Methods and apparatus for scrambling and unscrambling premium television channels

Claim 2

A subscriber television system comprising: a central unit having a source of first and second field synchronized television program signals; at least one local exchange unit for bilateral communication with a plurality of subscriber units and unilateral communication with the central unit; each subscriber unit including a television receiving device and a subscriber control unit coupled thereto; a plurality of video channels for conveying television program signals from said central unit to each subscriber unit; said central unit including means for selectively connecting at least one television program source to a first preselected channel for a first time period and to a second channel for a second time period, said central unit further including means for signalling a status of said connecting means to each of said local exchange units, and; means included within each subscriber control unit to supply said at least one television prOgram signal to the corresponding television receiving device from said first preselected channel for said first time period and from said second channel for said second time period, said supply means controlled by signals from said associated local exchange unit.

Claim 3

The system of claim 1 wherein the product of the television program signal field rate and the first time period as well as the product of the television program signal field rate and the second time period are integers.

Claim 4

The system of claim 1 wherein both television program signals begin field scan substantially contemporaneously, said means for selectively connecting being operable only during vertical retrace periods.

Claim 5

The system of claim 1 further comprising means for connecting the second television program signal source to said first preselected channel for said second time period and to said second preselected channel for said first time period, and means for synchronizing the last mentioned means and the means for selectively connecting to insure that no two television program sources are ever connected to the same channel at the same time.

Claim 6

The system of claim 1 wherein the said channels are frequency band channels and wherein the means included within each subscriber control unit includes mixer means and local oscillator means selectively operable when enabled to convert a signal received on one of said channels to a different channel.

Claim 7

The system of claim 5 further comprising filter means tuned to pass signals on said different channel, said filter means coupling the output of the mixer to the input of the television receiving device.

Claim 8

The system of claim 1 wherein the video channels comprise a pair of feeder lines, the means included within each subscriber control unit including switch means for alternately coupling the feeder lines to the input of the television receiving device.

Claim 9

A subscriber television system comprising: a central unit having a source of a first television program signal and a source of a second television program signal in field synchronization with said first television program signal; at least one intermediate processor for bilateral communication with a plurality of subscriber units and unilateral communication with the central unit; each subscriber unit including a television receiving device and a subscriber control unit coupled thereto; at least two video channels for conveying television program signals from said central unit to each subscriber unit; said central unit including a first switching matrix for coupling said first television program source to another of said video channels and selectively operable to repetitively simultaneously interchange the video channels to which said first and second television program sources are coupled to thereby provide on each of said two video channels a sequence of interleaved portions of signals from each television program source, said central unit including means for signalling activity of said first switching matrix to said intermediate processors; and each subscriber control unit including a second switching matrix operable in response to signals from said associated intermediate processor, said second switching matrix operating in unison with said first switching matrix for selectively coupling the television receiving device to the one of the two video channels currently conveying a desired television program signal.

Claim 10

A subscriber television system comprising: a central unit having a source of a first television program signal and a source of a second television program signal in field synchronization with said first television program signal; at least one intermediate processor for bilateral communication with a plurality of subscriber units and unilateral communication with the central unit; each subscriber unit including a television receiving device and a subscriber control unit coupled thereto; at least two video channels for conveying television program signals from said central unit to each subscriber unit; said central unit including a first switching matrix for coupling said first television program source to another of said video channels and selectively operable to repetitively simultaneously interchange the video channels to which said first and second television program sources are coupled to thereby provide on each of said two video channels a sequence of interleaved portions of signals from each television program source, said central unit including means for signalling activity of said first switching matrix to said intermediate processors; and each subscriber control unit including a second switching matrix operable in response to signals from said associated intermediate processor, said second switching matrix operating in unison with said first switching matrix for selectively coupling the television receiving device to the one of the two video channels currently conveying a desired television program signal.

Claim 11

The system of claim 8 wherein the first and second switching matrices are operable only during the time intervals between successive television program signal fields.

Claim 12

The system of claim 9 further comprising means for generating and transmitting to each subscriber control unit between fields a binary digit indicating which channel will carry the first television program signal on the next succeeding field.

Claim 13

The system of claim 9 further comprising register means for storing digital information identifying the sequence oF switching of said second switching matrix.

Claim 14

The system of claim 11 wherein the register means comprises an n-bit register each digital position of which identifies the channel on which an associated field of the first television program is being carried, the same bit being associated with every nth field of the signal.

Claim 15

The system of claim 11 wherein each intermediate processor forwards to individual subscriber units from said central unit the sequence identifying digital information and receiving from the subscriber units and recording subscriber viewing information.

Claim 16

The system of claim 13 wherein the subscriber viewing information is recorded after the elapse of a preview period for each premium program, said first switching matrix maintaining a fixed signal-channel distribution until after the expiration of the preview period.

