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The paper investigates the performance of a cyclic interleaved frequency division multiple access (CIFDMA) system proposed in our earlier works. In our present study, the carrier frequency offset (CFO) and the peak‐to‐average power ratio (PAPR) analysis are done for the proposed CIFDMA, supporting single and multiple data stream transmissions. The proposed system is analyzed without employing any compensation technique needed to alleviate the effect of CFO and PAPR. The CIFDMA delivers superior performance over the conventional IFDMA system under low and moderate CFOs. Besides, the bit error ratio (BER) versus signal‐to‐noise ratio (SNR) performance comparisons for constant and random CFOs reveal the dominance of the proposed system over the conventional system for both single and multiple data stream transmissions. The PAPR performance of the proposed system is superior to the orthogonal frequency division multiple access (OFDMA) system. However, the PAPR of the proposed system escalates by an acceptable margin to that of the conventional system, and the deviation in the PAPR value falls within the acceptable range. The simulation results conclude that the proposed CIFDMA system will better replace the conventional IFDMA system for next‐generation communications. [ABSTRACT FROM AUTHOR]

Single-photon avalanche diodes (SPADs) capable of single photon detection are promising optical sensors for use as receivers in optical wireless communication (OWC) systems. In SPAD-based receivers, the intersymbol interference (ISI) effect caused by dead time is an important drawback that limits performance. In this paper, we propose two novel SPAD operation modes to reduce the ISI effect in SPAD-based OWC. To validate the feasibility of these two modes, we designed a free-running SPAD front-end circuit with post-layout transient simulation results and some measurements to show its function and performance. This SPAD circuit is improved by a novel mixed passive-active quench and reset front-end circuit that achieves a very short dead time. Based on the traditional free-running mode, we design the clock-driven mode and time-gated mode to reduce the ISI effect through time-controlled operating signals. To accurately evaluate these three modes, we develop a new simulation system to assess the ISI effect in On-Off Keying (OOK) modulated communication. The simulation results demonstrate that the clock-driven mode and time-gated mode receivers can improve the bit error rate (BER) performance in low data rate communication and high data rate high optical power communication, respectively. Moreover, compared to the free-running mode, the two proposed time-controlled modes achieve higher data rate communication and better noise tolerance ability in SPAD-based OWC.

In this work, we introduce and evaluate the performance of a novel family of Nyquist (intersymbol interference free) pulses that outperform several existing ones available in the open technical literature. The proposed pulse design is based on a polynomial interpolation approach, which - to the best of our knowledge - is applied for the first time for a Nyquist pulse. In particular, we propose a geometrical approach in conjunction with the use of cubic spline functions for the construction of the transfer function of the considered pulses. The proposed methodology is quite flexible, as it allows for the efficient design of Nyquist pulses with improved performance, even after the choice of the roll-off factor. Four members of the proposed family of pulses are studied in detail in terms of their frequency and time domain response, the eye diagram and the achieved bit error rate. The proposed theoretical analysis is corroborated by extensive numerically evaluated results. Our results have shown that for given values of the roll-off factor, the timing jitter and the signal to noise ratio, certain members of the proposed family can achieve a lower bit error rate as compared to several state-of-the-art pulses.

Summary: A multi‐stream cyclic interleaving architecture for an interleaved frequency division multiple access (IFDMA) system is proposed. The proposed scheme exploits the full benefits of maximal length sequence (m‐sequence), in contrast to single data stream transmission scheme proposed in earlier works, thereby allowing simultaneous transmission of multiple data streams by each user. The cyclic spreading allows the separation of multiple data streams for each user in addition to intersymbol interference (ISI) minimization. The assignment of orthogonal subcarriers to each user compensates multiuser interference (MUI). The increase in the number of data stream transmission improves the data rate of the system. The proposed scheme employs maximal ratio combining (MRC) to maximize the instantaneous signal‐to‐noise ratio (SNR) of the multipath signal. The performances of the proposed interleaving scheme are compared with the minimum mean square error frequency domain equalization (MMSE‐FDE)‐based conventional interleaving scheme. Despite the simultaneous transmission of multiple data streams, the proposed scheme retains the performance of single data stream transmission. [ABSTRACT FROM AUTHOR]

High-data-rate impulse radio ultra-wideband (IR-UWB) wireless communication system suffers from serious intersymbol interference (ISI) issues in an indoor multipath environment. This paper proposes an auto-step least mean square time-domain equalization algorithm based on quadratic function (QA-LMS), which outplays the overall convergence speed, steady-state error, signal-to-noise ratio (SNR) threshold and robustness compared to the state of the art relevant to the adaptive step-size algorithms. The proposed algorithm does not need to preset the parameters according to channel conditions. The algorithm converges absolutely fast in the mean square error (MSE) learning curve. To meet the bit error rate (BER) of forward error correction (FEC) code, the algorithm improves the SNR threshold of traditional auto-step LMS (A-LMS) by 4.4 dB in CM1 and 3.6 dB in CM3 of 802.15.3a channel model respectively. The proposed algorithm is stable and robust in nonstationary environment with the advantage of vectorial step-size that based on the gradient of estimated error and high step detection.

