Joint estimation of data and timing in the presence of inter-symbol interference

Probabilistic finite-state automata are a formalism that is widely used in many problems of automatic speech recognition and natural language processing. Probabilistic finite-state automata are closely related to other finite-state models as weighted finite-state automata, word lattices, and hidden Markov models. Therefore, they share many similar properties and problems. Entropy measures of finite-state models have been investigated in the past in order to study the information capacity of these models. The derivational entropy quantifies the uncertainty that the model has about the probability distribution it represents. The derivational entropy in a finite-state automaton is computed from the probability that is accumulated in all of its individual state sequences. The computation of the entropy from a weighted finite-state automaton requires a normalized model. This article studies an efficient computation of the derivational entropy of left-to-right probabilistic finite-state automata, and it introduces an efficient algorithm for normalizing weighted finite-state automata. The efficient computation of the derivational entropy is also extended to continuous hidden Markov models.

This paper proposes and investigates a trellis coded modulation using time-varying mapping and encoders which is very useful to increase minimum Euclidean free distance(d free ) and obtain large coding gain by intentionally utilizing intersymbol interference(ISI) in a channel. If M-ary modulation signals are transmitted in a channel with ISI, the received signals will be mapped into more than M signal points due to ISI,i.e. a channel memory. In the presence of ISI, optimum allocation of distorted signal points due to ISI is derived so as to maximize Euclidean distance in the signal points at every instant considering the trellis diagram. In order to maintain the allocation in the state transition, a method to utilize time-varying mapping and encoders is described. In particular, the coded 4PSK using the time-varying mapping and encoders with a code rate 1/2 in the presence of ISI, 1+1/2D can achieve much larger d free and lower BER than the Ungerboeck's coded 4PSK using the time-invariant mapping and encoder in a channel without ISI, providing that their decoding complexity is equivalent. The improvement can increase as a constraint length of the encoder.

By dividing the available spectrum into multiple bands, multi-band ultra-wideband (UWB) systems possess many advantages, such as the flexibility to eliminate possible interference and coexistence problems with available wireless standards. UWB channels have large delay spread, causing inter- symbol interference (ISI) in high rate systems. The RAKE receiver is often used to capture multipath energy, but it is incapable of ISI compensation, causing severe bit error rate (BER) degradation in practical UWB channels. This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band UWB. The performance of the proposed receiver is compared with the RAKE receiver through analytical and simulation studies. The proposed equalizer has been shown to be able to handle ISI under any channel conditions or data rate presented, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. one. Therefore, equalization receiver based on adaptive algorithms seems to be an effective way to recover the transmitted data. With this consideration, we propose an over-sampling multi-channel equalizer per sub-band for a multi-band UWB system, which provides more effective inter-symbol interference (ISI) suppression compared with the conventional RAKE receiver when operating in channels with large delay spread. Through detailed theoretical analysis and extensive simulations, we are able to show that the proposed 4-arm equalizer scheme is superior to a 4-arm conventional RAKE receiver in the presence of ISI at all signal-to-noise ratios (SNRs). Based on the method presented in (4), the simulated performance is shown to conform to analytical predictions. The RAKE receiver is incapable of ISI compensation, and a moderate level of ISI is shown to cause severe bit error rate (BER) degradation. The proposed over-sampling equalizer, on the other hand, is able to handle ISI under any channel conditions or data rate, with an acceptable BER. Over- sampling is shown to be able to achieve diversity gain, and improves the output SNR.

A new approach to a reduced states Viterbi decoder (VD) is introduced which is based on a bounded metric. This approach is most attractive for combatting intersymbol interference (ISI) using a Viterbi algorithm, specifically if trellis coded modulation (TCM) is used. It has been shown that in the case of ISI the overall compound Viterbi decoding of ISI and TCM is much better than any other decoding algorithm, for example decision feedback. The most aggravating drawback of such an overall VD is its large number of states, resulting from both the TCM encoder and ISI memory. However, this large number of states can be substantially reduced by our method of a bounding metric, with a negligible performance degradation.

