Ghost Cancellation Research Articles

Holography, the Second Law and a tilde C-function in higher curvature gravity

We analyze the Second Law of black hole mechanics and the generalization of the holographic bound for general theories of gravity. We argue that both the possibility of defining a holographic bound and the existence of a Second Law seem to imply each other via the existence of a certain "c-function" (i.e. a never-decreasing function along outgoing null geodesic flow). We are able to define such a "c-function", that we call \tilde{C}, for general theories of gravity. It has the nontrivial property of being well defined on general spacelike surfaces, rather than just on a spatial cross-section of a black hole horizon. We argue that \tilde{C} is a suitable generalization of the notion of "area" in any extension of the holographic bound for general theories of gravity. Such a function is provided by an algorithm which is similar (although not identical) to that used by Iyer and Wald to define the entropy of a dynamical black hole. In a class of higher curvature gravity theories that we analyze in detail, we are able to prove the monotonicity of \tilde{C} if several physical requirements are satisfied. Apart from the usual ones, these include the cancellation of ghosts in the spectrum of the gravitational Lagrangian. Finally, we point out that our \tilde{C}-function, when evaluated on a black hole horizon, constitutes by itself an alternative candidate for defining the entropy of a dynamical black hole.

Phased array ghost elimination

Parallel imaging may be applied to cancel ghosts caused by a variety of distortion mechanisms, including distortions such as off-resonance or local flow, which are space variant. Phased array combining coefficients may be calculated that null ghost artifacts at known locations based on a constrained optimization, which optimizes SNR subject to the nulling constraint. The resultant phased array ghost elimination (PAGE) technique is similar to the method known as sensitivity encoding (SENSE) used for accelerated imaging; however, in this formulation is applied to full field-of-view (FOV) images. The phased array method for ghost elimination may result in greater flexibility in designing acquisition strategies. For example, in multi-shot EPI applications ghosts are typically mitigated by the use of an interleaved phase encode acquisition order. An alternative strategy is to use a sequential, non-interleaved phase encode order and cancel the resultant ghosts using PAGE parallel imaging. Cancellation of ghosts by means of phased array processing makes sequential, non-interleaved phase encode acquisition order practical, and permits a reduction in repetition time, TR, by eliminating the need for echo-shifting. Sequential, non-interleaved phase encode order has benefits of reduced distortion due to off-resonance, in-plane flow and EPI delay misalignment. Furthermore, the use of EPI with PAGE has inherent fat-water separation and has been used to provide off-resonance correction using a technique referred to as lipid elimination with an echo-shifting N/2-ghost acquisition (LEENA), and may further generalized using the multi-point Dixon method. Other applications of PAGE include cancelling ghosts which arise due to amplitude or phase variation during the approach to steady state. Parallel imaging requires estimates of the complex coil sensitivities. In vivo estimates may be derived by temporally varying the phase encode ordering to obtain a full k-space dataset in a scheme similar to the autocalibrating TSENSE method. This scheme is a generalization of the UNFOLD method used for removing aliasing in undersampled acquisitions. The more general scheme may be used to modulate each EPI ghost image to a separate temporal frequency as described in this paper.

Gravity à la Born–Infeld

A simple technique for the construction of gravity theories in Born–Infeld style is presented, and the properties of some of these novel theories are investigated. They regularize the positive energy Schwarzschild singularity, and a large class of models allows for the cancellation of ghosts. The possible correspondence with low-energy string theory is discussed. By including curvature corrections to all orders in α′, the new theories nicely illustrate a mechanism that string theory might use to regularize gravitational singularities.

Gauge fixing in higher-derivative gravity

Linearized 4-derivative gravity with a general gauge-fixing term is considered. By a Legendre transform and a suitable diagonalization procedure it is cast into a second-order equivalent form where the nature of the physical degrees of freedom, the gauge ghosts, the Weyl ghosts and the intriguing `third ghosts', characteristic to higher-derivative theories, is made explicit. The symmetries of the theory and the structure of the compensating Faddeev-Popov ghost sector exhibit non-trivial peculiarities. The unitarity breaking negative-norm Weyl ghosts, already present in the diff-invariant theory, are out of the reach of the ghost cancellation BRST mechanism.

