QAM Schemes Research Articles

On the performance of adaptive hybrid MQAM-MPPM scheme over Nakagami and log-normal dynamic visible light communication channels.

In this paper, we introduce the idea of using adaptive hybrid modulation techniques to overcome channel fading effects on visible light communication (VLC) systems. A hybrid $ M $M-ary quadrature-amplitude modulation ($ M{\rm QAM} $MQAM) and multipulse pulse-position modulation (MPPM) technique is considered due to its ability to make gradual changes in spectral efficiency to cope with channel effects. First, the Zemax optics studio simulator is used to simulate dynamic VLC channels. The results of Zemax show that Nakagami and log-normal distributions give the best fitting for simulation results. The performance of $ M{\rm QAM} $MQAM-MPPM is analytically investigated for both Nakagami and log-normal channels, where we obtain closed-form expressions for the average bit-error rate (BER). The optimization problem of evaluating the hybrid modulation technique settings that lead to the highest spectral efficiency under a specific channel status and constraint of outage probability is formulated and solved using an exhaustive search. Our results reveal that the adaptive hybrid scheme improves system spectral efficiency compared to ordinary QAM and MPPM schemes. Our results reveal that the adaptive hybrid scheme improves system spectral efficiency compared to ordinary QAM and MPPM schemes. Specifically, at low average transmitted power, $ - 32\;{\rm dBm} $-32dBm, the adaptive hybrid scheme shows 280% improvement in spectral efficiency compared to adaptive versions of ordinary schemes. At higher power, $ - 20\;{\rm dBm} $-20dBm, 6.5% and 725% improvement are obtained compared to ordinary QAM and ordinary MPPM, respectively. Also, the adaptive hybrid scheme shows great improvement in average BER and outage probability compared to ordinary schemes. The hybrid scheme shows 28%, 34%, and 38% improvement, respectively, for $ m = 1,2,3 $m=1,2,3 for Nakagami channels at $ {\rm BER}{ = 10^{ - 3}} $BER=10-3. Also, the outage probability of hybrid schemes of $ {\rm BER}{ = 10^{ - 3}} $BER=10-3 shows 30% and 14% better performance than ordinary $ M{\rm QAM} $MQAM and MPPM schemes, respectively.

Steepest Gradient-Based Orthogonal Precoder for Integer-Forcing MIMO

In this paper, we develop an orthogonal precoding scheme for integer-forcing (IF) linear receivers using the steepest gradient algorithm. Although this scheme can be viewed as a special case of the unitary precoded integer-forcing (UPIF), it has two major advantages. First, the orthogonal precoding outperforms its unitary counterpart in terms of achievable rate, outage probability, and error rate. We verify this advantage via theoretical and numerical analyses. Second, it exhibits lower complexity as the dimension of orthogonal matrices is half that of unitary matrices in the real-valued domain. For finding “good” orthogonal precoder matrices, we propose an efficient algorithm based on the steepest gradient algorithm that exploits the geometrical properties of orthogonal matrices as a Lie group. The proposed algorithm has low complexity and can be easily applied to an arbitrary MIMO configuration. We also confirm numerically that the proposed orthogonal precoding outperforms UPIF type II in some scenarios and the X-precoder in high-order QAM schemes, e.g., 64- and 256-QAM.

Combined Inter-layer FEC and Hierarchical QAM for Stereoscopic 3D Video Transmission

We consider an inter-layer FEC (IL-FEC) technique combined with hierarchical QAM for an efficient and reliable transmission of stereoscopic 3D video. The transmit sources are left and right video streams, and one of them is considered a more important stream for guarantee of conventional 2D service. The source node transmits both left and right videos to a destination node by using the IL-FEC and hierarchical 16QAM schemes, in which video peak signal-to-noise ratio (PSNR) performance varies with the hierarchical value $$(\alpha )$$. In this paper, we present the suitable hierarchical values to achieve the target PSNR performances even in low SNR environment. Numerical simulation results show that the proposed system using IL-FEC and hierarchial 16QAM schemes with the suitable $$\alpha$$ value can gain about 7.3–9.3 dB in the average PSNR performance, compared with the system using IL-FEC and conventional 16QAM schemes.

