Existing SCMA systems presented for multiuser detection has high computational complexity. The complexity is a prime concern considering its implementation in a machine-to-machine (M2M) communication involving limited capacity devices. Since these devices have low processing power, so practical implementation of SCMA needs to be optimised for better performance. This paper proposes an SCMA decoder with a soft demapping technique to reduce the computational complexity, providing better performance. To improve the stability of SCMA system for M2M communication, this paper proposes the use of noise variance threshold ψ, to handle the system’s stability. Results confirmed that the proposed soft demapper-based SCMA reduced the execution time to 33% and the iteration number to 63% compared to the conventional SCMA scheme deploying message passing algorithm (MPA)-based decoding. The proposed SCMA provides an improvement of 2.5 dB at a BER of 10−3under the block Rayleigh fading channels and an improvement of approximately 1.1 dB at a BER of 10−5dB under the fast Rayleigh fading channels. The improvements come from the fast convergence of iterative decoding using a soft demapper supported by a variance threshold ψ that avoids the duality decision at the border of the decision area.

Quantum has many unique characteristics for future applications in the sixth telecommunication generation (6G) 2030 based on entanglement and quantum teleportation. However, quantum communications are still vulnerable to errors and require quantum error corrections (QECC). This paper proposes quantum accumulate codes, where idea is coming from the classical accumulate codes that can provide good performances to remove or minimize the error-floor in classical communications. The proposed quantum codes can exactly satisfy both Hamming and Singleton bounds resulting in one of the smallest perfect quantum codes. This paper explains in details the steps to construct the codewords, syndrome extraction, error correction, and the quantum circuits. We perform a series of computer simulations to evaluate the quantum word error rate (QWR) and quantum fidelity performances under the depolarizing channels. Our results confirm that the stabilizers of the proposed codes can extract the syndrome and distinguish all error patterns of any single qubit errors of Pauli X, Y, and Z providing performances confirmed by the theoretical QWER curves. The results are expected to provide contributions to the development of quantum communications and future security issues.

This paper focuses on the encoding and decoding of Construction D' coding lattices that can be used with shaping lattices for power-constrained channels. Two encoding methods and a decoding algorithm for Construction D' lattices are given. A design of quasi-cyclic low-density parity-check (QC-LDPC) codes to form Construction D' lattices is presented. This allows construction of nested lattice codes which are good for coding, good for shaping, and have low-complexity encoding and decoding. Numerical results using$E_{8},\ BW_{16}$and Leech lattices for shaping a Construction D' lattice indicate that the shaping gains 0.65 dB, 0.86 dB and 1.03 dB are preserved, respectively.

Polar code lattices are formed from binary polar codes using Construction D. In this paper, we propose a design technique for finite-dimension polar code lattices. The dimension$n$and target probability of decoding error are parameters for this design. To select the rates of the Construction D component codes, rather than using the capacity as in past work, we use the explicit finite-length properties of the polar code. Under successive cancellation decoding, density evolution allows choosing code rates that satisfy the equal error probability rule. At an error-rate of 10−4, a dimension$n$= 128 polar code lattice achieves a VNR of 2.5 dB, within 0.2 dB of the best-known BCH code lattice, but with significantly lower decoding complexity.

In this paper, we propose a coding technique using Hybrid multikernel-constructed Polar codes for short blocklength transmission suitable for devices requiring low power consumption. The proposed coding scheme is based on normal recursive Polar codes with different matrix constituents. We evaluate the proposed codes in terms of the bit-error-rate (BER) performances under additive white Gaussian noise (AWGN) and Rayleigh fading channels via a series of computer simulations. We investigate the information bits and frozen bits of the proposed codes using the Bhattacharyya parameters. We found that in the Hybrid multikernel-constructed Polar codes the signal-to-noise power ratio (SNR) also affects the capacity and the positions of information bits. The results under AWGN channel show that the proposed codes improve performances. We also evaluate the performance of the proposed codes under block Rayleigh fading channels, where the superiority of the proposed codes is still confirmed. The results are expected to contribute to the development of coding techniques for disaster-and-recovery networks.

