Abstract: Typical forward error correction methods employ Trellis Code Modulation. By substituting low density parity check coding in place of the convolution code as part of a combined modulation and encoding procedure, low density parity check coding and modulation can be performed. The low density parity check codes have no error floor, no cycles, an equal bit error rate for the information bits and the parity bits, and timely construction of both a parity check matrix with variable codeword size and a generator matrix is possible.

Abstract: The disclosed watermarking method utilizes a transform technique for inserting an imperceptible digital watermark into digital data that is strongly resistant to unauthorized detection and decoding. Methods for embedding a watermark that is sufficiently robust to lossy compression and other image processing operations such as rescaling are also provided. The watermarking principle is based on wavelet transforms where the coefficients of the filters have binary values, and are thus very attractive for practical realization. The wavelet filters utilize complimentary polynomials and implement non-regular wavelet transforms upon which the digital watermark is inserted. Following the inverse transformation process, the digital watermark is spread across multiple frequencies of the original digital data thereby reducing the impact of signal processing operations such as compression or other frequency filtering based operations.

Abstract: A data compression scheme as described which improves upon and is compatible with the V.42bis data compression standard of the International Telecommunications Union (ITU). The data compression scheme provides an efficient algorithm to determine when as well as how to efficiently switch between transparent and compressed modes to provide and facilitate an improved compression ratio. Additionally, a temporary buffer is provided for use by the encoder in determining which of either transparent or compressed mode provides a more efficient transfer of a portion of data. In making a determination to transition between transmit modes, the incurred overhead associated with such transitions is also taken into account. An approach for evaluating when to discard a particular dictionary that has become inefficient is also provided thereby enabling an improvement in the transmission of multimedia data and the regeneration of a dictionary more representative of the presently evaluated data type.