A new GCR waveform for deghosting TV signals

Ghost canceling reference (GCR) signals have been introduced for the purpose of identifying TV channels for removing ghosts when they appear. A GCR signal should have the following features: the capability of exciting the maximum number of channel modes, simplicity of generation and detection with the minimum hardware, and fast adaptation to channel variations. A new GCR sequence is proposed in this paper. It is based on a bipolar binary (+1 or -1) waveform with a certain sequence. This binary GCR enables the receiver to determine the channel impulse response in a simple non-recursive way, hence speeding up the cancellation of ghosts. The technique does not require multiplication or division (only addition and subtraction are required), which accelerates the speed of ghost canceling, lowering its cost, and simplifying its implementation. The identification of the ghost channel using this GCR can be used along with a suitable algorithm to find the optimum tap coefficients of the equalizer which will remove ghost images. In comparison with existing GCR signals, the proposed approach is seen to be more efficient. Simulation results are included.

Frequency division algorithm for multi-path ghost cancellation

The frequency division algorithm for multi-path ghost cancellation is described through the frequency-domain optimization method for analog and digital TV transmission. Some guidelines for the frequency division method are provided. A novel method to calculate the FIR and IIR coefficients of the deghost systems from the results of the frequency division is proposed. The simulation results are presented by using a Grand Alliance vestigial sideband channel model.

VLSI array to speed up the computation of TV ghost canceler parameters

One of the most well-known adaptive algorithms that adjust conveniently the parameters of the TV ghost canceler is the least mean square (LMS) algorithm. The convergence rate of this algorithm is slow. In this paper a parallel processing technique to speed up the computation of the least square (LS) algorithm is studied. The technique is based on mapping the recursive modified Gram-Schmidt algorithm into two levels of linear systolic arrays. The arrays structure as well as the computation time are described. The performance of the system in terms of computational saving and the array utilization are evaluated. The system is shown to be composed of identical modules which makes it suitable for VLSI technology implementation. The great saving in computation will qualify the system for real-time applications.

Identification and minimization of IIR tap coefficients for the cancellation of complex multipath in terrestrial television

By using a deterministic approach, an exact form for the synchronous detected video signal under a ghosted condition is presented. Information regarding the phase quadrature-induced ghost component derived from the quadrature forming nature of the vestigial sideband (VSB) filter is obtained by crosscorrelating the detected video with the ghost cancel reference (GCR) signal. As a result, the minimum number of taps required to correctly remove all the ghost components is subsequently presented. The results are applied to both National Television System Committee (NTSC) and phase alternate line (PAL) television.

Ghost Cancellation with ITU System-C Standard Ghost Cancellation Reference Signal

From 1992 to early 1994, the ITU/B(CCIR) conducted an extensive investigation in ghost cancellation technology and defined an effective ghost cancellation reference (GCR) signal standard (System C) for 525-line and 625-line television systems to improve future television broadcasting quality for both terrestrial and cable environments. This paper will discuss the properties and applications of the GCR signal

Ghost cancellation implementation in television and VCR

As ghost cancellation becomes more popular, television receivers will include this feature. Integrating ghost cancellation into television requires some special consideration as is discussed in the paper.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

VSB modem subsystem design for Grand Alliance digital television receivers

The functions of the vestigial sideband modem for the Grand Alliance digital TV are described. The partitioning of these functions is discussed in terms of the prototype hardware and possible future development. The VSB modem subsystem (tuner/demodulator) includes the functions of RF selection, local oscillator, and conversion; IF amplification and band shaping; baseband demodulation; AGC; co-channel filtering; synchronization and phase tracking of the carrier, the bit clock, and the data framing; equalization (ghost cancellation); forward error correction (trellis and RS codes); and data de-interleaving. The interaction and partitioning of these functions is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Multighost cancellation technique for HDTV systems, using a derivation of the OLS learning algorithm

Very successful multiple video ghost cancellation simulations have been obtained with the application of a designed learning algorithm, based on the orthogonal least square method [OLS], to a channel identification process based on a FIR system model. The algorithm can be visualized by assuming the existence of a data matrix, at the input of the equalizer, which is created with a time shifting process, in order to generate "M" column vectors. The designed algorithm processes these vectors and, with the aid of an orthogonalization method, calculates a set of the most representative one, with respect to a desired output signal. The delays and amplitudes of the ghosts were obtained with the aid of a forward regressor method. The process has shown to be very effective for the accurate calculation of the ghost parameters, even in the presence of considerable noise levels, and is also used to train RBF approximation networks for the systematic selection of its centroids. In all the tests performed in the paper, the proposed technique has given much better results than using conventional algorithms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

