Quadrature Amplitude Modulation Schemes Research Articles

An efficient non-binary QC-LDPC coded modulation scheme for long-haul optical systems

Abstract Coded modulation (CM), which combines channel codes with high-dimensional modulation schemes, is an attractive technique to improve the spectral efficiency in high-speed optical transmission systems. Non-binary low-density parity check (NB LDPC) codes can provide larger coding gains with smaller codeword lengths compared to their binary counterpart, in addition to reducing the latency of the system. The majority of works based on NB LDPC CM focus on bit-interleaved CM (BICM) and the widely used additive white Gaussian noise (AWGN) channel model. However, the Gaussian channel model is not a realistic model for long-haul intensity-modulated direct-detection (IM/DD) optical systems using erbium-doped fiber amplifiers. In this paper, it is mathematically proved that noise in the received signals after photodetection can be more accurately represented using chi-squared distribution. The efficiency of CM depends on the mapping between coded symbols and the constellation signal points of the modulation scheme. Hence, a symbol interleaved CM with subcarrier modulation for NB LDPC codes based on the proposed channel model is presented in this paper to improve the bit-error rate (BER) performance. The simulation results show that the proposed CM for NB LDPC codes with M-ary quadrature amplitude modulation schemes provides better performance than BICM. The analysis of the error performance of the proposed system gives a coding gain of 1 dB at a BER of 10−7 compared to that of the AWGN channel model. The performance improvement of the system is also evaluated in terms of spectral efficiency and link distance.

Study of high-order non-equal probability QAM for visible light communication systems.

In this Letter, we propose and experimentally demonstrate a high-order non-equal probability quadrature amplitude modulation (NEP-QAM) scheme for visible light communication (VLC) systems, where NEP-72QAM is considered as an example. Nonlinear coding is introduced to generate the NEP-18QAM signal in the first quadrant, which is then jointly mapped with the other two bits to obtain the four-quadrant symmetric NEP-72QAM signal. Moreover, a bit-to-symbol labeling scheme is proposed to achieve thorough Gray mapping. The experimental results show that the NEP-72QAM scheme achieves better performance than the traditional 64QAM scheme regardless of whether the light-emitting diode (LED) operates in the linear or nonlinear range. Compared with the probabilistically shaped 72QAM scheme, the available range of the driving peak-to-peak voltage of the NEP-72QAM scheme is only reduced by 20 mV when 0.92 is used as the normalized generalized mutual information threshold, but the complexity is much lower.

Performance analysis of energy harvesting‐enabled relay networks inκ‐μfading channels

AbstractIn this paper, we investigate the performance of an energy harvesting (EH)‐enabled multiple relay network operating over generalized‐fading channels. Our approach involves utilizing a partial relay selection strategy and employing an amplify and forward relay protocol for efficient EH from RF signals. Additionally, we integrate a selection combining scheme at the receiver to combine both direct and relaying path signals. In our research, we first obtain the exact closed‐form expression of the cumulative distribution function (CDF) for the system under investigation. Subsequently, we derive expressions for the outage probability (OP) and the moment generating function (MGF) using the derived CDF expression. Furthermore, with the assistance of a CDF‐based approach, we derive closed‐form expressions for the average symbol error rate (ASER) for coherent quadrature amplitude modulation (QAM) schemes, including rectangular QAM (RQAM) and hexagonal QAM (HQAM). We also analyze the ASER expression for non‐coherent frequency shift keying (NCFSK), leveraging the derived MGF expression. To gain valuable insights into the performance of EH‐enabled multiple relay networks, we assess the asymptotic expression of the OP. The outcomes indicate how the behavior of the system is affected by various factors such as time switching ratio, channel fading components, number of relays, and the distance between nodes. To corroborate the accuracy of the analytical findings, Monte Carlo simulations are executed.

