Broadband communication system

Broadband communication system

The present invention relates to a broadband communication system such as a cable television (CTV) network, and more specifically to the communication of telephone signals and other or similar digital signals on CTV or similar networks.

A good CTV network system for the NTSC system has been established in the United States. Multiple system operators (MSOs) have a network that covers nearly 90% of the population and connects to nearly 60-65% of households. These networks will be upgraded in the future to have larger information transmission capacity and better serve the ever-increasing number of users.

Generally, the current CTV network is a coaxial cable or optical fiber broadband communication network that transmits multiple 6MHz AM video channels in a frequency division multiplexing manner. The bandwidth of the common CTV system is 50MHz to 550MHz, and the fiber used in the future can be increased to higher than 1GHz. The CTV network is very advantageous in providing a broadband communication path from a single point (head-end) to multiple distribution points (users), but it is very limited in its return path. One reason is that the components and equipment of the network, including amplifiers and compensation networks, are only suitable for forward spectrum frequency transmission. Another reason is the noise that propagates in the reverse frequency band from a single point to a multi-point distribution system such as a CTV network. Since the CTV network appears as an inverted tree in the opposite direction, the noise is transmitted back from each distribution point to a single point, the head end. All the individual noises are concentrated at the head end to create a very noisy environment and cause communication problems.

In the past, the advantages of using CTV networks for telephone signals as low-bandwidth voice signals requiring point-to-point distribution and simultaneous two-way communication were not recognized. On the other hand, due to bandwidth limitations, modern telephone networks have the ability to provide point-to-point communications. The emergence of click-to-call services, interactive TV applications and various data services for users has brought changes to the CTV network discussed. Although not every MSO provides a two-way communication system, most cable television equipment has been designed to allow limited upstream transmission (in the direction from the user to the headend).

In fact, all modern CTV networks provide a downlink or forward transmission spectrum. Usually from 50MHz to 550Hz, and another separate or two-way system for uplink or reverse transmission spectrum, usually from 5MHz to 30MHz. Generally, this reverse frequency band includes cable TV channels T7 (5.75-11.75MHz), T8 (11.75-17.75MHz), T9 (17.75-23.75MHz) and T10 (23.75-29.75MHz). These return path channels, each with a 6MHz TV channel bandwidth, can be used for various purposes.

Regardless of whether the CTV system is a so-called "sub-separation", "medium-separation" or "high-separation" system, the two-way transmission of these three separate forms of transmission systems usually includes a frequency band of at least 5-30 MHz. The transmission of telephone signals should be able to take into account the limited bandwidth on the reverse channel in the usual wired system so as not to increase the cost of the MSO already in the network or to rebuild the MSO to provide additional telephone services.

Another issue involving the transmission of telephone signals through the CTV network is that a head-end can serve hundreds of thousands of users at most. Because it replaces other charged services, the cost of adding the bandwidth required for the telephone service of this number of users to the CTV network is very high. Therefore, a superior method is needed to limit the bandwidth of the telephone service on the CTV network before this service becomes a reality.

Some CTV networks have recently developed a good architecture that allows the limited frequency domain to be reused for specific user groups. These networks with the so-called "Optical Service Area" (FTSA) architecture divide the user area of a CTV network into manageable service areas each with nearly 400-2500 users. Each service area is connected to the head end of the CTV network in a star-shaped structure through an optical fiber communication path terminated to an optical fiber node. The optical fiber node is used as a distribution point for high-quality broadband CTV signals. Then, it is connected to the users in the service area through the coaxial cable feeder distribution subnet in each service area. The forward broadband signal is the same for each service area, that is, the same user service is provided for all users in the user base area. In the opposite direction, it is desirable to have an independent spectrum associated with a specific service area for different purposes or for the same purpose multiple times.

The FTSA structure provides the advantage of expanding the bandwidth of the reverse part of the spectrum to several multiples of the service area. The broadband spectrum part of these systems including the T7-T10 channels in the reverse channel that are not used in the forward direction are space-division multiplexed so that different ancillary services can be provided to each service area.

