Multipath Mitigation Techniques for Range Error Reduction in PN Ranging Systems

In this paper, we investigate the Psuedo-Noise (PN)-sequence-based ranging technique for tracking an object by range measurements. PN-sequence-based signals for range measurements provide better range accuracies with secured data transmission. For range calculations, the delay parameter plays a major role. In real-time applications, the Line-of-Sight (LOS) link is not always guaranteed. The signal received at the receiver may contain reflected signals along with the direct path signals. Similar kind of range measurements are performed in Global Navigation Satellite System (GNSS) receivers, and the same can be applied for PN ranging sequence based object tracking, like UAVs, missiles, etc. The basic difference between GNSS and PN system is the ranging signal. In GNSS, for example, GPS and IRNSS, the Standard Positioning Service (SPS) comprises coarse acquisition code as the ranging sequence, which is of length 1023 chips transmitted at 1.023 Mbits/s. As per the Consultative Committee for Space Data Systems (CCSDS), two types of PN ranging sequences are proposed, weighted-voting-balanced Tausworthe codes abbreviated as T2B and T4B. Both the codes have the same lengths of 1,009,470 chips with different properties. Here the acquisition of the signal will be different in comparison with GNSS. Multipath signal propagation error can distort the actual signal, which leads to range measurement errors. In GNSS to reduce multipath error the conventional methods are based on Delay Locked Loop (DLL) feedback techniques. In order to reduce the multipath error, different methods which can be used to improve the range accuracy are discussed.