16-ary Quadrature Amplitude Modulation Research Articles

Modulation Mode Detection and Classification for In Vivo Nano-Scale Communication Systems Operating in Terahertz Band.

This paper initiates the efforts to design an intelligent/cognitive nano receiver operating in terahertz band. Specifically, we investigate two essential ingredients of an intelligent nano receiver-modulation mode detection (to differentiate between pulse-based modulation and carrier-based modulation) and modulation classification (to identify the exact modulation scheme in use). To implement modulation mode detection, we construct a binary hypothesis test in nano-receiver's passband and provide closed-form expressions for the two error probabilities. As for modulation classification, we aim to represent the received signal of interest by a Gaussian mixture model (GMM). This necessitates the explicit estimation of the THz channel impulse response and its subsequent compensation (via deconvolution). We then learn the GMM parameters via expectation-maximization algorithm. We then do Gaussian approximation of each mixture density to compute symmetric Kullback-Leibler divergence in order to differentiate between various modulation schemes (i.e., M -ary phase shift keying and M -ary quadrature amplitude modulation). The simulation results on mode detection indicate that there exists a unique Pareto-optimal point (for both SNR and the decision threshold), where both error probabilities are minimized. The main takeaway message by the simulation results on modulation classification is that for a pre-specified probability of correct classification, higher SNR is required to correctly identify a higher order modulation scheme. On a broader note, this paper should trigger the interest of the community in the design of intelligent/cognitive nano receivers (capable of performing various intelligent tasks, e.g., modulation prediction, and so on).

Uncoded M‐ary quadrature amplitude modulation space‐time labeling diversity with three transmit antennas

SummaryUncoded space‐time labeling diversity (USTLD) is a recent scheme that improves the error performance of space‐time block–coded wireless communication links. However, the existing space‐time labeling diversity technique used in USTLD only employs two transmit antennas. To further improve error performance in USTLD systems, this paper investigates USTLD systems with three transmit antennas. A heuristic approach is proposed to design the second and third mappers. Simulation results show superior error performance compared with the existing two transmit antenna USTLD. Furthermore, an analytical expression for a tight bound of the average bit error probability of the proposed system with three transmit antennas is derived. Moreover, complexity reduction analysis of the low‐complexity (LC) detector is proposed. It is shown that the proposed LC algorithm achieves near‐maximum likelihood detection accuracy, while reducing complexity by 51% and 96.5% for 16QAM and 64QAM, respectively.

Variable-Rate Variable-Power MQAM for Spectral Efficiency Maximization in Full-Duplex Systems

Full-duplex wireless communication becomes a promising technique for doubling the system spectral efficiency (SE). In this letter, we propose a variable-rate variable-power (VRVP) modulation scheme for the first time to increase the average system SE. The average SE maximization problem is formulated subject to average power and bit error rate constraints. Due to the unknown self-interference of the other side receiver, this problem is difficult to solve directly. Then, we study the problem for maximizing the lower bound of the average SE, which can be solved in a feasible way. Next, the analytical solutions of power and rate adaptation are obtained. Finally, numerical results show that, compared with the variable-rate constant-power ${M}$ -ary quadrature amplitude modulation, the proposed VRVP scheme increases the SE by 25% in the low average signal noise ratio region.

The Impact of Nonidentical Estimation Error on Performance of Scheduled STBC With MV Power Allocation in CR-MIMO Systems

This correspondence paper studies the impact of nonidentically distributed channel estimation error on performance of a scheduled space-time block coding with mean-value power allocation in cognitive-radio multiple-input multiple-output system. Using the derived probability density function, the exact closed-form expressions of the proposed system for outage probability, ergodic capacity, and symbol-error rate (SER) with both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rm M$</tex-math></inline-formula> -ary quadrature amplitude modulation and phase shift keying modulation are derived. Using asymptotic analysis, this paper quantifies the diversity order for both outage probability and SER in the presence of nonidentically distributed error. From the analysis results, this paper shows that the diversity order is enhanced by the multiuser diversity as the number of user terminals increases regardless of outage probability and SER, while the spatial diversity is eliminated.

