Radio access technologies for cellular mobile communications are typically characterized by multiple access schemes, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and OFDMA. In the 4th generation (4G) mobile communication systems such as Long-Term Evolution (LTE) (Au et al., Uplink contention based SCMA for 5G radio access. Globecom Workshops (GC Wkshps), 2014. doi:10.1109/GLOCOMW.2014.7063547) and LTE-Advanced (Baracca et al., IEEE Trans. Commun., 2011. doi:10.1109/TCOMM.2011.121410.090252; Barry et al., Digital Communication, Kluwer, Dordrecht, 2004), standardized by the 3rd Generation Partnership Project (3GPP), orthogonal multiple access based on OFDMA or single carrier (SC)-FDMA is adopted. Orthogonal multiple access was a reasonable choice for achieving good system-level throughput performance with simple single-user detection. However, considering the trend in 5G, achieving significant gains in capacity and system throughput performance is a high priority requirement in view of the recent exponential increase in the volume of mobile traffic. In addition the proposed system should be able to support enhanced delay-sensitive high-volume services such as video streaming and cloud computing. Another high-level target of 5G is reduced cost, higher energy efficiency and robustness against emergencies.

Non-Orthogonal Multiple Access (NOMA) for cellular future radio access

Sparse code multiple access (SCMA) is a class of non-orthogonal multiple access (NOMA) that is proposed to support uplink machine-type communication services. In an SCMA system, designing multidimensional constellation plays an important role in the performance of the system. Since the behavior of multidimensional constellations highly depends on the type of the channel, it is crucial to employ a constellation that is suitable for a certain application. In this paper, we first highlight and review the key performance indicators (KPIs) of multidimensional constellations that should be considered in their design process for various channel scenarios. We then provide a survey on the known multidimensional constellations in the context of SCMA systems with their design criteria. The performance of some of those constellations are evaluated for uncoded, high-rate, and low-rate LTE turbo-coded SCMA systems under different channel conditions through extensive simulations. All turbo-coded comparisons are performed for bit-interleaved coded modulation, with a concatenated detection and decoding scheme. Simulation results confirm that multidimensional constellations that satisfy KPIs of a certain channel scenario outperform others. Moreover, the bit error rate performance of uncoded systems, and the performance of the coded systems are coupled to their bit-labeling. The performance of the systems also remarkably depends on the behavior of the multiuser detector at different signal-to-noise ratio regions.

Multidimensional Constellations for Uplink SCMA Systems—A Comparative Study

Although 4G (fourth generation) i.e. LTE (long term evolution) systems are now in use world-wide. But today’s 4G systems have some challenges left such as spectrum scarcity and energy efficiency. The prime objectives of near-by-future 5G (fifth generation) wireless communications are reliability, higher data rate, higher bandwidth, high spectrum efficiency, higher energy efficient and that too at lower latency. Channel coding tend to increase the reliability of the wireless communications system by adding extra bits in a controlled fashion and is considered to be most persuasive element of communication system. 4G LTE Turbo Codes have already been replaced by LDPC (low density parity check) Codes in many of the standards including mMTC (massive machine type communication), D2D (device to device communication) and URLLC (ultra-reliable low latency reliable communications). LDPC Codes and Polar Codes are securing much more observation because of their inherent advantages of excellent bit-error-rate performance, fast encoding and decoding procedures; which make them the strong contenders for 5G Channel Codes too. This paper provides the broad survey and comparison of the LDPC and Polar Codes along with their advantages and drawbacks which will aid in further improvement of the next generation wireless networks. In order to enlighten future research possibilities in this direction, issues addressed by distinct researchers have been explored too.

A survey on channel coding techniques for 5G wireless networks

Quasi-cyclic LDPC (QC-LDPC) codes have been accepted as the standard codes of 5G enhanced mobile broadband data channel These standard codes are designed to support multiple lifting sizes and possess rate-compatible property, which can help adapt various information lengths and code rates well In this paper, we propose an algebra-assisted method for constructing QC-LDPC codes with such properties We will first review the encoding mechanism and requirements of 5G LDPC codes, and present cycle analysis for such emerging codes We then propose a metric, referred to as weighted average number of cycles (WANC), from the perspective of cycle structure for constructing the QC-LDPC codes that can support multiple lifting sizes  Based on the WANC metric and algebraic methods, we develop a simple and practical algorithm to construct this kind of QC-LDPC codes We finally apply the proposed algorithm to construct the exponent matrices for cases of 5G LDPC codes and the standard LDPC codes of consultative committee for space data systems, respectively Simulation results show that the proposed WANC metric and designed algorithm are feasible and effective, and thus can be utilized to design other similar QC-LDPC codes

