| Automatic vehicle location (AVL) was originally conceived to provide public services such as police and public transportation systems with the ability to automatically locate individual units. In the 1970s, as Bell Labs developed the concepts for what is now known as cellular mobile radio, researchers considered AVL techniques for performing handoffs from cell site to cell site. When the Advanced Mobile Phone System (AMPS) was put into service in Chicago in 1983, received signal strength from the mobile phone was used to determine when to initiate cell site handoffs. Since signal strength is the primary determinant of call quality, and because AMPS used relatively large cell sizes, handoffs tended to be infrequent, and knowing the mobile phone's exact location was not required. As such, AVL research waned during the 1980s.; In the 1990s, we have witnessed exponential growth in both the number of cellular users, and in the number of Personal Communication System (PCS) users. One motivating factor for this explosive growth is safety concerns. In 1994, approximately 18 million individuals placed emergency 911 calls using mobile phones, but only 25% of these users knew their location. Because of this, in 1996, the Federal Communications Commission (FCC) mandated that cellular and PCS providers eventually transmit user location data to 911 dispatchers. By October 2001, wireless providers will be required to locate wireless 911 callers with an accuracy of 125 meters 67% of the time. Because of the FCC mandate, AVL research has experienced a renewed emphasis.; This dissertation covers three main topics. First, the effects of multipath on AVL performance are studied. A multipath model for an FM-based phase ranging approach suggested by Joel Engel is extended to include Doppler effects. Simulations of circular multilateration AVL using the extension of Engel's model demonstrate that both Doppler and multipath contribute to AVL errors. Second, a single base station approach using a position location polar coordinate Kalman filter in conjunction with adaptive antenna arrays is developed. A Kalman filter cell site handoff model is also proposed. Simulation results show that this approach can outperform multilateration AVL systems. Third, a temporal smoothing extension to the MUSIC algorithm is derived to counter the effects of multipath in AVL using adaptive antenna arrays. |
