The combination of multiple-input multiple-output (MIMO) technology and sparse code multiple access (SCMA) can significantly enhance the spectral efficiency of future wireless communication networks. However, the receiver design for downlink MIMO-SCMA systems faces challenges in developing multi-user detection (MUD) schemes that achieve both low latency and low bit error rate (BER). The separated detection scheme in the MIMO-SCMA system involves performing MIMO detection first to obtain estimated signals, followed by SCMA decoding. We propose an enhanced separated detection scheme based on lightweight graph neural networks (GNNs). In this scheme, we raise the concept of coordinate point relay and full-category training, which allow for the substitution of the conventional message passing algorithm (MPA) in SCMA decoding with image classification techniques based on deep learning (DL). The features of the images used for training encompass crucial information such as the amplitude and phase of estimated signals, as well as channel characteristics they have encountered. Furthermore, various types of images demonstrate distinct directional trends, contributing additional features that enhance the precision of classification by GNNs. Simulation results demonstrate that the enhanced separated detection scheme outperforms existing separated and joint detection schemes in terms of computational complexity, while having a better BER performance than the joint detection schemes at high Eb/N0 (energy per bit to noise power spectral density ratio) values.

Energy harvesting has been widely investigated as a potential solution to supply power for Internet of Things (IoT) devices. Computing devices must operate intermittently rather than continuously, because harvested energy is unstable and some of IoT applications can be periodic. Therefore, processors for IoT devices with intermittent operation must feature a hibernation mode with zero-standby-power in addition to energy-efficient normal mode. In this paper, we describe the layout design and measurement results of a nonvolatile standard cell memory (NV-SCM) and nonvolatile flip-flops (NV-FF) with a nonvolatile memory using Fishbone-in-Cage Capacitor (FiCC) suitable for IoT processors with intermittent operations. They can be fabricated in any conventional CMOS process without any additional mask. NV-SCM and NV-FF are fabricated in a 180nm CMOS process technology. The area overhead by nonvolatility of a bit cell are 74% in NV-SCM and 29% in NV-FF, respectively. We confirmed full functionality of the NV-SCM and NV-FF. The nonvolatile system using proposed NV-SCM and NV-FF can reduce the energy consumption by 24.3% compared to the volatile system when hibernation/normal operation time ratio is 500 as shown in the simulation.

Sparse code division multiple access (SCMA) is a non-orthogonal multiple access (NOMA) technology that can improve frequency band utilization and allow many users to share quite a few resource elements (REs). This paper uses the modulation of lattice theory to develop a systematic construction procedure for the design of SCMA codebooks under Gaussian channel environments that can achieve near-optimal designs, especially for cases that consider large-scale SCMA parameters. However, under the condition of large-scale SCMA parameters, the mother constellation (MC) points will overlap, which can be solved by the method of the partial dimensions transformation (PDT). More importantly, we consider the upper bounded error probability of the signal transmission in the AWGN channels, and design a codeword allocation method to reduce the inter symbol interference (ISI) on the same RE. Simulation results show that under different codebook sizes and different overload rates, using two different message passing algorithms (MPA) to verify, the codebook proposed in this paper has a bit error rate (BER) significantly better than the reference codebooks, moreover the convergence time does not exceed that of the reference codebooks.

Sparse code multiple access (SCMA) based on the message passing algorithm (MPA) for multiuser detection is a competitive non-orthogonal multiple access technique for fifth-generation wireless communication networks Among the existing multiuser detection schemes for uplink (UP) SCMA systems, the serial MPA (S-MPA) scheme, where messages are updated sequentially, generally converges faster than the conventional MPA (C-MPA) scheme, where all messages are updated in a parallel manner. In this paper, the optimization of message scheduling in the S-MPA scheme is proposed. Firstly, some statistical results for the probability density function (PDF) of the received signal are obtained at various signal-to-noise ratios (SNR) by using the Monte Carlo method. Then, based on the non-orthogonal property of SCMA, the data mapping relationship between resource nodes and user nodes is comprehensively analyzed. A partial codeword transmission of S-MPA (PCTS-MPA) with threshold decision scheme of PDF is proposed and verified. Simulations show that the proposed PCTS-MPA not only reduces the complexity of MPA without changing the bit error ratio (BER), but also has a faster convergence than S-MPA, especially at high SNR values.