A Survey on Spatial Modulation OFDM: Optimal Detection and Performance Analysis

Spatial modulation is a novel modulation scheme that aims to acquire a trade-off between the two adverse purposes in wireless communications, namely the improvements of data rate and data reliability, by adjusting the operational transmit antenna index in the emitted bits. To fight against inter-symbol interference (ISI) present in frequency selective channels, orthogonal frequency division multiplexing (OFDM) as become a extensively accepted and used mechanism. We investigate in this work the performance of SM-OFDM modulation over frequency selective MIMO channel using quadrature amplitude modulation (QAM) scheme. At the receiver side, a group of detectors is proposed to recover the active transmit antenna index (Tx-antenna) and the emitted data sequence. In this paper, a new SM-OFDM-based scheme is proposed, which adds another element of information in the transmitted SM-data block consisting of a chosen constellation among the available rotated set. To attain this, an additional index is used to select the specific constellation. At the receiver, a set of detectors is proposed to jointly estimate the transmitted symbol, as well as the used constellation and the active transmit antenna indices. The comparison of the performance of this new scheme against the conventional SM-OFDM shows an increased spectral efficiency at the price of a slight degradation in bit error rate. The proposed scheme permits a trade-off between the quality of the communication and the achieved spectral efficiency. Some concluding remarks are drawn over simulation results.

Super-Regenerative Receiver Wake-Up Radio Solution for 5G New Radio Communications

Wake-up radio is a promising solution to reduce the energy wasted by mobile devices during an idle state. In this paper, we propose a new wake-up radio solution for 5G mobile devices based on a super-regenerative receiver characterized by its low cost and low power consumption and investigate how to build on the orthogonal frequency-division multiplexing (OFDM) modulation capability at the base station to generate optimal wake-up signals. After presenting the relevant features and limitations of super-regenerative receivers operating in different 5G New Radio (NR) frequency bands, we evaluate how the numerology, the number of resource blocks, and the quadrature amplitude modulation (QAM) scheme used affect the sensitivity of the super-regenerative wake-up receiver. The results show that a 256-QAM modulation scheme, together with the highest numerology values, achieves optimal receiver sensitivity with a minimal number of resource blocks, yielding higher duty cycle pulses that also facilitate symbol synchronization tasks.

DGT-based pulse shaping filter for Generalized Frequency Division Multiplexing system

The future wireless communication systems belonging to the next generation will encounter many diverse demands, like the need for data rates that surpass the capabilities of fifth-generation networks, ultra-low power consumption to cater to battery-operated communication sensors, and extremely short response times essential for control applications. A unified physical layer waveform is envisaged to address these flexible requirements, introduced as Generalized Frequency Division Multiplexing (GFDM) for beyond 5G (B5G) communication systems. One of the important features of GFDM is the utilization of flexible pulse shaping filtering in the time domain, resulting in improved performance. In this paper, a pulse-shaping filter is designed for the GFDM system using discrete Gabor representation, discrete biorthogonality condition and Wigner distribution. An analytical expression for the analysis window is derived using the biorthogonality condition. Further, the performance of the GFDM system is analyzed in terms of out-of-band (OOB) radiation and symbol error rate (SER). The results are presented for the Quadrature Amplitude Modulation (QAM) scheme over Additive White Gaussian Noise (AWGN), Rayleigh, Nakagami-m, two wave with diffuse power (TWDP), and Nakagami-q fading channels. The detailed analysis shows that the OOB radiation and SER performance exhibit strong dependence on the choice of the pulse shaping filter.

ASE noise mitigation with digital frequency offset loading for discrete spectrum nonlinear frequency division multiplexing systems.

We propose an amplified spontaneous emission (ASE) noise mitigation scheme utilizing digital frequency offset loading (DFO-loading) for discrete spectrum nonlinear frequency division multiplexing (DS-NFDM) systems. Firstly, based on the one-to-one mapping relationship between frequency offsets and eigenvalue positions, the transmitter side encodes 4-bit information onto 16 kinds of different digital frequency offsets. Then, a sliding window-assisted eigenvalue position (SWA-EP) decoding technology is further proposed to substitute the classical channel equalization and carrier phase recovery processes, with the purpose of recovering the original information. The numerical and experimental results demonstrate that, compared with b-coefficient 16 quadrature amplitude modulation (QAM) scheme, Q-factor gains are 2.1 dB under 15 dB optical signal-to-noise ratio (OSNR) and 1.8 dB after 800 km fiber transmission, respectively. Moreover, its complexity is only 0.6% of the b-coefficient scheme. The DFO-loading scheme offers an effective and low-complexity way to mitigate ASE noise of DS-NFDM system.

