Tap Gain Research Articles

Nonlinear Mobile Link Adaptation Using Modified FLNN and Channel Sounder Arrangement

In a typical mobile environment, the varying speeds of transmit–receive pairs make traditional channel estimation methods inefficient due to continuously altering requirement of high density reference symbols. It has been largely instrumental in driving efforts to formulate innovative solutions, which are appropriate for such situations. Previously, with high computational cost, autoregressive moving average (ARMA) models of the stochastic wireless channels though appeared to be effective but could not efficiently incorporate the true nonlinearities observed in a practical situation. Therefore, nonlinear ARMA models based on artificial neural networks gained popularity. Yet certain challenges continue to exist, which are related to approximating all aspects of a real time situation, encompassing the non-linearities observed in a stochastic wireless channel, reducing training latency, enhancing processing capability, and deriving appropriate neuro-computational topologies. Modified functional link neural network with linearized activation function (FLNNLA) with nonlinear functional expansion is found to be more suitable for modeling stochastic wireless channels and removing the above-mentioned shortcomings. The proposed FLNNLA models the nonlinear tap gain process efficiently, reduces computational complexity, and enhances receiver performance with less learning cycles, better spectral efficiency and emerges as a strong candidate for being a part of upcoming receiver designs.

A Dual-Purpose Reconfigurable Negative Group Delay Circuit Based on Distributed Amplifiers

In this letter, a novel reconfigurable negative group delay distributed amplifier (NGD-DA) circuit is proposed. This NGD-DA offers a new method to realize negative group delay. By properly choosing the gain coefficient of each tap for the DA, we can synthesize the negative group delay at the reverse port of the DA in the frequency band of interest, while maintaining a flat gain at the forward port; this results in a dual-purpose DA. Moreover, the proposed NGD-DA is reconfigurable; the phase response at the reverse port can be simply controlled by adjusting the tap gain coefficients, and therefore the bandwidth as well as the amount of negative group delay can be manipulated. The proposed active NGD circuit is validated through theoretical explanation and experimental results.

Genome-Wide Phylogenetic Comparative Analysis of Plant Transcriptional Regulation: A Timeline of Loss, Gain, Expansion, and Correlation with Complexity

Evolutionary retention of duplicated genes encoding transcription-associated proteins (TAPs, comprising transcription factors and other transcriptional regulators) has been hypothesized to be positively correlated with increasing morphological complexity and paleopolyploidizations, especially within the plant kingdom. Here, we present the most comprehensive set of classification rules for TAPs and its application for genome-wide analyses of plants and algae. Using a dated species tree and phylogenetic comparative (PC) analyses, we define the timeline of TAP loss, gain, and expansion among Viridiplantae and find that two major bursts of gain/expansion occurred, coinciding with the water-to-land transition and the radiation of flowering plants. For the first time, we provide PC proof for the long-standing hypothesis that TAPs are major driving forces behind the evolution of morphological complexity, the latter in Plantae being shaped significantly by polyploidization and subsequent biased paleolog retention. Principal component analysis incorporating the number of TAPs per genome provides an alternate and significant proxy for complexity, ideally suited for PC genomics. Our work lays the ground for further interrogation of the shaping of gene regulatory networks underlying the evolution of organism complexity.

Ergodic capacity formula of MIMO-OFDM systems under correlated frequency selective Rayleigh fading channels

An explicit formula for the ergodic capacity of Orthogonal Frequency Division Multiplexing (OFDM)-based Multiple-Input Multiple-Output (MIMO) systems under correlated frequency selective Rayleigh channels is derived, by simplifying the channel response matrix in frequency domain into the so-called Kronecker model composed of three kinds of correlations, i.e. multipath tap gain correlation and spatial fading correlations at both transmitter and receiver. The derived formula is very simple and convenient for one to estimate the effects of all three kinds of correlations on MIMO-OFDM capacity. If taps are independent, there is a very simple expression for the ergodic capacity. In case of tap correlation, the capacity formula could be further given in an integral expression. The validity of the new formula is verified and the effects of correlations, delay spread as well as the number of subcarriers on the ergodic capacity are evaluated via Monte Carlo simulations.

