Mai Ohta

Outlier detection methods of low SNR nodes for cooperative spectrum sensing

In this paper, we have studied methods of detecting low signal-to-noise ratio (SNR) nodes by outlier detection in cooperative spectrum sensing. In many studies in the field of cooperative sensing, it is assumed that an average received energy among sensing nodes is equal. However, in practical wireless environment, the performance of cooperative sensing with low SNR nodes located underground, indoor, and so on, is severely degraded. The goal of this research is to detect the low SNR nodes and minimizes the impacts caused by these low SNR nodes to the cooperative sensing performance. We propose an outlier detection algorithm to exclude low SNR nodes from cooperative sensing nodes by using past accumulated energy data. Several outlier detection methods are compared, and a suitable method for the low SNR node detection algorithm is selected. In addition, the required length of estimation period for the outlier detection is revealed. Simulation results show that the performance of cooperative sensing is improved even if the low SNR nodes exist in the cooperative nodes.

Iterative cooperative sensing on shared primary spectrum for improving sensing ability

In this paper, we propose a novel cooperative sensing method by iteratively improving the sensing ability. The proposed method can increase the number of cooperative sensing nodes. Moreover the harmful interference can be avoided, even if the sensing information of each sensing node is transmitted at the same spectrum of the primary system. In general, the cooperative sensing ability depends on the number of the cooperative nodes providing sensing information. If these pieces of information are exchanged in the same spectrum of the primary system, the number of cooperative nodes is limited by the transmit power of each node to avoid giving interference toward the primary system. In this paper, we propose an algorithm to improve the cooperative sensing ability by iteratively deciding the transmit power of sensing node and cooperation area.

A cooperative sensing area expansion using orthogonal frequency based information collection method

This paper evaluates the co-existence of a sensing information collection method, which collects the cooperative sensing information by using frequency based orthogonal narrow band signal overlaying to a primary system. In general, the cooperative sensing information is collected to a master node by using a different common channel with the primary system. However, the common channel decreases the channel efficiency and the secondary nodes have to prepare additional devices for sensing information collection. In this paper, we focus on the orthogonal frequency based sensing information collection method which can share the channel with primary system with small giving interference because the bandwidth of the signal is narrower than the primary system. We evaluate the performance of co-existence of the orthogonal frequency based sensing information collection method and a information collection method using whole band of the primary system without giving large interference to the primary system. From the computer simulation, we can confirm that the narrow band orthogonal frequency based sensing information collection method can expand the area of cooperative sensing with keeping the giving interference level to the certain level.