The field of the invention pertains to delivery of digital video programs over cable television (CATV) hybrid fiber coaxial (HFC) cable systems.
Many CATV systems exist in the world today. Until recently, they were used to distribute analog video broadcasts on 6 MHz wide radio frequency channels that were frequency division multiplexed.
In the last decade, with the development of MPEG compression standards and digital video program servers, video programs began to be delivered in compressed digital format. Direct broadcast satellite systems were probably the first to do this on a commercial scale. However, direct broadcast satellite systems do not have an ability to interact in real time with the user other than perhaps by telephone line modems, which to this point have only been used to collect payment information for near video on demand purchases (video programs transmitted on regular intervals which a subscriber can buy but which cannot be ordered on demand).
Cable operators would like to recover the bandwidth consumed by analog video signals and transmit more digital video channels within the same bandwidth. Digital video offers the ability to transmit more channels in the same bandwidth because approximately 10 digital, compressed video programs can be transmitted in the same 6 MHz bandwidth channel in which a single analog channel was previously transmitted. Digital video is transmitted in MPEG packets on MPEG transport streams. Each MPEG packet has a packet identifier in its header called a PID. Each video program is comprised of several program elementary streams (PES) such as video, audio, PCR timing, supplemental data, secondary language, etc. Packets of each PES of a given program have a unique PID.
The problem with substituting digital video for analog video is that, without some adapter, transmission of digital video instead of analog video on an HFC system would instantly obsolete millions of analog TVs and VCRs. Fortunately, adapters called set top decoders or set top boxes (STB) exist which can tune to RF channels on the HFC, extract the MPEG packets of a requested video program, decompress them and decrypte them, convert them to video signals, and modulate the video signals (which include audio information) onto whatever RF channel to which a TV or VCR is tuned.
In prior art set top boxes (STB), a separate remote control for the STB existed to tune the STB to a particular analog or digital video channel. The resulting output video signal would then be modulated upon analog TV channel 3 or 4 and the TV remote control did not need to be used since all channels on the HFC would be remodulated onto channel 3 or 4.
However, that leaves the problem with what to do about an analog VCR which has been programmed to record a program when the user is away. The VCR can be programmed to tune to channel 3 or 4 at a specific day and time, but this does not cause the STB to automatically tune to the appropriate channel that the user wanted to record. Some manufacturers such as Phillips (the manufacturer of TIVO® personal digital video recorders (which also can be programmed to record a program while the user is away) have attempted to solve this problem by providing an infrared transmitter that drives an infrared transducer. The infrared transmitter is controlled by the programming circuitry to generate a suitable infrared signal to cause a set top box to tune to a specific channel when the TIVO or VCR tunes to channel 3 or 4 to record the program. To use these systems, the infrared transducer must be taped or otherwise affixed to the STB in a position to direct the infrared signal into the infrared window. If something happens such as the infrared transducer being moved or dislodged or unplugged, the recording process can fail. The infrared transducer is also unsightly.
It would be more elegant and foolproof if the user could simply program an analog VCR to tune automatically to a channel to be recorded at the appropriate time and for the STB to do the rest. That is, the STB driving the VCR RF input would automatically sense to which channel the VCR just tuned. The STB would then automatically determine which video program that channel corresponds to, tune the appropriate channel, recover the appropriate MPEG or other packets, convert them to video and remodulate the video onto the RF channel to which the VCR or TV was tuned.
It would also be advantageous to be able to automatically sense the channel a user tuned to on an analog TV using the TV's remote control and determine which digtal video program that channel corresponds to and automatically tune to the channel on the HFC that program is being carried on and extract the packets carrying the data of the requested program, convert them to video signals and remodulate the video signals onto an RF carrier having the frequency of the channel to which the user tuned the TV.
Circuitry to infer the TV channel to which a user has tuned by detecting radiated energy from the local oscillator of an analog TV was disclosed in a U.S. patent application entitled METHOD AND APPARATUS FOR PROVIDING DIGITAL SET TOP BOX FUNCTION AND USING TELEVISION'S REMOTE CONTROL TO CONTROL SAME, filed Nov. 16, 2002, Ser. No. 10/295,184, which is hereby incorporated by reference. The circuitry disclosed there receives radiated energy from the local oscillator of the TV, counts its frequency and uses the frequency as a search key into a lookup table. The lookup table indicates the TV channel each local oscillator frequency corresponds to, the QAM channel on the HFC that the video program on the TV channel is being carried upon, and may, in some embodiments, indicate the PIDs of the requested program.
This approach has the weakness that spurious emissions from strong signals of local TV or radio stations, ham radio operators or harmonics thereof or electromagnetic interference from any other source can interfere with the frequency counter's accuracy. This can lead to mistakes in tuning of the STB.
Therefore, a need has arisen for a method and apparatus to reliably determine the channel to which a TVR is tuned for purposes of controlling a digital set top box to drive an analog TV or VCR.