Abstract
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 log2N=2 bits of information feedback instead of the exact channel phase for each sensor.
Highlights
Wireless sensor networks (WSNs) have found applications in diverse areas such as environmental data gathering [1], industrial monitoring [2] and monitoring of smart electricity grids [3], and mobile robots and autonomous vehicles [4]
Su and Nguyen EURASIP Journal on Wireless Communications and Networking (2016) 2016:214 this paper focuses on distributed estimation in WSNs based on analog transmission
6 Conclusions For WSNs consisting of a sufficient large number of sensors but operating under limited bandwidth resource, a novel semi-orthogonal multiple access scheme was proposed for transmission from K sensors to the fusion center (FC) over N orthogonal channels, where K ≥ N
Summary
Wireless sensor networks (WSNs) have found applications in diverse areas such as environmental data gathering [1], industrial monitoring [2] and monitoring of smart electricity grids [3], and mobile robots and autonomous vehicles [4]. While the semi-orthogonal MA scheme is designed based on the similar idea of sensor grouping in [17], the key difference is that, in the proposed MA scheme, the sensors in one group transmit simultaneously without the expensive phase synchronization operation This means that the signals from sensors within one group are directly superimposed instead of coherently combined as in the hybrid MAC. The system model of distributed estimation considered in the present paper is similar to the simple Gaussian sensor network in [10], albeit the novel semiorthogonal MAC is used instead of the coherent MAC It is shown in ([21] Chapter 5) that the semiorthogonal MAC with adaptive sensor grouping achieves the optimal scaling law.
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