A construction method based on the p-plane to design high-girth quasi-cyclic low-density parity-check （QC-LDPC） codes is proposed. Firstly the good points in every line of the p-plane can be ascertained through filt...A construction method based on the p-plane to design high-girth quasi-cyclic low-density parity-check （QC-LDPC） codes is proposed. Firstly the good points in every line of the p-plane can be ascertained through filtering the bad points, because the designed parity-check matrixes using these points have the short cycles in Tanner graph of codes. Then one of the best points from the residual good points of every line in the p-plane will be found, respectively. The optimal point is also singled out according to the bit error rate （BER） performance of the QC-LDPC codes at last. Explicit necessary and sufficient conditions for the QC-LDPC codes to have no short cycles are presented which are in favor of removing the bad points in the p-plane. Since preventing the short cycles also prevents the small stopping sets, the proposed construction method also leads to QC-LDPC codes with a higher stopping distance.展开更多
In this paper the regularity of set-valued martingales in the sense of JL is given first. Then we show some kinds of Doob's stopping theorems for set-valued (super, sub) martingales with continuous time.
为了解决构造任意长度、无小停止集且无短环QC-LDPC码的设计问题,研究了基于Tanner图的停止集、围长和最小码重三者之间的关系,提出了QC-LDPC码无短停止距离且无短环的充要条件.在此基础上,为了进一步降低编码复杂度并保留结构化特性,...为了解决构造任意长度、无小停止集且无短环QC-LDPC码的设计问题,研究了基于Tanner图的停止集、围长和最小码重三者之间的关系,提出了QC-LDPC码无短停止距离且无短环的充要条件.在此基础上,为了进一步降低编码复杂度并保留结构化特性,提出了一种具有线性编码复杂度的基于后向迭代的QC-LDPC码.仿真结果表明:所构造的QC-LDPC码的纠错性能与IEEE 802.11n中QC-LDPC码相近,与IEEE 802.16e中QC-LDPC码相比,在误码率为10^(-6)时,可获得0.15 d B的性能增益;此外,该码字只需存储移位因子和单位子矩阵的阶数,所占硬件存储空间明显小于另外2种QC-LDPC码.展开更多
A fast two-stage geometric active contour algorithm for image segmentation is developed. First, the Eikonal equation problem is quickly solved using an improved fast sweeping method, and a criterion of local minimum o...A fast two-stage geometric active contour algorithm for image segmentation is developed. First, the Eikonal equation problem is quickly solved using an improved fast sweeping method, and a criterion of local minimum of area gradient (LMAG) is presented to extract the optimal arrival time. Then, the final time function is passed as an initial state to an area and length minimizing flow model, which adjusts the interface more accurately and prevents it from leaking. For object with complete and salient edge, using the first stage only is able to obtain an ideal result, and this results in a time complexity of O(M), where M is the number of points in each coordinate direction. Both stages are needed for convoluted shapes, but the computation cost can be drastically reduced. Efficiency of the algorithm is verified in segmentation experiments of real images with different feature.展开更多
基金supported by the National Natural Science Foundation of China (60572093)Specialized Research Fund for the Doctoral Program of Higher Education (20050004016)
文摘A construction method based on the p-plane to design high-girth quasi-cyclic low-density parity-check （QC-LDPC） codes is proposed. Firstly the good points in every line of the p-plane can be ascertained through filtering the bad points, because the designed parity-check matrixes using these points have the short cycles in Tanner graph of codes. Then one of the best points from the residual good points of every line in the p-plane will be found, respectively. The optimal point is also singled out according to the bit error rate （BER） performance of the QC-LDPC codes at last. Explicit necessary and sufficient conditions for the QC-LDPC codes to have no short cycles are presented which are in favor of removing the bad points in the p-plane. Since preventing the short cycles also prevents the small stopping sets, the proposed construction method also leads to QC-LDPC codes with a higher stopping distance.
基金Supported by the National Natural Science Foundation of China !(19971072)
文摘In this paper the regularity of set-valued martingales in the sense of JL is given first. Then we show some kinds of Doob's stopping theorems for set-valued (super, sub) martingales with continuous time.
文摘为了解决构造任意长度、无小停止集且无短环QC-LDPC码的设计问题,研究了基于Tanner图的停止集、围长和最小码重三者之间的关系,提出了QC-LDPC码无短停止距离且无短环的充要条件.在此基础上,为了进一步降低编码复杂度并保留结构化特性,提出了一种具有线性编码复杂度的基于后向迭代的QC-LDPC码.仿真结果表明:所构造的QC-LDPC码的纠错性能与IEEE 802.11n中QC-LDPC码相近,与IEEE 802.16e中QC-LDPC码相比,在误码率为10^(-6)时,可获得0.15 d B的性能增益;此外,该码字只需存储移位因子和单位子矩阵的阶数,所占硬件存储空间明显小于另外2种QC-LDPC码.
文摘A fast two-stage geometric active contour algorithm for image segmentation is developed. First, the Eikonal equation problem is quickly solved using an improved fast sweeping method, and a criterion of local minimum of area gradient (LMAG) is presented to extract the optimal arrival time. Then, the final time function is passed as an initial state to an area and length minimizing flow model, which adjusts the interface more accurately and prevents it from leaking. For object with complete and salient edge, using the first stage only is able to obtain an ideal result, and this results in a time complexity of O(M), where M is the number of points in each coordinate direction. Both stages are needed for convoluted shapes, but the computation cost can be drastically reduced. Efficiency of the algorithm is verified in segmentation experiments of real images with different feature.
