Signal Constellation Research Articles

Benchmarking and Interpreting End-to-End Learning of MIMO and Multi-User Communication

End-to-end autoencoder (AE) learning has the potential of exceeding the performance of human-engineered transceivers and encoding schemes, without a priori knowledge of communication-theoretic principles. In this work, we aim to understand to what extent and for which scenarios this claim holds true when comparing with fair benchmarks. Our particular focus is on memoryless multiple-input multiple-output (MIMO) and multi-user (MU) systems. Four case studies are considered: two point-to-point (closed-loop and open-loop MIMO) and two MU scenarios (MIMO broadcast and interference channels). For the point-to-point scenarios, we explain some of the performance gains observed in prior work through the selection of improved baseline schemes that include geometric shaping as well as bit and power allocation. For the MIMO broadcast channel, we demonstrate the feasibility of a novel AE method with centralized learning and decentralized execution. Interestingly, the learned scheme performs close to nonlinear vector-perturbation precoding and significantly outperforms conventional zero-forcing. Lastly, we highlight potential pitfalls when interpreting learned communication schemes. In particular, we show that the AE for the considered interference channel learns to avoid interference, albeit in a rotated reference frame. After de-rotating the learned signal constellation of each user, the resulting scheme corresponds to conventional time sharing with geometric shaping.

Optical format interconversion nodes between OOK and QPSK enabled by a reconfigurable two-dimensional vector mover.

An optical format interconversion scheme between on-off keying (OOK) and quadrature phase shift keying (QPSK) is proposed and verified in this paper. The conversion system mainly consists of a coherent vector combiner and a reconfigurable two-dimensional (2D) vector mover. As a key element of the proposed conversion system, the 2D vector mover is implemented by a non-degenerate phase-sensitive amplifier (PSA). The operating principle and theoretical derivations of the PSA-based 2D vector mover are fully introduced. The reconfigurable transfer characteristics of the vector mover are analyzed under different parameter settings to exhibit the flexible 2D moving function. The signal constellations, eye diagrams, spectrum, error vector magnitudes, and bit error ratios are estimated and depicted to validate the proposed idea. With the input signal-to-noise ratios of 20 dB and 25 dB, error-free conversions are achieved between 50G Baud OOK and QPSK. The scheme proposed in this paper fills the lack of the one-to-one interconversion between OOK and QPSK, and has potential applications in optical interconnect nodes, across-dimensional optical transmissions, and flexible optical transceivers.

Development and Application of Smart Home Energy Management System Based on Wireless Network Technology

In order to solve the problem of integration of home energy management system and wireless network technology, the author proposes the development and application of a smart home energy management system based on wireless network technology. Divide the NB-IoT into different simulation levels, simulate the physical layer of the NB-IoT, and according to the household energy conservation rules, calculate the household energy distribution parameters, convert the intelligent control signal into a signal constellation point, calculate the deviation value of the control command corresponding to the energy equipment, build an intelligent control simulation algorithm, and finally complete the simulation of the intelligent control system. Experimental results show the following: The simulation method in the intelligent home language input terminal control system is based on the Internet of Things, the average time of simulating the test point of energy equipment is about 4.9 s, the required simulation time is long, and in the intelligent control system of the mobile road tunnel lighting vehicle, the simulation time required by the designed simulation method is about 6.8 s, and the simulation time is the longest. The average time of the method proposed by the author to simulate the energy distribution instruction is about 3.3 s. Conclusion. The application prospect of a smart home energy management system based on wireless network technology is very broad.

