91 research outputs found
Design Low Complexity SCMA Codebook Using Arnold’s Cat Map, Journal of Telecommunications and Information Technology, 2022, nr 4
In 5G wireless communications, sparse code multiple access (SCMA) – a multi-dimensional codebook based on a specific category of the non-orthogonal multiple access (NOMA) technique - enables many users to share non-orthogonal resource components with a low level of detection complexity. The multi-dimensional SCMA (MD-SCMA) codebook design presented in this study is based on the constellation rotation and interleaving method. Initially, a subset of the lattice Z 2 is used to form the mother constellation’s initial dimension. The first dimension is then rotated to produce other dimensions. Additionally, interleaving is employed for even dimensions to enhance fading channel performance. Arnold’s chaotic cat map is proposed as the interleaving method to reduce computational complexity. Performance of the SCMA codebook based on interleaving is evaluated by comparing it with selected codebooks for SCMA multiplexing. The metrics used for performance evaluation purposes include bit error rate (BER), peak to average power ratio (PAPR), and minimum Euclidean distance (MED), as well as complexity. The results demonstrate that the suggested codebook with chaotic interleaving offers performance that is equivalent to that of the conventional codebook based on interleaving. It is characterized by lower MED and higher BER compared to computer-generated and 16-star QAM codebook design approaches, but its complexity is lower than that of the conventional codebook based on interleaving
A Multistage Method for SCMA Codebook Design Based on MDS Codes
Sparse Code Multiple Access (SCMA) has been recently proposed for the future
generation of wireless communication standards. SCMA system design involves
specifying several parameters. In order to simplify the procedure, most works
consider a multistage design approach. Two main stages are usually emphasized
in these methods: sparse signatures design (equivalently, resource allocation)
and codebook design. In this paper, we present a novel SCMA codebook design
method. The proposed method considers SCMA codebooks structured with an
underlying vector space obtained from classical block codes. In particular,
when using maximum distance separable (MDS) codes, our proposed design provides
maximum signal-space diversity with a relatively small alphabet. The use of
small alphabets also helps to maintain desired properties in the codebooks,
such as low peak-to-average power ratio and low-complexity detection.Comment: Submitted to IEEE Wireless Communication Letter
SCMA with Low Complexity Symmetric Codebook Design for Visible Light Communication
Sparse code multiple access (SCMA) is attracting significant research
interests currently, which is considered as a promising multiple access
technique for 5G systems. It serves as a good candidate for the future
communication network with massive nodes due to its capability of handling user
overloading. Introducing SCMA to visible light communication (VLC) can provide
another opportunity on design of transmission protocols for the communication
network with massive nodes due to the limited communication range of VLC, which
reduces the interference intensity. However, when applying SCMA in VLC systems,
we need to modify the SCMA codebook to accommodate the real and positive signal
requirement for VLC.We apply multidimensional constellation design methods to
SCMA codebook. To reduce the design complexity, we also propose a symmetric
codebook design. For all the proposed design approaches, the minimum Euclidean
distance aims to be maximized. Our symmetric codebook design can reduce design
and detection complexity simultaneously. Simulation results show that our
design implies fast convergence with respect to the number of iterations, and
outperforms the design that simply modifies the existing approaches to VLC
signal requirements
SCMA Codebook Design
Multicarrier CDMA is a multiple access scheme in which modulated QAM symbols
are spread over OFDMA tones by using a generally complex spreading sequence.
Effectively, a QAM symbol is repeated over multiple tones. Low density
signature (LDS) is a version of CDMA with low density spreading sequences
allowing us to take advantage of a near optimal message passing algorithm (MPA)
receiver with practically feasible complexity. Sparse code multiple access
(SCMA) is a multi-dimensional codebook-based non-orthogonal spreading
technique. In SCMA, the procedure of bit to QAM symbol mapping and spreading
are combined together and incoming bits are directly mapped to
multi-dimensional codewords of SCMA codebook sets. Each layer has its dedicated
codebook. Shaping gain of a multi-dimensional constellation is one of the main
sources of the performance improvement in comparison to the simple repetition
of QAM symbols in LDS. Meanwhile, like LDS, SCMA enjoys the low complexity
reception techniques due to the sparsity of SCMA codewords. In this paper a
systematic approach is proposed to design SCMA codebooks mainly based on the
design principles of lattice constellations. Simulation results are presented
to show the performance gain of SCMA compared to LDS and OFDMA.Comment: Accepted for IEEE VTC-fall 201
Sub-graph based joint sparse graph for sparse code multiple access systems
Sparse code multiple access (SCMA) is a promising air interface candidate technique for next generation mobile networks, especially for massive machine type communications (mMTC). In this paper, we design a LDPC coded SCMA detector by combining the sparse graphs of LDPC and SCMA into one joint sparse graph (JSG). In our proposed scheme, SCMA sparse graph (SSG) defined by small size indicator matrix is utilized to construct the JSG, which is termed as sub-graph based joint sparse graph of SCMA (SG-JSG-SCMA). In this paper, we first study the binary-LDPC (B-LDPC) coded SGJSG- SCMA system. To combine the SCMA variable node (SVN) and LDPC variable node (LVN) into one joint variable node (JVN), a non-binary LDPC (NB-LDPC) coded SG-JSG-SCMA is also proposed. Furthermore, to reduce the complexity of NBLDPC coded SG-JSG-SCMA, a joint trellis representation (JTR) is introduced to represent the search space of NB-LDPC coded SG-JSG-SCMA. Based on JTR, a low complexity joint trellis based detection and decoding (JTDD) algorithm is proposed to reduce the computational complexity of NB-LDPC coded SGJSG- SCMA system. According to the simulation results, SG-JSGSCMA brings significant performance improvement compare to the conventional receiver using the disjoint approach, and it can also outperform a Turbo-structured receiver with comparable complexity. Moreover, the joint approach also has advantages in terms of processing latency compare to the Turbo approaches
Designing Enhanced Multi-dimensional Constellations for Code-Domain NOMA
This paper presents an enhanced design of multi-dimensional (MD)
constellations which play a pivotal role in many communication systems such as
code-domain non-orthogonal multiple access (CD-NOMA). MD constellations are
attractive as their structural properties, if properly designed, lead to signal
space diversity and hence improved error rate performance. Unlike the existing
works which mostly focus on MD constellations with large minimum Euclidean
distance (MED), we look for new MD constellations with additional feature that
the minimum product distance (MPD) is also large. To this end, a non-convex
optimization problem is formulated and then solved by the convex-concave
procedure (CCCP). Compared with the state-of-the-art literature, our proposed
MD constellations lead to significant error performance enhancement over
Rayleigh fading channels whilst maintaining almost the same performance over
the Gaussian channels. To demonstrate their application, we also show that
these MD constellations give rise to good codebooks in sparse code multiple
access systems. All the obtained MD constellations can be found in
https://github.com/Aureliano1/Multi-dimensional-constellation
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