Adaptive Coded Modulation Based on Continuous Phase Modulation for Inter-Satellite Links of Global Navigation Satellite Systems

The inter-satellite links (ISLs) will play an increasingly important role in improving the service performance and enhancing the survivability of global navigation satellite systems. The current signal transmission schemes in ISLs primarily employ constant coded modulation to guarantee a high reliable communication even for the worst channel status, and the adaptive coded modulation (ACM) schemes, such as binary low-density parity-check (LDPC) coded quadrature phase shift keying or $M$ -ary quadrature amplitude modulation ( $M$ QAM) have been introduced to improve spectral efficiency over inter-satellite channels recently. However, the phase discontinuity of the above modulations will widen frequency spectrum and cause the high-voltage transient of transmitter, and the $M$ QAM signal through high power amplifier onboard will result in non-linear distortion because of non-constant envelope. In this paper, the association between non-binary LDPC codes and high-order partial response continuous phase modulation with iterative detection is presented as the source of ACM schemes, which effectively inhibits information loss in the process of conversion between bit and symbol probabilities. According to the constellation of BeiDou navigation satellite system in 2020, an open loop ACM control mechanism based on inter-satellite distance is introduced, and implemented by the target bit error rate (BER) and the maximum ratio between the throughput and bandwidth algorithms. Simulation results show that the proposed ACM scheme can reduce the BER and improve the power efficiency in the requirement of target BER limit, and provide a higher spectral efficiency under the same transmitting power compared with the existing ACM scheme.

A Serial Concatenation of Binary-Input Nonbinary-Output Convolutional Code and Recursive Convolutional Lattice Code

The recently proposed recursive convolutional lattice code (RCLC) can form a signal with pseudo-Gaussian constellations, and their parallel concatenation is shown to approach the Shannon limit. A practical limitation is that its input symbol is limited to $L^{2}$ -ary quadrature amplitude modulation (QAM), which has non-power-of-two constellation points when $L$ is chosen from the odd numbers. Therefore, encoding binary information by the RCLC is not straightforward. Furthermore, the information rate is limited to $\log _{2}~L$ bits per complex dimension due to their parallel concatenation. In this paper, we tackle these issues by introducing a serial concatenation of binary-input nonbinary-output convolutional code (CC) and the RCLC, where the outer CC outputs an $L$ -ary symbol that is matched to the input of the inner RCLC. We demonstrate that even with $L=3$ , the proposed approach can achieve 2 bits per complex dimension and still is able to approach the Shannon limit with lower decoding complexity compared with its parallel concatenation counterpart. As is demonstrated through theoretical analysis, the major practical drawback of the constellation generated by the RCLC is its Gaussian-like distribution, which has large peak-to-average power ratio. Therefore, we further introduce an approach to reduce the signal dynamic range for the proposed system. It is shown that a remarkable gain can be achieved in terms of capacity compared with the conventional QAM signals under the constraint of comparable power amplifier efficiency.

Tight Upper Bound Performance of Full-Duplex MIMO-BICM-IDD Systems in the Presence of Residual Self-Interference

In this paper, we derive a tight upper bound on the performance of a coded full-duplex multiple-input multiple-output (MIMO)-based bidirectional transceiver. Iterative detection and decoding (IDD) are proposed to suppress the residual self-interference (SI) remaining after applying different stages of SI cancellation. IDD comprises an adaptive minimum mean-squared error filter with log-likelihood ratio demapping, while the soft decoder by using soft-in soft-out decoding utilizes the maximum a posteriori algorithm. Furthermore, bit-interleaved coded modulation is considered in the presence of additive white Gaussian noise over MIMO frequency non-selective Rayleigh fading channels. Simulation results are presented to demonstrate the bit-error rate (BER) performance as a function of the signal-to-noise ratio showing a close match to the SI-free case for the proposed system. Furthermore, we validate our results by deriving a tight upper bound on the performance of the proposed system using rate-1/2 convolutional codes together with $M$ -ary quadrature amplitude modulation, which asymptotically exhibits a close agreement with the simulated BER performance. Moreover, extrinsic information transfer chart analysis is used to investigate the convergence behavior of the proposed IDD receiver and to determine the number of iterations required for this convergence.

