Indoor Off-Body Wireless MIMO Communication With Dual Polarized Textile Antennas

Off-body data communication for firefighters and other rescue workers is an important area of development. The communication with a moving person in an indoor environment can be very unreliable due to channel fading. In addition, when considering off-body communication by means of textile antennas, propagation is affected by shadowing caused by the human body. By transmitting and receiving signals using multiple-input, multiple-output antennas (MIMO communication) a large improvement in reliability of the wireless link is obtained. In this contribution, the performance of wireless data communication using quadrature phase shift keyed (QPSK) modulated data in the 2.45 GHz ISM-band is evaluated in the case of firefighters walking indoor and communicating by means of a compact dual-pattern dual-polarization diversity textile patch antenna system integrated into their clothing. Simultaneous transmit diversity (at the firefighter) and receive diversity (at the base station) up to fourth order are achieved by means of orthogonal space-time codes, providing a maximum total diversity order of 16. The measurements confirm that MIMO techniques drastically improve the reliability of the wireless link. Measurements are compared for three test persons of significantly different sizes. For equal transmitted power levels, the bit error rates for the 2 × 2 and 4 × 4 links are much lower than for a system without diversity, with the 4 × 4 system clearly providing the best performance.