Abstract: Digital signals, such as digitized television signals, are subjected to a source coding step followed by a channel mapping step. The source coding step causes the television signal to be represented by two or more data streams while, in the channel mapping step, the mapping is such that the data elements of the various data streams have differing probabilities of being erroneously detected at the receiver. In preferred embodiments, a first one of the aforementioned data streams carries components of the overall television signal which are regarded as the most important--for example the audio, the framing information, and the vital portions of the video information, such as motion compensation information--and that data stream is mapped such that its data elements have the lowest probability of error.

Abstract: Digital signals, such as digitized television signals, are subjected to a source coding step followed by a channel mapping step. The source coding step causes the television signal to be represented by two or more data streams while, in the channel mapping step, the mapping is such that the data elements of the various data streams have differing probabilities of being erroneously detected at the receiver. In preferred embodiments, a first one of the aforementioned data streams carries components of the overall television signal which are regarded as the most important--for example the audio, the framing information, and the vital portions of the video information, such as motion compensation information--and that data stream is mapped such that its data elements have the lowest probability of error.

Abstract: A data receiver which includes a timing recovery circuit or periodically adjusting a timing signal used to control sampling of the received signal is arranged to reduce or eliminate phase jitter introduced as a result of the adjustments. Apparatus and a method are described for forming a correction factor which is a joint function of the timing adjustment increment and a previous correction factor. Typically, correction is accomplished by forming the complex product of the in-phase and quadrature-phase components of the received signal and the recursively updated correction factor.

Abstract: Half-duplex switched carrier operation is emulated in a full-duplex voiceband data transmission system by utilizing predetermined signal indications in each channel to signal the initiation and termination of user data in that channel and thus to control the Receive Line Signal lead extending to the terminals at respective ends of the transmission channel. The signal indication which signals the initiation of transmission is illustratively two scrambled spaces inserted into an idle-state sequence of continuous scrambled marks. The signal indication which signals the termination of transmission is illustratively a stream of 65 unscrambled marks.

Abstract: An n-dimensional channel code is used in a data transmission system. The alphabet of codewords (data symbols) comprises a subset of points of a selected coset of a selected lattice. The alphabet includes at least one point of the coset whose norm (signal energy) is greater than at least one other point of the coset which is excluded from the alphabet.

Abstract: Weighted sums of samples of an interference-corrupted data signal are generated to form phase-compensated, symbol-spaced samples. The interference-corrupted signal is at the same time subjected to conventional adaptive equalization and is otherwise processed so as to form tentative decisions as to the transmitted data. Cancellation signals representing the interference components of the phase-compensated samples are generated by forming respective weighted sums of the tentative decisions and each cancellation signal is combined with a respective phase-compensated sample to provide cancelled samples from which final data decisions are made. The weighting coefficients used to form the phase-compensated samples and the cancellation signals are adaptively updated in response to error signals derived from the difference between each cancelled sample and the corresponding final decision.

Abstract: Limit cycles are eliminated in digital filters driven by zero, d.c. and period 2 inputs, by adjusting the filter output in response to the state variables present within the filter. The filter includes a quantizer (201) adapted to provide a fixed length output word p in response to an input y, where p<y<p+k and k is the quantizer step size. The filter is further arranged to form the products a.multidot.X.sub.n and b.multidot.X.sub.n, where a and b are multiplier coefficients and X.sub.n and X.sub.n-1, the state variables, are once and twice delayed versions of the filter output X.sub.n+1, and to combine the aforesaid products and the filter input U.sub.n to yield the value y. In accordance with the invention, the quantizer output is adjusted to p+k, ifX.sub.n-1 >p+k orX.sub.n-1 =p and .vertline.X.sub.n +Sgn(a)X.sub.n-1 .vertline..gtoreq.T orX.sub.n-1 =p+k and .vertline.X.sub.n +Sgn(a)S.sub.n-1 .vertline.<T,where T is a fixed threshold value and Sgn(a) is the sign of the multiplier coefficient a.