A low complexity algorithm for frame synchronization in TDD-LCR system

Time synchronization is required in mobile terminals operating in any digital radio system to detect the radio frame start of the received signal. The main operation performed in the synchronization procedure is the correlation between the received signal and the known synchronization sequences transmitted in each frame. The UMTS standard for TDD Low Chip Rate (TDD-LCR) option (integrated by 3GPP in Release Four of the UTRA standard) defines 32 different synchronization codes (SYNC sequences). Each base station transmits one of these sequences always at the same position of a radio frame and the used sequence defines already a group of base stations to which this sequence belongs. In UMTS FDD or in the high chip rate TDD one common primary synchronization sequence is used which does not exist in the TDD-LCR. This forces the mobile set to calculate the correlation between the received signal and all 32 SYNC sequences and thus increases the computational complexity enormously. In this paper we propose a low complexity algorithm for the detection of the radio frame start and of the sequence number using an approximation with lowpass filtering and sample rate reduction in the frequency domain. The performance loss of this approximation is quite small and an implementation in currently available signal processors is possible. Furthermore, the proposed algorithm could be generalized to any case where a problem of computational complexity arises due to the calculation of the correlation between two signals.