Abstract
Sparse Code Multiple Access (SCMA) is a powerful multiple access technique for future generations of wireless communication where users are allowed to transmit through pre-defined channel resources with a controlled degree of collision. The base-station then recovers all the users' data through some iterative method. The well-known Message-Passing Algorithm (MPA) has excellent performance but has exponential decoding complexity. Alternative decoding algorithms, such as MPA in the log-domain (Log-MPA), have been proposed in the literature aiming to reduce the decoding complexity while not significantly decreasing performance. In recent work, the authors proposed a modification in the conventional Log-MPA by exploring a tree structure associated with the decoding equations. By properly avoiding symbols with low reliability, a pruned tree is obtained, yielding an arbitrary trade-off between performance and complexity in the joint detection. In the present work, we extend this contribution by showing that the advantages of the tree-based decoding algorithm are magnified when SCMA is coupled to an error-correcting code, in particular, a Low-Density-Parity-Check (LDPC) code. Through computer simulations, we show that an improved performance-decoding complexity trade-off is obtained.
Highlights
Sparse Code Multiple Access is a non-orthogonal multiple access technique proposed for future-generation wireless networks, which provides high efficiency and good performance [1]
We introduce error-correcting codes, in particular LDPC codes, to the Sparse Code Multiple Access (SCMA) system proposed in [9], and show that the performance of coded SCMA with the proposed decoding algorithm approaches the one with the conventional Log-Message-Passing Algorithm (MPA) with an even larger number of pruned nodes, with an even lower decoding complexity;
In our coded SCMA system, the rate 1/2 LDPC code of length 128 designed in [11] is adopted in all scenarios simulated
Summary
Sparse Code Multiple Access is a non-orthogonal multiple access technique proposed for future-generation wireless networks, which provides high efficiency and good performance [1]. In SCMA, the users’ data are mapped into codewords, that are allocated in a non-orthogonal way in resources such as sub-carriers of an Orthogonal Frequency Division Multiplexing (OFDM) [2]. SCMA is a generalization of Low-Density Spreading (LDS) [3], which, in turn, is a sparse version of Code Division Multiple Access (CDMA) with low density spreading sequences [4]. In the LDS technique, the information bits of each user is mapped into a complex symbol of a signal constellation, and this symbol is repeated in a small number of resources or slots (subcarriers, in the case of OFDM), while the other resources are not used (the power allocated to these resources is null). The low number of collisions per resource allows for a representation of LDS by a sparse graph so that the Message-Passing Algorithm (MPA) [3] can be used to recover the symbols transmitted from all users
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
