Search

It is well known that in order to build linear scramblers and stream ciphers that are robust against correlation-based reconstruction, primitive polynomials which do not have sparse multiples of moderate degrees must be used. In this paper, the existence and density of such 'good primitive polynomials' are studied. Two theoretical lower bounds on the degree d of the primitive polynomial are derived. When d is larger than the first lower bound, there exists at least one primitive polynomial of degree d which does not have any sparse multiple of moderate degree and when d is larger than the second lower bound, it is almost guaranteed that a randomly chosen primitive polynomial of degree d does not have any sparse multiples of moderate degree. To make the lower bound tight, the distribution of the minimum degrees of sparse multiples of primitive polynomials is investigated in this paper. From comparison, it can be seen that the lower bounds obtained in this paper are much better than the previous results reported in the literature. [ABSTRACT FROM AUTHOR]

The performance of speech coders, such as the ITU-T G.722.1 wideband speech coder, that employ non-self-synchronising variable-length codes is greatly degraded when the received bit stream is in error. The authors study the use of reversible variable-length codes (RVLC5) to replace the Huffman codes recommended in the G.722.1 coder. A modified trellis-based scheme to decode the RVLCs-encoded bit stream is proposed and applied to the coder to improve its performance when bit errors occur. Simulation results show that the modified coder is much more robust in segmental SNR performance as compared to the original G.722.1 coder when bit errors occur. [ABSTRACT FROM AUTHOR]

A simple and flexible bit-plane coding method is developed for scalable audio coding. It is different from the traditional bit-plane coding in that the optimal bit-plane scanning order is adapted to the scale between the energy of the residual signal and the audio mask. Both the perceptual quality and the lossless compression ratio at common lossy bitrates are greatly improved compared with the performance of state-of-the-art scalable audio. [ABSTRACT FROM AUTHOR]