A design of orthogonal interleavers for multimodes turbo en-decoders

By applying multi-mode turbo en-decoders to code division multiple access (CDMA) systems for channel multiplexing, the user capacity of the CDMA system could increase remarkably. In this paper, we present a design of orthogonal interleavers for multi-mode turbo en-decoders. Different from the most presented works, where an optimal interleaver is investigated to obtain the convolution codes with greater minimum distance under certain conditions, this paper focuses on different interleavers in the multi-mode turbo encoders for channel multiplexing. Through specific one-to-one mapping, a design method based on a prime sequence is demonstrated to generate an interleaver's index sequence set with optimal Hamming orthogonal or quasi-optimal Hamming orthogonal characteristics. According to these sequences, two families of interleavers for multi-mode turbo en-decoders in synchronous systems and asynchronous systems are constructed respectively. Theoretical deductions and computer simulations verified the approach is reasonable and effective.