WO1996028910A1 - Terminal pour recevoir des programmes video numeriques simultanees - Google Patents

Terminal pour recevoir des programmes video numeriques simultanees Download PDF

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Publication number
WO1996028910A1
WO1996028910A1 PCT/US1996/003680 US9603680W WO9628910A1 WO 1996028910 A1 WO1996028910 A1 WO 1996028910A1 US 9603680 W US9603680 W US 9603680W WO 9628910 A1 WO9628910 A1 WO 9628910A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
delay
digital
signals
receiver
Prior art date
Application number
PCT/US1996/003680
Other languages
English (en)
Inventor
Bruce Kostreski
Allan Schneider
Kamran Sistanizadeh
W. Tim Campbell
Original Assignee
Bell Atlantic Network Services, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/405,558 external-priority patent/US5651010A/en
Priority claimed from US08/555,373 external-priority patent/US5852612A/en
Application filed by Bell Atlantic Network Services, Inc. filed Critical Bell Atlantic Network Services, Inc.
Priority to AU54252/96A priority Critical patent/AU5425296A/en
Publication of WO1996028910A1 publication Critical patent/WO1996028910A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/18—Arrangements for synchronising broadcast or distribution via plural systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/65—Arrangements characterised by transmission systems for broadcast
    • H04H20/67—Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/60—Network streaming of media packets
    • H04L65/75—Media network packet handling
    • H04L65/764—Media network packet handling at the destination 
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
    • H04N7/17309—Transmission or handling of upstream communications
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
    • H04N7/17309—Transmission or handling of upstream communications
    • H04N7/17336—Handling of requests in head-ends
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/20—Adaptations for transmission via a GHz frequency band, e.g. via satellite
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/02—Arrangements for relaying broadcast information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/28—Arrangements for simultaneous broadcast of plural pieces of information
    • H04H20/33—Arrangements for simultaneous broadcast of plural pieces of information by plural channels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/53—Arrangements specially adapted for specific applications, e.g. for traffic information or for mobile receivers
    • H04H20/61—Arrangements specially adapted for specific applications, e.g. for traffic information or for mobile receivers for local area broadcast, e.g. instore broadcast
    • H04H20/63—Arrangements specially adapted for specific applications, e.g. for traffic information or for mobile receivers for local area broadcast, e.g. instore broadcast to plural spots in a confined site, e.g. MATV [Master Antenna Television]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/65—Arrangements characterised by transmission systems for broadcast
    • H04H20/76—Wired systems
    • H04H20/77—Wired systems using carrier waves
    • H04H20/81—Wired systems using carrier waves combined with telephone network over which the broadcast is continuously available
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
    • H04N2007/1739—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal the upstream communication being transmitted via a separate link, e.g. telephone line

