Abstract-In this paper, a numerical method for improving the performance of the beamforming algorithm and the MUSIC algorithm for TOA (Time-of-arrival) estimation is presented. It has been shown that the conventional beamforming algorithm and the MUSIC algorithm can be used for time delay estimation.Using the beamforming algorithm and the MUSIC algorithm for TOA estimation, the initial estimate for the TOA is obtained. To improve the accuracy of the TOA estimation, we apply the Newton iteration to the initial estimate. The initial estimates obtained from the beamforming algorithm and the MUSIC algorithm are updated to obtain the final estimates which are more accurate than the initial estimates in terms of the RMSE (Root Mean Square Error). To find the TOA which maximizes the beamforming spectrum or the MUSIC spectrum, we find

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The rapid growth of mobile communication and the proliferation of smart phones have drawn significant attention to location-based services (LBS). The Wi-Fi positioning system (WPS) is a newly attractive method as a widely applicable positioning technique in LBS. In WPS, the received signal strength indication (RSSI) data of all Wi-Fi access points (APs) are measured, and stored in a huge database, as a form of radio fingerprint map. Because of the millions of APs in urban areas, radio fingerprint data are seriously contaminated. Therefore, we present a coherent filtering method for radio fingerprint data. All fingerprints used in the developed test bed are harvested from actual radio fingerprint measurements taken throughout Seoul, Korea. This demonstrates the practical usefulness of the proposed methodology.

A number of nodes that are interested in the same content can be grouped into a cluster and the cluster head can be used to relay the content received from the base station (BS) to the cluster members using device-to-multidevice (D2MD) communication. However, the data rate of such multicast communication depends on the worst channel among the cluster members and the cluster head. The rate can be enhanced by increasing the transmit power; however, this approach may deteriorate energy efficiency (EE) performance of the system. In this paper, we propose transmitting the content from more than one cluster head simultaneously. A novel algorithm is proposed that selects the cluster heads to improve the data rate of the multicast communication while keeping the total transmit power from the cluster heads constant. The cluster members receive power from all the cluster heads within the cluster and hence the received signal to noise power ratio improves. The improved received power makes communication at higher data rates possible, thus reducing the total transmission time. Hence, the energy requirement per bit will reduce. Simulation results show that 19% of reduction in energy per bit is possible by using more than one cluster head within the cluster.