Pulse or digital communications – Transmitters
Patent
1992-11-10
1996-03-12
Chin, Stephen
Pulse or digital communications
Transmitters
H04L 2710
Patent
active
054992710
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for broadcasting a digitally coded stream of data containing information about one or a plurality of radio programs or other data, wherein the data stream is distributed to a plurality of RF carriers.
For the terrestrial transmission of digitally coded audio radio program signals it is known to employ the so-called DAB (digital audio broadcasting) system to divide the resulting data stream of several radio programs to a plurality of RF carriers. In order to keep the influences of Raleigh fading in multi-path reception, particularly in mobile reception situations, as low as possible, the frequency range occupied by these RF carriers lies in a range from 1 to 4 MHz. However, it is difficult to find such broad frequency ranges in the frequency spectra suitable and intended for radio broadcasting.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a transmission method which permits the additional utilization of an already occupied frequency spectrum for the radio transmission of a data stream without interfering with the services already established there.
This is accomplished according to the invention by employing a frequency band already occupied by FM services to transmit the plurality of RF carriers, with each FM service maintaining a sufficient frequency spacing from the FM services broadcast at the same location, and being sufficiently separated at a smaller frequency spacing from the other local FM services transmitting at closely adjacent locations. The plurality of RF carriers modulated with the data stream are transmitted either in the frequency gap between two adjacent FM services at the same location, or in the unoccupied frequency ranges on both sides of an FM service, thereby leaving out the rated frequency occupation of the FM service. The overall amplitude level of the plurality of RF carriers compared to the level of an RF carrier of an adjacent frequency FM service, or the FM service in the middle, is selected to be sufficiently low relative to a signal to noise ratio sufficient for the FM reception of the FM service or services, and sufficiently high to provide noise immunity against locally remote FM services that fall into the frequency range or frequency gap intended for the transmission of the plurality of RF carriers. The data stream modulating the RF carriers is provided with a greater error protection to provide sufficient noise immunity against the adjacent FM service or services, or the FM service in the middle. The data stream can be transmitted on both sides of an FM service, in which case a notch filter is employed to filter out the plurality of RF carriers, with a stop band of the notch filter corresponding to the frequency position of the respective FM service. Alternatively, the data stream can be transmitted in the frequency gap between two adjacent frequency FM services, in which case a bandpass filter is employed to filter out the plurality of RF carriers, with a passband of the bandpass filter being narrower than the frequency gap, and at least as wide as the frequency range occupied by the plurality of RF carriers. The data stream is preferably received so that existing noise components in the FM service or services are substantially suppressed in the data stream with the aid of an equalization algorithm when the data stream is processed, after evaluation of the FM signal or signals of the FM service or services.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to embodiments thereof that are illustrated in the drawings, in which:
FIG. 1 is a frequency diagram for a first embodiment of the method according to the invention; and
FIG. 2 is a frequency diagram for a second embodiment of the method according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The frequency diagrams according to FIGS. 1 and 2 depict the RF carriers f1, f2 and f3 of three FM services 1, 2 and 3 with a rated energy distribution curve for
REFERENCES:
patent: 5315583 (1994-05-01), Murphy et al.
Rundfunktechnische Mitteilungen, Bd. 29, Nr. 1, Jan. 1985, Norderstedt de, pp. 1-8; U. Messerschmid et al.: "Digitaler Horfunk im . . . ".
Rundfunktechnische Mitteilungen, Bd. 29, Nr. 6, Nov. 1985, Norderstedt de; L. Dudek: "Digitale Ubertragung uber . . . ".
Plenge Georg
Schneeberger Gunter
Chin Stephen
Institut Fur Rundfunktechnik GmbH
Phan Hai H.
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