Analysis and Design of Interleavers for Iterative Multiuser Receivers in Coded CDMA Systems

Abstract

Abstract-We deal with the design of interleavers in a coded code-division multiple-access (CDMA) scenario, where at the receiver an iterative turbo-like structure to perform multiuser detection is employed. The choice of the interleavers affects both the maximum-likelihood (ML) performance and the impact of the suboptimality of the iterative receiver. First, heuristic criteria of goodness for a set of interleavers, each assigned to a given active user, are introduced and motivated. One of these criteria is based on the intersection between the equivalent codes seen after the interleavers for each user pair. The design rules are valid for any kind of channel code. In particular, when the channel code used by every user is a terminated convolutional code, a very simple design rule, in the subset of congruential interleavers, is specified.The suitability of an interleaver set to iterative decoding is also treated. The analysis leads to a design rule which is shown to have great importance on the performance of a turbo-like receiver. Numerical results assess the validity of the derived design rules by showing that, for iterative multiuser receivers and reasonable block lengths, the suitability to iterative decoding is more important than the performance optimization.Index Terms-Coded code-division multiple access (CDMA), interleaver design, iterative multiuser receivers, permutations.

Iterative interference cancellation and channel estimation in multibeam satellite systems

“…No optimization is done for choosing pilot symbols, e.g. by choosing orthogonal training sequences, nor for interleavers [16], as this would not be relevant for an asynchronous channel.…”

“…As for channel estimation, we limit the MMSE combiner estimation in Equation (18), and consequently combining in Equation (16), to the kth beam and adjacent co-channel beams (Section 2.4, assumption (iii)).…”

Simple construction of multiple interleavers for concatenated zigzag codes

“…Multiple interleavers are considered in [9] and [10] in the context of multiuser detection in code division multiple access (CDMA) and in [11] for interleave division multiple access (IDMA).…”

“…Another design criterion is discussed in [9], where the authors use the heuristic criterion of minimizing the intersection, i.e. the set of common code words, between the resulting codewords after interleaving.…”

“…This again stresses the difficulties in finding appropriate design criteria and justifies to rely more on heuristic approaches and evaluation by simulations. Furthermore, except for the case of congruential symbol interleavers in combination with convolutional codes, no construction methods are given in [9].…”