Controlled Intersymbol Interference Research Articles

Computational complexity of algorithm with decision feedback and maximum reliable estimation of following symbols for receiving spectrally effective signals with controlled intersymbol interference

Computational complexity of algorithm with decision feedback and maximum reliable estimation of following symbols for receiving spectrally effective signals with controlled intersymbol interference

Experimental studies of radio modem for transmission and detection of optimal signals with controlled intersymbol interference based on eigenfunctions of band-limited kernels

Experimental studies of radio modem for transmission and detection of optimal signals with controlled intersymbol interference based on eigenfunctions of band-limited kernels

Practical Considerations in Direct Detection Under Tukey Signalling

The deliberate introduction of controlled intersymbol interference (ISI) in Tukey signalling enables the recovery of signal amplitude and (in part) signal phase under direct detection, giving rise to significant data rate improvements compared to intensity modulation with direct detection (IMDD). The use of an integrate-and-dump detector makes precise waveform shaping unnecessary, thereby equipping the scheme with a high degree of robustness to nonlinear signal distortions introduced by practical modulators. Signal sequences drawn from star quadrature amplitude modulation (SQAM) formats admit an efficient trellis description that facilitates codebook design and low-complexity near maximum-likelihood sequence detection in the presence of both shot noise and thermal noise. Under the practical (though suboptimal) allocation of a 50% duty cycle between ISI-free and ISI-present signalling segments, at a symbol rate of 50 Gbaud and a launch power of -10 dBm the Tukey scheme has a maximum theoretically achievable throughput of 200 Gb/s with an (8,4)-SQAM constellation, while an IMDD scheme achieves about 145 Gb/s using PAM-8. Note that the two mentioned constellations have the same number of magnitude levels and the difference in throughput is resulting from exploiting phase information under using a complex-valued signal constellation.

Direct Detection Under Tukey Signalling

A new direct-detection-compatible signalling scheme is proposed for fiber-optic communication over short distances. Controlled inter-symbol interference is exploited to extract phase information, thereby achieving spectral efficiencies about one bit less, per second per hertz, of those of a coherent detector.

Error-rate performance for signals with controlled intersymbol interference when applying detection algorithms of symbol-by-symbol processing with decision feedback

Error-rate performance for signals with controlled intersymbol interference when applying detection algorithms of symbol-by-symbol processing with decision feedback

ПРИМЕНЕНИЕ ЭКВАЛАЙЗЕРОВ ДЛЯ УСТРАНЕНИЯ МЕЖСИМВОЛЬНОЙ ИНТЕРФЕРЕНЦИИ В ТРОПОСФЕРНЫХ КАНАЛАХ СВЯЗИ

The article explores the possibility of using equalizers to create controlled intersymbol interference as a way of dealing with such interference arising in the troposcatter channel. The frequency-selective fading in multipath propagation of radio signals leads to their distortion, causing interference with intersymbol interference in channels with variable parameters, such as the troposcatter channel. With an appropriate choice of waveforms can significantly reduce the effect of intersymbol interference. For this purpose in the article defines the function F(ξ), which describes the waveform, whose frequency response has steeper slopes than the “raised cosine”. The impulse function h(y) is written through the function F(ξ). To determine it the Fredholm integral equation with a symmetric core is solved. Formulas for the value of F(ξ) in the zero and higher approximations are obtained. The equalizer schemes that implement the required F(ξ) are given. The core of an integral equation is represented as a sum containing modified Bessel functions of the first kind of fractional order. A system of linear equations is obtained. The solution of which is the function F(ξ). This function F(ξ) was found by while holding a different number of members of the series. The inaccuracy of the calculated functions F(ξ) are found. In the article is the equalizer schemes which to implement the task of this research. Considered options for constructing equalizers according to the scheme with a test signal, without a test signal and adaptive with a transversal filter. The result obtained in the article using the QPSK modulation method can be extended to the case of multiple phase modulation. The use of the equalizer schemes described in the article is determined, as a rule, by the developer depending on the requirements for the characteristics and parameters of the digital troposcatter system.

Microwave analog filter‐based modulators for partial response signals

AbstractPartial response (PR) modulations boost the spectral efficiency of baseband signals by introducing controlled intersymbol interference. In this paper, we report design guidelines for PR modulators based on analog filters. Moreover, we designed and manufactured filter prototypes following the proposed guidelines. Measurements confirm that the prototypes can modulate up to 5 levels PR signals at 10 Gbps.

MLSE Equalizer With Channel Shortening for Faster-Than-Nyquist Signaling

Faster-than-Nyquist (FTN) signaling by introducing controlled inter-symbol interference (ISI) has been viewed as a potential technique in future communication systems due to its higher spectrum efficiency. In order to achieve the high transmission rate, the effective receivers have to been designed to suppress the ISI and extract the transmit signals. Therefore, we propose a channel shortening-based maximum-likelihood sequence estimation (MLSE) scheme. In this scheme, the length of the shortening channel can be optimized for the different time-squeezing factor, which determines the transmission rate and ISI in FTN systems, to achieve a good tradeoff between the detection performance and the implementation complexity. The simulation analysis results show that the proposed MLSE equalizer with optimized channel shortening can achieve a good tradeoff between the performance and the complexity.

