Single-carrier Systems Research Articles

Adaptive arrangement of cyclic prefix length for MC-CDMA systems via multi-objective bat algorithm

Multi-carrier multiplexing systems, used in high bit rate communication applications, are more affected by the time- or frequency-dependent fading effects incurring in the channel than the single-carrier systems. When the fading effects at multi-carrier systems are not taken into consideration, inter-carrier interference or inter-symbol interferences that cause bit error rate increase at the receiver would occur. In order to eliminate these interference effects, the cyclic prefix is used in MC-CDMA systems, which are the kind of multi-carrier systems. However, determining how long the CP length is to be used will directly affect both the error and the capacity performance of the system. In this study, multi-objective bat algorithm is proposed for the adaptive arrangement of the CP lengths according to the channel conditions. Contrary to the standard CP determination methods, not only the bit errors are minimized, but also the maximization of the channel capacity is provided by the utilization of MOBA.

Implementation and Measurement of Blind Wireless Receiver for Single Carrier Systems

Theoretical studies on nondata aided (blind) parameter estimation algorithms for signals have been carried out over the past decades. However, most of them have not been implemented and measured in order to validate their feasibility. In this paper, at first, the blind parameter estimation algorithms have been presented, which facilitate to the design of a blind wireless receiver (BWR) where information bits are retrieved successfully. Next, a software-defined radio testbed has been implemented and a measurement method setup is proposed. Here, an uncertainty analysis for the estimation of single carrier system parameters, such as carrier frequency, symbol rate, and symbol timing offset, has been presented in terms of normalized mean-squared error between estimated and true values of the parameter. The success rate of blind modulation classification has been presented for four classes of a modulation scheme. These preliminary studies and measurement results demonstrate that the proposed BWR prototype is capable of estimating the concerned parameters and constellation symbols over an indoor propagation environment. The symbol-error rate for quadrature phase shift keying modulation is finally gained through simulations.

Iterative Decision Feedback Equalization for SC-FDE Systems Without Fine Timing Synchronization

This letter deals with frequency domain equalization (FDE) in the presence of residual timing offsets. A novel iterative decision feedback equalizer for single-carrier FDE systems is proposed. Different from conventional schemes based on explicit point time-delay estimates, the proposed scheme operates directly on the oversampled matched filter output. For each iteration, FDE is performed first, and based on which, joint posterior distribution of the channel and timing parameters is obtained. A set of weights obtained from the corresponding posterior distribution, rather than explicit point time-delay estimate, are utilized for the time-delay compensation, eliminating the need of fine timing synchronization. Simulation results show that the proposed scheme enables evident performance improvement in terms of symbol error rate compared with conventional schemes under relative low sampling rate.

Laser Phase Noise Effects and Joint Carrier Phase Recovery in Coherent Optical Transmissions With Digital Subcarrier Multiplexing

In this paper, we numerically and experimentally investigate the impairments related to laser phase noise in coherent digital subcarrier multiplexing (SCM) systems. Based on the evaluation in both back-to-back and transmission scenarios and the performance comparison between single carrier (SC) and SCM systems, we show that even though SCM systems suffer from degraded performance of carrier phase recovery (CPR) algorithms, they can potentially achieve an improved laser linewidth tolerance compared with SC systems after long-haul transmission attributed to the mitigation of equalization-enhanced phase noise. In addition, the effect of dispersion-enhanced phase noise is discussed in digital SCM systems, and a joint CPR (J-CPR) algorithm is proposed for cycle slip detection and correction. The effectiveness of the proposed J-CPR algorithm is then demonstrated in a 16-quadrature amplitude modulation (QAM) digital SCM system by both simulations and experiments.

