Superposition Modulation Research Articles

Power domain superimposed modulation method based on dimensional level transformation and 5D constellation shaping.

This paper proposes a power domain superposition modulation method based on dimensional level transformation and five dimensions (5D) constellation shaping. Stacking a regular triangular pyramid and enhancing it in terms of dimensions achieves the geometric shaping of the 5D constellation. Based on this, signal superposition in the power domain is achieved through dimensional transformation for data modulation. Experimental verification was conducted on a 2 km seven-core fiber in an IM/DD system. Compared to the traditional 2D-32QAM, this method can achieve a 0.7 dB gain at high received optical power and a 0.4 dB receiver sensitivity gain at a BER of 3.8 × 10-3.

A Reliable and Energy Efficient Superposition Modulation and SVD-Aided Detection Based Multiuser OFDM-DCSK Paired Transceiver for IoT Devices

A Reliable and Energy Efficient Superposition Modulation and SVD-Aided Detection Based Multiuser OFDM-DCSK Paired Transceiver for IoT Devices

AN OPTIMIZATION ALGORITHM FOR SPARSE CODE MULTIPLE ACCESS CODEBOOK TO MAXIMIZE MUTUAL INFORMATION IN 5G

Sparse code multiple access (SCMA) codebook optimization algorithms strive to reduce complexity with negligible loss at the transmitting end but add more complexity at the receiver, such that the retrieved information is minimal. To optimize mutual information in 5G using SCMA, an efficient codebook optimization algorithm is presented. The SCMA signal model is considered first using a superposition modulation structure with a column expanded channel matrix. The superposition model accurately describes the link between the received signal and the codebook matrix. An iterative codebook optimization approach based on the above model is suggested to maximize (continuous output and discrete input) mutual information. This method effectively adapts random channel coefficients to multiuser channels; both additive white Gaussian noise (AWGN) and non-AWGN channels are available to perform well with the proposed technique, according to simulation findings. Furthermore, the proposed optimization algorithm for SCMA codebook works well with the message passing algorithm.

Superposition Modulation for Physical Layer Security in Water-to-Air Visible Light Communication Systems

In this paper, we propose a physical layer security (PLS) scheme based on superposition modulation for water-to-air (W2A) visible light communication (VLC) systems. We characterize the high correlation between W2A and air-to-water (A2W) link gains from ray tracing simulation and experiments. The proposed scheme selects the modulation order and superposition parameter based on the high correlation between the W2A and A2W link gains. The scheme performance is studied by exploring its immunity against different types of attacks. The symbol error rates (SERs) are analyzed for both random and correlated attacks. Based on the link gains from real measurements, it is shown that under random attack Eve's SER exceeds 0.77 when Eve's signal-to-noise ratio (SNR) varies from 5 dB to 30 dB, and under correlated attack Eve's SER decreases only for a high correlation coefficient when Eve is close enough to Bob, which is unrealistic for eavesdropping. In addition, the entropy of potential set under post-processing attack is derived and the complexity of successful cracking increases with the modulation set size. For intelligent attack, two unsupervised algorithms, namely K-means clustering and expectation maximization (EM) algorithm, are adopted for modulation identification. The distributions of Eve' SER under all four attacks are investigated based on the measured link gains in the laboratory environment, which demonstrates that intelligent attack with K-means clustering possesses the highest eavesdropping capability. However, more numerical results show that for intelligent attack with K-means clustering under wavy water surface, the proportion of the case where Eve has a higher SER than Bob is lower than 0.5 only when Eve lies between Alice and Bob with small horizontal distance, which is unrealistic for eavesdropping operation.

On-Chip Circulator-Free Chirped Spiral Multimode Waveguide Grating for Dispersion Management

Waveguide gratings are one of the key optical dispersion handling devices and are highly desired for many on-chip photonic systems. However, most of the previously reported waveguide gratings require optical circulators to separate input and reflected signals. Here, a circulator-free chirped spiral multimode waveguide grating (SMWG) composed of an asymmetric chirped multimode waveguide grating and a mode (de)multiplexer is first proposed and demonstrated for dispersion management on a silicon-on-insulator (SOI) platform. The chirped SMWG reflects the TE0 mode into the TE1 mode so that input and reflected signals can be separated with the assistance of a mode (de)multiplexer instead of a circulator. The spiral waveguide with a continuously varying radius enables a large amount of dispersion within a compact footprint. Group delay ripples are suppressed by superposition modulation on lateral corrugations. The fabricated 5 mm chirped SMWG realizes a maximum group delay of 150 ps and dispersion of 6.49 ps/nm within a bandwidth of 22 nm. The proposed circulator-free chirped SMWG will find many applications such as optical communication, microwave photonics, and pulse compression.