Definitions

  • the present invention relates to wireless reception of program information, e.g. video, audio and data. More specifically, the present invention relates to simultaneous distribution of multiple RF channels from separately located transmitters, each RF channel carrying a digital transport stream containing multiplexed data relating to a plurality of different programs, and to terminal devices receiving programs from such a distribution system.
  • program information e.g. video, audio and data.
  • the present invention relates to simultaneous distribution of multiple RF channels from separately located transmitters, each RF channel carrying a digital transport stream containing multiplexed data relating to a plurality of different programs, and to terminal devices receiving programs from such a distribution system.
  • Wireless cable is a term usually used to refer to a multi-channel video distribution medium that resembles franchise cable television, but which uses microwave channels rather than coaxial cable or wire to transmit programming to the subscriber.
  • Programming for wireless cable systems is received at the headend of the wireless cable system in the same manner as it is for landline based cable television.
  • These programs are then re- transmitted, utilizing the high end of the Ultra High Frequency (UHF) portion of the microwave radio frequency spectrum (2.1 to 2.7 GHz), by a microwave transmitting antenna located on a tower or other tall structure to small antennas on subscriber rooftops, typically within a 40 mile radius.
  • UHF Ultra High Frequency
  • the transmission of wireless frequencies requires clear line-of-sight (LOS) between the transmitter and the receiving antenna. Buildings, dense foliage and topography can cause signal interference which can diminish or block signals. Certain LOS constraints can be reduced by increasing transmission power and using engineering techniques such as pre-amplifiers and signal repeaters.
  • wireless cable operates as a cable look-alike service.
  • microwave signals are received by an antenna, down- converted and passed through conventional coaxial cable to a descrambling converter located on top of a television set.
  • the signals are converted at the antenna location to lower frequencies in order to be carried over conventional in-house cable to a converter box, decoded and then output to a standard television set.
  • wireless cable signals are transmitted over the air rather than through underground or above-ground cable networks, wireless systems are less susceptible to outages and are less expensive to operate and maintain than franchise cable systems. Most service problems experienced by wireless cable subscribers are home- specific rather than neighborhood-wide, as is frequently the case with franchise cable systems.
  • Wireless cable technology has existed in a single channel version for commercial purposes since the 1970's and had been available even longer for educational use.
  • the FCC invoking the need to promote competition with conventional cable television systems, established a change in the rules for using a portion of the microwave spectrum previously designated for educational use.
  • 28 microwave channels had been available to accredited and non-profit educational organizations for educational use exclusively by Instructional Television Fixed Service (ITFS) operators.
  • ITFS Instructional Television Fixed Service
  • Rules reallocated eight of those channels for outright commercial use, and educational organizations were permitted to lease excess hours to commercial operators on the remaining 20 channels. In any local market, this makes it possible for a commercial operator to combine any or all of those 28 channels with five other channels already available for commercial use.
  • the available spectrum results in a maximum of 33 analog channels. This number of 'wireless cable' channels is less than the number offered on many competing franchise type cable television systems.
  • the 33 channels potentially available to wireless cable operators thus are subdivided into two types of channels. Twenty channels are referred to as ITFS. The remaining 13 channels are generally referred to as Multi ⁇ channel Multipoint Distribution Service (MMDS) .
  • MMDS Multi ⁇ channel Multipoint Distribution Service
  • the current UHF spectrum was originally licensed in blocks of four video channels each separately licensed, with each block allocated to a specific purpose. Five groups, each with four channels, were allocated to Instructional Television Fixed Service (ITFS) . ITFS spectrum was initially made available only to educational institutions. Two groups of four channels were made available to anyone wishing to provide an alternative multi-channel video program service. The final four channels were licensed individually to institutions for the purpose of providing a private video network. Over time, the FCC relaxed some of these operational rules. Through licensing and leasing arrangements, the FCC now allows all of the channels to be aggregated for the purpose of providing an alternative to cable television.
  • ITFS Instructional Television Fixed Service
  • Wireless cable technology provides a relatively low cost medium to transmit video and does not require extensive coaxial cable networks, amplifiers and related equipment.
  • the three major advantages of such service are variable cost technology where capital is spent in establishing cash flows, manageable financial risk because of variable costs, and the possibility of establishing broad based market entry more quickly than is feasible with wireline based video systems.
  • Wireless cable systems are attractive to potential subscribers not yet served by franchise cable operators and can provide customers in cabled areas with an economical alternative to both existing franchise cable and satellite television reception systems.
  • the current analog technology presents several problems which have severely limited actual use of 'wireless cable' .
  • a headend system H receives up to a maximum of 33 analog television program signals from a variety of satellite down-link receivers and other types of receivers, in the exact same manner as for a cable television system.
  • the headend system H frequency multiplexes those television program signals into a combined spectrum signal in the 50-450 Mhz range. This combined signal has a frequency distribution similar to that found on a cable television network.
  • the headend system upconverts the combined spectrum signal to the UHF frequency range, typically centered around 2.6 GHz.
  • the headend system supplies the UHF signal to a single transmitter antenna tower T which broadcasts the signal to subscribers who each have an individual home receiving system. Subscribers can call in to the headend to order pay-per-view events via the telephone network, and the headend transmits codes to the subscribers systems to enable descrambling of encoded pay-per-view programs.
  • FIG 1A shows a typical service area for a wireless cable type system of the type shown in Figure 1.
  • the wireless cable operator has a protected or 'primary' reception area P.
  • the primary area P is a circle having a radius of 15 miles from the operator's transmitter T. Within this area, the operator is guaranteed that there will be no interference with his transmissions on the assigned frequency channel(s) . However, at the allowable power levels, the transmissions from antenna tower T will propagate out over a secondary area S having a radius of up to 40 miles. Within the secondary area, some locations will receive sufficient signal strength to utilize the wireless cable services.
  • UHF signals in the relevant frequency band arrive at the customer location by direct line-of-sight (LOS) transmission.
  • LOS line-of-sight
  • an elliptical dish shaped antenna 18-36 inches long, formed of parallel curved elements, is aimed from the subscriber location to receive the strongest signal from the transmitter.
  • the captured signals are down-converted at the antenna from the microwave band to the broadcast band and transmitted via coaxial wiring into the house.
  • a set top converter functionally similar to a cable set top box is used.
  • a VHF/UHF off-air broadcast receive antenna is installed with the UHF antenna to pick up the local programming.
  • FIG. 1A also shows a simplified example of one such obstruction 0.
  • the obstruction O is within the primary reception area P.
  • the obstruction blocks line-of-sight transmissions from transmitter antenna tower T in a radially extending blockage or shadow area B. Receiving systems within this area can not receive the transmissions from antenna T, and potential customers in that area B can not subscribe to the wireless cable services broadcast from that tower.
  • a repeater receives the primary transmission from tower T on the tower side of the obstruction, amplifies the signal if necessary, and retransmits the signal into the area of blockage. This may be an effective solution to one blockage or obstruction 0, but in many major metropolitan areas there are many obstructions.
  • the power levels of such repeaters tend to be low, and overcoming blockages due to distortions that result when amplifying combined RF channels caused by many different obstructions to the primary transmissions would require an inordinate number of repeaters.
  • repeater transmissions may interfere with reception from the primary source in areas close to the blockage area B.
  • multi-path reflections of the desired signal arriving at the receiver by way of differing paths and therefore arriving with slight delay For analog video signals, multi-path appears as ghost images on the viewer's TV.
  • multi-path can cause intersymbol interference that results in multiple bit errors. In either case, near-coincident multi-path signals can cause a degree of signal cancellation that looks like additional propagation loss. Multi-path also results from reflections and diffraction. Path fading is another significant coverage factor.
  • Time-variant path fading can result from atmospheric effects, e.g., rain or temperature and pressure inversions. Rain can act to partially reflect or absorb the microwave signals. Weather inversions can result in an upward bending of the wave front due to refraction. There are engineering measures to mitigate the troublesome effects of time-variant path fading, such as suitable fade margins and antenna diversity.
  • the present invention provides methods and apparatus to address the above stated needs.
  • the present invention provides an improved arrangement for receiving transmitted signals in a reception area from an RF frequency simulcasting system that generates overlapping radio frequency propagation areas from corresponding transmitting sites.
  • Each transmitting site substantially simultaneously transmits (simulcasts) a signal including multiplexed channels of compressed digital broadband data, such as video data.
  • the method of receiving the transmitted signals from the RF frequency simulcasting system comprises the steps of receiving a signal containing a plurality of time delayed copies of the transmitted signal at a receiving site within the reception area, processing at least a portion of the received signal to acquire a single copy of a signal corresponding to a selected one of the multiplexed channels, and presenting a selected portion of the compressed digital broadband data contained in the acquired signal.
  • the transmitting sites propagate the signal into substantially overlapping regions of at least a major portion or the intended reception area.
  • Each of the transmitting sites will have a different propagation path to a subscriber premises.
  • a terminal device will receive a signal containing a plurality of time delayed copies of the transmitted signal.
  • At least a portion of the received signal is processed to acquire a single copy of a signal corresponding to a selected one of the multiplexed channels, and information contained in the acquired signal is presented, e.g. in a form that is sensorially perceptible to a user.
  • the processing of multiple copies utilizes a delay processor, such as a delay equalizer, or a rake receiver for signals that are received as spread spectrum signals.
  • the delay processing technique of the present invention enables a receiver to acquire an optimum representation of the simulcast signals transmitted from the multiple transmitting sites.
  • the receiver arrangement of the present invention enables subscriber receivers to receive a plurality of signals in a simulcast transmission system without the typical concerns of interference.