Signal Demodulation Using a Radial Basis Function Neural Network (RBFNN) in a Silicon Photomultiplier-Based Visible Light Communication System

A silicon photomultiplier (SiPM) contains an array of microcells that can each detect individual photons. Consequently, it can arguably result in the most sensitive receiver in visible light communication (VLC). However, each microcell needs a period of several nanoseconds to recover after detecting a photon. This creates a non-linear response and introduces a unique form of inter-symbol interference. In this paper, we first show that this interference splits each element of the received signal constellation into multiple clusters. This observation motivates the investigation into the use of a Radial Basis Function Neural Network (RBFNN) to deal with the impact of the nonlinearity. Both the training procedures and the performance of the RBFNN are explained and discussed in detail. The influence of the number of the RBFNN centers, the widths of the centers, the constellation size and the period of the transmitted signal samples on the system performance are investigated. In addition, two different RBFNN-based data demodulation methods are introduced. The simulation results suggest that the new RBFNN-aided receivers reduce the negative impacts of the SiPM nonlinearity and can result in lower bit error rates (BERs) for a wide range of irradiances on the SiPM.

Vortex Wave Directional Modulation With Time-Dependent Phase Offset FDA

A direction-range-time dependent vortex wave directional modulation (DM) scheme based on the frequency diverse array (FDA) is proposed for secure transmission. We design the random frequency offset for the array element in a circular arc FDA, which generates the quasi-helical phase front and the irregular phase front at the specific range. In order that the time-variance phase front can maintain the helical phase characteristics at the desired range, according to the designed frequency offset function, we design a DM excitation signal with the specific time-variance phase offset for each array element. The direction-range-time dependent phase pattern is modulated into the vortex signal constellation for the desired transmission. Theoretical analyses and numerical simulations validate the effectiveness of our proposed approach with no artificial noise.

Reduction of PAPR and improved BER using SLM technique

Abstract: With the introduction of 5G wireless technology, mankind has achieved a massive leap in data throughput of gigabits per second thanks to the combination of multiple input, multiple output, and orthogonal frequency division multiplexing technologies. Multiple (OFDM MIMO) can be achieved via frequency selective fading. PAPR (Peak-to-Average Power Ratio) is one of the most crucial performance concerns, since it makes OFDM particularly prone to harmonic distortion, reducing channel estimate accuracy and resulting in a lower bit error rate (BER). In the MIMO-OFDM system, we present a selective codeword shift mapping approach (SCS-SLM). It lowers the PAPR and forces the power amplifier to operate in the non-linear region, resulting in sub-carrier intermodulation, signal constellation, bit error rate distortion, and improved system performance. Additionally, using orthogonal frequency division multiplexing with space-time-frequency block code (STFBC OFDM) may increase BER performance. Selective Mapping is mentioned in this research as an effective approach for reducing PAPR. Furthermore, the bit error rate performance of this system is reviewed, as well as the process complexity as a result. A complete examination of the mutual independence of the alternative OFDM signals generated using this technique is also discussed, in addition to the previously mentioned analysis. Furthermore, the superfluous bits on the side of the transmitted OFDM signal are removed with this new technique. Keywords: (peak-average power ratio (PAPR), Multiple-input, multiple-output & orthogonal frequency-division multiplexing (MIMO-OFDM), space-time frequency block codes (STFBC), Selective Codeword Shift Selective mapping (SCS-SLM)

Method for Estimating and Compensating the Phase Imbalance of Quadrature Signal Components

Currently, methods of direct modulation using complex signals are widely used. A complex signal consists of in-phase I (In-phase) and quadrature Q (Quadrature) components. When a signal passes through a communication channel and a receiving path, mismatches of the signal components occur as a result of interference. The mismatch, in turn, leads to increase in bit error rate (BER) during signal demodulation. The quality of the received signal is expressed in terms of bit error rate. The article considers phase imbalance of the quadrature components of a complex signal. Phase imbalance occurs in the receive path and depends on the quality of the receiver's local oscillators, on the operating temperature and the difference in propagation time of the I and Q components. The article shows an algorithm for estimating the phase imbalance of the quadrature signal components for digital modulation methods. Examples of signal constellation distortions in case of phase imbalance of quadrature signal components are considered. The phase imbalance estimation is based on the modulation constellation method for measuring signal parameters. Formulas for calculating the angle of phase error and the magnitude of quadrature error are given. Formulas for compensating the phase imbalance are also given, taking into account the calculated quadrature error. A mathematical model of the transmitter, communication channel and receiver has been developed to study the method for estimating and compensating for phase imbalance. The mathematical model is built in the Matlab software environment and is an m-script software model. With the help of the mathematical model, method for estimating and compensating for phase imbalance has been studied. In the course of the study, relationships of error probability due to the mismatch of the quadrature components of the signal were obtained. The noise immunity of the receiver paths with and without compensation for the phase mismatch of the quadrature signal components is compared. Based on the results of the study, diagrams of the error probability and the phase mismatch of the receiver's local oscillators were obtained. The study shows that phase mismatch of the receiver local oscillators at a fixed signal-to-noise ratio leads to an increase in the probability of received bit errors. But when applying the phase imbalance compensation method, the error probability remains fixed as the phase mismatch of receiver local oscillators increases at a fixed signal-to-noise ratio.

