Can Code Redundancy Be Used to Improve GNSS Receiver Acquisition
Sensitivity?
Proc. of the IEEE Position Location and Navigation Symposium (PLANS), (2006)Abstract
Good acquisition sensitivity is important for those GNSS receivers
that are used to support location-based services and emergency calls
in mobile telephones. Current standards specify that the receivers
should be tested with satellite signals that are fifteen decibels
or more below the nominal level. Satellite acquisition is typically
accomplished by integrating a demodulated and despread signal first
coherently and then noncoherently. The sensitivity thus achieved
depends heavily on the length of the coherent integration which is,
however, limited due to the finite coherence time of the satellite
signal. The coherence time of the GPS C/A signal is fairly long due
to its bit length of 20 ms. The bit lengths of some new GNSS signals
are shorter, which makes them more difficult to acquire; they do,
however, contain redundancy in the form of convolutional error correcting
codes. It is conceivable that the redundancy could be used to regain
some of the lost acquisition sensitivity by increasing the effective
coherent integration time of the receiver. To gain insight into the
value of signal redundancy for GNSS acquisition, two prospective
strategies are analysed and compared with the standard methods. In
particular, the possibility of improving acquisition sensitivity
based on the rate 1/2 convolutional code that has been proposed for
several new GNSS signals is examined.