US 4,901,331 A · Trellis codes with passband spectral nulls

Abstract

In a data transmission system using a predetermined trellis code, the output signal points are selected from a predetermined alphabet representing (k+n)-bit input words by using the values of n bits of each input word, and bits from previous input words, to identify a particular one of 2.sup.m subsets of the signaling alphabet m>n. The other k bits of the input word identify an ensemble of four signal points of the identified subset. This ensemble is characterized by having a first signal point whose odd components and even components each sum to a value no less than zero, a second signal point whose odd components sum to a value no less than zero and even components a value no greater than zero, a third signal point whose odd components sum to a value no greater than zero and even components a value no less than zero, and a fourth signal point whose odd components and even components each sum to a value no greater than zero. Two running sums of odd and even cmponents of the signal points previously generated are separately maintained. At any point in time, the system always manages to select and output a signal point in the identified ensemble so as to drive the individual running sums of the respective odd components and even components toward zero simultaneously. This scheme provides a passband signal having a spectral null at a carrier frequency.

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Claims32

Dependent claims

A data transmission system adapted to transmit on a communication channel a sequence of passband signals in response to a sequence of (k+n)-bit input words, each of said passband signals representing a respective signal point of a predetermined alphabet of signal points, said system comprising

means responsive to the values of n bits of each input word in said input word sequence and the value of at least one bit of a previous input word in said input word sequence for identifying one of 2.sup.m predetermined subsets of said alphabet, m being an integer greater than n,
means responsive to the other k bits of said each input word for identifying a plurality of signal points of said one subset,
means for selecting one of said plurality of signal points as a function of two independent variables which are the respective odd and even components of the signal points represented by previously transmitted ones of said passband signals, and
a quadrature carrier modulator for generating on said communication channel as an individual one of said sequence of passband signals a signal representing the selected signal point, the in-phase and quadrature-phase inputs to said modulator respectively being the odd and even components of said selected signal point.

1 more element

A data transmission system adapted to transmit on a communication channel passband signals each representing a respective one of a sequence of signal points, each of said signal points being associated with a respective input word of a sequence of (k+n)-bit input words and being selected from a predetermined alphabet of 2.sup.(k+m+2) signal points, k, m and n being predetermined integers where m is greater than n, said system comprising

means for identifying one of 2.sup.m predetermined subsets of said alphabet for each input word of said input word sequence in response to the values of n bits of said each input word and the value of at least one bit of a previous input word in said input word sequence,
means responsive to the other k bits of said each input word for identifying an ensemble of four signal points of said one subset,
means for selecting one of said ensemble of four signal points in response to first and second sets of values of, respectively, odd and even components of previous signal points of said signal point sequence, and
a quadrature carrier modulator for generating on said communication channel as an individual one of said sequence of passband signals a signal representing the selected signal point, the in-phase and quadrature-phase inputs to said modulator respectively being the odd and even components of said selected signal point.

1 more element

A data transmission system for transmitting on a communication channel passband signals each representing a respective one of signal points which are generated by said system in response to a sequence of (k+n)-bit input words, k and n being predetermined integers, each of said signal points being selected from a predetermined alphabet of signal points, divided into 2.sup.m subsets, m being an integer greater than n, each of said subsets comprising 2.sup.k ensembles of four signal points, each of which comprises a first signal point having individual odd component and even component sums each at least equal to a particular predetermined value, a second signal point having an odd component sum at least equal to and an even component sum no greater than said particular predetermined value, a third signal point having an odd component sum no greater than and an even component sum at least equal to said predetermined particular value, and a fourth signal point having individual odd component and even component sums each no greater than said particular predetermined value, said system comprising

means for maintaining a first running sum and a second running sum of the values of, respectively, the odd and even components of signal points already generated by said system,
encoder means responsive to n of the bits of a particular input word of said input word sequence and at least one bit of a previous input word of said sequence for identifying the subset containing the signal point to be generated to represent said particular input word, said encoder means being further responsive to the other k bits of said particular input word for identifying the particular one of said ensembles in said subset containing said signal point to be generated, said encoder means being further responsive to the individual relative values of the first and second running sums and said particular predetermined value for identifying one of the signal points of said particular one of said ensembles as said signal point to be generated, and
a quadrature carrier modulator for generating on said communication channel as an individual one of said sequence of passband signals a signal representing the generated signal point, the in-phase and quadrature-phase inputs to said modulator respectively being the odd and even components of said generated signal point.

