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Novel secondary radar for precise distance and velocity measurement in multipath environments

The performance of wireless systems strongly depends on the characteristics of the radio channel. Multipath propagation and Doppler effect are two phenomena to be considered. We present a frequency-modulated continuous wave (FMCW) secondary radar concept to estimate the offset in time and in frequency of two wireless units and to measure their distance to each other. The distance can be measured with a standard deviation as low as 1 cm. However, the accuracy of the system is degraded in multipath environments or if the stations are moving relative to each other. In this paper we show a novel extension of the algorithm to cope with multipath propagation and the Doppler effect. The broadband measurement principle at hand is robust towards multipath interference. Additionally the Doppler effect is compensated for. By evaluating the Doppler frequency shift the relative velocity of the mobile units is measured directly. Measurement results prove the significant improvement in system performance if the extended algorithms are used.