Showing papers on "Adaptive filter published in 1975"

A normalized digital filter structure

Abstract: A normalized digital filter structure is presented, based upon an orthonormal polynomial expansion. This structure is recursively designed, has several predictable stability properties in the presence of time-varying parameters, and appears to have roundoff noise properties which are superior to other known filter structures, particularly in the presence of clustered poles. Each section of the filter can be precisely implemented by one complex multiply.

The importance of phase in image processing filters

Abstract: We demonstrate that phase accuracy is extremely important in image processing filters and express the hope that more work will be done on the development of filter design techniques which use phase as well as magnitude specifications.

New recursive digital filter structures having very low sensitivity and roundoff noise

Abstract: For poles close to the unit circle and near z = 1 , the usual realizations of recursive or IIR digital filters are highly sensitive to the coefficient quantization and have large roundoff noise. As the sampling rate is increased the poles approach z = 1 and the problems become more severe. For these situations several new digital filter structures are presented for which the above errors remain constant and generally insignificant as the sampling rate is increased. Results on sensitivity and the roundoff errors for these new structures are presented and compared with conventional realizations. Some numerical results are also presented showing order of magnitude improvements.

Coordinated Adaptive Washout for Motion Simulators

Abstract: This paper introduces a new method of providing motion cues to a moving base six-degree-of-freedom flight simulator utilizing nonlinear filters. Coordinated adaptive filters, used to coordinate translational and rotational motion, are derived based on the method of continuous steepest descent, and the basic concept of the digital controllers used for the uncoordinated heave and yaw cues is also presented. The coordinated adaptive washout method is illustrated by an application in a six-degree-of-freedom fixed-base environment.

Spread spectrum correlation receiver

Abstract: A spread spectrum communication system having a correlation receiver for decoding an information signal transmitted on a pseudo-noise (PN) carrier. The receiver synchronizes to the transmitted signal by performing a continuous sequence of correlations until a correlation output exceeding a predetermined threshold level is detected. Thereafter, the receiver performs a plurality of correlations during a sampling interval which is timed to occur at approximately the time when high subsequent correlation output signals are likely to appear. After enhancement through adaptive filter processing, the correlation outputs generated during each sampling interval are accumulated (integrated and the summed output present at the end of the sampling interval is representative of the transmitted data message (a binary bit). The adaptive filter develops and stores weighting values representing the expected signal strength of the correlation outputs and the actual correlation outputs are multiplied by the weighting values. Received signal energy representing atmospheric and specular multipath signal components are detected and channeled to the accumulator along with the main signal component. The accumulator thus realigns the multipath signals with the main signal, resulting in a significant increase in processing gain. An audio version of the system is also disclosed.

Optical-waveguide filters: Synthesis

Abstract: Analytical formulas for the synthesis of optical-waveguide filters having arbitrary spectral-response characteristics are derived from coupled-mode formalism. Use of these general formulas is illustrated by design of several filters, one of which is a linear power discriminator. The synthesis yields the functional dependence of spatial-perturbation period on the distance along the direction of wave propagation in the waveguide filter. The coupled-mode equations for the functional perturbation forms as determined by the synthesis process were solved numerically to find the actual response characteristics of the filter designs. Excellent agreement was found between the desired characteristics and those of the synthesized filters.

Realizations of two-dimensional recursive digital filters

Abstract: Algorithms are derived for realization of two-dimensional recursive digital filters using direct forms and continued fraction expansions. Included is a test for continued fraction expansion which at the same time determines the expansion coefficients. Transposed structures are also discussed, and a comparison is made of the various realizations.

On the stability of the forced response of digital filters with overflow nonlinearities

Abstract: The forced response of a general type of digital filter, implemented with overflow nonlinearities, is studied. A definition of stability of this forced response is given. It is indicated that this stability can be studied by means of the zero-input behavior of a system, with the same structure but with time-varying nonlinearities. A theorem is derived giving sufficient conditions for the stability of the forced response of a digital system. Some results of the application of this theorem to wave digital filters are given.

A New Type of Digital Filter for Data Transmission

Abstract: A digital filter is introduced consisting of a transversal part and a simple recursive network. The coefficients of the transversal part are equal to integer powers of two or zero; thus complicated multipliers are avoided and instead a simple routing circuit is used. Use of several types of the recursive network makes the filter applicable in different frequency ranges. The coefficients of the transversal part can be interpreted as differences of successive values of the impulse response of the filter. It is shown that this difference routing digital filter (DRDF) is especially suited for application in data transmission.

