On the Energy Utilization of WSN Communications Using Space-Time Block Coding Over BPSK and M-QAM Modulations

摘要

Energy is a scarce and most vital resource in a wireless sensor network (WSN). Since space-time block coding requires less transmission energy than SISO technique for the same bit error rate (BER), therefore, it is one of the most practical diversity technique for WSN studies. In this work, we have investigated the energy utilization of a simple multiple-input single-output system using STBC for a WSN scenario constituting a number of clusters communication under Rayleigh channels with popular modulation techniques like BPSK and M-QAM. By deriving the rationale expressions for energy utilized per bit metric (E_(bit)) in terms of various quantities such as-order of transmit diversity, data rate, BER and the distance between the cluster and the base station (BS) (cluster-BS), we have investigated the suitability of transmit diversity order for varying magnitudes of distances. It has been observed that for communication involving, medium and long cluster to BS distances, the diversity order constituting two transmit antennae results in better energy efficiency and enhances reliability, but, for smaller cluster-BS distances, the contribution is not significant for the case under consideration. Further, we have explored how the energy utilization levels are affected by transmission rates and acceptable error levels. In addition, we optimized the modulation constellation order and recommended best-fit modulation approaches for the varying ranges of cluster-BS distances. Simulation results demonstrate that with increasing cluster-BS distances, the optimized constellation order of the M-QAM modulated communications decreases. BPSK based communication are found to be better in performance for long cluster-BS distances in comparison to those in M-QAM. This work may help the network designers to tailor optimal permutation and combination of various physical layer parameters to facilitate energy-efficient WSN communications.