Note: Descriptions are shown in the official language in which they were submitted.
CA 02455737 2004-01-26
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SUPPRESSED CYCLE BASED CARRIER MODULATION USING AMPLITUDE
MODULATION
This invention relates, to methods for wireless transmission of data, and
specifically, to
a radio _frequency (RF) signal and to a carrier modulation method of
generating the signal
wherein the suppressed amplitude of the carrier signal for a cycle is used to
indicate a binary
zero or one, and the unsuppressed amplitude of a cycle indicates the opposite
binary number,
resulting in a RF signal and method of modulation that allows for high-speed
data transmission
that produces very little sideband energy.
Radio transmission of information traditionally involves employing
electromagnetic
lo waves or radio waves as a carrier. Where the carrier is transmitted as a
sequence of fully
duplicated wave cycles or wavelets, no information is considered to be
transmissible. To
convey information, historically, the carrier has superimposed on it a
sequence of changes that
can be detected at a receiving point or station. The changes imposed
correspond with the
information to be transmitted.
75 Where the amplitude of the carrier is changed in accordance with
information to be
conveyed, the carrier is said to be amplitude modulated (AM). Similarly, where
the frequency
of the carrier is changed in accordance with information to be conveyed,
either rarified or
compressed wave cycles are developed, and the carrier is said to be frequency
modulated (FM),
or in some applications, it is considered to be phase modulated. Where the
carrier is altered by
2o interruption corresponding with information, it is said to be pulse
modulated.
Currently, essentially all forms of the radio transmission of information are
carried out
with amplitude modulation, frequency modulation, pulse modulation or
combinations of one
or more. All such forms of modulation have inherent inefficiencies. For
instance, a one KHz
audio AM modulation of a Radio Frequency (RF) carrier operating at one MHz
will have a
25 carrier utilization ratio of only 1:1000. A similar carrier utilization
occurs with corresponding
FM modulation. Also, for all forms of currently employed carrier modulation,
frequencies
higher and lower than the frequency of the RF carrier are produced. Since they
are distributed
over a finite portion of the spectrum on each side of the carrier frequency,
they are called side
frequencies and are referred to collectively as sidebands. These sidebands
contain all the
30 message information and it has been considered that without them, no
message can be
transmitted. Sidebands, in effect, represent a distribution of power or energy
from the carrier
and their necessary development has lead 'to the allocation of frequencies in
terms of
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bandwidths by governmental entities in allocating user permits within the
radio spectrum. This
necessarily limits the number of potential users for a given RF range of the
spectrum.
To solve the bandwidth crisis in the RF Spectrum, multiple access systems were
developed. Multiple Access Systems are useful when more than one user tries to
transmit
information over the same medium. The use of multiple access systems is more
pronounced
in Cellular telephony; however, they are also used in data transmission and TV
transmission.
There are three common multiple access systems. They are:
1- Frequency Division Multiple Access (FDMA)
2- Time Division Multiple Access (TDMA)
3- Code Division Multiple Access (CDMA)
FDMA is used for standard analog cellular systems. Each user is assigned a
discrete slice
of the RF spectrum. FDMA permits only one user per channel since it allows the
user to use the
channe1100 % of the time. FDMA is used in the current Analog Mobile Phone
System (AMPS).
In a TDMA system the users are still assigned a discrete slice of RF spectrum,
but
multiple users now share that RF carrier on a time slot basis. A user is
assigned a particular
time slot in a carrier and can only send or receive information at those
times. This is true
whether or not the othe'r time slots are being used. Information flow is not
continuous for any
user, but rather is sent and received in "bursts". The bursts are re-assembled
to provide
continuous information. Because the process is fast, TDMA is used in IS-54
Digital Cellular
2o Standard and in Global Satellite Mobile Communication (GSM) in Europe. In
large systems, the
assignments to the time/frequency slots cannot be unique. Slots must be reused
to cover large
service areas.
CDMA is the basis of the IS-95 digital cellular standard. CDMA does not break
up the
signal into time or frequency slots. Each user in CDMA is assigned a Pseudo-
Noise (PN) code
to modulate transmi.tted data. The PN code is a long random string of ones and
zeros. Because
the codes are nearly random there is very little correlation between different
codes. The distinct
codes can be transmitted over the same time and same frequencies, and signals
can be decoded
at the receiver by correlating the received signal with each PN code. The
great attraction of CDMA technology from the beginning has been the promise of
extraordinary capacity increases over narrowband multiple access wireless
technology. The
problem with CDMA is that the power that the mobiles are required to transmit
goes to infinity
as the capacity peak is reached. i.e. the mobiles will be asked to transmit
more than their
capacity allows. The practical consequence of this is that the system load
should really be
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CA 02455737 2005-12-09
controlled so that the planned service area never experiences coverage failure
because of this
phenomenon. Thus CDMA is a tradeoff between maxunum capacity and maximum
coverage.
