WO1996008111A1

WO1996008111A1 - Apparatus and methods for scrambling and unscrambling video signals

Info

Publication number: WO1996008111A1
Application number: PCT/IB1994/000356
Authority: WO
Inventors: Yee Kong Ng
Original assignee: Yee Kong Ng
Priority date: 1994-09-07
Filing date: 1994-09-07
Publication date: 1996-03-14
Also published as: AU8002394A

Abstract

Apparatus and methods are provided for scrambling and unscrambling video signals. In one embodiment an apparatus (300) for scrambling video signals comprises a device for providing time, N devices for mixing a frequency with a video signal, each of the N devices for mixing a frequency, having a frequency distinct from frequencies of the other N-1 devices for mixing a frequency, a device for coupling each one of N video signals to each one of the N devices for mixing a frequency, and a device for controlling the device for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the N devices for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the device (303) for providing time. The output is a set of N scrambled video channels. To unscramble the scrambled video channels, apparatus is provided that reverses the scrambling.

Description

1 PCMB94/00356

APPARATUS AND METHODS FOR

SCRAMBLING AND UNSCRAMBLING VIDEO SIGNALS

Background of the Invention Field of the Invention: This invention relates to the transmission and reception of scrambled video signals and particularly to apparatus and methods for the scrambling and unscrambling of video signals.

Description of the Related Art: When video signals are transmitted via cable or over the air via satellite or via ground based antennas, and a supplier wishes to charge for the viewing of the video signals, the video signal is normally scrambled. To view the video signal the user must have a device for unscrambling the video signals in a manner that is the reverse of the method used for scrambling the video signals. Some methods for scrambling video signals and their corresponding drawbacks are discussed below. One method is called sine-wave modulation and with this method the video signal is scrambled by adding a predefined sine-wave onto the video signal so that a normal receiver will display a scrambled video signal to a user. This method of scrambling is inexpensive but very easy to unscramble. Also, the picture quality of the video signal can be affected because the sine-wave added to the video signal may be distorted after transmission, which may result in a distorted descrambling of the video signal.

Another method is called delete sync pulse method. In this method the synchronizing pulse from the video signal is replaced with some other wave form. With a proper descramble box the sync-pulse can be recovered from the other wave form. A normal receiver will not be able to recover the sync pulse and therefore will display a scrambled picture. The shortcoming of this method 1 PCΪ7IB94/00356

is that sync pulses have a very well defined format and thus it is possible to recover them without knowing the exact method used for replacing the sync pulse with the other wave form

Another method is called the line wrap around method. In this method the video signal is digitized line by line and then the video signal is reconstructed again by changing the starting point If the starting point chosen for each line changes, then the video signal becomes unviewable with a normal receiver A receiver must perform the descrambling in the reverse of the scrambling in order to recover the original video signal, which is very difficult for an unauthorized user to perform. However, this method requires a fast digital to analog converter, which is expensive. Also any distortion in the transmission of the video signal will result in a degraded unscrambled video signal.

In summary, the known methods for scrambling a video signal are either not very effective, or are expensive. Some of the methods are very easy to break and most of the methods result in noticeable picture degradation after descrambling.

Accordingly, there is a need in the art for apparatus and methods for scrambling and unscrambling video signals which overcome the foregoing shortcomings.

Summary of the Invention:

An object of the present invention is to provide apparatus and methods for scrambling and unscrambling video signals that solve the problems discussed above. In particular, an object of the invention is to provide apparatus and methods for reducing the risk that an unauthorized user will be able to unscramble video signals that are scrambled.

Another object of the invention is to provide a scrambling technique that does not degrade the video signal and that is not expensive.

According to the invention, methods and apparatus are provided for scrambling and unscrambling the channels of the video signals In one embodiment an apparatus for scrambling video signals comprises a device for providing time, N devices for mixing a frequency with a video signal, each of the N devices for mixing a frequency having a frequency distinct from frequencies of the other N-1 devices for mixing a frequency, a device for coupling each one of N video signals to each one of the N devices for mixing a frequency, and a device for controlling the device for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the N devices for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the device for providing time. The output is a set of N scrambled video channels. To unscramble the scrambled video channels, apparatus is provided that reverses the scrambling.

Other objects and many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed descriptions and considered in^' connection with the accompanying drawings in which like reference symbols designate like parts throughout the figures.

1

Brief Description of the Drawings:

FIG. 1 is a block diagram of an apparatus for scrambling video signals and transmitting the scrambled video signals according to the present invention;

FIG. 2 is a block diagram of a fixed RF converter according to the present invention;

FIG. 3 is a block diagram of an alternative apparatus for scrambling video signals and transmitting the scrambled video signals according to the present invention;

FIG. 4 is a block diagram of an apparatus for scrambling video signals on a single channel and transmitting the scrambled video signals according to the present invention;

FIG. 5 is a block diagram of a tunable RF generator according to the present invention;

FIG. 6 is a block diagram of a receiver for unscrambling scrambled video signals according to the present invention;

FIG. 7 is a block diagram of a RF tuner according to the present invention;

FIG. 8 is a timing diagram of a signal having a sequence of pseudorandom frequencies according to the present invention;

FIG. 9 is a timing diagram showing time inserted into a vertical blanking interval and a pseudorandom frequency signal according to the present invention;

FIG. 1 0 is a functional block diagram of a television video and data transmission system;

FIG. 1 1 is a timing diagram showing the vertical blanking interval (VBI) lines of field 1 and field 2 and showing time inserted into the VBI according to the present invention;

FIGS. 1 2A and 1 2B are flow diagrams of a method for scrambling video signals according to the present invention;

FIG. 1 3A and 1 3B are flow diagrams of another method for scrambling video signals according to the present invention; FIG. 14 is a flow diagram of another method of scrambling video signals according to the present invention;

FIG. 1 5 is a flow diagram of a method of performing step 544 of FIG. 14;

FIGS. 1 6A and 1 6B are flow diagrams of a method for unscrambling a scrambled video signal according to the present invention, and FIG. 1 7 is a flow diagram of a method of performing step 566 of FIG.

