Abstract: A cost-effective, bandwidth-efficient, and power-efficient system is provided in which data streams received from several different video sources are converted into sequences of symbols selected from a predetermined constellation and are multiplexed on a symbol-by-symbol basis into a single sequence of symbols for transmission on a channel. Using a symbol multiplexer helps to mitigate the effect of bursty noise in the receiver and reduces the processing speed requirement in the receiver.

Abstract: A trellis-coded modulation system is provided in which the output of the trellis encoder is used to select a subset of a multidimensional QAM constellation. The selection process is performed such that a) the minimum square Euclidean distance between valid sequences of successive selected subsets is maximized, b) the resulting code is rotationally invariant, and c) the selected subset corresponding to a transition of the trellis encoder from a present state i to a different next state j is different from the selected subset that corresponds to a transition of the trellis encoder from a present state j to a next state i.

Abstract: A modulation scheme for HDTV, for example, uses a concatenated code comprised of a Reed-Solomon coder followed by an N-dimensional trellis coder whose N-dimensional output symbols with N>1, are used to modulate a one-dimensional vestigial sideband modulator. Specifically, each N-dimensional symbol is a sequence of N one-dimensional signal points--specifically signal points of a one-dimensional VSB constellation.

Abstract: A multilevel coded modulation scheme trellis encodes a portion of the input data and the resulting encoded stream is used to identify a particular one of a predetermined number of subsets of symbols of a predetermined signal constellation. The remaining input data is coded using a Reed-Solomon (RV) code whose output is used to select for transmission a particular symbol from the identified subset. In applications in which phase hits or other channel phenomena may cause the received signal points to be phase-rotated versions of the signal points that were transmitted, differential encoding is included in the overall coded modulation scheme. In different embodiments, the differential encoding/decoding and RV encoding/decoding are in different orders. In one such embodiment, overlapped multilevel codes are used to preserve the advantages afforded by taking a multilevel coding approach.

Abstract: Digital data is transmitted over partial-response channels using a precoding technique which allows for the use of a wide variety of transmit constellations. A sequence of signal points is selected from a predetermined base constellation meeting particular criteria. A so-called combined signal point is developed for a present symbol interval by a) selecting a signal point from the base constellation as a function of input bits associated with the present symbol interval and b) combining the signal point thus selected with a feedback signal which is a function of one or more combined signal points that were developed for previous symbol intervals, that function being determined by the characteristic of the partial-response channel. A transmit signal which represents the combined signal points is then provided. In one implementation, the processing steps are performed explicitly using an integrated precoder/constellation mapper. In another implementation those steps are performed implicitly using table look-up.

Abstract: The decoding depth of a multidimensional trellis-coding scheme with X-fold time diversity is reduced, or minimized. As a result, an improvement in error rate performance is achieved for the multidimensional trellis code, which can then be favorably applied to a fading channel application.

Abstract: A multilevel coded modulation scheme trellis encodes a portion of the input data and the resulting encoded stream is used to identify a particular one of a predetermined number of subsets of symbols of a predetermined signal constellation. The remaining input data is coded using a Reed-Solomon (RS) code whose output is used to select for transmission a particular symbol from the identified subset. In applications in which phase hits or other channel phenomena may cause the received signal points to be phase-rotated versions of the signal points that were transmitted, differential encoding is included in the overall coded modulation scheme. In different embodiments, the differential encoding/decoding and RS encoding/decoding are in different orders. In one such embodiment, overlapped multilevel codes are used to preserve the advantages afforded by taking a multilevel coding approach.

Abstract: A high definition television (HDTV) signal is transmitted by a multi-subcarrier transmission scheme in which each subcarrier is used to carry a different class of HDTV information.

Abstract: A trellis-coded communications system for encoding a fractional number of bits is described. In this system, the number of allowed state transitions, originating from each state of a trellis encoder, is restricted to a number that is not an integral power of an integer. Furthermore, not all state transitions are used with equal probability.

Abstract: Unequal error protection is provided for an HDTV signal by separately coding each one of the classes of information in the HDTV signal by using a conventional coded modulation scheme and then time-division-multiplexing the various coded outputs for transmission. In particular, each class of information is separately coded by a 4-dimensional 8-state trellis code and a uniformly-spaced (QAM) signal constellation.

Abstract: In a communications system, a generalized partial response signaling (GPRS) technique is employed to compensate for intersymbol interference. To this end, signal points representative of data to be transmitted are selected from a signal constellation. This signal constellation includes a multiplicity of signal points which are regularly spaced within a polygonal region having more than four sides. The selected signal points are precoded in the transmitter in accordance with the GPRS technique. Because of the particular choice of the signal constellation used, the precoded signal points for transmission occupies a region identical to the polygonal region.

