Interactive video distribution systems – Video distribution system with upstream communication – Transmission network
Reexamination Certificate
1997-08-13
2001-06-05
Faile, Andrew (Department: 2611)
Interactive video distribution systems
Video distribution system with upstream communication
Transmission network
C370S487000, C370S528000, C370S262000, C725S098000
Reexamination Certificate
active
06243866
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for video, sound and data transmission, and more particularly to a method and device which provides a two-way transmission of data between a base station and users.
RELATED TECHNOLOGY
In the field of transmission of interactive television applications, certain methods permit the transmission of asymmetrical data streams and also of some symmetrical data streams. ATM (asynchronous transfer mode) and MPEG signals (video, sound, and data signals, coded according to the standard specifications of the Motion Picture Expert Group) can be transmitted simultaneously in both directions on the basis of this principle.
At the present time, work is underway in many countries on interactive broadband systems, such systems permitting two-way transmission through a forward and a backward channel. A high bandwidth is needed for the transmission of video signals. Some broadband systems are wireless. It is customary to use a frequency range near the forward channel for the high-frequency backward channel. The closer together the forward channel and the backward channel are, the better the propagation characteristics of the two channels conform and the more likely it is that the same antenna can be used for both channels.
One such method is described, for example, in DAVIC 1.1, Specification Part 08, Lower Layer Protocols And Physical Interfaces, LMDS Specifications, Revision 1.1 3/1996. The current standardization proposals of DAVIC (Digital Audio-Visual Council) are based on the assumption of such a frequency-separation of both channels.
FIG. 2
(prior art) illustrates the frequency allocation scheme in the case of a transmission between a STB (set-top box) and a bidirectional converter, which converts the transmitted and the received signal on the user side.
To provide decoupling, U.S. Pat. No. 4,747,160 and European Patent 0 282 347 propose using differing polarity of the field vectors. However, the disadvantage of this method is that it can only be used in the radio communication field and other methods have to be used for feeding the antenna systems.
Another drawback of a small distance between channels is that the transmitted signals can couple over to the receiving side. For that reason, some manufacturers favor using separated antennas. However, it should be possible to avoid the substantial outlay associated with this on the user side.
SUMMARY OF THE INVENTION
A goal of the present invention is to reduce costs on the user side, as well as for the base station. Therefore, an object of the present invention is to make double use of the antennas of the user and the base station side, to avoid using costly filters for separating the signal domains, and to provide a solution which can also be used for feeding pathways.
The present invention therefore provides a method for use in program transmission of digitalized TV-video, sound and data signals from a base station to users and back via a backward channel with time-division-multiplexing two-way operation and with HF modulation for wireless connection, characterized in that
on the transmitter side, following digitalization and prior to dispatching, temporal gaps (time intervals) are formed in the data stream;
during these gaps, the HF modulation is blanked, and the transmitting antenna is switched over to receive mode for the backward channel;
the same frequency band is used for the backward channel as for the program transmission;
the switching over of the users′ receiving antennas is controlled synchronously by the transmitter-side switch-over; and
a memory likewise controlled by said transmitter-side switch-over is read out and read in, respectively, on the transmitter and receiver side.
Advantageous further developments and improvements of the method include: (1) that an orthogonal multicarrier method is used for modulating the forward channel or the backward channel; (2) that a code-multiplexing method is used as modulation of the backward channel, for its simultaneous use by a plurality of users; (3) that gaps for the transmission of digital information and gaps for first-time calls (first user requests to send data) and user signals are formed by the base station and inserted into the data stream, and that the gaps for first-time calls and user signals are predefined in accordance with a time pattern as periodically recurring gaps, the period duration being fixed as a function of the volume of traffic and of the distance to the base station; and (4) that after the first-time call, each accepted user is assigned his or her own code, which in the event of a lasting interruption in the return call on the part of the user of a defined duration, which is preferably a function of the traffic density, is canceled and assigned elsewhere. The code multiplexing and the division of gaps into those for first time calls and those for transmission of digital information are similar to those known from the mobile telephone communications field.
The present invention also provides a device for transmission of digitized TV-video, sound and data signals, comprising transmitters or receivers with HF modulators or demodulators and antennas, which have available a backward channel for wireless connection, characterized in that assigned in each case to the base station and to the users are memory devices, converters, and switch-over devices for switching over the direction of the antennas as transmitting and receiving antennas, as well as a control device, which produces transmission gaps at the base station, and are switched in the case of the users as a function of the control of the base station and of predefined time periods.
Advantageous further developments of this device and improvements thereto include: (1) that the same oscillator is used in the converter of the base station and of the users, in each case for sending and receiving; (2) that a switching signal for activating the switch-over is fed via the HF feeder line to the converters; and (3) that in the case of intermediately switched cable distribution networks designed for one direction and comprising a head-end station at the receiving antenna and a plurality of users, the switching over of the antennas takes place in the head-end station and the storage with the user and the head-end station, and that the backward direction is bridged by means of additional wireless connection(s), preferably in the ISM band.
In a surprisingly simple manner, the present invention makes it possible to use the same HF channel to supply video signals, i.e. to use continuous data streams for the forward and backward directions. The somewhat contradictory goals of, on the one hand, providing continuous video data streams necessary for the forward path and, on the other hand, permitting larger gaps necessary in the backward channel data stream are overcome by interposing receiver-side memory devices. The method unites logical backward channels and logical forward channels in one physical channel (i.e. at a single transmission frequency).
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patent: 0 282 347 (
Boelike Bernd
Rudolph Dietmar
Brown Reuben
Deutsche Telekom AG
Faile Andrew
Kenyon & Kenyon
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