Performance Improvement in Channel-Estimated Implant Communication by Spatial Transmit Diversity and Signal Pre-emphasis Technique

Human body communication (HBC) technology in the 10–60 MHz band offers ample possibilities for high-speed and deep-implanted communications with data rates over 10 Mb/s. However, signals transmitted within the human body undergo power decay and waveform distortion, while different orientations of the implant antenna can further decrease communication performance. This study proposes a spatial transmit diversity combined with a signal pre-emphasis technique to improve bit error rate (BER) performance. First, a two-branch spatial transmit diversity is established by an anatomical human body model and MHz-band small helix/spiral antennas. Then, a signal pre-processing method is applied to the on-body transmitter to counteract the channel fading and distortion. It extracts the channel response through channel estimation and adaptively alters the transmitted signal waveform, consequently deriving received signals optimized for demodulation. Finally, the effect of spatial diversity and signal pre-emphasis is evaluated by calculating the BER performance in a maximal ratio combining (MRC) simulation. The results indicate that applying pre-emphasis significantly improves the BER performance while implementing spatial transmit diversity can further enhance the signal-to-noise ratio (SNR) by 2–5 dB when the BER equals 10 \(^{-3}\) at 20 Mb/s.