SIMULASI SKEMA MODULASI 1024-QAM DAN 4096-QAM PADA SISTEM KOMUNIKASI DIGITAL

Quadrature amplitude modulation (QAM) is a modulation scheme used by digital communication systems to obtain high data rates in bandwidth-limited channels. M-ary QAM schemes with M values greater than 256 are currently used by wireless network standards, such as WiFi 6 and WiFi 7 (final standard will be released in 2024), which use the 1024-QAM and 4096-QAM modulation schemes, respectively. With the continuous development of technology for digital communication systems, both wireline and wireless, it is essential to research regarding advanced modulation schemes. This study discusses the simulation of the 1024-QAM and 4096-QAM modulation schemes using MATLAB software to compare the performance of the two modulation schemes in data transmission through the AWGN channel without using an error control code. The simulation results show that 4096-QAM is superior to 1024-QAM but requires higher Eb/N0 and SNR values. The Eb/N0 value required by the 4096-QAM to achieve a bit error ratio (BER) of 10-4 is 31 dB, while the 1024-QAM requires an Eb/N0 value of 26 dB.

Design of Orthogonal Pulse Waveforms With Tunable Frequency and Bandwidth for Carrier-Free THz Communications

Carrier-free pulse-based waveforms are desired in terahertz (THz) communications since pulse-based systems have simpler transceiver architectures than carrier-based systems. For such a pulse-based THz communication system, there still lacks pulse waveforms that can support high-order modulation and flexible multiple access. In this paper, a pulse-based waveform with continuously tunable center frequencies and bandwidths is designed for carrier-free THz communications. More specifically, a Gaussian pulse is utilized as the basic pulse, and then the weighted sum of its high-order derivatives is used to generate waveforms with tunable frequencies and bandwidths according to the probability density function of Rice distribution. Such a pulse-based waveform is called frequency and bandwidth continuously tunable (FBCT) pulse. By making the derivative orders of all weighted terms odd or even, a pair of orthogonal FBCT pulses can be generated. Based on the pair of orthogonal FBCT pulses, a basic pulse-based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary quadrature amplitude modulation (P <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> QAM) scheme can be readily achieved. Moreover, with frequency and bandwidth tunability, FBCT pulse can support pulse division multiple access (PDMA) with tunable bandwidth, through which frequencies with high molecular absorption loss can be avoided. Numerical results demonstrate that FBCT pulse is significantly effective and flexible in supporting carrier-free THz communications.

Attention-assisted autoencoder neural network for end-to-end optimization of multi-access fiber-terahertz communication systems

We propose an end-to-end (E2E) fiber-terahertz (THz) integrated communication system based on an attention-assisted multi-access autoencoder (AMAE) neural network. The AMAE neural network comprises artificial neural networks (ANNs) that function as transmitters (T-ANNs), channel models, and receivers (R-ANNs) for multiple users. By connecting the computational graph of multiple T-ANNs and R-ANNs, we jointly optimize the AMAE to facilitate E2E multi-access communication. Attention mechanisms guide the optimization process to achieve fair and efficient power allocation and orthogonality among different users. We experimentally evaluated the performance of our proposed E2E framework in a 60 Gbit/s multi-channel (1, 5, and 10 km) fiber-THz hybrid system. The results indicate that our AMAE approach outperforms the conventional single-carrier quadrature amplitude modulation scheme by over 3 dB in receiver sensitivity and 11 Gbit/s in capacity under the 20% soft-decision forward error correction threshold in the same-channel back-to-back condition. Additionally, under the performance balance constraint, our approach achieves a transmission speed of 60 Gbit/s within a 10 GHz bandwidth in the multi-channel setting.

Enhancing security and capacity in FSO transmission for next-generation networks using OFDM/OCDMA-based ICSM codes

