Abstract: The aim of accurately outputting navigation data can not be achieved through usual search methods, because of the particular navigation data illegibility characteristic of time division data modulation (TDDM) split frequency spectrum signal as a new modulation signal. Wherefore, a de-illegibility search method is proposed, according to the TDDM split frequency spectrum signal characteristic and the deficiency of usual search methods. The unite-channels fast acquisition phase and the de-illegibility-judge phase are included in this method. The search range is reduced and the leak acquisition phenomenon is avoided through the unite-channels fast acquisition processing. The navigation data illegibility is eliminated and the navigation data is accurately output through the de-illegibility-judge processing. Furthermore, based on theoretical derivation, simulation tests are carried out from the perspectives of performance and the signal to noise ratio (SNR) limit, and the results show that the output accuracy of the navigation data reaches up to 100%.

Key words: time division data modulation, spread spectrum, search, acquisition, de-illegibility-judge, navigation data