GB2323748A - Video telephony - Google Patents
Video telephony Download PDFInfo
- Publication number
- GB2323748A GB2323748A GB9803518A GB9803518A GB2323748A GB 2323748 A GB2323748 A GB 2323748A GB 9803518 A GB9803518 A GB 9803518A GB 9803518 A GB9803518 A GB 9803518A GB 2323748 A GB2323748 A GB 2323748A
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- United Kingdom
- Prior art keywords
- signal
- subscriber
- video telephony
- video
- filter
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/14—Systems for two-way working
- H04N7/141—Systems for two-way working between two video terminals, e.g. videophone
- H04N7/148—Interfacing a video terminal to a particular transmission medium, e.g. ISDN
Abstract
A video modulator (114) modulates a baseband video telephony signal received from a communication system (102) to produce a modulated video telephony signal. The modulated video telephony signal is filtered 116 and shifted to a subscriber channel bandwidth and coupled through a directional coupler (110) to a subscriber cable network (118). The subscriber can view the video telephony signals on any television (122) connected to the subscriber cable network (118) by tuning the television (122) to the frequency of the subscriber channel bandwidth.
Description
2323748 METHOD AND APPARATUS FOR PROVIDING VIDEO SIGNAL DISTRIBUTION IN A
VIDEO TELEPHONY SYSTEM
Background
The present invention relates, in general, to video telephony and more particularly to distribution of video telephony signals.
Current audio/visual telephony systems are typically implemented on Personal Computer (PC) systems, as roll- about/room systems or as stand-alone videophones. These systems typically require new hardware, software, programming, and network connections such as Integrated Services Digital Network (ISDN).
Current systems are limited to providing audio/visual functionality only at designated nodes. For example, when a PC is equipped with the necessary hardware, software, programming and network connections, the audio/visual telephony function is available only at that PC. For other PCs to become audio/visual telephony capable, they too must be retrofitted with the necessary hardware, software, programming and network connection. Roll-about/room systems and stand-alone videophones also only allow for audio/visual functionality at their physical location.
The received video signal in conventional systems can only be observed by the subscriber on the video monitor coupled directly to the audio/visual equipment and does not allow for viewing the incoming telephony video signal at different locations within the subscriber premise.
Therefore, there exists a need for a method and apparatus for distributing a video telephony signal within a subscriber premise.
2 Brief Description of the Drawings
FIG. 1 is a block diagram of a video telephone system located at the subscriber premise in accordance with the present invention.
FIG. 2 is a block diagram of a video distribution apparatus in accordance with a preferred ercLbod-Lmen'g- of the present invention.
FIG. 3 is a flow chart of a method in accordance with a preferred embodiment of the present invention.
FIG. 4 is a block diagram of a first alternate embodiment in accordance with the present invention.
FIG. 5 is a flow chart of a method in accordance with a first alternate embodiment of the present invention.
FIG. 6 is a block diagram of a second alternate embodiment in accordance with the present invention.
FIG. 7 is a flow chart of a method in accordance with a second alternate embodiment of the present invention.
FIG. 8 is a block diagram of a third alternate embodiment in accordance with the present invention.
FIG. 9 is a flow chart of a method in accordance with a third alternate embodiment of the present invention.
Detailed Description of the Preferred Embodiment
The present invention provides a method and apparatus for distributing video telephony signals within a subscriber premise.
Video telephony signals, in addition to other signals such as downstream video programming signals, 3 are received through a coaxial cable at the subscriber premise. The video telephony signals are transmitted to the subscriber premise using a signaling protocol such as Integrated Services Digital Network (ISDN), Cable Access Communication System (CACS) (discussed below), V.34 or other protocols or combination of protocols capable of transmitting video telephony signals. A directional coupler directs incoming video telephOny signals to a cable access unit (CAU). The CAU demodulates the video telephony signals to produce a compressed video telephony signal. A video decompressor converts the compressed video telephony signals to a baseband video telephony signal. A video distribution apparatus modulates and filters the baseband video telephony signal to produce a radio frequency video telephony signal which is injected into the directional coupler and transmitted through the subscriber cable network.
FIG. 1 is a block diagram of a video telephone system 100 in accordance with the present invention. Video telephony signals are received at the subscriber premise 101 from a communication system 102 over a coaxial cable 104. The communication system 102 is, preferably, a cable television telephony system utilizing hybrid fiber/coax cabling. However, any communication system capable of transmitting video telephony signals can be used. Video telephony signals and other signals such as cable television programming channels are received at a video distribution apparatus 106. The video telephony signals are directed to a cable access unit (CAU) 108 by the directional coupler 110.
