MXPA02006552A

MXPA02006552A - Rf back channel for dtv.

Info

Publication number: MXPA02006552A
Application number: MXPA02006552A
Authority: MX
Inventors: Raymond C Hauge
Original assignee: Zentih Electronics Corp
Priority date: 1999-12-30
Filing date: 2000-11-21
Publication date: 2003-04-10
Also published as: KR20020067923A; BR0016856A; AU1662701A; WO2001050757A1; AR028885A1; CA2392683A1; TW506221B

Abstract

A communication system comprises a digital data source including a digital VSB remodulator, such as a VCR, and a downstream digital VSB device, such as a television. The digital VSB remodulator remodulates digital data from the data source received on one of a plurality of channels to digital VSB data on a downstream channel and transmits the digital VSB data to the downstream digital VSB device in the downstream channel at a symbol rate fs. The downstream digital VSB device transmits information, such as its identification, to the digital VSB remodulator in an upstream channel corresponding to a carrier frequency (NM)fs. The plurality of channels and the downstream channel occupy a bandwidth above about 50 MHZ, and (NM)fs is below this bandwidth.

Description

SECRET RF COMMUNICATION MEDIA FOR DTV TECHNICAL FIELD OF THE INVENTION The present invention relates to the digital VSB transmission in a downstream channel of a digital VSB source upstream to a VSB device, downstream and with the transmission of information in an upstream channel (i.e., a secret communication medium). from the digital VSB device downstream to the digital VSB source upstream.

BACKGROUND OF THE INVENTION The digital video and audio television communication systems are transmitted to a digital television over respective 6 MHZ channels that occupy a bandwidth of approximately 50 MHz at 1 GHz. Digital audio and video are provided as symbols at a symbol speed fs and transmitted as digital vestigial sideband (VSB) data. The digital television receives the digital VSB data, tunes it to one of the selected channels, demodulates and decodes the digital VSB data in the selected channel using a symbol clock synchronized with the symbol speed fs in order to recover the corresponding video and audio, and process the recovered video and audio to be supplied to a monitor and one or more speakers.

Certain auxiliary receivers, such as VCRs and cable and satellite converters, also receive the transmitted VSB data, are tuned to a first selected channel among the plurality of channels, demodulate the VSB data on the first selected channel, remodulate the demodulated data to a second selected channel (such as channel 3 or 4), and communicate the remodulated data on the second selected channel to a digital receiver as a digital television. These auxiliary receivers are also synchronized with the symbol clock. An auxiliary receiver among others can be referred to here as an upstream source. When an upstream source communicates digital VSB data over a downstream channel to a downstream device, such as another VCR, digital television or other downstream receiver, it may be necessary for the downstream device to communicate information back to the upstream source on an upstream channel. For example, some digital VSB data can be protected against copying so that only an authorized downstream device can receive the digital VSB data and display the audio and / or video contained therein. In the case of copy protection, and as will be described below, an upstream source of the data protected against copying transmits a message from a downstream channel to a downstream device which should receive the data protected against copying. This message requests the device below to identify itself as well. The device downstream In an upstream channel, respond to this request with your identification. The upstream source then transmits, in the downstream channel, a key to allow the downstream device to adequately present the material to be followed. The downstream device recognizes the reception of the key by transmitting an adequate acknowledgment in the upstream channel. After this, the upstream source transmits the digital VSB data in the downstream channel to the downstream device. The frequency of the carrier defining the upstream channel should preferably be different than the carrier frequency defining the downstream channel. The present invention is directed to an upstream channel defined by a carrier frequency that is different from the carrier frequency of the downstream channel and that is synchronized with the symbol rate at which the downstream digital VSB data is transmitted. The present invention therefore reduces the complexity required to define the upstream channel.