In the future Internet-of-Things (IoT) networks, some users or devices should be prioritized in access to the network, especially for applications rescuing the human life. The network should be well-designed such that the throughput of each group is maximum. In this paper, we propose a new multiple group access scheme for massive IoT networks with multiple priorities serving emergency applications. We classify the users into three groups, i.e., (a) top emergency (TE), (b) emergency (EM), and (c) normal groups (NM). We consider a new coded random access (CRA) scheme to simultaneously (i) serve massive number of users/devices and (ii) put priority to emergency applications, e.g., ambulances and fire trucks. We evaluate the performance of the proposed scheme in terms of packet-loss rate (PLR) and throughput. Furthermore, the degree distributions of networks serving user groups with multiple priorities are also evaluated, since the degree distributions are expected to be different compared to the network serving users with no priority. We found that multiple priorities are possible in a network serving multiple traffics and applications with different access priorities. These results are expected to be useful for artificial intelligence-based massive wireless communication network in the future.

The emergence of Internet-of-Thing (IoT) has driven tremendous growth of number of connected devices such that in the near future everything is connected to the networks forming super-dense networks. To cope with this challenge, this paper investigates networks with multiple relays serving massive number of devices (users), termed as multiway multirelay (MWMR) networks. Coded random access is adopted to simplify the transmission involving massive number of users. Iterative demapping (IDM) algorithm is proposed to be incorporated into successive interference cancellation (SIC) of random access decoding to significantly improve the network throughput. The relays employ modern decode-and-forward (mDF) protocol allowing the relays to keep forwarding (broadcasting) the decoded messages even though error is detected. To take the advantage of messages received from multiple relays, this paper then proposes a joint decoding technique exploiting source correlation of the messages to reduce the required transmit power and improve the network throughput. It is shown that the proposed techniques reduces bit-error-rate (BER) floor to the level below 10-5. Moreover, with Λa(x), more than two times throughput improvement is achieved using the proposed techniques. We also confirm that K = 2 relays is the practical optimal number of relays to serve massively distributed users in MWMR networks.

Highly dense wireless networks is one of the most important solutions for spectrum shortage expected by 2020. Motivated by a generally assumption that direct links between users in HD-MWR networks are usually ignored, this paper proposes high-dense multiway relay (HD-MWR) networks exploiting available direct links as side information (SI) to serve even higher number of users or devices required for the future networks. Due to the nature of massive number, we consider coded random access schemes, where all users transmit randomly, without coordination, to avoid scheduling complexity involving massive number of users or devices. Based on extrinsic information transfer (EXIT) analysis, this paper aims: (i) to investigate the increase of theoretical network capacity bounds for networks exploiting SI, and (ii) to propose efficient technique for multiple graphs-based joint decoding. A series of computer simulations is performed to confirm the theoretical network capacity bounds. We found that the network capacity increases with the increase of available direct links, where the maximum improvement achieved only with direct links of 50% from the total number of users or devices.

Densely deployed wireless networks is one of the most important solutions for spectrum shortage expected by 2020 with a huge economic impact. This paper proposes decoding schemes for high- dense vehicular multiway multirelaying (HDV-MWMR) systems comprising multiple multiway relays to serve huge number of users or devices. Due to the nature of huge number, instead of using perfect scheduling, we consider coded random access schemes, where all users transmit their messages uncoordinatedly. Although the transmission is random, the network structures still can be seen as codes-on-the-graph, resembling Low Density Parity Check (LDPC) codes structure, expected to provide an additional gain. The theoretical network capacity bound for HDV-MWMR systems exploiting multiple multiway relays is derived and confirmed via extrinsic information transfer (EXIT) chart analysis and computer simulations. To achieve the network capacity bound, we propose simple decoding schemes based on successive interference cancellation over a sparse graph involving multiple multiway relays. Suitable degree distributions for Rayleigh fading channels are investigated. The results confirm that multiple relays help both on (i) improving the throughput performances, and (ii) capturing the network diversity, which are highly required for future wireless networks.