Scaling supply voltage (VDD) and threshold voltage (Vth) dynamically has a strong impact on energy efficiency of CMOS LSI circuits. Techniques for optimizing VDD and Vth simultaneously under dynamic workloads are thus widely investigated over the past 15 years. In this paper, we refer to the optimum pair of VDD and Vth, which minimizes the energy consumption of a circuit under a specific performance constraint, as a minimum energy point (MEP). Based on the simple transregional models of a CMOS circuit, this paper derives a simple necessary and sufficient condition for the MEP operation. The simple condition helps find the MEP of CMOS circuits. Measurement results using standard-cell based memories (SCMs) fabricated in a 65-nm process technology also validate the condition derived in this paper.

Subcarrier mapping (SCM) is considered to be crucial for capacity-maximization in orthogonal frequency division multiplexing (OFDM) relaying networks and has been investigated extensively. However, no study has examined its exact or approximate close-form analysis under Nakagami-m fading. This paper considers the ordered subcarrier pairing schemes, i.e., worst-to-best (WTB) SCM and best-to-best (BTB) SCM, for the analysis of bit error rate (BER) and capacity of a dual-hop OFDM amplify-and-forward (AF) relay system. The system-analysis is presented for Nakagami-m fading with emphasis on two special cases: one-sided Gaussian fading ($(m=rac{1}{2})$) and Rayleigh fading (m=1). Close-form expressions for the probability density function (PDF) and moment generating function (MGF) of end-to-end SNR are derived while considering fixed gain AF relays. The classical MGF and PDF based approaches are used to compare the BER performance of the system with WTB SCM and BTB SCM schemes. Close-form expressions for the upper bound on ergodic capacity are derived by analyzing Jensen's inequality. Accurate analysis is presented for integer m while the non-integer m values allow the derivations of approximate expressions. The accuracy of the suggested approximation is verified analytically as well as numerically. The simulation results validate the analysis in Nakagami-m fading channel.

Co-channel interference (CCI) is becoming a challenging factor that causes performance degradation in modern communication systems. The receiver equipped with multiple antennas can suppress such interference by exploiting spatial correlation. However, it is difficult to estimate the spatial covariance matrix (SCM) of CCI accurately with limited number of known symbols. To address this problem, this paper first proposes an improved SCM estimation method by shrinking the variance of eigenvalues. In addition, based on breadth-first tree search schemes and improved channel updating, a low complexity iterative detector is presented with channel preprocessing, which not only considers the existence of CCI but also reduces the computational complexity in terms of visited nodes in a search tree. Furthermore, by scaling the extrinsic soft information which is fed back to the input of detector, the detection performance loss due to max-log approximation is compensated. Simulation results show that the proposed iterative receiver provides improved signal to interference ratio (SIR) gain with low complexity, which demonstrate the proposed scheme is attractive in practical implementation.

In time-varying frequency selective channels, to obtain high-rate joint time-frequency diversity, linear dispersion coded orthogonal frequency division multiplexing (LDC-OFDM), has recently been proposed. Compared with OFDM systems, single-carrier systems may retain the advantages of lower PAPR and lower sensitivity to carrier frequency offset (CFO) effects, which motivates this paper to investigate how to achieve joint frequency and time diversity for high-rate single-carrier block transmission systems. Two systems are proposed: linear dispersion coded cyclic-prefix single-carrier modulation (LDC-CP-SCM) and linear dispersion coded zero-padded single-carrier modulation (LDC-ZP-SCM) across either multiple CP-SCM or ZP-SCM blocks, respectively. LDC-SCM may use a layered two-stage LDC decoding with lower complexity. This paper analyzes the diversity properties of LDC-CP-SCM, and provides a sufficient condition for LDC-CP-SCM to maximize all available joint frequency and time diversity gain and coding gain. This paper shows that LDC-ZP-SCM may be effectively equipped with low-complexity minimum mean-squared error (MMSE) equalizers. A lower complexity scheme, linear transformation coded SCM (LTC-SCM), is also proposed with good diversity performance.

Beamforming with sparse constraint has shown significant performance improvement. In this letter, a least squares constant modulus blind adaptive beamforming with sparse constraint is proposed. Simulation results indicate that the proposed approach exhibits better performance than the well-known least squares constant modulus algorithm (LSCMA).