COMPENDIUM OF THE INVENTION In accordance with one aspect of the present invention, a communication system comprises a digital upstream VSB source and a downstream digital VSB device. The upstream digital VSB source transmits digital VSB data to the device Digital VSB downstream in a downstream channel at a symbol rate fs, and the downstream digital VSB device transmits information to the upstream digital VSB source modulated in a carrier that is synchronized to (N / M) fs. In accordance with another aspect of the present invention, a digital VSB apparatus has a transmitter and a receiver. The receiver receives digital VSB data in a downstream channel at a symbol rate fs, and the transmitter transmits information in an upstream channel corresponding to a carrier frequency (N / M) fs. According to yet another aspect of the present invention, a digital VSB apparatus comprises a transmitter and a receiver. The transmitter transmits digital VSB data in a downstream channel at a symbol rate fs, and the receiver receives information in an upstream channel corresponding to the transmitting frequency (N / M) fs. According to yet another aspect of the present invention, a downstream digital VSB device has a receiver and a transmitter. The receiver receives digital data having a frame synchronization transmitted by a digital VSB source upstream in a downstream digital VSB channel. The transmitter transmits information in a group of time slots to the digital VSB source upstream in an upstream channel. The transmitter synchronizes the group of time slots to the frame synchronization received by the receiver.

According to another aspect of the present invention, a downstream digital VSB device comprises a receiver and a transmitter. The receiver receives digital data transmitted by a digital VSB source upstream in a downstream digital VSB channel according to a symbol clock. The transmitter transmits upstream data to the digital VSB source upstream in an upstream channel. The transmitter synchronizes the data upstream to the symbol clock.

BRIEF DESCRPTION OF THE DRAWINGS These and other features and advantages of the present invention will become more apparent from the following detailed configuration of the invention taken in conjunction with the drawings in which: Figure 1 illustrates a communication system having a source upstream and one or more downstream devices wherein the upstream source communicates digital VSB data to the downstream devices in a downstream channel and wherein the downstream devices communicate information to the upstream source in an upstream channel according to the present invention; Figure 2 illustrates in detail, a portion of the upstream source of Figure 1 that will be relevant to the present invention; Figure 3 illustrates a further detail of the receiver of the upstream source shown in Figure 2; Figure 4 illustrates an exemplary time slot containing an upstream message; Figure 5 illustrates a plurality of time slots where downstream devices can communicate; and Figure 6 illustrates in detail, a portion of one of the representative devices downstream of Figure 1 wherein the portion is raised for the present invention.

DETAILED DESCRIPTION As shown in Figure 1, the communication system 10 includes an upstream source 12 and downstream devices 14, 16 and 18. The upstream source 12 and the downstream devices 14, 16 and 18 are interconnected by a means of communication 20 so that the upstream transmission path is the same as the downstream transmission path. Accordingly, the upstream source 12 communicates with the downstream devices 14, 16 and 18 downstream on the communication means 20, and the downstream devices 14, 16 and 18 communicate with the source up 12, upstream on the communication means 20. Although the communication system 10 is shown with three devices downstream, it should be understood that the communication system 10 can include any number of devices downstream. On the other hand, although the communication means 20 preferably comprises a cable interconnecting the upstream source 12 and the downstream devices 14, 16 and 18, the communication medium 20 may alternatively comprise a pair of wires, a transmission channel. wireless, and / or the like. The upstream source 12 and the downstream devices 14, 16 and 18 are preferably digital devices with the upstream source 12 allowing digital VSB data to the downstream devices 14, 16 and 18. For example, in digital television, a transmitter transmits digital VSB data to receivers such as a television and cable boxes using a standard symbol rate of approximately 10.76 MHz. Accordingly, the transmitter compresses data, encodes the compressed data as data symbols corresponding to the symbol rate fs, and modulates the coded symbols as a digital VSB modulated signal for transmission over a selected television channel to digital receivers. The transmitter includes a clock that operates at the symbol speed fs of approximately 10.76 MHz so that the digital VSB data is transmitted at this speed. The receivers receive the digital VSB data, demodulate the digital VSB data to recover the symbol clock of approximately 10.76 MHZ and recover the data symbols, and decode and decompress the data symbols in order to recover the original data to supply them to deployments and / or horns.