Static controller for power factor correction and adaptive filtering

Abstract: A polyphase cycloconverter operating in regenerative mode is connected between a voltage distribution system and a single phase high frequency resonant tank and controlled to produce essentially no real power flow to the resonant tank and a variable amount of leading (or lagging) reactive power. The static reactive power controller has fast response and can function as an electronically variable capacitor for power factor regulation, VAR control and adaptive filtering.

New Active Filter synthesis based on Scattering Parameters

Abstract: Inductorless active filters which are derived from double terminated classical reactance filters, such as gyrator-capacitor filters and filters using the FDNR concept, are known to exhibit low sensitivity. Stimulated by the ideas underlying the method of wave digital filters the attempt has been made to establish a concept for the synthesis of active filters which is based on processing of wave quantities. In this paper the method leading to this new kind of active filters is presented and possibilities for practical implementation are shown. Some experimental results confirm the feasibility of the principle.

Noniterative Automatic Equalization

Abstract: An equalizer based on the minimum mean-square error (MSE) criterion, but with direct solution of the resulting equations, is described. The direct solution is based on the algorithms devised by Levinson and Trench. With the availability of large-scale integration (LSI) bipolar computing elements, these algorithms are competitive with iterative procedures. A method is considered for the estimation of the required parameters, and for automatic adaption to a changing channel. It is shown that the delay can be adjusted to achieve minimum MSE with respect to that parameter. Simulations undertaken show the robust performance of the algorithm, and that the equalizer performance is not adversely affected by operation in decision-directed mode.

A new type of wave digital filter

Abstract: This paper proposes a new wave digital filter derived from doubly terminated LC-ladder networks by replacing each series or shunt arm element of the ladder by its equivalent digital two-port. It is shown that such two-ports may be cascaded without the use of adapters defined by Fettweis ( 1 ). A number of realizations of the wave digital two-ports, which are canonic with respect to both multipliers and delays, have been obtained. Also a realization which is canonic with respect to multipliers only is given and an example considered using this realization. The sensitivity of this filter with respect to the multiplier coefficient changes due to finite word length is compared with the conventional cascaded digital filter and also the one proposed by Renner and Gupta. It is found that the proposed filter appears to be a more desirable form of implementation than the conventional cascade form and comparable to that of Renner and Gupta ( 2 ).

Timing recovery and scramblers in data transmission

Abstract: This paper considers several problems associated with envelope-derived timing recovery, equalization, and scrambling in synchronous data transmission. Particular attention is focused on the time intervals in which periodic data sequences are transmitted, such as during start-up or when an idle code is being transmitted. It is shown that the standard envelope-derived timing-recovery system may be significantly improved by zonal filtering of the received passband signal prior to forming the envelope. For phase-modulated systems, we discuss the limitations of the “precession” technique employed for the purpose of providing a periodic timing wave when there is an input of short period. The advantages of using a phase-locked loop to filter the envelope instead of a narrow-band filter are also described. A study of scrambler operation has provided an extension of previous results concerning the relationship between the input and output period. It is shown that the output period of several scramblers connected in tandem does not necessarily double with the addition of a stage, and that if a particular stage does not lock up then no succeeding stage can lock up.

Non-recursive digital filter employing simple coefficients

Abstract: A non-recursive digital filter is disclosed, composed of a cascaded plurality of basic sections, each of which is characterized by coefficient values of integer powers of two's. No hardware multipliers are required in the filter and the operating speed is several times faster than other filters which utilize multipliers.

Self-adjusting digital notch filter

Abstract: Digital filter auto-adjustment to variations in input signals is achieved by normalizing the output of the second of two substantially identical series-connected digital filter stages and subtracting the normalized output of the second filter stage from its input to provide a measure of filter signal residue power Deviations of the signal residue power from the preset limits of a signal residue power standard are detected and signals responsive thereto are used to appropriately adjust variable bandwidth constants in both filter stages

The application of an approximate non-linear filter to systems governed by coupled ordinary and partial differential equations

Abstract: An approximate non-linear filter is applied to systems described by coupled ordinary and partial differential equations with both volume and boundary disturbances and measurement errors. Measurements are assumed to be carried out at u discrete number of spatial positions in the distributed portion of the system. The filter is applicable to cases in which the data are available continuously in time and at discrete sampling instants. Both versions of the filter are applied to an ingot heating problem of some interest in steel-making. The numerical results show that the filter is rapidly convergent and quite robust.