It is understood that the communication system 102 may be comprised of one or more individual systems and the video telephony signals and downstream video 4 programming signals may be transmitted over more than one cable. For example, a cable television system may be combined with an ISDN telephone system wherein the ISDN signals are transmitted over twisted pair wiring and the video programming signals are transmitted over a coaxial cable.
Continuing to refer to FIG. 1, the CAU 108 demodulates the video telephony signals which, in the preferred embodiment, are sent using time division multiplexing (TDM) techniques. Preferably, the video telephony signals are sent using video compression techniques. The resulting compressed baseband video telephony signals are coupled to a video decompression unit 112 which decompresses the compressed video telephony signal to produce a baseband video telephony signal.
The baseband video telephony signal is received at the video distribution apparatus 106. As will be discussed in detail below, the baseband video telephony signal is modulated onto a radio frequency carrier in the video modulator 114 and filtered in the distribution filter 116. The resulting radio frequency video telephony signal is coupled to a subscriber cable network 118 through the directional coupler 110.
The subscriber cable network 118 is, preferably, a coaxial cable network distributed throughout the subscriber premise 101 and connected to customer premise equipment 120 such as televisions 122, video cassette recorders (VCRs) 124, set-top cable boxes 126, and other (one-way or two-way) video communication devices. Other audio or data communication devices may also be connected to the subscriber cable network. The subscriber cable network 118 may have multiple configurations and may comprise several splitters 130, amplifiers 132 and sections of subscriber coaxial cable 134. Outgoing video telephony signals are sent to the video distribution apparatus 106 through the subscriber cable network 118 by coupling an RF video output of a video camera 128 to the subscriber cable network 118. Other RF video signal sources may be used for transmitting outgoing video telephony signals to the video distribution apparatus 106, such as a VCR 124. 10 The video distribution apparatus 106 couples the outgoing video signals to an RF demodulator 140 that demodulates the outgoing video signals to produce outgoing baseband video signals. The outgoing baseband video signals are compressed in the video compressor 15 142. The CAU 108 modulates outgoing compressed video signals, preferably, using the CACS protocol. CACS is a multi-layered protocol, developed by Motorola, Inc., consisting of a plurality of 768 kbps rI/4-DQPSK (differential quadrature phase shift keying) 20 modulated RF carriers (carriers) using TDM framing in the downstream path (from the communication system 102 to a cable access unit 108) and TDMA (time division multiple access) in the upstream path (to the communication system 102 from a cable access unit 108). In the preferred embodiment, each CACS carrier supports as many as eight time slots of individually addressable user data packets, in which each packet contains 160 bits of user data (the "payload" or 'communication information") plus address and error detection 30 information. The preferred CACS frame rate is 400 frames per second, providing a net user data throughput of 64 kbps (kilobits per second) for each assigned time slot. Time slots also may be concatenated to provide 6 even greater data rates, for example, up to 512 kbps when all eight time slots are assigned to a single user. The modulated outgoing signals produced by the CAU 108 are coupled through the directional coupler 110 to 5 the coaxial cable 104 communication system 102. FIG. 2 is a detailed block diagram of a video distribution apparatus 106 in accordance with a preferred embodiment of the present invention. Al vi%deo modulator 114 modulates a baseband video telephony signal producing a modulated video telephony signal. The modulated video telephony signal is filtered, shifted to an intermediate frequency, filtered and shifted to a subscriber channel bandwidth to produce a radio frequency video telephony signal. The radio frequency video telephony signal is coupled through a directional coupler 110 into the subscriber cable network 118. In the preferred embodiment, the subscriber channel bandwidth is a vacant downstream channel.
The video modulator 114 receives a baseband video telephony signal from the video decompressor 112. The video modulator 114 is, preferably, an integrated circuit such as the MC1374 manufactured by Motorola. A reference signal that is injected into the video modulator 114 is used to modulate the baseband video telephony signal to produce a modulated video telephony signal. In the preferred embodiment, the reference signal has a frequency of 44 MHz and is generated by dividing a 1443 MHz reference signal (used for other purposes discussed below) by 33 using a frequency divider 210. The modulated video telephony signal has a center frequency of 44 MHz. It is understood by those with ordinary skill in the art that other frequencies may be used and the choice of frequencies may depend on the particular video telephone system 100.
7 A vestigial sideband filter 202 in the distribution filter 116 is coupled to the video modulator and filters the modulated video telephony signal to produce a vestigial sideband signal. The filter attenuates adjacent and alternate channel energy as well as providing the vestigial sideband filtering for the desired channel. Preferably, the vestigial sideband filter 202 is a 44 MHZ surface acoustic wave (SAW) filter that has a nominal bandwidth of 6 MHz.