Over the previous few decades, electmnically derived infoxmation has taken the
form
of binary formatted data streams. These data streams are, for the most park,
transmitted
_ through telecommunica.tion systenzs, Le., wire. Binary industry
commurdcation in general
commenced with the networking of computer facilities in the mid 1960s. An
early networking
architecture was referred to as ""Arpanet". A short time later, Telenet, the
first public
packet-switched network, was introduced to connmerce. As these networks grew,
profocols for
their use developed. For example, a coding protocol, ASCII (American Standard
Code for
lnforniation Interchange) was introduced in 1964. Next, Local Area Networks
ON)
proliferated during the 1970s, the oldest and most prominent, that known in
the trade as,
Ethernet, having been developed in 1973. Under the Ethernet concept, each
station of a local
system connects by cable to a transceiver and these transceivers are then
irnter-Iinked. In 1983,
the Tnstitute of El.ectrical and Electronic Engineers (fESE) promulgated
Ethernet with some
modifications, as the first standard protocol for Local Area Networks. The
Ethernet protocol
remains a standard for e.ssexttially allfornns of database conveyance or
exchange.
While binary data stream transmission by wire has hnproved substantially in
ternns of
datatransferrates, thatimprovementhas notbeenthe case wh.ere transmissionis
byutilizatton
of the RF spectrum The ixansn-ission inefficiencies occasioned with the
modulation of an RF
carrier have remained to the extent that an efficient, high-speed
transrnissioin of binary
inforrmation utilizing an RF cattx.er remains as an ehxsive goal.
An object of the present invention is to provide a suppressed cycle based
carrier
modulation using amplitude modulation.
The pre,sent invention itucludes an modulated radio frequency carrier capable
of
ftmmitgng a b3tsary iarforznai3on stream made up of first and second binary
states coanprising
a carrier frequency waveform made up of a continuous sequence of wavelets,
said wavelets
being defined by a 360 degree cycle between crossover positions; said
crossover positions
representing a substantally zero energy level, said wavelets having been
modulated in
accordance with said infornnation stream by having suppressed the amplitude of
said wavelets
corresponding to said first binary states of said information stream and not
having suppressed
the amplitude of said wavelets corresponding to said second binary stafie.s of
said
information stream.
The invention also includes a method for transmitEing binary information from
a binary
information stream over a radio frequency carrier characterized by the steps
of generating a
radio frequency carrier at a select carrier frequency such that said radio
frequency carrier has
a waveform with a continuous sequence of wavelets with similar amplitudes,
said wavelets
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CA 02455737 2005-12-09
being defined by a 360 degree cycle between crossover positions of said radio
frequency carrier
waveform said crossover positions representing a substantially zero energy
level;
receiving said information stream as a binary data sequence of first and
second binary states,
modulating said radio frequency carrier in accordance with said binary data
sequence by
snppressing the axnplitude of said wavelets corresponding to said first binary
states to derive
first carrier binary signals and not suppressing the amplitude of said
wavelets corresponding
to said second binary signals to derive second carrier binary states thereby
generating a
suppressed cycle modulated carrier made up of said first carrier binary
signals and said second
caxrier binary signals, and broadcasting said suppressed cycle modulated
carner such that a
suppressed cycle modulated radio frequency signal is generated.
