Performance Evaluation of the Spread Spectrum Human Body Communication Devices

As a novel vital sign monitor, we have developed wireless ECG monitoring system with human body communication (HBC) technique. However, it was hard to ensure communication reliability because transmission channel is noisy and unstable. In order to solve the problem, we utilize spread spectrum (SS), which is known as robust communication technique even through poor transmission channel. In previous study, we have already developed a communication device using HBC enhanced by SS. In this paper, in order to evaluate the performance of the developed SS-HBC devices, we measured bit error rate (BER) of the communication. On the other hand, we made a simulation model of the signal process in SS-HBC device. These both results showed some differences of transmission performance. We compared these results and discussed about the causes of the performance deterioration with the hardware implementation. As a result, we considered that the two big causes of deterioration were the insufficiency of input dynamics range of the A/D converter and the thermal noise in the amplifier of receiver. However, from the discussion with realistic signal loss and noise characteristics of HBC transmission channel, we concluded that the performance of SS-HBC is enough high finally.