The last problem in the transmission of telephone signals through the CTV network is the interface between the telephone network and the CTV network. The CTV network is basically a local area network that receives programs fed by satellite or optical fiber links and is therefore limited to a small geographic area. In order to be able to be used to transmit telephone signals, the CTV network should be able to be equipped at a node for commercial operations, and a seamless interface to the telephone network to transmit these signals. It is also necessary to provide signals that can be transmitted to other parts of the interconnected telephone system without the need for extended modulation or protocol conversion to become part of the international telephone system.

The invention includes a device and method for providing broadband communication including two-way telephone communication to a CTV network user group.

In one embodiment, the method includes transmitting the telephone signal from the telephone network to the CTV user on the forward frequency band of the CTV network and transmitting the telephone signal from the CTV user to the telephone network on the reverse frequency band of the CTV network.

In another preferred embodiment, the method includes digitizing the telephone signal of each user into a multiplexed signal transmitted on a frequency division multiplexed carrier in the forward band of the cable network. The digital multiplexed signal is quadrature local response (QPR) modulated onto a carrier located in the unused part of the forward band of the CTV network. In the illustrated embodiment, the QPR signal bandwidth is preferably 3 MHz to leave a 1.5 MHz guard band between adjacent CTV channels. In another preferred embodiment, a pair of QPR signals can be put into the unused channels of the CTV line to utilize the 6MHz bandwidth. By making the system use a robust digital signal, the bandwidth of the forward CTV band can be effectively allocated. The system operator can plan and change these allocations in a flexible manner in order to add new services or cancel old services.

In a preferred embodiment, the user's telephone signal to the telephone network is digitized and individually modulated onto the carrier in the reverse frequency band of the CTV system. As an illustrative example, each user's telephone signal is QPSK modulated into a 50KHz bandwidth signal and frequency division multiplexed on the reverse frequency band of the CTV network. Each telephone signal is multiplexed into a standard TDM telephone signal, which can be adjusted to be directly connected to the SONET port of the telephone network or other connections such as DS1, DS2 or DS3 format signals.

By using the reverse frequency band of the CTV network in small steps of 50KHz, the flexibility of the reverse signaling frequency band will not be compromised. System operators can still provide interactive TV services, PPV services and other reverse path signals while providing telephone services.

If the CTV network is an FTSA network, the number of users supported by the telephone service can be increased several times. The space division multiplexing of the reverse frequency band can economically provide telephone service to all users in the service area. If a service area contains 500 users, the bandwidth required for a dual-path system with 50KHz per user is 25MHz, which is within the 5-30MHz reverse frequency band range of the most popular separated bandwidth system at present.

If you read the following detailed description in conjunction with the accompanying drawings, you will find that these and other objectives, features and aspects of the present invention can be better understood and described more fully. Among them: Figure 1 is a broadband telephone constructed according to the present invention System module diagram of the system; Figure 2 is a system module diagram of an embodiment of the broadband communication system connected to the telephone network illustrated in Figure 1; Figure 3A is a diagram illustrating a common separate CTV system with forward and reverse signaling frequency bands Diagram of frequency allocation; Fig. 3B is a diagram of frequency allocation of the broadband communication system illustrated in Fig. 2; Fig. 4 is a detailed block diagram of the telephone network for the CTV network input interface of the system illustrated in Fig. 2; Fig. 5 is A detailed module diagram of the telephone network for the CTV network output interface of the system illustrated in Figure 2; Figure 6 is a detailed module diagram of a telephone terminal that receives telephone signals from the telephone network through the CTV network and sends telephone signals to the telephone network through the CTV network Figures 7A and 7B are detailed block diagrams of the DS1 to DS2 multiplexers of the input interface illustrated in Figure 4; Figure 8 is a detailed block diagram of the modulator used in the telephone terminal illustrated in Figure 6; Figure 9 is The diagram of the framing protocol of the modulator illustrated in FIG. 8; and FIG. 10 is a detailed block diagram of the demodulator of the tuner/demodulator of the output interface illustrated in FIG. 6.

Referring now to FIG. 1, there is shown a broadband communication system constructed in accordance with the present invention. The system will be described in conjunction with the communication of telephone signals, but in fact other types of similar or identical equipment signals can also be used. Moreover, although the description is a digital telephone signal, the system can also transmit telephone signals of an analog telephone network or other types of digital signals. The telephone signal from the telephone network is connected to the CTV network 12 and transmitted through the CTV network to an addressed user residence 30. The addressed user 30 sends a telephone signal back through the CTV network 12 which is connected to the telephone network 10 again. The system can be used as an extension to the telephone network 10, whereby users can make calls to the telephone network 10 or receive calls from the telephone network. In addition to traditional video services, this service can also be audio, data and other services provided by the CTV network 12 to each user.