Controlled Intersymbol Interference Design Techniques of Conventional Interconnect Systems for Data Rates Beyond 20 Gbps

This paper presents a new design technique of high-speed interconnects with controlled intersymbol interference (ISI) to create efficient signaling over a band-limited channel. Performance of high-speed electrical links is limited by conductor loss, dielectric dispersion, and reflections in the board, package, and connector. These nonidealities result in significant ISI. In current systems, the effect of ISI is either mitigated through complex equalization, signal conditioning, and coding techniques, or through costly impedance control and manufacturing processes. In the proposed approach, instead of eliminating ISI, we shape the response of the channel into a set of channel characteristics with controlled ISI using simple passive structures in the board and the package. The resulting controlled ISI is exploited at the transmitter and receiver to simplify the architecture of the system and to achieve high data rates. The techniques to design interconnects with controlled ISI are reasonably simple to implement in conventional interconnect technologies. Simulation examples are given to demonstrate the validity and advantages of the design technique using duobinary and analog multitone (AMT) signaling methods.

Space–time receivers for GSM radio interfaces in subway tunnel environments

AbstractIn this paper, we investigate how to increase the capacity of GSM (Global System for Mobile communications) radio interfaces in subway tunnel environments by means of antenna arrays and Space–Time (ST) receivers. We address the modeling, both theoretically and experimentally, of the multiple‐antenna wireless channels encountered in subway tunnels. We demonstrate that propagation is conveniently modeled by a flat‐fading channel, but there exist strong spatial correlations among channel components that decrease capacity and affect receivers' performance. Different space–time GSM receiving strategies have also been investigated. We first consider ST equalization techniques that only account for the noise and the controlled Intersymbol Interference (ISI) introduced by the modulation format employed in GSM. Then, we analyze the performance of receivers that incorporate ST coding capabilities and show the superior performance of iterative MAP (Maximum a Posteriori) receivers that interchange soft information among the equalizer and the ST decoder. All receivers are evaluated with experimental channels measured in the subway of Paris. Copyright © 2002 John Wiley & Sons, Ltd.

Reduced complexity sequence detection for nonminimum phase intersymbol interference channels

Controlled intersymbol interference may be used to design bandwidth efficient coded modulation schemes. The performance of the optimum receiver depends only on the free distance of the code and is independent of its phase. Large reductions in receiver complexity are obtained by using reduced search detection techniques like the M-algorithm (MA). However, we show that MA detector performance depends critically on phase, and is characterized by the partial energy of the encoder or channel. The minimum phase encoder needs by far the least detector searching. We propose modifications to the receiver, so that the reduced search can operate on all nonminimum phase channels at this same low complexity.

SNR of NRZ receivers for the magnetic channel

The relative maximum SNRs of various receivers for NRZ codes are estimated for the Lorentzian channel. Receivers which use a detection filter to introduce controlled intersymbol interference followed by an appropriate decoder are shown to have the best potential performance.

Correlative level coding and maximum-likelihood decoding

Modems for digital communication often adopt the so-called correlative level coding or the partial-response signaling, which attains a desired spectral shaping by introducing controlled intersymbol interference terms. In this paper, a correlative level encoder is treated as a linear finite-state machine and an application of the maximum-likelihood decoding (MLD) algorithm, which was originally proposed by Viterbi in decoding convolutional codes, is discussed. Asymptotic expressions for the probability of decoding error are obtained for a class of correlative level coding systems, and the results are confirmed by computer simulations. It is shown that a substantial performance gain is attainable by this probabilistic decoding method.

A New Equalizer Structure for Fast Start-Up Digital Communication

The use of transversal filters for automatic equalization has made possible high-speed data communication over voiceband telephone channels. Recently much attention has been focused on the possible use of the high-speed data sets in private line multiparty polling systems. However, for such applications, it is necessary to reduce the start-up time of the present automatic equalizer drastically. This paper examines the start-up time (settling time) of the transversal filter equalizer for two important classes of data communication systems: Class IV partial-response systems and single-sideband Nyquist systems. (The latter represents the limiting case of vestigial-sideband systems with small roll-off bandwidth.) It is shown that in single-sideband Nyquist systems the input signals to the gain controls of the transversal equalizer may be nearly orthonormal. Consequently the equalizers may have a short settling time. It is also shown that the equalizer settling time is much longer in Class IV partial-response systems, because such systems use controlled intersymbol interference and the input signals to the gain controls are highly correlated. The possibility of reducing the settling time of the automatic equalizers is examined. A new equalizer structure is developed based on the following principles: (i) Equalizer settling time can be minimized by making the input signals to the gain controls orthonormal, and (ii) Such a minimization does not change the noise power, the mean-square equalization error, the convexity of the gain control adjustment, and the feedback control loops in the equalizer. These principles are general in that they apply regardless of the type of modulation — single-, vestigial-, or double-sideband (SSB, VSB, or DSB) — or the signaling scheme (Nyquist or partial-response). Application of these principles to Class IV partial-response systems is considered. For private line systems and systems where amplitude distortions in the communication channels are not severe (delay distortions can be arbitrary), the new equalizer can be implemented by simply adding a prefixed weighting matrix to the conventional transversal equalizer. Analysis and computer simulation show that the use of such a new equalizer can residt in a significant reduction in the system's start-up time.