Ziv-Zakai Bound and Multicorrelator Compression for a Galileo E1 Meta-Signal

We discuss robustness and accuracy of time of arrival (ToA) estimation using meta-signal combining (MSC). MSC is a receive strategy to process multiple navigation signals as a single wideband signal, even though they are transmitted on different carrier frequencies. This strategy was originally proposed due its potentially high ToA estimation accuracy in combination with good spectral efficiency and power efficiency. Furthermore, it offers the possibility to make optimal use of legacy signals and newly added signal components; in this work, we focus on the example of the E1 open serivce (OS) and the forthcoming E1-D signal. We discuss estimation robustness against noise on the basis of the Ziv-Zakai Lower Bound (ZZLB); our analytical results reveal that without large carrier-to-noise density ratio or long observation times, autocorrelation sidelobes make it impossible for an unbiased ToA estimator to attain the excellent performance promised by the simpler Cramér-Rao Lower Bound (CRLB). Furthermore, we demonstrate that a carefully configured bank of correlators should be used in order to avoid further performance losses.