Iterated SISO MUD for synchronous uncoded CDMA systems over AWGN channel: performance evaluation in overloaded condition

Abstract

Abstract-The performance of various iterated soft-input softoutput (SISO) multiuser detection (MUD) techniques is evaluated and compared for the case of overloaded condition for symbolsynchronous uncoded Code-Division Multiple Access (CDMA) systems over Additive White Gaussian Noise (AWGN) channel. We show that, via computer simulation, while the Bit-Error Rate (BER) performance of the serial version of the Symbol-Level iterated (SLi) SISO MUD technique is inferior to its parallel counterpart, its convergence rate is the faster between the two. Yet, the Chip-Level iterated (CLi) SISO MUD performs the best. Moreover, the Max-Log-MAP version of the CLi SISO MUD complementing the recently proposed Low-Density Signature (LDS) structure is introduced and compared to its Log-MAP version. The sensitivity of the various CLi SISO MUD techniques to the existence of the short-cycles in the underlying factor graph of the LDS structure is also analyzed. Our simulations confirm that the Max-Log-MAP version performs better compared to its more complex Log-MAP version in higher system loading condition. We also show that a performance close to single-user bound can be achieved at higher Signal-to-Noise Ratio (SNR) regime for system loading of up to 250%.

Dynamic Grouped Chip-Level Iterated Multiuser Detection Based on Gaussian Forcing Technique

“…In line with the investigation given in [9] that states parallel processing is more advantageous than serial processing where user/group ordering is much less sensitive, the same treatment is made when evaluating the groupḠ.…”

Improved algorithm for joint detection and decoding on the joint sparse graph for CDMA systems

“…As can be seen from 7, based on the received chip y n and a priori input information p n (v k ′ ,m ′ ), extrinsic values are calculated for all the constituent bits involved in (2). Substituting (8) and 9into 7, the message update becomes [10]…”

“…To address this problem, it has been studied that the sequences meeting the Welch-bound-equality (WBE) can minimise the variance of the MAI [6], and the family of hierarchy of orthogonal subsets is another attempt to handle the overloaded conditions [7]. Moreover, a low-density signature (LDS) technique has been developed to enable CDMA systems to operate in overloaded multiuser environments with the performance that is close to a single user bound [8][9][10]. The LDS was modelled by a bipartite graph, and the belief propagation (BP) algorithm [11] is applied to perform MUD in the LDS-CDMA receiver.…”

Joint sparse graph over GF( q ) for code division multiple access systems

“…In that case, the orthogonality of spreading signatures cannot be maintained [2][3][4], thus the multiuser interference (MUI) becomes inevitable even if complicated multiuser detection (MUD) such as combination of minimum-mean-square error (MMSE) and parallel interference canceller (PIC) is adopted [5,6]. In order to deal with such problem, spreading codes under overload conditions have been designed [7][8][9], and low-density signature for un-coded CDMA (low-density signature code division multiple access -LDS-CDMA) has been proposed [10,11]. The basic principles of the LDS-CDMA are (i) changing the interference pattern being seen by each user; and (ii) limiting the amount of interference occurred on each user.…”