TOA Positioning for a TDMA Localization System
Sihao Zhao, Xiaowei Cui, Shuang Xu, Mingquan Lu, Tsinghua University, China
A typical radio frequency positioning system is usually comprised of infrastructures and user devices between which one or more communications are conducted to obtain the user position. With more than one communications, the distances between infrastructures and the user device can be directly obtained. This scheme is easy to implement but the user capacity and position update rate for each user are limited due to the air time occupation. Using one-way communication can alleviate or even overcome this problem. For example, if the infrastructures transmit signals and the user devices only receive them, the system can achieve an unlimited user volume. Global navigation satellite systems (GNSS) are representative systems out of this idea, in which multiple infrastructures – the navigation satellites, simultaneously transmit signals using frequency division multiple access or code division multiple access.
In this work, a positioning system with broadcasting infrastructures and user receivers is designed and implemented. The infrastructures or base stations uses a time division multiple access (TDMA) to broadcast their positioning signals. These signals are received by the receiver to calculate the user position and also received by base stations to estimate the time offsets between them.
Firstly, the time of arrival (TOA) measurement model is given to illustrate how the time offsets between base stations are computed. The relationship between the user position and the pseudorange measurements from different reception epochs is also established and analyzed. A positioning algorithm using these pseudoranges from different epochs and different base stations is proposed. Then the proposed scheme is implemented using ultra-wideband transmitters and receivers to form a positioning system. With this system, tests are conducted to verify the performance of the proposed algorithm. Results show that the proposed positioning algorithm can calculate the user positioning correctly.
With such a TDMA scheme, the base stations can estimate their time offsets and broadcast positioning signals to the receiver at the same time, which saves the air time and cables for synchronization, decouples the connection between the base stations and the user devices and makes the user volume unlimited. For each user device, its position update rate can be easily adjusted and the upper limit is only associated with the broadcast frequency of the base stations, which makes the user device both electromagnetic silent and flexible.