Optimum mapping in an optical multiple pulse position modulation link using a maximum likelihood sequence detection scheme

The performance analysis of any multiple pulse position modulation (PPM) system is extremely time consuming because of the effects of different detection errors on the multiple PPM alphabet. In a small multiple PPM system such as (₂ ¹²), there are 64 codewords and each one can have ten possible false alarms, two possible erasures and four possible wrong-slot errors. The situation is worse if higher-order codes are considered. A novel algorithm, which reduces the time taken to predict the sensitivity of a multiple PPM system from almost 2 h of analysis to under a second, is presented. Results obtained using this method agree with those obtained using a full mathematical model. The authors also present a methodology that obtains a close to optimum mapping for any multiple PPM system. Detailed results show the effectiveness of this mapping routine.