This work addresses the issue of interference generated by co-channel users in downlink multi-antenna multicarrier systems with frequency-packed faster-than-Nyquist (FTN) signaling. The resulting interference stems from an aggressive strategy for enhancing the throughput via frequency reuse across different users and the squeezing of signals in the time-frequency plane beyond the Nyquist limit. The spectral efficiency is proved to be increasing with the frequency packing and FTN acceleration factors. The lower bound for the FTN sampling period that guarantees information losslesness is derived as a function of the transmitting-filter roll-off factor, the frequency-packing factor, and the number of subcarriers. Space-time-frequency symbol-level precoders (SLPs) that trade off constructive and destructive interblock interference (IBI) at the single-antenna user terminals are proposed. Redundant elements are added as guard interval to cope with vestigial destructive IBI effects. The proposals can handle channels with delay spread longer than the multicarrier-symbol duration. The receiver architecture is simple, for it does not require digital multicarrier demodulation. Simulations indicate that the proposed SLP outperforms zero-forcing precoding and achieves a target balance between spectral and energy efficiencies by controlling the amount of added redundancy from zero (full IBI) to half (destructive IBI-free) the group delay of the equivalent channel. [ABSTRACT FROM AUTHOR]

In direct current (dc) microgrids, communication between converters is necessary for better power distribution and finer energy scheduling. This article proposes an orthogonal frequency division multiplexing (OFDM) based carrier communication method for dc microgrid applications. The method integrates the communication function in the process of power conversion by modulating data into power control loop. To maximize the communication rate in a narrow band limited by pulsewidth modulation control, OFDM technology is applied in the data modulation process. The data is modulated to multiple low-frequency signal carriers, then the modulated wave is added to the output of the power control loop. Since no additional component is needed for sending data, this method has the advantages of low cost and simple implementation. In order to provide theoretical guidance for system design, the dc microgrid applying the proposed method is modeled. Furthermore, important issues of the communication system are discussed, including data frame format and intersymbol interference problem. At last, a 2 kW dc microgrid experimental platform is established and 9.6 kbps communication rate with a transmission distance of 200 m is achieved, which verifies the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Recently much research work has focused on employing deep learning (DL) algorithms to perform channel estimation in the upcoming 6G communication systems. However, these DL algorithms are usually computationally demanding and require a large number of training samples. Hence, this work investigates the feasibility of designing efficient machine learning (ML) algorithms that can effectively estimate and track time-varying, frequency-selective channels. The proposed algorithm is integrated with orthogonal frequency-division multiplexing (OFDM) to eliminate intersymbol interference (ISI) induced by the frequency-selective multipath channel and compared with the well-known least square (LS) and linear minimum mean square error (LMMSE) channel estimation algorithms. The obtained results have demonstrated that even when a small number of pilot samples, $N_{P}$ , is inserted before the $N$ subcarriers OFDM symbol, the introduced ML-based channel estimation is superior to the LS and LMMSE algorithms. This dominance is reflected in the bit-error-rate (BER) performance of the proposed algorithm, which attains a gain of 2.5 dB and 5.5 dB over the LMMSE and LS algorithms, respectively, when $N_{P}=\frac {N}{8}$ . Furthermore, the BER performance of the proposed algorithm is shown to degrade by only 0.2 dB when the maximum Doppler frequency is randomly varied. Finally, the number of iterations required by the proposed algorithm to converge to the smallest achievable mean-squared error (MSE) are thoroughly examined for various signal-to-noise ratio (SNR) levels.

Faster-than-Nyquist (FTN) signaling is a promising non-orthogonal pulse modulation technique that can improve the spectral efficiency (SE) of next generation communication systems at the expense of higher detection complexity to remove the introduced inter-symbol interference (ISI). In this paper, we investigate the detection problem of ultra high-order quadrature-amplitude modulation (QAM) FTN signaling where we exploit a mathematical programming technique based on the alternating directions multiplier method (ADMM). The proposed ADMM sequence estimation (ADMMSE) FTN signaling detector demonstrates an excellent trade-off between performance and computational effort enabling successful detection and SE gains for QAM modulation orders as high as 64K (65,536). The complexity of the proposed ADMMSE detector is polynomial in the length of the transmit symbols sequence and its sensitivity to the modulation order increases only logarithmically. Simulation results show that for 16-QAM, the proposed ADMMSE FTN signaling detector achieves comparable SE gains to the generalized approach semidefinite relaxation-based sequence estimation (GASDRSE) FTN signaling detector, but at an experimentally evaluated much lower computational time. Simulation results additionally show SE gains for modulation orders starting from 4-QAM, or quadrature phase shift keying (QPSK), up to and including 64K-QAM when compared to conventional Nyquist signaling. The very low computational effort required makes the proposed ADMMSE detector a practically promising FTN signaling detector for both low order and ultra high-order QAM FTN signaling systems.

Post-silicon electrical validation of high-speed input/output (HSIO) links is a critical process for product qualification schedules of high-performance computer platforms under current aggressive time-to-market commitments. Improvements in signaling methods, circuits, and process technologies have allowed HSIO data rates to scale well beyond 10 Gb/s. Noise and EM effects can create multiple signal integrity problems, which are aggravated by continuously faster bus technologies. The goal of post-silicon validation for HSIO links is to ensure design robustness of both receiver (Rx) and transmitter circuitry in real system environments. One of the most common ways to evaluate the performance of an HSIO link is to characterize the Rx jitter tolerance (JTOL) performance by measuring the bit error rate (BER) of the link under worst stressing conditions. However, JTOL testing is extremely time-consuming when executed at specification BER considering manufacturing process, voltage, and temperature test coverage. In order to significantly accelerate this process, we propose a novel approach for JTOL testing based on an efficient direct search optimization methodology. Our approach exploits the fast execution of a modified golden section search with a high BER, while overcoming the lack of correlation between different BERs by performing a downward linear search at the actual target BER until no errors are found. Our proposed methodology is validated in a realistic industrial server post-silicon validation platform for three different computer HSIO links: SATA, USB3, and PCIe3. [ABSTRACT FROM AUTHOR]