In order to address the growing demands for both enhanced security levels and increased transmission capacity, this research proposes a novel approach for free space optical (FSO) transmission. The proposed design incorporates an identity column shift matrix (ICSM) code to ensure robust security. Additionally, capacity enhancement is achieved through the utilization of a 4-level quadrature amplitude modulation (4-QAM) scheme in conjunction with an orthogonal frequency division multiplexing (OFDM) modulator. The performance of the system is evaluated across three channels, each transmitting data at a rate of 20 Gb/s, while operating in an FSO channel that is subjected to varying atmospheric attenuation effects and atmospheric turbulence. Real meteorological data from three different cities [Alexandria, Egypt; Jeddah, Kingdom of Saudi Arabia (KSA); and Hyderabad, India], situated across two continents, are incorporated to demonstrate the practicality of implementing the proposed model in real-world environments. The experimental results reveal that an increase in atmospheric turbulence leads to a higher bit error rate (BER) and lower received optical power (ROP), resulting in degraded data reception. Furthermore, the study examines the impact of weather conditions, indicating that the longest and shortest propagation ranges of 12.5 and 0.286 km, respectively, are achieved under clear weather and heavy dust storms. These conditions yield an ROP of −9.5 dBm and a log (BER) of approximately −2.5. Conversely, in the presence of strong turbulence, the performance further deteriorates. The proposed model demonstrates its ability to transmit a message signal over a distance of 0.8375 km, with a log (BER) of −2.6 under weak atmospheric turbulence. However, under strong atmospheric turbulence at the same distance, the log (BER) increases to −0.5. Regarding specific cities, the FSO range for transmitting information signals is found to be 9.58 km in Jeddah, which decreases to 6.58 km in Alexandria and 5.17 km in Hyderabad due to the increased atmospheric attenuation in these cities.

SNR Improved Digital-PCM Radio-Over-Fiber Scheme Supporting 65536 QAM for Mobile Fronthaul

We propose a digital pulse-code-modulation radio-over-fiber (DP-RoF) scheme and verify it experimentally in a 10-km standard single-mode fiber (SSMF) coherent system. The 20-Gbaud DP-RoF signal with a common public radio interface equivalent data rate (CPRI-EDR) of 112 Gb/s is successfully transmitted in the system with excellent performance. The recovered signal-to-noise ratio (SNR) of wireless signal in DP-RoF scheme is 50.14 dB, which is 26.62, 20.01 and 13.28 dB higher than that of analog radio-over-fiber (A-RoF), digital-analog radio-over-fiber (DA-RoF) and digital radio-over-fiber (D-RoF), respectively. The DP-RoF scheme meets the error vector magnitude (EVM) requirement of 65536 quadrature amplitude modulation (QAM), while A-RoF and DA-RoF schemes cannot reach the EVM threshold of 1024 QAM. With improved SNR, the proposed DP-RoF system is a promising scheme for ultra-high-order QAM transmission in future 6G fronthaul.

A nonbinary LDPC-coded product distribution matching probabilistic shaping scheme for high order modulation

In this paper, a non-binary low-density parity-check (LDPC)-coded low complexity product distribution matching (PDM) probabilistic shaping (PS) scheme for high-order modulation is proposed. Compared with conventional non-binary LDPC-coded regular quadrature amplitude modulation (QAM) schemes, the proposed non-binary LDPC-coded low complexity PDM-PS QAM scheme can obtain shaping gain, as evidenced through theoretical average mutual information and simulated error performance analyses. When the spectral efficiency is 4.5 bits/s/Hz, compared with the regular 64QAM system, the proposed 64QAM PDM-PS system can obtain 0.26 dB theoretical energy gain, while its simulated error performance is 0.30 dB. When the spectral efficiency is 6.0 bits/s/Hz, compared with the regular 256QAM system, the proposed 256QAM PDM-PS system can obtain 0.73 dB theoretical energy gain, while its simulated error performance is 0.93 dB. Compared with the conventional non-binary LDPC-coded PS QAM scheme, the proposed non-binary LDPC-coded PDM-PS QAM scheme can reduce the computational complexity by 33.1% and 49.7% under 64QAM and 256QAM, respectively, with acceptable error performance loss. The information-theoretic and error performance analyses both indicate the effectiveness and reliability of the proposed scheme.

Performance of orthogonal frequency division multiplexing based M‐ary quadrature amplitude modulation in asymmetrical dual‐hop mixed RF‐FSO transmission system

