|Número de publicación||WO1997039544 A1|
|Tipo de publicación||Solicitud|
|Número de solicitud||PCT/US1996/005284|
|Fecha de publicación||23 Oct 1997|
|Fecha de presentación||17 Abr 1996|
|Fecha de prioridad||17 Abr 1996|
|Número de publicación||PCT/1996/5284, PCT/US/1996/005284, PCT/US/1996/05284, PCT/US/96/005284, PCT/US/96/05284, PCT/US1996/005284, PCT/US1996/05284, PCT/US1996005284, PCT/US199605284, PCT/US96/005284, PCT/US96/05284, PCT/US96005284, PCT/US9605284, WO 1997/039544 A1, WO 1997039544 A1, WO 1997039544A1, WO 9739544 A1, WO 9739544A1, WO-A1-1997039544, WO-A1-9739544, WO1997/039544A1, WO1997039544 A1, WO1997039544A1, WO9739544 A1, WO9739544A1|
|Inventores||David L. Herrick, David K. Murotake|
|Solicitante||Lockheed Martin Corporation|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (6), Citada por (4), Clasificaciones (4), Eventos legales (7)|
|Enlaces externos: Patentscope, Espacenet|
METHOD FOR DIGITAL BROADCASTING OVER THE COMMERCIAL FM BAND
Background of the Invention Field of the Invention
The present invention generally relates to commercial FM broadcasting, and particularly, to digital broadcasting over existing FM station allocations. Statement of the Prior Art
FM broadcast stations and information service providers use a 20 MHz. frequency band which is divided by Federal regulation into 100 channels of 200 kHz. for each station. Currently provided services are typically analog and include either a monaural or stereo primary baseband signal and a maximum of two or three subcarrier or subsidiary broadcast signals. Broadcasters are prohibited from charging for their primary or main broadcast signal, but are permitted to use their subsidiary broadcasts for revenue bearing services such as functional or background music, specialized foreign language programs, radio reading services, utility load management, market and financial data and news, paging and calling, traffic control signal switching, bilingual television audio, and point to point or multipoint messages. These broadcast service providers are facing increased competition from other forms of transmission and entertainment media such as cable television, compact discs (CDs), satellite TV, and computer modems, many of which employ high quality digital formats. As a result, FM broadcasters are seeking additional revenue producing services for their subsidiary communications broadcasts. There is interest in transmitting CD quality digital audio, as evidenced by one transmission format called ln Band, On Channel (IBOC) Digital Audio Broadcast (DAB). Unfortunately, this format may not provide the bandwidth necessary to broadcast CD quality digital audio within the existing
SOBSTTΓUIE SHEET (RD1£ 26) station channel allocation, or may interfere with existing services. IBOC DAB may also fall outside the current limitations for the subsidiary communications services and thereby limit the digital broadcasts to "free access" services as required by Federal regulations. Thus, this technique would not improve the competitive position of FM broadcasters.
Summary of the Invention Accordingly, it is an objective of the present invention to provide a method for the FM broadcasting of digitally formatted data.
It is a further objective to provide such a method which operates within the currently regulated, subsidiary communications allocation.
It is yet a further objective to provide such a method which provides contemporaneous digital quality audio broadcasts.
The present invention provides a method for FM broadcasting digital data over a limited bandwidth, FM broadcast channel in addition to a normal monaural or stereophonic analog signal, comprising the steps of compressing or decimating the digital data to be transmitted, phase modulating the compressed or decimated digital data onto a subcarrier signal within an unused upper portion of the limited bandwidth channel to form a modulated digital data signal, modulating an FM transmission carrier signal with the digital data signal and a baseband monaural or stereophonic analog signal, and transmitting the modulated FM carrier signal.