This paper considers full data exchange for massive uncoordinated multiway relay networks (mu-mRN) applying coded random access for flexible topology changes and capable of serving massive number of users. We aim to maximize the normalized throughput of the mu-mRN using the multiuser detection (MUD) technique with MUD capability of K > 1. Specifically, our goal is multiple times improvement, i.e., ten times improvement, from the maximum normalized throughput of the mu-mRN applying slotted ALOHA (SA). First, we present a network capacity bound of the mu-mRN with general K. Then, we optimize many degree distributions for the MUD-based mu-mRN. However, as K increases, the distributions are no longer optimal to achieve the network capacity bound. We propose doubly irregular coded SA (dir-CSA) to solve the problem. Asymptotically, the mu-mRN applying dir-CSA with K = 4 can achieve the ten times throughput improvement. However, for finite number of time slots, we propose to exploit side information (SI) from neighboring users to improve the normalized throughput of the mu-mRN. The results show that the mu-mRN applying dir-CSA with SI and having optimal physical encoding can achieve ten times throughput improvement, compared with the conventional SA scheme.

This paper proposes a Partial Hybrid Automatic Repeat reQuest (P-HARQ) scheme where the relaying nodes select either forwarding the erroneous packets or requesting retransmission. In contrast to the conventional technique where the erroneous packets is always discarded, the packets found to have errors after decoding are interleaved, re-encoded, and forwarded if relay selects the forwarding mode. This technique is refer to as lossy forwarding. In this paper, the mode selection (either forwarding or requesting retransmission) is based on the confidence indicator (CI). Since the channels are assumed to suffer from block Rayleigh fading, the CI is calculated via online mutual information measurements, block-by- block. Results of computer simulations conducted to confirm the superiority of the proposed P-HARQ technique in terms of bit-error-rate, packet-error-rate and throughput performances in parallel multihop wireless multirelaying systems, are presented.

In this paper, we consider the problem of transmitting two correlated binary sources over orthogonal multiple access relay channel (MARC), where two sources are communicating with a common destination with the assistance of a single relay. We assume decode-and-forward relaying strategy, and bit-wise exclusive or (XOR) network coding is performed at the relay node. First, a joint source-channel-network (JSCN) decoding technique is proposed to fully exploit the correlation between the sources, as well as the benefit of network coding. Then the achievable compression rate region of this system is derived based on the theorem for source coding with side information. It is found that the region is a 3-dimensional space surrounded by a polyhedron. Furthermore, the performance limit in Additive White Gaussian Noise (AWGN) channels and the outage probability in block Rayleigh fading channels are derived based on the achievable compression rate region. It is shown that the outage probability can be expressed by a set of triple integrals over the achievable compression rate region. The impact of source correlation on the performance of the system is investigated through asymptotic tendency analysis. The effectiveness of the proposed JSCN decoding technique and the accuracy of the theoretical analysis have been verified through a series of computer simulations, assuming practical channel codes. It is also shown that, as long as the source-relay links are perfect, the 2nd order diversity is always achieved with our proposed technique regardless of the strength of the source correlation.

In this paper, the outage probability of a Slepian-Wolf transmission system is analysed theoretically. We consider two correlated binary information sequences where bit-flipping model is adopted, where the the information bits of the second source are the flipped version of the information bits of the first one, with a probability Pf. Here, we extend our previous work of the correlated sources transmission over block Rayleigh fading channels to such that the channel between one source and the destination is assumed to suffer from block Rayleigh fading, whereas the channel between the other source and the destination is assumed to suffer from block Rician fading. The outage probability is analysed theoretically. The results show that when Pf= 0, the outage curves versus signal-to-noise power ratio (SNR) exhibits sharper decay than that with the 2nd order diversity, as the line-of-sight (LOS) component power of Rician channel increases. It is also found that the outage curves asymptotically converge in to that with the 1st order diversity when Pf≠ 0. Furthermore, this paper also determines the optimal power allocation under the condition that total transmit power of the system is kept constant. It can be concluded that increasing the ratio of LOS component power of Rician channels can not always improve the outage performance, so far as Pf≠ 0.