On Bit Error Probability and Power Optimization in Multihop Millimeter Wave Relay Systems

5G networks are expected to provide gigabit data rate to users via the millimeter-wave (mmWave) communication technology. One of the major problems faced by mmWaves is that they cannot penetrate buildings. In this paper, we utilize multihop relaying to overcome the signal blockage problem in an mmWave band. The multihop relay network comprises a source device, several relay devices, and a destination device and uses device-to-device communication. Relay devices redirect the source signal to avoid the obstacles existing in the propagation environment. Each device amplifies and forwards the signal to the next device, such that a multihop link ensures the connectivity between the source device and the destination device. We consider that the relay devices and the destination device are affected by external interference and investigate the bit error probability (BEP) of this multihop mmWave system. Note that the study of the BEP allows quantifying the quality of communication and identifying the impact of different parameters on the system reliability. In this way, the system parameters, such as the powers allocated to different devices, can be tuned to maximize the link reliability. We derive exact expressions for the BEP of $M$ -ary quadrature amplitude modulation and $M$ -ary phase-shift keying in terms of multivariate Meijer’s G-function. Due to the complicated expression of the exact BEP, a tight lower bound expression for the BEP is derived using a novel Mellin-approach. Moreover, an asymptotic expression for the BEP at high SIR regime is derived and used to determine the diversity and the coding gain of the system. In addition, we optimize the power allocation at different devices subject to a sum power constraint such that the BEP is minimized. Our analysis reveals that optimal power allocation allows achieving more than 3-dB gain compared with the equal power allocation. This paper can serve as a framework for designing and optimizing mmWave multihop relaying systems to ensure link reliability.

Multi-RF Chain Time Successive Space-Shift-Keying-M-ary Modulation: A Transmit Diversity Scheme

A two-timeslot $N_{\text{RF}}$ radio frequency (RF) chain transmitter is proposed in this work that takes advantage of the independence of sum and difference of Gaussian random vectors to achieve second-order transmit diversity. Each RF chain in the transmitter is equipped with $N_t$ transmitter antennas such that the transmitter is capable of switching the modulation between space shift keying (SSK) and either $M$ -ary phase shift keying (MPSK) or $M$ -ary quadrature amplitude modulation (MQAM). In timeslot 1, the proposed multi-RF chain time successive SSK- $M$ -ary modulation (MRF-TSSM) uses SSK in each RF chain to transmit a block of $ N_{\text{RF}}$ information symbols. In timeslot 2, the same block of information symbols are transmitted using either MPSK or MQAM by activating all $ N_t$ antennas of every RF chain. For this system, the maximal likelihood detection metric, transmit diversity order, coding gain, and computational complexity are derived. The performance of MRF-TSSM is analyzed considering transmitter correlation using a tight upper bound of the bit error rate. The analysis is validated using simulation results, which show that MRF-TSSM achieves significant performance gains compared to some existing transmit diversity systems, and the transmit diversity of MRF-TSSM degrades only slightly even for high transmitter correlation. Furthermore, the performance of MRF-TSSM is studied with imperfect channel state information at the receiver.

ABER Performance of LDPC-Coded OFDM Free-Space Optical Communication System Over Exponentiated Weibull Fading Channels With Pointing Errors

A low-density parity-check (LDPC)-coded free space optical (FSO) orthogonal frequency-division multiplexing (OFDM) communication system over aggregated exponentiated Weibull (EW) fading channels with pointing errors considered is investigated. On the basis of the probability density function and cumulative distribution function of the composite channel gain, the analytical expressions of average bit error rate (ABER) of this FSO-OFDM system with on–off keying, K -ary quadrature amplitude modulation (QAM) and phase shift keying (PSK) modulation schemes are derived by using generalized Gauss–Lagurre quadrature rule, respectively. Monte Carlo simulations are provided to verify the validity of these three expressions. Furthermore, LDPC codes are applied in the simulation to improve the ABER performance. The results show that the ABER performance of 16-QAM-OFDM is better than that of the 16-PSK-OFDM system over composite EW fading channels, regardless of the turbulence strengths. For the modulation schemes involved, the degradation due to the increase of atmospheric turbulence strength for turbulence only scenario is more severe when compared with pointing errors included case. The study also demonstrates that significant coding gain improvement can be achieved by LDPC codes over EW fading channels, especially under strong turbulence condition. With pointing errors, more coding gain can be obtained when the jitter increases or beamwidth decreases.

