A Study On The Wireless Positioning System Based On OFDM SFN

OFDM (Orthogonal Frequency Division Multiplexing) is a kind ofMulti-Carrier Modulation technologies. It divides the serial high speed datastream into some parallel low data streams. These data streams then aremodulated by a set of orthogonal carriers, which makes the bandwidth ofevery parallel signal smaller than the coherence bandwidth and eliminate theinter symbol interference. SFN (Single Frequency Network) is a network of radiotransmitters which transmitter the same signal modulated with the same frequencycarrier at the same time, which results in better coverage of the desired area. Thefeatures of OFDM make SFN a perfect network solution, which reduces the cost andensures the coverage of the system.The rise of LBS (Location Based Service) makes our life moreconvenient and induces more studies on wireless positioning technology. Thewireless positioning system designed in this paper refers to the idea of GPS.Different transmitters transmit different PRN (Pseudorandom Noise) codes inthe positioning signal frame. We do correlation at receiver end to determinethe arrival time of signal. It needs at least4signals to use least squarealgorithm to calculate the3D coordinates of the receiver.Multipath and NLOS (Non-Line-of-Sight) propagation are major sourcescausing precision degradation of positioning system. This paper strengthensthe traditional MEDLL (Multipath Estimating Delay Lock Loop) byintroducing a feedback parameter decided by the square error between theestimated signal and the received signal, which effectively mitigates themultipath error. We also study the NLOS error by building a linear modelbetween the real distance and the mean NLOS error using linear regression.Matlab is used to do the system simulation and analysis in this paper.