Heuristic optimization of the cascade realization of fixed-point digital filters

Abstract: In the cascade realization of fixed-point digital filters under dynamic range constraints, the output noise due to accumulation of roundoff errors is highly dependent upon the order of the sections. For recursive filters it also depends on the pole-zero pairing that forms the individual second-order sections. The output noise may vary over several orders of magnitude for different cascade realizations of high-order filters. Therefore an optimization procedure to find a good ordering and pairing is very desirable. We propose a heuristic optimization procedure for finding a "near optimal" solution. The procedure is completely automatic and does not require any knowledgeable judgment. The number of function evaluations required for a filter of N-cascaded sections is proportional to N2. By using this procedure, "near optimal" solutions have been found for a 22nd-order recursive filter in 23 s, and for a 55th-order nonrecursive filter in 37.5 s, on an IBM 360-91 computer.

Detection, location, and removal of delay-free loops in digital filter configurations

Abstract: Simple graph-theoretic methods for the detection and location of delay-free loops in a digital filter configuration are outlined along with a method to develop an equivalent realization without delay-free loops.

Minimax optimization of recursive digital filters using recent minimax results

Abstract: The purpose of this paper is to use some recent work by the author on nonlinear minimax optimization to derive an efficient algorithm for the minimax optimization problem. This is followed by the application of the algorithm to the problem of choosing the coefficients of a recursive digital filter to meet arbitrary design specifications on the magnitude or the group delay characteristics.

Two-dimensional recursive filter design using differential correction

Abstract: This paper is based upon a presentation given at the 1974 Arden House Digital Signal Processing Workshop. The presentation discussed a method for designing two-dimensional recursive digital filters using a differential correction algorithm. A brief description of the algorithm and some design examples will be presented here. This design approach is compared to a similar approach used by Bednar and Farmer [1].

Two design techniques for digital phase networks

Abstract: Two computer-aided algorithms for the design of all-pass digital filters are presented. The first technique is based on a linear programming approach to solving the approximation problem posed by the minimax design of an all-pass digital filter. A new iterative algorithm with stability constraints is offered for direct form design. The second technique implements a gradient search for those quadratic factors of an all-pass transfer function that lead to a locally optimal approximation (in the least-squares sense) of a desired phase function. New initial guess procedures and the parameterization of linear-phase offset enhance the least-squares design procedure. Examples illustrating the result of both procedures are included.

Digital filter realization using successive multiplier-extraction approach

Abstract: A new approach to the digital filter realization problem is proposed in this paper. In this approach multipliers are extracted one at a time successively in the development of all realizations. The approach is illustrated by finding all possible realizations of a second-order transfer function containing two delays, four multipliers, and four two-input adders with the added restriction that no products of multipliers appear in the expression for the transfer function.

Single amplifier functionally tunable low-pass-notch filter

Abstract: The canonical network developed in this paper is an active RC negative feedback arrangement that uses a single op-amp and two capacitors to realize low-pass-notch filter characteristics. The filter parameters are adjustable through resistive trimming. This functional tuning process uses a signal generator, a dB-scale voltmeter and a phase meter. The analytical design procedure takes into account a single-pole amplifier model. The network has low-passive sensitivities and is suitable for moderate- Q applications ( Q \leq 5 ). An example is discussed giving the resistor's limits for a \pm 10 percent capacitance tolerance.

Digital filter device for processing binary-coded signal samples

Abstract: A digital filter is described in which the filter coefficients which differ from zero are coded in unequal numbers of multipliers which are equal to 2 n and in which immediately after each multiplication of a given signal sample by the multipliers of the relevant filter coefficent a new signal sample is processed in the multiplying devices by the relevant multipliers. Thus the signal samples are applied to the multiplying device at instants which are mutually set independently of one another.

On the evaluation of roundoff noise in digital filters

Abstract: The usual method of measuring the roundoff noise generated in a digital filter may lead, at least in case of sign-magnitude truncation, to an excessive result due to incomplete cancellation of the useful output signal. A simple method for determining a corresponding corrective term is presented.