Abstract: At a transmitter, a program is encrypting according to a one program key, the program key is encrypted, and the encrypted program, the encrypted program key, and non-encrypted PSI data to a receiver are transmitted. At a receiver, the encrypted program, the encrypted program key, and the non-encrypted PSI data are received, the encrypted program key is decrypted, the encrypted program is located according to the non-encrypted PSI data, and the located encrypted program is decrypted according to decrypted program key.

Abstract: Data is encrypted according to a plurality of data keys. During the encryption of the data, the data keys are rotated according to a data key rotation pattern, and the rotation of the data keys includes repetitive use of the data keys during the encryption of the data. The encrypted data is transmitted to a receiver. Additionally or alternatively, encrypted data is received from a transmitter. The encrypted data is decrypted according to a plurality of data keys. During the decryption of the encrypted data, the data keys are rotated according to a data key rotation pattern, and the rotating of the data keys includes repetitive use of the data keys during the decryption of the encrypted data.

Abstract: At a transmitter, a program is encrypting according to a one program key, the program key is encrypted, and the encrypted program, the encrypted program key, and non-encrypted PSI data to a receiver are transmitted. At a receiver, the encrypted program, the encrypted program key, and the non-encrypted PSI data are received, the encrypted program key is decrypted, the encrypted program is located according to the non-encrypted PSI data, and the located encrypted program is decrypted according to decrypted program key.

Abstract: Data is encrypted according to a plurality of data keys. During the encryption of the data, the data keys are rotated according to a data key rotation pattern, and the rotation of the data keys includes repetitive use of the data keys during the encryption of the data. The encrypted data is transmitted to a receiver. Additionally or alternatively, encrypted data is received from a transmitter. The encrypted data is decrypted according to a plurality of data keys. During the decryption of the encrypted data, the data keys are rotated according to a data key rotation pattern, and the rotating of the data keys includes repetitive use of the data keys during the decryption of the encrypted data.

Abstract: An HDTV receiver includes an AGC system that develops an RF AGC voltage that is derived on an analog basis and an IF AGC voltage that is derived on a digital basis. The digital voltage is developed from an error signal that comprises the most significant bits of a continuously operated large accumulator that is supplied with the algebraically combined output of the digital signal and an AGC reference number.

Abstract: A digital television signal includes successive frames of two fields each comprising 313 data segments with the first data segment in each field functioning as a field sync. The field sync segment comprises a 511 PN sequence and three 63 pseudo-random number (PN) sequences, with the middle one of the 63 PN sequences alternating polarity in successive fields. A reference data segment is compared with the 511 PN sequence in each data segment and the data segment with the least number of errors is identified as the first data segment in the field. The corresponding portion of the reference segment is compared with the middle 63 PN sequences in the identified first data segments and that with the least number of errors is determined to be the first segment in the frame. Confidence counters are used to assure reliable determinations.

Abstract: A technique and apparatus for developing AGC voltage in a receiver capable of receiving VSB signals that do not have the data symbol levels and the sync symbol levels related so as to produce the same average magnitude level. Successive portions of the signal are accumulated, stored and compared with the smaller of the samples to be used to develop the AGC voltage. By comparing the first and third of three successive samples, the effect of the larger than desired sync levels in the over-the-air VSB signals is completely eliminated.

Abstract: A VSB mode detection circuit with a comb filter solves the potential problem of lockout in a situation where an 8 VSB mode signal is being received, with the comb filter being effective, and a change in signal mode suddenly occurs. The arrangement inhibits the first two bytes of the three byte mode information, which two bytes are unspecified for all except the 8 VSB terrestrial mode, and replaces them with zero data. In another embodiment, the 12 symbol delay in the comb filter is bypassed with the complement of the input data for the third byte. When the 8 VSB terrestrial mode has been confidently determined to exist, the inhibition of the first and second bytes (and the inversion of the bypassed third byte) is removed in alternate fields to permit normal comb filter operation.

Abstract: A DC removal circuit for removing residual DC from a digitally encoded television signal including a plurality of multi level data symbols occurring at a constant symbol rate and formatted in repetitive data fields, each field including repetitive data segments having data segment sync of a fixed pattern of four symbols. A derived value of DC is subtracted from each of the received data symbols. The output of the subtractor is sampled, at the symbol rate or at one-half the symbol rate, and the sampled output is accumulated in an accumulator for generating the derived value. The sampling is continuous. The accumulator is preset to a zero value upon tuning to a different channel. An equalizer is supplied with the derived value of DC.

Abstract: A technique and apparatus for developing AGC voltage in a receiver capable of receiving VSB signals that do not have the average magnitudes of the data symbol levels and the sync symbol levels related so as to produce the same average level. One technique eliminates the sync symbols from determination of the AGC voltage. A preferred technique corrects for the different symbol levels of the sync by multiplexing in an offset at the proper time or multiplying the sync symbols by a compensating factor.

