Single-carrier Transmission Research Articles

A Novel Shaping Scheme for PAPR Reduction in Single-Carrier Modulation

A novel PAPR shaping technique intended for systems with high spectral efficiency and single carrier transmission is presented. This technique applies puncturing of error correction redundancy bits to achieve a desired Markovian symbol transmission probability distribution, which avoids symbol sequences with high peak values. For a 16-QAM system with transmission rate of 3 bit/symbol and a root raised cosine (RRC) pulse shape filter with roll-off factor 0.1 and duration of six symbols, an overall gain of about 2.2 dB is demonstrated by simulations using pragmatic binary turbo code for error correction. The technique can be used to improve any single carrier communication link limited by the high power amplifier (HPA) peak power.

Joint Channel-Estimation/Decoding With Frequency-Selective Channels and Few-Bit ADCs

We propose a fast and near-optimal approach to joint channel-estimation, equalization, and decoding of coded single-carrier (SC) transmissions over frequency-selective channels with few-bit analog-to-digital converters (ADCs). Our approach leverages parametric bilinear generalized approximate message passing (PBiGAMP) to reduce the implementation complexity of joint channel estimation and (soft) symbol decoding to that of a few fast Fourier transforms (FFTs). Furthermore, it learns and exploits sparsity in the channel impulse response. Our work is motivated by millimeter-wave systems with bandwidths on the order of Gsamples/sec, where few-bit ADCs, SC transmissions, and fast processing all lead to significant reductions in power consumption and implementation cost. We numerically demonstrate our approach using signals and channels generated according to the IEEE 802.11ad wireless local area network (LAN) standard, in the case that the receiver uses analog beamforming and a single ADC.

Secrecy Performance of Finite-Sized In-Band Selective Relaying Systems With Unreliable Backhaul and Cooperative Eavesdroppers

This paper investigates the secrecy performance of a finite-sized in-band selective relaying system with $M$ transmitters connected via unreliable backhaul links, $N$ decode-and-forward relays, and $K$ collaborative eavesdroppers. To send the source message to the destination, a transmitter-relay pair that achieves the highest end-to-end signal-to-noise ratio is selected for transmissions, while the $K$ eavesdroppers combine all the received signals from the selected transmitter and relay using maximal ratio combining. The proposed model introduces backhaul reliability and eavesdropping probability parameters to investigate practical constraints on the transmitter-relay cooperation and eavesdropper collaboration, respectively. Closed-form expressions are derived for the secrecy outage probability, probability of non-zero achievable secrecy rate, and ergodic secrecy rate for non-identical frequency-selective fading channels with robust cyclic-prefixed single carrier transmissions. These results show that the asymptotic secrecy outage probability and probability of non-zero achievable secrecy rate are exclusively determined by the number of transmitters $M$ and their corresponding set of backhaul reliability levels. Under unreliable backhaul connections, it is found that the secrecy diversity gain is determined by $M$ , $N$ , and the number of multipath components in the frequency selective fading channels. Link-level simulations are conducted to verify the derived impacts of backhaul reliability and collaborative eavesdropping on the secrecy performance.

Robust Single-Carrier Frequency-Domain Equalization for Broadband MIMO Systems With Imperfect Channel Estimation

Single-carrier frequency-domain equalization (SC-FDE) with multi-input multi-output (MIMO) has been recognized as an alternative technology to orthogonal frequency-division multiplexing with MIMO for broadband wireless communication systems because of its single carrier transmission advantages. Conventional SC-FDE MIMO schemes are designed under the assumption of perfect channel estimation. In this paper, we investigate the robust SC-FDE MIMO design for systems with imperfect channel estimation. Based on a statistical model for channel estimation, the optimal equalization coefficients for the robust SC-FDE MIMO schemes with both parallel interference cancellation and successive interference cancellation (SIC) are derived with the objective of minimizing the sum of the multiple data streams’ mean square errors (sum-MSE). We propose an optimal ordering algorithm in the sense of minimum sum-MSE for the SC-FDE MIMO scheme with SIC, and further propose a low complexity sub-optimal ordering algorithm. The bit-error-rate (BER) performance in the uncoded case is analyzed and a tight BER approximation is derived. Numerical results show that the proposed robust SC-FDE MIMO schemes achieve 1.5dB~4dB gains in $ E_{b}/N_{0}$ over the conventional non-robust schemes.

