Patent EA-001872-B1 (EA)
Title: System and method for spectrally shaping transmitted data signals
Inventor: EYUBOGLU M VEDAT
IPC: H03M5/00
Filed: 1998-04-03
Abstract: 1. A system for transmitting from a transmitter, on a per frame basis, digital information bits which are encoded into a predefined number of signed symbols per frame for transmission over a network to a receiver, wherein the transmitted signed symbols have a desired spectral shape; the digital information bits being divided into a first predetermined number of magnitude information bits and a second predetermined number of sign information bits per frame, the transmitter comprising: magnitude mapping device for mapping the magnitude information bits to the predefined number of symbol magnitudes per frame; a sign bit encoder for encoding the sign information bits into the predefined number of encoded symbol sign bits per frame; and a signal point selector, responsive to the magnitude mapping device and the sign bit encoder, which combines the symbol magnitudes and the encoded symbol sign bits to form the predefined number of transmitted signed symbols per frame; the sign bit encoder comprising: a coset representative generator which generates for each frame, coset representative sign bits for the sign information bits, defining a coset representative element for a convolutional code which identifies a coset of the convolutional code containing candidates of encoded symbol sign bits; and a symbol sign bit selector, responsive to the coset representative sign bits and the symbol magnitudes, which selects the encoded symbol sign bits from the candidates of encoded symbol sign bits that produce the transmitted signed symbols with the desired spectral shape. 2. The system of claim 1 wherein the first predetermined number of magnitude information bits is (r-n) bits and the second predetermined number of sign information bits is (n-r) bits, where n corresponds to the predefined number of symbols per frame and r corresponds to a number of redundancy bits used by the sign bit encoder. 3. The system of claim 2 wherein the coset representative generator includes a differential encoder to differentially encode predetermined bit positions of the (n-r) bits provided to the sign bit encoder to achieve polarity inversion invariance. 4. The system of claim 3 wherein the magnitude mapper maps the m magnitude information bits to n symbols per frame using a modulus conversion mapping scheme. 5. The system of claim 4 wherein the coset representative generator further includes a matrix block, which multiplies the (n-r) sign information bits by a matrix, H<-T>, to produce the n coset representative sign bits per frame. 6. The system of claim 5 wherein the symbol sign bit selector includes a selection controller and a filter; wherein the selection controller includes: logic for generating from the coset representative sign bits candidates of encoded symbol sign bits; logic for combing the candidates of encoded symbol sign bits with the symbol magnitudes to form encoded signed symbol candidates; wherein the filter includes: logic, responsive to the encoded signed symbol candidates, for determining the (RFS) for each of the encoded signed symbol candidates and logic for providing the RFS for each of the encoded signed symbol candidates to the selection controller; and wherein the selection controller further includes: logic, responsive to the determined RFS for each of the encoded signed symbol candidates, for choosing the encoded symbol sign bits associated with the encoded signed symbol candidate with the minimum determined RFS. 7. The system of claim 5 wherein the symbol sign bit selector utilizes lookahead and includes a selection controller and a filter; wherein the selection controller includes: logic for generating from the coset representative sign bits candidate sequences of encoded symbol sign bits; logic for combing the candidate sequences with the symbol magnitudes to form encoded signed symbol candidate sequences; wherein the filter includes: logic, response to the encoded signed symbol candidate sequences, for determining the RFS for each of the encoded signed symbol candidate sequences and logic for providing the RFS for each of the encoded signed symbol candidate sequences to the selection controller; and wherein the selection controller further includes; logic, responsive to the determined HFS for each of the encoded signed symbol candidate sequences, for choosing the encoded symbol sign bits from the encoded signed symbol candidate with the minimum determined RFS. 8. The system of claim 7 wherein the RFS for the j-th symbol is determined by the filter as follows:   where NA - the first number of coefficients, NB - the first number of coefficients, y - is a signal symbol, a and b real numbers selected so as to have a desired spectral shape. 9. The system of claim 8 wherein the RFS is determined on a frame basis for the k-th frame by the filter as follows:   where j is the symbol (time) index. 