1 6A. Detailed Description

Referring now to the drawings, and more particularly, to FIG. 1 , a block diagram is shown of an apparatus for scrambling a video signal according to the present invention. Multiple video channels labeled video channel 1 , video channel 2, video channel 3 to video channel N are each coupled to an inserter

306. The inserters 306 have the purpose of inserting time into each video channel in the vertical blanking interval or into a video sideband. Alternatively, the inserters 306 can just pass the video channels to multiplexer 301 . The time that is inserted is generated by clock 303, which is read by computer 302. The output of each inserter 306 is fed to a multiplexer 301 that has N inputs and

N + 1 outputs. Each of the N inputs to the multiplexer 301 are attached to one of the inserters 306. Each of the outputs of multiplexer 301 is coupled to a fixed frequency RF converter 308. It is possible to couple any of the inserters 306 to any of the fixed frequency converters 308 by controlling multiplexer 301 . The multiplexer 301 is controlled by computer 302. The program for computer

302 is stored in EEPROM 304. Each of the fixed frequency convertor outputs are summed together in summer 310. Then the output of the summer is transmitted via satellite antenna 31 2, broadcast antenna 314, or cable 31 6.

Time can also be read from clock 303 by computer 302 and broadcast via time channel 309. The time channel is also summed by summer 310 and broadcast via the satellite antenna 31 2, the broadcast antenna of 314 or cable 31 6. The purpose of inserting the time into a video channel via the VBI or a video sideband or transmitting the time on its own time channel will be further explained below. FIG. 2 is a detailed block diagram of a fixed frequency RF converter 308.

Each fixed frequency converter 308 has an oscillator 320 that outputs a signal at a selected frequency and a mixer 31 8. The input signal from one output line of the multiplexer and the signal from oscillator 320 are mixed together in mixer 31 8 to form an output signal. Each of the multiple fixed RF converters 308 has a distinct and different frequency that is generated by its oscillator 320. If each of the multiple video channels are coupled via multiplexer 301 to a distinct one of the fixed RF converters 308, then each video channel is transmitted on a different carrier frequency. Transmitting each channel on a different frequency is the normal method of transmitting multiple channels. In FIG. 1 , the multiplexer 301 scrambles video signals by multiplexing the video channels between the fixed RF converters 308. This is done under the control of computer 302. The computer 302 multiplexes video channels 1 through N to the fixed RF converters 308 in a pseudorandom fashion. Therefore video signals on a particular video channel are scrambled by multiplexing the particular video channel between fixed RF converters. The timing of switching a video channel from one fixed RF converter to another fixed RF converter is performed as a function of the time read from clock 303 by computer 302, which controls the pseudorandom switching of multiplexer 301 .

Since a particular video channel is multiplexed between fixed RF converters in a pseudorandom manner, a viewer watching a normal receiver tuned to a particular channel would see video from the multiple channels but would not see a particular video channel for an extended period of time.

Therefore, it would be impossible for the viewer to view a program on a normal receiver.

In one embodiment only one video channel is switched from one fixed RF converter 308 to another fixed RF converter 308 at any one time. Since there are N video channels and N + 1 fixed RF converters, it is guaranteed that there is one fixed RF converter that is not being used by a video channel immediately previous to switching a particular video channel from one fixed RF converter to another fixed RF converter. In this embodiment the video channel that is being switched from one fixed RF converter to another fixed RF converter can be momentarily coupled via multiplexer 301 to both the fixed RF converter to which it is switching from and to the fixed RF converter 308 to which it is switching to. This makes it easier for a receiver to unscramble the scrambled video signals of the selected video channel. Since the video channel being switched is coupled to two fixed RF converters at one time, the receiver can have additional time to switch to the proper frequency to match the fixed RF frequency of the fixed RF converter 308 to which the video channel is being switched.

Since the timing of switching video channels between fixed RF converters is controlled by the pseudorandom control generated computer 302 which is a function of time read from clock 303, it is advantageous to transmit the time read from clock 303 to receivers so that they can properly unscramble the video channels. Three alternative methods of transmitting the time to the receivers are shown in FIG. 1 . In the first method the time is inserted into the vertical blanking interval of each video channel. In the second method the time is inserted into a video sideband of each video channel. In another method the time is sent on a separate time channel which can be received by the receiver and decoded to determine the time. Each of these method allows the receiver to synchronize with the transmitter in order unscramble the scrambled video signals.