Performance analysis of NLOS ultraviolet communications with correlated branches over turbulent channels

Ultraviolet communication (UVC) is becoming increasingly popular due to its ability to effectively communicate in non-line-of-sight (NLOS) mode, which offers alternative communication system advantages over visible light communication and infrared links. However, the performance of UVC is affected by atmospheric turbulence, which is generally ignored under the assumption of short-distance links. In this paper, we consider a NLOS UVC system experiencing turbulence due to variation in the refractive index of the atmosphere. The atmospheric turbulence results in fading due to fluctuations in the received signal strength, thus deteriorating the quality of communication. Spatial diversity is proven to mitigate the effect of fading by introducing multiple parallel communication paths between the transmitter and receiver. We present a spatial diversity reception in the form of ${N_r}$-branches selection combining at the receiver. The channel coefficients are assumed to be exponentially correlated, and turbulence is modeled using log-normal distribution under weak turbulence conditions. Closed-form expressions for the outage probability and average symbol error rate for general order rectangular quadrature amplitude modulation (RQAM), cross-QAM, and hexagonal QAM schemes are derived. Furthermore, the ergodic capacity of the system is computed as a function of the channel correlation coefficient. The numerical values are compared with computer simulations to validate the accuracy of the theoretical analysis.

Bit error probability of the M‐QAM scheme subject to multilevel double gated additive white Gaussian noise and η‐μ, κ‐μ, or α‐μ fading

AbstractThis paper presents new and exact expressions for the bit error probability (BEP) of the square M‐ary quadrature amplitude modulation scheme subject to η‐μ, κ‐μ or α‐μ fading and multilevel double gated additive white Gaussian noise, which is composed by the sum of a white Gaussian component of variance and a white Gaussian noise component of variance gated by a discrete random process defined in continuous time, which takes values into a finite discrete set. BEP curves, with and without imperfect channel estimation, corroborated by simulations using the Monte Carlo method, are presented for different values of parameters that characterize mathematically the channel.

Performance analysis of QAM schemes for non-regenerative cooperative MIMO network with transmit antenna selection

In this paper, performance of a dual-hop cooperative multiple-input and multiple-output (MIMO) system for various futuristic QAM schemes is analyzed. A non-regenerative MIMO scheme with transmit antenna selection strategy is considered where a single transmit antenna maximizing the total received signal power is selected for transmission. In the considered system model, it is assumed that the source, relay and the destination are equipped with multiple antennas. As a performance measure, generalized expressions for average symbol error rate for hexagonal quadrature amplitude modulation, rectangular quadrature amplitude modulation, square quadrature amplitude modulation and 32-cross quadrature amplitude modulation are derived. The impact of pathloss is highlighted for the considered system model and finally, the derived analytical expressions are validated through Monte-Carlo simulations.

Bit error probability of the M‐QAM scheme under η‐μ fading and impulsive noise in a communication system using spatial diversity

SummaryThis paper presents a new and exact expression for the bit error probability (BEP) of the square M‐ary quadrature amplitude modulation (M‐QAM) scheme, with the channel under double gated additive white Gaussian noise (G2AWGN) and η‐μ fading in a communication system using the spatial diversity technique. The expression for the BEP is written in terms of the Appell function. The BEP curves are presented under different values of the number of branches of the maximum ratio combining (MRC) receiver, order of the constellation M, and parameters that characterize mathematically the channel, corroborated by simulations performed with Monte Carlo method.

Design and Optimization of HDL Code for SDR Transceiver Based QAM Scheme

Design and Optimization of HDL Code for SDR Transceiver Based QAM Scheme

A 5G mmWave Fiber-Wireless IFoF Analog Mobile Fronthaul Link With up to 24-Gb/s Multiband Wireless Capacity