Bit error rate (BER) is an important figure of merit to evaluate the performance of a communication system. Analyzing the BER of a linear-time-invariant system has been extensively studied. However, analyzing the BER of nonlinear circuits and systems is challenging because it cannot rely on linear time invariant (LTI) principles, while an exhaustive nonlinear simulation is computationally prohibitive. To find BER, an exhaustive approach requires nonlinear simulations of $2^{m}$ bit patterns for a channel of $m$ -bit memory, where $m$ can be larger than 100 in today’s high-speed and high-performance design. In this work, we develop a fast and accurate method to analyze the BER of large-scale nonlinear circuits. Only $O(k)$ nonlinear simulations are required, with $k$ much less than $2^{m}$ and independent of $2^{m}$. While performing $O(k)$ nonlinear simulations only, we find a method to determine the probability density function of the nonlinear responses, from which accurate BER results can be obtained. An error assessment method is also developed to evaluate the true error of the nonlinear signaling analysis without the need for knowing the entire nonlinear responses of the channel. Simulations of large-scale real-world nonlinear circuits have demonstrated the accuracy, efficiency, and capacity of the proposed method. A BER as low as 10-56 is accurately predicted. [ABSTRACT FROM AUTHOR]

Intersymbol interference (ISI) is introduced in a phased array when the beam is scanned. The cause of the ISI is demonstrated and its dependence on the phased array dimensions, scan angle, and symbol rate is derived. A mathematical model is created to simulate the ISI effects on transmitted (or received) symbols, and an equalizer model is introduced and achieves near-perfect equalization of the ISI. Also, for wideband signals, it is shown that large phased arrays result in amplitude modulation versus frequency. The effect of ISI on the error vector magnitude (EVM) is simulated using complex modulated signals, and the EVM before and after equalization is compared, using an adaptive 17-tap linear equalizer implemented in MATLAB. The results show that ISI in large phased arrays can be equalized regardless of the modulation, bandwidth, scan angle, and symbol rate. The EVM of 16-, 64-, and 256-quadrature amplitude modulation (QAM) signals is measured for a 256-element array in the transmit mode. The measurements verify the derivations, eliminating ISI and resulting in low EVM values after equalization. The effect of array tapering on EVM is also presented, and the results show no difference in the EVM for uniform and tapered excitations. [ABSTRACT FROM AUTHOR]

Heat-assisted interlaced magnetic recording (HIMR) with interlaced track layout architecture enables the further increased areal density compared to the conventional heat-assisted magnetic recording. However, the severe transition curvatures of low temperature written tracks cause noticeable nonlinear distortions of readback signal, and the 2-D intersymbol interference (ISI), media noise, and thermal jitter also bring the challenges for data recovery. Correspondingly, a multitrack detection scheme with 2-D iterative soft estimate aided neural network equalizer (2D-ISA NNE) is proposed for the HIMR system, which iteratively feeds back the soft estimate of reliable sidetracks’ information (e.g., high temperature written tracks) during the neural network equalization (NNE) of middle track (e.g., low temperature written track). Here, the Bahl–Cocke–Jelinek–Raviv (BCJR) detector and low-density parity-check (LDPC) decoder are utilized for the following data detection and error corrections. Then, the similar ISA NNE is implemented to recover the sidetracks’ data. It is found that the proposed 2D-ISA NNE algorithm mitigates the 2-D ISI and nonlinear distortion more effectively compared to the conventional 2-D linear equalizer (LE) and neural network equalizer (NNE). For HIMR at the channel bit density of 3.51 Tb/in2 and overlapping ratio of 0.46, the proposed 2D-ISA NNE algorithm significantly decreases the bit error rate gap between the low temperature and high temperature written tracks. For the low temperature written track, it provides 3.1 and 4 dB signal-to-noise ratio (SNR) gains compared to the conventional 2-D NNE and 2-D LE, respectively. [ABSTRACT FROM AUTHOR]

In high-speed digital wireless communication applications, the intersymbol interference channel may have spectral nulls or erasures, which may degrade the orthogonal frequency division multiplexing (OFDM) bit error rate (BER) performance. In this paper, we prove that the BER performance of the OFDM system is considerably refined if the erased symbols in erasure channel (or received symbols on the deep-faded subcarriers in Rayleigh fading channel) are estimated based on the rest symbols in each OFDM signal. Also, an oversampled OFDM scheme which is a particular form of the pre-coded OFDM schemes is considered to guarantee high enough sampling rate. Furthermore, a new iterative receiver is proposed for perfect symbol recovery. A comprehensive Monte Carlo simulation study is performed to validate the theoretical results and affirm the superior performance of the oversampled OFDM scheme with the iterative receiver, compared with the typical detector for the OFDM scheme.

While orthogonal frequency-division multiplexing (OFDM) has been studied for a decade, the study of nonorthogonal frequency-division multiplexing (NOFDM) in the underwater acoustics (UWA) communication has never been reported, to the best of our knowledge. Therefore, we investigate the NOFDM technique for the UWA communication considering the doubly dispersive channel. The main feature of the NOFDM is that it involves more closely packed subcarriers compared to the OFDM, which results in higher spectral efficiency. However, this transmission suffers from severe intercarrier interference. Since, we are considering the doubly dispersive channel, intersymbol interference is also encountered due to the multipath propagation. Therefore, the traditional receiver of the NOFDM system in the UWA channel tends to have high computational complexity. Considering this problem, we design a receiver for the NOFDM system, where the basis expansion model is used along with the compressed sensing channel estimation technique, i.e., orthogonal matching pursuit (OMP), which can effectively reduce the computational complexity. However, while implementing this technique in the real sea environment, the problem of long delay/Doppler spread is encountered due to guard intervals. Therefore, we propose the use of a time-domain equalizer to mitigate the effect of long delay/Doppler spread. Simulation and experimental results based on the bit error rate demonstrate the performance degradation due to severe interference in our proposed receiver. On the contrary, the mean-square-error performance shows that our proposed receiver with the OMP channel estimation outperforms the OFDM receiver. Similarly, higher spectral efficiency gain is attained due to the closely packed subcarriers. [ABSTRACT FROM AUTHOR]

