What are the benefits of narrow correlator spacing?
Narrow correlator spacing is a key technique for multipath mitigation in GNSS receivers. Whereas earlier GPS receivers used a 1.0 chip spacing in their delay lock loops (DLLs), the reduction of this spacing offers a number of benefits, reducing tracking errors in the presence of both general noise and multipath phenomena.
The reduction in noise is achieved with narrower spacing because the noise components of the early and late signals characterised by multipath interference are correlated and tend to cancel each other out, provided the early and late processing are simultaneous, rather than being dithered. Multipath effects are reduced because the DLL discriminator is less distorted by the delayed multipath signal.
This narrower spacing does require a wider precorrelation bandwidth in the receiver design as well as higher sample rates and faster digital signal processing than the traditional 1.0 chip spacing. However, today's DSPs and mixed-signal devices are more than capable of providing the required performance, with little impact on either the financial or power budget of the GNSS receiver.
Most modern receiver designs offer the facility for variable correlator spacing, and can vary the spacing of the early and late reference code from 0.05 to 1.0 C/A-code chip.
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