GPS Receiver Architecture Effects on Controlled Reception Pattern Antennas for JPALS

Stanford University is developing a controlled reception pattern antenna (CRPA) array with beamsteering/adaptive-null-forming capabilities as part of a research testbed to evaluate CRPA algorithms and software tools, and their effects on GPS signals and satellite tracking performance. The correlation power peak ratio (CPPR), defined as the ratio of the largest correlation peak to the next-highest peak (more than 1chip away), is used to evaluate tradeoffs between characteristics of multi-element GPS antenna systems. Based on this signal-quality-based metric, a trade-space was identified and simulations were developed to evaluate trades in front-end architecture for the steered-beam testbed. Specifically, the order of beam-forming and correlation operations was found to not introduce appreciable differences in the CPPR. However, the number of analog-to-digital (A/D) quantization levels and the A/D converter (ADC) dynamic range vs. signal amplitude (e.g., the signal variance for white-noisedominated signals) would cause changes in the CPPR – signals were degraded for fewer numbers of A/D quantization bits (most notably for a 1-bit ADC) and for sub-optimal ADC dynamic range. The conclusion was that the CRPA front-end hardware and A/D conversion plan are feasible with integrated components and postcorrelation beam-forming, even given the limitations in sampling frequency and numbers of A/D quantization levels in off-the-shelf components. Finally, a further program of numerical simulations is proposed which will lead to additional system design improvements and development of a software-defined radio.