In this paper, a new interleaving scheme for an interleaved frequency division multiple access (IFDMA) system is proposed. The proposed scheme combines the advantages of code division multiple access (CDMA) with maximal length sequence (m-sequence) and orthogonal frequency division multiple access (OFDMA). Multiaccess interference (MAI) among users is eliminated by employing orthogonal carriers, and the intersymbol interference (ISI) due to multipath channels is minimized by using cyclic interleaving. Diversity gain is achieved in the proposed method with maximal ratio combining (MRC) in the case of a Rayleigh environment. Compared to complex multiuser (MU) detection, the detection process in the proposed method is relatively simple. Multipath orthogonality is achieved in the proposed method, avoiding the need for channel equalization. The proposed method is compared with the conventional interleaving employing well-known minimum mean square error frequency domain equalization (MMSE-FDE). The Monte Carlo simulation results prove the superiority of the proposed interleaving over conventional interleaving with MMSE-FDE, showing that the present scheme is suitable for both uplink and downlink mobile radio transmissions. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the sequence estimation problem of faster-than-Nyquist (FTN) signaling as a promising approach for increasing spectral efficiency (SE) in future communication systems. In doing so, we exploit the concept of Gaussian separability and propose two probabilistic data association (PDA) algorithms with polynomial time complexity to detect binary phase-shift keying (BPSK) FTN signaling. Simulation results show that the proposed PDA algorithm outperforms the recently proposed SSSSE and SSSgb $K$ SE algorithms for all SE values with a modest increase in complexity. The PDA algorithm approaches the performance of the semidefinite relaxation (SDRSE) algorithm for SE values of 0.96 bits/sec/Hz, and it is within the 0.5 dB signal-to-noise ratio (SNR) penalty at SE values of 1.10 bits/sec/Hz for the fixed values of $\beta = 0.3$. [ABSTRACT FROM AUTHOR]

In this paper, we introduce and characterize a new filter bank multicarrier (FBMC) architecture, based on flexible zero padding (FZP), suitable for applications obeying stringent latency requirements. FZP conveniently distributes zeros between transmit (Tx) and receive (Rx) waveforms, and covers cyclic prefix (CP) and zero padding (ZP) as special extremal cases, providing, in this way, a bridge between classical CP-orthogonal frequency division multiplexing (OFDM) and ZP-OFDM. It has the merit of being the only possible architecture that guarantees optimum confined and autonomous transmission and reception of each OFDM symbol within the symbol period, leading to a minimized latency. We assess the best achievable signal-to-interference-plus-noise-ratio (SINR) performances, of all possible FBMC configurations, obeying the FZP architecture, through a systematic optimization of their Tx and Rx waveforms, using the ping-pong optimized pulse shaping (POPS) algorithm. We also assess the whole communication link performance, in terms of raw and coded bit error rate (BER), for several representative FZP configurations. It turns out that the medium alternative between CP and ZP, which evenly distributes FZP between the Tx and Rx waveforms, does not provide a significant improvement in signal-to-interference ratio (SIR) and BER, for slightly time dispersive channels, but brings more robustness to time synchronization errors. The conducted study shows that conventional CP-OFDM remains an interesting alternative since it leads to an insignificant degradation in SIR, compared to the optimal FZP configuration, while providing a decorrelated noise at the receiver, beneficial for short coded packets. [ABSTRACT FROM AUTHOR]

Sensitivity of high-speed optical receivers is heavily influenced by the performance of the optical detectors used in the receivers, the data rate, and the target bit-error-rate (BER). A simulation model for sensitivity of optical receivers based on electron-avalanche photodiodes (e-APDs) is presented. It allows for the optimization of avalanche width and operating voltage to achieve the optimum receiver sensitivity for given bit rate and target BER. The effects modelled include inter-symbol interference (ISI), various dark current components (tunnelling, diffusion, and generation), current impulse duration, avalanche gain, and amplifier's noise. The model was demonstrated through simulations of Indium Arsenide (InAs) e-APDs. For $10^{-12}$ target BER, the receiver's sensitivities were found to be −30.6, −22.7, −19.2, and −16.6 dBm, for 10, 25, 40, and 50 Gb/s data rate, respectively. Desirable avalanche properties of InAs e-APDs are counteracted by detrimental effects of high dark currents. Hence InAs e-APDs with lower dark currents are required to be more competitive with other optical detector technologies for high-speed optical receivers. The data reported in this article is available from the ORDA digital repository (DOI: 10.15131/shef.data.9959468). [ABSTRACT FROM AUTHOR]

The spatial and temporal focusing properties of time-reversal methods can be exploited for undersea acoustic communications. Spatial focusing mitigates channel fading and produces a high signal-to-noise ratio (SNR) at the intended receivers along with a low probability of interception elsewhere. While temporal focusing (compression) reduces significantly intersymbol interference (ISI), there always is some residual ISI depending upon the number of transmitters, their spatial distribution (spatial diversity), and the complexity of the channel. Moreover, a slight change in the environment over the two-way propagation interval introduces additional ISI. Using multilevel quadrature amplitude modulation (M-QAM) in shallow water, we demonstrate that the performance of time-reversal communications can be improved significantly by cascading the received time series with an adaptive channel equalizer to remove the residual ISI.