In accorda.nce with another aspect of the invention, there is provided a
method of
receiving radio frequency transmitted binary information that was
derived from a binary information stream composed of a binary data sequence of
first and
second binary states that was modulated onto a radio frecqttency carner which
has a waveform
with a contlnuous sequence of wavelets with similar amplitades defined by a
360 degree cycle
between crossover positions representing a substarYtialty zero energy level in
which the radio
frequency carrier has been modulated in accordance with said binary data
sequence by
suppressing the amplitude of said wavelets corresponding to said first biaary
states tD derive
first carrier binary signals and not suppressing the amplitude of said
wavelets correspondiT.tg
to said second binary states to derive second carrier-binary signa]s thereby
generating a
suppressedcycle modulated carriermadeup of saidiTSt carrferbinary signals and
said second
carrier binary signals such that a suppressed cycle modulated radio
ffirequency sig.nn.a1 was
generated and broadcasted cliaracterized by the steps of receiving said
sttppressed cycle
modulatedradiofreqaencysignalthroughanantennaxesponsiveto
saidcarrierradiofrequesucy
signal, exhacting said suppressed cycle modulated carrier from said suppressed
cycle
modulated carrier radio frequency signal received by said antenna,
demodulating said
suppressed cycle modulated carrier by detecting the respective amplitudes of
said wavelets to
identify said first bnlaty states and said second biaary states corresponding
with said first
carrier binary signals and said second carzier binary signals, and,
reconstructing said binary
data sequence from said first binary states and said second binary states
resulting in
regeneration of said information stream.
In accordance with another aspect of the invention, there is provided a method
for
transmitting binary information from a binary information stream over
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CA 02455737 2005-12-09
a radio frequency carrier, receiving the radio frequency carrier, and
converting the trarismitted
biriary information back into an information stream characterizedby the steps
of generatfing a
radio frequency carrier at a select carrier frequency such thatsaid radio
frequency carrier has
a waveform with a continuous sequence of wavelets with similar amplitudes,
said wavelets
being defined by a 360 degree cycie between crossover positions of said radio
frequency carrier
waveform, said crossover positions representing a substantially zero energy
level;
receiving said information stream as a binary data sequence of first and
second baiary states,
modulating said radio frequency carrier in accordance with said binary data
sequence by
suppressing the amplitude of said wavelets corresponding to said first binary
states to derive
first carrier binary signals and not suppressing the amplitude of said
wavelets corresponding
to said second binary states to derive second carrier binary signals so as to
generate a
suppressed cycle modulated carrier made up of said first carrier binary
signals and said second
carrier binary signals, broadcasting said suppressed cyde modulated carrier
such that a
suppressed cycle rnodulated radio frequency signal is generated, receiving
said suppressed
cycle modulated radio frequency signal through an antenna responsive to said
carrier radio
frequency signal, extracting said suppressed cycle modulated cairier fromsaid
suppressed cycle
modulated carrier radio frequency signal received by said antenna,
demodulating said
snppressed cycle modulated carrier by detecting the respective amplitudes of
said wavelets to
identify said first binary states and said second binary states corresponding
with said first
carrier birnary si.gnals and said second carrier binary signals, and,
reconshuctir-g said birnarj-
data seqaence from said first binary states and said second biztary, states
resulting in
regeneration of said infa~m stream.
Convenient]yp, the present invention is addressed to a RF signal and method
wherein
digital data streams are radio transmit6ed at a high level of efEioiency and
speed, and witliout
a large continuous concomitant formation of side frequency phenomena. Thus,
bandwidths
assigned for this transnaissional task are quifie narrow, with data
traasncrission speeds at the
singular frequency of the RF carrier itself. This invention can send high
speed data in RF
channels that are verynarrow and thatwould ordinarily be considered vseEul
only for very low
speed data or analog voice. This invention can also be used with multiple
access systems.
That method of modulation uses an RF carrier comprised of a continuum of full
cycle
sinusoidal wavelets extending between zero.crossover points or positions, and
that carrier is
thenmodulated to carrybinaryinformationby selectively deleting one or a
saccession of carrier
wavelets. Such a deletion may be assigned to represent either a binary one or
zero value. The
deletional modulation is carried out by the removal, by switchfng; of data
related wavelets at
the sinusoidal zero crossing positions defining them.
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Inasmuch as these zero posiiiorts correspond with the absence of elechro-
ntagnetic wave
energy, no wave disturbances are invoked which, would in turn, produce side
frequencies. As
a consequence, the assigned carrier frequencies may be quite dose together in
value to provide
a substantially improved utilization of the radio specirum for binary data
transmittal.
Tnthe presentinventionthe deletiorialmodulation of the original inventionis
modified
to merely suppress the amplitude of the cycle resulting in suppressed cycle
modulation (SC1VI).