We experimentally demonstrate a multiband intermediate frequency-over-fiber/mmWave (IFoF/mmWave) fiber/wireless mobile fronthaul link for gigabit capacity over the unlicensed V-band (57–64 GHz). Digital synthesis of the multiband radio waveforms is performed at the baseband unit using digital subcarrier multiplexing technique, whereas digital predistortion is exploited to cope with the analog IFoF channel impairments without any further baseband processing at the digital-free remote radio head. Commercial optoelectronic components and analog V-band radio and antenna equipment for 7-km fiber and 5-m wireless transmission are employed to successfully demonstrate both uplink and downlink connectivity. An aggregate capacity up to 24 Gb/s was demonstrated with a 6-band 1 Gbaud 16-QAM on a 7.2-GHz analog bandwidth over the combined fiber/wireless channel showing error vector magnitude (EVM) values below the 3GPP requirements (<12.5%) for 5G systems. Multiformat assignment on each subcarrier was also realized by using M-PSK and 16-QAM schemes to achieve 18-Gb/s connectivity for both uplink and downlink, while demonstrating flexible resource allocation capabilities. By replacing the stand-alone optical modulator with an InP-based externally modulated laser chip for the implementation of the IFoF transmitter, a 16-Gb/s aggregate capacity was showcased on a 7-km fiber link and 5-m wireless channel with a 4-band 16-QAM encoded at 1 Gbaud. Successful operation with robust EVM performance was demonstrated using also the 6-band scheme of 1 Gbaud QPSK bands.

On Performance of Hexagonal, Cross, and Rectangular QAM for Multi-Relay Systems

Error performance is considered as one of the most important performance measures, and deriving the closed-form expressions for efficient modulation techniques over generalized fading channels is important for future cellular systems. In this paper, the performance of a dual-hop amplify-and-forward multi-relay system with best relay selection is analyzed over independent and non-identically distributed (i.n.i.d.) Nakagami-m fading links with both integer and non-integer fading parameters. The impact of practical constraints of imperfect channel state information (CSI) and non-linear power amplifier (NLPA) at each of the relays are considered. Closed-form expressions for the outage probability are derived for both integer and non-integer fading parameters, and asymptotic analysis on the outage probability is performed to obtain the diversity order of the considered multi-relay system. Based on the cumulative distribution function approach, average symbol error rate (ASER) expressions for general order hexagonal QAM, general order rectangular QAM, and 32-cross QAM schemes are also derived. The comparative analysis of ASER for various QAM schemes with different constellations is also illustrated. Furthermore, the impact of the number of relays, fading parameter, channel estimation error, and non-linear distortion on the system performance is also highlighted. Finally, the derived analytical results are validated through Monte-Carlo simulations.

Average Symbol Error Rate Analysis of QAM Schemes Over Millimeter Wave Fluctuating Two-Ray Fading Channels

In this study, analytical expressions are derived by using probability density function approach over millimeter wave fluctuating two-ray (FTR) fading channels for average symbol error rate (ASER) of rectangular quadrature amplitude modulation (RQAM) and cross quadrature amplitude modulation (XQAM) schemes. First, an exact ASER expression for RQAM over millimeter wave FTR fading channels is derived. Second, two different upper bound ASER expressions of RQAM scheme under millimeter wave FTR fading conditions are obtained by using Chernoff and Chiani approximations of Gaussian Q-function. In addition to this, an asymptotic ASER expression for RQAM is also proposed. Then, an analytical formulation is presented for XQAM signaling over millimeter wave FTR fading channels in terms of infinite series representations which rapidly converge. Finally, the numerical results of the proposed analytical expressions are compared with the simulation results in order to validate the analytical findings in this work.

НОВЫЙ ФОРМАТ МОДУЛЯЦИИ 2-12QAM

The 16 Quadrature Amplitude Modulation (16QAM) is the preferred modulation format for many communication and broadcasting standards. However, performance of the overall “practical” communication/ broadcasting systems employing 16QAM is far from the Shannon limit as there is a requirement for power back-up to combat non-linear distortions generated by the output of high power amplifiers. In this paper we propose moving from 16QAM to a 12QAM modulation without any change of the hardware and with only minor changes in the mapping algorithm, by eliminating the four constellation points with highest signal energy. However, to ensure that no data is lost and spectral efficiency is preserved, we propose pairing two 12QAM symbols into a 4-dimensional signal with the appropriate mapping, obtaining the desired 2-12QAM modulation. We propose the use of a rate 6/7 forward error correcting (FEC) code combined with the 2-12QAM, which maps 7 binary input digits into 2 twelve-ary symbols which select corresponding signals from the conventional 16QAM modulator. The proposed new modulation format has a spectral efficiency of 3 bits/symbol, the same spectral efficiency as the legacy 16QAM scheme when the 16QAM modulation format is coupled with a rate 3/4 FEC. The removal of the 16QAM highest energy symbols represents a peak energy gain of 2.55 dB and an average energy gain of 1,35 dB which is offset by a 0.58 dB increase in code rate, from 3/4 to 6/7. In addition, the proposed scheme has a clear advantage of employing existing 16QAM modulator/demodulator hardware and maintaining compatibility with the legacy standards, albeit with simple changes in mapping which can be achieved via a software upgrade. We show that the proposed technique allows at least 2dB power gain without sacrificing spectral efficiency or additional hardware complexity.