Transform Methods for the Reduction of the Peak to Average Power Ratio for the OFDM Signal

The paper presents multitransform OFDM-OP system for an effective PAPR (peak to average power ratio) reduction that has a reasonable computational requirement, does not introduce any distortion, needs relatively insignificant decrease in the bandwidth efficiency, and provides a PAPR very close to that for the single carrier modulation systems thus effectively eliminating any PAPR penalty incurred by the multicarrier OFDM system. The PAPR system consists of a bank of multiple orthonormal transforms and a minimum PAPR evaluation unit for finding the optimum transform index. The paper also presents a hybrid OFDM-OP-DSI system comprised of the multiple transforms and a novel dummy symbol insertion. The PAPR reduction performance of the presented systems is compared with those of the various other transform techniques of the literature. Various simulations on the presented systems show that these can achieve a PAPR that is very close to that of a single carrier system for QAM modulation with the order of modulation selected to be 16, 64, and 256.

Nonlinear Interference Mitigation: Methods and Potential Gain

We explore the potential benefits of digital nonlinearity compensation (NLC) techniques in fully loaded coherent wavelength-division multiplexed (WDM) transmission systems. After providing an overview of the various classes of nonlinear interference noise (NLIN) and digital signal processing approaches for their mitigation, we consider the two practically most relevant digital NLC methods known today: back-propagation (BP) and equalization of nonlinear phase and polarization rotation noise (PPRN). We consider a wide range of system configurations including a variety of modulation formats from quadrature phase-shift keying (QPSK) to 256-ary quadrature amplitude modulation (QAM), single-carrier and digital subcarrier multiplexed (SCM) optical superchannels, as well as both point-to-point line systems and optically routed networks (ORNs). Using theoretical predictions from the time-domain model for NLIN, we show that the gain in peak signal-to-noise ratio in fully loaded WDM systems using single-channel and three-channel joint BP is typically limited to 0.5 and 1 dB. The additional gain provided by increasing the number of jointly back-propagated channels beyond three is limited to 0.1 dB per additional back-propagated channel. The remarkably slow growth of the BP gain with the bandwidth of the back-propagated signal is shown to apply also for systems in which the receiver employs PPRN removal. We additionally explore the potential benefits of SCM across a wide range of system configurations, including the impact of BP and PPRN removal on SCM systems. We show that while the BP gain is similar to single-carrier systems, PPRN removal can have a much stronger effect, particularly for higher order QAM systems, implying that SCM can be advantageous not only for constant modulus formats such as QPSK, but also for high spectral efficiency systems. In the context of ORNs, we find that SCM not only improves system tolerance to nonlinearities, but also induces significantly smaller performance variations in various ORN scenarios.

MIMO Detection and Equalization for Single-Carrier Systems Using the Alternating Direction Method of Multipliers

In this letter, a multiple-input multiple-output detection algorithm based on the alternating direction method of the multipliers (ADMM) is proposed for single-carrier transmissions in time dispersive channels. The ADMM is applied as a heuristic to solve the maximum likelihood detection problem for arbitrary signal constellations formulated in the frequency domain. This approach allows most of the decoding steps to be implemented in the frequency domain with an overall reduced complexity cost. Simulation results show that the performances close to the matched filter bound can be attained in large problem sizes, even in overloaded scenarios.

Joint CD and PMD monitoring based on a pair of low-bandwidth coherent receivers.

A joint chromatic dispersion (CD) and 1st order polarization mode dispersion (PMD) monitoring technique for both a coherent and a non-coherent single carrier system based on a pair of cost effective low-bandwidth coherent receivers is proposed and experimentally demonstrated. By jointly detecting the narrow band around ± 1/2 baud rate, the CD and PMD can be estimated simultaneously by time domain correlation and Stokes space rotational angle recovery, respectively. The CD estimation range is theoretically infinite and the PMD estimation range is limited to the maximum of 1/2 symbol period. Simulation results show that for a 28 G baud dual-polarization (DP)-16QAM transmission system, with dual 1 GHz coherent receivers, the monitoring error for CD and differential group delay (DGD) is 30 ps/nm and 0.5 ps, respectively. We also experimentally verified it for a 12 GBit/s NRZ-OOK transmission system with a full-bandwidth coherent receiver and two 1 GHz digital filters to simulate dual 1 GHz coherent receivers. The monitoring error for CD and DGD is 60 ps/nm and 1.5 ps, respectively.

