Signal-to-noise ratio (SNR) measurement is required in many receivers and systems of communications. In this brief, we derive a new SNR’s estimator based on the second and fourthorder 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 novel variable-length code (VLC), called alternate VLC(AVLC), is proposed, which employs two types of VLC to encode source symbols alternately. Its advantage is that it can not only stop the symbol error propagation effect, but also correct symbol insertion errors and symbol deletion errors, which is very important in video communication.

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.

In multimedia systems end to end delay jitter has a great impact on the continuity of information playback. Therefore, it is necessary to compensate for delay variations to preserve the intramedia and intermedia temporal relationships. A buffer at the destination site is often adopted to compensate for the delay jitter. In this paper, a mapping relationship from P_QoS to buffer which is used to compensate for delay variations is given based on delay jitter statistics, and its theoretical analysis is also shown. So the buffer size of multimedia synchronization system can be determined.

Based on the triple Data Encryption Standard(DES)block cipher frequency-hopping(FH)sequences, a kind of packet protocol for frequency-hopping multiple-access(FHMA)network is suggested in this paper. In theory, the performances of both the packet error and the throughput are derived, which shows that the ratio of the packet length M to the frequency slots number q is most key parameter to determine the FHMA system performance under the condition of large user number. Computer simulation results of 3-DES FH sequences compared with those of the chaotic FH sequences are also included to support our developments.