Figure 1 illustrates an optimal implementation of a broadband communication system. The system includes a telephone network 10 that interfaces with a CTV network 12 through an input interface 32. The CTV network 12 also interfaces with the telephone network 10 through an output interface 34. The telephone signal is transmitted to the user of the CTV network 12 through the input interface 32 to the user's residence 30. The telephone signal from the user residence 30 of the CTV network 12 is transmitted to the telephone network 10 through the CTV network 12 and the output interface 34. The broadband communication system does not perform switching operations, but uses the capabilities of the CTV network 12 to connect and switch between the broadband communication path and the telephone network 10.

The illustrated CTV network 12 has a fiber service area (FTSA) structure. A head end 14 provides CTV programs distributed through a distribution network to multiple users at its user residence 30. The distribution network serves multiple user groups, each with 400-2500 users, which are adjacent to each other in the service area, just like a group 20 cited in the text. The head end 14 is connected to each service area through a fiber 18 terminated at a fiber node 16 in a star configuration. At the head end 14, CTV programs and telephone signals are converted from RF broadband signals into optical modulation signals and sent out through the optical fiber 18, and then converted back into RF broadband signals at the optical fiber node 16. The coaxial subnet of the feeder 22 with the enhanced signal bidirectional amplifier 24 and the line extender 25 radiates from each optical fiber node 16 to the entire service area 20.

By using a tap 26 to extract a portion of the signal from the nearest feeder 22, then it is connected to the user's residence through a standard coaxial cable termination 28, and the RF broadband signal is distributed to each user's residence 30. In this way, the CTV network provides a broadband communication path from the head end 14 to as many as tens of thousands of user houses 30.

Although a preferred embodiment of the present invention provides an input interface 32 connected to the optical fiber node 16 and an output interface 34 connected to the head end 14, in fact, the insertion and extraction of RF telephone signals need not be limited to this single structure . The input interface 32 and the output interface 38 (shown in dashed lines in the figure) can be connected to the fiber node 16. In addition, both the input interface 36 (shown by the dashed line in the figure) and the output interface 34 can be connected to the head end 14. Moreover, the input interface 36 can be connected to the head end 14 and the output interface 38 can be connected to the fiber node 16. For wired structures that do not conform to the star structure, it is usually best to insert RF telephone signals at the head end and remove them from the system at the head end. The first structure has its own different advantages, which will be described more fully later.

The input and output interface creates a convenient way of inserting telephone signals in one direction and taking out telephone signals in the other direction. The telephone signal is converted into a compatible RF signal that can be inserted into or taken out of the CTV network 12 in the same manner as other program signals at various points in the network. The compatibility of the RF telephone signal and the previous RF signal in the network 12 allows transmission through the network in a transparent manner without affecting other signals and without having to provide a special transmission device.

In theory, the broadband communication path provided by the CTV network 12 is bidirectional, so that information can be transmitted in each direction. However, due to the convention and one-to-multipoint nature of most networks, the reverse path, that is, the communication from the user's residence 30 to the headend 14 is more restricted. Generally, the reverse amplifier 25 is bandwidth limited, and also includes a duplexer that divides the CTV spectrum into forward and reverse paths according to frequency.

Figure 2 illustrates a preferred embodiment of an extended broadband communication system configured as a telephone network. A type 5 switch 41 is used to connect to the telephone network 10. The switch 41 has appropriate circuits for processing conventional local, relay and interconnection signals, and it integrates the switch into a local local area, national or international call network. The switch 41 has a cross-point switching network that can switch any number of inputs to any number of outputs. Specifically, the switch 41 has a device for digitizing an outgoing call or a DS0 format signal. The DS0 format is concatenated into a DS1 format signal in a multiplexer. In addition, the switch 41 has the function of demultiplexing the DS1 signal into a plurality of DS0 signals, and then transmitting them to the outgoing site device. The system uses a forward path to receive multiple DS1 channel signals at the input interface 32 and connect the signals to the user residence 30 through the CTV network 12. The user residence 30 sends a telephone signal to the output interface 34 through the CTV network 12, and converts the signal back to the same number of DS1 signal channels for transmission to the switch 41. If the switch 41 is adjacent to the input interface 32 and the output interface 34, they can be directly connected. In addition, as the most common situation, that is, the head end or fiber node location is not adjacent to the type 5 (clars 5) switch, a fiber link can be used to connect the switch 41 and the interfaces 32 and 34.

