Effect Of Channel Noise Research Articles

New vector quantization-based techniques for reducing the effect of channel noise in image transmission

In this paper, new vector quantization (VQ) based techniques for reducing the effect of channel noise in image transmission are introduced. In one of the proposed methods, i.e., component VQ (CVQ), by transmitting the components of code-vectors (and not their indices), we will be able to reduce the effect of channel noise. To decrease the output rate of CVQ, a modification of CVQ called sub-index VQ (SIVQ) is introduced. This method has error-correcting capability as well. Simulation results show that CVQ and SIVQ techniques are robust to channel errors and surpass the conventional method, in which the indices of the selected code-vectors are protected using a Reed–Solomon code. An error concealment technique called shifted block concealment (SBC) has been also introduced. The stationarity assumption of small blocks of images has been utilized to conceal losses in this method.

Channel noise in Hodgkin–Huxley model neurons

We study the effect of channel noise on the firing properties of the Hodgkin–Huxley equations. The spectral properties of the currents and corresponding Hurst indices are determined, and their relevance for information processing is discussed. The interspike interval histograms and their properties are also discussed.

Blind identification with periodic modulation: a time-domain approach

We propose a method for blind identification of finite impulse response (FIR) channels with periodic modulation. The time-domain formulation in terms of block signals is simple compared with existing frequency-domain formulations. It is shown that the linear equations relating the products of channel coefficients and the autocorrelation matrix of the received signal can be further arranged into decoupled groups. The arrangement reduces computations and improves accuracy of the solution; it also leads to very simple identifiability conditions and a very natural formulation of the optimal modulating sequence selection problem. The proposed optimal selection minimizes the effects of channel noise and error in autocorrelation matrix estimation; it results in a consistent channel estimate when the channel noise is white. Simulation results show that the method yields good performance. It compares favorably with an existing subspace modulation-induced-cyclostationarity method, and it is robust with respect to channel order overestimation. The effect of modulation period and threshold of the modulating sequence are also discussed.

Message encoding and decoding through chaos modulation in chaotic optical communications

Chaos modulation for message encoding and decoding is investigated using two chaotic optical communication systems. With a message injected into the chaotic dynamics of the transmitter in chaos modulation, the complexity of the chaos is found to increase. Meanwhile, the synchronization quality is not influenced by the message encoding. The effect of channel noise is investigated and the bit error rate is calculated as a function of the signal-to-noise ratio for both systems.

Robust vector quantizer design using self-organizing neural networks

In this paper we propose a new method to design vector quantizers for noisy channels. Self-organizing neural networks are known for their efficiency in voice and image data compression; we use self-organizing algorithm to create a topological similarity between the input space and the index space. This similarity reduces the effect of channel noise because any single bit error in a transmitted index will be translated to a close codevector in the input space which yields relatively small distortion. For an 8-bit vector quantizer, the proposed system resulted in 4.59 dB spectral distortion in a highly noisy channel while a simple LBG, LBG with splitting and 2-D self-organizing map (SOM) resulted in 5.96, 5.46 and 5.02 dB of distortion, respectively.

Design of demodulator for the chaotic modulation communication system

Chaotic modulation has recently been proposed for spread spectrum (SS) and code division multiple access (CDMA) communication. It embeds the signal of transmission in the bifurcating parameter of a chaotic dynamical system, and uses the wide-band output of the chaotic system as the transmitted signal. Here we consider the demodulation of this communication scheme using an adaptive filter. Not only can an adaptive filter reduce the effect of channel noise, but it also estimates the bifurcating parameter (i.e., the signal of transmission) sequentially which is required in a communication system. Three kinds of adaptive filters: the least mean square (LMS) algorithm, the recursive least square (RLS) technique and the Kalman filter, are considered here. It is found that the demodulators based on these adaptive filters outperform the standard inversion approach used in the literature.

Comment on "Cycle slips in synchronizers subject to smooth narrow-band loop noise"

This comment pinpoints and rectifies the misconception in the paper of Moeneclaey, Starzac and Meyr (see ibid., vol.36, no.7, p.867-74, 1988) where additive channel noise effects have been confused with phase jitter effects, leading to wrong, interpretations of basic synchronizer functionalities.

Secure progressive transmission of compressed images

In most progressive image coding techniques the compressed data vary in importance for reconstructing the original image. Obtaining certain parts of these data by an eavesdropper could reveal significant information about the transmitted or stored image. In this paper different encryption methods to secure the transmission or storage of such data are proposed and evaluated. The methods are chosen in a manner that allows high encryption and decryption rates, simple key management and utilization of widely available encryption algorithms such as the DES (data encryption standard). Effects of channel noise on the encrypted data are also considered and a modification of these methods to combat channel errors is also proposed and evaluated.

Optimal receive filters for the suppression of ISI and adjacent channel interference

A new efficient method for the design of finite impulse response (FIR) digital receive filters is proposed. The authors formulate a cost function which minimises the total mean square error and thus reduces the effect of channel noise, intersymbol interference (ISI), and adjacent channel interference (ACI) simultaneously. Also, arbitrary fractional-sample delay can be compensated. The resulting filters are analysed in terms of bit error rate (BER) and implementation loss (IL) performance.