Non-orthogonal multiple access (NOMA) is a promising multiple access technique, proposed in literature for the fifth generation (5G) mobile networks. The NOMA system model consists of the conventional orthogonal frequency division multiplexing (OFDM), as a pulse shaping technique in conjunction with a variable power domain for various users, allocated in proportion to each user's channel gain. OFDM technique based on wavelet filter banks, namely wavelet OFDM (WOFDM) has been utilized in digital communication to improve the system robustness to noise and adjacent channel interference, and is therefore anticipated to be adopted for the NOMA technique. WOFDM in NOMA (WNOMA) outperforms OFDM-based conventional NOMA (CNOMA) with reference to interference mitigation, bandwidth efficiency, spectral confinement, and multi-user capacity. Most of the fourth generation (4G) networks are based on OFDM and its variants. Therefore, in this paper, keeping in view the interoperability with the 4G networks and the latency requirements in 5G, a dual physical layer based on conventional OFDM and WOFDM as pulse shaping methods, is proposed for the NOMA transceiver. Performance of WNOMA and CNOMA is analyzed for bit error rate in the presence of channel impairments including additive noise and IQ imbalance and multiuser capacity is also computed. Comparison of various parameters indicates the advantage of adopting WNOMA over its conventional counterpart for relatively poor channel conditions.

We consider designing demodulators for linear vector channels that use reduced-size trellis descriptions for the received signal. We assume an iterative receiver and use interference cancellation (IC) with soft-information provided by an outer decoder to mitigate the signal part that is not covered by a reduced-size trellis description. In order to reach a trellis description, a linear filter is applied as a front end to compress the signal structure into a small trellis. This process requires three parameters to be designed: (1) the front-end filter; (2) the feedback filter through which the IC is done; and (3) a target response which specifies the trellis. Demodulators of this form have been studied before under the name channel shortening (CS), but the interplay between CS, IC, and the trellis-search processes has not been adequately addressed in the literature. In this paper, we analyze two types of CS demodulators that are based on the Forney and Ungerboeck detection models, respectively. The parameters are jointly optimized with a generalized mutual information (GMI) function. We also introduce a third type of CS demodulator that is, in general, suboptimal, which has closed-form solutions. Furthermore, signal-to-noise ratio asymptotic properties are analyzed, and we show that the third CS demodulator asymptotically converges to the optimal CS demodulator in the sense of GMI maximization.

A follow-up on a recent analytical investigation into the statistical characteristics of the Intersymbol Interference (ISI) due to Faster-Than-Nyquist (FTN) signaling is presented. An asymptotic series expansion for the ISI Probability Density Function (PDF) is provided based on the Edgeworth expansion. The non-trivial Petrov’s formula (a compact form of the Edgeworth series) is expanded into a simpler-to-use form accurate up to the 14th-order statistics. The ISI cumulants used in this expansion are compactly expressed in terms of power series of the FTN base signaling pulse. Using computer simulations, we illustrate the merits and limitations of the Edgeworth-Petrov (EP) expansion in comparison to its previously-used Gram-Charlier (GC) counterpart. Namely, while the former has a better convergence profile when ISI is due to FTN with a negligible phase jitter, the latter seems to be more computationally desirable for FTN with larger phase-jitters. Some application notes are provided to further illustrate the use of these expansion results.

We propose a simple approach to simulate the convergence and the performance of high-speed serial interfaces with adaptive equalization. Such a method uses as input the pulse response of the channel (printed circuit board and cables, plus package/socket) that is then modified by adaptive techniques implementing feed-forward, decision-feedback, and linear-continuous time equalization. Probabilistic considerations are used in this novel method to estimate the evolution during time of the LMS loop and the resulting evolution of the eye diagram. Sample results are reported for a realistic link operating at 20 Gb/s. [ABSTRACT FROM AUTHOR]

Future wireless networks are required to offer new applications and services, which will experience high dispersions in time and frequency, incurred mainly by coarse synchronization. Coarse synchronization is induced by signaling overhead reduction and dictated by the tremendous optimization of the radio interface efficiency. It is expected to dramatically damage waveform orthogonality in conventional orthogonal frequency-division multiplexing (OFDM) systems and to result in oppressive intercarrier interference (ICI). To alleviate the degradation in performance caused by ICI, the concept of nonorthogonal multiplexing has been promoted, as a serious alternative to strict orthogonal multiplexing, for guaranteeing the OFDM benefits without requiring high-level synchronization. Within this nonorthogonal multiplexing framework, ping-pong optimized pulse shaping-OFDM (POPS-OFDM) has been introduced as a powerful tool to efficiently design waveforms, which withstand future multicarrier systems’ dispersion impairments. In this paper, we investigate the discrete time version of the POPS-OFDM approach and study its sensitivity and robustness against estimation and synchronization errors. Based on numerical results, we show that POPS-OFDM provides an important gain in the signal-to-interference ratio, typically higher than 5 dB, with respect to conventional OFDM. We also demonstrate that POPS-OFDM brings an increased robustness against synchronization errors and ensures a dramatic reduction in out-of-band emissions, enabling flexible and improved spectrum utilization. [ABSTRACT FROM AUTHOR]

Weighted sum subtract joint detector (WSSJD) was proposed by Fan et al. as an alternative way to implement maximum-likelihood (ML) detection for multihead multitrack (MHMT) systems. Different from the conventional ML detector, the trellis used in WSSJD is independent of the intertrack interference (ITI); therefore, WSSJD could efficiently adapt to the time-varying ITI environment. The channel transformation developed for WSSJD also naturally leads to a reduced-complexity implementation for the ML detector. In this paper, we generalize WSSJD to MHMT systems whose interference matrices satisfy the WSSJD property. The implementation details are given for a symmetric 3H2T system, as an example. Other interference matrices where WSSJD is applicable are also presented. [ABSTRACT FROM AUTHOR]

