Chi-Wah Kok

Efficient prediction algorithm of integer DCT coefficients for H.264/AVC optimization

This paper presents a novel efficient prediction algorithm to reduce redundant discrete cosine transform (DCT) and quantization computations for H.264 encoding optimization. A theoretical analysis is performed to study the sufficient condition for DCT coefficients to be quantized to zeros. As a result, three sufficient conditions corresponding to three types of transform and quantization methods in H.264 are proposed. Compared with other algorithms in the literature, the proposed algorithm derives more precise and efficient conditions to predict zero quantized DCT coefficients. Both the theoretical analysis and experimental results demonstrate that the proposed algorithm is superior to other algorithms in terms of the computational complexity reduction, encoded video quality, false acceptance rate, and false rejection rate.

MPEG-4 Video transmission over wireless networks: a link level performance study

With the scalability and flexibility of the MPEG-4 and the emergence of the broadband wireless network, wireless multimedia services are foreseen to become deployed in the near future. Transporting MPEG-4 video over the broadband wireless network is expected to be an important component of many emerging multimedia applications. One of the critical issues for multimedia applications is to ensure that the quality-of-service (QoS) requirement to be maintained at an acceptable level. This is further challenged in that such a service guarantee must be achieved under unreliable and time-varying wireless channels. In this paper we study the link level performance of MPEG-4 video transmission over the uplink of an unreliable wireless channel. We introduce the discrete time batch Markovian arrival process (DBMAP) with two types of arrivals to model the MPEG-4 video source, which takes into account the inherent nature of the adaptiveness of the video traffic. We prove that in a hidden Markov modeled (HMM) wireless channel with probabilistic transmission, the service time for an arbitrary radio link control (RLC) burst follows phase type (PH-type) distribution. We show that the link level performance of a wireless video transmission system can be modeled by a DBMAP/PH/1 priority queue, and present computation algorithm and numerical results for the queueing model. Extensive simulations are carried out on the queueing behavior of the video transmission buffer, as well as on the packet level error behavior of the video data. The results demonstrate that video quality can be substantially improved by preserving the high priority video data during the transmission.

ESPRIT-Like Two-Dimensional DOA Estimation for Coherent Signals

A second-order statistics-based algorithm is proposed for two-dimensional (2D) direction-of-arrival (DOA) estimation of coherent signals. The problem is solved by arranging the elements of the correlation matrix of the signal received from a uniform rectangular array to a block Hankel matrix. In noiseless cases, it is shown that the rank of the block Hankel matrix equals the number of the DOAs and is independent of the coherency of the incoming waves. Therefore, the signal subspace of the block Hankel matrix can be estimated properly and spans the same column space as the array response matrix. Two matrix pencil pairs containing the DOA parameters are extracted from the signal subspace. This matrix pencil-based estimation problem is then resolved using our previously proposed pairing-free 2D parameter estimation algorithm. Simulation results show that the proposed algorithm outperforms the spatial smoothing method in terms of mean square error (MSE).

Estimation of Two-Dimensional Frequencies Using Modified Matrix Pencil Method

The problem of multiple two-dimensional (2-D) sinusoidal frequency estimation is considered. A modified matrix pencil method is proposed to simultaneously estimate the frequency pairs in the signal, thereby bypassing the computationally expensive pairing operation as seen in the literature. Simulation results show that the accuracy of the estimates for each frequency from our technique is better than or comparable to that of existing methods and the variance of the estimates are close to the Crameacuter-Rao bound. Simulation results also show that our method provides accurate and consistent frequency estimation results that other methods cannot provide with less or comparable computational complexity

Efficient predictive model of zero quantized DCT coefficients for fast video encoding

Discrete cosine transform (DCT), quantization (Q), inverse quantization (IQ) and inverse DCT (IDCT) are the building blocks in video coding standards adopted by ITU-T and MEPG. Under these standards, a lot of computations are required to perform the DCT, Q, IQ and IDCT operations. With this concern, a novel statistical model based on Gaussian distribution is proposed to predict zero quantized DCT (ZQDCT) coefficients in order to reduce the computational complexity of video encoding. Compared with other predictive models in the literature, the proposed model can detect more ZQDCT coefficients. Simulation results demonstrate that the proposed statistical model is superior to others in terms of speeding up video encoders. Moreover, a hybrid model is derived based on the proposed statistical model and mathematical analysis of individual DCT coefficients to further improve the encoding efficiency.

Estimation of 2-dimensional frequencies using modified matrix pencil method

A modified matrix pencil method is proposed to simultaneously estimate the frequency pairs in multiple 2-D sinusoidal signals to bypass the computationally expensive pairing operation as seen in the literature. Simulation results show that the accuracy of the estimates for each frequency from our technique is better than or comparable to that of existing methods and the variance of the estimates are close to the Cramer Rao bound with lower computational complexity.

Analytical Model of Zero Quantized DCT Coefficients for Video Encoder Optimization

This paper proposes a novel analytical model to predict zero quantized DCT coefficients for fast video encoding. The dynamic range of quantized DCT coefficients are analyzed and a threshold scheme is derived in order to determine DCT and quantization computations to be skipped without video quality degradation. The proposed model is compared with other models in the literature. Experimental results demonstrate that the proposed analytical model can greatly reduce the computational complexity of video encoding without any performance degradation, and outperforms other models

Receiver-Buffer-Driven Layered Quality Adaptation for Multimedia Streaming

A novel receiver-buffer-driven layered quality adap- tation mechanism is proposed for multimedia streaming over the Internet. The receiver constantly monitors its buffer occupancy and initiates quality adaptation by sending back the request command to the sender when its buffer occupancy is out of range. The sender then adjusts the quality and the amount of layered multimedia packets to be sent out according to the requests. Simulation results show that by using the proposed mechanism, a steady buffer occupancy and overall quality improvement for the multimedia streams can be achieved. Moreover, an efficient utilization of network resources is ensured by using the spare time in the time window to transmit more higher level enhancement layer packets.

Two-dimensional angle and polarization estimation using ESPRIT without pairing

This paper proposed an ESPRIT based 2D joint direction and polarization estimation algorithm that does not require a separate pairing algorithm, thus does not suffer from incorrect pairing problem as existing algorithms in literature. Simulation results have shown that the proposed algorithm can achieve accurate and stable estimation results, and can potentially save the computational complexity of the estimation problem

Channel noise robust power optimized precoder for ISI channel with minimal complexity equalizer

A systematic method to design power optimized FIR precoder for a special class of ISI free noise robust precoder-equalizer structure is presented in this paper. The proposed equalizer has the lowest implementation complexity in theory, because the equalizer consists of a simple sampler only. It is also because of this simple equalizer, the proposed precoder-equalizer pair is robust to channel noise. The presented design method results in minimal power precoder with a given order such that the system achieve ISI free MMSE communication in ISI AWGN channel with a given SNR. Simulation results are presented to illustrate the performance of the proposed precoder-equalizer structure and compared it with that of the general linear precoder structure.