Performance analysis of a monolithic integrated transversal filter using mixed-mode scattering parameters

A broadband transversal filter based on a new cell design that enables positive and negative tap gain weight control is proposed and its behaviour is analysed in the frequency domain. The non-ideal behaviour of distributed circuits and associated effects on the functional characteristics of an integrated transversal filter design are examined through consideration of the principles of generic differential circuits. It is shown that the transversal filter can be modelled as a coupled-pair drain line structure with the ability to propagate both common and differential-mode signals. Coupled wave interactions on artificial transmission lines are characterised using a set of derived mixed-mode scattering parameters and voltage and current phasors at input/output ports of a monolithic filter design. Analytical and simulation results confirm the suitability of the approach for broadband filter implementations, in applications requiring predefined time-domain responses as in high-speed correlators and encoders as used in optical code division multiple access (CDMA) systems.

A 3-Tap FIR Filter With Cascaded Distributed Tap Amplifiers for Equalization Up to 40 Gb/s in 0.18-<tex>$mu$</tex>m CMOS

This paper describes a 3-tap finite impulse response programmable analog filter in 0.18-mum CMOS. The filter is intended for polarization-mode dispersion compensation in 40-Gb/s long-haul single-mode optical fiber links. A novel filter topology is employed, whereby each tap gain comprises a cascade of two distributed amplifiers with adjustable gain. The same lumped LC ladders that provide the 25-ps tap delays also serve as artificial transmission lines for the distributed tap amplifiers. The prototype is 1 mm times 1 mm (900 mumtimes600 mum active area) and consumes up to 70 mW from a 1.8-V supply depending on the tap gains. Linear equalization is demonstrated over a channel with 17 dB of loss at 20 GHz. A 50 mV per side eye amplitude with 14 dB signal-to-noise ratio is demonstrated at 30 Gb/s, and a modest 39 mV per side eye amplitude with 10 dB signal-to-noise ratio is achieved at 40 Gb/s

A CMOS Finite Impulse Response Filter With a Crossover Traveling Wave Topology for Equalization up to 30 Gb/s

This paper describes a fully differential 3-tap finite impulse response filter in 90-nm CMOS. A traditional traveling wave filter topology is modified to alleviate its inherent delay-bandwidth-gain tradeoffs. Each tap gain is comprised of two transconductors whose outputs superimpose with the same group delay, similar to a distributed amplifier. This doubles the bandwidth of the filter for a given tap spacing and gain. Digital control is provided for the tap gains, an integrated pre-amplifier, and tuning varactors. Coupled differential spirals are used in the delay lines to help the design fit into an area 600 /spl mu/m/spl times/500 /spl mu/m. A 1-V supply voltage and 25-mW power consumption are enabled by the use of parallel differential pairs for sign control of the transconductances instead of Gilbert cell amplifiers. The input return loss is better than 16 dB and the output return loss is better than 9 dB up to 30 GHz. Equalization of NRZ data over a coaxial cable channel was demonstrated up to 30 Gb/s, making it faster than any previously reported CMOS equalizer.

Effect of tap gain correlation on capacity of OFDM MIMO systems

The effects of tap gain correlation on the capacity of broadband multiple input, multiple output (MIMO) systems is investigated for orthogonal frequency division multiplexing (OFDM) signalling. A unified broadband MIMO fading channel model is proposed for capacity analysis using correlated tapped delay line fading channels for each antenna pair. It is shown that the amount of tap gain correlation strongly influences the capacity of the broadband MIMO system. When the tap gain correlation is greater than a certain threshold, the capacity advantage of the broadband system vanishes.

Efficient simulation of digital transmission over WSSUS channels

This paper proposes an efficient Monte Carlo method which reduces computation for digital communication simulations over a multipath Rayleigh fading, wide-sense-stationary uncorrelated-scattering (WSSUS) channel. An equivalent discrete-time channel representation, which can be realized by a FIR filter with time-variant tap gains, is employed. In the proposed method, the tap gains are generated from a linear transformation of a set of orthogonal zero-mean complex Gaussian random processes. By the central limit theorem, each random process is approximated by summing a finite number of randomly generated phasors (Monte Carlo approximation). When compared with the tap gain generation method, which approximates the physical channel by the Monte Carlo approximation first and then generates the tap gain values, the proposed method demonstrates a considerable reduction in the required simulation time as well as improved accuracy under similar conditions.