This modulation is accomplished when the carrier is amplitude modulated with a
modulation
signal that is equal in frequency to the carrier itself and the modulation
always begins or ends
upon the exact zero voltage crossing point of the RF cycle phase. The
modulation is applied as
a shift of the amplitude of any single cycie, each cycle representing a single
bit of data. In SCM,
each individual RF cycle represents one bit of data. A single cycle of RF will
either represent
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a"1T" or "0" depending upon the amplitude of the cycle, relative to other
adjacent cycles in the
same carrier. It is necessary to visualize the carrier as a bit stream, rather
than a carrier. The
relative amplitude of one bit to another will determine the logical state. For
instance, a cycle
which is relatively higher in amplitude than other cycles in the stream might
be considered to
represent a"1". Conversely, a cycle that is relatively lower in amplitude than
other cycles in
the bit stream might be considered to represent a "0".
In general, an assembly for transmitting a data stream of binary information
would
employ a local oscillator, or other means, to generate a RF carrier to be
transmitted. The
crossover positions defining wavelets of the carrier are then identified and
are synchronized
lo with the binary data of the data stream. A carrier modulator, which
suppresses carrier wavelets
in correspondence with the binary data being transmitted is used to modulate
the carrier.
Amplification of the modulated RF carrier for antenna-based transmission or
broadcast is
carried out using a non-resonating amplification architecture, such as a Class
A amplification
stage.
The receiver is designed to receive SCM binary radio signals and output them
as a TTL
compatible serial data stream. An assembly for receiving a data stream of
binary information
would employ a pre-selector that consists of a tuned antenna that is connected
to a series tuned
band-pass circuit that will reject signals outside the desired pass band.
Amplification of the
received signal using Class A Amplifiers would be required along with a low
pass filter to
2o eliminate any unwanted signals. A circuit to isolate or "clip " the
positive voltage portion of the
signal and provide amplification of that portion of the signal would then be
used along with
additional amplification to allow for easier differentiation between the two
logic states. A
sample and hold (S/H) circuit then receives and rectifies the signal,
resulting in a filtered pulse,
which represents RF pulses of the higher amplitude and excludes those of the
lower amplitude,
thus differentiating between the two logical states insinuated by this
particular modulation
scheme. A class B squaring amplifier is then used essentially as an
"overdriven" amplifier. This
amplifier receives the single binary pulses from the S/H circuit and amplifies
them to or near
the supply voltage, thus clipping at the maximum supply voltage. This cleans
up the signal
pattern and provides a squarer signal. Finally, a TTL compatible output
circuit performs
additional squaring and inversion of the signal logic twice, which results in
the original logic
polarity after two stages of squaring.
The invention will now be described, by way of example, with reference to the
accompanying drawings.
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FIG. 1 is a diagram showing suppressed cycle modulation for alternati.ng 1's &
0's (test
pattern);
FIG. 2 is a diagram showing spectral analysis of alternating l's & 0's for 5%
suppressed
cycle modulation;
FIG. 3 is a diagram showing suppressed cycle modulation for random l's & 0's;
FIG. 4 is a diagram showing spectral analysis of random l's & 0's for 5%
suppressed
cycle modulation;
FIG. 5 is a-block schematic diagram of a test pattern generator transmitting,
assembly
employing an embodiment of suppressed cycle modulation;
FIG. 6 is a schematic diagram of a test pattern generator transmitting
assembly
employing an embodiment of suppressed cycle modulation;
FIG. 7 is a block schematic diagram of a receiving assembly or station
employing an
embodiment of suppressed cycle modulation; and,
FIG. 8 is a schematic diagram of a receiving assembly employing an embodiment
of
suppressed cycle modulation.
The wireless transmission of digital binary data streams is the concept of
"suppressed
cycle modulation" (SCM) wherein sinusoidal-defining wavelets on a RF carrier,
each with a
period representing 360 , are selectively amplitude suppressed to represent a
select binary value.
For example, the suppression of such a wavelet, or sequence of them, from an
otherwise
continuous carrier sequence of wavelets defining a carrier waveform may
represent either a logic
zero or logic one depending upon the protocol utilized. Because these wavelets
are selectively
suppressed by acting upon the carrier waveform at zero crossing positions,
minimal side
frequencies or sidebands are generated. These sidebands occur for only one RF
cycle and the
power contained in the sideband is very low. The RF signal and method of the
invention can
perform with a very narrowly allocated bandwidth that approaches the
unmodulated carrier width
itself. Thus, bandwidths assigned for this transmissional task are quite
narrow, with data
transmission speeds at the singular frequency of the RF carrier itself. This
invention can send
high speed data in RF channels that are very narrow and that would ordinarily
be considered
useful only for very low speed data or analog voice. This invention can also
be used with
multiple access systems.
