Characteristics and tracking methods of TD-AltBOC signal

As a kind of modified AltBOC, TD-AltBOC modulation is capable of carrying two different services on the lower and the upper side-lobes of its split spectrum, and has advantages such as lower receiver complexity and an ideal multiplexing efficiency of 100% owing to its time-division multiplex scheme. This paper first derives the expression of the autocorrelation function (ACF) of the TD-AltBOC signal. It is shown that the sharper main peak of the ACF of TD-AltBOC brings slightly higher code tracking accuracy and better anti-multipath performance than AltBOC with a correlator spacing narrower than 0.25chip and a front end bandwidth larger than 40MHz. Then focus is put on special signal processing techniques for a TD-AltBOC receiver. Different options of the local reference code structures for SSB (Single Side Band) and DBM (Dual Band Matched) receivers are discussed. The correlation discriminator originally proposed for BOC(n, n) signals is introduced to the TD-AltBOC signal tracking with the complex correlator architecture modified. Finally, the SSB tracking, DBM tracking, and correlation discriminator-based tracking architectures are implemented in our software TD-AltBOC receiver, and he theoretical analyses of the signal performance are validated by the test results using a digital IF (Intermediate Frequency) signal simulator as the signal source. The study provides a reference for the selection of the baseline Beidou B2 signal as well as the design of TD-AltBOC(15,10) receivers.