Theoretical and experimental study of inversion of spectral absorption function using experimental data of laser absorption spectrum with slow scanning and fast modulation of wavelength

Based on the tested data of laser absorption spectra, a matrix slicing method is proposed to invert the absorption function of spectral lines by using the two parameters of laser modulation frequency and laser scanning range as well as transmitted wave signal and reference wave signal under the condition of slow uniform scanning wavelength and fast periodic modulation wavelength. When the modulation is single frequency sinusoidal modulation, an accurate contour of the spectral line absorption function can be obtained by using the matrix data consisting of the values of the transmitted wave signal by the reference wave signal through the minimum value of two slice integrals with the interval of half modulation period, and the amplitude of modulation can be estimated. When the fast modulation of the wavelength is distorted to the multi-frequency superposition modulation, the absorption function is also formed by using the complementarity of multiple slices. The method above is utilized for investigating a real absorption function inversion process involving multiple overlapping absorption lines in the range of the scanning wavelengths. Moreover, the scanning range of laser wavelength can be calibrated by the interval parameters of several spectral lines in the scanning wavelength range. The absorption function of CO at 4300.700 cm<sup>–1</sup> and CO<sub>2</sub> at 6336 cm<sup>–1</sup> are successfully obtained by using this matrix slice method for experimental verification.

Performance Analysis of Fountain Coded Non-Orthogonal Multiple Access With Finite Blocklength

Driven by the increasing demand for high reliability and low latency, finite blocklength communications have recently become the focus of the communication research field. In this letter, to achieve high reliability and low latency communication, we propose the cross-layer design of fountain coded two-user non-orthogonal multiple access (NOMA) system with finite blocklength. Specifically, the message for each user is firstly encoded by an application-layer fountain code at the base station (BS). Then, each fountain-coded packet for each user is encoded by a physical-layer channel code into a frame. Finally, the BS sends the frames to these two users by using superposition modulation. Under the reliability constraints of two users, the relationship among the application-layer code rate, the physical-layer data rate, and the optimal power allocation coefficient is derived to minimize the transmission latency. The numerical analysis and simulation results show that the message transmission latency of the proposed cross-layer scheme is much lower than that of the scheme which only adopts physical-layer channel codes in the finite blocklength NOMA system.

Multi-Frequency Multi-Amplitude Superposition Modulation Method With Phase Shift Optimization for Single Inverter of Wireless Power Transfer System

In wireless charging devices, different wireless charging standards have caused charging incompatibility, and the utilization rate of the DC voltage at the transmitter is not high, which brings challenges to the application of wireless charging. To solve these two problems, this paper proposes a multi-frequency multi-amplitude (MFMA) superimposition modulation method. This method superimposes multiple frequency signals, and then compares the synthesized signal with a high-frequency triangular carrier to output a square wave voltage signal containing information such as the frequency and amplitude of the pre-output signal. Furthermore, a phase-shifting optimization algorithm is proposed, i.e., based on the proposed MFMA superimposition modulation method, the utilization rate of the DC voltage of the system is improved by reasonably adjusting the initial phase of each frequency. Simulation and experimental results show that the proposed method can output at least four frequencies simultaneously by using a single inverter, effectively reducing the volume of the transmitter, and being compatible with the frequency range of several charging standards. The proposed phase-shifting optimization has a significant effect on improving the utilization of DC voltage with an increase of 44.88%.

On the Optimal Precoding for MISO-WSN: One Time Slot Detection of Multiple Binary Data on the Same Frequency Band

A fast multi-target detection technique-using a devised precoding in a wireless sensor network (WSN)-is proposed. The targets are detected by binary wireless sensors which only have one or zero logical outputs, indicating a target's presence or absence. The goal is to simultaneously decode all sensors' data in one time slot at the receiver node, where all sensors transmit data simultaneously on the same frequency band. For this to happen, a specific geometric deployment of the sensors is presented in the paper. The concept in this work might have similarities to the bijective mappings in the superposition modulation. Different channel gains and the additive white Gaussian noise are included in the model. The system model is described in detail and the communication scheme to fulfill a simultaneous decoding is mathematically formulated. Then, the parametric solutions to this general digital modulation problem are studied step by step through several theorems, and the optimal solutions that minimize the detection error are found. The combined effects of the noise and the non-perfect channel state information on the signal constellations are both analytically and numerically investigated. In addition, two other detection scenarios with a priori information about the targets are studied.

