement in the average error rate or in outage probability for the uncoded optimized systems.