Space-Time Network Coding With Multiple AF Relays Over Nakagami- $m$ Fading Channels

This paper first analyzes the symbol error rate (SER) performance of the space-time network coding (STNC) over independent but not necessarily identically distributed (i.n.i.d) Nakagami- $m$ fading channels, where multiple sources transmit information symbols to a destination through multiple helping amplify-and-forward (AF) relays. The exact expressions of the overall end-to-end received signal-to-noise ratio (SNR) via multiple STNC-AF relays and its moment generating function (MGF) are derived. Based on these results, the closed-form expression of STNC-AF for the SER with $M$ -ary phase-shift keying and $M$ -ary quadrature-amplitude modulation (QAM) modulations are then presented by adopting the unified MGF method. Furthermore, an approximate SER expression with low computational complexity is also given. In order to observe the performance limit, the diversity order and the nonorthogonality of STNC codes are discussed. Simulation results demonstrate our analytical results and it is illustrated that the diversity order of the STNC with multiple AF relay nodes is a sum function of the fading index of the direct link and the minimal fading indices of the multiple two-hop links.

Discrete Multi-Tone Digital Subscriber Loop Performance in the Face of Impulsive Noise

As an important solution to “the last mile” access, digital subscriber loops (DSLs) are still maintained in a huge plant to support low-cost but high-quality broadband network access through telephone lines. The discrete multi-tone (DMT) transmissions constitute a baseband version of the ubiquitous orthogonal frequency division multiplexing. While the DMT is ideally suited to deal with the frequency selective channel in DSL, the presence of bursty impulsive noise tends to severely degrade the transmission performance. In this paper, we analyze the statistics of impulsive noise and its effects on the received signals, with the aid of a hidden semi-Markov process. The closed-form bit error rate expression is derived for the DMT system for $Q$ -ary quadrature amplitude modulation under practical noise conditions and for measured dispersive DSL channels. Instead of relying on the simplified stationary and impulsive noise process, our noise model considers both the temporal and spectral characteristics based on the measurement results. The simulation results confirm the accuracy of the formulas derived and quantify the impact both of the impulsive noise and of the dispersive channel in DSL.

BER Performance of SFBC OFDM System Over TWDP Fading Channel

In this letter, the performance of uncoded and space frequency block coding (SFBC) orthogonal frequency division multiplexing (OFDM) system over two-wave with diffuse power (TWDP) fading environment is analyzed. A general closed-form expressions of average bit error rate for both $M$ -ary phase shift keying and $M$ -ary quadrature amplitude modulation are derived using moment generating function of TWDP fading distribution. Results are verified with the benchmark results available in the literature (i.e., Rayleigh and Rician). Numerical results with various TWDP fading channel parameter ( $K$ and $\Delta $ ) and with different modulation orders for uncoded and SFBC OFDM systems show excellent agreement with simulation results.

Average symbol error rate for M -ary quadrature amplitude modulation in generalized atmospheric turbulence and misalignment errors

A framework is presented for the analysis of average symbol error rate (SER) for M -ary quadrature amplitude modulation in a free-space optical communication system. The standard probability density function (PDF)-based approach is extended to evaluate the average SER by representing the Q -function through its Meijer’s G -function equivalent. Specifically, a converging power series expression for the average SER is derived considering the zero-boresight misalignment errors in the receiver side. The analysis presented here assumes a unified expression for the PDF of channel coefficient which incorporates the M -distributed atmospheric turbulence and Rayleigh-distributed radial displacement for the misalignment errors. The analytical results are compared with the results obtained using Q -function approximation. Further, the presented results are supported by the Monte Carlo simulations.

