M-ary Quadrature Amplitude Modulation Constellations Research Articles

Simulation-Enhanced MQAM Modulation Identification in Communication Systems: A Subtractive Clustering-Based PSO-FCM Algorithm Study

Signal modulation recognition is often reliant on clustering algorithms. The fuzzy c-means (FCM) algorithm, which is commonly used for such tasks, often converges to local optima. This presents a challenge, particularly in low-signal-to-noise-ratio (SNR) environments. We propose an enhanced FCM algorithm that incorporates particle swarm optimization (PSO) to improve the accuracy of recognizing M-ary quadrature amplitude modulation (MQAM) signal orders. The process is a two-step clustering process. First, the constellation diagram of the received signal is used by a subtractive clustering algorithm based on SNR to figure out the initial number of clustering centers. The PSO-FCM algorithm then refines these centers to improve precision. Accurate signal classification and identification are achieved by evaluating the relative sizes of the radii around the cluster centers within the MQAM constellation diagram and determining the modulation order. The results indicate that the SC-based PSO-FCM algorithm outperforms the conventional FCM in clustering effectiveness, notably enhancing modulation recognition rates in low-SNR conditions, when evaluated against a variety of QAM signals ranging from 4QAM to 64QAM.

Iterative frequency-domain detection and compensation of nonlinear distortion effects for MIMO systems

Single-carrier multi-input, multi-output (MIMO) systems are known to have low envelope fluctuations. However, the introduction of higher order modulations, such as M-ary quadrature amplitude modulation (M-QAM), and singular value decomposition (SVD) techniques, can lead to large envelope fluctuations, making the signals prone to nonlinear distortion effects during amplification.For this work we consider a MIMO-SVD system employing single-carrier with frequency-domain equalization (SC-FDE) and M-QAM constellations with M>4, together with strongly nonlinear amplifiers. To increase performance of the SVD technique, we interleave the singular modes among the antennas. Moreover, to handle the nonlinear distortion, we propose an iterative frequency-domain receiver that combines equalization with cancellation of nonlinear distortion effects.The performance results show that the proposed receivers can achieve excellent performance with only a few iterations, which makes this technique appealing for MIMO point-to-point communication systems.11A preliminary version of this work was published in ICUMT 2018.

Low-cost implementation of M-QAM signal constellations

This paper aims to discuss ways of reducing hardware resource usage required for implementing vectorial coding and detection of a variable-order M-ary quadrature amplitude modulation (M-QAM) constellations in digital communication systems. In this regard, we introduce two techniques that are capable of mapping both square and cross M-QAM constellation symbols to bits and vice-versa, with distinct levels of hardware resource utilizations when M increases. These techniques are named Generic M-QAM and Extended Heuristic Decision Region (HDR). The latter technique modulates, demodulates, and detects M-QAM symbols with look-up tables and state machines, while the former technique performs the same tasks by using few logical elements and eliminating memory usage. Based on additive white Gaussian noise model assumption and hard decision rule, we show the bit error rate performances obtained with both techniques are equal to theoretical ones. Additionally, the attained results show the Generic M-QAM technique offers the lowest hardware resource utilization when M increases (M>256) in comparison with the Extended HDR one. Moreover, we point out that the Extended HDR technique has the flexibility to be easily implemented in any published standards, while the Generic M-QAM technique applies a Gray mapping function that might require adjustment to make it compatible to published standards.

Achievable Rates of Space-Division Multiplexed Submarine Links Subject to Nonlinearities and Power Feed Constraints

We study the achievable rates of submarine fiber systems in the high-dimensional design space of variables including span length, launch power, number of spatial channels, and power feed current. We identify the regimes in which nonlinearities or power feed equipment constraints become dominant, and demonstrate that optimized system design evolves toward the linear regime as the system scales to a high number of spatial channels. We calculate the bit rate achievable by uniform and probabilistically shaped M-ary Quadrature Amplitude Modulation constellations to identify potential capacity-achieving implementations.

A Novel Cooperative Communication System Based on Multilevel Convolutional Codes

The authors propose a system where single antenna mobile users share antennas to transmit their information cooperatively to the common base station. Each mobile user overhears the coded information transmitted by other users, detects it and further encodes it along with its own information. The encoding is done using multilevel coding scheme with convolutional codes as component codes. The proposed system considers the self-information of user u at level u to reduce complexity while decoding. The coded symbols are mapped to M-ary quadrature amplitude modulation constellation using multi-resolution modulation partitioning. This enables the component codes to be designed for lower order constellation. Each cooperative user transmits multilevel coded symbols to the common base station, thus creating transmit diversity. The base station receives noisy superposition of independent Rayleigh faded signals transmitted by cooperative users and pass it through a multistage decoder. The multistage decoder employs maximum likelihood based Viterbi decoder at each stage to detect the information of each user. The Viterbi decoder applies max-log approximation to reduce the branch metric complexity. The proposed cooperative multilevel coding system outperforms non-cooperative multilevel coding system and is less complex than the existing cooperative multilevel coding system.

