Multipath Reduction with Signal Processing

The two techniques of mitigating multipath by choke ring antenna and by signal processing are two complimentary techniques and one cannot substitute for the other.

Choke ring antenna can mitigate multipath signals reflected from objects below the antenna. It has no effect on multipath signals reflected to the antenna from objects above the antenna (e.g. tall buildings or trees).

Signal processing techniques to mitigate the effect of multipath have little effect when the multipath distance (the difference in distance between the direct signal and the reflected signal) is less than few meters, irrespective of whether the reflected signal comes from objects above or below the antenna.

Fortunately most of the reflected signals from objects above the antenna (that cannot be mitigated by choke ring) have multipath distances of more than several meters which can be mitigated by signal processing techniques.

The new technique of multipath rejection employed in our receivers (patent pending) has a simpler hardware approach with improved performance over all that existed before. It also removes any possibility of false lock points that existed in some of the earlier techniques. The false lock points could occasionally introduce substantial error when a strong multipath distance is in the range of 30 to 300 meters. Figures below show the comparison with other techniques for multipath relative amplitude 0.5.

Comparison of multipath error envelopes of JPS choke ring and conventional antenna

a

b

Comparison of multipath error envelopes of JPS choke ring and conventional antenna (Minimum of Down/Up=-15 dB), (a) for phase and (b) code. Multipath from ground.

 

Comparison of multipath error envelopes of JPS techniques of multipath mitigation and other techniques

 

Comparison of multipath error envelopes of JPS techniques of multipath mitigation and other techniques

a

b

Comparison of multipath error envelopes of JPS techniques of multipath mitigation and other techniques, (a) for phase and (b) code. Multipath from objects above the antenna.