The whitened matched filter (WMF) is the optimum receiver filter for pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM) transmissions in the presence of intersymbol interference (ISI) and additive white Gaussian noise (AWGN). A new realization of the WMF is proposed, which incorporates very easy timing recovery for high-speed transmissions such as optical fiber communications. The proposed realization scheme uses a specially designed filter to equalize the ISI, such that only relatively simple timing recovery circuitry for ISI free signals will be needed. >

Free Space Optical (FSO) communication is an emerging technology to provide high bandwidth, secure and high quality communication. In this work we have determined the capacity of the Free Space Optical communication system with Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) technique under weak atmospheric turbulence conditions. To model the weak turbulence condition of the atmosphere lognormal channel model is used throughout the work. The capacity of MIMO-OFDM FSO is evaluated in the presence of Inter Symbol Interference (ISI) and is compared with MIMO FSO with ISI. The capacity of MIMO-OFDM FSO system increases in comparison to MIMO in the presence of ISI. It is found that the effect of ISI is mitigated by using OFDM and the capacity is enhanced. Since MIMO uses spatial divervity to mitigate the fading caused by turbulence hence the capacity of both MIMO-OFDM FSO and MIMO FSO also increases as the number of receiving antennas is increased.

The paper represents a major step toward receiver structures under the framework of the per-path pulse distortion using more realistic channel models. We extend our previous framework to include the important phenomenon of inter-symbol interference (ISI). ISI ultimately limits the maximum achievable data rate. We find that the per-path pulse distortion has impact on this maximum achievable data rate in the presence of ISI. As examples of this discovery, we investigate the optimum receiver structure and two sub-optimum receivers with zero-forcing and minimum mean square error (MMSE) equalizers. We use the high-rise building channel model as the underlying pulse propagation model. This model captures many properties that are not available in the IEEE 802.15.4a model.

In telecommunication, Intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible. In this paper, we design a zero forcing equalizer, which is a type of linear equalizer used to mitigate the effects of ISI (Intersymbol Interference). The zero forcing equalizer does this by finding the inverse of the impulse response of the channel. The ISI can be studied using eye diagram, which overlays many samples of a signal and can give a graphical representation of the signal characteristics. In this paper the results have been shown with proper eye diagrams. In this paper we also investigate the bit error rate, which is used to estimate the performance characteristics of the zero forcing equalizer.

Multicarrier modulation using orthogonal frequency division multiplexing (OFDM) is often recognized as an efficient solution for wireless communications. However, waveform bases other than sinusoidal functions can similarly be used for multicarrier systems in order to provide an alternative to OFDM. In this context, DWMT transmission systems are suggested. It is known that such systems suffer obviously from the two main problems of Inter Symbol Interference (ISI) and Inter-Carrier Interference (ICI). ISI may be considerably reduced via channel equalization. The effect of ICI can be reduced using high order Finite Impulse Response(FIR)wavelet filter banks, but at the expense of increased system complexity. Those FIR banks which are required to reduce effect the ICI should have autocorrelation functions approaching an impulse. On other hand, Infinite Impulse Response(IIR) filter banks can be used to replace those FIR counterparts to increase sub-band discrimination while reducing the required filter order, i.e., decreasing the complexity of system. In this paper, a special type of IIR filter banks is designed and implemented for such purpose. Bi- reciprocal lattice wave digital filters (BLWDFs) are utilized in an approximate linear phase design of 11th order IIR wavelet filter bank (FB) for discrete wavelet multi-tone (DWMT) transmission systems. The performances of the proposed DWMT for transmission over simulated wireless channels with additive white Gaussian noise (AWGN) are examined and compared with one of the recent FIR designs. Significant improvements over the classical DWMT approach are observed.