In the forward direction, the optical fiber transmitter 43 converts multiple DS1 telephone signals into optical signals that are sent to the optical fiber receiver 45. The optical fiber receiver 4S converts the optical signal into a telephone signal in the DS1 format. Similarly, the optical fiber transmitter 49 converts the outgoing DS1 telephone signal into an optical signal on the reverse path, and the optical fiber receiver 47 receives the telephone signal for conversion back to the DS1 format.

The DS1 telephone signal format was chosen because it is a standard telephone format and the conventional optical link used for conversion and transmission can easily be used for the transmitter 43, 49 and the optical receiver 45, 47.

The system uses this two-way communication mode in which each DS1 signal includes 24 DS0 channels, which can be considered as a 64kb/s digital data channel group. The 64kb/s channel can be used for voice, data, audio (music, stored information) Transmission and so on. Generally, for telephone-type signals, each DS0 channel is addressed to a specific user on the forward path and has a corresponding DS0 channel assigned to the user on the reverse path. This allows the switch 41 to connect any local, trunk or interconnection call point on the forward path to any DS0 channel and connect the corresponding DS0 channel on the reverse path to the same local, trunk or interconnection point to complete the communication path . Each user 30 appears as another DS0 user directly connected to the type 5 switch 41. The distribution system of the CTV network 12 is transparent to the switch 41 and does not require any other communication, information or connection to the broadband communication system.

Figure 3A illustrates a common frequency allocation used in many established separate band CTV networks. The frequency used to transmit programs that generate benefits for system operators in the forward frequency band is 50 MHz to about 550 MHz. Although frequencies above 550MHz are not currently used, there is increasing interest in providing additional services on the unused forward bandwidth, which is currently considered to be extended to approximately 1GHz. Usually the forward frequency band includes a series of video channels with a bandwidth of 6 MHz, which are frequency division multiplexed on the same frequency band before. Several areas are unused and each video channel has a 1.5MHz guard band between other adjacent channels.

Combined with the forward band, the common CTV spectrum also includes a reverse band of about 5-30 MHz. These frequencies are used to return the signal from the user to the headend. This kind of frequency band is generally quite narrow due to the strong noise caused by the concentration effect caused by the overlapping of multi-point signals added to a single point. Moreover, in the past, the bandwidth obtained from the forward band meant that the benefits of other services were reduced. The present invention solves these problems by providing a system for transmitting telephone signals to a user's residence on the forward frequency band of the frequency spectrum and transmitting telephone signals from a user's residence on the reverse frequency band of the CTV system.

As shown in FIG. 3B, the broadband communication system uses multiple frequency division multiplexed carriers on the forward frequency band to transmit telephone signals to each user. In the illustrated embodiment, five channels close to 3 MHz are used to transmit incoming telephone signals from the telephone network 10. Each forward channel is a QPR modulated carrier, where the modulation is carried out with a 6.312 Mb/s digital data stream, specifically in a DS2 telephone signal format including four DS1 telephone signals. The transmission capacity of such a system is 20 DS1 channels or enough to transmit 480 DS0 voice channels.

The bandwidth of each reverse frequency band signal is 50KHz, which is very narrow and can be easily placed at different frequency division multiplexing positions in the spectrum. The frequency of the modulator is flexible, and the frequency can be re-allocated according to the system transmission load, noise, channel conditions and use time. The 50KHz bandwidth carrier can be placed in any position vacated for it in the reverse frequency band. According to the CTV system, that is, according to whether there is a reverse amplification path in the distribution network, it can also be assigned a frequency normally reserved for forward band transmission. Moreover, the bandwidth of such a system is expandable for other purposes besides various telephone signals. For example, if a specific user needs a return path with a bandwidth greater than 50KHz, bandwidth can be easily allocated for this application without the need to completely reconfigure the system. Such applications can include high-speed data transmission, relay connections in small central offices, video services originating from the telephone network, and other applications that require non-standard bandwidth.