State space model and noise filtering design in transmultiplexer systems

A multirate Kalman filter-based transmultiplexer is proposed in this paper for multirate data transmission systems. The composite effect of combining filters and upsamplers at the transmitter is represented by a multirate state space model. The input signals of the transmultiplexer are contained in the state vector, and the channel noise is modeled as a measurement noise. Additionally, the separation filters and downsamplers at the receiver of a conventional transmultiplexer are replaced by the multirate Kalman filter to eliminate the effect of channel noise and reconstruct the input signals. This design is useful for improving the performance of a transmultiplexer system for simultaneous transmission of many data signals through a single noisy channel. Two simulation examples are provided to illustrate the significant improvement in performance.

Simultaneous estimation of echo path and channel responses using full-duplex transmitted training data sequences

To reduce the system initialization time in high-speed full-duplex data transmission over two-wire lines, we propose an efficient full-duplex fast training algorithm which can simultaneously estimate the impulse responses of echo paths and channels at both ends. Two mutually orthogonal periodic sequences are designed and used to co-estimate the near echo, the far echo with bulk delay, and the channel response. The new algorithm can reduce the tap-setting time to half of that required by the traditional half-duplex fast training schemes. The effects of channel noise and symbol rate offset between two ends are examined in terms of both mean-square error (MSE) and signal-to-noise ratio (SNR). Both the theoretical analysis and computer simulation show that there are three degrading factors due to symbol rate offset. The SNR is inversely proportional to the sum of the estimated coefficients, the half period of the training sequences, and the square of symbol rate offset. If the far-signal-to-channel-noise ratio is 30 dB, then the degradation is significant when the symbol rate offset is more than 10/sup -4/. If it is 40 dB, then the degradation is significant when the symbol rate offset is above 3/spl times/10/sup -5/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Using frequency hopping spread spectrum technique to combat multipath interference in a multiaccessing environment

The purpose of this paper is to conduct performance analysis for a frequency-hopped spread spectrum multiaccess network which is subject to the threat of multipath interference. Baseband modulation is done through frequency shift keying and signal detection is accomplished by a noncoherent type receiver. The quality of a signal is affected by the channel noise, multiuser interference, and multipath interference. Performance analysis is conducted on the basis of bit error rate. Due to the sophistication of the system exact analysis is not feasible. The accuracy of approximation is checked against simulations. One major discovery Is that when signal-to-noise ratio is low, multipath interference on the contrary may help to enhance the quality of the signal. Another discovery is that when signal-to-noise ratio is high enough, multipath/multiuser interference becomes the bottleneck of performance. The effect of channel noise can be eliminated by maintaining a large signal-to-noise ratio while spread spectrum technique is employed to reduce the effect of multipath/multiuser interference.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Noise reduction and concealment for block encoded images

A simple scheme to detect the presence of the channel noise on the vector quantized images are proposed. The channel noise effect is removed or concealed by utilizing the continuity of the image signal and the availability of the complete codebook at the receiver. Several coding techniques (such as channel-optimized vector quantization and vector quantization with pseudo-Gray coding) are tested. It is found that the proposed technique always improves the image quality under noisy channel. In addition, it provides the best image quality when vector quantization with pseudo-Gray coding is used as the coding technique. Under this scheme, the proposed technique provides 0.2-1.2 dB performance gain (in average) for a binary symmetric channel with bit error rate 0.1-1%, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Simulation study on effects of channel noise on differential conduction at an axon branch

Effects of membrane channel noise (random opening and closing of ion channels) are studied on spike conduction at a branching point on an axon. Computer simulation is done on the basis of a stochastic version of the Hodgkin-Huxley cable model, into which the channel noise is incorporated. It is shown that the channel noise makes conduction of spikes into daughter branches random; spikes randomly succeed or fail in conduction into daughter branches. The conduction is then randomly differential even though the forms and properties of daughter branches are the same. The randomness is considerable when the radius of an axon is small (approximately 1 microns).

Source coding and transmission of HDTV images compressed with the wavelet transform

Digital high-definition TV (HDTV) signals are generally compressed to reduce transmission bandwidth requirements. A compression algorithm for the bit rate reduction of an HDTV image using the wavelet transform is presented. The major problems related to the transmission of a compressed HDTV signal are analyzed. Transmission is examined both on a noisy channel and an asynchronous transfer mode (ATM) network. The effects of channel noise on the reconstructed image are determined, and a solution to mitigate the degradation of the image quality is presented. A model for the output bit rate of the HDTV coder is derived and used to simulate the transmission of an ATM multiplexer so that the network's main performance parameters can be determined. >

Intrafield transform image coding of composite video

Two different schemes, i.e. adaptive and nonadaptive systems, are developed for intrafield transform (2d-DCT) image processing of a digital NTSC color composite video signal, sampled at three times the color subcarrier frequency. The fast transform algorithm for 2d-DCT (8 × 8 subblock) is used. Based on the statistics of the transform coefficients, variable word length quantizers, optimized for minimizing the mean square error, are developed. These techniques lead to reduced bit rates for transmitting color video at broadcast standards. The performance of adaptive system is much better than that of nonadaptive system. Although the necessary hardware will likely exceed what is needed for a nonadaptive system, the benefits will more than offset the hardware complexity. The effect of channel noise in the adaptive system is investigated in terms of severity and propagation patterns. This is carried out by using a forced error scheme which selectively forces the error to occur in the different types of coding bits. Error propagation patterns are studied by series of computer printouts.

Comments on and Extensions on Wolf's Signal-to-Channel Noise Formulas for Delta-Modulated Systems

The channel noise effects on linear delta modulation (LDM) systems have not yet been adequately analyzed. This paper presents a new and general formulation of these effects, based on the theoretical work by Wolf [1]. A comparative discussion of our formulas with previous results is also included. Finally, the application of our methods and the validity of our comments are illustrated by some numerical examples.