This paper presents a comparative study, analyzing the potentials of pulse amplitude modulation (PAM) for implementing next generation high-speed copper wireline links. This comparative study analyzes the sensitivities of PAM2, PAM4 and PAM8 to inter-symbol interference (ISI), using four different channels (with their loss gradually increased) running at 28 Gb/s, 56 Gb/s, 112 Gb/s and 224 Gb/s. Each case is examined with and without equalization to properly assess the inherent limitations of the modulation schemes in the presence of ISI. This study shows that although higher order PAM offer a better spectral efficiency, this does not translate into the best performance in terms of signal integrity. Depending on the severity of ISI and the data rate, a lower order PAM can outperform a higher order PAM, especially for the low-loss cases.

This paper proposes a new channel estimation method for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems in the presence of intersymbol interference (ISI). The proposed method uses special training sequences (TS) mainly for two reasons. Firstly, to obtain a desirable crest-factor of the transmitted training signal. Secondly, to eliminate the influence of ISI on the channel estimation performance. By using the recommended training sequences, one can avoid the ill-conditioned least square (LS) problem. To illustrate the proposed method, we assume that the system does not use a guard interval (GI). Simulation results show that the proposed method outperforms conventional methods with respect to the mean square error (MSE) of the estimated channel by more than 20 dB if the signal-to-noise ratio (SNR) is high.

The presence of intersymbol interference (ISI), in addition to multiple access interference, severely hampers the performance of a code-division multiple-access (CDMA) communication system. In such a situation, channel coding can be used to obtain better performance, but at the cost of a reduction in rate of flow of information. In this paper, it is shown with the help of simulation results that the chip-interleaved CDMA system effectively combats ISI without requiring additional channel coding. The system differs from the conventional CDMA system in the sense that, the chip sequence resulting from the pseudo noise (PN) sequence modulation is interleaved before transmission. Two receivers are proposed, one based on the turbo equalization method which employs a maximum a posteriori equalizer of exponential complexity and the other based on minimum-mean square error-optimized iterative interference cancellation principles which is of linear complexity. Simulation results are provided which show that error rates close to the no-ISI single-user case can be obtained. The shortcomings of the coded CDMA with turbo detection system in the presence of ISI are also discussed.

Altairis MCS embodies an entirely new approach to the operation of complex systems through a unique automation technology based on Finite State Modeling (FSM). Conventional mission control systems provide extremely limited automation capabilities through limit checking and command scripts written in languages such as TSTOL or its variants, or can analyze at best a handful of telemetry parameters by means of a rule-based expert system application. Such applications have proven only marginally practical due to the great deal of time and expense required developing, testing and maintaining them. FSM, in contrast, captures human expertise in models as an adjunct to the normal systems engineering process all space missions must undergo. These models provide automated analysis of the entire telemetry stream during real time operations.

Diffusion-based molecular communication system (DBMC) is a system in which information-carrying molecules are sent from the transmitter and passively transported to the receiver in a fluid environment. Nanomachines, which are the main part of this system, have limited processing capacity. Besides, at the receiver, high inter-symbol interference (ISI) occurs due to free movement of molecules and the variance of the observation noise is signal dependent. Hence, it is important to design high-performance and low complexity receiver detection methods. In this paper, finite impulse response (FIR) Wiener filter is introduced for the first time, which has considerably less computational complexity compared to the minimum mean square error (MMSE) algorithm proposed in the literature. Moreover, extended Kalman filter is introduced for the first time to DBMC as a receiver detection method. Finally, Viterbi algorithm is modified and used as a benchmark for performance evaluation.

In this paper, we propose a novel Cooperative Model for natural language understanding in a dialogue system. We build this based on both Finite State Model (FSM) and Statistical Learning Model (SLM). FSM provides two strategies for language understanding and have a high accuracy but little robustness and flexibility. Statistical approach is much more robust but less accurate. Cooperative Model incorporates all the three strategies together and thus can suppress all the shortcomings of different strategies and has all the advantages of the three strategies.