Abstract: 8VSB-compatible DTV broadcasting that employs outer coding of a sort in which interleaved data and outer coding parity are inner coded by the ? trellis code encoder is improved. This is done by recoding each nibble of the interleaved data and outer coding parity in accordance with an anti-Gray code before being inner coded by the ? trellis code encoder. Accordingly, in the DTV receiver an adjacent-bin error during data slicing may generate a double-bit error in a nibble as received, but this is reduced to a single-bit error after the nibble is recoded in accordance with a Gray coding procedure. In one example of such recoding, 10 and 11 nibbles of the interleaved data and outer coding parity are recoded to 11 and 10 nibbles respectively, but the 00 and 01 nibbles are not recoded. In another example of such recoding, 00 and 01 nibbles of the interleaved data and outer coding parity are recoded to 01 and 00 nibbles respectively, but the 10 and 11 nibbles are not recoded.

Abstract: A DTV signal is transmitted that avoids legacy DTV receivers regarding data segments used in other than ordinary 8VSB transmissions being mistaken for (207, 187) R-S FEC codewords that appear to free of byte error or can be corrected to appear so. The DTV signal is analyzed prior to its transmission, for detecting those data segments used in other than ordinary 8VSB transmissions that legacy DTV receivers could mistake for correct (207, 187) R-S FEC codewords or correctable (207, 187) R-S FEC codewords. Twenty bytes of each segment of data that could be so mistaken are modified to prevent such mistake. Complementing certain bits in the final twenty bytes of each segment of data is preferred if data are transmitted at one-half or one-quarter ordinary 8VSB code rate. Segments of control data, each pertaining to a respective future group of said segments of data, are transmitted in a further aspect of the invention for indicating which data segments are modified.

Abstract: Procedures performed prior to convolutional interleaving of 8VSB digital television signals restrict the alphabet of symbols in novel methods of generating trellis-coded digital television signals that include more robust symbol coding using a restricted alphabet of symbols selected from a full 8VSB symbol alphabet consisting of ?7, ?5, ?3, ?1, +1, +3, +5 and +7 normalized modulation levels superposed on a background modulation level. Certain of these novel procedures generate pseudo-2VSB or P-2VSB robust symbol coding with a restricted alphabet of symbols consisting of ?7, ?5, +5 and +7 normalized modulation levels superposed on a background modulation level. Others of these novel procedures generate prescribed-coset-pattern-modulation or PCPM robust symbol coding intermixing two restricted alphabets of symbols according to a prescribed pattern. One of the two restricted alphabets of symbols used in PCPM consists of ?3, ?1, +5 and +7 normalized modulation levels superposed on a background modulation level.

Abstract: To increase the robustness of a broadcast DTV signal, complete (207, 187) Reed-Solomon forward-error-correction codewords are coded using binary linear block codes that reduce code rate by two or slightly less, enabling a DTV receiver to correct bit errors. Also, a DTV receiver can use a (15, 8), (16, 8) or (8, 4) block code to locate erroneous bytes for decoding (207, 187) Reed-Solomon code, so twice as many erroneous bytes can be corrected in a 187-byte data packet. The reduced code rate permits robust transmission of a 187-byte data packet in only two data segments and its super-robust transmission using a restricted symbol alphabet in only four data segments. This simplifies time-division multiplexing of data segments used for ordinary 8VSB transmissions with those used for robust and super-robust transmissions. Procedures to make legacy DTV receivers disregard data segments used for robust and super-robust transmission are disclosed.

Abstract: Synchrodyning apparatus in which a PAM IF signal is mixed with unmodulated carriers nominally at the frequency of the carrier, which unmodulated carriers are in quadrature with respect to each other. E.g., the PAM IF signal may be an intermediate-frequency 8VSB digital television signal. The baseband signals resulting from the mixing procedures are additively combined and differentially combined to generate real and imaginary components of a complex baseband signal. The real component of the complex baseband signal is processed for reproducing the digital signal used to modulate the transmitted RF carrier. An automatic frequency and phase control (AFPC) signal for controlling the oscillator circuitry generating the unmodulated carriers is generated by an AFPC detector responding to the imaginary component of the complex baseband signal or to both components of the complex baseband signal.

Abstract: Different sets symbols are precluded at prescribed times in time-dependent trellis coding. This increases the distances between different individual symbols as well as the distances between trellis codes, which increases the robustness of data transmission. The symbols that are precluded in this time-dependent trellis coding are determined in advance according to a prescribed pattern, which pattern does not depend on the history of previous symbols. The Viterbi decoder used for trellis decoding in a receiver can be designed to take advantage of knowledge concerning which different sets of symbols are precluded at prescribed times.

Abstract: A PAM receiver for reproducing a baseband signal that symbol codes digital data is combined with an decision-feedback equalizer (DFE) incorporating first adaptive digital filtering as a feed-forward element and second adaptive digital filtering as a feedback element. The DFE response is supplied to symbol decoding circuitry for reproducing the digital data. A de-rotator re-samples the first adaptive digital filtering response before it is combined with the second adaptive digital filtering response to generate an equalizer response. The resulting baud-rate equalizer response is sampled at baud rate and quantized to generate baud-rate decisions that applied to the second adaptive digital filtering as input signal, for completing the decision-feedback loop. The re-sampling of the first adaptive digital filtering response by the de-rotator is controlled, so as to provide a phase-tracker that reduces phase noise and intersymbol interference, prior to the making of decisions for decision feedback.

Abstract: Digital HDTV signals are exemplary of vestigial sideband (VSB) signals, which signals include a pilot carrier and sidebands generated in response to symbol codes descriptive of digital signals. A radio receiver for such VSB signals includes automatic gain control (AGC) circuitry that generates AGC signal by synchronously detecting the pilot carrier.