LMS iterative algorithms applied to the computation of TV ghost canceller parameters

Three iterative forms of the LMS learning algorithm were tested for the calculation of the coefficients of FIR filters used as TV ghost cancellers. These computational forms are: the stochastic gradient fixed-step (SGLMS) and a variable step (SLS-CD), algorithms, as well as the recursive modified Gram-Schmidt RMGS algorithm. Because of the iterative nature of the selected algorithms, they are very convenient to be used in on-line LTF filter coefficient adaptations. This makes it possible to compute the coefficient values of the ghost canceller, when the sampling of the signal generates a huge amount of data, which is very hard to be handled with a PC. The aforementioned algorithms are written in a very powerful and flexible matrix oriented software, and all the tests were performed using a very flexible TV system simulator. During the tests, fast convergence of the ghost canceller coefficients to the theoretical values have been observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new ghost cancellation system for Korean GCR

This paper describes a new ghost cancellation system built-in NTSC television based on the Korean ghost cancellation reference (KGCR) signal. The system has a highly integrated transversal filter, an unique circuit for control of the system and a high performance algorithm for calculating the filter coefficients. Laboratory and field test results confirm that the system is effective in canceling several combination of ghosts, which exist in real situations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An enhanced ghost cancellation reference signal

It is proposed to enhance the ghost cancelling reference (GCR) signal so that it can provide additional information about the channel characteristics. The proposed enhancement consists of the addition of a very short modulated or unmodulated staircase signal to detect the nonlinear behaviour in the transmission channel. Tests have shown that this modification does not affect the operation of ghost cancelling equipment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low cost stand-alone ghost cancellation system

A new low cost ghost cancellation system is being developed for the consumer market that uses the high energy US reference signal to provide excellent cancellation of ghosts. The complete system consists of 3 ICs. This paper describes how these ICs work together to cancel ghosts without the need for micro-controllers, DSPs, or external control systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A single-chip video ghost canceller

A 450 K-transistor video ghost canceller chip, which implements a flexibly configurable IIR and FIR filter, is described. A very compact digital filter tap operating at a pixel rate of 14.32 MHz (4*F/sub sc/) allows 180 programmable taps to be implemented in a die area of 56.25 mm/sup 2/ in a 1 mu m TLM CMOS process. The device operates with 3.3- or 5-V power supplies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An advanced single chip digital filter for ghost canceller

A single-chip 398-tap digital filter LSI was developed using a modified adaptive delayed ghost canceling filter configuration. It has 12.3-mm*12.5-mm die size and is in 0.8- mu m CMOS technology. It was realized by a combination of fixed and variable delayed filters. It has 398-tap transversal filters and 11 kbit memory for variable delay lines. Using this chip, board size is reduced to 30% of the present size, and system unit size is reduced to about that of a cigarette case. It easily achieves a high-performance ghost canceller.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ghost cancellation system for the US standard GCR

The high energy US standard ghost cancellation reference (GCR) signal has the capability to give excellent ghost cancellation quality under adverse conditions such as high noise and changing channel characteristics. To achieve the high level of performance possible with this signal an equally high performance system must be available. This paper discusses the first system developed which uses the GCR recently approved as the American standard.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A cost effective time domain TV ghost canceling system simulator

A new very cost effective, flexible and economic discrete time domain simulation technique for almost any TV ghost cancelling approach is described. The simulations were performed with the aid of a properly adapted off the shelf system simulator software for PCs, provided with an improved, newly designed model generator. This generator allows the creation of complex and very powerful models for the systems software library, such as FIR and IIR filter cells, used in the approach of ghost cancellation techniques for advanced NTSC TV systems. The source files used by the model simulator are written in FORTRAN code and are used like functional blocks, which can be configured appropriately for the ghost cancellation process. Astonishing results have been obtained with the proposed technique, which has shown to be very flexible, accurate, simple and cost effective. >