  • the overlapping transmission or propagation areas in the simulcast transmission system enhance reception by reducing or eliminating blockage zones and effects of fading.
  • This technique also limits the number of receivers effected by equipment outages at a transmission site.
  • a directional receiving antenna can be aimed toward at least one strong line-of-sight transmission source.
  • each of the multiplexed channels carries a multiplexed stream of digital data representing a plurality of programs.
  • the programs may be audio or data, but in the currently preferred embodiment, the programs comprise audio/visual information such as television programming.
  • each program is digitally encoded into compressed digital data.
  • a multiplexer combines the compressed digital data for a group of programs into one of the digital multiplexed data streams for transport through one of the channels.
  • the presentation of one program to a user entails selecting one of the channels, selecting data from the multiplexed stream of digital data carried in that channel, and reproducing the selected data as the sensorially perceptible information, e.g.
  • each transmitter may transmit a plurality of spread spectrum signals, whereby each spread spectrum signal is spread spectrum processed using a corresponding code sequence, and comprises a corresponding plurality of multiplexed channels of compressed digital broadband data.
  • the receiver may selectively process one of the transmitted spread spectrum signals by selecting one of the code sequences stored at the receiver premises.
  • a receiver may effectively increase the number of available channels for viewing by selecting one of the transmitted signals carrying a corresponding plurality of multiplexed channels.
  • real-time encoders receive video programs and encode the information for those programs into packets of compressed digital data, e.g. in accord with a recognized video compression standard.
  • the headend may also receive previously encoded video program material from other sources, such as a digital server or a digital transmission media.
  • Multiplexers combine digital data for groups of programs into the multiplexed packet data streams.
  • a digital modulator such as a 64 or 256 QAM modulator, modulates each digitally multiplexed packet data stream for transport in one unique RF channel.
  • a combined spectrum signal containing the RF channels is upconverted to place the channels into available frequency channels in the UHF range.
  • the combined spectrum signal is supplied to a plurality of microwave broadcast transmitters located at spaced apart sites about the service area or reception region. Appropriate delays are imposed in one or more of the lines to the transmitters so that the transmissions from all the transmitter antennae occur simultaneously and in phase with each other.
  • an antenna receives a signal from at least one of the transmitters.
  • the antenna is a directional antenna aimed at one of the transmitters for line-of-sight reception therefrom.
  • the signal from the receiving antenna is downconverted and supplied to a wireless signal processor.
  • the wireless signal processor typically part of an interface module connected by a cable to the downconverter, processes the received wireless signal to select one of the channels.
  • the wireless signal processor effectively acquires a digital multiplexed data stream from the selected channel and supplies that data stream to a digital signal processor.
  • the digital signal processor selects packets of data relating to a selected one of the programs.
  • the digital processing section processes the compressed, digitized data from those packets to produce signals presentable to a user.
  • the digital signal processor produces signals to drive a standard television set.
  • Figure 1 is a simplified diagram of a prior art wireless cable television system.
  • Figure 1A shows service areas relating to a single wireless transmitter in the system of Figure 1.
  • Figures 2 and 3 show propagation areas for multi- transmitter systems used in other types of prior art systems, e.g. paging.
  • Figure 4 depicts an exemplary service area and transmitter layout for simulcast transmissions into a receiving area.
  • Figure 5A depicts exemplary propagation patterns
  • Figure 5B depicts a more specific example of transmitter antennae locations, in accord with the present invention.
  • FIG. 6 depicts in functional block diagram form the elements of the transmission system used in accord with the present invention.
  • Figure 7 illustrates the functional elements of a customer premises receiver system used in accord with the present invention.
  • Figure 8 illustrates in block diagram form the elements of one terminal device used in the system of Figure 7.
  • Figures 9A and 9B are block diagrams illustrating the elements of alternative transport interface modules for use in the terminal of Figure 8.
  • the present invention is directed to the receiver arrangement for use in an improved simulcast transmission system for broadband data, such as video.
  • a description of the transmission system itself will first be provided, followed by a detailed description of the receiver arrangement of the present invention for receiving the broadband data from the simulcast transmission system.
  • groups of program signals are digitally encoded and compressed, and the compressed program streams are time division multiplexed into digital transport streams.
  • Each digital transport stream is modulated and/or upconverted into one RF channel, in the preferred embodiment a channel in the high end of the ultra high frequency (UHF) microwave range (e.g. 2.1 to 2.7 GHz), although other frequency channels could be used.
  • UHF ultra high frequency
  • Separately located transmitters simultaneously broadcast an UHF frequency signal containing all of the channels.
  • the transmitter antennae are located and the transmitter emission patterns are designed so that the waves from the transmitters propagate throughout substantially overlapping portions of the service area.
  • the overlapping portions may extend throughout the intended reception area.
  • Existing regulations relating to the relevant frequency allocations specify a primary service area and a secondary service area. Within the primary service area, the regulations protect the licensee from any interference on the relevant frequency channel.
  • the overlapping areas of propagation from the multiple transmitters would cover at least a major portion of the primary reception area and preferably also cover a substantial portion of the secondary reception area.
  • Some portions of the secondary reception area may be covered by propagating waves from only one of the transmitters. All of the primary and secondary areas would be covered by propagating waves from at least one of the transmitters.
  • the circle P defines the Protected Area or primary area which may be serviced from a primary transmitting antenna T p .
  • the radius of this circle is 15 miles.
  • usable signal and acceptable reception generally occurs to a radius of 40 miles which is here defined by the circle M indicating the Maximum Area.
  • the region between the 15 mile radius and the 40 mile radius forms a 'secondary' service area.
  • all or part of the rights of the educational institution for ITFS service are leased.
  • licenses are aggregated, from companies currently licensed to use MMDS channels.
  • the central antenna T p broadcasts in an omni-directional propagation pattern.
  • the secondary antenna T SJ , T s2 , and T S3 are provided as directional antennas.
  • the directional secondary antennae may radiate back lobes, albeit much smaller and lower in power than the cardioid shaped front lobes.
  • reflectors may be provided so that these antennae substantially radiate only forward lobes as shown, TS1F for antenna T S1 , TS2F for the T S2 antenna and TS3F for the T S3 antenna. As shown, most locations within the primary service area P actually are within the radiation patterns of all four transmitting antennae.
  • receivers are within the radiation patterns of the primary transmitter antenna T p and at least one and sometimes two of the secondary transmitter antennae. It will be seen that there is a radical departure from the minimum overlap approach which is conventional in the systems illustrated in Figures 2 and 3.
  • a directional antenna having approximately a 12 degree field of view can be aimed to receive transmissions from a single one of the transmitting antennae.
  • a receiving antenna having a narrow field of view could be aimed at any of the four transmitting antennae which presents clear line of site reception.
  • the receiving antenna can be aimed at the primary transmit antenna T p or at the secondary transmit antenna T S1 , whichever presents a stronger, unobstructed line of transmission to that location. Because of the directionality of the receiving antenna, the signal from the other non-selected transmitters will not interfere with the signal selected by the aiming of the directional antenna, e.g. if the antenna at location X R1 is aimed at transmitter T S1 , the antenna will not receive any substantial transmissions from primary transmitter antenna T p .
  • a second receive location X M is somewhere along line 1 to the right of the primary transmitter antenna T p .
  • a directional antenna at that location aimed at the primary transmitter antenna T p is also aligned to receive the simulcast transmission from secondary transmitting antenna T S1 .
  • all of the secondary transmitter antennae T S1 , T s2 and T S3 are disposed along the boundary of the Protected Area P and therefore are substantially equidistant from the primary transmitter T p .
  • the primary area P has a radius of 15 miles ( Figure 4) .
  • the secondary transmitters all transmit simultaneously (and preferably in phase with each other) . Electromagnetic waves propagate through atmosphere at a rate of approximately 5.3 microseconds per mile. Consequently, the transmission from one of the secondary antennae aimed inward will arrive at the location of the primary antenna T p arrives arrive approximately 79.5 microseconds later.
  • the primary antenna T P will broadcast the same signal at approximately the same time as each of the secondary antennae T S1 , T S2 and T S3 .
  • the signal from primary antenna T p therefore arrives at a location, such as X ⁇ / which is aligned with the primary antenna and one of the secondary antenna (T S2 in the illustrated example) approximately 79.5 microseconds before the broadcast of the corresponding signals from the aligned secondary transmitter antennae (e.g. from T S3 ) reaches that location.
  • many systems in accord with the present invention will provide service in densely populated metropolitan areas.
  • high-rise buildings reflect signal transmissions in the relevant frequency range.
  • the multiple transmitters create increased numbers of reflected signals off of the high-rise buildings.
  • a delay processor in the receiving terminal processes signals from multipath reflections and in some cases from line of sight transmissions from multiple transmitter antennae to produce a single enhanced copy of the digital transport stream carried on a selected channel.
  • the equalizer has a delay processing window which is at least as large as the longest delay offset between arrival times of signals from two aligned transmitter antennae. In the above example, the difference in arrival time is approximately 79.5 microseconds.
  • the delay processing window preferably is large enough to compensate for multipath interference from reflections of signals from the more distant transmitter.
  • an equalizer should be able to process multipath signals having up to a 20 microsecond offset from a directly received source signal.
  • the adaptive delay equalizer has a processing window 20 microseconds longer than the delay of the last received direct transmission, i.e. 79.5 + 20 microseconds or approximately 100 microseconds.
  • the length of the delay processing window of the equalizer will vary depending on the precise location of the broadcast transmitters. If the transmitters are nearer to each other, then the difference in arrival times is smaller, therefore the delay processing window will be smaller than that in the above example. Similarly, if the transmitters are farther apart from each other, then the difference in arrival times is larger, therefore the delay processing window will should be larger than that in the above example.
  • FIG. 5B presents a somewhat more complicated transmitter site layout.
  • the central transmitter T p radiates an omni-directional pattern, and the secondary transmitters T S1 , T S2 and T S3 radiate directionally inward across the primary service area P and out into the secondary service area.