The vestigial sideband filter 202 is coupled to an intermediate frequency converter 204. The intermediate frequency converter 204 is preferably a radio frequency (RF) mixer. A first local oscillator (first L.O.) 206 coupled to a phase lock loop circuit 208 is used to generate a first L.O. reference signal using known techniques. In the preferred embodiment, the first L.O. reference signal has a frequency of 1443 MHz and is also used to generate the reference signal needed for the video modulator 114. The first L.O. reference signal is injected into the intermediate frequency converter 204.
The intermediate frequency converter 204 shifts the vestigial sideband signal to an intermediate frequency by mixing the first L.O. reference signal with the vestigial sideband signal to produce an intermediate frequency signal. Preferably, the intermediate frequency is 1400 MHz. The intermediate frequency converter 204 is an RF mixer such as the MCL RMS11. The intermediate frequency signal is amplified by a first amplifier 212 and coupled to an intermediate frequency filter 214. The intermediate frequency filter 214 is a bandpass filter with a nominal bandwidth of 10 MHz and attenuates the 1443 MHz carrier and undesired mixing products such as a 8 88 MHz mixing product of the intermediate frequency converter 204.
A radio frequency converter 218 shifts the modulated video telephony signal to a subscriber channel bandwidth by mixing the vestigial sideband signal with a second L.O. reference signal. The subscriber channel bandwidth preferably has a frequency and a bandwidth consistent with standard television programming chaimels (downstream programming signals). The radio frequency converter 218 is preferably a RF mixer such as the MCL RMS-11X. The second L.O. reference signal is generated using an oscillator 220 coupled to a phase locked loop (PLL) circuit 222. In the preferred embodiment, the frequency of the second L.O. reference signal is chosen such that the mixing product of the second L.O.
reference signal and the vestigial sideband signal is a radio frequency video telephony signal with a frequency equal to a standard television channel such as one of the downstream video programming signals. The subscriber channel bandwidth is, preferably, the bandwidth of a standard television channel that is vacant. In other words, no television programming is transmitted to the subscriber premise 101 within the bandwidth of the particular channel that will be used to carry the radio frequency video telephony signal. The frequency of the second L.O. reference signal may be adjusted in order to place the modulated video telephony signal in appropriate subscriber channel bandwidth. In the preferred embodiment, the subscriber channel bandwidth may be any of the downstream channels that is vacant.
The radio frequency video telephony signal is amplified by an amplifier 224 and injected into a low pass filter 226. The low pass filter 226 attenuates any undesired mixing products of the radio frequency 9 converter 218 and any high order harmonic energy. The radio frequency video telephony signal is coupled through the directional coupler 110 and transmitted to the subscriber cable network 118.
Therefore, in the preferred embodiment of the invention, the distribution filter 106 receives a modulated video telephony signal from the video modulator 114, filters and shifts the modulated video telephony signal to an intermediate frequency, filters the modulated video telephony signal further and shifts the modulated video telephony signal to a subscriber channel bandwidth. FIG. 3 is a method in accordance with the preferred embodiment of the invention. 15 A baseband video telephony signal, received from a communication system 102 through a cable access unit 108, is modulated to produce a modulated video telephony signal at step 310. Preferably, the baseband video telephony signal is modulated onto a 44 MHz carrier. 20 At step 312, the modulated video telephony signal is filtered to produce a radio frequency video telephony signal adapted for transmission through a subscriber cable network. Step 312 begins with shifting the modulated video telephony signal to an intermediate frequency to produce an intermediate frequency signal at step 314. At step 320, the modulated video telephony signal is filtered to produce a vestigial sideband signal. Preferably, a vestigial filter 202 such as a 44 MHz SAW filter having a nominal bandwidth of 6 MHz attenuates adjacent and alternate channel energy and well as providing vestigial sideband filtering for the desired channel.
The vestigial sideband signal is shifted to an intermediate frequency to produce an intermediate frequency signal at step 330. In the preferred embodiment, a frequency converter 204 such as an RF mixer mixes the vestigial sideband signal with a first L.O. reference signal having a frequency of 1443 MHz.
Step 312 continues with step 340, wherein the intermediate frequency signal is filtered. Preferabl__ - Y I CL 1400 MHz bandpass filter 214 attenuates the 1443 MHz reference signal and undesired mixing products in the subscriber channel bandwidth such as the 88 MHz product signal while allowing the intermediate frequency signal to pass with minimal loss.