Multidimensional PAM With Pseudo-Gray Coding for Flexible Data Center Interconnects

Conventional modulation formats for single carrier transmission do not provide the flexibility to gradually scale the data rate and spectral efficiency. By using multidimensional pulse-amplitude modulation, fractional numbers of bits per symbol can be achieved, which extends the flexibility and reach of intensity modulation and direct detection systems but keeps the signal processing simple. By using pseudo-Gray coding, we are able to achieve optimum mappings for various non-integer bits-to-symbol assignments. We show a transmission experiment with data rates ranging from 56 to 168 Gb/s in fine granularity over different link lengths at a symbol rate of 56 GBd.

Distributed Space Time Block Transmission and QRD Based Diversity Detector in Asynchronous Cooperative Communications Systems

Based on the zero prefix (ZP) structure, we propose an efficient block transmission algorithm using distributed space-time codes in the asynchronous cooperative communication systems. To accomplish the new frame, ZP is inserted in front of the data block to combat the relative delay between the asynchronous relays, while zero suffix (ZS) is appended at the end of the block to remove the interblock interference caused by the time dispersing channel; so, we employ this ZP–ZS precoding form to make the coded frames synchronous. It should be noted that single carrier transmission and orthogonal frequency division multiplexing (OFDM) are both compatible with the frame. For single carrier transmission, conventional space-time equalizers can be investigated at the destination node to cancel the multipath interference. To further improve the performance, an improved QR decomposition-based recursive interference cancellation (QRD-RIC) detector is employed, where joint QRD is adopted on the combination of channel matrices from different relays, and then spatial-and-multipath diversity combinations are introduced and improved into the proposed system, where the spatial and multipath diversities are acquired. For OFDM, the fractionally spaced frequency-domain MMSE diversity receiver is employed, since the guard interval in our framing scheme implies oversampling in the frequency domain. Numerical simulations show that the proposed algorithms are effective for the asynchronous transmissions under frequency selective fading channels.

Joint Channel-Estimation and Equalization of Single-Carrier Systems via Bilinear AMP

We propose a novel soft-input soft-output equalizer for single-carrier transmissions over unknown frequency-selective block-fading channels. Our equalizer leverages the recently proposed parametric bilinear generalized approximate message passing algorithm for joint channel-estimation and symbol-detection, and exploits fast Fourier transform (FFT)-processing to achieve a per-symbol complexity that grows only logarithmically in the channel delay-spread. Furthermore, it supports the use of Gaussian mixture models to support the approximately sparse nature of wideband wireless channel responses. Numerical experiments, conducted using physically motivated Saleh–Valenzuela channel models, show that the proposed approach achieves channel normalized mean square error and bit error rate that are significant improved over existing turbo frequency-domain equalization approaches for unknown channels. Additional experiments show that the proposed scheme facilitates much higher spectral efficiencies than sparse deconvolution methods based on convex relaxation.

Uplink Spectral Efficiency Analysis and Optimization for Massive SC-SM MIMO With Frequency Domain Detection

Recently the combination of massive multiple-input multiple-output (MIMO) and spatial modulation (SM), has been considered as a promising concept for uplink transmission, in which each user equipment (UE) uses SM for uplink transmission and base station (BS) is equipped with massive antennas. In this paper, we evaluate a massive single-carrier (SC) SM-MIMO system with frequency domain equalization, where SC transmission is combined with SM (SC-SM) to combat the negative impact of broadband frequency-selective fading, and frequency domain equalization is utilized to mitigate the intersymbol-interference with a low complexity. With frequency domain processing, a framework is proposed to analyze the achievable uplink spectral efficiency (SE) of single-cell massive SC-SM MIMO systems. Based on this framework, the closed-form SE lower bound of frequency domain maximum ratio combining is derived, and both the derivation of framework and SE lower bound are much more complicated than those of systems with time domain combining. Monte Carlo simulations verify the tightness of proposed SE lower bound, and show that massive SC-SM MIMO systems can outperform the SE of conventional single transmit antenna (TA) massive MIMO systems. The systems can even have a better SE performance than massive MIMO systems with spatial multiplexing UEs in a low signal-to-noise ratio. Finally, the SE gain is found to be mainly dependent on the specific number of UE's TAs, which facilitates an SE maximization via optimizing the number of TAs.

