We propose a trellis-coded modulation system using continuous-phase frequency-shift keying (CPFSK) and ring convolutional codes for transmitting the bits generated by an embedded zerotree wavelet encoder. Improved performance is achieved by using maximum a posteriori decoding of the zerotree symbols, and ring convolutional trellis codes are determined for this decoding method. The CPFSK transmitter is decomposed into a memoryless modulator and a continuous phase encoder over the ring of integers modulo 4; the latter is combined with a polynomial convolutional encoder over the same ring. In the code design process, a search is made of the combined trellis, where the branch metrics are modified to include the source transition matrix. Simulation results of image transmission are provided using the optimized system, including mismatched channel cases.

A distributed kinetic spanning tree algorithm is proposed for routing in wireless mobile ad hoc networks. Assuming a piecewise linear motion model for the nodes, the sequence of shortest-path spanning trees is determined, valid until the time of the next node trajectory change. By computing the sequence of trees using one execution of the distributed routing algorithm, in contrast to computing the tree for a single time instant, the number of routing messages is substantially reduced. Moreover, the total power required to route through the trees as a function of time is also lower.

Access to multimedia data has become much easier due to the rapid growth of the Internet. While this is usually considered an improvement of everyday life, it also makes unauthorized copying and distributing of multimedia data much easier, therefore presenting a challenge in the field of copyright protection. Digital watermarking, which is inserting copyright information into the data, has been proposed to solve the problem. In this paper, we first discuss the features that a practical digital watermarking system for ownership verification requires. Besides perceptual invisibility and robustness, we claim that the private control of the watermark is also very important. Second, we present a novel wavelet-based watermarking algorithm. Experimental results and analysis are then given to demonstrate that the proposed algorithm is effective and can be used in a practical system.

Previously, we proposed a trellis coded modulation system using CPFSK and ring convolutional codes for transmitting the bits generated by an embedded zerotree wavelet encoder. Improved performance is achieved by using maximum a posteriori (MAP) decoding of the zerotree symbols. In this paper, the optimal ring convolutional trellis codes are determined for MAP decoding. The CPFSK transmitter is decomposed into a memoryless modulator and a continuous phase encoder over the ring of integers modulo 4; the latter is combined with a polynomial convolutional encoder over the same ring. In the code design process, a search is made of the combined trellis, where the branch metrics are modified to include the source transition matrix. Simulation results of image transmission are provided using the optimized system.

The emergence of several radio technologies such as Bluetooth, and IEEE 802.11 operating in the 2.4 GHz unlicensed ISM frequency band may lead to signal interference and result in significant performance degradation when devices are co-located in the same environment. The main goal of this paper is to present a simulation environment for modeling interference based on detailed MAC and PHY models. This framework is then used to evaluate the impact of interference on the performance of Bluetooth and IEEE 802.11. We use several simulation scenarios and measure performance in terms of packet loss, residual number of errors, and access delay.

A novel robust image coding and adaptive packetization algorithm suitable for very low-bit-rate transport is suggested. This algorithm can be applied to any zerotree-based encoder, such as the embedded zerotree wavelet coder of Shapiro (1993) and set partitioning in hierarchical trees by Said and Pearlman (1996). A very explicit segmentation and packetization method of an image bitstream, where the lowest frequency subband is separately encoded from the higher frequency subbands for unequal protection over a noisy channel, is proposed. The trees in the higher frequency subbands are split, classified, and assembled for efficient image coding and packetization according to their initial threshold and subband. The use of these classified trees enables one to make robust packets, while giving priority to some packets. In practice, each packet has a different initial threshold and can be decoded independently. In spite of additional overhead bits required for packetization, the algorithm reported is comparable to the original zerotree-based image coders at low bit rates. Additionally, simulation results show that the new method is resilient under severe packet losses.

