Soft-decision Reed-Solomon decoding strategies for code group identification and frame synchronization in UMTS WCDMA

In UMTS WCDMA, the secondary synchronization channel uses (15,3) comma-free Reed-Solomon codes for code group identification and frame synchronization. Each code symbol of Reed-Solomon code sequence is chosen from 16 different Hadamard codes of 256 chips. After receiving a code signal of 256 chips, it is sent into correlation bank to measure the correlation values between the receiving code signal and 16 Hadamard codes. Using the 16 correlation values, we determine the hard-decision symbol value and evaluate the reliability value. Then, we apply the generalized minimum distance like (GMD-like) decoding algorithm to decode the code sequence of 15 hard-decision code symbols and corresponding reliability vector. Moreover, we can receive next 15 code symbols of the next frame and then update the symbol values as well as reliability values to further improve the performance. Also, we find a simple property to detect the frame boundary after the Reed-Solomon decoder return a cyclic-shift code sequence. These decoding strategies, compared with the method used before, need less computation and less memory. It is shown in simulations that they achieve good performance with reasonable time delay for more receiving information.