Reconfigurable address generator for multi-standard interleaver

This paper presents low-complex and novel techniques for designing reconfigurable architectures for multi-standard address generator and interleaver. The emphasis of this work is on hardware re-use, but it also focuses on optimizing the hardware to support multiple standards. A low-cost reconfigurable architecture for address generator and interleaver is proposed which operates in WLAN (802.11a/b/g and 802.11n), WiMAX (802.16e) and 3GPP LTE standards. A simple algorithm and a reconfigurable architecture that eliminates the computationally intricate mod function for LTE, and floor as well as mod function for WLAN/WiMAX, are proposed to reduce the hardware cost as well as implementation complexity. Novel architectures are also proposed to select the increment values for 16-QAM and 64-QAM schemes. A unique configurable subtracting sub-block for each modulation scheme is also presented. Software simulation is carried out to authenticate the functionality of the algorithm. The proposed reconfigurable architectures are realized on FPGA and tested on board. Synthesis results on Spartan-3 FPGA display 66% reduction in FPGA resource utilization and 74% increase in operating frequency compared to the cited address generators. Implementation results on Kintex UltraScale FPGA display a reduction of 34% in resource utilization and 20% in total on-chip power compared to the cited interleavers. This design is also implemented using 45 nm CMOS standard cell technology, and ASIC synthesis results of the reconfigurable address generator exhibit 76.4% improvement in data rate and 52.23% decrease in latency compared to the state-of-the-art address generators. The proposed multimode interleaver also exhibit 60.28% reduction in hardware complexity.

Exact and approximate log-likelihood ratio of M-ary QAM with two-time dimensions

Abstract A ( 3 × 2 m )-ary QAM scheme maps a binary symbol into two-consecutive signal points (signal vector). It provides very lower PAPR than the conventional QAM because it removes corner signal points. For the scheme, this paper discusses an exact analysis of log-likelihood ratio calculation of the signal vector and signal point, and an approximated method to reduce hardware complexity for the channel coding. Numerical results show that the approximated method provides lower hardware complexity and small performance gap compared to exact one. Also, the PAPR and error performances of ( 3 × 2 m )-ary QAM are compared with the one of conventional QAM.

Performance analysis of OFDM based 3-hop AF relaying network over mixed Rician/Rayleigh fading channels

In this paper, performance of an orthogonal frequency division multiplexing (OFDM) based 3-hop variable-gain amplify and forward (AF) relaying network is analyzed over independent and non-identically distributed (i.n.i.d.) mixed Rician/Rayleigh fading environment. Analytical expression of outage probability is derived and diversity order of the considered system is found. Further, average symbol error rate (ASER) expressions of general order hexagonal quadrature amplitude modulation (HQAM), general order rectangular QAM (RQAM) and 32-XQAM are derived. A comparative analysis of ASER for different QAM schemes with different constellations is also presented. Ergodic capacity with optimum rate adaptation is also derived for the considered system model. Further, the impact of Rician K-factor on the performance of the considered system is highlighted. Finally, the derived analytical results are verified through Monte-Carlo simulations for different signal-to-noise ratio (SNR) levels.

Impact of Imperfect CSI on ASER of Hexagonal and Rectangular QAM for AF Relaying Network

In this letter, we derive the closed-form expression of outage probability for a dual-hop variable-gain amplify-and-forward relay network. The maximal ratio combining receiver over independent and non-identically distributed frequency flat Nakagami-m fading channels with integer-valued fading parameter and imperfect channel state information (CSI) is considered. Asymptotic analysis on outage probability is also performed. Average symbol error rate (ASER) expressions are derived for general-order hexagonal and rectangular QAM schemes using the cumulative distribution function-based approach. The impact of the fading parameter and imperfect CSI are highlighted on the system performance. Comparative analysis of ASER performance for different QAM constellations is also illustrated. Monte Carlo simulations are performed to validate the derived analytical results for both perfect and imperfect CSI.

