Symbol Error-Rate Analytical Expressions for a Two-User PD-NOMA System with Square QAM

Power domain non-orthogonal multiple access (PD-NOMA) is one of the most perspective multiplexing technologies that allows improving the capacity of actual networks. Unlike orthogonal multiple access (OMA), the PD-NOMA non-orthogonally schedules multiple users in the power domain in the same orthogonal time-spectrum resource segment. Thus, a non-orthogonal multiplexed signal is a combination of several user signals (usually, modulation and coding schemes (MCS) based on quadrature amplitude modulation) with different power weights. The symbol error rate (SER) and bit error rate (BER) performances are one of the main quality characteristics of any commutation channel. The issue is that a known analytical expression for BER and SER calculation for conventional OMA cannot be applied in terms of the PD-NOMA. In the following work, we have derived the SER and BER analytical expressions for gray-coded square quadrature amplitude modulation (QAM) user channels that are transmitted in two-user PD-NOMA channel under additive white Gaussian noise (AWGN). Through the simulation, the verification of the provided expressions is presented for four multiplexing configurations with various user power weights and QAM order combinations.

The effects of the cross-entropy stopping criterion and quadrature amplitude modulation on iterative turbo decoding performance

One of the most often-used stopping criteria is the cross-entropy stopping criterion (CESC). The CESC can stop turbo decoder iterations early by calculating mutual information improvements while maintaining bit error rate (BER) performance. Most research on iterative turbo decoding stopping criteria has utilised low-modulation methods, such as binary phase-shift keying. However, a high-speed network requires high modulation to transfer data at high speeds. Hence, a high modulation technique needs to be integrated into the CESC to match its speed. Therefore, the present paper investigated and analysed the effects of the CESC and quadrature amplitude modulation (QAM) on iterative turbo decoding. Three thresholds were simulated and tested under four situations: different code rates, different QAM formats, different code generators, and different frame sizes. The results revealed that in most situations, the use of CESC is suitable only when the signal-to-noise ratio (SNR) is high. This is because the CESC significantly reduces the average iteration number (AIN) while maintaining the BER. The CESC can terminate early at a high SNR and save more than 40% AIN compared with the fixed stopping criterion. Meanwhile, at a low SNR, the CESC fails to terminate early, which results in maximum AIN.

Adaptive filtering of harmonic interference when receiving signals with quadrature amplitude modulation.

Quadrature amplitude modulation (QAM) signals are widely used in modern information transmission systems. The quality of the receiver of such signals is significantly reduced if non-fluctuation interference is present in the communication channel. Narrow-band (harmonic) interference with the frequency of the useful signal is especially dangerous. The aim of this work is to develop and study an adaptive algorithm for suppressing such interference when receiving QAM signals. The algorithm is based on a non-recursive digital filter with adjustable weights. It uses known information about the shape of the phase pulse of the signal. The efficiency of the algorithm is investigated by the method of computer simulation. When checking the performance of the algorithm, the spectrum of the signal and noise, the amplitude-frequency characteristic of the adaptive filter and the change in its shape over time were estimated. For 4-QAM and 16-QAM signals, the dependences of the bit error probability on the intensity of harmonic interference and on the signal-to-noise ratio are obtained. It is shown that the adaptive filter effectively suppresses harmonic interference with a relative intensity µ> 0.2 when receiving a 4-QAM signal. The energy advantage is 2 dB or more. When receiving QAM signals with M ≥16, which also have amplitude modulation, the algorithm remains operational, but the efficiency of using this adaptive filter is much lower. The energy advantage does not exceed 0.5 dB.

Quadrature Amplitude Modulation for Acoustic Data Communication in Ultrasonic Structural Health Monitoring Systems

Delivering information from the transducers to the base station is one of the main challenges in current guided wave-based structural health monitoring (SHM) systems. In recent years, novel solutions started to be investigated, which are based on guided ultrasonic waves (GWs). These waves experience mild power dissipation, hence being capable to travel comparatively long distances. The key idea is to exploit GWs as a means to transmit digital information (e.g. a damage indicator) directly over the mechanical waveguide. The advantage is that conventional radio-frequency communication is not needed and this is of the uttermost importance in harsh environments. Among the very different modulation techniques, a Quadrature Amplitude Modulation (QAM)–based modulation strategy is specifically employed in this work and numerical results are presented. More in detail, finite element simulations based on frequency steerable acoustic transducers (FSAT) are performed showing spatial multiplexing capabilities as widely used in modern 5G data communication systems.

High Capacity 64-Quadrature Amplitude Modulation Based Optical Coherent Transceiver for 60 GHz Radio Over Fiber System

Today’s world demands for maximum bandwidth utilization in the area of optical fiber network to achieve serious progress due to data consumption has been grown by > 25% as compared to last year. 5G system is one of the promising technology cater for high bandwidth utilization between multiple transceivers and have the advantages to operate in the milli-meter wave (mm-wave) of 60 GHz. There is much interest of photonic technique such as optical heterodyne coherent detection to produce mm-wave frequencies. We propose a 60 GHz radio over fiber (RoF) link using 168 Gb/s high capacity input data rate based 64-Quadrature amplitude modulation (64-QAM), coherent detection using optical heterodyning and advanced digital signal processing (ADSP) based system. An optimized version of optical heterodyne technique is used to derive 60 GHz radio frequency (RF) signal for connecting radio nodes over wireless link. In order to compensate the irregularities effect of standard signal mode fiber (SSMF), a novel ADSP technique is used which allows good improvement in the spectral signal efficiency and achieved longer distance communication. The ADSP technique plays a key role to achieve high capacity data rate requirements for forthcoming 5G technologies. The proposed RoF system shows that an error free transmission is accomplished over 170 km SSMF and achieved BER is 2.7×10-3 against 7.015 % error vector magnitude (EVM) with 30 dB Signal to Noise ratio (SNR).

Influence of phase and clock synchronization errors on the noise immunity of coherent reception of signals with quadrature amplitude modulation

Signals with quadrature amplitude modulation (QAM) is widely used for high-speed transmission of information in many radio systems and, in particular, in digital television systems. In the receiver, which is part of the transceiver equipment of such systems, there is a block for the formation of reference oscillations and a clock synchronization block. Due to hardware instabilities and propagation conditions, phase and clock errors may occur, which cause additional errors during demodulation of the received signal, and which can significantly impair the noise immunity of the reception. The paper investigates the effect of phase and clock synchronization errors on the noise immunity of coherent reception of QAM signals. Using the methods of statistical radio engineering, the parameters of the distributions of processes in the receiver are obtained and the probability of bit error is estimated. The dependences of the probability of bit error on the magnitude of the phase error in the formation of the reference oscillations and on the relative displacement of the clock moments, as well as on the signal-to-noise ratio, are obtained. It is shown that these errors can greatly reduce the noise immunity of the reception, and with an increase in the positioning of the signals, this effect increases. If we assume that the admissible reception energy loss is 0.5 dB due to each of these errors, then the allowable phase error is from ~3° at M = 4 to ~1° at M = 64, and the allowable clock synchronization error, respectively, is from ~5% at M = 4 to ~2% at M = 64. To provide more stringent requirements for the magnitude of losses, the requirements for the indicated errors increase significantly.