Study On Wireless Location Positioning For OFDM-based Communication Networks

Modern mobile communication systems aim to provide high-speed, broadband and personal services. Since the orthogonal frequency division multiplexing (OFDM) technique has the advantages of bandwidth efficiency and robustness for the frequency selective fading, it has been the first choice of the key technologies for the latest broadband wireless communication networks in which an effective means for the personal services is based on the location information of mobile subscribers, which can be applied to emergency calling, intelligent transportation system and network planning and resource management etc., Therefore, with the development of the future broadband wireless communication techniques, OFDM-based ranging and wireless positioning technologies attract more and more attentions of the academic and industrial circles.This thesis studies the wireless location positioning for OFDM-based wireless communication networks and the application of the location information back to the communication systems, which completes the following tasks:(1) Propose a multicarrier transmission based wireless positioning protocol. For the design of the protocol, this thesis considers the features of the general localization methods, such as time-based, received signal strength-based and angle of arrival-based positioning schemes, and analyzes the ranging performance of multicarrier transmission for timing-based approaches. Consequently, the proposed positioning protocol takes the advantages of the orthogonal property between subcarriers of multicarrier transmission and utilize the time-based location methods, which locates the mobile station via the MS managed solution, the network aided solution and the network managed solution. This localization protocal can provide not only the navigation applications but also the tracking ones. Finally, the performance of the proposed protocol is analyzed in terms of efficiency, bandwidth utilization and signal processing load. Since the protocol makes the best use of the inherent properties of a multicarrier transmission, it can provide more location accuracy, high efficiency and the flexibility of selecting bandwidth.(2) Analyze the positioning accuracy of the location methods for the multicarrier transmission based wireless localization protocol theoretically. Firstly, in terms of the feature of each positioning solution, the available localization methods are presented, which include round trip delay (RTD) based location scheme, time of arrival (TOA) based location one, time difference of arrival (TDOA) based location one, RTD-TOA based location one and RTD-time sum of arrival (TSOA) based location one. Secondly, Crame-Rao lower bounds (CRLBs) are derived for all positioning schemes and the close form solutions are given. Based on these CRLBs, the localization performance of them are discussed and compared. Theoretical analyses and the computation results show that TSOA based location method and TDOA based one have the same positioning performance on the average. Moreover, for time-based positioning scheme, RTD information is helpful to improve the localization accuracy. These conclusions have not only the theoretic benefits but also the practical ones for the selection of positioning approaches.(3) Present an ellipse based best linear unbiased estimator (BLUE) localization algorithm. Firstly, in order to locate a mobile station, BLUE is utilized to implement the different positioning methods in this thesis. Theoretical analysis and the simulation results demonstrate that BLUE-based location algorithms can approach the CRLB asymptotically if the measurement noise of ranging is Gaussian white noise. Secondly, for TSOA positioning technique, in terms of an ellipse formula, an ellipse based BLUE location algorithm is derived. Therefore, one can implement TSOA based BLUE from another angle. The simulation results show that the proposed algorithm can attain the similar positioning accuracy with TSOA based BLUE. Finally, two-step least square positioning algorithm and approximate maximum likelihood one are extended to TSOA based localization method and the algorithm implementation are provided.(4) Propose a interference cancellation method based on localization information. The effect of timing synchronization error on an Alamouti-OFDM cooperative communication system is analyzed in this thesis, then, apply the location information of the relay nodes to cancelate the inter symbol interference problem resulting from the time delay error when the length of cyclic prefix is not enough comparing to the maximum time delay. Firstly, the time delay estimate is calculated according to the coordinates of the relay nodes. Through selecting the transmission time of the relay nodes, the time delay error coming from the relay nodes is made to be smaller than the length of cyclic prefix. The proposed approach implements simply; moreover, it can solve the ambiguity problem of choosing the relay nodes in a cooperative communication system.