In this paper, partial response signalling and trellis coded modulation are considered together to improve bandwidth efficiency and error performance for M-QAM and denoted as Modified/Quadrature Partial Response-Trell...
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In this paper, partial response signalling and trellis coded modulation are considered together to improve bandwidth efficiency and error performance for M-QAM and denoted as Modified/Quadrature Partial Response-trellis Coded Modulation (M/QPR-TCM) and two new non-catastrophic schemes M/6QPR-TCM and M/9QPR-TCM are introduced for 4QAM, In colored noise with correlation coefficient less than zero, the proposed schemes perform better than in AWGN case. Another interesting result is that when the combined system is used on a Rician fading channel, the bit error probability upper bounds of the proposed systems are better than their counterparts the 4QAM-TCM systems with 2 and 4 states, respectively for SNR values greater than a threshold, which have the best error performance in the literature.
In this paper, a high quality, and in many prospects, efficient, wavelet color image codec (WCIC) is introduced. This codec allows to achieve high compression ratios with little degradation in visual quality. WCIC sim...
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ISBN:
(纸本)0819422355
In this paper, a high quality, and in many prospects, efficient, wavelet color image codec (WCIC) is introduced. This codec allows to achieve high compression ratios with little degradation in visual quality. WCIC simultaneously exploits several characteristics of the wavelet transforms (multiresolution decompositions). Wavelet transform is formed using wavelet packets via lattice structures. Bit allocation algorithm is developed to distribute the bits between and in the colors such that minimal mean-squared-error (MSE) is introduced in each color component. This proves to be beneficial at low bit rates which keeps the color distribution in balance. The wavelet coefficients are quantized using either trellis or zero-tree quantizers depending on their statistics. Quantized coefficients are further compressed with adaptive arithmetic coding resulting in the final coded bit stream. This codec is applied to a wide range of images, from computer animations to natural pictures. The results are compared to other algorithms, including fractals and JPEG, and relative merits of the proposed algorithm are presented.
The evaluation of a low error probability of a trellis-coded modulation scheme by an ordinary Monte-Carlo simulation method is almost impossible since the excessive simulation time is required to evaluate it. The redu...
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The evaluation of a low error probability of a trellis-coded modulation scheme by an ordinary Monte-Carlo simulation method is almost impossible since the excessive simulation time is required to evaluate it. The reduction of the number of simulation runs required is achieved by an importance sampling method, which is one of the variance reduction simulation methods. The reduction of it is attained by the modification of the probability density function, which makes errors more frequent. The error event simulation method, which evaluates the error probability of finite important error events, cannot avoid a truncation error. It is the fatal problem to evaluate the precision of the simulation result. The reason of it is how to design the simulation probability density function. We propose a evaluation method and the design methods of the simulation conditional probability density function. The proposed method simulates any error event starting at the fixed time, and the estimator of it has not the truncation error. The proposed design methods approximate the optimum simulation conditional probability density function. By using the proposed method for an additive non-Gaussian noise case, the simulation time of the most effective case of the proposed method is less than 1/5600 of the ordinary Monte-Carlo method at the bit error rate of 10(-6) under the condition of the same accuracy if the overhead of the selection of the error events is excluded. The simulation time of the same bit error rate is about 1/96 even if we take the overhead for the importance sampling method into account.
The application of the well-known technique of trellis Coded Modulation to coherent optical communications using Polarization Shift Keying (POLSK) is described and analyzed. The resulting receiver is formed by a front...
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The application of the well-known technique of trellis Coded Modulation to coherent optical communications using Polarization Shift Keying (POLSK) is described and analyzed. The resulting receiver is formed by a front-end which performs the heterodyne detection and the Stokes parameter extraction;cascaded with an electronic Viterbi processor operating the maximum likelihood estimate of the transmitted sequence. Results in terms of the error event probability using optimum as well as a simpler suboptimum branch metric show power gains on the order of 3-4 dB, at the expense of a reasonable increase in complexity, only concerning the processing in the electronic domain. These coding gains are not lost even in the presence of high levels of phase noise, to which POLSK in general is highly insensitive.
In Code Division Multiple Access (CDMA) systems forward error correction (FEC) is animportant factor in improving system perfonnance. Because of the multiple accessinterference observed in asynchronous CDMA, FEC is re...
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In Code Division Multiple Access (CDMA) systems forward error correction (FEC) is an
important factor in improving system perfonnance. Because of the multiple access
interference observed in asynchronous CDMA, FEC is required to improve system
capacity. Several alternative coding techniques are available, including "trellis codes"
specifically designed for CDMA, very low rate convolutional codes and conventional
convolutional codes.
An analytic approach is developed to compare the perfonnance of different coding
techniques for CDMA on the same basis by extending several improved analysis
techniques which were developed for uncoded CDMA. Analytic results are presented for
additive white Gaussian noise (AWGN) channels and frequency non-selective Rician
Fading (FNRF) channels. The perfonnance of coded CDMA systems in frequency
selective Rayleigh fading channels is also analyzed using simulation techniques.