A data transmission system comprising

means operative for generating in response to each of a series of received multi-bit input words an individual signal point of a predetermined alphabet of signal points, divided into 2.sup.m subsets, each of said subsets comprising 2.sup.k ensembles of four signal points, m and k being integers, each of said ensembles comprising a first signal point and a second signal point each having the sum of odd components thereof no less than a particular predetermined value, and a third signal point and a fourth signal point each having same no greater than said particular predetermined value, said first signal point and said third signal point each having the sum of even components thereof no less than said particular predetermined value and said second signal point and said fourth signal point each having same no greater than said particular predetermined value,
means for maintaining a first running sum and a second running sum of the values of, respectively, the odd and even components of the signal points previously generated by said data transmission system, and
a quadrature carrier modulator for generating on said communication channel a passband signal representing said individual signal point generated by said data transmission system, the in-phase and quadrature-phase inputs to said modulator respectively being the odd and even components of said individual signal point,
each of said input words comprising (k+n) bits, n being less than m, and said generating means being adapted to trellis-code n bits of successive one of said subsets as containing the signal point to be generated, said generating means being further adapted to identify a particular one of said ensembles associated with the other k bits of said particular input word, said identified signal point being said first signal point of said particular one of said ensembles if the first and second running sums are each less than said particular predetermined value, being said second signal point of said particular one of said ensembles if said first running sum is less than and said second running sum is greater than said particular predetermined value, being said third signal point of said particular one of said ensembles if said first running sum is greater than and said second running sum is less than said particular predetermined value, and being said fourth signal point of said particular one of said ensembles if said first and second running sums are each greater than said particular predetermined value.

1 more element

A method for use in a data transmission system adapted to transmit on a communication channel a sequence of passband signals in response to a sequence of (k+n)-bit input words, each of said passband signals representing a respective signal point of a predetermined alphabet of signal points, said method comprising the steps of

identifying one of 2.sup.m predetermined subsets of said alphabet in response to the values of n bits of each input word in said input word sequence and the value of at least one bit of a previous input word in said input word sequence, m being an integer greater than n,
identifying a plurality of signal points of said one subset in response to the other k bits of said each input word,
selecting one of said plurality of signal points as a function of two independent variables which are the respective odd and even components of the signal points represented by previously transmitted ones of said passband signals, and
generating on said communication channel as an individual one of said sequence of passband signals a signal representing the selected signal point, said signal being comprised of a plurality of pulses whose individual in-phase and quadrature-phase amplitudes being respectively associated with the odd and even components of said selected signal point.

1 more element

A method for use in a data transmission system adapted to transmit on a communication channel passband signals each representing a respective one of a sequence of signal points, each of said signal points being associated with a respective input word of a sequence of (k+n)-bit input words and being selected from a predetermined alphabet of 2.sup.(k+m+2) signal points, k, m and n being predetermined integers where m is greater than n, said method comprising the steps of

identifying one of 2.sup.m predetermined subsets of said alphabet for each input word of said input word sequence in response to the values of n bits of said each input word and the value of at least one bit of a previous input word in said input word sequence,
identifying an ensemble of four signal points of said one subset in response to the other k bits of said each input word,
selecting one of said ensemble of four signal points in response to first and second sets of values of, respectively, the odd and even components of previous signal points of said signal point sequence, and
generating on said communication channel as an individual one of said passband signals a signal representing the selected signal point, said signal being comprised of a plurality of pulses whose individual in-phase and quadrature-phase amplitudes being respectively associated with the odd and even components of said selected signal point.

