To improve information throughput conventional single-pulse M -ary pulse-position-modulation (PPM) scheme, multi-pulse PPM has been proposed on the optical intensity-modulated and direct-detection channel. Although the multi-pulse M -ary PPM scheme significantly enhances throughput performance, nevertheless, the symbol error rate (SER) increases due to the loss of orthogonality between different pairs of symbols. In this study, the authors first derive the SER performance of general L pulses M -ary PPM scheme under Poisson channel statistic. Moreover, as the green radio is essential in future network, energy efficiency becomes the major concern. Hence, they evaluate L pulses M -ary PPM scheme by the number of reliable bits transmitted per joule of energy consumed. They analyse the trade-off between throughput and power consumption.