At step 350, the intermediate frequency signal is shifted to the subscriber channel bandwidth to produce a radio frequency video telephony signal. Preferably, a second L.O. reference signal is mixed with the intermediate frequency signal in a radio frequency converter 218 such as an RF mixer. The frequency of the second L.O. reference signal is chosen such that the resulting radio frequency video telephony signal is placed in a subscriber channel bandwidth that is in a vacant channel. As explained above in reference to FIG. 2, no television programming or other signals are transmitted to the subscriber premise 101 in the vacant channel.
At step 360, the radio frequency video telephony signal is filtered by attenuating undesired mixing products produced by the radio frequency converter 218 and other noise. Preferably, the radio frequency video telephony signal is passed through a 450 MHz, low-pass filter 226, coupled through a directional coupler 110 and transmitted through the subscriber cable network 118.
11 Therefore, the baseband video telephony signal received form the CAU 108 is modulated onto a fixed RF carrier having a frequency of 44 MHz producing a modulated video telephony signal. The modulated video telephony signal is upconverted to a 1400 MHz intermediate frequency, filtered and mixed down to a vacant channel within the 53 - 450 MHz frequency range. The resulting radio frequency video telephony signal ILS modulated and adapted to be received by standard customer premise equipment. Therefore, it can be transmitted throughout the subscriber premise 101 through the existing subscriber cable network 118. Video telephony signals can be viewed on any television 122, recorded on any VCR, or received through any other receiving type of subscriber premise device (120) coupled to the subscriber cable network 118.
FIG. 4 is a block diagram of a video distribution apparatus 106 in accordance with a first alternate embodiment of the invention. A baseband video telephony signal is modulated onto a radio frequency carrier within a subscriber channel bandwidth, filtered, and coupled through a directional coupler 110 into the subscriber cable network 118. A band-stop filter 412 is switched into the transmission path between the communication system 102 and the directional coupler 110 in order to remove signals within the subscriber channel bandwidth transmitted from the communication system 102 to the subscriber premise 101.
A video modulator 402, coupled to the video decompressor 112, modulates a baseband video telephony signal onto a radio frequency carrier producing a modulated video signal within a subscriber channel bandwidth. The video modulator 402 such as the MC1374 integrated circuit uses the third overtone of a crystal 12 404 to derive the appropriate carrier frequency. The carrier frequency is chosen to correspond to a standard programming channel that will be used for the subscriber channel bandwidth. For example, a carrier frequency of 55.25 MHz is used if Channel 2 is used for the subscriber channel bandwidth.
A vestigial sideband filter 406, coupled to the video modulator 402, filters the modulated video telephony signal by attenuating signals not in a subscriber channel bandwidth and by providing vestigial sideband filtering to produce a vestigial sideband signal. In the first alternate embodiment, the vestigial sideband filter 406 is an inductor and capacitor network and has a center frequency equal to the frequency of the carrier.
The vestigial sideband signal is amplified in an amplifier 408 coupled to the vestigial sideband filter 406. A band-pass filter 410, coupled to the amplifier 408, attenuates noise not in the subscriber channel bandwidth.
In the first alternate embodiment, the subscriber channel bandwidth may be used for television programming or for transmitting other signals from the communication system to the subscriber premise 101. Signals in the subscriber channel bandwidth that are transmitted from the communication system 102 are attenuated in a channel band-stop filter 412. When a video telephony call is in progress, the band-stop filter is connected into the transmission path between the communication system 102 and the directional coupler 110. Switches 414, 416 are used to connected the band-stop filter 412. A first switch 414 connects the coaxial cable 104 from the second switch 416 to the band-stop filter 412. The second switch 416 connects the directional coupler from 13 the first switch to the band-stop filter 412. In the first alternate embodiment, the switches 414, 416 are relays and are controlled by the CAU 108. Signals not in the subscriber channel bandwidth are allowed to pass to the directional coupler 110. The band-stop filter 412 provides a high impedance at the frequency of the subscriber channel bandwidth so that the desired radio frequency video telephony signal is not shorted.
The radio frequency video telephony signal is coupled to the directional coupler and transmitted through the subscriber cable network in the subscriber channel bandwidth which is vacant after passing through the band-stop filter 412.
When the video call complete, the band-stop filter 412 is switched out of the transmission path between the communication system 102 and the subscriber cable network 118 by switching in a direct connection between the switches 414, 416.
FIG. 5 is a flow chart of a method in accordance with the first alternate embodiment of the invention. At step 510, a baseband video telephony signal received from the video decompressor 112 is modulated onto an RF carrier in a video modulator 402. In the first alternate embodiment, the video modulator 402 uses the third order of a crystal 404 to derive a RF carrier frequency. The video modulator 402 modulates the baseband video telephony signal onto the RF carrier to produce a modulated video telephony signal that is in a subscriber channel bandwidth.
