Pulse or digital communications – Systems using alternating or pulsating current – Amplitude modulation
Reexamination Certificate
1999-12-20
2002-02-26
Tse, Young T. (Department: 2634)
Pulse or digital communications
Systems using alternating or pulsating current
Amplitude modulation
C375S301000, C375S321000, C332S170000, C329S357000, C455S047000, C455S109000
Reexamination Certificate
active
06351500
ABSTRACT:
This invention relates to a method of communication and a transmitter and receiver system for the terrestrial radio-frequency (RF) broadcast and reception of a digitally encoded signal together with an analog signal in the conventional AM-band of broadcast frequencies. The digital signal represents general digital (bit) information and may include a compressed digital audio signal. In certain embodiments, the spectrum of the composite digital signal includes either an upper inner or lower inner sideband about the allocation center frequency, and an analog signal representing monophonic audio occupies the other inner sideband. In other embodiments, a baseband digital signal is combined with an analog monophonic signal, and the composite signal is transmitted in the upper inner and lower inner sidebands using nonlinear compatible quadrature amplitude modulation (NC-QAM). The analog monophonic signal may be received by conventional AM-band receivers using envelope detection. For applications requiring additional bit capacity, for example, digital audio, supplemental bit information is represented by generating additional digital signals in the upper outer and lower outer sidebands. The digital receiver system of the invention detects and determines bit information from the inner sideband signals and outer sideband signals. In certain embodiments, the system of the invention is robust against the effects of one-sided first and second adjacent channel interference and other frequency-selective forms of interference due to the transmission of replicas of part of the codeword information in both the upper outer and lower outer sidebands, with or without diversity delay between the upper outer and lower outer sideband information.
CLAIM TO COPYRIGHT IN REFERENCE TO MICROFICHE APPENDIX
A portion of the disclosure of this patent application contains material which is subject to copyright protection. The copyright owner has no objection to the reproduction by anyone of the patent document as it appears in the Patent and Trademark Office files or records, but otherwise reserves all copyrights whatsoever. Software for carrying out some of the methods and systems described herein has been filed with the United States Patent and Trademark Office herewith in the form of a microfiche appendix including numerous frames, one of which being a title frame. The microfiche appendix is entitled AM-COMPATIBLE DIGITAL BROADCASTING METHOD AND SYSTEM and includes two (2) sheets of microfiche containing one hundred fifty-one (151) frames.
The microfiche includes two ASCII files: CODE.TXT and DATA.TXT, CODE.TXT including source code for redundant modulation and demodulation of sideband digital signals using pragmatic trellis coded modulation and a dynamic codeword diversity selector/combiner. DATA.TXT includes OFDM subcarrier signal representations for inner and outer sideband waveforms, as well as Hilbert transform tap weights for an SSB embodiment of the analog signal.
BACKGROUND OF THE INVENTION
There is a scarcity of contiguous amounts of available (unused) spectrum at those radio frequencies which are desirable for wide-coverage terrestrial broadcast communication systems in the high frequency (HF) band, between 3 megaHertz (MHz) and 30 MHz, and especially in the low frequency (LF) band, between 300 kilohertz (kHz) and 3,000 kHz. In certain cases, the spectrum of certain conventional information-bearing signals does not entirely occupy a particular frequency allocation, and/or the existing signals may not utilize all of the signaling dimensions, for example, having only amplitude modulation or phase modulation, but not both at once. As a result, it is desirable to generate supplemental signals, especially digitally-encoded signals, in the unoccupied parts of existing bandwidth allocations and/or by making use of underutilized signaling dimensions in order to provide capacity for digital (bit) information in a manner that does not introduce significant amounts of interference to existing signals. The additional information capacity is used for the introduction of new broadcast services, for example, navigation and subscription messaging, and/or the enhancement of existing broadcast services, for example, digital audio broadcasting to provide recovered audio quality comparable to high fidelity tape and compact disc (CD) recordings.
In the United States, the commercial (expanded) AM broadcast band presently occupies a part of the LF band of frequencies between 535 kHz and 1705 kHz, inclusive. The frequency region is subdivided into a plurality of channel allocations with an interchannel frequency separation of 10 kHz (an interchannel frequency separation of 9 kHz allocations has been proposed). Licensed radio stations are subject to restrictions on permissible AM-band signal power, spectrum occupancy (i.e. bandwidth), and geographic location in order to control the expected amounts of interference between stations. Rules and regulations regarding the licensing and operation of AM-band stations are enacted and enforced by the Federal Communications Commission (FCC) in the United States. A restriction for AM-band sound broadcast signals is determined by the FCC “emissions mask”. The emissions mask specifies a power spectrum density curve which defines the maximum allowable power of a discrete emission with respect to the licensed power as a function of the frequency offset from the nominal AM-band channel center frequency. Discrete emission compliance at a particular frequency is measured over a 300 Hz integration bandwidth. States. The abscissa values are the frequency offset with respect to nominal AM-band channel allocation center frequency
1
. The ordinate values are the decibel spectrum magnitudes with respect to the licensed modulated carrier power (dBc). The emissions mask is shown as bold curve
3
. Conventional monophonic analog AM signal
7
is the modulated signal representation of the arithmetic sum L+R of the left (L) and right (R) conventional analog audio signals. Conventional monophonic AM signal
7
is substantially confined within, under, and/or beneath emissions mask
3
. The center region of mask
3
includes upper inner
5
and lower inner
9
sidebands and occupies a two-sided bandwidth of about 20.4 kHz (i.e. 9.9 kHz+0.3 kHz+0.3 kHz+9.9 kHz) around channel center frequency
1
. In the center region, the maximum emission power may be as large as the licensed power; in other words, −0 dBc. Outer sideband regions
13
and
11
are disjoint and immediately adjacent to inner sidebands
5
and
9
, respectively, at positive and negative frequency offsets, respectively, with respect to center frequency
1
. Upper outer sideband region
13
occupies 9.8 kHz, beginning at a positive 10.2 kHz offset and extending to a 20 kHz offset. Lower outer sideband region
11
also occupies 9.8 kHz, beginning at a negative 10.2 kHz frequency offset with respect to center frequency
1
and extending to a negative offset of 20 kHz. It will be understood by those of skill in the art that the bandwidth occupancies of sidebands
5
,
9
,
11
, and
13
are to change.
In outer sidebands
11
and
13
, the maximum power of a discrete emission is attenuated by at least 25 decibels with respect to the licensed power; in other words, −25 dBc. Conventional AM-band broadcasting uses large-carrier amplitude modulation so that a significant fraction of the RF signal power is emitted as the sinusoidal carrier component with center frequency
1
. In many circumstances, analog signal
7
may be substantially confined in a spectrum region within inner sidebands
5
and
9
, closer to a two-sided bandwidth of 14 kHz (±7 kHz) than 20.4 kHz around center frequency
1
, with outer sidebands
11
and
13
substantially unoccupied. There are additional sideband regions defined in emissions mask
3
which are not shown in
FIG. 1
, beginning at ±20 kHz with respect to center frequency
1
, which extend significantly beyond outer sidebands
11
and
13
.
Since the bandwidth of conven
Digital Radio Express, Inc.
Liniak, Berenato, Longacre & White LLC
Tse Young T.
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