10. The system of claim 9 wherein the RFS is determined using look-ahead as follows:   where Δ is the look-ahead depth. 11. The system of claim 10 wherein the receiver includes a magnitude and sign extractor which separates the transmitted signed symbols into the encoded symbol sign bits and symbol magnitudes and a sign bit decoder which decodes the encoded symbol sign bits into the sign information bits. 12. The system of claim 11 wherein the sign bit decoder includes a matrix block having a matrix H<T> by which the encoded symbol sign bits are multiplied to recover the sign information bits. 13. The system of claim 12 further including a differential decoder which differentially decodes the predefined bit positions of the recovered sign information bits. 14, The system of claim 13 further including an octet converter, responsive to the signal point selector, for transmitting over the network octets corresponding to the signed symbols. 15. The system of claim 13 wherein n is equal to six, r is equal to one and matrix H<-T> is defined as follows:   where D is frame delay. 16. The system of claim 15 wherein convolutional code is defined as follows: G(D) = [1+D 1 1+D 1 1+D 1]. 17. The system of claim 16 wherein the matrix H' is defined as follows:   18 The system of claim 7 wherein the RFS is the running digital sum (RDS) and the RDS for the i-th  simbol is determined by the filter as follows:   where j is the symbol (time) index. 19. The system of claim 18 wherein the RDS is determined on a frame basis for the k-th frame by the equivalence class selector as follows:   where j is the symbol (time) index. 20. The system of claim 19 wherein the RDS is determined using lookahead as follows:   where Δ is the look-ahead depth. 21. A method for transmitting from a transmitter, on a per frame basis, digital information bits which are encoded into a predefined number of signed symbols per frame for transmission over a network to a receiver, the symbols having a desired spectral shape, the digital information bits being divided into a first predetermined number of magnitude information bits and a second predetermined number of sign information bits per frame, the method comprising: mapping the magnitude information bits to the predefined number of symbol magnitudes per frame: encoding the sign information bits into the predefined number of encoded symbol sign bits per frame; and combining the symbol magnitudes and the encoded symbol sign bits to form the predefined number of transmitted signed symbols per frame; the step of encoding including: generating for each frame coset representative sign bits for the sign information bits, defining a coset representative element for a convolutional code which identifies a coset of the convolutional code containing candidates of encoded symbol sign bits; and selecting, using the coset representative sign bits and the symbol magnitudes, the encoded symbol sign bits from the candidates of encoded symbol sign bits that produce the transmitted signed symbols with the desired spectral shape. 22. The method of claim 21 wherein the first predetermined number of magnitude information bits is m bits and the second predetermined number of sign information bits is (n-r) bits, where n corresponds to the predefined number of symbols per frame and r corresponds to a number of redundancy bits used in the encoding step. 23. The method of claim 22 wherein the step of generating includes differentially encoding predetermined bit positions of the (n-r) bits to achieve polarity inversion invariance. 24. The method of claim 23 wherein the step of mapping maps the m magnitude Information bits to n symbols per frame using a modulus conversion mapping scheme. 25. The method of claim 24 wherein the step of generating further includes multiplying the (n-r) sign information bits by a matrix, H<-T>, to produce the n coset representative sign per frame. 26. The method of claim 25 wherein the step of selecting includes: generating from the coset representative sign bits candidates of encoded symbol sign bits; combing the candidates of encoded symbol sign bits with the symbol magnitudes to form encoded signed symbol candidates; determining the RFS for each of the encoded signed symbol candidates and logic for providing the RFS for each of the encoded signed symbol candidates to the selection controller, and choosing the encoded symbol sign bits associated with the encoded signed symbol candidate with the minimum determined RFS. 27. The method of claim 25 wherein the step of selecting utilizes lookahead and includes: generating from the coset representative sign bits candidate sequences of encoded symbol sign bits; combing the candidate sequences with the symbol magnitudes to form encoded signed symbol candidate sequences; determining the FlFS for each of the encoded signed symbol candidate sequences and logic for providing the RFS for each of the encoded signed symbol candidate sequences to the selection controller; and choosing the encoded symbol sign bits from the encoded signed symbol candidate with the minimum deter