Both analytic and simulation results show that by using trellis codes or very low rate
convolutional codes significant perfonnance improvement is achieved over conventional
convolutional codes. trellis codes outperfonn very low rate convolutional codes in
AWGN and FNRF channels while both codes show similar perfonnance in frequency
selective Rayleigh fading channels.
When bit error probability of a trellis-coded modulation (TCM) scheme becomes very small, it is almost impossible to evaluate it by an ordinary Monte-Carlo simulation method. Importance sampling is a technique of redu...
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When bit error probability of a trellis-coded modulation (TCM) scheme becomes very small, it is almost impossible to evaluate it by an ordinary Monte-Carlo simulation method. Importance sampling is a technique of reducing the number of simulation samples required. The reduction is attained by modifying the noise to produce more errors. The low error rate can be effectively estimated by applying importance sampling. Each simulation run simulates a single error event, and importance sampling is used to make the error events more frequent. The previous design method of the probability density function in importance sampling is not suitable for the TCM scheme on an additive non-Gaussian noise channel. The main problem is how to design the probability density function of the noise used in the simulation. We propose a new design method of the simulation probability density function related to the Bhattacharyya bound. It is reduced to the same simulation probability density function of the old method when the noise is additive white Gaussian. By using the proposed method for an additive non-Gaussian noise, the reduction of simulation time is about 1/170 at bit error rate of 10(-6) if the overhead of the calculation of the Bhattacharyya bound is ignored. Under the same condition, the reduction of the simulation time by the proposed method is 1/65 of the ordinary Monte-Carlo method even if we take the overhead for importance sampling into account.
This paper considers the application of trellis coding techniques to direct-sequence spread-spectrum multiple-access (DS/SSMA) communication. The unique feature of the trellis codes considered is that they are constru...
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This paper considers the application of trellis coding techniques to direct-sequence spread-spectrum multiple-access (DS/SSMA) communication. The unique feature of the trellis codes considered is that they are constructed over the set of possible signature sequences rather than over some standard 2-D signal constellation. The resulting codes have a small number of signals per dimension. We present several examples of these trellis codes, and suggest possible methods of implementation. We also present a detailed error analysis for this system, which employs techniques developed by Lehnert and Pursley to accurately model the multiple access interference. We generate numerical results for several examples and conclude that the proposed trellis coded systems yield significant performance improvements over binary antipodal DS/SSMA systems. In addition, the new trellis codes perform better than standard error control techniques with the same complexity and code rate. Analytic results are verified with simulations.
Random overlapping pulse-position modulation (OPPM) sequences result in an unrecoverable error floor on both the probability of erroneous synchronization and the probability of symbol error when only chip synchronizat...
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Random overlapping pulse-position modulation (OPPM) sequences result in an unrecoverable error floor on both the probability of erroneous synchronization and the probability of symbol error when only chip synchronization is present. It is known, however, that for a given sequence length M, a subset of the set of all possible sequences is synchronizable in the sense that in the absence of noise, the receiver can correctly symbol synchronize by observing M or more symbol intervals. In this paper we design finite-state machines and codes over a J-ary alphabet, which produce sequences with the property that every subsequence of length L is synchronizable. Some of the codes, in addition to being synchronizable, produce a coding gain. For an optical Poisson channel we introduce joint synchronization and detection algorithms that utilize the memory in the encoded sequences to produce joint estimates of timing and sequences. Their performance is analyzed through simulations and analytical results.
Reduced-state sequence detection (RSSD) reduces the state trellis of a channel code by forming the states into classes. States within a class are such that paths into the states lie further than a distance parameter d...
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Reduced-state sequence detection (RSSD) reduces the state trellis of a channel code by forming the states into classes. States within a class are such that paths into the states lie further than a distance parameter d from each other. An RSSD decoder retains only one survivor per class at each trellis level. We apply RSSD to ordinary binary convolutional codes. We first give a class-forming algorithm that finds the greatest reduction. It turns out that no commonly tabulated good code benefits from RSSD. However, RSSD is an effective way to repair weaker codes, such as Quick Look-In and RCPC codes. Finally, we show that RSSD cannot be more efficient than the M-algorithm.
An innovative method of coding Line Spectrum Pair (LSP) parameters for transmission over noisy channels is presented. Typically, low bit-rate speech coders use these parameters to convey perceptually important spectra...
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An innovative method of coding Line Spectrum Pair (LSP) parameters for transmission over noisy channels is presented. Typically, low bit-rate speech coders use these parameters to convey perceptually important spectral information. Thus it is necessary that these parameters are not only efficiently quantized but preserved during transmission. The scheme uses a joint source and channel coding technique applied to a concatenated trellis structure. Operating as a source coder, the system encodes below the 1 dB spectral distortion limit. It is shown that by modifying the encoder cost function to include the expected channel distortion, the code exhibits improved robustness to channel errors. This is accomplished with minimal increase in complexity and without increase in bit-rate. It is noted that the scheme performs well over a wide range of channel bit error rates and compares favourably with a standard scalar LSP quantizer tandemed with a channel coder both in terms of bit-rate and channel noise immunity,
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