As stated, broadband communication systems have many advantages. It effectively uses the reverse band and only uses the required part of the forward band. The use of digital QPR and QPSK modulation allows to provide users with digital and telephone services and provides a way to place forward or reverse signals at any position in the CTV frequency band at high or low frequencies without having to consider the robustness of its signal-to-noise ratio Signaling method. Moreover, in the forward direction, the carrier signal is minimized so that carrier overload does not occur and the 3MHz channel can be placed in a position where it is found to be empty.

FIG. 4 illustrates a detailed block diagram of the input interface 32. The function of the input interface 32 is to convert 20 DS1 telephone signals into five QPR modulated RF signals and send them to the user on the forward frequency band of the CTV system 12. The input interface 32 includes an optical receiver 40 that converts the optical signal into an RF digital signal in a standard telephone format. The optical receiver provides the optical signal to the RF signal converter and also allows an addressing and control unit 42 to decode from the signal and extract additional and framing bits. A demultiplexer 44 receives the digital DS3 telephone number and divides it into 28 component DS1 signals, where each DS1 signal includes 24 DS0 signals. Next, each of the five multiplexers 46 in series takes 4 DS1 signals from the demultiplexer 44 and combines them with the signaling and addressing bits from the addressing and control unit 42 to form 6.312 Mb/sec Serial digital signal. Each of the five digital signals is modulated by a corresponding QPR modulator 48 to a selected carrier frequency. The five telephone channels output by the modulator 48 are frequency division multiplexed together in the RF combiner 50 before being inserted on the CTV network 12.

The output interface 34 will now be described more fully with reference to FIG. 5. The function of the output interface 34 is to convert the 480 DS0 digital signals modulated by QPSK onto the reverse frequency band carrier into optical format signals that can be transmitted to the telephone network 10. The output interface 34 takes the reverse frequency band signals in a conventional manner and uses the signal divider 60 to fan them out to a plurality of tuners/demodulators 62. Each tuner/demodulator 62 is used to tune a carrier frequency of the reverse band signal and demodulate it into a DS0 format digital signal. The tuner of the tuner/demodulator 62 may be variable or fixed, or may only tune certain frequency bands of the reverse spectrum. The output of the tuner/demodulator 62 is 480 DS0 signals, which are concentrated into a group of DS1 signals by a group of multiplexers 64 under the control of the addressing and control unit 66. Each multiplexer 64 inputs 24 DS0 format signals and outputs a DS1 format signal. The 20 DS1 signals obtained are concentrated by the multiplexer 68 in the same way, and then a digital signal is output to the optical transmitter 70. The addressing and control unit 66 adds necessary control information in the optical transmitter 70 before sending the digital DS1 signal in the optical format. The optical transmitter 70 converts the RF signal into an optical signal so that the optical fiber of the telephone network can be transmitted.

FIG. 6 shows detailed modules of the system equipment at the user's residence 30. Generally, users want to maintain CTV video or other services and have a CTV terminal 84 for this purpose connected between the CTV terminal 28 and the television receiver 88. The CTV terminal is connected to a splitter/combiner/duplexer 80 connected to the termination 28 of the CTV coaxial subnet feeder. Since the broadband communication system currently described will not affect or replace conventional CTV program transmission and frequency allocation, the CTV terminal 84 can be used without modifying or changing the operation of existing terminal settings. The system operator does not need to change or reconfigure the operation of its distribution network, and the new telephone service is compatible with its established CTV user terminal facilities.

The broadband communication service is provided by connecting the telephone terminal 82 between the splitter/combiner/duplexer 80 and the telephone device 86. The telephone terminal 82 converts an incoming telephone signal to a user into an analog signal that can be used by a standard telephone handset 86 via a pair of twisted pair wires 85. Moreover, the telephone terminal 82 converts the analog signal representing the outgoing telephone signal from the mobile phone 86 into a QPSK modulated signal that can be transmitted to the CTV network. For illustrative purposes, a standard telephone handset 86 is given, but in fact any device that is normally connected to a telephone line for digital communication is available.