Complexity reduction and performance improvement of a decision feedback equalizer for 16QAM in land mobile communications

This paper proposes a complexity-reduced decision feedback equalizer (DFE) for 16-ary quadrature amplitude modulation (16QAM) using tap gain interpolation, bi-directional equalizing (BDE) and space diversity combining (SDC) to achieve high spectral efficiency and high quality data transmission over frequency-selective fading channels in land mobile communications. To reduce the amount of computation required for BDE and SDC, we propose a tap gain interpolation scheme and pre-decision schemes for both processes. Computer simulation of a (16QAM/TDMA system) confirms that the proposed scheme improves frequency-selective fading compensation performance by 6 dB or more while using only 27% of the computation of conventional single branch DFE receivers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Means for improving the speech quality in multi‐pulse excited linear predictive coding

A technique that reconciles the differences between the estimator and the filter of a multi-pulse linear predictive voice encoder achieves a higher quality in the output speech. The technique simultaneously solves for the pulse amplitudes and pitch tap gain to minimize the estimator bias in the multi-pulse excitation and thereby improves, performance of the system. The increased signal-to-noise ratio is accomplished by first modifying the pitch predictor such that the pitch synthesis filter accurately reflects the estimation procedure used to find the pitch tap gain and, second, improving the excitation analysis technique such that the pitch predictor tap gain and pulse amplitudes are solved for simultaneously, rather than sequentially. Neither of these modifications results in an increased transmission rate and they do not significantly increase the complexity of the multi-pulse coding algorithm.

Method for improving speech quality in code excited linear predictive speech coding

By reconciling differences between the estimator and the filter of a code excited linear predictive (CELP) voice coder, higher quality is achieved in the output speech. The pulse amplitudes and pitch tap gain are solved for simultaneously to minimize the estimator bias in the CELP excitation. Increased signal to noise ratio is accomplished by modifying the pitch predictor such that the pitch synthesis filter accurately reflects the estimation procedure used to find the pitch tap gain, and by improving the excitation analysis technique such that the pitch predictor tap gain and codeword gain are solved for simultaneously, rather than sequentially. These modifications do not result in an increased transmission rate or significant increase in complexity of the CELP coding algorithm.

A design method for optimum equalization in magnetic recording with partial response channel coding

Equalization is of such importance as to dominate linear density in magnetic recording when partial response channel coding is employed. This paper describes an advanced design method for optimum equalization in Interleaved NRZI recording by means of a transversal equalizer. Error rate analysis proceeds through a series expansion. This is done in order to consider the tradeoff between equalizing error and equalizer output noise, which has been neglected in conventional design. Key input data for the design are readback pulse shape, noise power spectrum, and linear density. The results of the design are given as optimum tap number and optimum tap gain. Analysis through application of this method makes it possible to clarify the following. The optimum tap number is 8 to 14. The optimum equalizer produces about a 1.4 times linear density improvement in comparison with a conventional 4-tap transversal equalizer. An about 1.5 times linear density improvement compared with the

Adaptive Walsh equaliser for data transmission

The realisation of a Walsh network is proposed. This network is built from a set of Walsh functions which are either odd or even binary value functions in their defined domain. The network is employed as an adaptive equaliser for which an algorithm for recursively adjusting the tap gain coefficients minimising the mean-square estimation error at the output is proposed. Some desirable properties of the covariance matrix of the equaliser are discussed. Examples of equalisation of a practical channel demonstrate the effectiveness of the Walsh equaliser.

An automatic equalizer using block‐iterative algorithm

AbstractThis paper presents an automatic equalizer consisting of transversal‐type circuits which uses a block‐iterative algorithm for tap‐gain adjustment. The taps of an FIR filter are divided into groups. The proposed algorithm seeks the optimum tap gain for each group in one step. This algorithm may be regarded as an extension of the Gauss Seidel algorithm, which is a solution method for first‐order simultaneous equations. Unlike the ordinary steepest‐descent method, it is guaranteed to converge to the global optimum even for transmission lines having totally unknown channel distortion. Computer simulations reveal that the block‐iterative algorithm, by allocating two to three taps in a group, converges faster than the ordinary steepest‐descent method and requires fewer computational steps.