In an exemplary television environment for the communication system 10, the upstream source 12 can be a digital VCR as a cable converter, or a satellite converter, the downstream device 14 can be a digital VCR, and the downstream devices 16 and 18 can be digital televisions. However, other digital equipment may be provided for the upstream source 12 and the downstream devices 14, 16 and 18. As shown in Figure 2, the upstream source 12 may include, for example, a processor 30, a remodulator 32, a diplexer 34, a switch 36, and a reflector 38. Thus, in the case where the upstream source 12 is a digital converter or a digital VCR, the upstream source 12 receives a plurality of channels occupying the normal television bandwidth of approximately 50 MHz to approximately 1 GHz and tuned to one of these selected channels. The digital VSB data on that selected channel is supplied downstream by the upstream source 12, for example to the downstream device 18, either in real time or to be viewed later. In each case, the remodulator 32 remodulates the digital VSB data received in the selected tuned channel to a preselected downstream channel, such as channel 3 or channel 4, and supplies the remoulded digital VSB data to the communication means 20 through the diplexer. 34 and the switch 36 for communicating with one or more of the downstream devices 14, 16 and 18. The remodulator 32 also retrieves the fs symbol clock of the VSB data that it is remodulating. In some cases, it is necessary that the upstream source 12 receive information from the downstream devices 14, 16 and 18. Therefore, the upstream source 12 is provided with the receiver 38. The remodulator 32 supplies the recovered symbol clock. fs and an internally generated frame synchronization signal FSYNC to the receiver 38. Also, the diplexer 34 couples the information it receives from one or more downstream devices 14, 16 and / or 18 to the receiver 38. The receiver 38 demodulates the received information coupled by the diplexer 34 and uses the clock signal fs to synchronize this demodulation function to the upstream channel.

The receiver 38 is shown in detail in Figure 3 and includes a demodulator 40 and a carrier recovery module 42. The carrier recovery module 42 receives the clock signal fs from the remodulator 32 and applies an N / M multiplexer thereto to be able to recover the carrier frequency that is used by the devices downstream 14, 16 and 18 to transmit data to the upstream channel. The carrier recovery module 42 also receives the data upstream to be able to recover the phase of the upstream carrier. In this way, the carrier recovery module 42 supplies a synchronization clock signal to the demodulator 40 so that the demodulator 40 is synchronized with the upstream carrier in frequency and phase. As shown in Figure 5, the current devices down 14, 16 and 18 transmit their information in corresponding time slots, where the start of each group of time slots is synchronized with the frame synchronization (FSYNC) that is being retrieved from the data downstream, ie the data digital TVs transmitted downstream by the upstream source 12. The number of time slots in a group depends on the amount of time allocated to each time slot. On the other hand, the time slots in a group can be divided between fixed time slots and contention time slots. The containment time slots can be used by downstream devices to be able to reserve a fixed time slot where a message can be transmitted to the upstream source 12. Therefore, when a downstream device has a message to be transmitted, randomly selects it. one of the containment time slots. Each of the other downstream devices does the same. If the reservation request is received by the upstream source 12 without containing the reservation requests of the other downstream devices, the upstream source 12 assigns a fixed time slot to the downstream device which then transmits its message in the Fixed time slot assigned. If the low current device is not assigned with a fixed time slot, it recognizes that its reservation request was not received by the upstream source 12 without contention and, therefore, will try once more in a randomly containing time slot selected Without However, time slots do not need to be divided between fixed time slots and containment slots in this manner, and, instead, each downstream device can be pre-assigned with one or more time slots of each group of time slots. . The data transmitted in a time slot by the downstream devices 14, 16 and 18 is transmitted as a data message having the form shown in Figure 4. Each message has a clock portion (a series of "one" bits). logic modulating the RF carrier to provide a constant CW signal), a preamble portion, a data portion, and a CRC error revision portion. The data received by the demodulator 40 is analogously found. A sampler 44 of the receiver 38 samples the demodulated data at the output of the demodulator 40 in order to convert the demodulated data to a digital form. The sampler 44 is supplied with a sampling clock signal by a clock phase circuit 46. The sampling clock signal is divided by a splitter 43 to provide a frequency that matches the data clock that is used by the devices. downstream 14, 16 and 18 when transmitting upstream data. A preamble correlator 48 uses a preamble in the upstream data message to be able to synchronize the phase of the sampling clock signal supplied by the clock phase circuit 46 to the data clock of the downstream devices 14, 16 and 18 A time slots generator 45 responds to the signal of frame synchronization FSYNC to generate a signal representing the received time slots that are used by the clock phase circuit 46 as a window to facilitate the identification of the preamble in each received message. Accordingly, the sampler 44 samples the data in the upstream data message and supplies the sampled data to the processor 30. The processor 30 responds to the preamble in each received message to locate the data in the respective message. Also, the sampler 44 supplies the sampled data to a CRC 50 reviewer using the CRC portion of the upstream data message in order to determine the presence of transmission errors. A portion of a downstream device 60 is shown in Figure 6. The downstream device 60 represents each of the downstream devices 14., 16 and 18 so that each of the downstream devices 14, 16 and 18 can be constructed in the same way to the downstream device 60. The portion of the downstream device 60 shown in Figure 6 is the portion involved in the current transmission above the information to the upstream source 12. The downstream device 60 includes a diplexer 62, a tuner 64, a demodulator VSB 66, a downstream processor 68, an upstream control processor 70, a blocked pass circuit 72 and a transmitter 74. The diplexer 62 receives digital VSB data that is transmitted by the upstream source 12 in the downstream. The diplexer 62 it couples this digital VSB data to the tuner 64 which is tuned to the downstream channel and which supplies the digital VSB data in IF to the demodulator VSB 66. The VSB 66 demodulator retrieves the symbol clock fs and the frame synchronization FSYNC of the digital VSB data received. The VSB demodulator 66 supplies the symbol clock fs to the upstream control processor 70 and the locked phase circuit 72, and supplies the frame synchronization FSYNC to the upstream control processor 70. The VSB demodulator 66 also demodulates the digital VSB data receiver to retrieve the data symbols, and provides these data symbols to the downstream processor 68.

