Citation
Abstract
M-ary pulse-position modulation (PPM) has received considerable attention for direct-detection photon communications over unguided channels. The analysis generally assumes that the signaling set is orthogonal. However, the orthogonality of the signaling set will be destroyed by the finite area and bandwidth of optical detectors, resulting in severe intersymbol interference. This article presents the analysis of a trellis-based pulse-position modulation (T-PPM) scheme for photon communications with non-rectangular pulses. The novelty of the scheme includes the use of a set-partitioning methodology to increase the minimum distance using a simple convolutional encoder. The Viterbi algorithm is used at the receiver to separate the signaling set as part of the demodulation process. It has been shown that T-PPM will restore performance losses due to reduced peak intensity during the detection process. Furthermore, for a large range of background radiation levels, the average number of photons per information bit for T-PPM is smaller than that of the regular PPM. Numerical examples show that for a symbol-error rate of 10^-3 when the received pulses extend over 4 PPM slots, the average laser energy per symbol for 256-ary T-PPM could be reduced by as much as 2 dB.
Keywords
Details
- Volume
- 42-135
- Published
- November 15, 1998
- Pages
- 1–16
- File Size
- 590.1 KB