FIG. 3 is another embodiment for scrambling the channels carrying video signals. The embodiment is very similar to the embodiment of FIG. 1 except that the N by N + 1 multiplexer 301 of FIG. 1 is replaced by an N by N multiplexer

332 as shown in FIG. 3. The operation of the apparatus of FIG. 3 is similar to the apparatus of FIG. 1 except that because there are N video channels and N fixed RF converters 308, all of the video channels are switched between the fixed RF converters 308 at one time. Thus, in the same manner as in FIG. 1 a particular video channel is switched between frequencies, because each fixed RF converter 308 is tuned to generate a different RF frequency. The outputs of the fixed RF converters 308 are summed in summer 310 and then the output of summer 310 is transmitted by satellite antenna 31 2, broadcast antenna 314 or cable 31 6. FIG. 4 is another embodiment for scrambling video signals assigned to a single channel. In FIG. 4 the video signals for a particular video channel are input to an inserter 342 which inserts a time into either the vertical blanking interval or into a video sideband of a video channel. The time is read from clock 303 by computer 346. The computer 346 is under the control of a program stored in an EEPROM 350. The output of inserter 342 is sent to a tunable RF converter

344. FIG. 5 shows a detail of tunable RF converter 344 which includes a mixer 360 and a tunable oscillator 362. The oscillator 362 is controlled by computer 346 to generate a signal having a sequence of pseudorandom frequencies. The timing of the sequence of pseudorandom frequencies is a function of the time read from clock 303. The output of the tunable RF converter 344 is a video channel that has a pseudorandom carrier frequency. The output of the tunable RF converter is sent to transmitter 348 which then transmits the scrambled video signal via satellite antenna 352, broadcast antenna 354, or cable 356.

In the embodiment shown in FIG. 4 it is also possible to transmit time to the receiver via a separate time channel as shown by time channel 309 which is connected to computer 346 and transmitter 348. Time is transmitted via the VBI or video sideband or separate time channel for the same purpose as discussed above.

FIG. 6 is a block diagram of an apparatus for unscrambling a scrambled video signal according to the present invention. As shown in FIG. 6 the scrambled video signal can be received via an antenna 384, a cable 386, or a satellite antenna 388. Each of these possible sources are coupled to an input amplifier 382 which selects between the sources under the control a microcomputer 392. The output of the input amplifier 382 is sent to an RF tuner 384 and to a time extractor 388, which has the purpose of extracting from the received signal the time that has been transmitted from the transmitter as discussed above in the description of the embodiments of FIGS. 1 , 3 and 4. The microcomputer 392 is under the control of a program stored in EEPROM 394 and uses the extracted time to synchronize a pseudorandom frequency control sent from the microcomputer 392 to the RF tuner 384. The time is extracted from either a vertical blanking interval or video sideband of a received signal or from a separate time channel. Knowing the time allows the receiver to synchronize the timing of the RF tuner 392 to the pseudorandom switching frequency of a video channel to a transmitter. If the clock 393 at the receiver and the clock 303 at the transmitter are accurate, then the time read from clock 393 can be used to synchronize the receiver rather than extracting time from the received signal. Using a clock 393, which can be reset to accurate time whenever desired either manually or automatically by time setting information sent via the VBI or other means, may also be less expensive.

The program for controlling the descrambling can be supplied by disk and downloaded over a phone line connection to the microcomputer 392 or carried via the VBI of one or more programs or channels for setting up the receiver for descrambling. Each such program may be useful for a selected period of time, such as a day or week, before being replaced by a new scrambling/descrambling program.

FIG. 7 shows a detailed diagram of the RF tuner 384 which consists of a mixer 41 2 and an oscillator 410. The oscillator is controlled to switch between frequencies by the pseudorandom frequency control signal received from microcomputer 392 under the control of the program in the EEPROM 394. The time that is extracted from the RF signal or read from clock 393 indicates how to synchronize the pseudorandom frequency control signal with the received scrambled video signal. Thus, the output of RF tuner 384 is a video signal which is unscrambled. The output is sent to IF amplifier and demodulator 386 to mix the RF signal down to video frequencies. An automatic gain control circuit 400 and an automatic frequency tracking circuit 402 are connected to the output of the IF amplifier and demodulator 386, as shown in FIG. 6, and provide an input to microcomputer 392 to provide gain control and frequency tracking functions for the receiver. The output of the IF amplifier and demodulator 386 is composed of an audio signal and a video signal. The audio signal is sent to audio control 398, which is controlled from microcomputer 392 to lower the volume of the audio when the microcomputer 392 controls the RF tuner 384 to switch frequencies. This volume control of the audio output reduces noise that would otherwise result in the audio output when the RF tuner is switched between frequencies. An RF modulator 404 converts the audio and video output signals back to an RF output signal to be used by other equipment. Any external control for any initializing setting required by microcomputer 392 can be provided via a keypad 397 or from a remote controller via IR receiver 396. The initializing settings can also be downloaded over a phone line connection to the microcomputer 392 or carried via the VBI of one or more selected programs or channels.

FIG. 8 is a timing diagram illustrating the timing of shifting frequencies on a particular video channel. During time period T, the channel is illustrated at carrier frequency 1 . During time period T + 1 the frequency has shifted to frequency 5. During time period T + 2 the frequency is frequency 2, and during time period T + 3 the frequency is frequency 9. During time period T + 4 the frequency is frequency 4. Frequencies 1 , 5, 2 etc. represent the pseudorandom carrier frequencies for a video channel. Only a portion of the frequency changes for a channel is illustrated in FIG. 8. The change in frequency is continued to scramble the desired program or series of programs or all programs of a channel.