The telephone terminal 82 has two communication paths. The first path is for incoming signals and includes a tuner/demodulator 92, demultiplexer 96 and part of the line card 98 and the second path is for outgoing signals including part of the line card 98 and a modulator 94 . The tuner/demodulator 92, the modulator 94 and the line card 78 are controlled by the addressing and control unit 90.

For the incoming telephone signal received in the 3MHz channel modulated onto the FDM carrier, the control unit 90 causes the tuner/demodulator 92 to tune the carrier carrying the specific call information transmitted to the user. This carrier defines one of five 3MHz channels with 4 DS1 or 3 E-1QPR modulated telephone signals.

The telephone signal is demodulated by the tuner/demodulator 92 into a serial digital stream containing 4 DS1 or 3 E-1 telephone signals before being input to the demultiplexer 96. The demultiplexer 96 selects the specific DS0 digital telephone channel assigned to the user at an input rate of 64 kb/s and inputs the data to an input terminal of the line card 98. The control unit 90 determines the forward telephone channel to be tuned according to the signal and addressing information received on the connection to the splitter/combiner/duplexer 80 via the line 89 and selects a DS0 signal from the channel.

The DS0 digital format provides a voice channel with sufficient bandwidth for voice quality communication. The DS0 format is a 64kb/s data byte stream that constitutes the time sampling value of the analog voice signal. This produces a speech signal that is quantized to 8 bits per sample (256 values) at an 8KHz sampling rate and has a 4KHz bandwidth.

The line card 98 receives the digital telephone signal in DS0 format and converts it into an appropriate analog voltage and signal to drive the telephone handset 86. In addition, the line card 98 provides ringing current, terminal identification and other standard functions under the control of the control unit 90. The line card 98 receives analog telephone signals from the telephone handset 86 and converts them into digital DS0 format. Dial signals and other addressing and control signals from the mobile phone 86 are also digitized by the line card 98. Then the digitized outgoing telephone signal is combined and formatted by the line card 98 or 64 kb/s DS0 format and input to the modulator 94.

Under the control of the control unit 90, the modulator 94 selects a carrier frequency in the reverse frequency band and performs QPSK modulation on the DS0 telephone signal on it. The QPSK modulated carrier wave with a bandwidth close to 50KHz is transmitted to the CTV network through the splitter/combiner/duplexer 80.

7A and 7B illustrate a detailed block diagram of a conversion device for converting 4 DS1 digital format signals into a DS2 digital format signal. If transmitted through a standard telephone optical receiver, each DS1 signal will be in the form of an analog voltage and be differentially transmitted through a user loop. This signal is converted to a digital signal level by a converter and then input to a clock recovery circuit that divides the DS1 signal into a data stream and timing. The data and clock pair with the DS1 data transfer rate is input into an 8-bit buffer. The buffer allows time base conversion from the DS1 data rate to the DS2 data rate in the multiplexer. The multiplexer obtains data from each of the four buffers and multiplexes them onto a single data channel, which is output to the QPR modulator through the buffer amplifier. The clock used for the DS2 format data is retrieved from the oscillator driving the multiplexer.

Each buffer is allowed to send data to the multiplexer by indicating that the buffer represented by STUFF REQ is almost full. When this happens, the buffer sends data at the DS2 data rate until there is enough space to allow the DS1 signal to be filled again. The multiplexer includes a 4:1 multiplexer, using two non-inverted states DS1 The channel and the two inverted state DS1 channels are time-division multiplexed into serial data signals and then randomized by the PRBS random function generator. Then, the randomized data is framed by the data framer and finally resynchronized with the DS2 data rate through the DS2 clock.

Control of the buffer and multiplexer is provided by multiplexer control including counters and decoders. The multiplexer control also controls the two multiplexers to provide data and framing bits for DS2 signaling attached to the correct time and position in the signal.

FIG. 8 illustrates a more detailed schematic diagram of the modulator 94 for each terminal. The modulator is used to change the data rate on the line card from 64kb/s voice signal to 68kb/s, thus allowing framed bytes to be added to the signal. The modulator also combines the data with a pseudo-random bit sequence (PRBS) to randomize the data transmitted through the CTV network. The signal is QPSK modulated onto a carrier using differential coding.

Referring now to the drawings, the voice data is digitally encoded and moved into the three-stage buffer at a rate of 64 kb/s and moved out at a rate of 68 kb/s. This allows an extra byte to be added to the data stream every 16 bytes to produce a 17-byte subframe. Specific bytes or framing bytes are used for signaling, frame identification, error detection and correction, etc.