Multi-User Millimeter Wave MIMO With Full-Dimensional Lens Antenna Array

Millimeter wave (mmWave) communication by utilizing lens antenna arrays is a promising technique for realizing cost-effective 5G wireless systems with large MIMO (multiple-input multiple-output) but only limited radio frequency (RF) chains. This paper studies an uplink multi-user mmWave single-sided lens MIMO system, where only the base station (BS) is equipped with a full-dimensional (FD) lens antenna array with both elevation and azimuth angle resolution capabilities, and each mobile station (MS) employs the conventional uniform planar array (UPA) without the lens. By exploiting the angle-dependent energy focusing property of the lens antenna array at the BS as well as the multi-path sparsity of mmWave channels, we propose a low-complexity path division multiple access (PDMA) scheme, which enables virtually interference-free multi-user communications when the angle of arrivals (AoAs) of all MS multi-path signals are sufficiently separable at the BS. To this end, a new technique called path delay compensation is proposed at the BS to effectively transform the multi-user frequency-selective MIMO channels to parallel frequency-flat small-size MIMO channels for different MSs, for each of which the low-complexity single-carrier(SC) transmission is applied. For general scenarios with insufficient AoA separations, analog beamforming at the MSs and digital combining at the BS are jointly designed to maximize the achievable sum-rate of the MSs based on their effective MIMO channels resulting from path delay compensation. In addition, we propose a new and efficient channel estimation scheme tailored for PDMA, which requires negligible training overhead in practical mmWave systems and yet leads to comparable performance as that based on perfect channel state information (CSI).

Achieving Full Diversity on a Single-Carrier Distributed QOSFBC Transmission Scheme Utilizing PAPR Reduction

In this paper, a cooperative single-carrier transmission scheme considering a distributed quasi-orthogonal space-frequency block code (QOSFBC) that provides improved peak-to-average power ratio (PAPR) performance is constructed for uplink communications. Focused on reducing the size and computational complexity, the source node, i.e., the mobile devices, is equipped with two transmit antennas, while only one antenna is required at the relay node in order to collaboratively generate a distributed QOSFBC signal using four transmit antennas. To achieve full diversity, a phase rotation strategy is proposed at the relay node. In addition, since single-carrier schemes considering SFBCs re-permute the spectral components of the transmitted signal and induce high PAPR value, a modified SFBC coding technique is proposed that allows the high-PAPR problem to be mitigated. Consequently, the designed distributed single-carrier frequency-division multiple access (SC-FDMA) QOSFBC scheme is able to provide full transmit diversity over frequency-selective fading channels, with a lower PAPR value on mobile devices when compared with a conventional SC-FDMA QOSFBC scheme.

Time reversal based frequency-domain equalization for underwater acoustic single-carrier transmissions

Time reversal processing generates a time-focused signal, after combining dispersive reception from a hydrophone array in the underwater acoustic channel. Because of this property, the time reversal method has been studied as a preprocessing scheme to support decision feedback equalization for underwater acoustic communications. Orthogonal frequency division multiplexing has also been combined with time reversal processing to improve spectral efficiency, as the equivalent compact channel impulse response allows short prefixes in the acoustic channel. Here, we show that time reversal processing can be used to facilitate prefix-free frequency domain equalization. Traditional frequency domain equalization schemes rely on the use of periodic prefixes, which bring a loss of spectral efficiency in the already-bandlimited underwater channel. The core idea is to use time reversal pre-processing to generate a delta-like equivalent impulse response to facilitate robust reconstruction of prefixes at the receiver for prefix-free single-carrier transmissions. The resultant receiver not only improves the spectral efficiency, but also supports communications over channels of variable fluctuation rates. The effectiveness of the receiver has been tested using the field measurements from the Gulf of Mexico in August 2016.

Millimeter-Wave Integrated Photoreceivers for High Data Rate Photonic Wireless Communication

We report on the use of 30 and 100 GHz integrated millimeter-wave photoreceivers in high data rate photonic wireless communication. The role of the bandwidth of a narrow-band photoreceiver in increasing the data rate of wireless single carrier transmission is discussed. An 11-GHz bandwidth photoreceiver achieved a data rate of 44.6 Gb/s using an 8 GBd, 64-QAM (quadrature amplitude modulation) signal. A wider bandwidth (19 GHz) integrated photoreceiver was designed and fabricated for use in the 100-GHz range. High-frequency response photoreceivers have the following advantages: they operate in a wide bandwidth easily, use frequency resources efficiently, and are subject to low amounts of atmospheric attenuation. In addition to the single carrier wireless transmission study, a high data rate (12 Gb/s) multicarrier radio over fiber (16-QAM in orthogonal frequency division multiplexing) transmission experiment was demonstrated in order to confirm the ability to increase the data rate with a wide operational bandwidth.