FIG. 9 is a timing diagram of a video signal indicating that a time 452 is inserted into a vertical blanking interval 450. As shown in FIG. 9, the time is inserted immediately before a frequency shift. The insertion of time into the vertical blanking interval 450 can be continuous or periodic, as shown in FIG. 9.

The switching of the video signal from frequency 1 to frequency 5 is illustrated as occurring during a vertical blanking interval 450. Switching the video signal frequency during a vertical blanking interval helps to reduce or eliminate any signal degradation. A detailed explanation of normal television raster scan and the vertical blanking interval is in U.S. Patent application Serial No. 08/1 76,852, which is incorporated herein by this reference as though set forth in full. Also the insertion of data such as closed caption information and extended data service information is disclosed in detail in the application and it is also incorporated herein by this reference for this description.

FIG. 10 is a functional block diagram of a data transmission system. As used herein, the terms "broadcast" and "transmit" are used interchangeably for the transmission of signals over cable or fiber optics, to or from satellites, to or from ground based antennas and the like. A network head end 10001 transmits a composite television signal containing inserted information in a portion thereof, typically the vertical blanking interval, to a satellite 10002 which rebroadcasts the same to a local affiliate 10003. The affiliate 10003 may further insert data into the vertical blanking interval of the received television signal and transmit the same to a local cable head end 10004. The cable head end 10004 receives television signals from a plurality of sources (including satellites) and may further insert data into the vertical blanking interval of any of the television signals. The signals from the plurality of sources are combined into a composite television signal, amplified, and provided over a cable to a plurality of individual receivers 1 0005, which can include televisions, cable boxes, VCRs and satellite receivers. In addition, the individual receivers 1 0005 may receive signals directly from the local affiliate 10003 by air, which may include the use of a satellite 10002, or by cable.

More specifically, the network head end has a video tape recorder (VTR) 10006 for providing a program signal to an inserter 10007. A controller 10008 also at the head end controls the scheduling of loading tapes from a cart (a machine with a plurality of video tape cassettes which are moved by a robotic arm from a storage location and inserted into a video tape recorder and vice versa). Furthermore, the controller 1 0008 controls the lighting of stages during live broadcasts, such as news broadcasts. The controller 10008 is typically a microprocessor based system. A traffic computer 10009 controls the exact timing of playing individual segments of video tapes and inserting commercials therebetween as well as switching between different programs. Some network head ends have both a traffic computer 10009 and a controller 10008. The controller 10008 provides data and commands to the inserter 10007 The traffic computer 10009 provides data and commands to the controller if present. Otherwise, the traffic computer 10009 provides these signals directly to the inserter 10007. The inserter 10007 inserts data into the vertical blanking interval of the composite television signal, as will be described below, and provides the television signal to a transmitter 10010 which in turn provides the television signal on a microwave carrier to a satellite dish 1001 1 for transmission to the satellite 10002. The satellite 10002 retransmits the received signal, which is received by a satellite dish 1001 2 at the affiliate 10003. The dish provides the signal to a station inserter 1001 3 at the local affiliate 10003. The affiliate may also insert data into the composite television signal as will be described below. The television signal is then provided to a transmitter 1 001 4 and then to a transmitting antenna 1001 5.

A local cable operator 10004 has a plurality of satellite dishes 1001 6 and antennas 10017 for receiving signals from a plurality of networks 10001 and affiliates 10003. The received signal from each of the dishes 1001 6 and antennas 10017 is provided to a respective input of a multi-channel inserter 1 001 8, which can input data into the vertical blanking interval of a received signal. The multi-channel output from the inserter 1 001 8 is amplified in an amplifier 1001 9 and provided over a cable 10020 to individual receivers 10005.

Alternately the receivers 10005 could receive broadcast information via antennas or satellite receivers.

Each receiver 10005 includes a VBI decoder, which can include a VBI slicer and closed caption decoder, that scans VBI lines 10-21 of both fields 1 and 2. In addition it is possible to use the first few visible lines in each video frame for VBI data, for example, lines 22-24. Lines 1 through 9 are typically used for vertical synchronization and equalization and, thus, are not used to transmit data. Closed captioning and text mode data are generally transmitted on VBI line 21 , field 1 of the standard NTSC video signal, at a rate of 2 bytes for each VBI line 21 , field 1 , as shown by closed caption data 1 1 2 in FIG. 1 2. The text mode fields fill the entire screen with text. The default mode is an open ended mode in which the page is first filled up and then scrolled up. The individual recipient of such data has no control over the data. Extended data services (EDS) data can be transmitted on VBI line 21 , field 2, as shown by EDS data 1 1 6 in FIG. 1 1 , at a rate of 2 bytes per VBI line 21 , field 2.

^• By way of background, the data in the vertical blanking interval can be described in terms of the wave form, its coding and the data packet. The closed caption data wave form, for example, has a clock run-in followed by a frame code, followed by the data as shown in the above referenced U.S. Patent application Serial No. 08/1 76,852. The coding of the data is non-return-to-zero

(NRZ) 7 bit odd parity.

The data inserted into the television signal by the various inserters typically includes closed captioning data and EDS data. The inserted data can also include other data such as the time, as shown by data 1 1 4 in FIG. 1 1 . The data can be inserted into either or both fields in any VBI line between 10 and 20.