1 more element

Dependencies are inferred from the claim text.

Description6,944 words

Summary886 words

#The present invention relates to data transmission systems and, in particular, to channel coding in such systems.

#Much attention has been focused in recent years on channel codes which provide so-called coding gain. Prominent among these are the so-called "trellis" codes described in such papers as G. Ungerboeck, "Channel Coding with Multilevel/Phase Signals," IEEE Trans. Information Theory, IT-28, 1982, pages 55-67; A. R. Calderbank and N. J. A. Sloane, "A New Family of Codes for Dial-Up Voice Lines," Proc. IEEE Global Telecomm. Conf., November 1984, pages 20.2.1-20.2.4; A. R. Calderbank and N. J. A. Sloane, "Four-Dimensional Modulation With an Eight-State Trellis Code," AT&T Technical Journal, Vol. 64, No. 5, May-June 1985, pages 1005-1018; A. R. Calderbank and N. J. A. Sloane, "An Eight-Dimensional Trellis Code," Proc. IEEE, Vol. 74, No. 5, May 1986, pages 757-759; and L. F. Wei, "Rotationally Invariant Convolutional Channel Coding with Expanded Signal Space--Part I: 180 Degrees and Part II: Nonlinear Codes," IEEE J. Select. Areas Commun., Vol. SAC-2, September 1984, pages 659-686, all of which are hereby incorporated by reference. Commercial use of these codes has, for the most part, been concentrated in voiceband data sets and other carrier data communications systems.

#Moreover, it may be advantageous in such systems to have a spectral null in the passband signal at, for example, the carrier frequency so as to minimize the data signal energy concentration around that frequency.

Brief description of the drawings5 figures

#In the drawing,

#FIG. 1 is a block diagram of a data transmitter according to principles known to the prior art;

#FIG. 2 is a block diagram of a data transmitter embodying the principles of the invention;

Detailed description5,963 words

#FIG. 1 shows a prior art arrangement based on the disclosure in the Lee and Calderbank reference. Lee and Calderbank discloses a technique that creates a spectral null at, for example, dc, in a baseband signal. In accordance with this technique, the signal point to be transmitted is determined as a function of not only the input bits, at least ones of which have been trellis coded, but also as a function of a running value which is a function of the components of the signal points previously transmitted. In particular, by bounding the running sum of the values of these components, a spectral null at dc is guaranteed in a baseband signal.

#In furtherance of this technique, a spectral null created in a baseband thereby can be frequency-translated to a passband using conventional modulation techniques. Because of the relatively high bandwidth efficiency afforded by QAM, this modulation technique is conventionally used in prior art. (For details on QAM, see, for example, J. G. Proakis, Digital Communications (New York: McGraw-Hill) 1983, pages 105-106, hereby incorporated by reference.) In particular, by applying QAM to two of the aforementioned baseband signals with spectral nulls at dc, a passband signal with a spectral null at the carrier frequency results.

#In the particular prior art arrangement shown in FIG. 1, serial data bits from data source 105 are alternately applied at the inputs of 2-dimensional signal point encoders 107 and 109 which operate independently but are structurally identical. 2-dimensional signal points are thus generated by these two encoders, each of which is, for example, a scaled-down version of encoder 10 as disclosed in FIG. 1 of the aforementioned Lee and Calderbank reference. This scaling-down results from the fact that the dimensionality of signal points generated by the encoder in Lee and Calderbank is four as opposed to two in this particular arrangement. The actual design of encoders 107 and 109, based on the simplification of that encoder in Lee and Calderbank, is readily realized by one skilled in the art and thus need not be dwelled upon here.

Trellis codes with passband spectral nulls

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Trellis codes with passband spectral nulls

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Life of this patent

Abstract

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Claims32

Description6,944 words

Classification2 codes

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Description6,944 words

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