Distance estimation using multifrequency phases measurement is a common practice in many areas of engineering. This method brings in the issue of phase ambiguity. Some Chinese remainder theorem (CRT) based phase unwrapping algorithms have been suggested to solve the problem, however, these algorithms either have high complexity or lack precision. In this paper, we propose an efficient algorithm to reconstruct the unknown distance from the contaminated wrapped phases. The proposed method can be separated into two stages. The first stage is to obtain the optimal estimate of the common remainder which is significant to the estimation. In the second stage, the indefinite distance is estimated by using the extended CRT. Simulations test the validity of the proposed algorithm.

This paper investigates the secret key generation from multiple cooperative sources. We assume that the public communication between the legitimate users has unlimited capacity. In this case, the secret key rate is the upper bound of a practical system with limited public communication. The random signals from the multiple helpers can help to create correlated Gaussian sources for the legitimate users to generate secret key, and only local channel state information (CSI) is needed by the helpers to cooperate with others. The power allocation between the helpers is studied with a total transmit power constraint, which results in a non-convex optimization problem. A high efficiency sub-optimal solution is proposed. And even when the legitimate users have no idea about the eavesdropper, the scheme still can help the system to achieve fairly good performance.

A distributed localization method has been proposed recently based on a novel concept of angle of departure (AOD) to estimate the angle information and achieve localization. Based on the AOD estimation, we introduce a synthetic uniform circular array (SUCA) synthesized by a rotary antenna to get the distributed localization of the sensors in multi-path environments. The rotated operation of antenna can create the SUCA with a larger aperture to deal with AOD of multi-path components (MPCs) and relaxes the condition that array aperture should be greater than the number of MPCs. This method only relies on radio transceivers without requiring extra measuring equipments, and the sensor nodes conduct localization in a completely distributed manner instead of centralized processing.

This letter investigates a novel two-stage cooperative scheme to secure the communication system with one source, one destination and multiple helpers. Herein, the source mixes the confidential messages with the interferences transmitted by the helpers and destination. Since the helpers and destination serve to suppress interferences, the destination can acquire an interference-free signal, however the eavesdropper is still confused. This scheme can achieve positive secrecy rate even when the eavesdropper's channel is much better than the legitimate link, and only requires local channel state information (CSI) and a few parameters of the main link. An efficient sub-optimal algorithm for the majorization of system parameters is proposed to avoid global search and the practical case without eavesdropper's CSI is also considered. Simulation results demonstrate the effectiveness of the proposed scheme and algorithm.