For example the data can be inserted into line 20 of field 2, as shown by the data 1 14 in FIG. 1 1 . The data may be inserted into the VBI at the closed caption rate ( 1 X format) or at two times the closed caption rate (2X format). These data rates are fully explained in U.S. Patent application Serial No. 08/1 76,852; which is incorporated herein by this reference as though set forth in full. The standard data transmission rate is defined in the Recommended Practice for Line 21 Data Service. Electronics Industries Association, EIA-608 (drafts October 1 2, 1 992 and June 1 7, 1 993) (referred to as "EIA-608" standard"). The subject matter of which is incorporated herein by reference.

The data may be manually entered from a local terminal 10021 . The local terminal 10021 may be used to pre-build, recall, or edit messages. The terminal 1 0021 typically includes a computer. In addition, a modem 10022 may be used to provide data to the inserter 10007. The data may be provided manually or automatically from remote sites, such as a television program guide publisher or the network head end. The output of the inserter 10007 is a composite television signal with the data inserted. The video signal can also be sent in the PAL format, which is used in many countries including China and time can be inserted into the video signal in the manner described above.

FIG. 1 2A is a flow diagram of a method for scrambling video signals using the apparatus if FIG. 4. In step 500 a time is read from a clock. Then in step 502 a signal having a sequence of pseudorandom frequencies is generated as a function of the time read from the clock. In step 504, the time read from the clock is inserted into a vertical blanking interval of a video signal or into a video sideband of a video signal or into a separate time transmission channel Then in step 506 the signal having a generated sequence of pseudorandom frequencies is combined with the video signal to form a combined signal. Then if time has been inserted into a separate time channel, then in step 508 the time channel is summed together with the combined signal. If a time channel is not used then step 508 is skipped. Then in step 510 the signal is transmitted over the air via satellite or via ground based antenna or via cable. FIG. 1 2B is a method of generating a pseudorandom frequency. In step

51 2, the time read from the clock is converted to a pseudorandom code. Then in step 514 a signal is generated having a frequency that is a function of the pseudorandom code.

FIG. 1 3A is a flow diagram of a method for scrambling a video signal using the apparatus shown in FIG. 3. In step 520 a time is read from a clock.

Then in step 522 the time read from the clock is inserted into a vertical blanking interval of N separate video signals, or into a video sideband of N separate video signals, or the time is inserted into a separate time channel. Then in step 524, a switch is controlled as a function of the time read from the clock to pseudorandomly couple each one of N video signals to a distinct one of N mixers. Each of the N mixers mixes a frequency distinct from the other N- 1 mixers with the video signal coupled to that mixer. Then in step 526 the outputs of the N mixers are summed. If time is being transmitted in a time channel then in step 528 the time channel is summed with the outputs of the N mixers. Then in step 530 the summed output is transmitted over the air via satellite or via ground based antennas or via cable. FIG. 1 3B is a flow diagram of a method for controlling the switch to pseudorandomly couple the video signals to the mixers. In step 532, the time read from the clock is converted to a pseudorandom code. Then in step 534 control is generated to the switch, the control being a function of the pseudorandom code. FIG. 14 is a flow diagram of a method for scrambling video channels using the apparatus shown in FIG. 1 . In step 540, time is read from a clock. Then in step 542, the time read from the clock is inserted into a vertical blanking interval of N separate video signals, or into a video sideband of N separate video signals. Alternately the time can be inserted into a separate time channel. Then in step 544 a switch is controlled to pseudorandomly couple as a function of the time read from the clock, each one of N video signals to a distinct one of N + 1 mixers. Each of the N + 1 mixers mixes a frequency distinct from the other N mixers with the video signal coupled to that mixer. Then in step 546 the output of the N + 1 mixers is summed. If a time channel is being used to transmit the time, then in step 548 the time channel is summed with the output of the N + 1 mixers. Then in step 550, the summed output is transmitted over the air via satellite or ground based antennas or via cable.

FIG. 1 5 is a step that further refines step 544 of FIG. 14. In step 552, multiplexer 301 is controlled so that only one of the N video signals is switched at any one time from a first one of the N + 1 converters to a second one of the

N + 1 converters. The second one of the N + 1 converters is not coupled to any of the N video signals immediately previous to the time of the coupling of one of the N video signals to the second one of the N + 1 converters.

FIG. 1 6A is a flow diagram of a method for unscrambling a video signal according to the present invention. The apparatus shown in FIG. 6 can be used to perform this method. In step 560, time is read from a clock or extracted from a vertical blanking interval or from a video sideband of a received signal or from a separately received time channel. Then in step 562, a frequency generator is controlled as a function of the time read from the clock or the extracted time, to generate a signal having a sequence of pseudorandom frequencies. Then in step 564 a received video signal is mixed with the generated signal having a sequence of pseudorandom frequencies to form a mixer output signal. Then in step 566 an audio output of the mixer is controlled to control the volume of the audio output.

FIG. 1 6B is a method of generating a sequence of pseudorandom frequencies, as shown in step 562. In step 568, the time read from the clock or the extracted time is converted to a pseudorandom code. Then in step 570 a frequency generator is controlled to generate a signal having a frequency that is a function of the pseudorandom code.

FIG. 1 7 is a further refinement of step 566 as shown in FIG. 1 6. In step 572 the volume of the output is lowered when the frequency generator is controlled to switch from one frequency to another frequency.