Brief Description of the Drawings The present invention is illustratively described in reference to the appended drawings in which: Fig. 1 is a baseband frequency spectrum diagram ofthe currently regulated FM broadcast format showing transmission schemes used in the Prior Art;
SUBSπiUTE SHEET (RULE 26) Fig. 2 is a baseband frequency spectrum diagram of an FM broadcast signal used in accordance with one embodiment of the present invention; and
Fig. 3 is a block diagram of a system constructed in accordance with another embodiment of the present invention. Detailed Description of the Drawings
Fig. 1 shows a frequency spectrum diagram of a single sideband of a 200 kHz. wide commercial FM broadcast channel as established by 47 C.F.R. 73.201. The horizontal axis shows frequency in kHz. and thus spans 1 00 kHz., or a full side band of the normal FM channel allocation. The signals represented would be used to frequency modulate a carrier signal in accordance with a regulated channel assignment. The arrow or signal spike 1 10 would represent the location of the carrier frequency upon modulation.
The standard FM signal shown includes a baseband monaural signal 1 12 which spans 50 Hz. to 15 kHz., a stereo pilot signal 1 14 at 19 kHz., and a suppressed stereo subcarrier 1 15 at 38 kHz. surrounded by lower and upper stereo sidebands 1 16, 1 17, respectively, between 23 kHz. and 53 kHz.. In addition, the signal includes a pair of subsidiary signals 1 1 8, 1 19 at 63 kHz. and 93 kHz., located within the subsidiary communications allocation (SCA) 120 between 53 kHz and 99 kHz., as defined by 47 C.F.R. 73.319. These supplemental carriers 1 18, 1 19 are currently used by a number of FM stations to transmit revenue bearing, subscriber services such as background music and data (i.e. stock quotes). The SCA 120 is limited in the percentage of overall station power it can contain and signals therein are restricted from interfering with the primary signal or adjacent channels. Fig. 2 shows an FM broadcast spectrum diagram 123 used in accordance with the present invention. The spectrum diagram 123 is similar to that of Fig. 1 except that the supplemental carriers 1 1 8, 1 19 are replaced by a modulated signal 122 in accordance with the method of the present invention. Modulated signal
SUBSTITUTE S8EET (RULE 26) 122 may take the form of a single signal or a plurality of signals. The remaining elements shown in Fig. 2 are identical to the elements in Fig. 1 which bear the same identification numbers.
The signal 122 is located in the SCA 120 between 53 kHz. and 99 kHz. and it may be modulated by any suitably efficient method. In one embodiment the subsidiary signal may be produced by quadrature amplitude modulation (QAM) of a subcarrier signal by the digital data to be transmitted. This method varies the phase and amplitude ofthe subcarrier in accordance with the digital data. In one example of QAM, a sixteen point constellation is used made up of four different amplitude levels and four different phase values between -π and +π, with each point representing a binary value between 0 and 15. The digital data to be transmitted would be directly represented by the constellation points during transmission. The digital data used for transmission may be of any form such as unprocessed, compressed, decimated, coded, etc., depending upon the desired transmission efficiency.
Fig. 3 shows a block diagram of a transmitter/receiver system 130 generally including transmitter portion 132 and at least one receiver portion 134. Transmitter portion 132 includes an analog transmitter 136 coupled to an antenna 138. The input signal for transmitter 136 is formed in a phase linear pre-equalizer 140 which receives a baseband signal from a summation module 142 and a subcarrier modulated subsidiary signal from a digital SCA modulator/multiplexer (digital m/m) 144. Pre-equalizer 140 pre-compensates for phase nonlinearity which is inherent in transmitter 136. The inputs to summation module 142 are the traditional elements depicted in Fig. 1 and are labeled accordingly. Provision is even made for optionally inputting traditional SCA signals 1 18,1 19.
