Search

Symbol synchronization offset of orthogonal frequency division multiplexing (OFDM) communication system will cause the rotation of data constellation at receiver even if such offset falls in the range of the appended cyclic prefix. When OFDM modulation is combined with spread spectrum technique, e.g., OFDM code division multiple access (OFDM-CDMA), the problem becomes more serious since OFDM-CDMA communication system generally works under very low signal-to-noise ratio. This paper focuses on symbol timing synchronization of OFDM-CDMA communication system and proposes an effective sequence structure on the basis of circular conjugate-symmetric properties of discrete Fourier transform. The proposed frequency-domain sequence not only can generate real time-domain signal to reduce calculation complexity, but also can resist peak-to-average power ratio of OFDM modulation by exploiting suitable computer search algorithm. The simulation results show a sharp cross-correlation peak can be obtained, which is quite helpful for accurate symbol timing synchronization of OFDM-CDMA communication system.

Modified largest weighted delay first (M-LWDF) is a typical packet scheduling algorithm for supporting hybrid real-time services over wireless networks. However, so far, there is little literature available regarding the theoretic analysis of M-LWDF fairness. This paper gives a theoretic analysis of M-LWDF fairness, which shows that M-LWDF fairness is related to channel condition, packet's arrival process and the ratio of quality of service (QoS) requirements of different service queues. Given service QoS requirements and other parameters related to channel model and packet's arrival process, the fairness is merely related to the ratio of the number of users in the service queues. Based on the analysis, an enhanced M-LWDF algorithm (EM-LWDF) is proposed and demonstrated in this paper. EM-LWDF is strictly designed in light of the fairness criteria of QoS requirements, so its fairness is almost not related to the ratio of the number of users in the service queues, and the theoretical value of fairness index is equal to 1. Simulation results validate the theoretic analysis and show the effectiveness of EM-LWDF in improving fairness.

Based on the convolutional code model of error-correction coding theory, we propose an approach to characterize and compare DNA sequences with consideration of the effect of codon context. We construct an 8-component vector whose components are the normalized leading eigenvalues of the L/L and M/M matrices associated with the original DNA sequences and the transformed sequences. The utility of our approach is illustrated by the examination of the similarities/dissimilarities among the coding sequences of the first exon of beta-globin gene of 11 species, and the efficiency of error-correction coding theory in analysis of similarity/dissimilarity of DNA sequences is represented.

This paper addresses the applications of the improved representation method of DNA sequences based on symbolic dynamics. This method can visualize DNA sequences in three-dimensional coordinates with no loss of information in the transfer of data from a DNA sequence to its mathematical representation, and be applied to solve fundamental problems in bioinformatics fields. Graphical alignment of two shorter DNA sequences is exemplified for the application of the symbolic-dynamics-based representation method to sequence alignment. With the truncated length of DNA representation being chosen as the number of nucleotides in a codon, the application can be then extended to codon alignment. Based on the applications of alignment, the examination of similarities/dissimilarities among the coding sequences of the first exon of β-globin gene of different species illustrates the utility of the improved representation approach.

The representation of a DNA sequence is the first stage of genome analysis. A wide variety of approaches has been proposed for different applications in bioinformatics. In this letter, based on the principle of symbolic dynamics, a novel representation approach is proposed, which maps DNA sequence into 3-D chaotic sequences of sawtooth function and completely conserve its biological information. With the application of the new representation approach to DNA sequence, three extended Kalman filters are used to implement gene prediction. Simulation results are presented to illustrate the validity and feasibility of the proposed representation approach to DNA sequence.