A Collision Resolution Protocol for Random Access in Massive MIMO

In 5G and beyond wireless scenarios, it is expected to support tremendous amount of communicating machines. With an exponential increase of machine-to-machine (M2M) system deployments, efficient approaches to massive access by a large number of devices are to be studied. In this paper, we propose a massive multiple-input multiple-output (MIMO) based grant-free random access (RA) with resolution of preamble collision for massive access. Based on the channel hardening and favorable propagation characteristics of massive MIMO, collided signals processed at the base station (BS) can be viewed as a variation of superposition modulation, and are to be recovered by successive interference cancellation (SIC) techniques. Besides, taking into consideration the effect of pass loss and fractional power control (FPC), analytic expressions of success probability of the proposed collision resolution with conjugate beamforming (CB) and zero-forcing beamforming (ZFB) are derived. With simulation results, we verify the analyses and show that the proposed protocol can resolve most preamble collisions.

Efficient Information Transmission Using Smart OFDM for IoT Applications

Orthogonal frequency-division multiplexing (OFDM) is one of the most widely adopted modulation schemes because it offers several desirable features, such as spectral efficiency and low complexity implementation. Moreover, it is highly suitable for adaptive implementation. Nevertheless, OFDM does not have any special immunity against multipath fading as compared to single-carrier systems. Therefore, we propose in this article a new OFDM configuration, denoted as OFDM-smart (OFDM-S), where superposition modulation is used to introduce transmit diversity to reduce the bit error rate (BER) while maintaining the spectral efficiency and bit rate fixed. The proposed scheme is based on clustering specific subcarriers that can cooperate by sharing their transmission resources. The cooperation is performed such that all subcarriers transmit their data jointly using all the subcarriers within their cluster. The system performance is derived in terms of BER performance over Nakagami- $m$ frequency-selective fading channels where efficient expressions are presented in terms of a single finite integral, and closed-form expressions are derived for the asymptotic BER. The obtained analytical results corroborated by simulation show that the OFDM-S can provide substantial BER improvement over conventional OFDM, due to the transmit diversity.

A PAPR reduction scheme combining superimposed O-OFDM and [formula omitted]-law mapping for VLC-OFDM systems

Due to the high peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals, the inherent nonlinearity of light emitting diodes (LEDs) is a challenge for optical OFDM (O-OFDM) schemes in visible light communication (VLC) systems. In order to reduce PAPR to mitigate the effects of the nonlinearity of LEDs, and avoid the asymmetric clipping interference in the conventional hybrid O-OFDM schemes, a novel superimposed O-OFDM scheme is proposed in this paper, which reduce the PAPR by combining the μ-law mapping and the superposition modulation. Moreover, at the transmitter, the hybrid O-OFDM components are superimposed in an interference-free way, the receiver does not require the operation of interference cancellation, and the symbols of each branch can be demodulated independently. Simulation results verify that the proposed scheme can significantly reduce the PAPR. At the same time, the comprehensive performance of the proposed scheme outperforms other competing schemes under the constraints of the nonlinearity and limited dynamic range of LEDs.

Superposition modulation–based new structure of four-dimensional turbo code (4D-TC) using modified interleaver and its application in WiMAX & LTE systems

Performance estimations of various kinds of turbo codes (TCs) and their applications in modern communication systems have been emerged as one of the potential research areas in recent past. In this paper, a modified interleaver-driven binary 4-Dimensional Turbo Code (4D-TC) using superposition modulation (SM) technique has been projected to intensify the minimum hamming distance (MHD). MHD (dmin) of the proposed structure has been amplified by incorporating feedback polynomial in primitive form for a fixed interleaver length. Moreover, improved dmin has further been achieved by introducing a modified interleaver which has been used to ensure scattering and mixing operation on the incoming bits in an appropriate manner. Furthermore, upper bound of the proposed structure has been evaluated and comprehensive asymptotic behavior of the proposed code has been analyzed in terms of dmin by adopting two analytical approaches namely finite length rule and asymptotic spectral shape function. Finally, to prove the superiority of the proposed structure, a comparative study of the BER performance of different forms of TCs have been carried out in WiMAX under numerous fading settings. Moreover a comparative BER analysis has also been done in long term evolution (LTE) system as well.