Low‐complexity EDAS and low‐complexity detection scheme for MPSK spatial modulation

Euclidean-distance antenna selection (EDAS) is an effective transmit AS technique for spatial modulation (SM). This study presents a low-complexity (LC) EDAS scheme for the M-ary phase shift keying (MPSK) SM. The LC-EDAS for MPSK SM (LC-MPSK-EDAS) is achieved by exploiting the rotational symmetry of the MPSK constellation and using singular value decomposition (SVD_EDAS) for factorisation of the modified channel matrix. A further reduction in complexity is achieved by eliminating the process of conditioning on elements of the MPSK symbol set. The complexity of the proposed scheme is independent of the order M of MPSK. Also, in this study, an LC near maximum likelihood (ML) detection scheme for MPSK SM systems, signal vector-based detection (SVD), is implemented. Though this scheme provides poor results when using the M-ary quadrature amplitude modulation constellation, it is found that the error performance of this scheme for MPSK constellations has very near ML results. The simulation results show that even at high signal-to-noise values this scheme maintains near ML performance. To support the results, the closed-form expression of the bit error rate for the MPSK constellation is derived.

Channel Estimation and Detection in Hybrid Satellite–Terrestrial Communication Systems

We address the problem of amplify-and-forward (AF) relaying in a hybrid satellite-terrestrial communication system with unknown channel gains. A masked destination earth station (ES) receives the signal forwarded by a relaying ES, i.e., from a terrestrial link. There is no direct transmission from the satellite to the destination ES. The satellite-relay ES (satellite link) and relay ES-destination ES (terrestrial link) links are assumed to follow shadowed Rician fading and Nakagami-m fading, respectively. A scheme for channel estimation and detection of transmitted signal from the satellite to the destination ES is proposed. The terrestrial link is estimated separately, whereas the cooperative hybrid link (satellite-relay-destination) is estimated jointly with symbol detection. The average symbol error rates of the M-ary phase-shift keying and M-ary quadrature amplitude modulation constellations are derived for the considered hybrid communication system. Moreover, we also derive the analytical diversity order of the considered system with estimated channel gains. It is shown by simulation and analysis that the estimation error does not affect the diversity order of the system. Furthermore, the average and asymptotic capacity of the system is also derived by using the moment-generating function approach.

Exact MGF-Based Performance Analysis of Dual-Hop AF-Relayed Optical Wireless Communication Systems

In this paper, we analyze the subcarrier intensity modulation-based-relayed optical wireless communication system in the presence of various channel impairments such as turbulence, path loss and pointing errors. The relay follows an amplify and forward relaying protocol and the optical links are modeled assuming independent but not necessarily identically distributed (i.n.i.d) gamma-gamma fading statistics. We derive the novel analytical expressions for the moment generating function and cumulative distribution function of the equivalent end-to-end signal to noise ratio (SNR) at the destination and utilize these results to obtain the exact analytical expressions for outage probability and average symbol error rate for M-ary phase shift keying and M-ary quadrature amplitude modulation constellations, respectively. The results are obtained in terms of special function such as generalized bivariate Meijer's G-function and to get insight further, we present asymptotic analysis at high SNR values to find the effect of various parameters on the system performance.

Relay Assisted Bi-directional Communication in Generalized Turbulence Fading

The bi-directional relaying has recently emerged as the spectrally efficient communication technique. In bi-directional relaying, two users exchange their information, with the help of a relay, in two time slots and, hence, achieve full-rate transmission. This paper considers a relay assisted bi-directional free-space optical communication system under the influence of generalized atmospheric turbulence fading and misalignment errors. The turbulence induced fading channels, which are independent but not necessarily identical, are modeled with M-distribution. In the presence of the misalignment fading characterized by the pointing errors, the new closed-form expressions for the outage probability and error rate are derived. The error performance of the considered system is analyzed for subcarrier intensity modulation-based M-ary phase-shift keying and M-ary quadrature-amplitude modulation constellations. The analytical results are validated through Monte Carlo simulations.

Coded QAM using a binary convolutional code

As an alternative to trellis coding, a binary convolutional code is considered for use with such nonbinary modulation schemes as quadrature amplitude modulation (QAM). A Gray code is used to map the encoder output to the M-ary QAM constellation. The focus is on the design of 16-ary coded QAM with a rate 3/4 punctured convolutional code of a constraint length 7. A quantized binary metric generation method is proposed and shown to be suboptimum as compared to the direct use of a M-ary unquantized metric. Impressive coding gains and bandwidth efficiency are shown in comparison with uncoded systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>