Improved Detection Schemes for Non-coherent Pulse-Position Modulation

Energy-detection (ED) pulse-position modulation (PPM) receivers exhibit poor performance and low rates. Coherent receivers do not have such problems but their complexity is unacceptable. We propose two detection schemes to increase the performance of non-coherent PPM receivers. Unlike the ED-PPM receiver, the first proposed receiver cubes the absolute value of the received signal before demodulation and achieves a considerable performance gain. This gain is obtained because the absolute-value cubing (AVC) operation reduces the effect of low-SNR samples and increases the effect of high-SNR samples on the decision statistic. To further increase energy efficiency and rate of the non-coherent PPM receivers at almost the same complexity, we use the weighted-transmitted reference (WTR) system instead of the ED-based receiver. The WTR system has adequate robustness to weight coefficients and integration interval variations. To generalize the AVC concept to the WTR-PPM receiver, the reference pulse is first passed through a polarity-invariant squaring (PIS) operation and then is correlated with the data pulses. In this paper, the performance of different receivers employing the binary PPM (BPPM) is investigated at data rates of 2.08 and 9.1 Mbps over in-vehicle channels in the presence of noise, inter-block interference, inter-pulse interference, and inter-symbol interference (ISI). Simulations show that the proposed AVC-BPPM receiver outperforms the ED-based one in the absence of ISI and offers the same performance in the presence of strong ISI, the WTR-BPPM system considerably outperforms the ED-BPPM system (especially at high rates), and the proposed PIS-based WTR-BPPM system considerably outperforms the conventional WTR-BPPM system.