  • the secondary transmitter antennae T S1 , T S2 and T S3 are not all equidistant from the primary transmitter antenna T p .
  • the secondary transmitters will all be located at different distances from the primary transmitter antenna T p .
  • two of the secondary transmitter antennae are equidistant but one or more of the other secondary transmitter antennae is at a different distance from the primary transmitter antenna T p .
  • secondary transmitter antennae T S2 and T S3 are equidistant from the primary transmitter antenna T p/ i.e. 15 miles from the primary transmitter antenna T p .
  • the other secondary transmitter antenna, secondary transmitter antenna T S1 is located 14 miles from the primary transmitter antenna T p . All of the transmitters transmit the same signal at approximately the same time. In the preferred embodiment, the actual transmission are simultaneous and in-phase with each other. Signals from the secondary transmitter antennae T S2 and T S3 propagate to the location of the primary transmitter in approximately 79.5 microseconds and arrive at any aligned receivers approximately 79.5 microseconds after arrival of signals broadcast by the primary transmitter antenna T p . Signals from the secondary transmitter antennae T S1 propagate to the location of the primary transmitter in approximately 74.2 microseconds and arrive at any aligned receivers approximately 74.2 microseconds after arrival of signals broadcast by the primary transmitter antenna T p .
  • a delay equalizer having 100 microsecond delay processing window will be able to process multipath signals and multiple direct reception in an implementation such as shown in Figure 5B.
  • FIG. 5B the reception of signals at various locations in line with two of the transmitting antennae.
  • location X R - shown on the right of Figure 5B.
  • location X- ⁇ is 30 miles from the site of primary antenna T p .
  • the receiving antenna receives broadcast transmissions from the primary antenna T p and the first secondary transmitter antenna T S1 .
  • the location X R2 is 44 miles from the site of the secondary transmitter antenna T S1 .
  • Signals from the primary antenna T p reach location X R2 after 159 microseconds (30x5.3), and signals from the first secondary transmitter antenna T S1 reach location X * ⁇ after 233.2 microseconds (44x5.3) .
  • the difference in the arrival time is 74.2 microseconds, i.e. within the 100 microsecond delay processing window of the adaptive delay equalizer.
  • the equalizer window will also process multipath signals arriving as much as 25.8 microseconds after the signal from the secondary transmitter antenna T S1 .
  • location X R3 shown in the lower left portion of Figure 5B.
  • location X ⁇ is 20 miles from the site of primary antenna T p .
  • the receiving antenna at that location receives broadcast transmissions from the primary antenna T p and the third secondary transmitter antenna T s3 .
  • the location X R3 is 35 miles from the site of the secondary transmitter antenna T S3 .
  • Signals from the primary antenna T p reach location X R2 after 106 microseconds (20x5.3), and signals from the third secondary transmitter antenna T S3 reach location X R3 after 185.5 microseconds (35x5.3).
  • the difference in the arrival time is 79.5 microseconds, which again is within the 100 microsecond delay processing window of the adaptive delay equalizer.
  • the equalizer window will also process multipath signals arriving as much as 20.5 microseconds after the signal from the third secondary transmitter antenna T S3 .
  • receiver location X R4 in Figure 5B, and assume that the secondary antennae radiate cardioid patterns substantially similar to those shown in Figure 5A. As shown by comparing Figure 5B to Figure 5A, the location X R4 approximately 40 miles due south of the primary transmitter T p is within the radiation area from the primary transmitter T p and the front lobe radiation area TS3F from the secondary transmitter T S3 . The directionality of the receiving antenna may not be sufficiently narrow to select one transmission and reject the other. However, as discussed below, the delay processing window of the adaptive delay equalizer (100 microseconds in the present example) is sufficient to process the signals from the two transmitters as well as 20 microseconds or more of multipath delay signals following arrival of the more distant signal transmission. The receiver at location X R4 therefore can resolve the two transmission signals.
  • the distance between the receiver location X R4 and the secondary transmitter T s3 can be geometrically calculated as approximately 53.5 miles. Signals propagate from the secondary transmitter T S3 to the receiver location X R4 in 283.55 microseconds (53.5x5.3). At forty miles from the primary transmitter T p , signals from that transmitter require 212 microseconds to propagate to the receiver location X R4 . The difference in the arrival time is 71.5 microseconds, which again is within the 100 microsecond delay processing window of the adaptive delay equalizer. The equalizer window will also process multipath signals arriving as much as 28.5 microseconds after the signal from the third secondary transmitter antenna T S3 . Details of a specific implementation of a broadcast system and a receiver terminal in accord with the present invention are set forth below.
  • the simulcast transmission from the broadcast antennae include a plurality of frequency multiplexed channels. Each channel contains a digital transport stream carrying a number of programs, in compressed digital form.
  • the programs may be audio only programs, or data, but in the preferred embodiments, the programs are television type programs.
  • the television type programs contain video and audio information, and may include data information, e.g. for closed captioning and the like.
  • the broadcasting portion of the system includes a headend 10.
  • the headend includes a number of Sources SI to SN for producing digital transport streams, each of which contains a plurality of programs encoded as digital, compressed data.
  • the number of such sources corresponds to the number of frequency channels available for use in a particular geographic region.
  • the FCC licenses up to 33 channels of MMDS and ITFS services in a given area. It may be possible to aggregate rights to use all such channels, but to provide a commercially viable service, typically only 20-25 such channels are necessary.
  • the headend 10 therefore typically comprises 20-25 of the Sources SI to SN, but may include as many as 33 such sources.
  • the Sources SI to SN may convert analog program information from video sources, (e.g. off-the-air feeds, satellite receivers, VCRs, etc.) into compressed, digital data form.
  • the headend 10 may also receive and process previously encoded material.
  • FIG. 6 illustrates the overall architecture of the broadcasting system.
  • the headend 10 that figure provides a simplified diagram of the source encoder functionality, e.g. at SI, for preparing a group of original analog source signals for transport through the network.
  • each analog television signal e.g. in NTSC format, is applied to an MPEG encoder 11.
  • the encoder 11 digitizes both audio and video for a program, and packetizes the compressed digital data in accord with the appropriate standard.
  • the encoder may also encrypt the data before insertion thereof into the transport packets.
  • MPEG is a bi-directional predictive coding compression system, utilizing discrete cosine transformation (DCT) processing. Picture elements are converted from spacial information into frequency domain information. Compression begins by discarding information to which eyes are insensitive. From the remaining information, the encoder will develop reference
  • the number of frames to be coded for each I frame is set in the standardized MPEG syntax, e.g. one reference frame for each group of fifteen frames, or every half second.
  • a prediction is made of the composition of a video frame, termed a P frame, to be located a specific number of frames forward and before the next reference frame, this specific number also is set in the MPEG syntax.
  • Information from previous video frames as well as later video frames is used in formulating the prediction.
  • "Delta" or "B frame information is developed for coding the video frames between the actual and predicted frames, also by looking at frames in both directions. Rather than updating a whole frame, only the changed (or delta) information is provided for the delta video frames.
  • the total information coded, and then transmitted is considerably less than that required to supply the actual information in the total number of frames.
  • the frame sequence consists of a repetitive succession of two B frames followed by one P frame.
  • the MPEG II standard provides a standardized format for packetizing the compressed audio and video information and for transporting other data.
  • incoming individual video signals and related audio signals are encoded and packetized into respective Video and Audio Packetized Elementary Streams (PES) .
  • PES Video and Audio Packetized Elementary Streams
  • the video and audio PES's from one or more sources of video programming may be combined into a transport stream for transmission or storage.
  • Each frame of compressed program information (audio, video or data) is broken down into a series of transport packets. Although the frames can vary in length, e.g. between a full reference I-frame and a delta B-frame, the transport packets have a fixed 188 byte size. Thus, different frames are broken down into different numbers of MPEG transport packets.
  • a group of frames consisting of a total of 15 frames for one-half second of video (one I frame and a number of P and B frames) , breaks down into 2000 transport packets (or 4000 transport packets per second) .
  • Each 188 byte transport stream packet consists of two sections, a 4 byte packet header section, an optional adaptation field and a payload section.
  • the header information includes, inter alia, a synchronization byte, a variety of different flags used in reconstruction of the frames, and a thirteen bit program identification (PID) number.
  • PID value 0 is reserved as an indication that the packet includes program association table data.
  • PID value 1 is reserved for identification of packets containing conditional access data, such as encryption information.
  • Other program identification numbers are utilized to identify transport packets with the program or source from which they originate.
  • the transport packet for each program will also include a program reference clock (PRO value within the optional adaptation field.
  • PRO value program reference clock
  • the optional adaptation field includes a section for miscellaneous flags, such as discontinuity counter, private data flag, etc.
  • PRC program clock reference
  • the adaptation field (AF) also includes a section designated for AF options. One of the options this section may carry is the PRC value.
  • the decoder in sequence reconstructs the frames for a particular program from packets bearing the appropriate PID value, uses the reference frame to form the prediction frames, and then uses the prediction frames and delta information to construct full frames from the delta frames.
  • the MPEG II standard facilitates time division multiplexing of MPEG packets from a plurality of programs.
  • the encoders 11 supply MPEG packets streams for multiple programs to an MPEG multiplexer 12.
  • the number of programs may vary depending on the bandwidth.
  • the MPEG multiplexer 12 may receive digitized and compressed (MPEG) video from other sources 11' .
  • Typical digital sources 11' include digital server (storage) systems and digital video transmission systems (e.g. satellite or optical fiber) .
  • a typical multiplexed digital transport packet stream used in the present invention has 27 Mbits/s of capacity.
  • a mixture of program streams for individual programs at different individual rates e.g. 1.5 Mbits/s, 3 Mbits/s and 6 Mbits/s, are combined to fully utilize the 27 Mbits/s capacity.
  • the 27 Mbits/s multiplexed digital transport packet stream might consist of three 3 Mbits/s programs and three 6 Mbits/s programs.
  • the multiplexer 12 combines four MPEG II packet streams of four such programs for output on each broadband rail. The simplified example therefore provides four programs for one RF channel, i.e.
  • PID values for packets of a particular television type program encoded in MPEG II form there are at least three PID values for packets of a particular television type program encoded in MPEG II form, a first PID value for packets containing video, a second PID value for packets containing audio and another PID value for a packet containing a program map.