Digital m/m 144 alternatively receives inputs from the various types of digital data which may be transmitted. Included in this variety are ordinary
SUBSπTUTE SHEET (RULE 26) digital data 146, digital audio which is first passed through a decimation module 148 and digital multimedia 150 which is first passed through a decimation/compression module 152. The decimation and/or compression modules 148, 152 are required for the efficient use of the limited broadcast spectrum of the SCA 122. This allows the SCA to accommodate a pair of digital quality audio channels to be broadcast in a single SCA as well as for higher speed video than would otherwise be available in a single SCA. Maintaining the necessary bandwidth below that of a single SCA allows optimum usefulness by single station broadcasters. Dual station broadcasters benefit from a proportional bandwidth increase.
Receiver portion 134 may be one of many within system 130 and includes an analog receiver 160 having an input coupled to an antenna 162 and a demodulated output coupled to a channel equalizer 164. The output of channel equalizer 164 is coupled to a digital SCA demodulator/demultiplexer (digital d/d) 166 which separates whichever form of digital data has been transmitted over the SCA 120. The baseband audio signal which is also transmitted may be demodulated elsewhere by an ordinary FM receiver such as 160. Any decimated and/or compressed digital multimedia may be coupled through a comparable bit smoother/decompressor 168 for the appropriate signal reconditioning.
The benefits of decimation, compression, etc. in combination with the remainder of the described embodiments are readily apparent. The standard data rate for digital audio compact disc (CD) and CD- ROM playback is 1.5 mbps. Psychoacoustic decimation techniques, such as the Bose AC-2 method, can reduce the required signal data rate to 180-256 kbps, depending upon a quality factor, which decimated signal, according to broadcast industry experts, cannot be aurally differentiated from an undecimated CD playback by a human listener. Similarly, digital compression and video frame decimation methods can
SUBSπTUTE SHEET (RULE 26) reduce the data rate of multimedia transmissions to 420 kbps or less, resulting in an audio-visual multimedia presentation similar in quality to current music videos. To accomplish this, full motion video frame update rates of 30 frames per second are decimated to an average of 8 frames per second or less, with interpolation used for "bit smoothing".
In certain transmission environments multipath signal reception may be as problematic with embodiments ofthe present invention as it is with existing FM broadcasts. Basic multipath causes interference as a delayed echo of the received signal. Receiver 160 may include one or more algorithms for reducing the problem. One simple approach would be to subtract a delayed fraction of the received signal from itself to cancel the delayed multipath signal. Monitoring the phase synchronism ofthe QAM signal would provide data for adjusting the delay and determining the appropriate fraction of the received signal. The delay could be smoothly adjusted by use of a dispersive delay line whose delay is proportional to it's center frequency. This dispersive delay line would have an up converter on the input and a down converter on the output, with both converters being fed by the same local oscillator to cancel short term frequency drift. Varying the frequency of this local oscillator would allow for smooth and continuous adjustment of the time delay. Multipath compensation may also be accomplished by digital algorithms which would also provide greater flexibility for dealing with more than one multipath signal.
The present invention enables FM broadcast stations to add revenue bearing broadcast services within the subsidiary communications allocation without interfering with existing "free access" broadcast services. Such services may include one or two CD quality digital stereo audio channels, or some combination of digital multimedia, digital audio, and digital data services. Thus,
SUBSΠΠΠE SHEET (Mft£ 26> existing transmitters and receivers would remain in use while the market is expanded via the subsidiary broadcasts. Optimum use is made of the limited SCA bandwidth, enabling income producing use by even single station broadcasters. The present invention further avoids any need for changing current broadcast regulations and readily accommodates future digital upgrades io the main broadcast signals of any station.
The embodiments described above are intended to be taken in an illustrative and not a limiting sense. Various modifications and changes may be made to the above embodiments by persons skilled in the art without departing from the scope of the present invention as defined in the appended claims. The term 'commercial' used in describing the Federally regulated FM broadcast channels is intended to include not-for-profit, public broadcast allocations.
SUBSTITIITE SHEET (RULE 26)
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|Clasificación cooperativa||H04H20/34, H04H2201/183|
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