The upstream control processor 70 decodes any control information that may be contained in the downstream data that is demodulated by the demodulator VSB 66. Such control information, for example, may be used to set the data rate at which the processor upstream control 70 supplies data to transmitter 74, to establish the time slot in which upstream device 60 is to transmit upstream data, if any, and / or set the N / M value to be described further ahead. The upstream control processor 70 receives from the downstream processor 68 the data to be transmitted in the upstream channel and causes this upstream data to be transmitted in a selected time slot. Accordingly, each of the devices downstream 14, 16 and 18 transmit messages in different time slot. Alternatively, upstream messages can be transmitted in containment slots. In order to determine the start of each time slot group, the upstream control processor 70 receives FSYNC from demodulator VSB 66 and synchronizes the start of each group with FSYNC- Moreover, the data clock that the current control processor up 70 used to insert data upstream between the time slot can be set equal to or can be a fraction of the symbol clock fs. This fraction, for example, can be 3/50, 1/50 or 1/100 of the symbol clock fs. If a fraction of the symbol clock fs will not be used, the symbol clock f¡¡ is divided by a divider 71 and the divided symbol clock is used by the upstream control processor 70 to be able to generate the data clock for the upstream messages. The locked phase circuit 72 produces a carrier signal having a desired frequency (N / M) fs, where N / M is a value that is supplied to the locked phase circuit 72 by the upstream control processor 70. Alternatively, one or more values for N / M may be preset in the locked phase circuit 72 and may selectively be used to generate a carrier frequency. The blocked phase circuit 72 supplies another carrier signal to the transmitter 74 which will be used as the carrier for the upstream channel. When the upstream control processor 70 determines the presence of the ground slot assigned to the downstream device 60, the upstream control processor 70 supplies data upstream to the transmitter 74, and at the same time turns on the transmitter 74. The transmitter 74 then modulates the data upstream on the carrier supplied by the locked phase circuit 72 so that the upstream data is transmitted in the upstream channel defined by the carrier frequency (N / M) fs. The upstream control processor 70 otherwise keeps the transmitter 74 off so that the transmitter 74 reproduces interference in the upstream channel. As mentioned above, the carrier frequency of the upstream channel is defined by a value related to the symbol clock fs. This value depends on the N / M ratio, where N and M are preferably integral. For example, the N / M ratio can be 1/3, Yz, 1, 3/2, 2, and the like. The value of N / M can be chosen so that (N / M) fs is below the normal television band amplitude of about 50 MHz to about 1 GHz. In this way, the upstream channel is linked to the clock of symbol fs. The processors 30 and 68 determine, at least in part, information that will be transmitted between the upstream source 12 and the upstream devices 14, 16 and 18. The processors 30 and 68, for example, can be configured to provide copy protection according to the copy protection protocol 5C. According to this protocol, the processor 30 in the source upstream 12 causes the upstream source 12 to transmit to the downstream device, such as the downstream device 16 which should receive data protected against copying, a message requesting that the downstream device 16 be identified as well. The downstream processor 68 of the downstream device 16 recognizes this message and, consequently, causes the transmitter 74 to transmit the identification of the downstream device 16 in the upstream channel defined by the carrier frequency (N / M) fs. The receiver 38 receives this message and passes this message to the processor 30 of the upstream source 12. If the processor 30 recognizes the identification of the downstream device 16, the processor 30 causes the upstream source 12 to transmit in the downstream channel a key that allows the downstream device 16 to properly encrypt the material protected against copying that it must follow. The downstream processor 68 of the downstream device 16 recognizes the reception of the key causing the transmitter 74 to transmit a suitable recognition in the upstream channel assigned to the downstream device 16. The acknowledgment received by the receiver 38 reviews the recognition to the processor 30. After this, the processor 30 causes the upstream source 12 to transmit the digital data VSB protected against copying in the downstream channel to the downstream device 16. The downstream processor 68 decrypts the digital VSB data. protected against copying and provides this decrypted copying-protected digital VSB data to appropriate audio and video processing modules. Accordingly, only an authorized downstream device can properly receive the display of the audio and / or video contained in the digital VSB data protected against copying. As previously described, the upstream source 12 transmits modulated VSB data to the downstream devices 14, 16 and 18. The downstream devices 14, 16 and 18 may use a different type of modulation, however when they are transmitting information in the channels upstream to the upstream source 12. For example, as indicated by the drawings, the transmitters 74 of the downstream devices 14, 16 and 18 can be BPSK transmitters that use BPSK modulation in transmitting upstream information in a carrier that has a frequency equal to (N / M) fs. If the transmitters 74 of the downstream devices 14, 16 and 18 are BPSK transmitters, then the receiver 38 of the upstream source 12 is a BPSK receiver. The switch 36 is providing so that an external source, such as an antenna, can be connected directly to the downstream devices 14, 16 and 18. Certain modifications and alternatives of the present invention have been discussed above. Other alternative modifications will occur to those skilled in the art of the present invention.

