OFDM ranging in multipath channels using time reversal method

With the development of wireless positioning and popularity of OFDM (orthogonal frequency division multiplexing) as a key technology in wireless systems, such as 3GPP LTE, WLAN, and WiMAX, precise OFDM-based ranging has become of particular interest. In this paper, we propose a ranging method measuring the round-trip time-of-flight of an OFDM symbol. Timing measurements are vulnerable to symbol-timing synchronization error. We propose a novel approach to overcome such errors. This approach is based on the time-reversal technique in which multipath effect appears as an advantage. In frequency selective channels, where different OFDM subcarriers experience different delays, time-reversal method conveniently eliminates the effect of the channel phase response. Thus, phase rotation of the signal caused by the timing offset in the OFDM system can be determined and removed from the measurements. We derive an approximate maximum likelihood method for estimating the phase rotation. Simulation studies demonstrate that the method provides high-quality estimates even for noisy frequency selective channels.