At step 520, the modulated video telephony signal is filtered in a vestigial sideband filter 406 to produce a radio frequency video telephony signal. In this embodiment, the vestigial sideband filter 406 is an inductor and capacitor network that attenuates signals 14 not within the subscriber channel bandwidth as well as providing vestigial sideband filtering. The radio frequency video telephony signal is amplified in an amplifier 408 and bandpass filtered in a bandpass filter 410 in order to remove signals and noise outside the subscriber channel bandwidth.
At step 530, signals transmitted from the communication system in a subscriber c%l-Lannell. bandj-4d4-.'-.
are attenuated in a band-stop filter 412. Switches 414, 416 are used to connect the band-stop filter 412 into the transmission path between the communication system 102 and the directional coupler.
At step 540, the radio frequency video telephony signal is coupled through the directional coupler 110 and transmitted through the subscriber cable network 118. Co-channel interference is minimized since the band-stop filter 412 has attenuated the signals transmitted by the communication system 102.
Therefore, in the first alternate embodiment, the video modulator 402, modulates a baseband video telephony signals onto a radio frequency carrier. The modulated video signal is filtered to produce a radio frequency video telephony signal. Signals transmitted from the communication system 102 to the subscriber premise 101 that are in a subscriber channel bandwidth are attenuated before entering the subscriber cable network 118 through the directional coupler 110. The radio frequency telephony signal is transmitted in the subscriber channel bandwidth through the subscriber cable network 118. The video telephony signals are, therefore, transmitted through the subscriber premise 101 on coaxial cable in a channel that is normally used for television programming or for other signals. The subscriber can view the video signals on any television 122 connected to the subscriber cable network 118. The signals band-stop filter 412 is used to attenuate the incoming signals within the subscriber channel bandwidth only for the duration of the video call. After the video call is complete, a direct connection is made between the communication system 102 and the subscriber cable network 118.
FIG. 6 is a block diagram of a second alternate embodiment in accordance with the present invention. In the second alternate embodiment, the modulated video telephony signal is vestigial filtered and shifted to one of a plurality of subscriber channel bandwidths. A selectable band-stop filter 631 connects one of a plurality of band-stop filters 632-636 within a the transmission path between the communication system 102 and the subscriber premise 101. The selected band-stop filter (636) corresponds to the subscriber channel bandwidth being used for transmission of the modulated video telephony signal and is switched into the transmission path between the communication system 102 and the directional coupler 110 for the duration of the video call. A video modulator 402, crystal 404 and vestigial sideband filter 406 operate as described above in the alternate embodiment except that the carrier frequency does not necessarily correspond to a standard program channel. For example, a 15 MHz crystal could be used to produce a 45 MHz carrier for the vestigial sideband signal. 30 In the second alternate embodiment, the vestigial sideband signal is shifted to a subscriber channel bandwidth by a radio frequency converter 618. The radio frequency converter 618 is a radio frequency mixer such as the RMS-11X. A reference oscillator 620 coupled to a 16 phase locked loop (PLL) circuit 622 generates a reference signal that is mixed with the vestigial sideband signal by the frequency converter 618 to produce an intermediate frequency signal. The reference signal frequency is controlled by the CAU as explained below.
The intermediate frequency signal is amplified in a first amplifier 624 and iltered in a bandpass f.2j-'L'ter 626. In the second alternate embodiment, the bandpass filter 626 has a pass-band of 54 to 88 MHz and attenuates undesired mixing products outside the pass band such as the signal produced by the sum of the reference signal and the modulated video telephony signal. The intermediate frequency signal is amplified further in a second amplifier 628 and filtered in a second bandpass filter 630 to produce a radio frequency video telephony signal adapted for transmission through a subscriber cable network 118. In the second alternate embodiment, the first amplifier 624 and the second amplifier 628 are amplifiers such as the UPC1678. The second bandpass filter 630 has the same characteristics as the first bandpass filter 626 and further attenuates undesired signals and noise outside the subscriber channel bandwidth.
The radio frequency video telephony signal is placed within the desired subscriber channel bandwidth by controlling the frequency of the reference signal.
The frequency of the reference signal is variable and is controlled by the CAU 108 through the PLL circuit 622.
The frequency of the reference signal is chosen such that the radio frequency video telephony signal is shifted to the desired subscriber channel bandwidth. For example, if the frequency of the reference signal is 100.25 MHz, the 45 MHz vestigial sideband signal is 17 mixed with the reference signal to produce a radio frequency video telephony signal with a frequency of 55.25 MHz. This places the radio frequency video telephony signal within the subscriber channel bandwidth commonly referred to as Channel 2. A reference signal frequency of 112.25 MHz produces a radio frequency video telephony signal within the subscriber channel known as Channel 4. Further, the radio frequency video telepliony signal is placed within Channel 6 if 128.25 MHz is selected as the reference signal frequency.