For example, the P transmit 74 of the downstream devices 14, 16 and 18 are described above as BPSK transmitters and the receiver 38 of the upstream source 12 is described above as a BPSK receiver. However, the transmitters 74 of the downstream devices 14, 16 and 18 and the receiver 38 of the upstream source 12 can implement other types of modulation such as QAM, QPSK, or PSK. Accordingly, the description of the present invention should be taken as illustrative only and for the purpose of teaching those skilled in the art the best mode for carrying out the invention. The details may vary substantially without departing from the spirit of the invention, and exclusive use is reserved for all modifications within the scope of the appended claims.

Claims

CLAIMS 1. - A digital VSB apparatus (14) having a receiver (62, 64, 66, 68 and / or 72), wherein the receiver (62, 64, 66, 68 and / or 72) receives digital data in a downstream digital VSB channel at a symbol rate fs, the digital VSB apparatus is characterized in that : the digital VAB device also has a transmitter (70 and / or 74), wherein the transmitter (70 and / or 74) transmits information in an upstream channel corresponding to a carrier frequency (N / M) fs. 2. The digital VSB apparatus according to claim 1, wherein the transmitter (70 and / or 74) is a BPSK transmitter (74). 3. The digital VSB apparatus according to claim 1, wherein the transmitter (70 and / or 74) is based on a different type of modulation than the receiver (62, 64, 66, 68 and / or 72). ). 4. The digital VSB apparatus according to claim 1, wherein the receiver (62, 64, 66, 68 and / or 72) comprises a VSB demodulator (66) and a blocked phase circuit (72), wherein the demodulator VSB (66) recovers the symbol rate fs, and wherein the locked phase circuit (72) carries the carrier (N / M) fs to the transmitter (70 and / or 74) in response to the symbol rate fs recovered by the VSB demodulator (66). 5. The digital VSB apparatus according to claim 1, wherein the downstream digital VSB channel corresponds to a carrier frequency of at least 50 MHZ, and wherein (N / M) fs < 50 MHZ. 6. The digital VSB apparatus according to claim 5, wherein the receiver (62, 64, 66, 68 and / or 72) comprises a VSB demodulator (66) and a blocked phase circuit (72), wherein the demodulator VSB (66) recovers the symbol rate fs, and wherein the locked phase circuit (72) carries the carrier (N / M) fs to the transmitter (70 and / or 74) in response to the symbol rate fs recovered by the VSB demodulator (66). 7. The digital VSB apparatus according to claim 5, wherein the transmitter (70 and / or 74) is a BPSK transmitter (74). 8. The digital VSB apparatus according to claim 1, wherein the transmitter (70 and / or 74) transmits an identification of the digital VSB apparatus in the upstream channel, and wherein the receiver (62, 6466, 68 and / or 72) receives a copy protection key in the downstream digital VSB channel. 9. The digital VSB device according to claim 1, wherein the receiver (62, 64, 66, 68 and / or 72) receives a frame synchronization, wherein the transmitter (70 and / or 74) transmits the information in a group of time slots, and wherein the transmitter (70 and / or 74) synchronizes the group of time slots to the received frame synchronization. 10. The digital VSB device according to claim 1, wherein the transmitter (70 and / or 74) transmits information according to a clock signal synchronized to kfs. 11.- The digital VSB device according to the claim 10, where k is less than one. 12. The digital VSB apparatus according to claim 1, wherein the digital VSB apparatus is a downstream digital VSB apparatus (14), wherein the downstream digital VSB apparatus is coupled to an upstream digital VSB source (12). ) through the digital VSB channel downstream and the upstream channel, where the upstream digital VSB source (12) transmits digital data to the downstream digital VSB apparatus (14) in the downstream digital VSB channel at the symbol rate fs, and wherein the downstream digital VSB apparatus 140 transmits information to the upstream digital source VSB (12) modulated in a carrier that is synchronized to (N / M) fs. 13. The digital VSB apparatus according to claim 12, wherein N / M < 14. 