Security Enhancement in Coherent OFDM Optical Transmission With Chaotic Three-Dimensional Constellation Scrambling

In this paper, we propose and experimentally demonstrate a novel hybrid chaos-based three-dimensional (3-D) constellation scrambling scheme to simultaneously improve the physical layer security and transmission performance of the coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. A 3-D regular hexahedron signal constellation is constructed by the constellation figure of merit principle, which not only expands the encryption dimension but improves the error performance. The dynamic parameters for constellation scrambling are generated by the 5-D hybrid chaotic scheme based on the combination of a 3-D hyperchaotic Hénon mapping and two independent 1-D Logistic mappings, as such a key space of ∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">133</sup> is introduced to enhance the security level of OFDM data encryption during transmission. Furthermore, a transmission experiment for encryption of 144 Gbps 16-quadrature-amplitude-modulation OFDM data over a 100 km standard single-mode fiber in a CO-OFDM system is demonstrated. Compared with the case of using the 3-D rectangular constellation, a 2 dB bit error rate performance improvement is achieved. The results show that the proposed scheme could effectively enhance the system security and transmission performance, which suggests a scalable strategy for future physically secured CO-OFDM systems.

Extended Space Index Modulation

In this letter, a new scheme called extended space index modulation (ESIM) is proposed and investigated. Different from previous works, both the signal constellation and index domains are exploited, and the performance of the spectral efficiency and the reliability can be further enhanced. Specifically, in the ESIM, an antenna index (AI) vector set is designed to convey more extra index bits, which consists of two AI vector subsets. The two AI vector subsets, which are respectively used to modulate the quadrature amplitude modulation (QAM) and secondary QAM (S-QAM) symbols, include the AI vectors having two non-zero elements from <inline-formula> <tex-math notation="LaTeX">$\{(1,1),(1,j),(j,1),(j,j)\}$ </tex-math></inline-formula> to activate two transmit antennas and the AI vectors having only one non-zero element equaling to &#x201C;1&#x201D; to activate one transmit antenna. Furthermore, the S-QAM constellation is designed to enhance the squared Minimum Euclidean Distance. Simulation results are provided to show a close match with analytical results particularly in the high signal-to-noise ratio (SNR) region and demonstrate that significant performance gain can be achieved in the proposed ESIM.

Adaptive Opportunistic Spatial Modulation for Boosting Transmit Diversity

In this paper, we propose an adaptive opportunistic spatial modulation scheme (AOSM), in which, our unique opportunistic group-antenna-selection scheme is amalgamated with a simple phase alignment (PA) transmit pre-scaling to boost the transmit-diversity of SM. To characterize and analytically evaluate the AOSM, a comprehensive error performance analysis is presented with single antenna reception. We theoretically derive a tight upper-bound for the symbol error probability (SEP) in closed-form based on an improved union-bound. The exact explicit asymptotic formula of the SEP at high SNR is provided as well. These results demonstrate that the transmit-diversity of proposed AOSM-(multiple-input single-output) MISO scheme is not only successfully achieved, but also elevated to be equal to the number of antennas in each antenna group. Moreover, it also reveals an important performance trend: at high SNR, with a fixed number of transmit antennas and a given data-rate, the SEP performance of the AOSM-MISO scheme can be successively enhanced by utilizing less antennas groups and bigger size of the signal constellation, because of the increase in transmit-diversity. Furthermore, the PA-aided SM-MISO is a special case of our AOSM-MISO. We are the first to provide the exact transmit-diversity gain for this conventional system and show that the PA pre-scaling scheme only can not improve the transmit-diversity of SM. This result sharpens the empirical diversity approximation results proposed in the existing literature. Simulation results well validate the analytical derivations, and indicate that our AOSM system can effectively improve system performance with high transmit-diversity at low-complexity.

