A correlation-based method for direction finding of multipath signals in frequency hopping systems

Abstract

Direction finding is of great interest in many applications such as GPS (Global Positioning System), radar, sonar and wireless communication systems. In smart antenna systems, the direction of users is an important factor to increase the capacity, and an antenna array is usually used at the base station to estimate and track the direc-tion of users. Conventional direction finding methods solve the problem of direction-of-arrival (DOA) estimation for narrowband signals, and usually these methods require that the number of array elements be larger than the number of signal sources. In military communications and some short-range wireless communication systems (e.g. Blue-tooth), frequency hopping technique is widely used. In such systems, it is difficult to equip a large size antenna array. Therefore, it is necessary to solve the direction finding problem for the frequency hopping systems by using an antenna array with a lesser number of elements. In this thesis, a new method is proposed to estimate and track the directions of frequency hopping signals under multipath propagation. Only the power of trans-mitted signal is needed to be known in this method. With a two-element array at the receiver, the objective function is established by minimizing the differece between the estimated correlations and the measured correlations of the received signals. The Gauss-Newton algorithm is utilized to find the optimum parameters including direc-tions. Compared with an existing method, the proposed method has more accurate converged results. Additionally, the new method is easy to implement as analog de-vices can be used to measure the correlations of received signals. Future work can be carried out to reduce the computational complexity by de-creasing the number of unknown parameters. Further analysis can be done in the tracking scenario if more parameters vary with respect to time or hops.