Pilotless Frame Synchronization via LDPC Code Constraint Feedback

In traditional receiver architectures, frame synchronization is performed using pilot symbols and a correlation rule. In this paper we show that outputs from the constraint node side of a bipartite decoding graph can be used to achieve frame synchronization in a pilotless low-density parity-check (LDPC) coded transmission, thereby avoiding the bandwidth cost inherent in use of pilot symbols. The complexity of the frame synchronizer is kept relatively low due to its XOR-based approach.     

Robust video coding algorithms and systems

Wireless video communication is particularly challenging because it combines the already difficult problem of efficient compression with the additional and usually contradictory need to make the compressed bit stream robust to channel errors. We describe design and implementation strategies for error-robust video communications with an emphasis on techniques compatible with the coding approaches used in the ISO (MPEG-4) and ITU standards organizations. These techniques include modifications to the video coding algorithms as well as to the system layers that perform packetization and multiplexing     

Type of cottonseed and level of gossypol in diets of lactating dairy cows: effects on lactation performance and plasma gossypol

Objectives were to determine the effects of feeding whole linted Upland (WUP) and cracked Pima cottonseed (BUPCP) to lactating cows on plasma gossypol concentrations and lactation performance. Holstein cows (n = 813) from three commercial dairies were assigned to one of two diets starting at 13+/-11 d in milk (DIM) for a 170-d experimental period. Cottonseed was included at 10% of the diet dry matter, and treatments consisted of replacing WUP with a 1:2 blend of BUPCP. Blood was collected from all cows at 61 and 91 DIM and from a subset of 56 cows on one dairy at 10, 33, 61, 91, 120, and 152 DIM. Intakes of free gossypol increased 32% in cows receiving the BUPCP diet, and concentrations of total gossypol (TG), as well as the proportion of TG as minus (-) isomer in plasma, were higher for cows fed BUPCP than WUP. Plasma TG increased linearly with increasing DIM, but cows fed the BUPCP, especially multiparous cows, had a higher increase in plasma TG over time. Yields of milk and milk components did not differ between the two treatments, although, yields of milk and milk components were greater in cows with higher plasma TG. Replacement of WUP cottonseed with BUPCP cottonseed increased plasma gossypol, but dry matter intake and yields of milk and milk components were not affected.     

Very low variable-rate convolutional codes for unequal errorprotection in DS-CDMA systems

Convolutional codes based on Hadamard sequences can achieve both orthogonality and variable rate. In contrast with other convolutional coding techniques, these codes incur no processing gain penalty in direct-sequence code-division multiple-access (DS-CDMA) systems. We describe a class of such codes called “telescopic protection codes”. These codes enable variable-rate error protection in the manner of rate-compatible punctured-convolutional (RCPC) codes, but preserve the Hadamard orthogonality properties necessary to maintain processing gain that RCPC codes lack     

Soft-input soft-output decoding of variable length codes

We present a method for utilizing soft information in decoding of variable length codes (VLCs). When compared with traditional VLC decoding, which is performed using "hard" input bits and a state machine, the soft-input VLC decoding offers improved performance in terms of packet and symbol error rates. Soft-input VLC decoding is free from the risk, encountered in hard decision VLC decoders in noisy environments, of terminating the decoding in an unsynchronized state, and it offers the possibility to exploit a priori knowledge, if available, of the number of symbols contained in the packet     

Visibility of wavelet quantization noise

The discrete wavelet transform (DWT) decomposes an image into bands that vary in spatial frequency and orientation. It is widely used for image compression, measures of the visibility of DWT quantization errors are required to achieve optimal compression. Uniform quantization of a single band of coefficients results in an artifact that we call DWT uniform quantization noise; it is the sum of a lattice of random amplitude basis functions of the corresponding DWT synthesis filter. We measured visual detection thresholds for samples of DWT uniform quantization noise in Y, Cb, and Cr color channels. The spatial frequency of a wavelet is r2^-λ, where r is the display visual resolution in pixels/degree, and λ is the wavelet level. Thresholds increase rapidly with wavelet spatial frequency. Thresholds also increase from Y to Cr to Cb, and with orientation from lowpass to horizontal/vertical to diagonal. We construct a mathematical model for DWT noise detection thresholds that is a function of level, orientation, and display visual resolution. This allows calculation of a “perceptually lossless” quantization matrix for which all errors are in theory below the visual threshold. The model may also be used as the basis for adaptive quantization schemes     

Combining hidden Markov source models and parallel concatenatedcodes

We present here a framework for modifying a decoder for parallel concatenated codes to incorporate a general hidden Markov source model. This allows the receiver to utilize the statistical characteristics of the source during the decoding process, and leads to significantly improved performance relative to systems in which source statistics are not exploited. One of the constituent decoders makes use of a modified trellis which jointly describes the source and the encoder. The number of states in this modified trellis is the product of the number of states in the hidden Markov source and the number of states in the encoder     

Complex, linear-phase filters for efficient image coding

With the exception of the Haar basis, real-valued orthogonal wavelet filter banks with compact support lack symmetry and therefore do not possess linear phase. This has led to the use of biorthogonal filters for coding of images and other multidimensional data. There are, however, complex solutions permitting the construction of compactly supported, orthogonal linear phase QMF filter banks. By explicitly seeking solutions in which the imaginary part of the filter coefficients is small enough to be approximated to zero, real symmetric filters can be obtained that achieve excellent compression performance     

Trellis-based R-D optimal quantization in H.263+

We describe a trellis-based algorithm which enables R-D optimum quantization decisions in the H.263+ video coding standard. The algorithm allows the quantization decisions for all coefficients in a block to be made jointly, and experiments conducted using H.263+ for video coding rates of 40-50 kbps show an average improvement of 3.5% in bitrate relative to implementations which follow the International Telecommunications Union (ITU) Test Model specifications in making quantization decisions.     

Decorrelation in interferometric radar echoes

A radar interferometric technique for topographic mapping of surfaces, implemented utilizing a single synthetic aperture radar (SAR) system in a nearly repeating orbit, is discussed. The authors characterize the various sources contributing to the echo correlation statistics, and isolate the term which most closely describes surficial change. They then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time. It is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible. The authors present such a map of a forested area in Oregon which also includes some nearly unvegetated lava flows. Such a technique could provide a global digital terrain map