14.- The digital VSB device according to the claim 12, where N and M are integers. 15. The digital VSB apparatus according to claim 12, wherein N / M is fixed by the upstream digital source VSB (12). 16.- The digital VSB device according to the claim 12, wherein the downstream digital VSB apparatus (14) includes a BPSK transmitter (74) that transmits the information to the upstream digital VSB source (12) in the upstream channel in the carrier, where the current digital VSB source top (12) includes a BPSK receiver (38) that receives information from the digital VSB device downstream 14 in the upstream channel, and wherein the BPSK receiver (38) includes a BPSK demodulator (40) and a carrier recovery module (42) wherein the BPSK demodulator (40) demodulates the information received from the current VSB apparatus down (14) in the upstream channel, and where the carrier recovery module (42) retrieves the carrier (N / M) fs. 17. The digital VSB device according to claim 12, wherein the upstream digital source VSB (12) includes a demodulator (40) and a carrier recovery module (42), wherein the demodulator (40) demodulates the information received from the downstream digital VSB apparatus (14) in the upstream channel, and wherein the carrier recovery module (42) retrieves the carrier (N / M) fs. 18. The digital VSB apparatus according to claim 12, wherein the upstream digital source VSB (12) modulates the digital data on a carrier frequency fc, and wherein (N / M) fs < fe 19.- The digital VSB apparatus according to claim 12, wherein the downstream digital VSB apparatus (14) includes a VSB demodulator (66) and a locked phase circuit (72), wherein the VSB demodulator (66) ) retrieves the symbol speed fs, and wherein the locked phase circuit (72) produces the bearer (N / M) fs in response to the symbol rate fs recovered by the demodulator VSB (66). 20.- The digital VSB device according to the claim 19, wherein the upstream digital VSB source (12) includes a non-VSB demodulator (40) and a carrier recovery module (42), wherein the non-VSB demodulator (40) demodulates the information received from the device. Digital VSB downstream (14) in the upstream channel, where the carrier recovery module (42) retrieves the carrier (N / M) fs. 21. The digital VSB device according to claim 12, wherein the upstream digital VSB source (12) comprises a VSB remodulator (32), wherein the VSB remodulator (32) receives the digital data, wherein the remodulator VSB (23) remodulates the received digital data on one of the plurality of downstream digital VSB channels, and wherein the VSB remodulator (32) transmits the remodulated digital data to the downstream digital VSB apparatus (14) on the current digital VSB channel down at the symbol speed fs. 22. The digital VSB apparatus according to claim 21, wherein the upstream digital source VSB (12) includes a demodulator (40) and a carrier recovery module (42), wherein the demodulator (40) demodulates the information received from the downstream digital VSB apparatus (14) in the upstream channel, and wherein the carrier recovery module (42) retrieves the carrier (N / M) fs. 23. The digital VSB apparatus according to claim 21, wherein each of the plurality of downstream digital VSB channels has a carrier frequency, and wherein (N / M) fs is less than the carrier frequency of each of the plurality of downstream digital VSB channels. 24.- The digital VSB device according to the claim 21, wherein the plurality of downstream digital VSB channels each occupies a bandwidth above about 50 MHZ, and wherein (N / M) fs is below the bandwidth. 25. The digital VSB device according to claim 21, wherein the downstream digital VSB apparatus (14) includes a VSB demodulator (66) and a locked phase circuit (72), wherein the VSB demodulator (66) recovers the symbol speed fs, and wherein the locked phase circuit reduces the carrier (N / M) fs in response to the symbol speed fs recovered by the VSB demodulator (66). 26.