This paper proposes a simple coding structure with iterative spatial demapper (ISM) for single carrier transmission of two correlated sources (with instantaneous power control) over fading multiple access channel (Fading MAC) where the receiver has only a single receive antenna. The correlation between the sources is exploited via vertical iteration (VI) loop between the two decoders and analyzed based on the Slepian-Wolf (SW) coding theorem. The proposed structure, of which potential applications are sensor or relay systems requiring relatively small number of the transmission phases, can achieve turbo-like performance over Fading MAC even with short memory convolutional codes (CC). The rate-1 doped accumulator (DACC) is used to flexibly adapt the variation of the correlation between the sources which makes the convergence tunnel between the demapper and decoder open until a point very close to (1,1) mutual information (MI) point. The results of computer simulations confirm that the proposed structure can achieve close performance to the Slepian-Wolf/Shannon limit of two correlated sources using single transmission phase.

A goal of this paper is to theoretically derive the outage probability of the correlated source transmission in block Rayleigh fading channels. The correlation between the two information sources is assumed to be expressed by the bit flipping model, where the information bits transmitted from the second transmitter are the flipped version of the information bits transmitted from the first one, with a probability pe. The source sequences are independently channel-encoded, and then transmitted to the destination block-by-block via different time- or frequency-slots. The channels are assumed to be suffering from independent block Rayleigh fading. This paper shows that the outage probability of this system can be expressed by double integrals with respect to the probability density functions (pdf) of the instantaneous signal-to-noise power ratios (SNRs) of those channels, where the range of the integration is determined by the Slepian-Wolf theorem. The most significant finding made by this paper is that the asymptotic diversity order is one so far as pe is non-zero, and the 2nd order diversity can be achieved only if pe = 0. The major applications of this paper's results include outage evaluation of extract-and-forward (EF) relay systems allowing intra-link (source-relay link) errors, sensor networks, and wireless mesh networks. The latter half of this paper provides results of outage probability calculations for one-way EF relay scenario utilizing the concept of the technique presented in this work.

In this paper, we propose a new joint source-channel decoding technique for transmitting binary Markov sources over AWGN channels. Our approach is based on serially concatenated coding and code doping for inner code. By combining the Markov source and the outer code trellis diagrams, a super trellis is constructed to exploit the time-domain correlation of the source. A modified version of BCJR algorithm is derived based on this super trellis, that can achieve considerable gain in terms of mutual information. The standard BCJR algorithm is used for decoding of inner code where code doping is adopted for better matching of extrinsic information transfer (EXIT) characteristics. EXIT chart analysis is performed to investigate convergence property of the proposed technique and to optimize the code parameters. Simulation results for bit error rate (BER) evaluation and EXIT chart analysis indicate that the proposed technique can achieve significant gains over the system in which source redundancy are not exploited, and thereby the BER performance of the proposed system is very close to the Shannon limit.

In this paper, we propose three low-complexity strategies for Multiple Access Relay Channel (MARC) based on the concept of bit-flipping model. By estimating the error rates of the links between the sources and the relay, and by utilizing the estimate as side information at the destination, it is shown that the proposed relay strategies are superior to the Decode-and-Forward (DF) relay strategy when all links are suffering from Additive White Gaussian Noise (AWGN). Furthermore, extrinsic information transfer (EXIT) analysis is used to track the convergence property with the aim of being able to search for suitable codes, the proposed relay strategies can achieve the performance close to those strategies utilizing relatively strong codes, such as turbo code or LDPC code, with iterative decoding at the relay in order to make intra links error free.