  • there could be a data channel associated with the program which would include data for closed captioning for the hearing impaired and/or related control signaling information.
  • the program map specifies the PID values for the various packets containing video, audio and/or data from the particular source.
  • the PID values for each program will be unique, and each such program is assigned a unique program number (PN) .
  • PN program number
  • HBO might have a program number '1'
  • the program map for HBO might be found in packets corresponding to PID 132.
  • Showtime might have a program number of '2'
  • the program map for Showtime might be found in packets identified by PID 87 and so forth.
  • the program map for HBO in the packet with PID 132 would then identify the PID numbers for the actual packetized elementary streams (PES) for the video, audio and data (if any) channels associated with the HBO program.
  • the program map for Showtime in the packet with PID 87 would then identify the PID numbers for the actual packetized elementary streams (PES) for the video, audio and data (if any) channels associated with the Showtime program.
  • each multiplexer 12 outputs a group of MPEG encoded programs, i.e. four if the encoding rate of all encoders 11 is 6 Mbits/s, at a combined payload rate of 27 Mbits/s (it may be necessary to pad the steam with dummy packets to reach the full 27 Mbits/s) .
  • the MPEG II standard also requires that a packet stream containing packets relating to one or more programs includes a program association table in a packet identified by PID 0. The program association table maps each program number with the PID value associated with the program map related to that source.
  • each MPEG II multiplexer 12 combines MPEG packet streams for the four (or more) input programs and adds a PID 0 packet containing the program association table to the combined stream.
  • the program association table would map program number '1' (HBO) with PID value 132 indicating that the program map for HBO is contained in repeating packets identified by PID 132.
  • the program association table would map program number 's' (Showtime) with PID value 87 indicating that the program map for Showtime is contained in repeating packets identified by PID 87.
  • reception of a particular digital program requires that the CPE terminal device know the RF channel transporting the program and the program number (PN) associated with the program.
  • the decoder uses the information contained in the PID 0 packet to identify the PID value for the program map for the particular desired program, e.g. 132 in the above HBO example, and uses the program map to identify the PID values needed to capture the video, audio and user data (if any) for the desired program.
  • each MPEG multiplexer 12 goes to a modulator 13.
  • U.S. Patent No. 5,231,494 to Wachob the disclosure of which is incorporated herein in its entirety by reference, teaches quadrature phase shift keyed (QPSK) modulation of a plurality of video, audio and data signals into a single data stream within a standard six Mhz channel allocation for transmission over a cable television type distribution network.
  • QPSK quadrature phase shift keyed
  • the currently preferred implementation uses 64 QAM (quadrature amplitude modulation) or 16 VSB (vestigial sideband) modulation techniques in the modulators 13.
  • each modulator 13 produces a 6 Mhz bandwidth output at an intermediate carrier frequency. Each modulator 13 outputs the intermediate frequency signal to an individual upconverter 14.
  • the upconverter converts the frequency of the QAM modulated signal up to one of up to thirty-three RF channel frequencies in the 50-450 MHz range.
  • the upconverter 14 may be an element of the QAM modulator 13 or a separate element as shown hard wired to process the output of the QAM modulator.
  • Each upconverter 14 outputs a different 6MHz bandwidth RF channel to an RF combiner 15 for combining with the other 6MHz RF signals from the other upconverters 14.
  • the RF combiner 15 thereafter outputs the combined RF signals in the normal video channel range of approximately 50-450 Mhz.
  • the upconverters 14 and the RF combiner 15 may be the same as components currently used for RF signal processing in cable television systems.
  • a transmission network supplies the combined spectrum signal in the UHF range from the combiner 15 to a number of transmitter systems 11 to 17 n .
  • the transmitter systems 17 x to 17 n correspond to the transmitters TX1 to TX4 described above with respect to Figures 4 and 5.
  • coaxial cable, wireless microwave relay transmissions or other media could be used, in the preferred embodiment, the transmissions from the headend 10 ride on optical fiber lines 18.
  • an electrical to optical converter system 16 converts the signal from combiner 15 into optical signals for transmission over a plurality of optical fibers 18.
  • An optical to electrical unit 20 at each transmitter site converts the optical signal back to the combined electrical signal and supplies that signal to one of the transmitter systems.
  • An important feature of the present invention relates to simulcasting, i.e.
  • the system shown in Figure 6 therefore includes some form of delay 19 in one or more of the transport lines 18.
  • the delay may take the form of coils of fiber to equalize the optical transport paths and therefore the time through each path.
  • one or more electronic delay devices may be imposed in the relevant paths, either at the headend prior to optical transport or at the respective transmitter location subsequent to conversion back to electrical signal form.
  • TXl there may be as few as two transmitters.
  • the headend may be close to the central transmitter site TXl, therefore the transport distance to that site would be the shortest.
  • TX4 is the longest distance from the headend.
  • the delay produced by delay device 19 will be equal to the difference in the time required to transport optical signals from the headend to those two sites, i.e. so as to result in simultaneous in-phase transmission of the exact same signal from the antennae at the two transmitters TXl and TX4. Similar delays are imposed in the lines 18 to the other transmitter systems.
  • FIG. 6 also shows details of one of the transmitter systems 17N, by way of an example.
  • Each transmitter system includes a splitter 21.
  • the splitter 21 together with associated channel selection filters 22 divide the received combined signal (50-450 MHz) into its constituent 6MHz wide RF channels.
  • An RF power amplifier 23 amplifies each UHF channel.
  • a delay device may process each channel signal, and by way of example, Figure 6 shows a delay device 26 processing the output of each of the upconverters 24.
  • the delay devices 26 provide precise delay compensation on each respective channel to compensate between variations in throughput processing time of the various components at different transmitter sites operating on the signal to be broadcast on a particular microwave channel.
  • a microwave combiner 25 combines the UHF channel signals back into a combined spectrum signal in the UHF range and supplies that signal to a microwave broadcasting antenna 27.
  • Each transmitting antenna may be an omni-directional antenna or a directional antenna.
  • the type of antenna at each transmitter site is selected to give the optimum coverage in a particular geographic service area.
  • the antenna 27 emits UHF waves to propagate through a portion of the service area.
  • the resultant broadcasts from all of the transmitters are synchronized and in phase with each other.
  • the transmitted microwave signals propagate into substantially overlapping portions of the service area and into some non-overlapping portions of that area, for example in patterns such as shown in Figures 4 and 5.
  • the headend and transmission systems is one example of an overall system for providing the simultaneous, synchronized, in-phase broadcasts from multiple transmitters having substantially overlapping propagation areas.
  • Other headend and transmitter systems could be used.
  • the headend 10 could perform the digital multiplexing, and the transport network to the transmitters TXl to TXN could carry the multiplexed transport streams in digital form.
  • the individual transmitter systems would further include at least the QAM modulators for each RF channel.
  • the transmitters may include means to synchronize processing and broadcast transmissions to some common clock, e.g. from a geo-positioning type satellite system, to achieve the simulcast transmission.
  • FIG. 7 provides a high-level functional diagram of a receiving system at one subscriber's premises.
  • Each subscriber has a receiving antenna 31.
  • the receiving antenna 31 is a directional antenna. At most potential receiving sites, it will be possible to aim the antenna 31 toward at least one of the transmitters and receive line-of-sight transmissions therefrom. Transmissions from one transmitter, e.g. TX2, may be blocked by an obstruction (not shown) , but line-of-sight transmissions from at least one of the other transmitters, such as TXl, is more likely to be unobstructed.
  • the directional antenna 31 is aimed at the one transmitter TXl to TXN which produces the strongest received signal through the antenna at the subscriber's particular location. Even so, the antenna receives multiple copies or replicas of the transmitted waveform signals. These multiple copies include a primary direct line-of-sight transmission of a signal from the transmitter the antenna is directed towards together with delayed copies (typically attenuated and distorted) caused by reflections of the transmissions from one or more of the multiple broadcast sites. Also, at locations in the secondary reception area, the direction of reception by the antenna 31 may actually be substantially in line with two of the transmitters, as discussed above relative to Figures 4, 5A and 5B. In such a case, the antenna would receive a first copy of the combined spectrum transmission from the closest transmitter followed by a delayed copy transmitted from the more distant of the two aligned transmitters.
  • the present invention therefore contemplates inclusion of a delay processor in the receiver to compensate for the reception of multiple delayed copies of the transmitted program signals.
  • One implementation of the delay processor utilizes a delay equalizer.
  • An alternative implementation of the delay processor utilizes spread spectrum technology, as discussed in more detail in below in reference to Figure 9B and as disclosed in commonly assigned U.S. Patent application Serial No. 08/405,685, filed March 17, 1995 (attorney docket no. 680-117) entitled “Television Distribution System and Method, " the disclosure of which is incorporated in its entirety herein by reference.
  • the receiving antenna 31 supplies the 2.6 GHz spectrum (through appropriate filtering not shown) to a block down-converter 33.
  • the block down-converter converts the 2.6 GHZ signal, containing all of the RF channels, back down to the video channel band of 50-450 MHz.
  • the block down-converter supplies the 50-450 MHz combined spectrum signal via a coaxial cable to one or more terminal devices 100 located at various places in the subscriber's home.
  • Each terminal 100 includes some form of wireless signal processor 35 for processing a selected one of the 6MHz channels to recover the digitally multiplexed transport stream carried in that channel.
  • Each terminal connects to an associated television set 100' .
  • the digital signal processor 37 processes data packets for the selected program from the multiplexed stream to produce signals to drive the TV 100'.
  • the TV '100' presents the program to the viewer in sensorially perceptible form, in this case, as a standard audio/visual output.
  • FIG 8 illustrates the functional elements of the terminal 100.
  • the terminal 100 is a digital entertainment terminal, or 'DET.
  • the DET 100 will include a transport interface module (TIM) 101 providing the actual physical connection to the coaxial cable network in the subscriber's premises.
  • the transport interface module (TIM) 101 will also perform the format conversion necessary between signal formats utilized by the network and signal formats used within the digital processing portion of the DET 100.
  • the TIM performs RF tuning and QAM demodulation. If the programming is encrypted, the TIM also includes the necessary decryption circuitry.
  • the TIM 101 therefore serves as the wireless signal processor 35.
  • the main portion of the DET 100 serves as the digital signal processor 37.