Blind beamforming plays an important role in multiple-input multiple-output (MIMO) Systems, radar, cognitive radio, and system identification. In this paper, we propose a new algorithm for multiple blind beamforming algorithm based on the least square constant modulus algorithm (LSCMA). The new method consists of the following three parts: (a) beamforming of one signal with LSCMA. (b) direction-of-arrival (DOA) estimation of the remaining signals by rooting the weight vector polynomial. (c) beamforming of the remaining signals with linear constraints minimum variance (LCMV) method. After the convergence of LSCMA, one signal is captured and the arrival angles of the remaining signals can be obtained by rooting the weight vector polynomial. Therefore, beamforming can be quickly established for the remaining signals using LCMV method. Simultaneously the DOA of the signals can also be obtained. Simulation results show the performance of the presented method.

To mitigate the asynchronous ICI (Inter-Cell Interference), SCM (Spatial Covariance Matrix) of the asynchronous ICI plus background noise should be accurately estimated for MIMO-OFDMA (Multiple-input Multiple-output-Orthogonal Frequency Division Multiple Access) system. Generally, it is assumed that the SCM of the asynchronous ICI plus background noise is estimated by using training symbols. However, it is difficult to measure the interference statistics for a long time and considering that training symbols are not appropriate for OFDMA system such as LTE (3GPP Long Term Evolution). Therefore, noise reduction method is required to improve the estimation accuracy. Although the conventional time-domain low-pass type weighting method can be effective for noise reduction, it causes significant estimation error due to the spectral leakage in practical OFDM system. Therefore, we propose a time-domain sinc type weighing method which can not only reduce noise effectively minimizing estimation error caused by the spectral leakage but also can be implemented using frequency-domain weighted moving average filter easily. We also consider the iterative CFR (Channel Frequency Response) and SCM estimation method which can effectively reduce the estimation error of both CFR and SCM, and improve the performance for LTE system. By using computer simulation, we show that the proposed method can provide up to 2.5 dB SIR (Signal to Interference Ratio) gain compared with the conventional method, and verify that the proposed method is attractive and suitable for implementation with stable operation.

We propose frequency shifted optical single sideband (OSSB), a novel OSSB modulation scheme. It uses a continuous wave to up-convert the source signal, and the signal and the continuous wave then undergo suppressed carrier OSSB modulation simultaneously. This scheme inherently has no unwanted sidebands, even if the suppressed carrier OSSB modulator is defective. Experiments of 12 GHz RF signal transmission confirm that it achieves 2.4 dB relaxation in chromatic dispersion power fading under the condition of 15 dB SSR.

We propose optical wireless multiple-input multiple-output (OMIMO) communications to achieve high speed transmission with a compact transmitter and receiver. In OMIMO, by using zero forcing (ZF), minimum mean square error (MMSE) or other detection techniques, we can eliminate the interference from the other optical transmit antennas. In this paper, we employ ZF as the detection technique. We analyze the signal-to-interference-plus-noise ratio (SINR) and the bit error rate (BER) of the proposed OMIMO with a linear array and a square array of optical transmit and receive antennas, where we employ subcarrier multiplexing (SCM) for each optical transmit antenna. Note that the proposed OMIMO is applicable to other arrangements of optical transmit and receive antennas. We show that the proposed OMIMO system can realize MIMO multiplexing and achieve high speed transmission by correctly aligning the optical transmit and receive antennas and the transmitter semiangle.

Fiber-optic access system integration is the key to providing various kinds of services to home users. The combination of ATM- and SCM-PON systems is essential to support a high-speed data service and analog/digital video distribution services. From this viewpoint, a frequency-division- multiplexing technique for digital baseband and subcarrier multiplexed signals is required to achieve system integration. However, system integration for these two access systems has not been fully investigated yet. The SCM-PON system, which uses a super wideband optical FM converter, will enable these two different kinds of access system (ATM and SCM) to be integrated. In this paper, we describe experimentally obtained results for frequency- division-multiplexed signals consisting of digital baseband and subcarrier- multiplexed signals. The experiments were carried out using a 622-Mb/s baseband signal and an FM-converted signal containing AM and 64QAM signals. The experimental results reveal that the inter-channel interference between the digital baseband and FM-converted signals restricts the number of subcarriers for AM and 64QAM. With an intermediate frequency of 3 GHz for the FM-converted signal, an FDM signal consisting of 622-Mb/s baseband, 30 carriers of 64QAM, and 11 carriers of AM was successfully transmitted.

