Aperture Jitter Effects in Software Radio GNSS Receivers

Increasingly, software radio techniques are being used in the implementation of communications receivers in general, and GNSS receivers in particular. In such a receiver, the received signal is sampled as close to the receive antenna as possible, and all subsequent processing uses digital signal processing (DSP) techniques. The sampling clock will suffer from phase noise instabilities, leading to a phenomenon known as aperture jitter. This paper examines the effects of aperture jitter for a number of “typical” software radio GNSS receivers. A jitter specification is derived which restricts the noisy effects due to jitter to 10dB below thermal noise. It transpires that regardless of the new signals that are selected to accompany it, it is the L1 signal that drives this jitter specification.