Abstract: Digital signals, such as digitized television signals, are subjected to a source coding step in which a class of "most important" data elements represents a proportionately greater amount of the information to be communicated than the rest of the data elements. This is followed by a constellation mapping step which is carried out in such a way that those data elements have a lower probability of being erroneously detected at the receiver than the others. The constellation mapping step uses coded modulation in order to provide enhanced noise immunity for the "most important" data element class.

Abstract: Interleavers used in fading channel applications can be matched to a particular trellis or block code being used. This matching can occur even in a particular transmission scheme such as TDMA. Matching both the interleaver and the code increases the separation between interdependent signal points and provides an improvement in error performance, without an increase in time delay over known interleaver design.

Abstract: In a wireless local area network, predetermined interference-detection sequences of signal points, known at both the transmitter and receiver, are transmitted over a plurality of hopping frequencies along with a sequence of data signal points taken from a modulated code exhibiting built-in diversity. In the receiver, the extent to which there are errors in the received interference-detection signal points is used as a mechanism for identifying the likely occurrence of strong interference. If there are no, or few, errors, decoding proceeds normally. However, if the number of errors is above a predetermined threshold, it is assumed that the transmitted signal was subjected to significant interference and an erasure is declared. This is used as "side" information by the decoder to improve its ability to accurately recover data in the presence of interference.

Abstract: Interleaved block-coded modulation with built-in time diversity is used for fading channel applications. Various modulated block codes of various dimensionalities are disclosed, each built up from an M-DPSK constellation. The signal points making up each codeword are re-ordered by an interleaver in a way which matches the interleaving to the block code, thereby increasing the effective size of the interleaver.

Abstract: This invention is a Local Area Network (LAN) which comprises a plurality of NIU's, each arranged to transmit on a separate set of frequencies and to receive on a separate set of frequencies. During operation, a data packet is multihopped from a source NIU, through intermediate NIUs, until reaching an NIU which can transmit a frequency which the destination NIU is capable of receiving. The packet is then forwarded to the destination NIU. The source NIU may also send a control packet and cause the destination NIU to adjust its receive frequency so that subsequent packets may be transmitted directly to the receiving NIU. In an alternative embodiment, the multihopping may be accomplished using specialized headnode modems.

Abstract: A signal coding technique for use with fractional bit rates is disclosed which, for a given dimensionality, allows the use of smaller constellations, and thus provides greater robustness in the presence of various impairments, than would otherwise be the case yet entails essentially no decoding delay penalty. In this technique, one or more of the input bits are trellis encoded and the trellis-encoded bits identify one of a predetermined plurality of subsets of the signal constellation and the particular symbols selected for transmission from two or more identified subsets are chosen by the non-trellis-encoded bits interdependently.

Abstract: A family of multi-dimensional convolutionally coded modulation systems achieves enlarged minimum distance between possible sequences of signal points, reduced number of error events with the minimum distance, acceptable peak-to-average power ratio, reduced number of signal points in each constituent two-dimensional constellation, immunity to rapid carrier phase changes, and reduced complexity, resulting in a reduced error probability when maximum likelihood decoding is used.These advantages are achieved by the construction and by the partitioning into subsets of the multi-dimensional constellation, by the design of convolutional codes using those multi-dimensional subsets, by using a bit converter and a block encoder to convert a multi-dimensional constellation mapping into multiple two-dimensional constellations mappings, and by a simplified decoding technique.

Abstract: Frame synchronization is accomplished in a trellis-coded communication system by causing the sequence of signal points that results when the receiver incorrectly determines the start of each frame to be an impermissible sequence, and detecting the existence of the impermissible sequence by monitoring the rate of occurrence of non-zero difference between the minimum branch metric and the minimum path metric of a maximum likelihood decoding algorithm, such as the Viterbi decoding algorithm. In another aspect, an interleaver and a deinterleaver are used to assure that impermissible sequences result when frame synchronization is lost.

Abstract: A technique for converting a sequence of binary digits into a sequence of signalling alphabets of a modulated carrier signal for data transmission. By differentially encoding incoming data, non-linearly encoding the differentially encoded output in a state-dependent sequential manner and mapping the non-linearly encoded output into an expanded set of signalling alphabets having 90, 180 and 270 degree phase ambiguities, enlarged minimum Euclidean distance between possible sequences of signalling alphabets is achieved while the effect of the phase ambiguities of the expanded set of signalling alphabets can be removed in the receiver. This results in a reduced error probability when maximum likelihood decoding and differential decoding are applied in the receiver.