Abstract: An equalization device has a digital equalizer for joint tuning of a data-carrying signal distorted by analog transmission. The digital equalizer includes a closed-loop automatic gain control (AGC) circuit for applying a compensatory frequency-independent gain to the distorted signal followed by a frequency filter for applying a compensatory frequency-dependent gain to the signal. Joint tuning produces an output signal which more closely resembles the originally transmitted signal, facilitating recovery of implicit clock and more reliable data recovery. The digital equalizer may be advantageously stage-implemented as a preliminary digital equalizer which is preceded by an analog equalizer and followed by a final digital equalizer.

Abstract: A method and apparatus are provided for convolutionally encoding digital data with a rate 4/5 convolutional code. A nonoptimal rate 1/2, sixteen-state convolutional code is punctured to rate 4/5 using a puncture map of ##EQU1## and octal generators 25, 37 wherein .nu.=4. An incoming data stream is processed using the rate 4/5 code. Punctured rate 3/4 and 6/7 codes are also provided.

Abstract: Digital data is communicated using trellis coded QAM. Symbols are coded for transmission using a rate 1/2 convolutional encoder punctured to rate 2/3. The coded symbols are transmitted for receipt at a receiver. At the receiver, two sets of branch metrics are computed for each received symbol. The received symbols are decoded by using the branch metrics to effect two passes through a modified rate 1/2 Viterbi decoder for each symbol.

Abstract: A desired information stream is recovered from a pair of independent bitstreams transmitted using quadrature modulation. One of the independent bitstreams is altered by an invertible alteration function prior to transmission. The quadrature modulated bitstreams are demodulated at a receiver to provide a demodulated I bitstream and a demodulated Q bitstream. One of the demodulated I and Q bitstreams is tentatively provided for decoding. The tentatively provided bitstream can be optionally inverted. One of the tentatively provided bitstream and the optionally inverted bitstream is decoded if it is desired to recover the bitstream that was not altered by the alteration function prior to transmission. One of the tentatively provided bitstream and the optionally inverted bitstream is decoded after applying the inverse of the alteration function thereto if it is desired to recover the bitstream that was altered by the alteration function prior to transmission.

Abstract: Punctured binary convolutional codes are used in a trellis coded modulation scheme to achieve spectral efficiencies as high as those of multi-dimensional codes, using simple hardware. A base rate 1/2 binary convolutional code is punctured to rate n/k. The output of the punctured encoder is mapped to a four-way partition of a 2.sup.N point two-dimensional QAM constellation. The four-way partition consists of a two-way partition in both the I and Q dimensions. The two-way partitions of each dimension are used to transmit the two level output of the rate n/k binary convolutional coder. (N-2) "uncoded" bits are transmitted by selecting the unique constellation point in a partition group. The code has an average throughput of (N-2)+2n/k bits per symbol. The invention is also applicable to trellis coded amplitude modulation schemes based on 2.sup.N possible amplitude levels provided along a one-dimensional constellation.