- The digital VSB device according to the claim 12, wherein the downstream digital VSB apparatus (14) has an identification, wherein the downstream digital VSB apparatus (14) transmits its identification in the upstream channel, wherein the upstream digital source VSB (12) comprises a VSB remodulator (32), wherein the VSB remodulator (32) receives the digital data, wherein the VSB remodulator (32) remodulates the received digital data on the downstream digital VSB channel, where the VSB remodulator (32) transmits a protection key against copying to the digital VSB device downstream (14) in the downstream digital VSB channel, and where the VSB remodulator (32) transmits the demodulated digital data to the downstream digital VSB apparatus (14) on the downstream digital VSB channel at the symbol rate fs. 27. The digital VSB apparatus according to claim 26, wherein the VSB remodulator (32) includes a demodulator (40) and a carrier recovery module (42), wherein the demodulator (40) demodulates the information received from the downstream digital VSB apparatus (14) in the upstream channel, and wherein the carrier recovery module (42) retrieves the carrier (N / M) fs. 28. The digital VSB apparatus according to claim 26, wherein each of the plurality of channels downstream has a carrier frequency, and wherein (N, / M) fs is smaller than the carrier frequency of each current channel down. 29.- The digital VSB device according to the claim 26, wherein each of the plurality of downstream channels occupies a bandwidth above about 50 MHZ, and wherein (N / M) fs is below the bandwidth. 30.- The digital VSB device according to the claim 26, wherein the downstream digital VSB apparatus (14) includes a VSB demodulator (66) and a locked phase circuit (72), wherein the VSB demodulator (66) recovers the symbol speed fs and wherein the blocked phase (72) produces the carrier (N / M) fs in response to the symbol speed fs recovered by the VSB demodulator (66). 31. The digital VSB device according to claim 12, wherein the digital source VSB upstream (12) receives the digital data, wherein the digital source VSB upstream (12) transmits the digital data to the current digital VSB device. down (14) in one of the plurality of digital VSB channels downstream at the symbol rate fs, wherein the plurality of channels occupies a bandwidth above about 50 MHZ, where (N / M) fs is by below the bandwidth. 32.- The digital VSB device according to the claim 12, wherein the upstream digital VSB source (12) includes a modulator (32) that implements a first type of modulation for downstream communication wherein the downstream digital VSB apparatus (14) includes a modulator (70 and / or 74) that implements a second type of modulation for upstream communication, and wherein the first and second type of modulation are different. 33. The digital VSB apparatus according to claim 12, wherein the downstream digital VSB apparatus (14) receives a frame synchronization transmitted by the upstream digital VSB source, wherein the downstream digital VSB apparatus (14) transmits the information in a group of time slots to the upstream digital VSB source (12), wherein the downstream digital VSB apparatus (14) synchronizes the group of time slots to the frame synchronization transmitted by the digital VSB source upstream (12). 34. - The digital VSB apparatus according to claim 12, wherein the downstream digital VSB apparatus (14) transmits information to the digital source VSB upstream in response to a synchronized clock signal in kfs. 35.- The digital VSB apparatus according to claim 34, wherein k is less than one. v > ('t - "- 28 SUMMARY A communication system comprises a digital data source that includes a digital VSB remodulator, such as a VCR, and a downstream digital VSB device, such as a television. The digital VSB remodulator remodulates digital data from the received data source into one of the plurality of digital VSB data channels in a downstream channel and transmits the digital VSB data to the downstream digital VSB device in the downstream channel at a speed of symbol fs. The downstream digital VSB device transmits information, such as its identification, to the digital VSB remodulator in an upstream channel corresponding to a carrier frequency (N / M) fs. The plurality of channels and the downstream channel occupy a bandwidth above about 50 MHZ, and (N / M) fs is below this bandwidth.