  • the transport interface module (TIM) 101 presents two connections to the rest of the DET, a high bit rate broadband connection for received broadband signals and a low bit rate signaling connection to permit control and monitoring of the TIM by a microprocessor within the main portion of the DET. For a selected channel, the TIM hands off the 27 Mbits/s baseband digital transport stream captured from that RF channel to the main portion of the DET.
  • the structure of the TIM 101 is described in more detail below with regard to Figures 9A and 9B.
  • the DET 100 includes a CPU 105, comprising a 386, 486 or Pentium microprocessor 110 and associated system memory 120.
  • the system memory 120 includes at least 2 mbytes of volatile dynamic RAM 122 and 1 mbyte of non ⁇ volatile RAM 121.
  • the microprocessor 110 includes a small amount of ROM (not shown) storing "loader" programming needed to control wake-up.
  • An EPROM memory (not shown) also may be added.
  • a digital audio/video signal processor 125 controlled by the CPU 105, produces digital uncompressed audio and video signals from the audio and video MPEG encoded packets received from the network through the interface module 101.
  • the audio/video processor 125 includes an MPEG system demultiplexer 127, an MPEG video decoder 129, an MPEG audio decoder 131, a graphics overlay controller 133 and at least two frames (e.g. 8 mbytes) of video RAM 135.
  • the MPEG system demultiplexer circuitry 127 recognizes packets in the MPEG data stream received over the broadband channel through the transport interface module (TIM) 101 and routes the packets having predetermined PID values to the appropriate components of the DET. For example, under CPU control, the MPEG system demultiplexer 127 circuitry recognizes audio and video packets in the MPEG data stream as audio and video relating to a selected program and routes those packets to the decoders 129, 131, respectively. The MPEG system demultiplexer circuitry 127 route packets having specified PID values identified as user data packets to the CPU 105 for further processing. The MPEG system demultiplexer circuitry 127 recognizes program map packets (and program association packets if necessary) and supplies those packets to the CPU 105.
  • TIM transport interface module
  • the MPEG video decoder 129 decompresses received video packet signals to produce a digital video signal
  • the MPEG audio decoder 131 decompresses received audio packets to produce left and right digitized stereo signals.
  • the MPEG decoders 129, 131 may be controlled in response to signals from the microprocessor 110.
  • the MPEG video decoder 129 will internally include at least two frames (e.g. 8 mbytes) of RAM (not separately shown) for use as a frame reorder buffer during the MPEG video decoding process, and the MPEG audio decoder 131 also may include some buffer memory.
  • the video RAM 135 is not a specialized "video RAM” as that term is sometimes used in the television art.
  • the RAM 135 is actually a standard digital data RAM, of appropriate size, which is used in the DET to store digitized frames of video data.
  • the RAM within the MPEG video decoder 129 likewise consists of standard digital data RAM.
  • the graphics display generator produces displays of text and graphics data, such as the initial turn-on selection menu received over the signaling channel, in response to instructions from the CPU 105.
  • the video RAM 135 sequentially receives each frame of digitized, uncompressed video information, as output from the MPEG video decoder 129.
  • the video RAM 135 also receives digital information and read/write control signals from the graphics overlay controller 133 representing the several planes of text and graphics information and combines that information with the frames of decompressed video to produce composite video frames.
  • the graphics overlay controller 133 and the video RAM 135 actually cooperate to manipulate five different planes of video information, four of which can be active at any one time, to produce the composite video fame output signals.
  • the individual planes comprise the decoded MPEG video frames, a cursor, two graphics/text image planes manipulated by the microprocessor 110 and a backdrop plane.
  • the backdrop plane would be switched in to replace the plane representing the decoded MPEG video frames, e.g. to present a blue background instead of the MPEG video background.
  • the composite frames When there are no graphics or text, the composite frames would correspond entirely to the uncompressed received video frames output by the MPEG video decoder 129.
  • the information from the graphics overlay generator 133 would specify a background and the active planes of text or graphic information.
  • the composite video frames include the uncompressed received video frames with selected pixels thereof replaced with graphics or textual data display pixels specified by the graphics overlay controller 133. In this last situation, the graphics overlay controller would deactivate the backdrop plane.
  • the DET also includes audio and video digital to analog converters and appropriate drivers to produce output signals compatible with a conventional television set.
  • the converter and driver circuitry of the DET 100 includes audio digital to analog converters (DAC's) 135 L , 135 R , an audio mixer 136, an NTSC encoder 137, and an RF modulator 139.
  • DAC's audio digital to analog converters
  • the DAC's 135 L and 135 R receive the uncompressed left and right digitized audio signals output by the MPEG audio decoder 131. In response, the DAC's 135 L and 135 R produce baseband analog audio signals for output to individual baseband output terminals.
  • the audio mixer 136 also receives the baseband audio signals from the DAC's 135 L and 135 R . The mixer 136 combines the left and right analog audio signals to produce a monaural audio signal as the audio input to modulator 139.
  • the NTSC encoder 137 also performs a digital to analog converter (DAC) function. In response to the digitized video output signals from the video RAM 135, the NTSC encoder 137 produces a baseband analog video signal in standard NTSC format.
  • the baseband NTSC video signal is supplied to an output terminal of the DET 100.
  • the baseband NTSC video signal is also supplied to the RF modulator 139.
  • the RF modulator 139 responds to the mono audio signal, the NTSC video signal and an RF signal from a local RF oscillator 141, to produce a standard RF television signal on an available TV channel, typically channel 3 or channel 4.
  • the type of connection of the DET 100 to the television set depends on the capabilities of the user's television set. If the user has a monitor type television capable of receiving baseband video and stereo audio inputs, the appropriate terminals of the television would connect directly to the video and audio output terminals of the DET 100. If the subscriber does not have such a television monitor, then the RF output of the modulator 139 would be connected to the cable or antenna input connection of the television, e.g. by coaxial cable. Alternatively, the digitized video and audio may go to separate output terminals (not shown) for connection to inputs of digital display devices, for example, for high definition television (HDTV) sets.
  • HDMI high definition television
  • Each DET also includes means to receive selection signals from a user.
  • the DET 100 includes an infrared (IR) receiver 145.
  • the (IR) receiver 145 responds to inputs signals from a user operated IR remote control device (not shown) similar to that used today for controlling televisions and video cassette recorders.
  • the receiver 145 produces corresponding digital data output signals.
  • the microprocessor 110 interprets the digital data signals by the IR receiver 145 as input commands. The precise interpretation of specific command signals can vary based on applications programming and/or operating system software stored in the system memory 120.
  • the microprocessor 110 may control a cursor position and display received user data in the form of alphanumeric information displayed as graphics and text on the associated television set 100' .
  • the microprocessor 110 will also respond to an appropriate input command from the user to select a broadcast program as discussed in more detail below.
  • Figure 9A depicts in block diagram form the structure of a TIM 101.
  • the structure illustrated is based in part on the current preference for the 64 QAM modulation techniques for the digital video signals in transmission system of the type shown in Figure 6.
  • the input to the TIM is a broadband RF signal in the 50-450 MHz range provided from a coaxial cable from the down converter.
  • the tuner 201 selects a specific 6 MHz channel from the broadband input spectrum and presents it at an intermediate frequency to the digital communications receiver section 203.
  • the digital receiver 203 includes an intermediate frequency band-pass filter, a demodulator (e.g. 64 QAM) , a time domain adaptive digital equalizer 204, and forward error correction circuitry.
  • a demodulator e.g. 64 QAM
  • a clock circuit provides synchronization for the digital output of the demodulator, the adaptive digital equalizer, and the forward error correction circuitry.
  • the forward error correction circuit processes the recaptured symbols (e.g. Is and 0s) to determine if each is in the proper position in the stream.
  • the time domain adaptive digital equalizer 204 receives the output of the QAM demodulator. Because of the overlapping transmissions from multiple transmitter sites and multi-path delays, i.e. reflections of signals transmitted from one or more broadcast sites, the output of the demodulator will not be a clean digital pulse stream. Instead, the signal will be a composite of time delayed copies of the transmitted digital information.
  • the time domain adaptive equalizer includes a multi-tap digital delay line. The outputs from the taps of the delay line may be weighted and summed, and the sum processed by a level detector or the like to recapture the original symbols (e.g. Is and 0s of a digital stream) . Examples of digital delay equalizers which may be used in the receivers of the present invention are described in Proakis, "Digital Communications," second edition, 1989, McGraw-Hill, Inc., chapter 6, although still other types of delay equalizers known to skilled technicians may be used.
  • the length of the digital delay line in equalizer 204 and the number of taps off of the digital delay line determine the delay processing window of the equalizer.
  • the precise window of the equalizer is selected to compensate for the longest delay interval between different transmitters that may be aligned to transmit signals to a single receiving location.
  • the delay window is longer than this maximum delay by some amount chosen to permit processing of multipath delayed signals from the more distant transmitter.
  • a control interface provides appropriate control signals to the elements of the digital receiver 207 in response to instructions from the transport interface module (TIM) controller 210.
  • the digital receiver processes signals selected from one of the RF channels by operation of the tuner 210 to capture one of the digital transport streams (e.g. 27 Mbits/s payload assuming 64 QAM) .
  • the digital processor outputs the transport stream as a corrected serial baseband digital feed.
  • a decryption module 207 is optional. If included, this module controls access to digital broadcast services.
  • the decryption module 207 comprises a decryptor and an interface to a renewable security device 211.
  • the renewable security device 211 may be a card reader for accepting a TV Pass Card.
  • An access control processor within the decryption module 207 controls the operation of the decryptor.
  • the decryptor in module 207 decrypts payload data within packets of a selected program in the transport stream.
  • the composite MPEG transport multiplex with appropriately decrypted components for the selected program is output from the TIM 101 to the host DET's demultiplexer 127 and decompression circuitry as shown in detail in Figure 8.
  • the TIM controller 210 and/or the decryption module 207 receive instructions from the CPU 105 ( Figure 8) as to channel and program selections via the TIM/DET interface 209.
  • the 100 will store a channel map for the digital broadcast programs available through the system.
  • the map includes information defining a logical network channel number for the program.
  • the logical channel number is the channel the DET will display on a front panel display (not shown) or on the screen of the associated television set 100' and is the number that the user inputs via the remote control to select the program.