Claim 17

In a subscriber television system the improved method of scrambling and unscrambling a television program signal wherein said subscriber television system includes a central unit having a source of a first television program signal and a second television program signal in field synchronization with the first television program signal and at least one intermediate processor for bilateral communication with a plurality of subscriber units and unilateral communication with the central unit, said subscriber television system further including at least one control unit remote from the central unit associated with and coupled to each preselected intermediate processor, comprising the steps of: transmitting the television program signal over a first video channel for a first time period and over a second video channel for a second time period; generating an n-bit number at the central unit; transmitting the n-bit binary number to said intermediate processors; repetitively sequentially examining the bits at the field rate and transmitting the first television program signal on the first video channel and the second television program signal on the second video channel if the most recently examined bit is a ''''one'''' and transmitting the first television program signal on the second video channel and the second television program signal on the first video channel if the most recently examined bit is a ''''zero;'''' examining the transmitted n-bit binary number at the said intermediate processors in synchronism with the examination thereof at the central unit; and selectively connecting a television receiving device to the first video channel for the first time period if the most recently examined bit is a ''''one'''' and to the second video channel for the second time period if the most recently examined bit is a ''''zero,'''' the first and second time periods being integral multiplex of the time of duration of one field of the television program signal.

Claim 18

In a subscriber television system the improved method of scrambling and unscrambling a television program signal wherein said subscriber television system includes a central unit having a source of a first television program signal and a second television program signal in field synchronization with the first television program signal and at least one intermediate processor for bilateral communication with a plurality of subscriber units and unilateral communication with the central unit, said subscriber television system further including at least one control unit remote from the central unit associated with and coupled to each preselected intermediate processor, comprising the steps of: transmitting the television program signal over a first video channel for a first time period and over a second video channel for a second time period; generating an n-bit number at the central unit; transmitting the n-bit binary number to said intermediate processors; repetitively sequentially examining the bits at the field rate and transmitting the first television program signal on the first video channel and the second television program signal on the second video channel if the most recently examined bit is a ''''one'''' and transmitting the first television program signal on the second video channel and the second television program signal on the first video channel if the most recently examined bit is a ''''zero;'''' examining the transmitted n-bit binary number at the said intermediate processors in synchronism with the examination thereof at the central unit; and selectively connecting a television receiving device to the first video channel for the first time period if the most recently examined bit is a ''''one'''' and to the second video channel for the second time period if the most recently examined bit is a ''''zero,'''' the first and second time periods being integral multiplex of the time of duration of one field of the television program signal.

Claim 19

In a subscriber television system having a central processor and a plurality of intermediate processors for bilateral communication with a plurality of subscriber units and unilateral communication with the central processor, a subscriber control unit coupling an individual subscriber televison receiving device to an intermediate processor comprising: a variable frequency oscillator; a mixer having one input coupled to a source of television program signals including field synchronized scrambled television program signals and another input coupled to the variable frequency oscillator; filter means coupling the mixer output to the television receiving device for supplying a single predetermined channel thereto; means for selectively varying the frequency of the variable frequency oscillator immediately prior to each field of the received scrambled television signals in accordance with an unscrambling code supplied to said intermediate processors from said central processors; and a subscriber operable free-premium switch effective in the ''''free'''' position to bypass the mixer and to supply television Program signals to the television receiving device and effective in the ''''premium'''' position to supply television program signals to the mixer, and key lock switch means having a removable key for preventing unauthorized use of the subscriber control unit when the free-premium switch is in the ''''premium'''' position.

Claim 20

In a subscriber television system having a central processor and a plurality of intermediate processors for bilateral communication with a plurality of subscriber units and unilateral communication with the central processor, a subscriber control unit coupling an individual subscriber televison receiving device to an intermediate processor comprising: a variable frequency oscillator; a mixer having one input coupled to a source of television program signals including field synchronized scrambled television program signals and another input coupled to the variable frequency oscillator; filter means coupling the mixer output to the television receiving device for supplying a single predetermined channel thereto; means for selectively varying the frequency of the variable frequency oscillator immediately prior to each field of the received scrambled television signals in accordance with an unscrambling code supplied to said intermediate processors from said central processors; and a subscriber operable free-premium switch effective in the ''''free'''' position to bypass the mixer and to supply television Program signals to the television receiving device and effective in the ''''premium'''' position to supply television program signals to the mixer, and key lock switch means having a removable key for preventing unauthorized use of the subscriber control unit when the free-premium switch is in the ''''premium'''' position.

Claim 21

The improvement of claim 16 wherein the free-premium switch is a double-pole single-throw switch with one pole thereof in series with the key lock switch means and coupling the variable frequency oscillator to an energy source therefore to thereby prevent operation of the variable frequency oscillator unless the key lock means is in the ''''on'''' position and the free-premium switch in the ''''premium'''' position.

Claim 22

The improvement of claim 6 wherein the variable frequency oscillator is voltage controlled, the control voltage determined by a plurality of binary input signals, and wherein the means for selectively varying comprises the key lock switch, the key lock switch grounding a one of said binary input signals when the switch is not in the ''''premium'''' position.