SummaryThis paper investigates the performance of a dual‐hop mixed relay system with radio frequency (RF) and free‐space optics (FSO) communication under the effect of pointing error (PE) and atmospheric turbulence (AT). This paper considers a system where RF and FSO links are cascaded. The RF link is modeled by Nakagami‐m fading, and the FSO link is modeled as gamma–gamma (G‐G) fading channel. Both the channel models use orthogonal frequency division multiplexing (OFDM) with M‐ary quadrature amplitude modulation (QAM). The expressions for probability density function, cumulative distribution function, signal‐to‐noise ratio, and ergodic capacity are derived. The moment generating function (MGF) of fading and the bit error rate (BER) of the OFDM‐based M‐ary QAM scheme is derived in terms of Meijer's G‐function. It has been observed that, in fixed gain relay systems, the modulation scheme's BER is dominated by the SNR of the RF link. While in a variable gain relay system, the turbulence conditions of the FSO system affect the SNR and the BER of the modulation method. The feasibility of heterodyne detection and intensity modulation direct detection (IM/DD) is analyzed in terms of outage probability and ergodic capacity. The results can be used to choose the optimal modulation order and relay system for QAM‐OFDM‐based optical wireless systems.

Real-time demonstration of a low-complexity PS scheme for 16QAM-DMT signals in an IM-DD system.

We experimentally demonstrated a low-complexity probabilistic shaping (PS) 16-ary quadrature amplitude modulation (16QAM) scheme based on intra-symbol bit-weighted distribution matching (Intra-SBWDM) for discrete multi-tone (DMT) symbols with field-programmable gate array implementation in an intensity modulation and direct detection (IM-DD) system. Different from the traditional PS scheme such as Gallager many-to-one mapping, hierarchical distribution matching and constant composition distribution matching, the Intra-SBWDM scheme with lower computation and hardware complexity does not need to continuously refine the interval to find the target symbol probability, nor does it need a look-up table, so it does not introduce a large number of extra redundant bits. In our experiment, four PS parameter values (k = 4, 5, 6, and 7) are investigated in a real-time short-reach IM-DD system. 31.87-Gbit/s net bit PS-16QAM-DMT (k = 4) signal transmission is achieved. The results show that the receiver sensitivity in terms of the received optical power of the real-time PS scheme based on Intra-SBWDM (k = 4) over OBTB/20 km standard single-mode fiber can be improved by about 1.8/2.2 dB at the bit error rate (BER) of 3.8 × 10-3, compared to the uniformly-distributed DMT. In addition, the BER is steadily lower than 3.8 × 10-3 during a one-hour measurement for PS-DMT transmission system.

Performance analysis of cooperative spectrum sensing using double dynamic threshold

&lt;p&gt;Increased use of wireless technologies and in turn more utilization of available spectrum is subsequently leading to the increasing demand for wireless spectrum. This research work incorporates spectrum sensing detection consisting of a double dynamic threshold followed by cooperative type spectrum sensing. The performance has been analyzed using two modulation schemes, quadrature-amplitude-modulation (QAM) &amp;amp; binary-phase-shift-keying (BPSK). Improved probability of detection has been witnessed using the double dynamic threshold where a comparison of average values of local decision (LD) and the observed value of energy (EO) has been considered instead of using direct values of local decisions and energy. Further, the probability-of-detection ( ) is found to be better with QAM as compared to the BPSK. From the results, it has been observed that the detection of primary users is also affected by the number of samples. The simulation environment considered for this work is MATLAB and the performance of cooperative spectrum sensing for 500 and 1000 samples with -9db and -12 SNR by considering different false alarm values i. e 0.1,0.3 and 0.5 has been analyzed. The further scope shall be to enhance the primary user detection by considering different QAM schemes and different SNRs.&lt;/p&gt;

A Review of Integrated Systems and Components for 6G Wireless Communication in the D-Band