  • the map also includes RF channel information needed to tune to the RF channel carrying the program and the program number (PN) uniquely identifying the program within the multiplexed digital transport stream.
  • PN program number
  • the microprocessor 110 in the main portion of the DET accesses the listing for that channel in the channel map stored in the system memory 120.
  • the microprocessor 110 supplies a message containing the RF channel number and the program number (PN) to the TIM controller 210 via interface 209.
  • the TIM controller 210 activates the tuner 201 to tune to the identified channel.
  • the program is encrypted, the TIM uses the program number, the program association table in the packet identified by PID 0 and the program map to identify the packets carrying audio, video and data (if any) for the program.
  • the decryption module 207 uses a decryption key from its memory or from the renewable security device 211 to descramble the information in the payloads of the packets of the selected program.
  • the TIM 216 passes digital signals from the RF channel through the interface to the MPEG system demultiplexer 129 in the main portion of the DET wherein at least the information for the selected program is now in unencrypted form.
  • the MPEG demultiplexer 127 supplies information from the PID 0 packet, i.e. the program association table to the CPU 105.
  • the microprocessor 110 uses the program number (PN) from the channel map stored in system memory 120 to identify the PID value for the correct program map from the program association table.
  • the CPU 105 supplies that PID value to the MPEG demultiplexer 127.
  • the MPEG demultiplexer 127 receives a packet containing that PID, it supplies information from the packet identified by the PID (the program map) to the CPU. From the program map, the CPU identifies the PID values for the video and audio for the program and instructs the demultiplexer 127 to supply those packets to the respective MPEG decoders 129, 131 to begin MPEG decoding of the selected program for presentation to the user via the associated television set 100' .
  • Figure 9B discloses an alternative TIM 101' according to the present invention.
  • the TIM 101' is adapted to receive spread spectrum signals from the transmitters disclosed in Figures 4 and 5.
  • Each of the transmitters may simulcast transmit only one spread spectrum signal carrying the multiplexed channels of MPEG data.
  • each of the transmitters may transmit a plurality of spread spectrum signals, each having a corresponding spreading code.
  • the TIM 901 may selectively despread one of the spread spectrum signals to receive the corresponding set of multiplexed channels.
  • each of the transmitters in Figures 4 and 5 simulcast one spread spectrum signal carrying sixteen (16) multiplexed channels
  • the channel capacity for the user is sixteen channels.
  • each receiver can selectively despread one of the four spread spectrum signals carrying sixteen multiplexed channels, effectively increasing the user's channel capacity to sixty-four (64) channels.
  • a modulation technique is utilized in which a transmitted signal is spread over a wide frequency band within the communication channel.
  • the frequency band is much wider than the minimum bandwidth required to transmit the information being sent.
  • Carrier frequency shifting in discrete increments in a pattern dictated by a code sequence are called “frequency hoppers.”
  • the transmitter jumps from frequency to frequency within some predetermined set; the order of frequency usage is determined by a code sequence.
  • time hopping and time-frequency hopping have times of transmission which are regulated by a code sequence.
  • Pulse-FM or "chirp” modulation in which a carrier is swept over a wide band during a given pulse interval.
  • Information i.e., the message signal
  • the message signal can be embedded in the spread spectrum signal by several methods.
  • One method is to add the information to the spreading code before it is used for spreading modulation. This technique can be used in direct sequence and frequency hopping systems. It will be noted that the information being sent must be in a digital form prior to adding it to the spreading code. Alternatively, the information or message signal may be used to modulate a carrier before spreading it.
  • a spread spectrum system must have two properties: (1) the transmitted bandwidth should be much greater than the bandwidth or rate of the information being sent and (2) some function other than the information being sent is employed to determine the resulting modulated channel bandwidth.
  • Spread spectrum communication systems can be implemented as multiple access systems in a number of different ways.
  • One type of multiple access spread spectrum system is a code division multiple access (CDMA) system.
  • CDMA spread spectrum systems may use direct sequence (DS-CDMA) or frequency hopping (FH-CDMA) spectrum spreading techniques.
  • FH-CDMA systems can further be divided into slow frequency hopping (SFH-CDMA) and fast frequency hopping (FFH-CDMA) systems.
  • SFH-CDMA slow frequency hopping
  • FFH-CDMA fast frequency hopping
  • a communication between two communication units in a particular communication channel is accomplished by using a frequency synthesizer to generate a carrier wave in a particular portion of a predetermined broad frequency band for a brief period of time.
  • the frequency synthesizer uses an input spreading code to determine the particular frequency from within the set of frequencies in the broad frequency band at which to generate the carrier wave.
  • Spreading codes are input to the frequency synthesizer by a spreading code generator.
  • the spreading code generator is periodically clocked or stepped through different transitions which causes different or shifted spreading codes to be output to the frequency synthesizer.
  • the carrier wave is frequency hopped or reassigned to different portions of the frequency band.
  • the carrier wave is modulated by data symbols representing a sequence of data bits to be transmitted.
  • Multiple communication channels are allocated by using a plurality of spreading codes.
  • transmitted signals are in the same broad frequency band of the communication channel, but within unique portions of the broad frequency band assigned by the unique spreading codes.
  • These unique spreading codes preferable are orthogonal to one another such that the cross- correlation between the spreading codes is approximately zero.
  • Particular transmitted signals can be retrieved from the communication channel by despreading a signal representative of the sum of signals in the communication channel with a spreading code related to the particular transmitted signal which is to be retrieved from the communication channel.
  • the received signal can be correlated with a particular spreading code such that only the desired signal related to the particular spreading code is enhanced while the other signals are not enhanced.
  • frequency hopping spread spectrum is preferably utilized in the simulcast transmission system. Additional details of the frequency hopping spread spectrum transmission techniques are disclosed in commonly-assigned, copending application Serial No. 08/405,685, filed March 17, 1995, entitled “Television Distribution System and Method” (attorney docket no. 680-117) , the disclosure of which is incorporated in its entirety herein by reference. Alternative forms of spread spectrum processing may be used, however, such as code division multiple access (CDMA) .
  • CDMA code division multiple access
  • the TIM 101' is substantially similar to the TIM 101 shown in Figure 9A, except for variations described below to accommodate spread spectrum signals.
  • the input to the TIM 101' is a spread spectrum signal in the 50-450 MHz range provided from a coaxial cable from the down converter.
  • the despreader 901 selects a specific 6 MHz channel from the broadband input spectrum under control of the frequency synthesizer 916 and presents it at an intermediate frequency to the digital communications receiver section 903.
  • the spaced antennas simulcast transmit the same signal to provide overlapping propagation areas.
  • the despreader 901 includes a delay processor, preferably a rake receiver, to acquire an optimized representation of the multiple time-delayed copies of the transmitted signal received at the receiver.
  • the synthesizer 916 executes the same frequency hopping pattern as the local oscillator at the transmission site and is synchronized with that oscillator in a known manner. As a result, that spread spectrum receiver 901 outputs a faithful reproduction of Channel 1.
  • the transmitted signal representing Channel 1 is encountering a 2 microsecond delay a duplicate pattern is created which lags the primary pattern by 2 microseconds.
  • this signal is utilized by the rake receiver in the despreader 901 in response to the signals from the frequency synthesizer 916 running the Channel 1 sequence.
  • the rake receiver internal to the despreader 901 will use the despreading code twice with the second occurrence offset by the tl-2 microsecond delay.
  • the duplicate pattern having the 2 microsecond delay is despread by the rake receiver.
  • the rake receiver may be designed to select the strongest of the despread signals having different multipaths, or alternatively may combine the despread signals to reduce the number of bit errors in the received signal . Additional details of the rake receiver are disclosed in the above-identified copending application no. 08/405,685, filed March 17, 1995 (attorney docket No. 680-117) , the disclosure of which is incorporated herein by reference.
  • the rake receiver in the despreader 901 is functionally similar to the time domain adaptive digital equalizer 204 in that both obtain an optimum representation of a transmitted signal from the plurality of time delayed copies.
  • the rake receiver will therefore have a similar delay processing window to compensate for the largest delay interval between different transmitters that may be aligned to transmit signals to a single receiving location, disclosed above as 100 microseconds.
  • the despreader 901 outputs the despread signal representing an optimized representation of the received signals to a digital receiver 903 that includes a low- pass filter, a demodulator (e.g., 64 QAM), and forward error correction circuitry.
  • a clock circuit provides synchronization for the digital output of the demodulator, despreader, and the forward error correction circuitry.
  • the system memory 120 of the main portion of the DET 100 will store a channel map for the digital broadcast programs available through the system.
  • the map includes information defining a logical network channel number for the program.
  • the logical channel number is the channel the DET will display on a front panel display (not shown) or on the screen of the associated television set 100' and is the number that the user inputs via the remote control to select the program.
  • the map also includes RF channel information needed to tune to the RF channel carrying the program and the program number (PN) uniquely identifying the program within the multiplexed digital transport stream.
  • the microprocessor 110 in the main portion of the DET accesses the listing for that channel in the channel map and the despreading code table stored in the system memory 120.
  • the microprocessor 110 supplies a message containing the RF channel number and the frequency hopping code to the TIM controller 210 via interface 209.
  • the TIM controller 210 activates the frequency synthesizer 916 to synchronize the frequency hopping code fed from the memory 120 through the microprocessor to the frequency synthesizer.
  • the frequency synthesizer 916 feeds the code to the despreader 901 which in turn delivers the selected channel to the LPF in the digital receiver 903.
  • the TIM uses the program number, the program association table in the packet identified by PID 0 and the program map to identify the packets carrying audio, video and data (if any) for the program. If authorized to receive the program as indicated via the renewable security device 211, the decryption module 207 uses a decryption key from its memory or from the renewable security device 211 to descramble the information in the payloads of the packets of the selected program. As a result, the TIM 101 passes digital signals from the RF channel through the interface to the MPEG system demultiplexer 129 in the main portion of the DET wherein at least the information for the selected program is now in unencrypted form.

