Threshold Discrimination and Blanking for Large Near–Far Power Ratios in UWB Networks

Abstract

A simple chip-discrimination technique is presented for use with ultra-wideband (UWB) impulse radio (IR) that improves performance for large near-far interference power ratios. A typical spread-spectrum IR that employs a matched-filter sum for bit decisions is susceptible to small numbers of large power pulses that can dominate the bit decision-threshold statistics. This letter describes a technique for chip discrimination prior to the spreading summation, that can greatly reduce the effects of large near-far power ratios among interferers. The technique exploits the very narrow pulsewidth and resulting low-duty-cycle characteristic only achievable with ultra-wide bandwidth. A statistical model is developed that predicts bit-error performance for binary offset pulse position modulation as a function of near-far density and power for varying discrimination thresholds. An analytic solution for perfect chip blanking is developed, and is in good agreement with chip discrimination for large near-far power ratios. We find that even a small number of very near interferers can greatly reduce the performance of a system without blanking or discrimination. Results show substantial improvement using this method for near interferers with near-far power ratios greater than 20 dB.