Faster-than-Nyquist (FTN) signaling is a promising non-orthogonal transmission technique to considerably improve the spectral efficiency. This paper presents the first attempt in the literature to estimate the transmit data symbols of any high-order quadrature amplitude modulation (QAM) FTN signaling in polynomial time complexity. In particular, we propose a generalized approach to model the finite alphabet of any high-order QAM constellation as a high degree polynomial constraint. Then, we formulate the high-order QAM FTN signaling sequence estimation problem as a non-convex optimization problem. As an example of a high-order QAM, we consider 16-QAM FTN signaling and then transform the high degree polynomial constraint, with the help of auxiliary variables, to multiple quadratic constraints. Such transformation allows us to propose a generalized approach semidefinite relaxation (SDR)-based sequence estimation (GASDRSE) technique to efficiently provide a sub-optimal solution to the NP-hard non-convex FTN detection problem, with polynomial time complexity. For the particular case of 16-QAM FTN signaling, we additionally propose a sequence estimation technique based on concepts from the set theory. We show that the set theory SDR-based sequence estimation (STSDRSE) technique is of lower complexity when compared with the proposed GASDRSE. Simulation results show the effectiveness of the proposed GASDRSE and STSDRSE techniques in increasing the data rate and spectral efficiency of 16-QAM FTN signaling, without increasing the bit-error-rate, the bandwidth, or the data symbols energy, when compared with the Nyquist signaling.

In this paper, we investigate the sequence estimation problem of binary and quadrature phase shift keying faster-than-Nyquist (FTN) signaling and propose two novel low-complexity sequence estimation techniques based on concepts of successive interference cancellation. To the best of our knowledge, this is the first approach in the literature to detect FTN signaling on a symbol-by-symbol basis. In particular, based on the structure of the self-interference inherited in FTN signaling, we first find the operating region boundary defined by the root-raised cosine pulse shape, its roll-off factor, and the time acceleration parameter of the FTN signaling where perfect estimation of the transmit data symbols on a symbol-by-symbol basis is guaranteed, assuming noise-free transmission. For noisy transmission, we then propose a novel low-complexity technique that works within the operating region and is capable of estimating the transmit data symbols on a symbol-by-symbol basis. To reduce the error propagation of the proposed successive symbol-by-symbol sequence estimator (SSSSE), we propose a successive symbol-by-symbol with go-back-K sequence estimator (SSSgbKSE) that goes back to re-estimate up to K symbols, and subsequently improves the estimation accuracy of the current data symbol. Simulation results show that the proposed sequence estimation techniques perform well for low intersymbol interference scenarios and can significantly increase the data rate and spectral efficiency. Additionally, results reveal that choosing the value of K as low as 2 or 3 data symbols is sufficient to significantly improve the bit-error-rate performance. Results also show that the performance of the proposed SSSgbKSE, with K = 1 or 2, surpasses the performance of the lowest complexity equalizers reported in the literature, with reduced computational complexity.

This paper presents an electronic dispersion compensation (EDC) transceiver to encompass extended reach of both 10- and 28-Gb/s directly modulated lasers (DMLs). In DML-based links, direct modulation of laser diodes induces power-dependent frequency chirp on the generated optical signals, which causes severe chromatic dispersion as well as pattern dependence on the received signal after optical fiber transmission. Such time-varying nature of the dispersion makes conventional equalization methods ineffective for compensation. The proposed EDC-based clock and data recovery (CDR) IC overcomes the chirp-induced dispersion via a linear equalizer followed by a double-sampling decision feedback equalizer (DFE) at the receiver and a pattern-dependent pulse shaping filter at the transmitter. The chirp-managed EDC improves the receiver sensitivity at a bit error rate (BER) of 10−6 by 1.3 dB in a 3-km link using a DML at a modulation rate of 28 Gb/s, where transient chirp is dominant, and by more than 7 dB in a 105-km link at 10 Gb/s, where adiabatic chirp is dominant. The chip prototype is fabricated in a 40-nm CMOS process and packaged in a flip-chip ball grid array (BGA). The single-chip IC containing dual-lane transceivers and a global clock generator (CG) occupies an active area of 2.8 mm2. The test chip consumes 236 mW, wherein a single-lane transceiver consumes 105.5 mW and a global CG consumes 25 mW from a 0.9-V supply at 28 Gb/s. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic element matching (DEM) decoder incorporating both intersymbol interference (ISI) and mismatch error shaping. From the analysis of ISI error in multi-bit DACs, an algorithm is developed that deterministically controls the element transitions, such that on each conversion cycle the instantaneous number of on transitions is set to a constant value, while the instantaneous number of off transitions varies with the decoder input signal. The technique achieves greater ISI error mitigation than previous approaches using less hardware. To further reduce the logic area, a hierarchical DEM structure, whereby the DEM decoder is split into multiple sub-DEM decoders, is presented. [ABSTRACT FROM AUTHOR]

In this paper, we consider the potential of data transmission in a system with a massive number of radiating and sensing elements, thought of as a contiguous surface of electromagnetically active material. We refer to this as a large intelligent surface (LIS), which is a newly proposed concept and conceptually goes beyond contemporary massive MIMO technology. First, we consider capacities of single-antenna autonomous terminals communicating to the LIS where the entire surface is used as a receiving antenna array in a perfect line-of-sight propagation environment. Under the condition that the surface area is sufficiently large, the received signal after a matched-filtering operation can be closely approximated by a sinc-function-like intersymbol interference channel. Second, we analyze a normalized capacity measured per unit surface, for a fixed transmit power per volume unit with different terminal deployments. As terminal density increases, the limit of the normalized capacity [nats/s/Hz/volume-unit] achieved when wavelength $\lambda$ approaches zero is equal to half of the transmit power per volume unit divided by the noise spatial power spectral density. Third, we show that the number of independent signal dimensions that can be harvested per meter deployed surface is $2/\lambda$ for one-dimensional terminal deployment, and $\pi /\lambda ^2$ per square meter for two- and three-dimensional terminal deployments. Finally, we consider implementations of the LIS in the form of a grid of conventional antenna elements, and show that the sampling lattice that minimizes the surface area and simultaneously obtains one independent signal dimension for every spent antenna is the hexagonal lattice. [ABSTRACT FROM AUTHOR]