Performance Evaluation of QAM Schemes for Multiple AF Relay Network Under Rayleigh Fading Channels

In this work, we propose theoretical expressions of the moments for instantaneous signal to noise ratio (SNR), the amount of fading, and the average symbol error rate (ASER) for rectangular quadrature amplitude modulation (RQAM), 32-cross QAM, differentially encoded quadri-phase shift keying and $$\pi /4$$ź/4-QPSK modulation schemes in multiple amplify-and-forward relay network for maximal ratio combining receiver. To measure the number of independent fading paths over the channel, we provide asymptotic analysis of ASER expression for RQAM at high SNR. The impact of system parameters is also highlighted on the performance metrics. To investigate the correctness of theoretical expressions, we compare numerical results with Monte' Carlo simulations.

Channel estimation and channel tracking for correlated block-fading channels in massive MIMO systems

This paper presents a channel estimation and tracking method for correlated block-fading channels in massive MIMO wireless cellular systems. In order to conserve resources, the proposed algorithm requires the uplink pilot signal only once, at the start of communication. By utilizing the temporal correlation between consecutive Resource Blocks (RBs) and the error correction capability of turbo codes, the channel matrix in subsequent RBs is estimated at the Base Station (BS) itself using the uplink data of current the RB and the estimated channel matrix of previous the RB. Compared to existing blind estimation methods, the proposed method places fewer limitations on the system settings such as the number of BS antennas, the number of users, and the number of coherent channel usage compared to existing blind estimation methods. Simulation results show that the proposed algorithm provides better performance for a moderate RB size, a high-order of QAM scheme, and a smaller ratio of the number of BS antennas and mobile terminals (N/K). For a reasonably small N/K (order of 10), the proposed scheme achieves a lower symbol error probability than the conventional pilot-based estimation approach.

Exploiting the Fast Spectral Roll-Off of CPM Sidelobes to Improve Bandwidth Efficiency in Satellite Communications

Simple and efficient carrier-overlapping and interference-reduction techniques are addressed for frequency-division multiplexing–continuous phase modulation (FDM–CPM) schemes. CPM carriers are densely multiplexed (packed) in the frequency-domain, without leaving any guard bands, thus allowing frequency content in adjacent bands to overlap, so as to enhance the bandwidth efficiency. The intentional adjacent channel interference, introduced by carrier-overlapping during transmission, is combated at the receiver front-end using simple interference-reduction filters that are designed to exploit the fast roll-off of CPM spectral sidelobes. The receiver back-end is governed by a serially concatenated CPM iterative demodulation/decoding detector. Numerically optimal carrier-packing ratios are determined with respect to information-theoretic bounds. The presented method does not require cooperation among users, and is extended to QAM and PSK schemes as well. Bit error rate analyses show that the proposed non-cooperative receiver design facilitates bandwidth and energy-efficient communication for both the nonlinear and linear satellite channels, without resorting to multiuser detectors, and becomes an attractive solution when cooperation may not be feasible among users that are geographically spread-out.

Joint Channel and Phase Noise Estimation in MIMO-OFDM Systems

The combination of multiple-input multiple-output (MIMO) techniques withorthogonal frequency division multiplexing (OFDM), MIMO-OFDM, is a promising way ofachieving high spectral efficiency in wireless communication systems. However, the performanceof MIMO-ODFM systems is highly degraded by radio frequency (RF) impairments such asphase noise. Similar to the single-input single-output (SISO) case, phase noise in MIMO-OFDMsystems results in a common phase error (CPE) and inter carrier interference (ICI). In this paperthe problem of joint channel and phase noise estimation in a system with multiple transmit andreceive antennas where each antenna is equipped with its own independent oscillator is tackled.The technique employed makes use of a novel placement of pilot carriers in the preamble anddata portion of the MIMO-OFDM frame. Numerical results using a 16 and 64 quadratureamplitude modulation QAM schemes are provided to illustrate the effectiveness of the proposedscheme for MIMO-OFDM systems.