When the frequency of the data stream has increased, the random function generator operates on the data to distribute the signal energy over a longer period of time. This randomization is known to be beneficial to the clock recovery of the demodulator at the center or head end. Circuit. Randomization is accomplished by generating a string of pseudo-random bits PRBS and adding it to the data signal byte by byte. The longer the bit string, the more random, the better the randomization effect such an operation adds to the data. There are many ways to generate PRBS, and the simplest is to use a shift register to continuously recycle the sequence. In the preferred embodiment, the 127-bit mode is used. As is well known, the process of de-randomizing the output can be achieved by taking out the sequence in the same order as adding the sequence to the bit stream.

Then insert special framing bytes every 16 data bytes to assemble the signal into a frame in the framer. The framing format is similar to the European E-1 format, that is, bytes are added to the data signal at the time of even and odd frames. This is caused by two reasons, that is, the DS0 format is already byte-oriented, and the bundled framing sequence is easier to assemble into a frame on the non-bundling sequence.

An illustrative framing sequence of the preferred embodiment is given in Figure 9, where the frame is organized into even and odd subframes of 17 bytes, and each subframe has a different FAS byte. In the multi-frame, the sub-frame is divided into multiples of 8 to allow higher-level operations such as CRC calculation. The framing sequence is X0011011 in even-numbered subframes, and X1XXXXXX in odd-numbered subframes. The extraneous (X) bit can be used in special cases but is not important for framing. The framing mode uses primary and secondary FAS values to ensure that there are no erroneous framing positions in the data. The primary FAS must have 7 bits to match and the secondary FAS has only one bit to match, and it is in the position where the primary FAS is zero. If the primary mode appears in the data, the chance of data 1 appearing at the same time in the secondary FAS is low.

The framer can work in two modes, one with cyclic redundancy code (CRC) and the other without CRC. If the first bit in each FAS byte is always 1, CRC is not used and there are only two subframes (non-multiframes). If the even number and the first bit in the frame are the pattern given in Figure 9. It is recognized as a CRC multiframe. The definition of a multiframe allows a CRC remainder to be carried in the first bit of the FAS of an even-numbered subframe. The C1, C2, C3, and C4 bits carry the CRC-4 remainder for the previous frame. The CRC formula is X4+X+1. Defined by CCITTG.704 for the E1 phone format. The CRC formula will indicate the quality of the data transmission. This framing format allows alternate channels to be used as data transmission channels. And it can transmit any 64kb/s data stream (data or voice) that allows support of DDS type services.

The DL bit constitutes a 500 bit per second data link. The data link uses an HDLC level formatter to send message packets or bit-oriented status information. The AL bit is an alarm bit that indicates a problem on the line card. When the data bit is 1, no alarm is given, and when the data bit is 0, the alarm is issued. Bits A, B, C, and D are signaling bits, providing 16 possible signaling states. In fact, more states can be defined by triggering individual bits at a certain rate. The signaling bits are defined as: bit A=1 means on-hook; bit A=0 means off-hook; bit B21 means no ringing; and bit B=0 means ringing. The state of the appropriate state grid detector is read every 4ms and inserted into the appropriate bit of the odd FAS.

The RF modulator receives the 68kb/s data stream and QPSK modulates it to the RF carrier (5MHz to 30MHz) and transmits the information to the head end in a SOKHz channel through the coaxial cable subnet. The digital data is divided into I and Q channels by the encoder and differentially encoded to remove phase ambiguity in carrier recovery at the receiving end. The I and Q channels of the encoded information are separately filtered in the filter to ensure that data can be transmitted with minimal inter-symbol interference. The filter is digital and is similar to a raised cosine filter with ulpha=1.5. Separate filtering at the baseband allows the use of a low-pass filter on the output of the modulator instead of a more complex band-pass filter.

Then the I and Q signals are amplified to an appropriate level to ensure that the mixer can work properly. The modulator generates two phase-locked IF carriers with a phase difference of 90°, and each carrier is DSK modulated with a coded filtered data channel.