Thus apparatus and methods have been described for scrambling and unscrambling video signals, which reduce the risk that an unauthorized user will be able to unscramble video signals that are scrambled and provide a scrambling technique that does not degrade the video signal. The described embodiments of the invention are only considered to be preferred and illustrative of the inventive concept, the scope of the invention is not to be restricted to such embodiments. Various and numerous other arrangements may be devised by one skilled in the art without departing from the spirit and scope of this invention. It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1 . An apparatus for scrambling video signals comprising: means for generating a signal; means for providing time; means for controlling the means for generating a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the means for providing time; and means for mixing the generated signal having a sequence of pseudorandom frequencies with a video signal to form an output signal.

2. The apparatus of Claim 1 further comprising a means for transmitting the output signal.

3. The apparatus of Claim 1 wherein the means for controlling the means for generating a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the means for providing time further comprises: means for converting time read from the means for providing time to a pseudorandom code; and means for generating a signal having a frequency, the frequency being a function of the pseudorandom code.

4. The apparatus of Claim 1 further comprising means for inserting time read from the means for providing time into a vertical blanking interval of the video signal.

5. The apparatus of Claim 1 further comprising means for inserting time read from the means for providing time into a video sideband of the video signal.

6. The apparatus of Claim 1 further comprising: means for inserting time read from the means for providing time into a time transmission channel; and means for transmitting the time transmission channel.

7. The apparatus of Claim 1 wherein the means for controlling comprises a computer.

8. The apparatus of Claim 1 wherein the means for mixing comprises a mixer.

9. An apparatus for scrambling video signals comprising: means for providing time;

N means for mixing a frequency with a video signal, each of the N means for mixing a frequency having a frequency distinct from frequencies of the other N- 1 means for mixing a frequency; means for coupling each one of N video signals to each one of the N means for mixing a frequency; and means for controlling the means. for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the N means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the means for providing time.

10. The apparatus of Claim 9 further comprising: means for summing an output of each of the N means for mixing a frequency with a video signal; and means for transmitting the summed output.

1 1 . The apparatus of Claim 9 wherein the means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the N means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the means for providing time, further comprises: means for converting time read from the means for providing time to a pseudorandom code; and means for generating a control to the means for coupling, the control being a function of the pseudorandom code.

1 2. The apparatus of Claim 9 further comprising means for inserting time read from the means for providing time into a vertical blanking interval of the N video signals.

13. The apparatus of Claim 9 further comprising means for inserting time read from the means for providing time into a video sideband of the N video signals.

14. The apparatus of Claim 9 further comprising: means for inserting time read from the means for providing time into a time transmission channel; and means for transmitting the time transmission channel.

1 5. The apparatus of Claim 9 wherein the means for controlling comprises a computer.

1 6. The apparatus of Claim 9 wherein the means for coupling comprises a crossbar switch.

1 7. An apparatus for scrambling video signals comprising: means for providing time; a plurality of at least N + 1 means for mixing a frequency with a video signal, each of the plurality of at least N + 1 means for mixing a frequency having a frequency distinct from frequencies of the other means for mixing a frequency; means for coupling each one of N video signals to each one of the plurality of at least N + 1 means for mixing a frequency; and means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the plurality of at least

N + 1 means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the means for providing time.

1 8. The apparatus of Claim 1 7 wherein the means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the plurality of at least N + 1 means for mixing a frequency further comprises first means for only switching at one time the coupling of one of the video signals from a first one of the plurality of means for mixing a frequency to a second one of the plurality of means for mixing a frequency.

1 9. The apparatus of Claim 1 8 wherein the second one of the plurality of means for mixing a frequency is not coupled to any of the N video signals immediately previous to being coupled to one of the N video signals.

20. The apparatus of Claim 19 further comprising: means for summing an output of each of the plurality of means for mixing a frequency with a video signal; and means for transmitting the summed output.

21 . The apparatus of Claim 1 7 wherein the means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the plurality of means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the means for providing time, further comprises: means for converting time read from the means for providing time to a pseudorandom code; and means for generating a control to the means for coupling, the control being a function of the pseudorandom code.

22. The apparatus of Claim 1 7 further comprising means for inserting time read from the means for providing time into a vertical blanking interval of the N video signals.

23. The apparatus of Claim 1 7 further comprising means for inserting time read from the means for providing time into a video sideband of the N video signals.

24. The apparatus of Claim 1 7 further comprising: means for inserting time read from the means for providing time into a time transmission channel; and . means for transmitting the time transmission channel.

25. The apparatus of Claim 1 7 wherein the means for controlling comprises a computer.

26. The apparatus of Claim 1 7 wherein the means for coupling comprises a crossbar switch.

27. An apparatus for unscrambling video signals comprising: means for providing time; means for generating a signal; means for controlling the means for generating a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the means for providing time; and means for mixing the generated signal having a sequence of pseudorandom frequencies with a received video signal.

28. The apparatus of Claim 27 further comprising a means for controlling an audio output of the means for mixing, the means for controlling an audio output coupled to the means for controlling the means for generating a signal.

29. The apparatus of Claim 28 wherein the means for controlling an audio output further comprises means for lowering the volume of the audio output when the means for controlling switches the means for generating a frequency from one pseudorandom frequency to another pseudorandom frequency.

30. The apparatus of Claim 27 wherein the means for controlling the means for generating a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the means for providing time further comprises: means for converting time read from the means for providing time to a pseudorandom code; and means for generating a signal having a frequency, the frequency being a function of the pseudorandom code.

31 . The apparatus of Claim 27 wherein the means for providing time further comprises a clock.