Various criteria may be used in selecting a subscriber channel bandwidth. For example, the subscriber may manually select the subscriber channel bandwidth because of personal preference. The subscriber may choose a channel that contains programming that is rarely viewed by anyone at the subscriber premise 101. In this way, others may watch video programming on other channels without being disturbed by the video call.
Before the radio frequency video telephony signal is coupled into the subscriber cable network, one of a plurality of band- stop filters 623-636 in the selectable band-stop filter 631 attenuates downstream video programming signals in the subscriber channel bandwidth. The band-stop filter 632-636 provide a high impedance at the frequency at each of the subscriber channel bandwidths respectively when connected in thetransmission path so that the desired radio frequency video telephony signal is not shorted. Switches 638, 640 within the selectable band-stop filter 631 are controlled by the CAU and are used to connect the desired band-stop filter (632-636) into the transmission path between the communication system and the subscriber cable network 118 for the duration of the video call. Preferably, the switches 638, 632 are constructed using 18 relays using known techniques. The CAU selects the appropriate band-stop filter (632-636) that attenuates signals within the subscriber channel bandwidth used for transmitting the radio frequency video telephony signal. As explained above, if the frequency of the reference signal is 100.25 MHz, the 45 MHz vestigial sideband signal is mixed with the reference signal to produce a radio frequency video telephony signal with a frequency of 55.25 MHz which is within channel 6. The band-stop 10 filter 636 has a frequency response such that signals in the subscriber channel bandwidth that correspond to channel 6 are attenuated, while other signals pass with minimal loss. If the radio frequency video telephony signal has a frequency of 55.25 MHz the CAU selects the 15 band- stop filter 636, in the selectable band-stop filter 631, that blocks signals in the subscriber channel bandwidth corresponding to channel 6. Preferably, the other band-stop filter 632 and band-stop filter 634 attenuate signals within the other subscriber channel 20 bandwidths corresponding to Channel 2 and Channel 4, respectively. FIG. 7 is a flow chart of a method in accordance with the second alternate embodiment. At step 710 a baseband video telephony signal 25 modulated to produce a modulated video telephony signal as described above in the description of the method in accordance with the first alternate embodiment of the invention. At step 720, the modulated video telephony signal 30 is filtered to produce a vestigial sideband signal as described above in reference to the first alternate embodiment. The CAU selects a subscriber channel bandwidth from any one of at least two selectable subscriber channel
19 bandwidths at step 730. Preferably, the CAU selects a subscriber channel bandwidth based on a subscriber preference.
At step 740, the vestigial sideband video signal is shifted to the subscriber channel bandwidth. Preferably, a frequency converter 618 mixes the vestigial sideband signal with a reference signal to produce an intermediate frequency signal. As explained above in reference to FIG. 6, the reference is variable and is controlled by the CAU. By changing the reference signal, the frequency of the intermediate frequency signal can be selected.
At step 750, signals in the subscriber channel bandwidth are attenuated. A selectable band-stop filter 631 attenuates signals transmitted from the communication system to the subscriber premise 101 before the signals enter the subscriber cable network 118. As explained above, the selectable band-stop filter is controlled by the CAU. The CAU selects the band-stop 20 filter (632 - 636) that attenuates the signals within the selected subscriber channel bandwidth. At step 760, a signals not in a subscriber channel bandwidth are attenuated to produce a radio frequency video telephony signal. The intermediate frequency signal is amplified by a first amplifier 624, filtered by a first bandpass filter 626, amplified by a second amplifier 628, and further filtered by a second bandpass filter 630. As described above in reference to FIG. 6, the amplifiers 624, 628 are of the same type and provide additional gain to increase signal quality. Each of the bandpass filters 626, 630 has a pass-band which allows any signal in any of the possible subscriber channel bandwidth to pass with minimal loss while undesired mixing products are attenuated.
In the second alternate embodiment, the intermediate frequency signal and the radio frequency video telephony signal have the same frequency and, therefore, the subscriber channel bandwidth used for transmitting the radio frequency video telephony signal is selected by changing the reference signal frequency.
The radio frequency video telephony signal is transmitted through the subscriber cable network 118 at step 770. As explained above, the radio frequency video telephony signal is injected into the directional coupler 110 and combined with the downstream video programming signals and coupled into the subscriber cable network 118. When the video call is complete the selectable band-stop filter allows all the downstream signals to enter the subscriber cable network 118.
