Ultrasonic Indexed Modulation and Multiple Access for Intra-Body Networks

Intra-body communication (IBC) plays a significant role in future health care systems. This article proposes a pulse-based ultrasonic index modulation (UsIM) to enable high data rate and low power IBCs. Two grouping-based UsIM strategies, namely ultrasonic grouped-chip indexed modulation (UsCIM) and ultrasonic chip-group indexed modulation (UsGIM), are proposed to implement multiple access for intra-body networks (IBNs). UsCIM uses the chip indices in a group to convey additional information bits for a biosensor node, while UsGIM uses the group indices and each node occupies one chip in a group. Three receivers, including the maximum likelihood (ML), the maximum ratio combination (MRC), and the energy detection (ED) receivers, are then proposed and studied. The theoretical bit-error rate (BER) upper bound for the ML receiver, and theoretical BER expressions for the MRC and ED receivers are derived. The system performance metrics in terms of complexity, throughput and energy efficiency are analyzed. The analytical and simulation results reveal that UsGIM achieves a lower BER than UsCIM under channel fading and multipath effect. Both UsCIM and UsGIM achieve higher throughput and energy efficiency than the existing IBC systems, and both strategies are important for energy-constrained implanted IBNs.