Biocle II
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Overview
Wireless body-area network (WBAN) is an emerging area that combines health care and comsumer electronics applications and its standardization is still in progress. The WPAN standards such as IEEE 802.15.4 and 4a do not meet the WBAN requirements such as energy efficiency on the body, scalable QoS, and inter-networks isolation. Due to energy absorption in the human tissue, propagation loss of the WPAN channel is over 50dB, and the channel characteristics strictly depend on the locations in the body. The long-distance coverage of the WPAN makes it difficult to isolate the channel from the adjacent networks. On the other hand, the body-channel communication(BCC), which uses the human body as a communication channel, can achieve low path-loss without body shadowing effect. BCC utilizes low-frequency bands (under 200MHz) without a large antenna and without following the FCC radiation regulation because of its very short communication distance, <2m. As a result, the recent BCC optimized its data rate and power consumption for WBAN applications. However, its coverage is still less than 1m in actual on-body measurements because of its signal instablilty. The signal instability is due to interferences coupled to the receiver through human body antenna effect. The 50 to 110MHz band is for FM radio and TV broadcasting, and the interference is even -30dBm near the radio broadcasting tower, degrading the SIR of BCC to -15dBm. For the stable BCC, robustness to SIR is more important than to SNR. In this Biocle II project, a body-channel transceiver(BCT) that cancels over -20dBm in-band interference is designed, fabricated and tested. It also meets the QoS, requirements for multimedia and health care WBAN applications. BCT divides the 90MHz band into 4 sub-bands and utilizes adaptive frequency hopping (AFH). Instead of hopping sub-bands randomly, the proposed AFH controller performs channel classification first. Then, the sub-bands that show a pre-defined packet-success-ration are selected as the communication channel.