Therefore, in the second alternate embodiment, a baseband video signal is modulated and vestigial sideband filtered. The resulting vestigial sideband signal is shifted to one of at least two selectable subscriber channel bandwidths producing an intermediate frequency signal. The intermediate frequency signal is amplified and filtered in order to attenuate undesired mixing products and other noise to produce a radio frequency video telephony signal adapted for transmission through a subscriber cable network 118. A selectable band- stop filter attenuates downstream signals transmitted from the communication system 102 to the subscriber premise 101 within the selected subscriber channel bandwidth. The radio frequency video telephony signal is injected into a directional coupler and combined with the downstream signals before coupled to the subscriber cable network 118.
A subscriber can watch the video telephony signals on a television 122 connected in the subscriber cable 21 network 118 by tuning the television 122 to the appropriate channel (the selected subscriber channel bandwidth). The subscriber may select the channel used to display the video telephony signals by selecting the subscriber channel bandwidth. others at the subscriber premise 101 can continue watching other downstream video programming signals.
FIG. 8 is block diagram of a video distribution apparatus in accordance with a third alternate embodiment of the invention. In the third alternate embodiment, a selectable band-stop filter 631 is connected between the communication system 102 and the directional coupler 110 in a distribution apparatus 106 according to the preferred embodiment.
The video modulator 114 and the distribution filter 116 operates as described in reference to FIG. 3 except that the subscriber channel bandwidth may be a vacant channel or a channel used for downstream video programming channels. If a vacant channel is used, the distribution filter operates as described in reference to FIG 3. In this situation no band-stop filters are switched into the transmission path between the communication system 102 and the subscriber cable network 118.
If a channel carrying video programming signals is used for the subscriber channel bandwidth, the selectable band-stop filter 631 operates as described in reference to FIG. 6 to attenuate signals in the subscriber channel bandwidth transmitted to the subscriber cable network 118. The appropriate band-stop filter (632, 634, 636) is switched into the transmission path between the communication system 102 and the subscriber cable network 118 for the duration of the video call.
22 FIG. 9 is a flow chart of a method in accordance with a third alternate embodiment of the invention.
Steps 910 - 940 are performed as described above in reference to steps 310 - 340 in FIG 3.
At step 950, the CAU 108 selects a subscriber channel bandwidth from any one of at least two selectable subscriber channel bandwidths as described in reference to FIG. 6 and FIG. 7.
At step 960, the intermediate frequency signal is shifted to a subscriber channel bandwidth as described above in reference to step 350 in FIG. 3.
At step 970, the CAU 118 determines if the subscriber channel bandwidth is within a vacant channel. Preferably, the CAU 108 has list of channels stored in memory indicating which channels are vacant and determines whether the subscriber channel bandwidth is within a vacant channel by comparing the channel by used for the subscriber channel bandwidth to the list. However other methods may be used to determine whether the channel is vacant. For example, the subscriber may provide information to the CAU 108 to indicate whether the channel is vacant, or the CAU 108 may sense the channel for RF signals.
If the subscriber channel bandwidth is vacant, the method proceeds to step 990 where the radio frequency video telephony signal is filtered and coupled through the directional coupler 110 as described in reference to step 360 in FIG. 3. The direct connection within the selectable band-stop filter 631 remains connected.
If the subscriber channel bandwidth is not vacant, the appropriate bandstop filter (632-636) is switched into the transmission path as described in reference to step 750 in FIG. 7 and the signals within the subscriber channel bandwidth transmitted to the subscriber cable network 118 are attenuated at step 980.
The method then proceeds to step 990 where the radio frequency telephony signals are coupled through the directional coupler and transmitted through the subscriber cable network 118.
Therefore, in the third alternate embodiment, if a vacant channel is available, a baseband video LelepLiony signal is modulated, filtered and shifted to a subscriber channel bandwidth within a vacant channel. If a vacant channel is not available, the baseband video telephony signal is modulated, filtered and shifted to a subscriber channel bandwidth. A band-stop filter (632636) attenuates signals within the subscriber channel bandwidth transmitted from the communication system 102 to the subscriber cable network 118 for the duration of the video call.
Therefore, the present invention provides a method and apparatus for distributing video telephony signals within a subscriber premise 101 allowing for the subscriber to view the incoming video telephony signals on any television 122 connected within the subscriber cable network 118.
Claims (9)
- We claim:24 CLAIMS 1. An apparatus comprising: a video modulator modulating a baseband video telephony signal when receiving the baseband video telephony signal to produce a modulated video telephony signal; and a distribution filter coupled to the video modulator filtering the modulated video telephony signal to produce a radio frequency video telephony signal adapted for transmission through a subscriber cable network.