The embodiment RF signal and method is accomplished when the carrier is
slightly
amplitade modulated with a modulation signal that is equal in frequency to the
carrier itself
and the modulation always begins or ends upon the zero voltage crossing point
of the RP cycle
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phase. The modulation is applied as a shift of the amplitude of any single
cycle, each cycle
representing a single bit of data. In the preferred embodiment, each
individual RF cycle
represents one bit of data. A single cycle of RF will either represent a "1"
or "0" depending
upon the amplitude of the cycle, relative to other adjacent cycles in the same
carrier. It is
necessary to visualize the carrier as a bit stream, rather than a carrier. The
relative amplitude
of one bit to another will determine the logical state. For instance, a cycle
which is relatively
higher in amplitude than other cycles in the stream might be considered to
represent a"1".
Conversely a cycle that is relatively lower in amplitude than other cycles in
the bit stream might
be considered a"0". By treating each individual RF cycle as a logical bit,
information will be
transmitted at a speed equal to the carrier frequency.
In the preferred embodiment the slight amplitude shift is performed at the
zero voltage
crossing point. This is done to minimize any sideband or harmonic radiation.
Therefore, only
RF carrier cycles of pure sinusoidal form are transmitted.
When a carrier is un-modulated it usually is considered to carry no
information.
However in SCM, the opposite is true. A carrier that has no modulation is
considered to
represent all "1's" or all "0's". The relative amplitude of each cycle is used
to judge the binary
representation intended by the transmitter. When a carrier is steady and un-
modulated, it also
generates no sidebands. Therefore, we can limit the discussion of sidebands to
only those
carrier cycles that are different in amplitude, one to another and are
adjacent in sequence.
Consider for example the binary sequence "1111001". The first four "l's" will
cause the
carrier to consist of four RF cycles of relatively high amplitude, assuming a
protocol of full
amplitude cycles representing "1's". A steady carrier creates no sidebands so
four "1's" are
transmitted without sideband energy.
The transition of the fourth bit, a"1", to the fifth bit, a "0", will cause
the fifth RF cycle
to have a relatively lower amplitude, beginning exactly at the start of the
cycle at the zero
voltage point. This change of amplitude will generate one single cycle of RF
sideband at some
integer or fractional multiple of the carrier frequency. Since this sideband
consists of one single
cycle of RF energy at twice the carrier frequency, the power contained in this
sideband is very
low as compared to the power in the carrier. The power contained in that
single cycle of
sideband energy relative to the power of the carrier is determined by the
ratio of the amplitude
of the previous cycle to the amplitude of the current cycle. This is the
modulation index.
The next bit is a "0". Since the previous bit was also a "0", there will be no
transition of
amplitude, thus no sideband.
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Finally, the last bit is a"1", causing a relative shift in the amplitude of
that
corresponding RF cycle arid a sideband again, consisting of one single RF
cycle at some integer
or fractional multiple of the carrier frequency. In this example, 7 bits of
data were transmitted
while radiating only 2 cycles of RF sideband.
Looking now to figure 1, a representation of a suppressed cycle modulated RF
signal is
presented. The waveform shows a variation of carrier amplitude representing
alternating
digital values of "ones" and "zeros" from an otherwise continuously repetitive
state. This is a
worst-case scenario because the maximum amount of sideband energy to be
radiated would
happen when the binary data pattern consists entirely of alternating "1's" and
"0's". The
1o circuitry of the transmitter generating this waveform is shown in figures 5
and 6. The spectral
analysis of alternating "1's" and "0's" generated by the transmi.tter of this
preferred
embodiment is shown in figure 2. In this case there would be different
relative amplitudes for
each subsequent cycle resulting in two sidebands at 1/2 and 2X the carrier
frequency (the upper
sideband is filtered by low pass filters in the test pattern generating system
shown in figures 5
and 6).
Real data is random in nature, or at least not repetitioia.s ad-infinitum, as
shown by the
waveform disclosed in figure 3. Since a single cycle of RF sideband energy can
only exist during
the transition from one binary state to another, any repeating "0's" or "1's"
will reduce the
average sideband power.
The following abbreviations and symbols are used to find the expression for
the power
in the carrier and in the sideband.