Summary: This paper presents redundancy‐bandwidth scalable techniques to deal with the intersymbol interference distortions for current‐steering digital‐to‐analog converters in high‐speed applications. A switching strategy that explores the use of redundant current sources is proposed to realize a signal‐independent element transition rate, ie, the number of switching activities during the transition of successive sampling clock cycles. With a certain number of redundant current sources, this strategy significantly reduces the intersymbol interference distortions without oversampling operation or causing signal attenuation, which makes it appealing for high‐speed applications. As analyzed in this paper, the number of required redundant current sources is scalable for different bandwidth requirement in specific applications, leading to 3 redundancy‐bandwidth scalable trade‐offs between the cost from redundant current sources and the high‐dynamic‐range bandwidth. In implementation, we propose a custom‐designed decoder, named as the overlap‐controlled data‐weighted averaging (OC‐DWA). Compared with the existing similar‐purpose designs, the proposed OC‐DWA decoder realizes the current sources selection with a simple barrel rotator, which is of much lower hardware complexity and energy consumption. Simulations of a digital‐to‐analog converter with this decoder exhibit an enhanced dynamic range over the entire Nyquist band, which verifies the redundancy‐bandwidth scalability of the proposed techniques. [ABSTRACT FROM AUTHOR]

A 12.5-Gb/s complete near-ground transceiver is demonstrated. The output stage of the transmitter (TX) employs 2-tap finite-impulse response equalization (EQ) and also performs ac-coupled EQ for an additional EQ. A continuous-time linear equalizer (CTLE) on the receiver (RX) side compensates for the channel attenuation. Based on the maximum eye algorithm, the peaking gain of CTLE is adaptively controlled to track a time-variant environment, such as PVT variations. Each TX and RX is implemented with clocking circuits: a differential PLL, and a dual-loop clock and data recovery circuit. The proposed transceiver is fabricated in a 45-nm CMOS process, and the entire TX and RX, respectively, consume 92 and 138 mW under a 1.2-V supply while operating at 12.5 Gb/s. [ABSTRACT FROM AUTHOR]

Low-power and low-jitter equalization techniques become increasingly crucial for the wire-line receivers operating at data rates more than tens of gigabits per second. This brief reports an inductorless and power-efficient 32-Gb/s hybrid analog equalizer. The hybrid analog equalizer utilizes a triple-gate control to achieve equalization over a range of channel loss resulting in an inductorless and area-efficient design. The triple-gate controls entail that a low-frequency equalization is achieved in addition to the intermediate and high-frequency equalization, at minimum area overhead. The prototype is realized in a 65-nm CMOS, occupying a compact active area of 0.013 mm2. The maximum equalization achieved is 21 dB at Nyquist with a measured peak-to-peak data jitter of 5.25 ps (0.17 unit interval) at 32 Gb/s for a 231 – 1 pseudorandom bit sequence signal. The measurement shows a vertical eye-opening recovery rate of up to 61% at 32 Gb/s, for a channel loss of 21 dB. The prototype exhibits a competitive power efficiency of 0.53 mW/Gb/s under a supply voltage of 1.2 V. [ABSTRACT FROM AUTHOR]

The capacity region of a two-user linear Gaussian compound Multiple Access Channel with common message (CMACC) and intersymbol interference (ISI) under an input power constraint is derived. To obtain the capacity region we first convert the channel to its equivalent memoryless one by defining an n-block memoryless circular Gaussian CMACC model. We then make use of the discrete Fourier transform (DFT) to decompose the nblock circular Gaussian CMACC into a set of independent parallel channels whose individual capacities can be found easily. Finally we derive the capacity of this n-block memoryless circular Gaussian CMACC (n-CGCMACC) based on the DFT decomposition. Since our channel is a special case of a synchronous multi-terminal channel, the capacity region of the Gaussian CMACC with ISI is the same as the capacity region of the n-CGCMACC in the limit of infinite block length. We also investigate the capacity regions for some special cases of the Gaussian CMACC with ISI using the obtained capacity region, and finally, provide some numerical results to show the loss in the rate caused by ISI.

This paper analyzes the possibility of increasing the spectral efficiency of phase radio-technical data transmission systems that operate under conditions of mutual interference of symbols when “transparency windows” are used. The conditions for emergency of “transparency windows” are defined, recommendations for their application with the purpose of increasing the spectral efficiency of communication systems being considered are presented. Changes in time characteristics of “transparency windows” are analyzed (their lengths over the range of channel symbol time duration) depending on the frequency detuning. [ABSTRACT FROM AUTHOR]

The analytical calculation of the bit error rate (BER) of digital optical receivers that employ avalanche photodiodes (APDs) is challenging due to 1) the stochastic nature of the avalanche photodiode's impulse-response function and 2) the presence of intersymbol interference (ISI). At ultrafast transmission rates, ISI becomes a dominant component of the BER, and its effect on the BER should be carefully addressed. One solution to this problem, termed the bit-pattern-dependent (PD) approach, is to first calculate the conditional BER given a specific bit pattern and then average over all possible bit patterns. Alternatively, a simplifying method, termed the bit-pattern-independent (PI) approach, has been commonly used whereby the average bit stream is used to calculate the distribution of the receiver output, which, in turn, is used to calculate the BER. However, when ISI is dominant, the PI approximation is inaccurate. Here, the two approaches are analytically compared by analyzing their asymptotic behavior and their bounds. Conditions are found to determine when the PI method overestimates the BER. The BER found using the PD method exponentially decays with the received optical power, whereas for the PI approach, the BER converges to a constant, which is unrealistic. For an InP-based APD receiver with a 100-nm multiplication layer, the PI method is found to be inaccurate for transmission rates beyond 20 Gb/s.