Involvement of l-type amino acid transporter 1 in the transport of gabapentin into human placental choriocarcinoma cells

Gabapentin (GBP) is a widely used antiepileptic drug, with potential for use in the treatment of epilepsy in pregnant women. Although studies have examined GBP transport mechanisms across the blood-brain barrier, kidney, and intestine, the mechanism in the placenta has not been fully elucidated. We previously reported that GBP accumulates at high concentrations in human placental choriocarcinoma BeWo cells. The purpose of this study was to examine the transport mechanism of GBP in placental choriocarcinoma cells (BeWo and JEG-3), and to identify the carrier involved. High concentrations of intracellular GBP accumulations were also found in JEG-3 cells. A kinetic analysis showed that a single carrier system was involved in the uptake of GBP. Furthermore, substrates for l-type amino acid transporter (LAT) and siRNAs targeted to LAT1 significantly decreased GBP uptake. Our observations from this study suggest that LAT1 is the main contributor to GBP transport in placental choriocarcinoma cells.

Blind symbol timing synchronization scheme for real-time industrial wireless control network using high-speed preambleless OFDM systems over multipath fading channels

An accurate estimation of symbol timing is crucial for orthogonal frequency division multiplexing (OFDM) demodulation, since synchronization errors might destroy the orthogonality among all subcarriers and have greater impact on the system performance than single carrier systems. The symbol timing offset (STO) that leads to inter-symbol interference (ISI) and inter-channel interference (ICI) must be avoided as much as possible. In this paper, a novel symbol timing synchronization algorithm is proposed for OFDM systems on the basis of cyclic prefix (CP). A metric function and a positioning function have been designed by taking advantage of the correlation properties of OFDM signals. Computer simulations demonstrate that the schemes are superior because they achieve accurate timing offset estimation with smaller standard deviation (SD) and relatively lower computational complexity compared with the existing methods based on CP under high signal–noise ratio (SNR) assumption over frequency-selective channels, which can meet the real-time requirements in wireless local area network (WLAN) environments for factory automation (FA).

Linear Precoded THP-FDE for Single-Carrier Broadband MIMO Systems

Tomlinson–Harashima precoding with frequency-domain equalization (THP-FDE) is a promising approach for multiple-input multiple-output (MIMO) single-carrier broadband systems. By performing interference cancelation at the transmitter, THP-FDE performs better than frequency-domain decision-feedback equalization (FD-DFE) via eliminating the error propagation problem resulting from incorrect symbol decisions. One of the drawbacks for MIMO THP-FDE systems is that the spatial stream with the largest mean square error (MSE) dominates the error performance. To alleviate this problem, conventional design adopts a sorting algorithm (a permutation matrix) to minimize the worst-case stream MSE. Since the difference of stream MSEs roots in the nonequal diagonal entries of the MSE matrix in the time domain, we are motivated to apply a general linear precoder based on geometric-mean decomposition to balance these MSEs. By jointly optimizing the precoder and equalizer, we are able to minimize the arithmetic MSE, geometric MSE, and the worst stream MSE simultaneously for the MIMO THP-FDE system. Simulation results are presented to demonstrate the superior bit-error-rate (BER) performance of the proposed transceiver architecture for MIMO THP-FDE systems.

Modulation Designs for Visible Light Communications With Signal-Dependent Noise

This paper proposes efficient modulation design methods for single-carrier and multicarrier visible light communication systems with signal-dependent shot noise (SDSN). Improved constellations are obtained through solving optimization problems aiming at minimizing the system symbol error rate, subject to lighting constraints. For single-carrier systems, maximum likelihood based detection, is applied. Constellation and threshold values are optimized jointly. The proposed method outperforms both the uniform signaling and the square-root signaling. It is also observed that the uniform signaling outperforms the square-root signaling through the medium-to-high signal to noise region, while the latter performs better in lower SNR region. For multicarrier systems, we formulate a new channel model with the SDSN taken into account. By maximizing the minimum Euclidean distance between the symbols, improved constellations are designed under different lighting constraints. Furthermore, the multicarrier part of design embraces the DC-informative design framework, and thus achieve high power efficiency. The performance gain of our DC-informative optical OFDM (DCIO-OFDM) over OFDM-QPSK ranges from 5 to 30dB even in moderate dimensional signal space.

