Multiplex communications – Communication over free space – Combining or distributing information via frequency channels
Reexamination Certificate
1998-01-29
2001-07-03
Vu, Huy D. (Department: 2664)
Multiplex communications
Communication over free space
Combining or distributing information via frequency channels
C370S334000, C370S480000, C370S487000, C370S495000
Reexamination Certificate
active
06256302
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for common transmission of digital-modulated and analog-modulated radio and/or television signals, especially over a broadband cable system.
The journal “Funkschau” [Broadcasting Review] No. 9, 1995, p. 46, discloses a transmission method in which a flexible multiplexer at the output of a video server combines a plurality of program signals with different data rates into a transmission package; the digital summation signal is QAM-modulated (QAM=quadrature amplitude modulation) and is then transmitted parallel to the analog TV signals already fed into a cable. The digital signal then occupies one entire TV channel of the kind that was previously needed for a single analog television program.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method for common transmission of digital-modulated and analog-modulated radio and/or television signals, especially over a broadband cable system, which provide increased transmission capacity without significantly increasing side channel interference.
According to the invention the method for common transmission of digital-modulate and analog-modulated radio and/or television signals comprises the steps of:
a) transmitting at least one digital signal together with an analog television signal in a common channel of at least one communications channel;
b) controlling a signal level of the at least one digital radio and/or television signal so that it does not exceed a predetermined digital signal level;
c) controlling a signal level of the analog television signal so that it does not drop below a predetermined analog signal level which is much greater than the predetermined digital signal level of the at least one digital radio and/or television signal;
d) controlling the at least one digital radio and/or television signal so that an amplitude of a frequency spectrum of the at least one digital radio and/or television signal does not exceed a predetermined amplitude value, which is much lower than an amplitude of a video carrier of the analog television signal; and
e) controlling the at least one digital radio and/or television signal so that the frequency spectrum of the at least one digital radio and/or television signal is limited to a frequency range smaller than a width of the common channel.
The method of the invention has the advantage over the prior art that the transmission of digital-modulated radio and/or television signals with an analog television signal in one and the same channel leads to a marked increase in transmission capacity, so that substantially more radio and/or television programs can be transmitted.
In a preferred embodiment of the method the data quantity of the at least one digital radio and/or television signal is reduced by coding so that additional digital radio and/or television signals can be transmitted together with the analog television signal in the one channel, thus further increasing the transmission capacity.
It is also advantageous to utilize the channel for transmitting further supplementary data. Once again, still a further increase in transmission capacity is thereby achieved.
By suitably disposing the frequency range of the at least one digital radio and/or television signal between two carrier frequencies, possible influences of the digital and analog signals on one another can advantageously be kept slight and below a threshold of perceptibility.
By transmitting audio carrier frequency components of the analog television signal with predetermined attenuation it is possible in a preferred embodiment to obtain an improvement in the signal to noise ratios for the digital signals by attenuation of interfering video and audio carrier frequency components of the transmitted analog radio and/or television signals.
In a preferred embodiment of the method the individual digital radio and/or televisions signals are combined into blocks in the at least one channel and the frequency ranges of at least two of the transmitted digital radio and/or television signals are separated from one another by a protective frequency spacing. The advantage of this feature is that mutual interference between the signals is avoided.
An advantage in the modulation of one or more digital radio and/or television signals combined into a multiplex signal in accordance with a preferred embodiment of the method is the selection of carrier frequencies that for at least one audio carrier frequency, color auxiliary carrier frequency or video carrier frequency of the analog television signal do not fall below a predetermined frequency spacing. In this way, because critical video and audio carrier frequencies are blanked out, interference of carrier frequencies on the analog television signal with the spectrum of the digital multiplex signal is prevented.
The frequency range of one or more digital radio and/or television signals, combined into a multiplex signal, is advantageously split between video and audio carrier frequencies of the analog television signal, and the corresponding video and audio carrier frequencies of the analog television signal are advantageously separated by one protective frequency spacing each. In this way, even digital multiplex signals that because of the width of their frequency range can be accommodated in the channel of the analog television signal only with difficulty without interfering superposition with video and audio carrier frequencies of the analog television signal, can be accommodated entirely without problems between the individual interfering video and audio carrier frequencies of the analog television signal because of the described splitting of their frequency range, for instance by blanking out carrier frequencies of the multiplex signal, thus averting their superposition on one another, which would cause interference.
In a preferred embodiment advantageously the transmission of one or more digital radio and/or television signals, can be combined into a multiplex signal, in an arbitrary direction. In this way, via the broad band cable system, interactive radio or television and/or telecommunications can be carried out, above all including the utilization of the transmission of digital supplementary data in accordance with the preferred embodiment described above.
Another advantage of this preferred embodiment is also the realization of reverse data channels in broad band cable systems, without requiring additional frequencies or without having to change the conventional frequency allocation of the broad band cable system.
An apparatus transmitting and receiving digital multiplex signals modulated according to an OFDM method, preferably digital radio and/or television signals, comprises, for reception, a tuner circuit for selecting a channel of the transmitted frequency band, a demodulator for demodulating the OFDM modulated signals, a decoder for error evaluation of the received digital signals, a demultiplexer for splitting the corresponding multiplex signal into individual digital signals and an interface device for connection of data playback devices and/or optical broadband distribution network, especially using fiber optic devices; and, for transmission, a channel adaptation unit for coding and combining individual digital signals transmitted via the interface device from a data playback device and/or from the optical broadband distribution network connected to the interface device into a multiplex signal; a modulator for modulating the multiplex signal at carrier frequencies in frequency channels, especially for transmission of analog television signals and a coupler for connection to a broadband cable system, which is connected to the tuner circuit and the modulator. The apparatus according to the invention has the advantage that interactive radio or television and/or telecommunications using digital multiplex signals modulated by an OFDM method is enabled by coupling both receiving and transmitting components to the broad band cable system.
Advantageous pref
Amor Hamed
Mahn Hendrick
Siegle Gert
Phan M.
Robert & Bosch GmbH
Striker Michael J.
Vu Huy D.
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