Energy-efficient off-body data transmission by means of antenna diversity and tracking of the time-variant wireless channel state

Textile antennas integrated into the garment of rescue workers offer a convenient way for implementing an off-body communication system. When operating indoors, the link reliability is compromised by fading and shadowing. For a SISO system, the transmitted power needs to be very large to allow an acceptable bit error rate at the receiver. Employing front and back dual-polarized textile antennas creates fourth order diversity at the body. Equipping also the base-station with such a pair of antennas results in diversity at both sides, in this case realizing a 4 × 4 MIMO system. The MIMO techniques counter the effects of fading and shadowing and allow the system to achieve low bit error rates at the receiver with a minimum of transmitted power. Long data frames are used with a minimum pilot symbol overhead, also reducing the transmitted power per data bit. Although the propagation channel is time-varying during the transmitted frame, the channel variation is tracked at the receiver with a minimal processing power.