Improving the peak-to-average power ratio of single-carrier frequency division multiple access systems by using an improved constellation extension scheme with error correction

Single-carrier frequency division multiple access (SC-FDMA) is currently a widely used transmission technology that has been designated as the uplink transmission technology for the 4G mobile communications standard. SC-FDMA also has a lower peak-to-average power ratio (PAPR) compared with orthogonal frequency division multiple access (OFDMA), where OFDMA is the downlink transmission technology in the 4G standard. However, the PAPR of SC-FDMA increases with the M value in an M-ary modulation scheme, causing a decrease in the efficiency of high-power amplifiers at the transmission end. This study proposes a technique for minimizing the PAPR in SC-FDMA systems by dividing a 16-QAM product code (PC) into two subblocks, one of which is dedicated to encoding transmission data for enhanced error correction, and the other is for generating PAPR-reduction signals. Moreover, this study employed the constellation extension scheme to generate PAPR reduction signals because it can prevent additional data loss caused by the generated PAPR reduction signals. Simulation results show that the proposed technique not only reduces PAPR in SC-FDMA system, but its transmission signals also outperform conventional SC-FDMA signals in error correction because of the incorporated PCs.

DSP algorithms for recovering single-carrier Alamouti coded signals for PON applications.

Alamouti space-time block code (STBC) combined with a simple heterodyne coherent receiver enables phase diverse coherent detection without any optical polarization tracking. While such a system consisting of only a 3-dB coupler and a single balanced photodiode has been recently demonstrated using orthogonal frequency-division multiplexed (OFDM) signals, herein we report the first application to single-carrier systems. Applicability of such technique for single-carrier systems is not straightforward since specialized digital signal processing (DSP) algorithms are required for data recovery. In this paper, we address the implementing issues and DSP algorithms applicable for single-carrier (SC) Alamouti STBC based simplified heterodyne receivers. Polarization-insensitive operation of the proposed scheme and its performance are verified by means of simulation for a 12-Gbits/s quadrature phase-shift keying (QPSK) transmission system.

Optimal Channel Shortener Design for Reduced- State Soft-Output Viterbi Equalizer in Single-Carrier Systems

We consider optimal channel shortener design for reduced-state soft-output Viterbi equalizer (RS-SOVE) in single-carrier (SC) systems. To use RS-SOVE, three receiver filters need to be designed: a prefilter, a target response and a feedback filter. The collection of these three filters are commonly referred to as the \lq\lq{}channel shortener\rq\rq{}. Conventionally, the channel shortener is designed to transform an intersymbol interference (ISI) channel into an equivalent minimum-phase equivalent form. In this paper, we design the channel shortener to maximize a mutual information lower bound (MILB) based on a mismatched detection model. By taking the decision-feedback quality in the RS-SOVE into consideration, the prefilter and feedback filter are found in closed forms, while the target response is optimized via a gradient-ascending approach with the gradient explicitly derived. The information theoretical properties of the proposed channel shortener are analyzed. Moreover, we show through numerical results that, the proposed channel shortener design achieves superior detection performance compared to previous channel shortener designs at medium and high code-rates.

Linear Precoder Design for MIMO-ISI Broadcasting Channels Under Channel Shortening Detection

We consider optimal precoder design for multiuser multiple-input multiple-output broadcasting channels in single-carrier systems. Instead of linear detection, we assume that the advanced nonlinear channel shortening detectors are utilized at the receivers. Such a scenario is challenging for precoder design as the uplink–downlink duality is inapplicable. The target of our linear precoder design is to maximize the sum of the achievable information rate (sum-AIR), with AIR of each user being explicitly derived. We analyze such a precoder design in general, and provide an efficient per-user based optimization algorithm for the design of block-diagonalization precoder.