Performance of M ‐ary quadrature amplitude modulation ‐based orthogonal frequency division multiplexing for free space optical transmission

In this study, the authors analyse the performance of the free space optical (FSO) transmission link using orthogonal frequency division multiplexing (OFDM) modulation with M -ary quadrature amplitude modulation (QAM) encoder. For strong and weak atmospheric attenuation, the analysis of channel distribution in FSO is carried out using gamma–gamma model. In this analysis, the expressions for probability density function and cumulative density function of OFDM-based FSO channel have been derived in terms of Meijer's G-function. Also, the bit error rate and outage probability of M -ary QAM-based OFDM for an FSO transmission link has been derived. The feasibility of the system and the derived expressions are verified using Opti-system and MATLAB. From the analysis, it is observed that the performance of OFDM using M -ary QAM modulation is feasible for 7000 m, owning to its simplicity and good performance.

On the Spectral Efficiency of Rate and Subcarrier Bandwidth Adaptive OFDM Systems Over Very Fast Fading Channels

In this paper, rate and subcarrier bandwidth adaptation (RSBA) on the average spectral efficiency of orthogonal frequency-division multiplexing (OFDM) systems using $M$ -ary quadrature amplitude modulation ( $M$ -QAM) is investigated in the presence of frequency-selective and very rapidly time-varying fading channels. The closed-form expressions for rate and capacity with perfect channel state information (CSI) and imperfect CSI are derived. In this paper, imperfect CSI is caused jointly by channel estimation error and unavoidable delay between when CSI is estimated and when the estimation results are used for actual transmission. The capacity with perfect CSI is just a special case of imperfect CSI. Based on the closed-form expressions of the maximum capacity, optimal RSBA algorithms with perfect and imperfect CSI are proposed, respectively. Theoretical and numerical results show that the RSBA scheme can improve the system performance effectively under the perfect-CSI case. It can make a tradeoff between intercarrier interference (ICI) and transmission efficiency by considering the cyclic prefix. The results also show that the RSBA scheme is effective in repelling the impact of outdated CSI, as well as in reducing the impact of channel estimation error, but to a lesser extent.

Performance of Multihop Wireless Networks in Fading Channels Perturbed by an Additive Generalized Gaussian Noise

In the literature, the performance of multihop wireless networks is extensively analyzed over various fading channels subject to an additive white Gaussian noise (AWGN). However, and to the best of authors’ knowledge, the generalized Gaussian noise case has not been considered before. Motivated by this, we therefore analyze the system performance—in terms of the average bit error rate—of a multihop wireless communication system that operates over the $\alpha$ - $\mu$ fading channels perturbed by an additive white generalized Gaussian noise (AWGGN). To this end, we obtain an exact closed-form expression for the average bit error rate (BER) for $M$ -ary quadrature amplitude modulation ( $M$ -QAM) over the $\alpha$ - $\mu$ fading channels with AWGGN. Some representative numerical results are presented to study the influence of the fading parameters, as well as the influence of the shaping noise parameter. These results are supported with Monte-Carlo simulations to validate our analysis.

Error Rate and Power Allocation Analysis of Regenerative Networks Over Generalized Fading Channels

Cooperative communication has been shown to provide significant increase of transmission reliability and network capacity while expanding coverage in cellular networks. The present work is devoted to the investigation of the end-to-end performance and power allocation of a maximum-ratio-combining based regenerative multi-relay cooperative network over non-homogeneous scattering environment, which is the realistic case in many practical wireless communication scenarios. Novel analytic expressions are derived for the end-to-end symbol-error-rate of both M -ary phase-shift keying and M -ary quadrature amplitude modulation over independent and non-identically distributed generalized fading channels are given by exact analytic expressions that involve the Lauricella function and can be readily evaluated with the aid of a proposed computing algorithm. Simple analytic expressions are also derived for the corresponding symbol-error-rate at asymptotically high signal-to-noise ratios. The derived expressions are corroborated with respective results from computer simulations and are subsequently employed in formulating a sum-power optimization problem that enhances the system performance under total sum-power constraint within the multi-relay cooperative system. It is also shown that asymptotically optimum power allocation provides substantial performance gains over the corresponding equal power allocation, particularly, when the source-relay and relay-destination paths are highly unbalanced.

