Distributed estimation in wireless sensor networks with semi-orthogonal MAC
Jian Su, Ha H. Nguyen · EURASIP Journal on Wireless Communications and Networking · 2016
This paper is concerned with distributed estimation of a scalar parameter using a wireless sensor network (WSN) that employs a large number of sensors operating under limited bandwidth resource. A semi-orthogonal multiple-access (MA) scheme is proposed to transmit observations from K sensors to a fusion center (FC) via N orthogonal channels, where K ≥ N . The K sensors are divided into N groups, where the sensors in each group simultaneously transmit on one orthogonal channel (and hence the transmitted signals are directly superimposed at the FC as opposed to be coherently combined). Under such a semi-orthogonal multiple access channel (MAC), performance of the linear minimum mean squared error (LMMSE) estimation is analyzed in terms of two indicators: the channel noise suppression capability and the observation noise suppression capability. The analysis is performed for two versions of the proposed semi-orthogonal MA scheme: fixed sensor grouping and adaptive sensor grouping. In particular, the semi-orthogonal MAC with fixed sensor grouping is shown to have the same channel noise suppression capability and two times the observation noise suppression capability when compared to the orthogonal MAC under the same bandwidth resource. For the semi-orthogonal MAC with adaptive sensor grouping, it is determined that N =4 is the most favorable number of orthogonal channels when taking into account both performance and feedback requirement. In particular, the semi-orthogonal MAC with adaptive sensor grouping is shown to perform very close to that of the hybrid MAC, while requiring only log2 N =2 bits of information feedback instead of the exact channel phase for each sensor.