Secrecy Performance of Finite-Sized Cooperative Single Carrier Systems With Unreliable Backhaul Connections

In this paper, the secrecy performance of finite-sized cooperative cyclic prefixed single carrier systems with multiple eavesdroppers and unreliable wireless backhaul connections across multiple transmitters is investigated. For nonidentical frequency-selective fading channels between the relay and destination nodes, secrecy performance metrics including the secrecy outage probability, ergodic secrecy rate, and probability of nonzero achievable secrecy rate are derived. Furthermore, the existence of performance limits on the secrecy outage probability and probability of non-zero achievable secrecy rate are verified for various backhaul scenarios. These limits are found to be exclusively determined by the backhaul reliability. For imperfect backhaul connections, it is found that the diversity gain promised by cooperative cyclic prefixed single-carrier systems cannot be achieved in the conventional asymptotic high signal-to-noise ratio region. Link-level simulations are conducted to verify the derived impact of backhaul reliability on the secrecy performance.

Carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool

This paper proposes a new carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool used in a cylindrical borehole environment during oil-based mud drilling processes. The new tool is an orthogonal frequency division multiplexing access-based contactless multi-measurand detection tool. The tool can measure formation resistivity in different azimuthal angles and elevational depths. It can measure many more measurands simultaneously in a specified bandwidth than the legacy frequency division multiplexing multi-measurand tool without a channel-select filter while avoiding inter-carrier interference. The paper also shows that formation resistivity is not sensitive to frequency in certain frequency bands. The average resistivity collected from N subcarriers can increase the measurement of the signal-to-noise ratio (SNR) by N times given no amplitude clipping in the current-injection electrode. If the clipping limit is taken into account, with the phase rotation of each single carrier, the amplitude peak-to-average ratio can be reduced by 3 times, and the SNR can achieve a 9/N times gain over the single-carrier system. The carrier-interleaving technique is also introduced to counter the carrier frequency offset (CFO) effect, where the CFO will cause inter-pad interference. A qualitative analysis and simulations demonstrate that block-interleaving performs better than tone-interleaving when coping with a large CFO. The theoretical analysis also suggests that increasing the subcarrier number can increase the measurement speed or enhance elevational resolution without sacrificing receiver performance. The complex orthogonal multi-pad multi-carrier resistivity logging tool, in which all subcarriers are complex signals, can provide a larger available subcarrier pool than other types of transceivers.

Novel Pilot Position Detection for SC-FDE Systems With Frequency Domain Pilot Multiplexing Technique

Frequency domain pilot multiplexing technique (FDPMT) has recently emerged as an appealing technique for channel estimation in single-carrier frequency domain equalization systems as it achieves high spectral efficiency at the expense of tiny signal distortion. In FDPMT, pilot positions are dynamically selected to achieve a relatively low level of signal distortion, rendering pilot position detection (PPD) indispensable at the receiver. In this letter, by exploiting both the prior known pilots and the statistical information of the data tones, we propose a novel PPD scheme based on the maximum-likelihood criterion. Simulation results show that our proposed PPD scheme significantly improves the PPD accuracy and outperforms the existing counterparts in terms of bit error rate.

Numerical Analysis of a Multi-Function Photonic Integrated Circuit for Coherent Radio-Over-Fiber

A digital coherent radio-over-fiber (RoF) system comprising a microwave photonic integrated circuit (MPIC) as the main building block is proposed. The multifunction MPIC circuit is analyzed to operate as a single-sideband (SSB) modulator and as an in-phase and quadrature modulator (IQM) of a baseband signal in the RoF downlink. The circuit is also analyzed in the uplink as an SSB of a 60-GHz frequency-shifted input. The performance of the MPIC is assessed through numerical simulations, computing the harmonic distortions in the SSB, as well as the error vector magnitude in the IQM and coherent RoF system. Obtained results illustrate the advantage of the proposed MPIC for heterodyne mixing by providing the upper and lower sidebands spatially located in distinct ports. Moreover, simulation results yield insights into the feasibility of the circuit as an IQM of both baseband and low-power intermediate frequency signals. A comparison of an orthogonal frequency division multiplexing system and a single carrier system employing the proposed circuit in the end-to-end transport of high data rate is presented through error vector magnitude calculations.