This paper proposes chained turbo equalization (CHATUE) algorithm, a simple detection scheme for block transmission without guard interval (GI), where turbo equalizers for the several consecutive frames exchange information about the interference components. Although the block transmission without GI can significantly increase bandwidth efficiency, the received signal suffers from inter-block interference (IBI) and intersymbol interference (ISI), which can't be effectively compensated by block-by-block equalization.With the CHATUE algorithm, the IBI components are cancelled by utilizing a posteriori feedback from the decoders of the neighboring equalizers (future and past). To best utilize the latest results of the sub-optimal reduced complexity equalization, frequency domain soft cancellation and minimum mean squared error filtering (FD/SC-MMSE), we exploit J matrix to convert the Toeplitz channel matrix structure to a circulant matrix. Results of the computer simulation for single carrier block transmission (SCBT) show that the proposed scheme can achieve good performance.

This paper proposes an effective iterative clipping (IC) on a coded carrier interferometry OFDM (CI/OFDM) system for improving the system performances over the nonlinearity of a solid state power amplifier (SSPA). An additional filtering is not required to remove the out-of-band (OOB) spectrum radiation as required in the conventional clipping method. The IC is designed with a minimized computational complexity though the iteration is performed. The results confirm that the CI/OFDM with the proposed IC presents many advantages in terms of BER performance and OOB spectrum radiation. Based on the optimization on BER and OOB spectrum, it is found that 2 and 3 iterations is an effective number for the IC in OFDM and CI/OFDM systems, respectively. The total degradation (TD) improvement by the effective IC in CI/OFDM is about 0.32 dB for QPSK and 2.1 dB for 64 QAM symbol on an SSPA with an output-back-off (OBO) 4dB and 8 dB, respectively.

Recently, there is an interest to increase capacity of multicarrier code division multiplexing (MC-CDMA) and orthogonal frequency division multiplexing (OFDM) by using spreading codes. Some spreading codes only support up to K = N+M, where M \le N. In this paper, we propose a new spreading code with low cross correlation and high autocorrelation while capable of supporting K = 2N+1 users. It means that 2N+1 users or data symbols are able to be transmitted over only N subcarriers. The numerical results show that our proposed code outperforms current Pseudo- Orthogonal Carrier Interferometry (POCI) code with gain of 3dB in additive white Gaussian noise (AWGN) channel and more than 4dB in multipath fading channel at bit-error-rate (BER) level of 10-5. By the proposed code, peak-to-average power ratio (PAPR) problem as a typical problem in multicarrier system is also able to be reduced up to the PAPR level of single carrier system (with roll-of-factor=0.10).

An interest to increase the capacity of multicarrier system such as multi-carrier code division multiple access (MC-CDMA) is attracting many studies to develop spreading code for a higher user capacity. In this paper, we proposes a new large spreading code set that is capable of increasing the capacity of MC-CDMA more than twice, offering better performance due to its uniform low cross correlations and high autocorrelation properties and has an additional advantage to reduce peak power of the orthogonal frequency division multiplexing (OFDM) transmit signals. By the proposed code, peak-to-average power ratio (PAPR) of OFDM system can be reduced up to the PAPR level of single carrier system (for some roll-of-factor values). Our proposed code with code length of N, has large code number of K=2N+1 for supporting 2N+1 users, while the conventional spreading codes is up to K=N+M, where M≥N. The capacity of 2N+1 means that 2N+1 users or data symbols are able to be transmitted over only N subcarriers. Our results confirms that the proposed code outperforms current famous pseudo-orthogonal carrier interferometry (POCI) code with gain of 3dB at bit-error-rate (BER) level of 10−6 in additive white Gaussian noise (AWGN) channel and gain of more than 4dB in multipath fading channel.