Semi-Blind Sparse Channel Estimation Using Reduced Rank Filtering

This paper develops a novel method for semi-blind estimation of sparse channels in single-input, multiple-output and multiple-input, multiple-output single-carrier transmission systems, using single/multiple transmit and multiple receive antennas. Very little work exists on semi-blind sparse channel estimation. By a novel formulation of the received data matrix (called reduced data matrix) for sparse channels, semi-blind channel/data estimation problem has been cast into a reduced-rank filtering problem. The estimation operates on selected, non-uniformly spaced equalizer taps. Then two classes of semi-blind channel/data estimation are developed, the first being a pseudo-inverse based linear prediction method and the second based on reduced rank multi-stage Wiener filtering. The second class has the advantage of not requiring the rank of the reduced data matrix, but estimating it adaptively via stage-by-stage updates. The computational complexity of the novel reduced channel estimators are compared with the full channel estimators, which use all available equalizer taps. Simulation results show that the reduced semi-blind estimators perform much better than the full estimators and existing sparse channel estimators, with limited number of training symbols, at much reduced computational complexity.

An Approximate ML Detector for MIMO Channels Corrupted by Phase Noise

We consider the multiple-input multiple-output (MIMO) communication channel impaired by phase noises at both the transmitter and receiver. We focus on the maximum likelihood (ML) detection problem for uncoded single-carrier transmission. We derive an approximation of the likelihood function, based on which we propose an efficient detection algorithm. The proposed algorithm, named self-interference whitening (SIW), consists in: 1) estimating the self-interference caused by the phase noise perturbation; 2) whitening the said interference; and 3) detecting the transmitted vector. While the exact ML solution is computationally intractable, we construct a simulation-based lower bound on the error probability of ML detection. Leveraging this lower bound, we perform extensive numerical experiments demonstrating that SIW is, in most cases of interest, very close to optimal with moderate phase noise. More importantly and perhaps surprisingly, such near-ML performance can be achieved by applying only twice the nearest neighbor detection algorithm. In this sense, our results reveal a striking fact: near-ML detection of phase noise corrupted MIMO channels can be done as efficiently as for conventional MIMO channels without phase noise.

Wireless Information and Power Transfer: Nonlinearity, Waveform Design, and Rate-Energy Tradeoff

The design of wireless information and power transfer (WIPT) has so far relied on an oversimplified and inaccurate linear model of the energy harvester. In this paper, we depart from this linear model and design WIPT considering the rectifier nonlinearity. We develop a tractable model of the rectifier nonlinearity that is flexible enough to cope with general multicarrier modulated input waveforms. Leveraging that model, we motivate and introduce a novel WIPT architecture relying on the superposition of multicarrier unmodulated and modulated waveforms at the transmitter. The superposed WIPT waveforms are optimized as a function of the channel state information so as to characterize the rate-energy region of the whole system. Analysis and numerical results illustrate the performance of the derived waveforms and WIPT architecture and highlight that nonlinearity radically changes the design of WIPT. We make key and refreshing observations. First, analysis (confirmed by circuit simulations) shows that modulated and unmodulated waveforms are not equally suitable for wireless power delivery, namely, modulation being beneficial in single-carrier transmissions but detrimental in multicarrier transmissions. Second, a multicarrier unmodulated waveform (superposed to a multicarrier modulated waveform) is useful to enlarge the rate-energy region of WIPT. Third, a combination of power splitting and time sharing is in general the best strategy. Fourth, a nonzero mean Gaussian input distribution outperforms the conventional capacity-achieving zero-mean Gaussian input distribution in multicarrier transmissions. Fifth, the rectifier nonlinearity is beneficial to system performance and is essential to efficient WIPT design.

Prefix-Free Frequency Domain Equalization for Underwater Acoustic Single Carrier Transmissions

Prefixes, in forms of cyclic-prefixes or zero-padding, have often been viewed as indispensable in underwater acoustic single-carrier transmissions to avoid inter-block interference (IBI) and to formulate circular convolution. However, the prefix introduces overhead and reduces spectral efficiency. This is especially true in fast time-varying channel conditions. Here, we propose a prefix-free scheme to facilitate frequency-domain equalization (FDE) in an underwater acoustic communication system, based on the time-reversal processing. In the proposed scheme, three main procedures, block partitioning, IBI cancellation, and prefix reconstruction, precede the FDE operation. The block partitioning at the receiver provides flexibility to support channel equalization in different channel fluctuation rates. The utilized prefix reconstruction scheme requires a strong first arrival to minimize the noise enhancement. Our solution is to use the time-reversal processing, because the resultant equivalent impulse response, also known as the $q$ -function, has a stable and compact peak. To further enhance receiver performance, we incorporate two strategies. One is overlapping partitioning. The other is iterative prefix reconstruction. The proposed schemes have been tested using the field measurements obtained from the Gulf of Mexico in August 2016. Communications over four ranges at the carrier frequency of 85 kHz with a symbol rate of 17 kHz have been demonstrated. The overlapping partitioning and iterative prefix reconstruction strategies have been shown to generate improvements in the receiver performance.

