Abstract-To address the coordination issue of sensors communicating with a fusion center, we propose a spreading sequence based non-coherent detection scheme for sensor networks to reduce the coordination between sensors to the largest extent. In this scheme, sensors employ independent spreading sequences to transmit their measurements. Non-coherent detection is conducted at the fusion center where only statistics regarding channel gains and sensor measurement uncertainties are needed. To evaluate the detector's performance, we first derive the large deviation exponents of detection error probabilities and then compare them with the approaches assuming orthogonal channel allocation (e.g.TDMA/FDMA). Numerical and simulation results demonstrate the dependence of large deviation exponent on the asymptotic number of sensors per chip (defined as c), as well as the better performance of our proposed scheme than the one using non-coherent detection with orthogonal link, for some c.
Keywords: Spreading Sequence, Large Deviation Exponents and Non-coherent Detection.I.
INTRODUCTIONIn this paper, we are mainly concerned with how to effectively send data from a set of sensor nodes to a fusion center via a one-hop network. In particular, we are interested in how to reduce the coordination among sensor nodes to the minimum and how fusion performance in terms of binary detection error probability varies with respect to the size of sensornet as a consequence of such reduced coordinations.In a one-hop sensor network for data fusion, the conventional wisdom was the measured data from each sensor is immediately available at the fusion center. This holds when sensors are traditional radars and a wired link exists between each front end radar and the fusion center. One step further to a more realistic scenario for sensornet with large amount of sensors is to allow orthogonal channel allocation such that signals sent by each sensor go through independent and orthogonal wireless links (e.g. TDMA, FDMA), where distortion and interference are possibly introduced, to the fusion center[1], [2]. However, we can foresee that coordination and resulting overheads are overwhelming in order to achieve exact orthogonalization in large scale sensor networks.Recently, A. Anandkumar and L. Tong based transmission schemes, where each element of possible quantized outputs is assigned an orthogonal spreading code. At the fusion center, what matters to detector's performance is the superposed signals corresponding to each orthogonal sequence. However, they have shown that when channel experiences zero mean fading, the detection error no longer scales exponentially with respect to the number of sensors.When we use sensor net to facilitate a binary decision at a fusion center, the ultimate objective is to distinguish between two hypothesis corresponding to the presence or absence of a target. Therefore, there is no necessity to faithfully reconstruct the measurements taken at each sensor node as long as the fusion/detection performance satisfies our need...