This paper reports an area-efficient and tunable bandwidth (BW)-extension technique for a wideband CMOS amplifier to handle very high rate (50+ Gb/s) signaling while keeping a low jitter penalty. We identify its architectural advantages by correlating the performances with the frequency domain (magnitude and group delay (GD) responses) and time domain (impulse and step responses) and comparing them with the existing solutions. Specifically, our technique enables a flexible ac characteristic by introducing a tunable grounded active inductor in the bridged-shunt peaking topology, offering: 1) a high BW enhancement ratio (BWER = $2.65\times$ ); 2) BW-power scalability with small in-band gain variation; and 3) fine tunability of the passband gain without affecting the BW, GD, and power. The experimental prototype is a 65-nm CMOS four-stage differential amplifier occupying just 0.0077 mm2. It delivers a 15-dB gain over a 43-GHz BW with 45-mW power consumption. Small in-band gain variation (0.58 dB) and ripple (1.53 dB) are concurrently achieved with low in-band GD variation (17 to 35.3 ps) and ripple (18.3 ps). The achieved figure of merit of 5.48 [(dc Gain $\times$ BW)/Power] compares favorably with the prior art. [ABSTRACT FROM AUTHOR]

The paper presents analytical and experimental results of a turbo equalizer based on MAP algorithm, including an assessment of its performance by means of computer simulation. Capitalizing on the tremendous performance gains of turbo codes and the turbo decoding algorithm, turbo equalization is an iterative equalization and decoding technique that can achieve equally impressive performance gains for communication system that sends digital data over channels that require equalization, i.e. those which suffer from intersymbol interference(ISI).In this paper, we discuss the turbo equalization approach to coded data transmission over ISI channels, with an emphasis on the basic ideas and some of the practical details. The above practices are just some steps to find out the best equalization technique that should be employed in the process so that at the receiving side we get a signal which is very nearly a replica of the transmitted signal. This clearly reflects that the BER is minimized. Simulation results are included. [ABSTRACT FROM AUTHOR]

Multitrack detection with array-head reading is a promising technique proposed for next generation magnetic storage systems. The multihead multitrack (MHMT) system is characterized by intersymbol interference in the downtrack direction and intertrack interference (ITI) in the crosstrack direction. Constructing the trellis of a MHMT maximum likelihood (ML) detector requires knowledge of the ITI, which is generally unknown at the receiver. Furthermore, in a time-varying ITI environment, updating ML trellis labels using adaptively-generated ITI estimates could incur significant delay. In this paper, we propose one approach to solve these issues. The proposed detector uses a different trellis structure whose output labels are independent of the ITI level, with ITI-dependence appearing only in a scale factor used to suitably weight the computed path metrics in order to retain ML optimality. The detector formulation facilitates the design of a gain loop structure that can track the time-varying ITI and provide ITI estimates to adaptively adjust the weights in the path metric evaluation. Simulation results show that the proposed detector architecture with ITI estimation offers a substantial performance advantage over ML detection using a static ITI estimate. [ABSTRACT FROM PUBLISHER]

We propose a hybrid filter to reduce the peak-to-average power ratio (PAPR) on the transmitter side in a long-term evolution uplink scheme. The design of the proposed filter is based on two key components: a finite impulse response filter and a Nyquist-I pulse. We consider an envelope-constrained filter design to optimize the impulse response of the proposed filter in terms of PAPR reduction. Moreover, we propose a new family of Nyquist-I pulses, the exponential linear pulse, which has a new design parameter that helps reduce PAPR for a given roll-off factor and transmission scheme. Theoretical and numerical results show that the proposed filter outperforms existing filters in terms of PAPR and symbol error rate, and it has a less computationally complex impulse response expression than existing filters for the interleaved subcarrier mode of single-carrier frequency-division multiple access. [ABSTRACT FROM PUBLISHER]

This paper presents a 9/12 2-D modulation code to overcome 2-D interference effects in bit-patterned media recording (BPMR) systems. Next-generation storage systems that are challenged by the superparamagnetic effect require new technologies to be developed, and for magnetic recording, BPMR technology is regarded to be one of the most promising candidates to extend area density beyond 1 Tb/in2. BPMR systems not only help to reduce transition noise and non-linear bit shift, but they also simplify the tracking operation. Nevertheless, some challenges arise for BPMR systems from a signal processing point of view. One of the primary challenges in the systems is the 2-D interference due to the effects of both the along- and across-track intersymbol interference. Moreover, the effect of media noise and the physical limits of the electromechanical components also negatively impact the system performance. The proposed modulation code converts 9 b sequences of user data into 2-D output codewords in 6-by-2 arrays to avoid fatal interference as much as possible, and a reasonable Hamming distance is also ensured for the codeword set. The proposed code achieves gains of about 2 and 1 dB over a system without encoding and a system with 6/8 modulation coding at the same code rate, respectively. Moreover, the performance of the 9/12 2-D modulation codes according to the different array sizes is also investigated. [ABSTRACT FROM AUTHOR]

Audio watermarking (AW) technology is considered for stealthy information embedding directly into audio signal. Inherent in analog radiotelephone channel interferences against watermarks are analyzed. Robust encoding/decoding algorithms are presented and appropriate project of AW system named as Automatic Radio Telephone Identification System (ARTIS) is proposed. Experimental results for the practical VHF radio channel are presented. Relating on processing complexity the designed system enables imperceptibly transmit data on a rate up to 260 bit/sec in the standard VHF radio channel. ARTIS provides the full compatibility with the existing radio installation, and doesn’t require replacement of standard VHF transceivers and operational procedures. Besides, automatic identification the system may be used in the special applications, for example, under the threat of terrorist attack; generally contributes to navigation safety and information security.