Search

To deal with the degradation of the synchronization performance in low SNR condition, a novel DRM (Digital Radio Mondiale) synchronization algorithm is proposed. The proposed algorithm employs cyclic prefix for timing synchronization and fractional frequency offset estimation like conventional methods, but accomplishes frame synchronization and integer frequency offset estimation using time pilot cells and differential coding technologies, which are designed specially for the DRM system. After channel estimation and equalization, frequency pilot cells are used to estimate residue fractional frequency offset and subsequent sample offset as well as fixed phase offset to achieve complete synchronization. Simulation results show that the proposed algorithm can possesses better time and frequency synchronization performance than the conventional method in the multi-path fading channel with low SNR condition.

Embedded zerotree (EZW) and Set Partitioning in Hierarchical Trees (SPIHT) coding, introduced by J.M. Shapiro and Amir Said, are very effective and being used in many fields widely. In this study, brief explanation of the principles of SPIHT was first provided, and then, some improvement of SPIHT algorithm according to experiments was introduced. 1) For redundancy among the coefficients in the wavelet region, we propose differential method to reduce it during coding. 2) Meanwhile, based on characteristic of the coefficients' distribution in subband, we adjust sorting pass and optimize differential coding, in order to reduce the redundancy coding in each subband. 3) The image coding result, calculated by certain threshold, shows that through differential coding, the rate of compression get higher, and the quality of reconstructed image have been get raised greatly, when bpp (bit per pixel)=0.5, PSNR (Peak Signal to Noise Ratio) of reconstructed image exceeds that of standard SPIHT by 0.2~0.4db.

This paper describes a new low-power, area-, and pin-efficient alternative to differential encoding for high-performance chip-to-chip and backplane signaling. The technique, called multi-bit-differential-signaling (MBDS), consists of a new design for the driver and link termination network coupled with a novel coding system based on "N choose M (nCm)" codes. In an nCm-coded MBDS channel, there are n physical interconnections over which all code symbols carry exactly m 1-bits. This property gives MBDS links signal-to-noise and transmission characteristics comparable to pair-wise differential links such as low-voltage differential signaling (LVDS). Moreover, MBDS is compatible with commercial LVDS receivers in point-to-point and multi-point bus topologies. However, because MBDS channels have a higher information density, they use up to 45% less power and up to 45% fewer I/O pads than equivalent differentially encoded buses.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We consider techniques for applying DC control (DCC) to a multilevel modulation data stream for optical data storage. We describe basic algorithms for controlling DC content, analyze their effectiveness in suppressing low-frequency and DC content, compare their performance and complexity against binary modulation schemes (EFM for CD and EFM+ for DVD), and prove that they guarantee bounded digital sum value for all input patterns. We also briefly discuss how these DCC codes are used within a larger system containing a multilevel modulation encoder.

This paper will investigate differential space frequency coding and its applicability to multipath fading High Frequency (HF) radio channels. Orthogonal Frequency Division Multiplexing (OFDM) will be combined with differential Alamouti space frequency codes to measure performance on the Watterson HF channel model. Differential coding facilitates non-coherent reception and can thus also reduce receiver complexity. Numerical results will be shown for the CCIR poor (2ms, 1Hz) and extra poor (2ms, 2Hz) channel conditions for a system comprised of 2 transmit antennas and a single receive antenna. For comparison, performance will also be shown vs. a new single transmit and receive antenna HF OFDM Code Division Multiple Access (CDMA) scheme.

Recently, a new differential detection scheme for transmit diversity was proposed by Tarokh and Jafarkhani, which can achieve full diversity without the requirement to estimate the channel state at the receiver. In this paper, we investigate the effect of the carrier frequency offset on the performance of the transmit diversity with differential encoding scheme and present some results on its maximal tolerable frequency offsets for different MPSK signals. The results have shown that the differential encoding transmit diversity is very robust to the frequency offset and is very feasible in practice.