Abstract: A digital video field identification system includes video signals formatted in blocks of video symbols in repetitive data segments with each data segment including a synchronizing signal character. One data segment includes a field timing signal. A reference data segment which includes a reference field timing signal is developed at the receiver. A portion of each data segment is compared with the reference field timing signal and the number of symbol errors is accumulated for each data segment. The data segment exhibiting the least number of symbol errors is identified as the one having the field timing signal. A confidence counter stabilizes the identification of the one data segment. For terrestrial transmission, the video signals are precoded in modulo N form to enable NTSC co-channel interference rejection in the receiver by a linear filter.

Abstract: A digital data transmission system includes data signals formatted in successive fields consisting of blocks of video symbols in repetitive data segments with each data segment including a synchronizing signal character for providing data segment sync. The first data segment in each field includes a field timing signal that provides field sync. The digital data is in the form of M-level symbols and the sync information (both data segment and field) is in the form of N-level symbols, where M is greater than N.

Abstract: A DC removal circuit for removing residual DC from a digitally encoded signal including a plurality of multi level data symbols occurring at a constant symbol rate and formatted in repetitive data fields, each including repetitive data segments having data segment sync. A derived value is subtracted from each of the received data symbols. The output of the subtractor is sampled, at a rate that is less than the symbol rate, and the sampled output is accumulated in an accumulator for generating the derived value. The sampling is synchronized with the data segment sync to avoid sampling the data segment sync and the accumulator is disabled until data segment lock is achieved.

Abstract: A digital video field identification system includes video signals formatted in blocks of video symbols in repetitive data segments with each data segment including a synchronizing signal character. One data segment includes a field timing signal. A field reference data segment which includes the field timing signal is developed at the receiver. Each data segment is compared with the field reference data segment and the number of symbol errors is accumulated for each data segment. The data segment exhibiting the least number of symbol errors is identified as the field timing segment. A confidence counter stabilizes the identification of said one data segment. The video signals are precoded in modulo N form to enable NTSC co-channel interference rejection in the receiver by a linear filter. The linear filter undesirably reduces the S/N ratio by 3dB.

Abstract: A CATV television system has the sync and color subcarrier reference information replaced in the horizontal blanking intervals with compressed digital audio data. The digital audio data is in the form of a modified duobinary signal having data sampling points selected to coincide with the zero crossings of a color reference subcarrier. A phase locked loop provides the master clock for the signal generator and the data sampler. A horizontal interval detector circuit recovers a 1.8 MHz CW signal of greater than one half line duration, followed by a white horizontal identification pulse of 4.7 microseconds width, that are supplied in place of the pre-equalizing, vertical sync and post equalizing pulses in the vertical interval.

Abstract: In an NTSC television system there are an odd number (262.5) of horizontal lines in each field. This relationship causes a 50% duty cycle horizontal rate signal (H) to be high during one specific horizontal half line in one field and low for that same horizontal half line in the other field. A 2H rate signal is normally divided by 525 with counters to obtain a field rate. The outputs of the counters are combined with a regenerated horizontal rate signal (H) to generate a plurality of unique addresses. This provides a mapping for each field to within a half horizontal line resolution. These addresses can be decoded by a programmable logic device or other devices to define half, single or groups of horizontal lines in one or both fields.

Abstract: Noise in a composite video signal is detected by looking for the presence of excessive pulses resembling broad pulses or insufficient horizontal sync pulses. The output of the detector is averaged by a low pass filter, the output of which is, in turn, applied to a comparator for comparison with a reference DC level in generating a signal representing the noise level in the composite video signal.

Abstract: The horizontal sync component of a composite video signal having a rate H is provided to a phase locked loop (PLL) in the front end of a video signal receiver for synthesizing a horizontal rate signal. A composite sync signal and a 2H signal from the PLL are provided to a vertical reference signal identification circuit which samples the composite sync signal with the positive-going edge of the 2H pulse. The composite sync signal will only be high on a positive-going edge of the 2H pulse during the broad pulses of the composite sync signal. The vertical reference signal identification circuit counts six 2H pulses to establish a precise three horizontal line reference. If the width of the vertical sync pulse from the first encountered broad pulse to the last, without the occurrence of any discontinuities as defined by a high sample obtained by the positive transition of the 2H pulse, is equal to the three horizontal lines, then a vertical reference signal is provided.

Abstract: A color control circuit for selectively modifying the red, green and blue color signals developed at the output of a teletext-type decoder comprises a common input stage responsive to the teletext decoder for developing a bi-level control voltage identifying the portions of the color signals representing background and foreground display information. Each color signal is coupled to a respective output stage which causes the associated color signal to assume a first intensity level in response to the control voltage being at its first level and a second intensity level greater than the first intensity level in response to the control voltage being at its second level. As a result, background colors are displayed at a reduced contrast level relative to foreground colors. In addition, selected single color foreground information may be displayed at a further increased intensity level to improve the readability of the display.