An Improved Hybrid Turbo Equalizer for Single Carrier Transmission with Impulsive Noise and ISI

In this paper, we propose an improved hybrid turbo equalizer (TEQ) for single-carrier transmission over multipath channels with symmetric alpha-stable noise. First, a nonlinear myriad filter is adopted for combating the effect of impulsive noise. The noise output of this nonlinear filter is analyzed by an asymptotic statistic method and shown to be asymptotically Gaussian. Then, a matched minimum mean square error based linear TEQ is proposed for further mitigating the effects of the residual impulsive noise and the intersymbol interference caused by multipath fading. In our proposed TEQ design procedure, the instantaneous estimation of the noise variance is exploited to obtain robust TEQ coefficients. Simulation results show that the proposed hybrid TEQ provides geometric signal-to-noise ratio improvements (of up to 4.5 dB) compared to conventional algorithms designed for Gaussian channels.

Extreme Speed Power-DAC: Leveraging InP DHBT for Ultimate Capacity Single-Carrier Optical Transmissions

Power-digital-to-analog converters (DAC) circuits for high capacity and high spectral efficiency optical transmitters are presented in this paper. They are based on a 0.7- μ m InP DHBT semiconductor process, of which main differentiating characteristics are highlighted. We introduce the Power-DAC circuit concept, its usual architectures, and we provide design details of its latest generation. Named SPDAC, it integrates multiplexing front-end blocks composed of three 2:1-selectors. With this architecture, the input interface operates at half rate. 107-GBd operation for PAM-4 and 64-GBd for PAM-8 were demonstrated with quality suitable for direct detection and datacenter applications. 90-GBd operation in a PDM-64QAM transmitter with coherent detection was also enabled by SPDAC modules. With 3.7 to 4 V differential output voltage swing, Power-DAC circuits can be directly connected to different types of E/O modulators (Mach–Zehnder, EAM). We show in particular how the SPDAC circuit enables single-carrier transmission at 100-GBd in PAM-4 IM/DD modulation for datacenters. In this experiment, the feed-forward equalizer combined with stacking a <3-symbol memory sequence estimator demonstrated signal recovery for 107-GBd PAM-4 in back-to-back configuration, after 500 m and 1 km of transmission over standard single-mode fiber for 100- and 84-GBd PAM-4 configuration, respectively.

Iterative IQ Imbalance Compensation Receiver for Single Carrier Transmission

It is well known that low-cost RF front-end implementation such as direct conversion transmitter suffers from serious in-phase/quadrature phase (IQ) imbalance. Most existing works in single carrier transmission employ linear compensation methods, such as Least Square and minimum mean square error, to combat the interference caused by IQ imbalance. Actually, for single carrier transmission, it is possible for the receivers to adopt advanced nonlinear compensation methods to improve the system performance under IQ imbalance. In this paper, we design a new iterative decision feedback receiver to compensate the IQ imbalance caused by unideal radio front end for single carrier frequency domain equalization (SC-FDE). Numerical results shows that, compared with the conventional linear method, our proposed iterative IQ imbalance compensation can significantly improve the performance of SC-FDE system under IQ imbalance.

Cost-Effective Millimeter-Wave Communications with Lens Antenna Array

MmWave communication is a promising technology for 5G wireless systems. However, the large number of antennas used and the wide signal bandwidth in mmWave systems render the conventional multi-antenna techniques increasingly costly in terms of signal processing complexity, hardware implementation, and power consumption. In this article, we investigate cost-effective mmWave communications by first providing an overview of the main existing techniques that offer different trade-offs between performance and cost, and then focusing our discussion on a promising new technique based on the advanced lens antenna array. It is revealed that by exploiting the angle-dependent energy focusing property of lens arrays, together with the angular sparsity of the mmWave channels, mmWave lens antenna system is able to achieve capacity-optimal performance with very few RF chains and using low-complexity single-carrier transmission, even for wideband frequency-selective channels. Numerical results show that the lens-based system outperforms the benchmark schemes for mmWave communications in both spectrum efficiency and energy efficiency.