Piecewise linear (PL) image coding proceeds in three steps: 1) a digital image is converted into a 1D-signal using a scanning procedure, for example by scanning lines in a zig- zag or Hilbert order. 2) The signal is approximated by the graph of a piecewise linear function, which consists of a finite number connected line segments. 3) Entropy encoding of the sequence of the segment end points. In this step differential coding can be used for one or both coordinate sequences of the end points. In this step differential coding can be used for one or both coordinate sequences of the end points. To ensure a desired approximation quality a constraint is imposed, e.g., on the root-mean-square error of the PL signal. In this paper we consider uniform approximation. Two problems are addressed: first, an optimal PL approximation in the sense of a minimal number of segments is to be obtained. Second, when entropy coding of the segments is used, how can one jointly optimize the variable length code and the PL approximation yielding a better or even minimal rate without violating the uniform error bound. The first problem is solved by dynamic programing, the second is approached by using Huffman coding and an annealing procedure in which the design of the Huffman tables and the dynamic programming is alternately iterated using a cost function that reflects the codework lengths of the current variable length code. This algorithm is guaranteed to converge to a minimum length code. We describe the algorithms, implementation issues, compare two different scanning procedures, the zig-zag line scan and the Hilbert scan, and report results for encoding various test images.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper presents a general procedure for determining the optimal MPEG coding strategy in terms of the selection of macroblock coding modes and quantizer scales. The two processes of coding mode decision and rate control are intimately related to each other and should be determined jointly in order to achieve optimal coding performance. We formulate the constrained optimization problem and present solutions based upon rate- distortion characteristics, or R(D) curves, for all the macroblocks that compose the picture being coded. Distortion of the entire picture is assumed to be decomposable and expressible as a function of individual macroblock distortions, with this being the objective function to minimize. The determination of the optimal solution is complicated by the MPEG differential encoding of motion vectors and dc coefficients, which introduces dependencies that carry over from macroblock to macroblock for a duration equal to the slice length. Once the upper bound in performance is calculated, it can be used to assess how well practical sub-optimum methods perform.

To obtain a high level of quality when coding a TV color video signal with a high compression rate, the spatial subband decomposition and the differential coding with motion compensation and psychovisual quantization have been previously successfully used for coding a color television sequence at a rate of 10 Mbit/s. However these techniques are not sufficiently efficient to achieve the objective of a rate of 5 Mbit/s without any significant reduction of the spatial resolution and of the quantification quality. We present a subband coding method which allows the user to simultaneously maintain the full spatial resolution and the quantization quality. This method is based on a frame skipping algorithm; it primarily uses motion compensation techniques for the interpolation of non coded frames and the prediction of coded frames and secondarily a spatial subband decomposition of the prediction error before a coding step which uses a set of visually optimized scalar quantizers -- the quantization in the spatial frequency domain is adapted to the visual perception by incorporating some important aspects of the human visual system (frequency dependence and masking).© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper summarizes a research study on data compression techniques applicable for Remote Piloted Vehicles (RPV). Interframe techniques are considered and algorithms are determined to account for motion in frame-to-frame aerial photographs resulting in large bit reduction ratios provided that the various parameters of the mission such as altitude, velocity, etc. are accurately known. Differential encoding is used to further reduce bandwidth. Intraframe techniques suitable for the RPV mission including two-dimensional transform techniques and hybrid coding schemes are investigated and evaluated. It is shown that the hybrid schemes using Hadamard transform in one spatial direction and DPCM in the other spatial direction performs equivalent and at times superior to 2-dimensional transform techniques. The effects of channel errors on both the transform and hybrid coding schemes are investigated. Although the hybrid coding scheme is shown to be more sensitive to noise, optimization of the prediction coefficient results in satisfactory performance in a noisy environment. An adaptive scheme is considered which shows improved resolution in regions of high activity within the picture.© (1976) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The hybrid coding technique developed here involves a function of two concepts: progressive interactive image transmission coupled with transform differential coding. There are two notable features in this approach. First, a local average of an mxm (typically 5 x 5) pixel array is formed, quantized and transmitted to the receiver for a preliminary display. This initial pass provides a crude but recognizable image before any further processing or encoding. Upon request from the receiver, the technique then switches to an iterative transform differential encoding scheme. Each iteration progressively provides more image detail at the receiver as requested. Secondly, this hybrid coding technique uses a computationally efficient, real, orthogonal transform, called the Modified Hermite Transform(MHT) [1], to encode the difference image. This MHT is then compared with the Discrete Cosine Transform(DCT) [2] for the same hybrid algorithm. For the standard images tested, we found that the progressive differential coding method per-forms comparably to the well-known direct transform coding methods. The DCT was used as the standard in this traditional approach. This hybrid technique was within 5% of SNR peak-to-peak for the "LENA" image. Comparisons between MHT and DCT as the transform vehicle for the hybrid technique were also conducted. For a transform block size N=8, the DCT requires 50% more multiplications than the MHT. The price paid for this efficiency is modest. For the example tested ("LENA"), the DCT performance gain was 4.2 dB while the MHT was 3.8 dB.