Single-carrier Quadrature Amplitude Modulation Research Articles

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.

Frequency-Domain Hybrid Modulation Formats for High Bit-Rate Flexibility and Nonlinear Robustness

Since the deployment of the first commercial polarization-multiplexed (PM) QPSK 100G systems, the evolution of coherent optical communications in the last decade has been largely dominated by single-carrier quadrature amplitude modulation (QAM) based modulation of increasing constellation size. However, as the data traffic becomes more dynamic and heterogeneous, an efficient use of the optical link requires more flexible modulation schemes, capable of adapting data-rate and distance with fine granularity. While typical multi-carrier modulation schemes composed of hundreds of subcarriers may be inadequate for optical transmission, namely due its high peak-to-average power ratio and increased nonlinearity penalties, it has been recently shown that few-carrier modulation (with symbol rate in the order of 2–4 GBaud) can provide an increased robustness to nonlinear propagation impairments. In this paper, we exploit the concept of frequency-domain hybrid modulation formats (FDHMF) based on electronic subcarrier multiplexing with the use of different QAM formats on each subcarrier to simultaneously enhance the data-rate flexibility and the nonlinear propagation performance of the optical link. In addition, by properly designing the FDHMF signal, an increased tolerance against optical filtering can also be achieved. Using the enhanced Gaussian noise model, we report a comprehensive theoretical study on the performance of FDHMF, considering independent- and joint-subcarrier forward-error correction strategies, optimization of power ratio between subcarriers, and corresponding impact of fiber nonlinearities. These theoretical insights are then validated by a broad range of wavelength-division multiplexing experiments with per-channel bit-rates in the range of 150G to 250G. The obtained results demonstrate that FDHMF is an effective solution for the implementation of flexible transponders capable of adapting the data rate to the lightpath quality of transmission: An enabling technology for the introduction of future elastic optical networks.

Nonlinearity and Noise Effects in Multi-Level Signal Millimeter-Wave Over Fiber Transmission Using Single and Dual Wavelength Modulation

We transmit multilevel quadrature amplitude modulation (QAM) data-IEEE 802.16 schemes-at 20 MSps and an orthogonal frequency-division multiplexing (OFDM) 802.11 g signal (54 Mbps) with a 25 GHz millimeter-wave over fiber system, which employs a dual wavelength source, over 20 km of single mode fiber. Downlink data transmission is successfully demonstrated over both optical and wireless (up to 12 m) paths with good error vector magnitude. An analysis of two different schemes, in which data is applied to one (single) and both (dual) of the wavelengths of a dual wavelength source, is carried out. The system performance is analyzed through simulation and a good match with experimental results is obtained. The analysis investigates the impact of Mach-Zehnder modulator (MZM) and RF amplifier nonlinearity and various noise sources, such as laser relative intensity noise, amplified spontaneous emission, thermal, and shot noise. A comparison of single carrier QAM IEEE 802.16 and OFDM in terms of their sensitivity to the distortions from MZM and RF amplifier nonlinearity is also presented.

Data sources for simulation of m-ary systems

It has been generally assumed that binary data from a maximum-length pseudo-random binary source can be grouped into m-ary symbols that will uniformly cover constellation points in a modulation scheme due to the central limit theorem. This is not the case. Sources based on the Galois field GF(16) are introduced and compared to binary, GF(2), ones in terms of the mean and variability of the resulting bit error rate (BER) estimate using a single carrier quadrature amplitude modulation (16-QAM) system as an example. The use of data sources over GF(16) for Monte Carlo simulation of the example system eliminates BER estimate variability with certain channels. Such variability is important when the channel is such that some of the constellation points cause higher probabilities of error than others. The approach is then extended to orthogonal frequency division multiplex (OFDM) m-ary systems. It is found that it is important to map separate Galois field data sources to each sub-carrier in the case of OFDM systems. There is found to be some residual BER estimate variability. The extension of the approach to systems employing forward error correction coding and interleaving is discussed.

Optimization and performance evaluation of multicarrier transmission

Optimization of the performance of multicarrier transmission over a linear dispersive channel is presented. The optimum data and power assignment to the subcarriers are derived for both the conventional error probability criterion, and a new criterion based on the normalized mean-square error. The assignments and algorithms hold for channels where performance is degraded by additive noise, intersymbol and interchannel interference. Lower bounds on throughput are derived and are used to compare multicarrier performance with conventional single-carrier quadrature amplitude modulation (QAM) with both linear and decision feedback equalization. It is seen that multicarrier transmission can provide a significant improvement at low and intermediate channel signal-to-noise ratios. As an example, the optimization is applied to the high-speed digital subscriber loop, and multicarrier transmission is demonstrated to be superior to decision feedback equalized single-carrier QAM.