- 2. An apparatus according to claim 1 further comprising a channel band-stop filter coupled to the subscriber cable network attenuating signals in a subscriber channel bandwidth transmitted to the subscriber cable network when the radio frequency video telephony signal is transmitted through the subscriber cable network.
- 3. An apparatus according to claim 2 wherein the band-stop filter attenuates signals in a subscriber channel bandwidth transmitted to the subscriber cable network only for a duration of a video call.
- 4. An apparatus according to claim 3 wherein the channel band-stop filter is a selectable channel bandstop filter adapted for attenuating any one of at least two selectable channel bandwidths.
- 5. An apparatus according to claim 1, the distribution filter comprising: a vestigial sideband filter coupled to the video modulator filtering the modulated video telephony signal to produce a vestigial sideband signal; a frequency converter coupled to the vestigial sideband filter shifting the vestigial sideband signal to a subscriber channel bandwidth; and a subscriber channel bandpass filter coupled to the frequency converter attenuating signals not in the subscriber channel bandwidth to produce a radio frequency video telephony signal for transmitting through a subscriber cable network.
- 6. An apparatus according to claim 1, the distribution filter comprising:an intermediate frequency converter shifting the modulated video telephony signal to an intermediate frequency to produce an intermediate frequency signal; an intermediate frequency filter coupled to the intermediate frequency converter attenuating mixing products; and a radio frequency converter coupled to the intermediate frequency filter shifting the intermediate frequency signal to a subscriber channel bandwidth to produce a radio frequency video telephony signal adapted for transmission through a subscriber cable network.26
- 7. An apparatus according to claim 6, wherein the distribution filter further comprises a vestigial sideband filter filtering the modulated video telephony signal to produce a vestigial sideband signal, the intermediate frequency converter shifting the vestigial sideband signal to produce an intermediate frequency signal.
- 8. An apparatus according to claim 7, the distribution filter further comprising a low pass filter coupled to the radio frequency converter.
- 9. An apparatus according to claim 8, the low pass filter attenuating at least undesired mixing products produced by the radio frequency converter.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80882897A | 1997-02-28 | 1997-02-28 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9803518D0 GB9803518D0 (en) | 1998-04-15 |
| GB2323748A true GB2323748A (en) | 1998-09-30 |
Family
ID=25199864
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9803518A Withdrawn GB2323748A (en) | 1997-02-28 | 1998-02-20 | Video telephony |
Country Status (4)
| Country | Link |
|---|---|
| CN (1) | CN1230852A (en) |
| AU (1) | AU5205398A (en) |
| DE (1) | DE19807362A1 (en) |
| GB (1) | GB2323748A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9291695B2 (en) * | 2012-08-06 | 2016-03-22 | Fluke Corporation | Real-time RF signal visualization device |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2242335A (en) * | 1990-03-19 | 1991-09-25 | Sony Corp | Videophones |
| EP0458523A2 (en) * | 1990-05-22 | 1991-11-27 | Gold Star Co. Ltd | A method and apparatus for transmitting/receiving signals in a video phone |
| US5539452A (en) * | 1990-02-21 | 1996-07-23 | Alkanox Corporation | Video telephone system |
| US5541640A (en) * | 1992-06-23 | 1996-07-30 | Larson; Craig R. | Videophone for simultaneous audio and video communication via a standard telephone line |
-
1998
- 1998-01-14 AU AU52053/98A patent/AU5205398A/en not_active Abandoned
- 1998-02-20 GB GB9803518A patent/GB2323748A/en not_active Withdrawn
- 1998-02-21 DE DE1998107362 patent/DE19807362A1/en not_active Withdrawn
- 1998-02-26 CN CN 98105341 patent/CN1230852A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5539452A (en) * | 1990-02-21 | 1996-07-23 | Alkanox Corporation | Video telephone system |
| GB2242335A (en) * | 1990-03-19 | 1991-09-25 | Sony Corp | Videophones |
| EP0458523A2 (en) * | 1990-05-22 | 1991-11-27 | Gold Star Co. Ltd | A method and apparatus for transmitting/receiving signals in a video phone |
| US5541640A (en) * | 1992-06-23 | 1996-07-30 | Larson; Craig R. | Videophone for simultaneous audio and video communication via a standard telephone line |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9803518D0 (en) | 1998-04-15 |
| CN1230852A (en) | 1999-10-06 |
| AU5205398A (en) | 1998-09-03 |
| DE19807362A1 (en) | 1998-09-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |