Scrambling a compression-coded signal
View Patent ↗This invention provides methods and apparatus for protecting data transmitted using standard compression techniques such as Huffman coding. After input data is preprocessed (filtered, quantized, etc.), the data is encoded using a Huffman coder based on Huffman codes or code books which have been scrambled to change the order of the code books and/or codes from established standard Huffman code books and/or codes. When the transmitted information is received by a Huffman code receiver, the received data may be decoded using the scrambled Huffman code book/codes to obtain the data that was transmitted by the transmitter.
1. A method comprising the steps of accepting a stream of data, developing from said data a stream of codewords, where each codeword belongs to a code book, where
in connection with a selected portion of said data, each codeword is developed in accordance with process A, or process B, where
(a) from strings of data bits, process A creates codewords consisting of one or more concatenated bits b 0 , . . . b j , where j is an integer that may differ from codeword to codeword, pursuant to a standard first code book, followed by replacing the created codewords with another created codeword consisting of one or more concatenated bits a 0 , . . . a k , that is different from said created codebook and belongs to a second code book, said another created codeword being created by other than setting
(i) j to k,
(ii) a 0 , . . . a j-1 to b 0 , . . . b j-1 , and
(iii) a j either to b j or an inverse thereof,
(b) from strings of data bits, process B creating codewords pursuant to a non-standard code book said created codewords being converted codewords;
in connection with other than said selected portion of said developed codewords, if any, each codeword, consisting of one or more concatenated bits b 0 , . . . b j , where j is an integer that may differ from codeword to codeword, is created pursuant to said standard first code book; and
transmitting said codewords created in connection with said selected portion, and in connection with said other than said selected portion, if any
where codewords provided by process A or process B to said step of transmitting have a length that is equal to codewords that would have been created by employing said standard first code book.
2. The method of claim 1 where said second code book is other than said standard code book.
3. The method of claim 1 where said second code book is said standard code book.
4. The method of claim 1 where said selected portion comprises sub-portions, and each of the sub-portions develops codewords pursuant to in accordance with process A, or process B that employs its own second code book.
5. The method of claim 1 where said selected portion is based on information content.
6. The method of claim 1 where said selected portion is time intervals based.
7. The method of claim 1 where said selected portion is based on spectrum of information contained in said data stream.
8. The method of claim 1 where said second code book is selected from a set of preselected code books, and the selection of said second code book is not fixed.