Multi-satellite time-delay estimation for reliable high-resolution GNSS receivers

Reliable estimation of position in time and space has become a key necessity in several technical applications like mobile navigation, precision farming or network synchronization. While the increasing amount of operating Global Navigation Satellite Systems (GNSS) offers diverse possibilities to receive GNSS signals worldwide and to determine position accurately, inter- and intrasystem interference has been identified as a problem of growing importance. The performance of receivers which track all in-view satellites individually degrades if mutual interference is not taken into account. Therefore, we consider the problem of joint signal parameter estimation. For scenarios where the signals of different satellites superimpose at the receiver a joint maximum likelihood estimator for all relevant signal parameters is derived. In order to keep the computation of the related likelihood function, and the determination of its maximum, feasible for a low-complexity receiver, an iterative Expectation-Maximization (EM) algorithm is applied. Simulations for different scenarios show that this approach is efficient in the estimation theoretic sense, and robust against interference that is caused by signals with known structure.