Recently, a novel multiple access scheme has been introduced by Liu et al. (2003),
Li et al. (2006) and Pupeza et al. (2006), known as Interleave Division Multiple
Access (IDMA) scheme, which employs the interleavers as the only means of user
separation. Initially, in Code Division Multiple Access (CDMA), interleaving was one of the
most popular ways to spread out the errors so that they appear random to the
decoder. Recently, interleaving has also been recognized as the efficient means of
user separation. An interleaver-based multiple access scheme gives high spectral
efficiency, improved performance and low receiver complexity (Li et al., 2006; and Pupeza et al., 2006). IDMA inherits many advantages from CDMA, such as diversity against
fading and mitigation of the worst-case other-cell user interference problem.
Basically, interleaving is a permutation rule that scrambles data to break
up neighborhood relations. Interleavers used for the purpose of user separation in
IDMA scheme should have specific properties such as easy implementation and
minimum collisions. There is a potential risk that some of the interleavers of users may be
with high correlation, which may lead to inferior performance in the
communication system. The user-specific interleaves need to be orthogonal to each other so as
to minimize the cross talk between them. Also, once interleavers are assigned to
users, they are never changed. So, it is important to establish the model of interleavers
and analyze the characters in them. |