The two channels are recombined to produce a positive signal and amplified before being frequency converted to an appropriate transmission channel. The switching operation is frequency-variable and the transmission channel can be programmed through the forward data link. The transmission signal is then amplified by a buffer amplifier to allow a fully loaded system with 480 channels to produce almost the same load as the 5 video channels in the reverse band.

The demodulator with a bandwidth of 50KHz for QPSK signals will be described more fully below with reference to FIG. 10. The specific carrier frequency of the modulated QPSK signal is tuned by a converter which takes the channel number from the authorization and data controller as an input. The converter selects a specific frequency and converts it to an intermediate frequency, preferably 455KHz. The intermediate frequency signal is filtered by a band-pass filter and amplified by an amplifier with automatic gain control. The clock used for the QPSK signal is recovered through an envelope detector and a bandpass filter that allows a certain rate, in the example, 32KHz, to pass through to the comparator. This clock is used for the I of the two sampled QPSK signals. The D-shaped bistable circuit in phase and Q phase provides the clock. The samples of the I and Q phases are differentially decoded and converted into a parallel series in the converter to be output as a 64kb/s digital signal.

The demodulation is performed in a dual-path demodulator that multiplies the recovered carrier from the VCO with each phase of the signal. The VCO is usually four times the symbol rate and is divided into an in-phase path and a quadrature-phase path. A phase of the carrier signal is added to a multiplier, which generates a demodulated signal and its inverted signal, which is then filtered by a low-pass filter and differentially compared in a comparator, thereby serving as the input of the D-shaped bistable circuit . The other phase of the carrier is added to a multiplier, which demodulates the intermediate frequency signal with the recovered carrier, low-pass filters the result and provides it to a comparator. The output of the comparator is used as the input of the D-shaped bistable circuit and is sampled at the symbol time to decode the bit value.

By driving the voltage controlled oscillator, the carrier can be recovered from the output of an integrator that differentially compares the phases of the demodulated signals and their inverted signals through a multiplexer. According to the signal channel and the value of its inverted output, the input of the multiplexer is selectively controlled.

In summary, the present invention provides broadband communication including digital communication, telephone and telephone-related services by using the CTV system in an effective manner, without the need for additional switching equipment and redesign of the CTV system. When connecting a telephone-based call from or to a user, the broadband communication system does not need to perform exchanges in the usual sense. By effectively using the wide bandwidth of the CTV network to give full play to the best features of the CTV network and making the call connection through the telephone network to give full play to the best features of the telephone network, multiple calls can be made through the system.

There are two types of telephone calls in broadband communication systems, one is incoming calls and the other is outgoing calls. Combining these types of calls can complete all required connections to or from another telephone device and to or from a CTV network user. The user can call (or be called to) a user in another CTV network, can call (or be called to) a local telephone device in the local telephone network or call (to be called to) a telephone that interfaces with the long-distance and international telephone system network.

When it is recognized that an incoming call is directed to a user in a user group belonging to the CTV network, the telephone network connects the call to a specific user of the CTV network. Then in the time slot assigned to the user, the call is switched by the telephone network to OC-1 or other standard telephone signals connected to the CTV network. Then the addressing and control system of the CTV network decodes the multiplexed information and converts it to the frequency and time position in the forward multiplex that has been assigned to the specific user. The addressing and control system also provides the necessary control to make the user's equipment ring or alert the user that there is an incoming call.

The telephone network and the CTV network maintain the connection until there is an "on hook" signal indicating that one party has hung up or another signal indicating the end of the communication, such as the termination of a message data mode. Maintaining the connection means that the telephone network continues to place the called party's data packet in the position given in the standard telephone signal, while the broadband communication system continues to convert the data packet to the forward multiplex that is connected to the specific user Location and frequency.

For outgoing calls, the telephone network identifies data packets belonging to a specific CTV network calling user from the DS0 position in the standard telephone signal. The DS0 position is an assigned position, and the CTV system uses the carrier frequency input to the demodulator to convert the data to the assigned position in the inverse multiplexing. Therefore, for outgoing calls, the telephone network will treat the standard telephone signal as a group of separate DS0 signals whose position in the reverse multiplexing indicates the calling party.

The best embodiment of the present invention has been illustrated and described here, and in fact, those skilled in the art can make the case without departing from the purpose and scope of the present invention as set forth in the appended claims and the equivalent description therein. Various modifications or changes.