Predicting the outage performance of an equalized-QPSK system over indoor wireless channels

The need to design wide-band wireless indoor systems with low outage probab ilities (on the order of 1% to 2%) implies the need to study system perform ance at the 99th-percentile as a function of several variables, In this let ter we investigate the performance of a 15-MBaud quantenary phase-shift-key ing (QPSK) system combined with decision-feedback equalization. The study a ttempts to identify, and quantify, trends in the system outage performance as a function of the equalizer span, the ensemble averaged rms-delay-spread (<(tau)over bar>(rms)) of the environment, and the ensemble averaged input signal-to-noise ratio (SNR), The letter introduces a novel figure of merit termed 99%-SNR-loss, which when plotted as a function of the normalized-eq ualizer-span shows a trend in the system's outage performance as a function of the desired parameters. These trends suggest a pattern that can help pr edict, to the first order, the performance of such a system without the nee d to resort to time-consuming simulations. The results suggest a 0.79-dB im provement in the 99%-SNR-loss per normalized equalizer span, and a 2-dB imp rovement with a doubling of <(tau)over bar>(rms) with the same normalized e qualizer span.