(p, q) Alternate-Decimal Interleavers in IDMA system

Multiple access technology is a great problem in communication systems. Code-division multiple-access (CDMA) is one of the most attractive technologies and has been widely used all over the world. It has a good advantage of anti-fading and strong ability to overcome the inter-symbol interference. But its complexity becomes a big concern when the number of users is large. Interleave-division multiple-access (IDMA) is a new scheme of multiple access technology. Many researches have been done on this area in the communication systems. IDMA is considered to be the promising technology for the future mobile communication system for its low cost multi-user detector (MUD) and robustness to interference and noise. It employs a chip by chip iterative multi-user detector to separate data from different users. Since interleavers are the only means to separate data from different users, it is important to design a good set of interleavers. Interleavers which are low correlated with each other and can be generated with low memory cost are considered good. A set of interlevers based on reversal of (p, q) alternate-decimal indexing are designed for IDMA systems. With proper selection of p and q, orthogonal interleavers can be designed. Few registers are needed because only the values of p and q should be stored for each user. If both p and q are powers of two, the algorithm is easy to be realized in hardware. The index after interleaving can be generated by reversing the binary form block by block, and no more operations are excluded. The peak basis correlation (PBC) of the proposed interleavers and random interleavers has been analyzed in this paper. The PBC of the proposed interleavers is orthogonal, which outperform random interleavers. Bit error rate (BER) simulation results show that the IDMA system using the proposed interleavers performs better than that using random interleaves.