A = Amplitude of the carrier (Volts)
Pc= Discrete Carrier Power (Watts)
PsB = Power in Sideband (Watts)
m = modulation index
R Load connected at the output '(SZ)
f; = Carrier Frequency
The voltage expression for the unmodulated carrier is given as:
. V=A sin 27rfct ........................................eq (1)
The expression of the modulation envelope of the AM Signal is A + mAsin 27cfmt
Where fm is the frequency of the data to be transmitted
Voltage expression for the modulated signal is given as:
V'= (A + mAsin 21rfmt) sin 27cft .... ... ... .... .....eq (2)
V'= A sin 27rf,,t + mAsin 27cft sin 27cf,,t .... .... ..eq (3)
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In case of Suppressed Cycle Modulation, the carrier and the data are at the
same
frequency, so substituting
fc = fm in equation (3) we get:
V'= A sin 27rf,,t + mA Sin' (27itt) ........ .. .... .. . ..eq (4)
Since co,= 27cf,,
Y' = A sin w t + ~ - ~ cos 2cv,t . . .. . .. . . . ... . . . ...eq (5)
c 2 2
From Equation (5), Discrete RMS Carrier power is given as:
Pc =A'/2R (Watts) ...................eq (6)
RMS Power in Sideband is given as:
Psa = m'A' / 8R (Watts) ................eq (7)
In this equation, A and R are fixed, so the only thing that affects the power
in sidebands
is the modulation index'm', so to have less power in sidebands, the modulation
index needs
to be lower.
Equation (7) can also be written as:
2 2
m A
Pss = 4 (Watts) eq (8)
2R
Substituting equation (6) in equation (8), we get
Psa = 4 P, . . ... .. . .... . . . . . . . .. . .. . .. eq (9)
PSB m'
Pe 4 ...............................eq (10)
In terms of dB:
PdB = 10 log (m' / 4) (dB) .............eq (11)
Good results are obtained where the modulation index is small enough so
thatthe power
in sideband is at least 30dB below the carrier. The spectral analysis of a
random signal is shown
in figure 4.
Looking to Fig. 5, a transmission station or assembly capable of generating
and
transmitting SCM is generally represented and denoted as 1. The transmitter
(1) of figure 5 is
used as a test pattern generator to transmit the carrier with alternating
"1's" and "0's" and
transmits the carrier at a frequency of 16MHz. This circuit is but one
embodiment of many
various circuits that could generate and transmit the SCM signal and is used
for the purpose of
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showing single cycle modulation is possible. Those skilled in the art will be
able to design many
variations of this and other circuitry that will generate and transmit the
invented RF signal and
method. The test station is formed with a local oscillator (2), or clock,
which generates a carrier
waveform at a select carrier frequency that is, in the test generator
embodiment of this disclosure,
16MHz. This type of standard oscillator is well known to those skilled in the
art. Those skilled
in the art will also recognize that any carrier frequency can be used with
this modulation
technique. As noted above, the RF carrier exhibits a waveform with a
continuous sequence of
wavelets, and the wavelets will be represented as sinusoids of at least 3 60
extent defined between
crossover positions and commencing in a positive going sense.
A phase adjuster (3) is used to synchronize the carrier frequency with the
modulating
signal generated by the modulator (7), which would be the data stream to be
transmitted. This
allows the amplitude suppression to be performed precisely at the zero voltage
crossing point
of the carrier frequency. This mini_m;zes any sideband or harmonic radiation .
The phase
adjusting (3) function may be carried out, for example, by a phase detector
such as that
marketed by Mini-Circuits, Inc. as a model MPD-21. A variety of high-speed
operational
amplifier implementations for detecting zero thresholds are available in the
art.
Minimal sidebands are still generated using this method of modulation since
the
switching may not be perfectly synchronized to occur in conjunction with a
zero crossing
location. Therefore, in accordance with good engineering practice, filters (4)
are employed to
strip off any residual harmonics or spurious radiation otherwise generated due
to switching
imperfections. The thus filtered transmission output is provided to a radio
frequency (RF)
transmission assembly that is comprised of a Class A type of radio frequency
amplifier (5) and
a transmission antenna (6). Class A amplification is called for inasmuch as no
ringing or tank
circuit type of amplification iinplementation is desired which would tend to
recreate sinusoid
signals and potentially alter the suppressed nature of the carrier amplitude,
which in this case
would define digital data.
The transmdssion station (1) generally will exhibit a capability for
transmitting or
broadcasting data at speeds, which are equal to the carrier frequency when
using SCM
transmission. For example, a one MHz RF carrier will transmit data at one
Megabit Per Second
(MBPS) where the system designer chooses to use a single wavelet to represent
one bit of data.