A New Approach to Improve the Performance of OFDM Signal for 6G Communication

The orthogonal frequency division multiplexing is a very efficient modulation technique that can achieve very high throughput by transmitting many carriers simultaneously and it is spectrally efficient because of the proximity of the subcarriers. OFDM is used in 5G communication for higher data transmission. 6th generation communication also demands OFDM, since it is more spectrally efficient and suitable for high data transmission. The drawback of the OFDM includes peak to average power ratio and sensitivity to carrier offsets and drifts. The usage of a non-linear power amplifier causes the signal spreading and leads to inter-modulation and signal constellation distortion. These two distortions have an impact on the signalto-noise ratio and hence reduce the efficiency. The methods used to reduce PAPR are clipping and filtering, selective mapping, partial transmit sequence, tone reservation, and injection and non-linear commanding. The drawbacks of the above methods are computational complexity, spectrum inefficiency, increase in bit error rate and PAPR rate. In this work, three effective methods are discussed and compared to improve the performance parameters. These are adaptive peak window method based on harmonize clipping, harmonics kernel adaptive filter and Slepian-based flat-top window techniques are presented to reduce the BER, PAPR, and CCDF to improve the signal-to-noise of the system. This window technique averages out the noise spread out in the spectrum and thus reduces the signal loss by minimizing peak to average power ratio. The results are analyzed and compared with the existing conventional methods. Finally, the reductions in PAPR, BER and CCDF obtained are discussed in the results and comparison section. The proposed work has a higher signal-to-noise ratio than the conventional methods.

Investigation of a coherent dual-polarized 16-QAM 16-channel WDM FSO gamma–gamma fading system under various atmospheric losses

This work presents the dual-polarized quadrature amplitude modulated (QAM) signals transmitted via a sixteen-channel wavelength division multiplexing (WDM) and free-space optics (FSO) communication link. Through an FSO link up to 98 km, it achieves a transmission rate of 120 Gbps per channel. The system's performance is evaluated by calculating atmospheric attenuations in clear, hazy, rainy, and fog situations. Optisystem, an optical network design tool, examined the proposed link. Bit error rate, received signal constellation, error vector magnitude, and geometric loss for various FSO channel lengths were calculated. According to the results, the system can successfully transmit a data rate of 1.92 Tbps over the 98 km range of the FSO link under clear weather, 18.5–3.8 km under haze, 6.25–2.3 km in the rain, and 4.55–2.15 km in fog conditions. Comparing results to previous reports showed that the proposed system was found to be better in dynamic atmospheric circumstances.

Generalized Receiver Designs for OFDM Systems with Alamouti Decoding in Fast Fading Channels

In the present paper, the generalized receiver designs for orthogonal frequency-division multiplex-ing (OFDM) systems that exploit the Alamouti transmit diversity technique are addressed. In Alamouti space-time coded OFDM systems, the simple Alamouti decoding at the generalized receiver relies on the assumption that the channels do not change over an Alamouti codeword period (two consecutive OFDM symbol periods). Unfortunately, when the channel is fast fading, the assumption is not met, resulting in severe performance deg-radation. In the present paper, a sequential decision feedback sequence estimation (SDFSE) scheme based on the generalized receiver with an adaptive threshold, a traditionally single-carrier equalization technique, is used to mitigate the performance degradation. A new method to set the threshold value is proposed. For small signal constellations like binary phase-shift keying (BPSK) and quadrature phase shift-keying (QPSK), the SDFSE generalized receiver with the adaptive threshold requires much lower complexity than a previous minimum me-an square error (MMSE) approach based on the generalized receiver at the cost of small performance degradati-on. Furthermore, we show that the performance difference becomes smaller when the channel estimation error is included. Adaptive effort sequence estimation (AESE) scheme based on the generalized receiver is also pro-posed to further reduce the average complexity of the SDFSE generalized receiver scheme with the adaptive threshold. The AESE generalized receiver scheme is based on the observation that a high Doppler frequency does not necessarily mean significant instantaneous channel variations. Simulations demonstrate the efficacy of the proposed SDFSE generalized receiver with the adaptive threshold and AESE generalized receiver schemes.