Optimum Detection of Two-Dimensional Carrier Modulations With Linear Phase Noise Using Received Amplitude and Phase Information and Performance Analysis

We consider the design of the optimum detector for two-dimensional amplitude/phase modulated signals received in additive white Gaussian noise (AWGN) and a Gaussian distributed phase reference error (PRE) due to imperfect carrier phase estimation. We propose a novel approach of using the amplitude and phase information of the received signal, based on viewing the AWGN as an equivalent additive observation phase noise (AOPN) whose statistics is derived in our earlier work. This allows the AOPN to be combined with PRE, and the maximum $a posterior$ probability (MAP)/maximum-likelihood (ML) detection scheme to be readily derived in amplitude-phase form. This amplitude-phase approach is simpler and more convenient than the conventional method of using the in-phase and quadrature components of signals in phase noise. For $M$ -ary phase-shift keying, which only has one ring of signal points, the ML detector here turns out to be the same as the conventional minimum Euclidean distance (MED) detector which is derived without taking the PRE into account, and leads to angular bisector decision boundaries (DB). However, for constellations which have multiple rings, e.g., $M$ -ary quadrature amplitude modulation ( $M$ -QAM) and amplitude phase-shift keying ( $M$ -APSK), the ML detector here is very computationally inefficient. Thus, simpler and closed-form approximations to the ML detector for equiprobable signals are given, which can be easily implemented online. All these simplified ML detectors are shown via simulations to perform almost the same as the exact one and perform much better than the MED detector. The approximate ML DB for both 8-star QAM and rotated 8-star QAM are illustrated as examples and shown to be not necessarily straight lines. As the variance of PRE or the signal-to-noise ratio (SNR) or both increases, the DB between two signal rings asymptotically becomes circular. This leads to an annular sector as the decision region for each signal point. For annular-sector decision regions, simple, accurate, and closed-form approximations to the symbol error probability (SEP) are obtained for both 8-star QAM and the rotated case, 16QAM and even general $M$ -APSK. These expressions provide explicit insight into how the PRE variance affects the performance. Within a wide range of PRE variances, our SEP approximations agree very well with the Monte Carlo simulations for all SNR values of interest. For the special case of an $M$ -APSK constellation which has the same number of points and the same phase values on each ring, such as 8-star QAM, one of the suboptimal ML detectors further simplifies to a structure that performs ring detection and phase detection separately, and the decision regions are always annular sectors.

Outage Analysis of Mixed FSO/WiMAX Link

In this paper, we study the outage performance of a complex system consisting of a free-space optical (FSO)/radio-frequency (RF) link. Using radio over free-space optics technology, the FSO link carries Worldwide Interoperability for Microwave Access (WiMAX) signals from a core network to a WiMAX base station, delivering traffic to multiple end RF users. A novel closed-form analytical expression for overall outage probability is derived when $M$ -ary phase-shift keying ( $M$ -PSK) and $M$ -ary quadrature amplitude modulation ( $M$ -QAM) are applied. The analysis is performed when the FSO link is under the influence of the Gamma–Gamma turbulence, path loss, and misalignment between the transmitter and receiver apertures, and the RF part is influenced by the Gamma-shadowed Nakagami- $m$ multipath fading. To illustrate the usefulness of the derived expressions, we present some numerical results that enable us to estimate the effects of different transceiver and channel parameters on the outage probability. The results are used for optimizing the transmitter laser beam radius at the waist to achieve the minimal overall outage probability in the case of different conditions over the RF part. The numerical and simulation results show that multipath fading severity and shadowing spread over the RF part have a significant effect on the optimal value of the laser beam waist and can decrease the overall outage probability for several orders of magnitude.