Abstract

Dans une zone de service désirée, plusieurs émetteurs sur des sites séparés diffusent simultanément le même signal multiplex pour plusieurs programmes. Chaque canal transporte un flux multiplex de données numériques contenant des paquets d'informations pour plusieurs programmes, notamment pour des programmes de télévision. Le système récepteur comprend une antenne (31) conçue pour recevoir des transmissions en direct ainsi que des signaux à trajets multiples provenant, dans les deux cas, de deux émetteurs ou plus. Pour compenser la réception de signaux potentiellement interférents, le terminal comprend un processeur de retard, qui peut être soit un compensateur adaptatif (204) de retard soit un récepteur (901) à fonction de râclage des signaux de retard. La fenêtre temporelle maximale dudit processeur est au moins aussi longue que la différence de temps de propagation vers le récepteur en provenance de deux des émetteurs, et excède de préférence ce temps de propagation dans des proportions calculées de manière à permettre le traitement des signaux de retard multiplex provenant de l'émetteur le plus éloigné.
PCT/US1996/003680 1995-03-16 1996-03-18 Terminal pour recevoir des programmes video numeriques simultanees WO1996028910A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU54252/96A AU5425296A (en) 1995-03-16 1996-03-18 Terminal for receiving simulcast digital video programs

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US08/405,558 1995-03-16
US08/405,558 US5651010A (en) 1995-03-16 1995-03-16 Simultaneous overlapping broadcasting of digital programs
US08/441,976 US5559808A (en) 1995-03-16 1995-05-16 Simulcasting digital video programs
US08/441,976 1995-05-16
US08/555,373 1995-11-09
US08/555,373 US5852612A (en) 1995-03-16 1995-11-09 Terminal for receiving simulcast digital video programs

Publications (1)

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WO1996028910A1 true WO1996028910A1 (fr) 1996-09-19

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AU (1) AU5425296A (fr)
WO (1) WO1996028910A1 (fr)

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US8539530B1 (en) 1998-10-30 2013-09-17 Intel Corporation Method and apparatus for ordering entertainment programs from different programming transmission sources

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US4517601A (en) * 1982-03-09 1985-05-14 Sony Corporation Power-responsive ghost cancelling system
US5109390A (en) * 1989-11-07 1992-04-28 Qualcomm Incorporated Diversity receiver in a cdma cellular telephone system
US5231494A (en) * 1991-10-08 1993-07-27 General Instrument Corporation Selection of compressed television signals from single channel allocation based on viewer characteristics

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Publication number Priority date Publication date Assignee Title
US4517601A (en) * 1982-03-09 1985-05-14 Sony Corporation Power-responsive ghost cancelling system
US5109390A (en) * 1989-11-07 1992-04-28 Qualcomm Incorporated Diversity receiver in a cdma cellular telephone system
US5231494A (en) * 1991-10-08 1993-07-27 General Instrument Corporation Selection of compressed television signals from single channel allocation based on viewer characteristics

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US8539530B1 (en) 1998-10-30 2013-09-17 Intel Corporation Method and apparatus for ordering entertainment programs from different programming transmission sources
US9485529B2 (en) 1998-10-30 2016-11-01 Intel Corporation Method and apparatus for ordering entertainment programs from different programming transmission sources

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