Referring now to figure 6, a schematic diagram showing actual components
implementing the block diagram of figure 5 is disclosed and would be easily
replicated by
anyone skilled in the art. The transmitter (1) is comprised of the following
circuitry the
CA 02455737 2004-01-26
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description of which contains a more detailed disclosure of the components
making up the
circuits.
The local oscillator (2) is comprised of a Master Clock that generates a 16
MHz square
wave. The 16 MHz square wave goes to a Low Pass filter (4) and to JK flip flop
74F112. C5 is
used to block DC from the Master Clock. The Low Pass filter (4) is a seven-
pole Butterworth
filter and has a cutoff frequency of 16 MHz. Cl, C2, C3, C4, L1, L2 and L3
forms the seven poles
of the filter (4). The filter (4) is designed for a 50 Ohms input and a 50
Ohms output. R1 and R2
form a 50 Ohms input and a 50 Ohms output combination. This Low Pass filter
(4) performs
two functions: First it filters the square wave, and second, it converts the
square wave into 16
MHz sine wave.
R3 and C6 form the phase adjuster (3) circuitry so that amplitude suppression
in the
cycles begins at zero crossings. The JK Flip flop 74F112 that receives the
signal from the Master
Clock is configured in a"divide by two" mode. The output of this flip flop is
an 8MHz square
wave.
R5, R6, and R8, together with Q1 form the suppressed cycle modulator (7). R4
and R7
are the biasing resistors for Q1. The output of the modulator (7) feeds into
another 7 pole
Butterworth Low Pass filter (4). C7, C8, C9 C13, L4, L5, and L6 form the seven
poles of the filter
(4). This filter (4) has a cutoff frequency of 16MHz. C12 is another blocking
capacitor connected
between th.is filter (4) and the Class A Amplifier.
The Class A amplifier (5) is made with transistor Q2 which is an MMBR941. R15
and
R14 are used as biasing resistors for Q2, whereas R9, R13, and C11 provide
gain to this amplifier
(5). The output of this amplifier (5) is taken from the collector of 'Q2. A 50
Ohm load resistor,
R12, is connected at the output with a blocking capacitor C10.
The output of this Class A amp.lifier (5) goes to 9 pole butterworth low pass
filter (4)
having a cutoff frequency of 16MHz. C14, C15, C16, C17, C18, L7, L8, L9, and
L10 form the 9
poles of the filter (4). The output of the filter (4) is matched to a 50 Ohm
resistor, R10, and is fed
to the antenna (6).
Looking to Fig. 7, a receiver station or assembly for receiving the test
pattern is generally
represented and denoted as 10. The receiver (10) of figure 7 is used to
demonstrate that it is
possible to receive the carrier with SCM binary digital signals of alternating
"1's" and "0's at a
frequency of 16ililHz and output them as a TTL compatible serial data stream.
The receiver (10) is comprised of the following circuits: A Pre-selector (11)
that consists
of a tuned antenna and a series tuned circuit that will reject signals outside
the desired pass
band; a front end pre-amp (12) made up of two Class A type of RF amplifiers to
amplify the
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WO 03/013089 PCT/US01/31105
received signal; a low pass filter (13) to eliminate any unwanted signals; an
additional class A
amplifier (14) for further amplification; a Class B amplifier (15) that
performs as a high-speed
rectifier and amplifier without the diode voltage drop which would be
associated with typical
rectifier/ detector circuits. This circuit acts to isolate or "clip "the
positive voltage portion of the
signal waveform and to provide amplification of that portion of the signal; a
Class B amplifier
second stage (16) that performs the similar function as the previous class B
amplifier (15) with
the overall effect being to amplify the difference between the "1" signal
level and the "0" signal
level allowing for easier differentiation between the two logic states; a
sample and hold circuit
(17) that receives the signal, rectifies the signal and results in a filtered
pulse, which represents
RF pulses of the higher amplitude and excludes those of. the lower amplitude,
thus
differentiating between the two logical states insinuated by this particular
modulation scheme;
a squaring amplifier (18), which is a class B amplifier that essentially is an
"overdriven"
amplifier such that this amplifier receives the single binary pulses from the
sample and hold
circuit (17) and amplifies them to or near the supply voltage, thus clipping
at the maximum
supply voltage acting to clean up the signal pattern and provide a squarer
signal; a TTL
compatible output (19) that performs additional squaring, inversion of the
signal logic twice,
resulting in the original logic polarity after two stages of squaring; and
finally, a load (20) for '
the output of the receiver (10) for testing purposes.
