Abstract: The application of time division data modulation (TDDM) signal greatly improves the frequency band utilization rate and the ability to adapt to complex environments of spread spectrum communication system.For the ambiguity problem of the baseband data reverse position during TDDM signal capture， a N-χ coefficient capture decision method is proposed, in whichthe unique modulation characteristics of TDDM signals and the shortcomings of the existing capture decision methods are considered. The proposed method is to establish the χ coefficient decision formulabased on the linear relationship between the baseband data reverse position and the correlation result in parallel processing， and the accurate position of the baseband data reverse is obtained by dividing the current accumulation time into N segments and measuring the average value of χ coefficient in each segment.The accuracy of the N-χ coefficient capture decision method to determine the baseband data reverse position is more than 99% for the number of segments N≥4. The proposed method is compared with the ambiguity suppression capture decision method.The simulated results show that N-χ coefficient capture decision method is better than ambiguity suppression capture decision methodin term of capture accuracy or environmental adaptability，verifying the effectiveness of this method in eliminating the ambiguity problem of baseband data reverse position.

Key words: communicationsystem, timedivisiondatamodulation, basebanddatareverse, capturedecision