In this paper, we develop an error resilient variant of the MPEG-4 embedded zerotree wavelet coder, suitable for mobile fading channels. The residual redundancy in the compressed bit stream provides implicit error protection through the use of source-controlled channel decoding; no explicit channel coding is used. We propose two slight modifications to the MPEG-4 coder. The first removes the arithmetic coding in the lowest frequency subband so that hidden Markov model-based MAP estimation of both the source index and the channel state can be easily applied. The change in bit rate is negligible, while performance during severe channel fading conditions can be greatly increased. The second modification adds variable length packetization to the compressed bit stream created from the higher frequency subbands. The individual packets are independently decodable. An optional rearrangement of the bits in each packet allows MAP estimation to be applied to these subbands as well. Simulation results show a significant performance improvement for the overall system.

The transmission of video over time-varying wireless communication channels can benefit from the use of joint source-channel (JSC) coding methods. We survey relevant research in JSC code design and discuss how this work can be used for video compression and transmission. A main focus is the use of estimation-based techniques to take advantage of the residual redundancy present at the output of the source encoder. As noted in previous work, the combination of the source encoder and channel can often be modeled as a hidden Markov model. This statistical framework is the basis for state estimation and minimum mean-square error estimation procedures for JSC decoding, and it can also be used to develop channel state and channel parameter estimation methods. We discuss these approaches, along with work that also incorporates modulation, channel coding, and rate allocation within the JSC design. The integration of these methods into video compression standards is considered.

In this paper, we examine the design of a continuous phase frequency-shift keying (CPFSK) system with trellis-coded modulation (TCM) when the detection is noncoherent. A multi-symbol correlation method is used to provide improved branch metrics for the Viterbi decoder. A suboptimal detector structure is then created that provides essentially identical results with a decrease in complexity. Simulation results show that for adequate signal-to-noise ratios (SNRs), the noncoherent CPFSK-TCM system can out-perform a non-coded, noncoherent CPFSK system at the same bit rate and bandwidth. Work to design optimal codes is continuing.

A subband decomposition using wavelet filters has become an effective basis for image compression. The use of a ladder structure for the subband filtering provides a fast implementation and allows the system to be useful at video rates. A system is proposed that provides good quality video for moderate motion, roughly common intermediate format-f 0-t (CIF-) sized images at bit rates under 500 kb/s, and for teleconferencing scenes at bit rates from 180 kb/s to below 128 kb/s (basic rate ISDN). The system uses subband coding, a modified version of H.261, and entropy-constrained quantization to achieve the desired bit rate and image quality.

Subband coding and vector quantization combined can provide a powerful method for compressing color images. The use of properties of the human visual system can increase the performance of such a system and allow one to achieve very high quality reconstructed images at compression ratios exceeding 10:1. The authors design a color subband-vector quantization system, and formulate the bit allocation problem as an optimization problem where the objective function depends on the distortion-rate curves of the quantizers and on a set of perceptual weights. These weights are derived from data provided by measurements of the mean detection threshold of the human visual system for color transitions along the luminance, red-green, and blue-yellow directions. Minimization of the objective function constrained by the desired bit rate gives a perceptually optimal bit allocation. Three subband/VQ cases are examined. In the first two cases (case 1 and case 2), the color components of the lowest frequency subband are scalar quantized. Case 1 combines the three color components of each pixel of the higher frequency subbands into a three-dimensional vector, while case 2 creates four-dimensional vectors from 2/spl times/2 blocks in each subband color component. The third case (case 3) is the same as case 2, except that the chrominance components of the lowest frequency subband are also vector quantized with 2/spl times/2 blocks in each component. To obtain the required compression ratio and the high color fidelity required for HDTV applications, the vector quantization is done in C.I.E. L*a*b* space and AC/sub 1/C/sub 2/ space.>

A subband/VQ coder that combines the three color components of each subband pixel into a length 3 vector and then vector quantizes each subband is presented. Perceptual weights derived from subjective visual experiments are used along with the rate-distortion curves to determine a perceptually optimal bit allocation. Advantages of this method are that fewer codebooks need to be designed and the resulting bit allocation problem is simplified. Preliminary results show that this method achieves results comparable to the more standard subband/VQ method where the color components of each subband are vector quantized separately using the perceptually optimal bit allocation algorithm. To obtain the required compression ratio and the high color fidelity required for HDTV applications, the vector quantization is done in a perceptually uniform color space.>