Efficient relay selection scheme utilizing superposition modulation in cooperative communication

In this paper, a cooperative communication scheme is proposed utilizing superposition modulation (SM) in orthogonal frequency division multiplexing (OFDM). The proposed relay selection scheme selects an optimal relay and improves the BER performance by utilizing SM in cooperative communication. Also, the proposed cooperative communication scheme transmits the signal of source and relay at the same time by utilizing SM. As a result, the proposed schemes select the optimal relay and improve the reliability and throughput compared with the conventional cooperative communication scheme.

Multiple non-diffracting beams by reflective surface based on admittance superposition

A method to produce multiple nondiffracting beams by a reflective metasurface is introduced. The reflective metasurface is realized by admittance superposition modulation. Only one artificial admittance surface can generate a single nondiffracting beam. The admittance superposition of multiple surfaces will produce multiple beams, which can propagate in different directions with good nondiffracting properties. Finally, the metasurface is fabricated and experimentally tested, and the results demonstrate that the design is logical. The multiple nondiffracting beams may have potential applications in imaging, multipoint communications, and object detection and identification.

Optimized Low Density Superposition Modulation for 5G Mobile Multimedia Wireless Networks

Optimized Low Density Superposition Modulation for 5G Mobile Multimedia Wireless Networks

An Efficient SCMA Codebook Design Based on 1-D Searching Algorithm

This letter proposes an efficient sparse code multiple access (SCMA) codebook design, in which 1-D searching algorithm is introduced to minimize the upper bound of pair-wise error probability (PEP). Firstly, an SCMA signal model is given according to superposition modulation. Our analysis shows that under the proposed amplitude and phase rotation settings, each user has the same mutual information lower bound. In addition, the superimposed constellation points on each sub-channel belong to the same set, which depends on only one amplitude variable. Therefore, 1-D searching on this variable is introduced and the performance metric is upper bound of PEP. It is demonstrated that the calculated upper bound can well predict the receiver performance with maximum likelihood detection. In addition, the performance of the proposed codebook is verified with message passing algorithm at the receiver. The simulation results show that the PEP and bit error rate of the proposed codebook is better than that of the existing codebooks.

An Efficient SCMA Codebook Optimization Algorithm Based on Mutual Information Maximization

An efficient codebook optimization algorithm is proposed to maximize mutual information in sparse code multiple access (SCMA). At first, SCMA signal model is given according to superposition modulation structure, in which the channel matrix is column‐extended. The superposition model can well describe the relationship between the codebook matrix and received signal. Based on the above model, an iterative codebook optimization algorithm is proposed to maximize mutual information between discrete input and continuous output. This algorithm can efficiently adapt to multiuser channels with arbitrary channel coefficients. The simulation results show that the proposed algorithm has good performance in both AWGN and non‐AWGN channels. In addition, message passing algorithm (MPA) works well with the codebook optimized according to the proposed algorithm.

Superposition Modulation-Based Cooperation for Oversampled OFDM Signals

This paper proposes an iterative detector for uncoded OFDM signals in cooperative networks, where the information symbols are simply partitioned through a time-domain matrix at the OFDM transmitter. We analytically show that our proposed iterative detector at the partner node converges and can completely recover the user’s data from its partitioned version, if sufficient redundancy is inserted in the user’s data. For efficient use of the redundancy in the user’s data, a coded cooperative transmission based on superposition modulation is proposed. Additionally, a closed-form input–output relationship for the partitioning and reconstruction algorithm in the proposed cooperative scenario is derived. We also obtain closed-form expressions for symbol error rate performance of the proposed coded cooperative scenario over Rayleigh frequency-selective fading channels. Numerical comparisons shed light on the relative merits of the proposed coded cooperation under various inter-user and uplink channel conditions.

A Channel Estimation and Data Transmission Scheme Utilizing Superposition Modulation for Cooperative Communication

In cooperative communication, the channel estimation is important because the channel influences the transmission signal. General channel estimation schemes are conducted before the information signal. But, the channel is time-varying, dynamic and unpredictable. To cope with a constantly changing channel, a new scheme is proposed. In the proposed scheme, the new transmission signal utilizing superposition modulation is used. The proposed transmission signal is superimposed to the pilot signal for the channel estimation and the information signal for the transmission of information signal. As a result, the proposed scheme has similar to the bit error rate performance and throughput compared to when the channel estimation perfectly is performed. By using the proposed transmission signal in cooperative communication, the proposed scheme can estimate the channel through information signal and transmit the information signal at the same time. Therefore, the proposed scheme can estimate the channel that passes information signal and transmit information signal at the same time.