Algebra-Assisted Construction of Quasi-Cyclic LDPC Codes for 5G New Radio

This paper presents a novel efficient encoding method and a high-throughput low-complexity encoder architecture for quasi-cyclic low-density parity-check (QC-LDPC) codes for the 5th-generation (5G) New Radio (NR) standard. By storing the quantized value of the permutation information for each submatrix instead of the whole parity check matrix, the required memory storage size is considerably reduced. In addition, sharing techniques are employed to reduce the hardware complexity. The encoding complexity of the proposed method was analyzed, and indicated a substantial reduction in the required area as well as memory storage when compared with existing state-of-the-art encoding approaches. The proposed method requires only 61% gate area, and 11% ROM storage when compared with a similar LDPC encoder using the Richardson–Urbanke method. Synthesis results on TSMC 65-nm complementary metal-oxide semiconductor (CMOS) technology with different submatrix sizes were carried out, which confirmed that the design methodology is flexible and can be adapted for multiple submatrix sizes. For all the considered submatrix sizes, the throughput ranged from 22.1–202.4 Gbps, which sufficiently meets the throughput requirement for the 5G NR standard.

https://www.mdpi.com/2079-9292/8/6/668/pdf

Efficient QC-LDPC Encoder for 5G New Radio

In this letter, we study the construction of quasi-cyclic (QC) low-density parity-check (LDPC) codes by array dispersion and masking. We first propose a class of arrays of circulant permutation matrices (CPMs) of arbitrary size obtained by dispersion. Based on this class of arrays of CPMs, a class of QC-LDPC codes is constructed. For these resulting codes, we analyze their cycle structure and derive the numbers, which indicate how many cycles pass through each CPM in their parity-check matrices. Following the indication numbers with the order from largest to smallest, we replace the corresponding CPMs with zero matrices (ZMs) of the same size one by one until a targeted masking termination condition is satisfied. Then, the resultant arrays of CPMs and ZMs give a large class of QC-LDPC codes. Numerical results show that the codes constructed perform well over the additive white Gaussian noise (AWGN) channel when decoded with the sum-product algorithm.

Construction of Quasi-Cyclic LDPC Codes via Masking With Successive Cycle Elimination

In this letter, we consider the construction of $q$ -ary low-density parity-check (LDPC) codes by jointly optimizing the girth and number of shortest cycles in the frame of superposition. We begin with constructing binary quasi-cyclic LDPC codes by superposition. By replacing the nonzero entries of the parity-check matrices of the resulting binary codes with the nonzero elements of GF $(q)$ , a class of $q$ -ary LDPC codes is obtained. Furthermore, we analyze the cycle structure of the constructed codes for a given degree distribution and code length, and present a search algorithm for finding $q$ -ary LDPC codes with few cycles of length $g$ , where $g$ is the optimized girth value. Simulation results show that the proposed codes perform well under the iterative decoding algorithms.

Superposition Construction of $Q$ -Ary LDPC Codes by Jointly Optimizing Girth and Number of Shortest Cycles

This paper presents a nonbinary low-density parity-check (LDPC) coded spatial modulation (CSM) for multiple-input multiple-output communication systems, in which the information bits for choosing active transmit antennas and the bits for choosing constellation signals are protected by a nonbinary LDPC code. We apply a many-to-one mapping known as Gallager mapping to signal constellation, resulting in an improved constellation design for the CSM system. Furthermore, we propose a Gallager mapping-based scheme to solve the design problem of the CSM system with arbitrary transmit antennas, in which Gallager mapping is used to map the index information bits to the active antenna, thus an integer-bit transmission can be achieved for any number of transmit antennas. With the use of nonbinary LDPC codes, a non-iterative receiver is able to recover the undistinguished information caused by the many-to-one mapping. Several communication scenarios are studied and simulation results show that the proposed scheme can offer substantial performance gains with design flexibility over the Rayleigh fading channel.

Nonbinary LDPC-Coded Spatial Modulation

In this paper, we investigate the application of nonbinary LDPC codes to spatial modulation, and a nonbinary LDPC coded spatial modulation (NBLDPC- SM) system is proposed. In the system, the symbols for choosing the active antennas and the symbols for choosing constellation signals are protected by a nonbinary LDPC code. Furthermore, we combine the NBLDPC-SM system with Gallager mapping, a method of constellation shaping, to improve the system spectral efficiency. We demonstrate that such NBLDPC-SM system can achieve low probability of bit error at near SM capacity. Several communication scenarios are investigated to verify good performance of the proposed system and simulation results are also given to provide substantial performance gains in different channel conditions.

Hengzhou Xu

Papers

Algebra-Assisted Construction of Quasi-Cyclic LDPC Codes for 5G New Radio

Construction of Quasi-Cyclic LDPC Codes via Masking With Successive Cycle Elimination

Superposition Construction of $Q$ -Ary LDPC Codes by Jointly Optimizing Girth and Number of Shortest Cycles

Nonbinary LDPC-Coded Spatial Modulation

Nonbinary LDPC Coded Spatial Modulation