32. The apparatus of Claim 27 wherein the means for providing time further comprises means for extracting time from a vertical blanking interval of the received video signal.

33. The apparatus of Claim 27 wherein the means for providing time further comprises means for extracting time from a video sideband of the received video signal.

34. The apparatus of Claim 27 wherein the means for providing time further comprises means for extracting time from a transmitted time channel.

35. The apparatus of Claim 27 wherein the means for controlling comprises a computer.

36. A method for scrambling video signals comprising the steps of: generating a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time; and mixing the generated signal having a sequence of pseudorandom frequencies with a video signal to form an output signal.

37. The method of Claim 36 further comprising the step of transmitting the output signal.

38. The method of Claim 36 wherein the step of generating a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time further comprises the steps of: converting time read from the means for providing time to a pseudorandom code; and generating a signal having a frequency, the frequency being a function of the pseudorandom code.

39. The method of Claim 36 further comprising the step of inserting time into a vertical blanking interval of the video signal.

40. The method of Claim 36 further comprising the step of inserting time into a video sideband of the video signal.

41 . The method of Claim 36 further comprising the steps of: inserting time into a time transmission channel; and transmitting the time transmission channel.

42. A method for scrambling video signals comprising the steps of: providing N means for mixing frequency with a video signal, each of the N means for mixing a frequency, having a frequency distinct from frequencies of the other N-1 means for mixing a frequency; coupling each one of N video signals to each one of the N means for mixing a frequency; and controlling the coupling to pseudorandomly couple each one of the N video signals to a distinct one of the N means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time.

43. The method of Claim 42 further comprising the steps of: summing an output of each of the N means for mixing a frequency with a video signal; and transmitting the summed output.

44. The method of Claim 42 wherein the step of controlling the coupling to pseudorandomly couple each one of the N video signals to a distinct one of the N means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time, further comprises the steps of: converting time to a pseudorandom code; and generating a control, the control being a function of the pseudorandom code.

45. The method of Claim 42 further comprising the step of inserting time into a vertical blanking interval of the N video signals.

46. The method of Claim 42 further comprising the steps of inserting time into a video sideband of the N video signals.

47. The method of Claim 42 further comprising the steps of: inserting time into a time transmission channel; and transmitting the time transmission channel.

48. A method for scrambling video signals comprising the steps of: providing a plurality of at least N + 1 means for mixing a frequency with a video signal, each of the plurality of at least N + 1 means for mixing a frequency, having a frequency distinct from frequencies of the other means for mixing a frequency; coupling each one of N video signals to each one of the plurality of at least N + 1 means for mixing a frequency; and controlling the coupling to pseudorandomly couple each one of the N video signals to a distinct one of the plurality of at least N + 1 means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time.

49. The method of Claim 48 wherein the step of controlling further comprises the step of only switching at one time the coupling of one of the video signals from a first one of the plurality of means for mixing a frequency to a second one of the plurality of means for mixing a frequency.

50. The method of Claim 49 wherein the second one of the plurality of means for mixing a frequency is not coupled to any of the N video signals immediately previous to being coupled to one of the N video signals.

51 . The method of Claim 50 further comprising the steps of: summing an output of each of the plurality of means for mixing a frequency with a video signal; and transmitting the summed output..

52. The method of Claim 48 further comprising the step of inserting time into a vertical blanking interval of the N video signals.

53. The method of Claim 48 further comprising the steps of inserting time into a video sideband of the N video signals.

54. The method of Claim 48 further comprising the steps of: inserting time into a time transmission channel; and transmitting the time transmission channel.

55. A method for unscrambling video signals comprising the steps of: controlling the generation of a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time; and mixing the generated signal having a sequence of pseudorandom frequencies with a received video signal.

56. The method of Claim 55 further comprising the step of controlling an audio output of the step of mixing.

57. The method of Claim 56 wherein the means for controlling an audio output further comprises the steps of means for lowering the volume of the audio output when the means for controlling switches the means for generating a frequency from one pseudorandom frequency to another pseudorandom frequency.

58. The method of Claim 56 wherein the step of controlling the generation of a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time further comprises the steps of: converting time to a pseudorandom code; and generating a signal having a frequency, the frequency being a function of the pseudorandom code.

59. The method of Claim 56 further comprising the step of extracting time from a vertical blanking interval of the received video signal.

60. The method of Claim 56 further comprising the step of extracting time from a video sideband of the received video signal.

61 . The method of Claim 56 further comprising the step of extracting time from a transmitted time channel. AMENDED CLAIMS

[received by the International Bureau on 8 January 1996 (08.01 .96) ; new claims 62-79 added ; remai ning claims unchanged (7 pages ) ] 55. A method for unscrambling video signals comprising the steps of: controlling the generation of a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time; and mixing the generated signal having a sequence of pseudorandom frequencies with a received video signal.

61 . The method of Claim 56 further comprising the step of extracting time from a transmitted time channel.

62. A system for scrambling video signals at a central stations and unscrambling the video signal at a plurality of receiving stations, the system comprising: central station equipment comprising; 08111 PCMB94/00356

first means for generating a signal, first means for providing time, means for controlling the first means for generating a signal to generate a first signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the first means for providing time, means for mixing the generated first signal having a sequence of pseudorandom frequencies with a video signal to form an output signal, and means for transmitting the output signal, and equipment at each receiving site comprising; second means for providing time, means for generating a signal, means for controlling the means for generating a signal to generate a second signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the second means for providing time, means for receiving the output signal, and means for mixing the generated signal having a sequence of pseudorandom frequencies with the received output signal.