Fast start-up equalization with periodic training sequences

Prior knowledge of the typical signal spectrum at the equalizer input can be used to speed up the convergence of a least mean-square error nonrecursivc equalizer by placing a weighting matrix in the path of the coefficient (tap gain) corrections. When the training sequence is periodic with period equal to the time-spread of the nonrecursive equalizer, the weighting matrix is not only symmetric and Toeplitz, but also circulant. Thus the fast update algorithm can be implemented by inserting a single nonrecursive filter in the path of the periodic input sequence before it is used for computing coefficient correction terms. The stability and convergence of the fast start-up algorithm with "stochastic" update in the presence of noise are examined. In the absence of prior information about the channel characteristics, this fast converging training procedure may be easily extended to a one-shot method of equalizer setup. The one-shot method, which involves estimation of the inverse filter from one period of the received signal, proves to be robust in the presence of noise. Simulation resuits are given for class I partial-response and Nyquist (20 percent roll-off raised cosine) data transmission systems with quadrature amplitude modulation over a dial-up telephone connection.

A note on the modified Kalman filter for channel equalization

An application of the Kalmsn filter to equalization of a digital communication Chmnnel is described. The resultant modified Kalman equalizer (KE) is a nonlinear system in which the channel tap gain are estimated via a decision feedback approach and the state variable is estimated by a prediction process.

On the use of Channel Introduced Redundancy for Error Correction

The problem considered is that of reducing intersymbol interference caused by time dispersive channels. Similarity between the response of a time dispersive channel and that of a cyclic algebraic encoder has led to a method of treating the dispersive channel as a linear encoder. A tapped delay line equalizer is used to complete the encoding process so that the result can be decoded and errors corrected. The tap gain vector for the equalizer is developed, and an upper bound on the probability of error is derived. The analysis and computer simulation results show that under certain conditions the error rate can be reduced by orders of magnitude.

Automatic Equalization for Digital Communication

Distortion in transmission channels causes intersymbol interference in digital communication systems. This distortion may be partially corrected at the receiver through the use of a tapped delay line having adjustable tap gain settings (transversal filter), The problem of minimizing distortion with a finite-length transversal filter is examined. In the region of small initial channel distortion where most existing systems operate, the best tap gain settings satisfy a set of simultaneous linear equations. For larger initial distortion, iterative techniques are required to find best gain settings. The distortion is shown to be a convex function of the tap gains, so mathematical programming techniques may be employed for optimization. The practical problem is that of evolving a logical strategy whereby the tap gains of the transversal filter may be set to optimum values. An easily implemented system for automatic equalization is described which makes use of a steepest-descent technique of minimization. The equalizer is automatically set prior to data transmission in a training period during which a series of test pulses is transmitted. Only polarity information is required, so digital logic may be used in the equalizer. For application to high-speed data transmission, great accuracies are required for the tap gain settings. Thus the problem of noise in the channel during equalization is quite important. The final error due to noise and channel distortion and the equalizer settling time are discussed and evaluated. Finally, the effect of a transversal filter equalizer in terms of the system frequency-domain characteristics is considered.

Correlation functions in a tapped delay line model of the orbital dipole channel

This paper considers the properties of the tap gain functions in a tapped delay line model of the orbital dipole channel. Specifically, auto-correlation and cross-correlation functions are computed for these tap functions in terms of assumed statistics for the motion of illuminated dipoles. It is demonstrated that when a certain inequality involving the transmitted signal bandwidth is satisfied, these correlation functions become identical to those which would arise from the corresponding tap gain functions of a suitably defined channel consisting of a continuum of motionless scintillating uncorrelated scatterers. In effect, this inequality sets an upper bound to the bandwidth of the transmitted signal, beyond which the orbital dipole channel may not be modeled as such a continuum of uncorrelated scatterers. Simplified expressions for tap gain correlation functions are derived for the case of large signal bandwidths, including the subcase in which the above mentioned inequality is satisfied. In the latter case the tap gain functions are shown to become mutually uncorrelated for all time shifts.