Leveraging iNKT cells to identify signals driving B cell memory commitment

Abstract Intense scrutiny of the process of memory B cells (MBC) over the last decade has improved our understanding of MBC development especially for vaccines against viruses capable of rapid diversification like SARS-CoV-2. Most memory responses develop in germinal centers (GC), but the constellation of specific signals which commit B cells to a memory fate is poorly understood. Identification of discrete T and B cell factors leading to MBC commitment is hindered by a lack of murine models with essential controls. We report a unique system harnessing iNKT cell help for B cells to create two conditions, both of which expand NP+ B cells in a class-switched primary response, but only one of which produces a MBC response. In the first case, NP+ B cells receive exclusive cognate iNKT cells upon immunization with the Nitrophenyl-haptenated iNKT cell agonist alphaGalactosylCeramide (NP-aGC) leading to an expansion of NP+ GC B cells, but not MBCs. In contrast, NP+ B cells helped by conventional T cells adjuvanted by iNKT cell activation by vaccinating with haptenated protein (NP-KLH) plus aGC drives a conventional GC B cell expansion and development of NP+ MBCs. Interestingly, cognate antigen which does not induce B memory also elicits fewer pre-memory B cells, compared to non-cognate antigen. These different immunization regimens allow a unique comparison of activated B cells recognizing identical epitopes and producing similar primary humoral responses but with contrasting memory outcomes. Importantly, this also controls for the GC environment which is unaccounted for in other model systems. Examination of these B cell populations will better define the transcriptional landscape of MBC and pinpoint key signals which dictate MBC fate. Supported by AAI Careers in Immunology Fellowship 2021

Algorithmic decoding of dense OAM signal constellations for optical communications in turbulence.

We demonstrate an optical detection and decoding strategy to increase the information rate and spectral efficiency of free-space laser communication links affected by turbulence by means of dense orbital angular momentum (OAM) modulation. Using three candidate receiver architectures-based on a Shack-Hartmann sensor, a Mode Sorter, and a complex conjugate projection scheme as a base case-we demonstrate an algorithmic classification system based on the received OAM spectra produced by these architectures. This classification scheme allows low-error-rate data transmission in turbulence using 16-OAM, 32-OAM, and 64-OAM symbol constellations, with OAM states between -20 and 20. We evaluate and compare their performance under weak to strong atmospheric turbulence conditions using an accuracy metric and confusion matrices.

Adaptive protograph-based BICM-ID relying on the RJ-MCMC algorithm: a reliable and efficient transmission solution for plasma sheath channels

For reentry communication, owing to the influence of the highly dynamic plasma sheath (PS), the parasitic modulation effect can occur and the received phase shift keying (PSK) signal constellation can be severely rotated, leading to unacceptable demodulation performance degradation. In this work, an adaptive non-coherent bit-interleaved coded modulation with iterative decoding (BICM-ID) system with binary PSK (BPSK) modulation and protograph low-density parity-check under the PS channel is proposed. The proposed protograph-based BICM-ID (P-BICM-ID) system can achieve joint processing of demodulation and decoding, where the soft information is adaptively estimated by reversible-jump Markov chain Monte Carlo (RJ-MCMC) algorithms. Simulation results indicate that compared to existing algorithms, the proposed system can adapt well to the dynamic characteristics of the PS channel and can obtain a 5 dB performance improvement at a bit error rate of 10−6.

