Cross-layer energy efficiency of orthogonal modulations in TDMA-based wireless sensor networks

Energy conservation is a critical problem in recently emerging wireless sensor networks (WSNs). Orthogonal modulations appropriate for the energy-limited WSN setup have been investigated at link layer, but their energy efficiency is not very clear in cross-layer design. In this paper, based on a physics-link-MAC cross-layer design in WSNs, which integrates battery discharge models, node circuit and transmit power consumption, orthogonal modulations and a variable-length TDMA scheme, we investigate the energy efficiency of two M-ary orthogonal modulation schemes, namely pulse position modulation (PPM) and frequency shift keying (FSK). And to minimize the total energy consumption of WSN, we further have an optimization for the cross layer design. The numerical results show that the design with PPM has a noticeable energy efficiency advantage over that with FSK in densely-deployed WSN, and the optimization for cross-layer design can gain more energy conversation with both PPM and FSK.