63. The system of claim 62 wherein: the means for controlling the first means for generating a signal to generate a first signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the first means for providing time comprises: means for converting time read from the first means for providing time to a pseudorandom code; and means for generating a first signal having a frequency, the frequency being a function of the pseudorandom code; and the means for controlling the second means for generating a signal to generate a second signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the second means for providing time comprises: means for converting time read from the second means for providing time to a pseudorandom code; and 8111 PCMB94/00356

means for generating a second signal having a frequency, the frequency being a function of the pseudorandom code.

64. The system of claim 62 further comprising: means for inserting time read from the first means for providing time into a vertical blanking interval of the output signal; and means for extracting the inserted time from the vertical blanking interval and loading the extracted time into the second means for providing time.

65. The system of claim 62 further comprising: means for inserting time read from the first means for providing time into a time transmission channel; means for transmitting the time transmission channel; and means for extracting the inserted time from the time transmission channel and loading the extracted time into the second means for providing time.

66. A system for scrambling video signals at a central station and unscrambling the video signal at a plurality of receiving stations, the system comprising: central station equipment comprising: first means for providing time;

N means for mixing a frequency with a video signal, each of the N means for mixing a frequency, having a frequency distinct from frequencies of the other N-1 means for mixing a frequency, means for coupling each one of N video signals to each one of the N means for mixing a frequency, means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the N means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the first means for providing time, means for summing an output of each of the N means for mixing a frequency with a video signal, and means for transmitting the summed output, and equipment at each receiving site comprising; second means for providing time, second means for generating a signal, means for controlling the second means for generating a signal to generate a second signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the second means for providing time, means for receiving the transmitted output, and means for mixing the second generated signal having a sequence of pseudorandom frequencies with the received output.

67. The system of claim 66 wherein: the means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the

N means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the first means for providing time, further comprises: means for converting time read from the first means for providing time to a pseudorandom code, and means for generating a control to the means for coupling, the control being a function of the pseudorandom code, and the means for controlling the second means for generating a signal to generate a second signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the second means for providing time comprises: means for converting time read from the second means for providing time to a pseudorandom code, and means for generating a second signal having a frequency, the frequency being a function of the pseudorandom code.

68. The system of claim 66 further comprising: means for inserting time read from the first means for providing time into a vertical blanking interval of the N video signals; and means for extracting the inserted time from the received output and loading the extracted time into the second means for providing time.

69. The system of claim 66 further comprising: means for inserting time read from the first means for providing time into a video sideband of the N video signals; and means for extracting the inserted time from the received output and loading the extracted time into the second means for providing time.

70. The system of claim 66 further comprising: means for inserting time read from the first means for providing time into a time transmission channel; means for transmitting the time transmission channel; and means for extracting the inserted time from the received output and loading the extracted time into the second means for providing time.

71 . The system of claim 66 wherein the means for coupling comprises a crossbar switch.

72. A system for scrambling video signals at a central station and unscrambling the video signal at a plurality of receiving stations, the system comprising: central station equipment comprising; first means for providing time, a plurality of at least N + 1 means for mixing a frequency with a video signal, each of the plurality of at least N + 1 means for mixing a frequency, having a frequency distinct from frequencies of the other means for mixing a frequency, means for coupling each one of N video signals to each one of the plurality of at least N + 1 means for mixing a frequency, and means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the plurality of at least N + 1 means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the first means for providing time, means for summing an output of each of the N + 1 means for mixing a frequency with a video signal, means for transmitting the summed output, and equipment at each receiving site comprising; second means for providing time, means for generating a signal, means for controlling the means for generating a signal to generate a signal having a sequence of pseudorandom frequencies, the pseudorandom frequencies being generated as a function of time read from the second means for providing time, means for receiving the transmitted output, and means for mixing the generated signal having a sequence of pseudorandom frequencies with the received output.

73. The system of claim 72 wherein the means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the plurality of at least N + 1 means for mixing a frequency further comprises first means for only switching at one time the coupling of one of the video signals from a first one of the plurality of means for mixing a frequency to a second one of the plurality of means for mixing a frequency.

74. The system of claim 73 wherein the second one of the plurality of means for mixing a frequency is not coupled to any of the N video signals immediately previous to being coupled to one of the N video signals.

75. The system of claim 72 wherein the means for controlling the means for coupling to pseudorandomly couple each one of the N video signals to a distinct one of the plurality of means for mixing a frequency, the controlling of the pseudorandom coupling being a function of time read from the first means for providing time, further comprises: means for converting time read from the means for providing time to a pseudorandom code; and means for generating a control to the means for coupling, the control being a function of the pseudorandom code.

76. The system of claim 72 further comprising: means for inserting time read from the first means for providing time into a vertical blanking interval of the N video signals; and means for extracting the inserted time from the received output and loading the extracted time into the second means for providing time.

77. The system of claim 72 further comprising: means for inserting time read from the first means for providing time into a video sideband of the N video signals; and means for extracting the inserted time from the received output and loading the extracted time into the second means for providing time.

78. The system of claim 72 further comprising: means for inserting time read from the first means for providing time into a time transmission channel; means for transmitting the time transmission channel; and means for extracting the inserted time from the received output and loading the extracted time into the second means for providing time.

79. The system of claim 72 wherein the means for coupling comprises a crossbar switch.