Generalized Multistream Spatial Modulation Based on Frequency-Phase Modulated Signals

In this letter, we present an approach to building a new generalized multistream spatial modulation system (GMSM), where the information is conveyed by the two active antennas with signal indices and using all possible active antenna combinations. The signal constellations associated with these antennas may have different sizes. In addition, four-dimensional hybrid frequency-phase modulated signals are utilized in GMSM. Examples of GMSM systems are given and computer simulation results are presented for transmission over Rayleigh and deep Nakagami-<inline-formula> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> flat-fading channels when maximum-likelihood detection is used. The presented results indicate a significant improvement of characteristics compared to the best-known similar systems.

Performance analysis of optical spatial modulation over a correlated gamma-gamma turbulence channel.

In this paper, theoretical closed expressions for the symbol error rate (SER) of two optical spatial modulation (OSM) schemes in a free-space optical (FSO) communication system-optical spatial pulse amplitude modulation (OSPAM) and optical spatial pulse position modulation (OSPPM)-over correlated gamma-gamma fading channels are derived. To study practical optical channels affected by atmospheric eddies, the effect of arbitrary atmospheric channel correlation is considered particularly, and it is shown that the correlation can degrade system performance. The parameters of atmospheric turbulence and the number of optical antennas are also under consideration in performance analysis of the FSO multiple input, multiple output system. All analytical results are validated with Monte Carlo simulations, which clearly illustrate the effect of spatial constellation and signal constellation on the average SER. In addition, it is shown by comparison that turbulence fluctuation and channel correlation have less influence on the OSPPM system than the OSPAM system. Overall, the framework proposed in this paper is proven to be effective and conducive to algorithm research on reducing the effect of correlated channels on OSM FSO systems.

An efficient modulation classification method using signal constellation diagrams with convolutional neural networks, Gabor filtering, and thresholding

AbstractRecently, automatic modulation classification (AMC) has extensively and commonly been utilized in several modern wireless communication systems as a significant tool of signal detection for civilian and military applications and cognitive radio systems. Although several methods have been established to identify the modulation scheme of a received signal, they show a difficulty of learning radio characteristics for most conventional machine learning algorithms. This article focuses on the deep learning (DL) classification technique to solve these problems. To improve the classification accuracy of a communication signal modulation type, we apply a new model that combines Gabor filtering and thresholding with the help of convolution filters implemented in DL. A basic convolutional neural network, AlexNet, and a residual neural network are used for being compatible with constellation diagrams in order to achieve a superior classification performance. Moreover, the Gabor filter can effectively extract spatial information, including edges and textures. In terms of classification accuracy, the proposed AMC system improves the signal modulation classification accuracy significantly, and achieves competitive results. We use seven modulation types over the range of signal‐noise ratio (SNR) values from −10 to 30 dB. The performed experiments reveal that the proposal guarantees a remarkable classification accuracy of approximately 100% at a 10 dB SNR over AWGN and Rayleigh fading channels. Therefore, to prove the functional viability of our proposed method, it can be applied in adaptive modulators that can be used in many devices in applications such as Internet‐of‐Things (IoT).

Noncoherent Two-Way Relaying With Decode and Forward: Two Versus Three Phases

Noncoherent two- and three-phase two-way relaying (TWR) techniques are bandwidth efficient and entail no pilot symbol–related rate loss. However, noncoherent two-phase TWR (2P-TWR) has not been compared with three-phase TWR (3P-TWR), and several unanswered questions remain. In this paper, we focus on the noncoherent detection of the relay with the decode-and-forward technique. For the noncoherent maximum-likelihood detector at the relay, we propose a distance measure for the transmitted signals of the two terminal nodes. For 2P-TWR, we propose that the signal constellation of one terminal node is the signal constellation of the other terminal node rotated by an angle. Using the proposed distance measure, we obtain the optimal angles and thus resolve those unanswered questions pertaining to 2P-TWR. Finally, noncoherent 3P-TWR was found to significantly outperform noncoherent 2P-TWR in simulations and distance analyses.