Post-detection Integration Techniques Research Articles

Optimal Post-Detection Integration Techniques for the Reacquisition of Weak GNSS Signals

This paper tackles the problem of finding the optimal non-coherent detector for the reacquisition of weak Global Navigation Satellite System (GNSS) signals in the presence of bits and phase uncertainty. Two solutions are derived based on using two detection frameworks: the Bayesian approach and the generalized likelihood ratio test (GLRT). We also derive approximate detectors of reduced computation complexity and without noticeable performance degradation. Simulation results reveal a clear improvement of the detection probability for the proposed techniques with respect to the conventional detectors implemented in high sensitivity GNSS (HS-GNSS) receivers to acquire weak GNSS signals. Finally, we draw conclusions on which is the best technique to reacquire weak GNSS signals in practice considering a trade-off between performance and complexity.

C/N0 estimators for high-sensitivity snapshot GNSS receivers

We address the problem of estimating the carrier-to-noise ratio (C/N0) in weak signal conditions. There are several environments, such as forested areas, indoor buildings and urban canyons, where high-sensitivity global navigation satellite system (HS-GNSS) receivers are expected to work under these reception conditions. The acquisition of weak signals from the satellites requires the use of post-detection integration (PDI) techniques to accumulate enough energy to detect them. However, due to the attenuation suffered by these signals, estimating their C/N0 becomes a challenge. Measurements of C/N0 are important in many applications of HS-GNSS receivers such as the determination of a detection threshold or the mitigation of near-far problems. For this reason, different techniques have been proposed in the literature to estimate the C/N0, but they only work properly in the high C/N0 region where the coherent integration is enough to acquire the satellites. We derive four C/N0 estimators that are specially designed for HS-GNSS snapshot receivers and only use the output of a PDI technique to perform the estimation. We consider four PDI techniques, namely non-coherent PDI, non-quadratic non-coherent PDI, differential PDI and truncated generalized PDI and we obtain the corresponding C/N0 estimator for each of them. Our performance analysis shows a significant advantage of the proposed estimators with respect to other C/N0 estimators available in the literature in terms of estimation accuracy and computational resources.

Noncoherent Integration for Signal Detection: Analysis Under Model Uncertainties

The performance of postdetection integration (PDI) techniques for the detection of Global Navigation Satellite Systems (GNSS) signals in the presence of uncertainties in frequency offsets, noise variance, and unknown data-bits is studied. It is shown that the conventional PDI techniques are generally not robust to uncertainty in the data-bits and/or the noise variance. Two new modified PDI techniques are proposed, and they are shown to be robust to these uncertainties. The receiver operating characteristics (ROC) and sample complexity performance of the PDI techniques in the presence of model uncertainties are analytically derived. It is shown that the proposed methods significantly outperform existing methods, and hence they could become increasingly important as the GNSS receivers attempt to push the envelope on the minimum signal-to-noise ratio (SNR) for reliable detection.

Generalized and Average Likelihood Ratio Testing for Post Detection Integration

In the context of spread spectrum communications, this paper investigates the use of likelihood ratio testing techniques for the design of post detection integration (PDI) methods for code acquisition in the presence of phase and frequency uncertainty. The proposed methods are derived as theoretical and pragmatic alternatives to the conventional approach based on noncoherent integration, which would be optimal in the absence of frequency uncertainty. Two competing alternatives are introduced to handle the unknown frequency error, respectively based on the generalized and average likelihood ratio tests, and identified as generalized PDI (GPDI) and average PDI (APDI). The GPDI versus APDI tradeoff is far from trivial and leads to numerous interesting insights, particularly with respect to the impact on performance of the frequency offset entity. Performance is also contrasted to that of conventional PDI techniques, i.e., noncoherent and differential PDI, to reveal significant gains in favor of the proposed methods.

Signal processing for a benchmark for radar resource allocation in the presence of ECM

A simple post-detection integration technique is proposed to solve the benchmark problem for radar resource allocation in the presence of false alarms (FA) and electronic counter measurements (ECM). The benchmark problem is considered only from the point of view of target detection, and as a result, two new algorithms for adaptive radar resource allocation are presented. The algorithms proposed adaptively select radar dwells (type and number), form thresholds for signal detection and RGPO elimination, and evaluate current estimates of target and SOJ parameters. Simulation results show that the non-coherent integration technique is the most effective in the presence of stationary radar environment while improving the target-to-signal ratio (SNR). In the presence of ECM, however, the non-coherent technique is desired only at the first several scans, at which the more accurate measurements of target and SOJ parameters are produced. In the presence of RGPO, the excision technique is used to remove RGPO from the range gate before target detection.

Performance analysis of multi-path searcher for mobile station in W-CDMA system employing transmit diversity

The performance analysis of a multi-path searcher operating over Rayleigh fading channels is presented when transmit diversity and post-detection integration techniques are employed in a mobile station. Receiver operating characteristics are obtained by computer simulations, which corroborate the theoretical analysis. A procedure to find the optimum parameters of the double-dwell serial searcher is also proposed.