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 multipleinput, 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 dualpattern 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

MIMO and beamforming techniques for reliable off-body communication using textile antennas

Wireless communication systems with textile antennas can be entirely integrated into clothing or garment and do not hinder the user’s movements. Great interest in such an off-body communication system exists in the field of rescue operations, such as firefighting, where the automated communication of vital data between rescue workers or to a base station improves the coordination of the operation and the safety of the rescue workers. To set up a reliable wireless off-body communication link, a number of specific challenges need to be overcome. Persons equipped with wearable antennas constantly change position, orientation, walking pace and body posture. This results in unpredictably variable fading and shadowing on the received signals, producing bit errors, even in case of a high average received signal-to-noise ratio. Fading and shadowing hence dramatically limit the reliability of a communication system with single antennas at both link ends. Using multiple textile antennas, the performance degradation is drastically limited, by means of MIMO and/or beamforming techniques, which mitigate the signal variation and/or produce a higher average signal-to-noise ratio at the receiver, respectively. The research documented in this PhD thesis includes multiple measurement campaigns and their analysis for a diverse number of off-body communication configurations, using MIMO and beamforming techniques with textile antennas. Off-body MIMO techniques are shown to result in a significant improvement of the reliability of the communication, an improvement which further increases when more antennas are used. Channel variation typically of the off-body scenario is tracked with a computationally low-cost system, using adaptive digital low-pass filtering on decision-oriented channel estimation information. Off-body static beamforming techniques are shown to often outperform transmit diversity systems, producing a lower bit error rate at the receiver, provided that receiver diversity is employed to compensate for the channel variation. Finally, a new theoretical model specifically for the off-body MIMO communication channel is presented, allowing an accurate reproduction of bit error rate and channel capacity characteristics as well as the generation of measurement-like random off-body MIMO channel realizations for simulation purposes

Recent Advances in Wireless Communications and Networks

This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters