lei cao - Academia.edu (original) (raw)

Papers by lei cao

Proceedings of the 2007 international conference on Wireless communications and mobile computing - IWCMC '07, 2007

Instead of using product codes for progressive image transmission over noisy fading channels, we ... more Instead of using product codes for progressive image transmission over noisy fading channels, we extend, in this paper, a recently proposed image transmission method by the authors by interleaving each coded packet to fading channels so that the effect of burst error can be converted into the random bit errors. As a result, the design of unequal error protection for

VTC-2005-Fall. 2005 IEEE 62nd Vehicular Technology Conference, 2005., 2005

Maximum a posteriori probability (MAP) decoding of Huffman-equivalent variable-length codes (VLCs... more Maximum a posteriori probability (MAP) decoding of Huffman-equivalent variable-length codes (VLCs) has two undesired features. One is the high decoding complexity, and the other is the discrepancy between the objective of MAP decoding and the Levenshtein distance which is commonly used as the performance metric. In this correspondence, improvement over these two issues is targeted through extracting self-synchronization information in VLC coded sequence and incorporating it into MAP decoding. It will be shown that self-synchronization strings (SSSs) are concatenation of Huffman codewords and can be readily found. Occurrence probabilities of SSSs are then analyzed. By using this self-synchronization information, MAP decoding is split into multiple decoding of short data segments so that both decoding performance improvement and complexity reduction are obtained. Simulation results demonstrate the effectiveness of the proposed method.

2007 IEEE International Symposium on Circuits and Systems, 2007

ABSTRACT In this paper, we consider the transmission of progressive image data over noisy channel... more ABSTRACT In this paper, we consider the transmission of progressive image data over noisy channels with the protection of rate-compatible punctured turbo codes (RCPT) concatenated with multiple cyclic redundancy check (CRC) codes. To optimally allocate the given bandwidth resource for unequal error protection (UEP), a genetic algorithm (GA) based method is proposed to reduce the optimization complexity. In addition, a structure of multiple CRC blocks is employed in some data packets so that more correctly decoded data could be used in decoding. Simulation has demonstrated promising results of the proposed scheme

Wireless Communications and Networking, IEEE Conference, 2006

In this paper we compare the performance of companding schemes to reduce the peak-to-average-powe... more In this paper we compare the performance of companding schemes to reduce the peak-to-average-power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal. Literature discussing companding for PAPR reduction do not consider the impact of out of band filtering on PAPR and bit error rate (BER) performance of companded OFDM systems. In this paper, impact of filtering on companded OFDM signal is studied. BER performances of different companding schemes are compared for both AWGN and fading channel and error mechanisms are outlined. It is shown that filtering has a significant impact on the performance of the system and must be taken into account before a design choice is made. A simple method based on using unmatched compand and decompand transforms is proposed and is found to perform better than other companding schemes

Journal of Electronic Imaging, 2004

ABSTRACT A scheme with three key components including wavelet tree coding, error resilient entrop... more ABSTRACT A scheme with three key components including wavelet tree coding, error resilient entropy coding (EREC), and error concealment is proposed for robust image coding and transmission over noisy channels. First, we individually encode the spatial-orientation trees in the wavelet domain using the algorithm of set partitioning in hierarchical trees (SPIHT). Error propagation is thus limited because multiple independent bit streams are generated. Meanwhile, a high source coding efficiency is also preserved because the self-similarity property in each wavelet tree remains intact. Next, we use EREC to reorganize these variable-length bit streams into fixed-length data slots before multiplexing and transmission. Therefore, the synchronization of the start of each bit stream can be automatically obtained at the receiver Finally, to alleviate the possible catastrophic image degradation that may result from errors in the beginning of the bit streams, we propose an error concealment technique to constrain the EREC decoding as well as to postprocess the decoded wavelet coefficients. As a result of the error concealment, the EREC decoding complexity is reduced and the reconstructed image quality is significantly improved. Experimental results demonstrate an excellent error resilient performance of the proposed scheme. (C) 2004 SPIE and IST.

Wireless Communications and Networking, IEEE Conference, 2004

A turbo coded hybrid automatic repeat request (TC-HARQ) scheme is proposed based on packet combin... more A turbo coded hybrid automatic repeat request (TC-HARQ) scheme is proposed based on packet combining technique and segment selective repeat. First, we demonstrate through simulation that, data combining gives substantial performance improvement over log-likelihood ratio (LLR) combining with the cost of more buffers. Second, we propose a novel retransmission strategy for TC-HARQ: segment selective repeat (SSR), which intends to select

IEEE Transactions on Image Processing, 2002

We propose a novel combined source and channel coding scheme for image transmission over noisy ch... more We propose a novel combined source and channel coding scheme for image transmission over noisy channels. The main feature of the proposed scheme is a systematic decomposition of image sources so that unequal error protection can be applied according to not only bit error sensitivity but also visual content importance. The wavelet transform is adopted to hierarchically decompose the image. The association between the wavelet coefficients and what they represent spatially in the original image is fully exploited so that wavelet blocks are classified based on their corresponding image content. The classification produces wavelet blocks in each class with similar content and statistics, therefore enables high performance source compression using the set partitioning in hierarchical trees (SPIHT) algorithm. To combat the channel noise, an unequal error protection strategy with rate-compatible punctured convolutional/cyclic redundancy check (RCPC/CRC) codes is implemented based on the bit contribution to both peak signal-to-noise ratio (PSNR) and visual quality. At the receiving end, a postprocessing method making use of the SPIHT decoding structure and the classification map is developed to restore the degradation due to the residual error after channel decoding. Experimental results show that the proposed scheme is indeed able to provide protection both for the bits that are more sensitive to errors and for the more important visual content under a noisy transmission environment. In particular, the reconstructed images illustrate consistently better visual quality than using the single-bitstream-based schemes.

IEEE Transactions on Image Processing, 2007

In this paper, we consider the unequal error protection (UEP) for progressive image transmission ... more In this paper, we consider the unequal error protection (UEP) for progressive image transmission when the coded packet size is fixed. First, we prove that, for the source code with convex rate-distortion (R-D) function and practically used channel codes, the channel code rate for each packet in the optimal rate allocation is nondecreasing indeed. Then, we give an upper bound for the channel code rate of the last packet so that the number of rate allocations in the exhaustive search can be predicted. Further, we propose a heuristic optimization method which has low complexity and obtains performance approaching to the optimal solutions for various channel conditions and transmission rates.

IEEE Transactions on Image Processing, 2000

In this paper, we propose an unequal error protection (UEP) framework for progressive image trans... more In this paper, we propose an unequal error protection (UEP) framework for progressive image transmission over wireless networks with both random errors and packet loss. By sophisticatedly interleaving each coded frame, the packet loss is converted into randomly punctured bits in a Turbo code. Therefore, error control of channels with both types of distortions is equivalent to dealing with random bit errors only through turbo codes with reduced rates. To optimally allocate the overall transmission rate between the source and channel codes, a genetic algorithm (GA) based method is proposed which not only largely reduces the optimization complexity but also gives results close to the brute force search in tested scenarios. Then, we extend the UEP to a product code scheme by adding Reed-Solomon (RS) code across the frames. An efficient rate allocation method for this product code with the use of interleaving is further presented. The effectiveness of the proposed schemes is demonstrated with extensive simulation results.

IEEE Transactions on Antennas and Propagation, 2000

In this paper, a new solution for electrical characteristics of electromagnetic scattering by a r... more In this paper, a new solution for electrical characteristics of electromagnetic scattering by a radially multilayered gyroelectric sphere is proposed. The spherical geometry is divided into regions (where can be an arbitrary integer), and each layer is characterized by a scalar permeability and a gyrotropic permittivity tensor. Electromagnetic fields inside and outside the sphere are theoretically formulated based on the eigenfunction expansion technique in terms of vector spherical wave functions. Numerical calculations are subsequently performed using those derived formulas. The derived formulas and the developed source codes are partially verified by the good agreement between our numerical results of radar cross sections with those obtained by Geng et al. using the Fourier transform method. After the validations, some new specific examples are further considered and their results are presented, so as to investigate specific characteristics of these electromagnetic scattering problems.