Yilin Chang

Synchronization method based on a new constant envelop preamble for OFDM systems

The synchronization method using the available constant envelop preamble is analyzed, and a new preamble weighted by pseudo-noise sequence is proposed, with which a novel timing and frequency offset estimation method is presented for orthogonal frequency division multiplexing (OFDM) systems in this paper. By the proposed method, the accuracy of the timing offset estimator is significantly improved, and the estimate range of the frequency offset estimator is greatly enlarged with no loss in accuracy. The performance of the proposed method is demonstrated by simulations.

Model-Based Joint Bit Allocation Between Texture Videos and Depth Maps for 3-D Video Coding

In 3-D video coding, texture videos and depth maps need to be jointly coded. The distortion of texture videos and depth maps can be propagated to the synthesized virtual views. Besides coding efficiency of texture videos and depth maps, joint bit allocation between texture videos and depth maps is also an important research issue in 3-D video coding. First, we present comprehensive analyses on the impacts of the compression distortion of texture videos and depth maps on the quality of the virtual views, and then derive a concise distortion model for the synthesized virtual views. Based on this model, the joint bit allocation problem is formulated as a constrained optimization problem, and is solved by using the Lagrangian multiplier method. Experimental results demonstrate the high accuracy of the derived distortion model. Meanwhile, the rate-distortion (R-D) performance of the proposed algorithm is close to those of search-based algorithms which can give the best R-D performance, while the complexity of the proposed algorithm is lower than that of search-based algorithms. Moreover, compared with the bit allocation method using fixed texture and depth bits ratio (5:1), a maximum 1.2 dB gain can be achieved by the proposed algorithm.

Robust automatic white balance algorithm using gray color points in images

A robust automatic white balance algorithm is proposed in this paper, using extracting gray color points in images for color temperature estimation. A gray color point is the point where R, G and B components are equivalent under the canonical light source. A little color deviation of the gray color point from gray under different color temperature is used to estimate the color temperature of the light source. The test results show that the proposed algorithm can provide a good perceive effect and has the advantage of easy realization, low complexity and robust convergence.

A novel objective no-reference metric for digital video quality assessment

A novel objective no-reference metric is proposed for video quality assessment of digitally coded videos containing natural scenes. Taking account of the temporal dependency between adjacent images of the videos and characteristics of the human visual system, the spatial distortion of an image is predicted using the differences between the corresponding translational regions of high spatial complexity in two adjacent images, which are weighted according to temporal activities of the video. The overall video quality is measured by pooling the spatial distortions of all images in the video. Experiments using reconstructed video sequences indicate that the objective scores obtained by the proposed metric agree well with the subjective assessment scores.

SNR estimation algorithm based on the preamble for OFDM systems in frequency selective channels

We propose a new SNR estimation method based on the preamble for OFDM systems in frequency selective channels. The OFDM training symbols in the preamble are equalized by the known data in frequency domain and employed to estimate the noise variance. The second order moments of the received symbols are used to estimate the signal plus noise power in the OFDM packets. The SNRs on the subchannels and the average SNR of the packets can all be estimated. Simulation results show that the proposed method is robust to frequency selectivity in wireless channels, and its performance is considerably improved compared with the available methods.

A complementary clipping transform technique for the reduction of peak-to-average power ratio of OFDM system

A novel transform technique is proposed for reducing the peak-to-average ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. Large OFDM signals are replaced by small complementary signals according to the proposed method. It has a low SNR loss in bit error rate while achieving a significant reduction of PAPR. It is shown by computer simulations that the proposed method can outperform the well-known clipping filtering scheme and /spl mu/-law companding technique substantially.

A TDOA location scheme in OFDM based WMANs

A time difference of arrival (TDOA) location scheme for the orthogonal frequency division multiplexing (OFDM) based wireless metropolitan area networks (WMANs) is presented. A novel TDOA estimation algorithm for OFDM signals is proposed and adopted in this scheme. The algorithm enhances the location performance by utilizing the information in the time and frequency domains obtained from the received location OFDM signals. The simulations are implemented with an 802.16e configuration considering an outdoor wireless scenario. The simulation results show that the scheme can meet the E911 requirements in even complex multipath channel conditions, and outperform the location schemes with traditional correlation detection TDOA estimations.

An Efficient Frequency Offset Estimation Method With a Large Range for Wireless OFDM Systems

An efficient frequency offset estimation method is proposed for wireless orthogonal frequency-division multiplexing (OFDM) systems. In the proposed method, the received samples of the training symbol are processed by a novel envelop equalized processing method, and the estimation of the frequency offset in the OFDM systems turns out to be the frequency estimation of a complex tone. A novel frequency estimation method is employed to estimate the frequency offset. The estimation range of the proposed method is as large as the bandwidth of the OFDM signal, and the performance of the proposed method is independent of the structure of the training symbol.

A new SNR's estimator for QPSK Modulations in an AWGN channel

Signal-to-noise ratio (SNR) measurement is required in many receivers and systems of communications. In this brief, we derive a new SNRs estimator based on the second and fourth-order moments of the complex signals of quadrature phase-shift keying modulations. The mean square error of the estimated SNR by the proposed algorithm is smaller than that by other methods for a low SNR with limited samples.

A Generic Framework for Optimal Mobile Sensor Redeployment

Wireless sensor networks (WSNs) are widely used for various applications. In some applications, it is very likely that the number of sensors is limited, the initial deployment is random, and deployment “holes” (i.e., subareas where there is no sensor) may exist. Therefore, a major challenge in WSNs is to improve the network coverage. A viable solution is to enhance some sensors with mobility capability so that they can move inside the WSNs after the initial deployment, which is referred to as mobile sensor redeployment. In this paper, we target at a generic framework for the optimal mobile sensor redeployment problem in WSNs. In particular, in this paper, the area of a WSN is partitioned into a number of grids, and the gap of each grid is defined as the difference of the number of sensors in the grid from the desired number of sensors. Then, the mobile sensor redeployment problem is formulated as an optimization problem with three optimization requirements: to minimize the sum of gaps of all grids, to minimize the Lp-norm (1 ≤ p ≤ ∞) of the gap vector (where Lp-norm represents a family of optimization objectives when p takes different values), and to minimize the total movement cost of all mobile sensors. Bipartite matching-based redeployment (BMrD) algorithms are provided to solve the optimization problems with different values of p. In this paper, the framework is generic for mobile sensor redeployment because 1) the mobility capabilities of the sensors, the initial sensor distribution, the movement cost measures, and the sensor types are all arbitrary; 2) the coverage requirements in different grids can be heterogeneous; and 3) the BMrD algorithms are generic for different p values. The effectiveness of the BMrD algorithms is validated through theoretical proofs and extensive simulations.