The evolution of wireless communication points to increasing demands on throughput for data-intensive applications in modern society. Integrated millimeter-wave systems with electrical beam-steering capabilities are promising candidates for wireless technologies of the future and are currently the subject of widespread academic and commercial research. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band, ranging from 110–170 GHz, offers high aggregate bandwidths (BWs), low atmospheric absorption, and multi-GHz operation at amenable fractional BWs. It, therefore, has the potential to foster efficient, highly integrated wireless-communication systems with data rates approaching 100 Gb/s. This article reviews all aspects of hardware integration against the backdrop of an extensive literature review and outlines the challenges and possible solutions for practical 6G wireless systems in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band. To this end, this article covers a number of related topics in depth, which includes system definition, possible radio architectures and array configurations, the scope and potential of integrated circuit (IC) technologies, the design and characterization of key circuit blocks, advances in antenna and packaging technologies for high-frequency systems, and an overview of measurement techniques currently employed at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band frequencies. A system-level study based on radio-link simulations of different single-carrier quadrature amplitude modulation (QAM) schemes is presented, which quantifies that the impact physical nonidealities, such as signal-to-noise ratio, phase noise, intermodulation distortion, and amplitude and phase imbalances in quadrature signal paths, have on bit-error rates in broadband <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band communication systems. This is followed by a comparative assessment of different arrayed-system configurations that include traditional phased arrays, the use of polarization diversity for the transmission of different or identical data streams, and multiple input multiple output (MIMO) operation. The article also presents an overview of possible transceiver architectures for implementing beam-steering arrays and an outline of the associated tradeoffs. The beam-squinting effect seen in large arrays is also investigated in detail. On the implementation front, we present a comparison between different integrated-circuit technologies for high-frequency applications. These include CMOS and SiGe bipolar complementary metal oxide semiconductor (BiCMOS) heterojunction bipolar transistors (HBTs) in silicon technologies, and MOSFETs, HBTs, and HEMTs in III–V technologies, such as InP and GaAs. Implementation challenges are then addressed, and these include the design of high-frequency circuits in the latest IC technologies, current advances in antenna and packaging technologies, and emerging solutions for hybrid integration. The article also details the design and characterization of critical <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band transceiver circuit blocks, namely, power and low-noise amplifiers, mixers, phase shifters, passive components for quadrature-phase generation, and radiators exploring hybrid antennas, which we have developed over the course of the past five years. These results compliment the literature survey with comparisons with state-of-the-art designs and are applied to radio-link simulations to predict the performance of practicable wireless links.

Average symbol error rate analysis of reconfigurable intelligent surfaces-assisted free-space optical link over log-normal turbulence channels

&lt;span&gt;Optical wireless communication (OWC) has attracted significant interest recently in academia and industry. Free-space optical (FSO) communication systems are where free space acts as a communication channel between transceivers that are line of sight (LOS) for the successful transmission of optical signals. The FSO transmissions through the atmosphere, nevertheless, bring significant challenges, besides the uncertainty of atmospheric channels, especially the signal fading due to the atmospheric turbulence, attenuation and pointing errors caused by the random beam misalignments between transceivers, signal obstruction due to buildings or trees can pre-vent the transmitted message to reach the destination. This study theoretically investigates the average symbol error rate (ASER) of reconfigurable intelligent surfaces (RIS) assisted FSO link over log-normal turbulence channels. The RIS effect is examined by considering the influence of link distance, transmitted optical power, and quadrature amplitude modulation (QAM) scheme on the ASER.&lt;/span&gt;

Coded Asymmetric Modulation Design for Block-Fading Channels With Nonlinear Energy Harvesting

In this letter, the design of coded modulation for simultaneous wireless information and power transfer (SWIPT) block-fading channels is proposed, for both power-splitting (PS) and time-switching (TS) nonlinear energy harvesting (EH). With PS, although the diversity-rate tradeoff is not affected, nonlinear EH requires asymmetric modulations design which leads to an information transfer (IT) performance penalty. We thus design an asymmetric circular quadrature amplitude modulation (ACQAM) scheme that provides large performance gains compared to conventional modulations. On the other hand, we show that TS negatively impacts the diversity-rate tradeoff of the coded modulation, while an optimal QAM can be employed in the IT phase. We next derive an upper bound on the average word error rate (WER) based on a pairwise error probability analysis for both EH methods. Finally, WER simulation results are shown together with the derived bounds.

On the Performance of Square, Rectangular, Star, and Hexagonal QAM for Backscatter Systems

Applications on wireless sensing and internet of things (IoT) require communication systems based on low power with high data rates. Thus, backscatter communication plays an important role in the new emerging IoT communications. In the literature, several works have been reported about backscatter modulators with high-order modulation formats. However, only the square quadrature amplitude modulation (S-QAM) scheme is considered, although it is not optimal in the sense of power efficiency. In this letter, the performance of two dimensional (2-D) signal constellations is evaluated, namely rectangular QAM, star QAM, and hexagonal QAM, in terms of the symbol error rate, in backscatter systems context. A power consumption analysis is presented for these modulation schemes. To provide the symbols of the aforementioned constellations, a practical high-order backscatter modulator, corroborated by measurement campaigns, is implemented. Several SER curves are also presented in this work.