In this paper, we present the theoretical analysis of the bit error rate (BER) performance of Single-Carrier Modulation (SCM) and Orthogonal Frequency Division Multiplexing (OFDM) systems under two types of temporally localized man-made noises (generalized shot noise and bursty noise models) environments. The robustness of OFDM system against these two kinds of man-made noises is discussed and then compared with that of SCM system at the same transmission rate. We show that for OFDM system, the BER performance highly depends on the number of subcarriers and the strength of the man-made noise, i.e., the level of the power spectral density of the man-made noise. In addition to the common knowledge on OFDM, we show that OFDM system is sometime less robust to the man-made noises than SCM system.

This paper proposes a nonlinear distortion suppression scheme for optical direct FM Radio-on-Fiber system. This scheme uses the interaction between the nonlinearities of DFM-LD and OFD to suppress a 3rd order intermodulation distortion. We theoretically analyze the carrier to noise-plus-distortion ratio (CNDR) and show a controlling method in the MZI type OFD to realize the proposed suppression scheme.

This paper proposes a nonlinear distortion suppression scheme for optical direct FM Radio-on-Fiber system. This scheme uses the interaction between the nonlinearities of DFM-LD and OFD to suppress a 3rd order intermodulation distortion. We theoretically analyze the carrier to noise-plus-distortion ratio (CNDR) and show a controlling method in the MZI type OFD to realize the proposed suppression scheme.

This paper describes the implementation and demonstration of local networks for the hyper-media photonic information network (HM-PIN), a candidate for the information service platform offering broadcast and telecommunication services. In addition, the feasibility of the HM-PIN is also demonstrated using prototype local network systems. This local network adopts architecture based on wavelength-division-multiplexing (WDM) and broadcast-and-select (B&S) switching, and supports all HM-PIN services except inter-local-network communication. The major issues of this proposed network are the technologies that support many broadcast channels and reduce channel selection cost. This paper also considers the combination of WDM technology and three alternatives: electrical TDM, subcarrier multiplexing (SCM or electrical FDM), and optical TDM (O-TDM). Three 128 ch (8 wavelengths 16 channels) WDM B&S prototype systems are built to demonstrate the feasibility of the proposed HM-PIN. In WDM/SCM, 30 and 20 Mb/s channels are realized as 16-QAM and 64-QAM, and 155 Mb/s channels are realized by WDM/TDM. Moreover, these three prototypes were connected to form a small HM-PIN and applications such as video distribution and IP datagram cut-through are demonstrated. Furthermore, the delay and throughput of the HM-PIN are evaluated by connecting a local network to a 200-km WDM-ring backbone network. Our discussions and demonstrations confirm the impact and feasibility of the proposed hyper-media photonic information network.

This paper describes the implementation and demonstration of local networks for the hyper-media photonic information network (HM-PIN), a candidate for the information service platform offering broadcast and telecommunication services. In addition, the feasibility of the HM-PIN is also demonstrated using prototype local network systems. This local network adopts architecture based on wavelength-division-multiplexing (WDM) and broadcast-and-select (B&S) switching, and supports all HM-PIN services except inter-local-network communication. The major issues of this proposed network are the technologies that support many broadcast channels and reduce channel selection cost. This paper also considers the combination of WDM technology and three alternatives: electrical TDM, subcarrier multiplexing (SCM or electrical FDM), and optical TDM (O-TDM). Three 128 ch (8 wavelengths 16 channels) WDM B&S prototype systems are built to demonstrate the feasibility of the proposed HM-PIN. In WDM/SCM, 30 and 20 Mb/s channels are realized as 16-QAM and 64-QAM, and 155 Mb/s channels are realized by WDM/TDM. Moreover, these three prototypes were connected to form a small HM-PIN and applications such as video distribution and IP datagram cut-through are demonstrated. Furthermore, the delay and throughput of the HM-PIN are evaluated by connecting a local network to a 200-km WDM-ring backbone network. Our discussions and demonstrations confirm the impact and feasibility of the proposed hyper-media photonic information network.

We propose a method of reducing laser-clipping-induced distortion in a subcarrier multiplexed (SCM) optical-cable TV system. This scheme reduces amplitude peaks of the SCM signal by controlling the phases of video carriers to prevent the clipping which occurs when these peaks fall below the threshold of a laser-diode. It is experimentally shown that using this method reduces the bit error rate in an AM-VSB / QAM hybrid optical-transmission system.