Figures 8A and 8B disclose the schematic diagram of the circuitry implementing
the
2o block diagram of figure 7 in sufficient detail such that anyone skilled in
the art would be capable
of building one. The receiver (10) of this test pattern embodiment is designed
and implemented
in the circuitry disclosed in figures 8A and 8B to receive SCM binary digital
signals and output
them as a TTL compatible serial data stream. The receiver (10) is comprised of
the following
circuitry the description of which contains a more detailed disclosure of the
components making
up the circuits.
As disclosed in figure 8A the pre-selector (11) consists of the tuned antenna
along with
C3 and U. C3 and L3 comprise a series tuned circuit that will reject signals
outside the desired
pass band.
The front end pre-amplifier (12) amplifies the desired signal. R19 and R7
comprise Class
A biasing for Q5, a bi polar transistor. R11 is the load resistor and R10 is
the emitter resistor,
providing gain reduction and negative self-biasing. Coupling to Q3 is provided
by C7. R18 and
R14 provide class A biasing for Q3. R20 is the load resistor and R21 provides
negative self-
biasing.
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C11 provides AC coupling from Q3 to Q6, another Class A amplifier (12). As in
the
previous amplifier (12), R24 and R25 provide Class A biasing for Q6 while R23
acts as a load
resistor and R22 provides negative biasing.
C10 couples the signal to the Low Pass Filter (13) comprised of L1, L2, C4, C5
and C6.
R12 adds loading to the filter (13) to assist in control of the filter (13).
Cl Couples the signal out of the LPF into a Class A amplifier (14) comprised
of biasing
resistors R8, R2, transistor Q1, load resistor R6, and emitter resistor R1.
Figure 8B shows the first stage Class B amplifier (15) that performs as a high-
speed
rectifier and amplifier without the diode voltage drop that normally would be
associated with -
1o typical rectifier/ detector circuits. R3 and R9 bias Q2 to Class B
operating mode. R13 acts as a
load resistor. This circuit acts to isolate or "clip" the positive voltage
portion of the signal
waveform and to provide amplification of that portion of the signal.
The second stage Class B amplifier (16) performs the similar function as the
previous
Class B amplifier (15). Overall, the effect will be to amplify the difference
between the "1 "15 signal level and the "0" signal level allowing for easier
differentiation between the two logic
states. C8 couples the signal from stage one to stage two where R26 and R27
bias Q4 into Class
B operation. R28 acts as the load resistor for Q4.
The sample and hold circuit (17) receives the signal through C9 and Dl. Dl
rectifies the
signal and charges C12 in only the positive polarity. R15 and R16 comprise a
bleeder/ discharge
20 path for C12 while also comprising a scaling or voltage divider circuit
from which the now
filtered signal is coupled. Dl also reduces the amplitude of those signal
pulses that occur when
the signal is at the reduced level mode. Overcoming the voltage drop imposed
by Dl results
in coupling of signals only large enough to do so, generally those
representing binary "1's" if
that particular logic representation is used. The result will be a filtered
pulse, which is imposed
25 upon C13, which represents RF pulses of the higher amplitude and excludes
those of the lower
amplitude, thus differentiating between the two logical states insinuated by
this' particular
modulation scheme.
The squaring amp (18) is a Class B amplifier that essentially is
an"overdriveri' amplifier.
This squaring amplifier (18) receives the single binary pulses from the sample
and hold circuit
30 (17) and amplifies them to or near the supply voltage, thus clipping at the
maximum supply
voltage. This acts to clean up the signal pattern and provide a squarer signal
to the TTL
compatible output circuitry (19).
The TTL compatible output circuitry (19) prepares the signal for output. U1A
and U2A,
both binary Schmitt triggers/inverters, and the resistor R32 perform
additional squaring,
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WO 03/013089 PCT/US01/31105
inverting the signal logic twice, resulting in the original logic polarity
after two stages of
squaring. R32 provides a 50 ohm load for the output (20) of the receiver (10)
for testing
purposes.
As shown by the simplicity of the test pattern transmitter (1) ' and receiver
(10),
Suppressed Cycle Modulation (SCM) is a simple and innovative RF signal and
modulation
technique that is also fully compatible with present multiple access
techniques (like FDMA and
TDMA).
Some of the advantages of this RF signal and modulation.scheme, particularly
when
used with multiple access techniques, are:
a. Theoretically nearly zero bandwidth per channel.
b. High-speed data transrnission.
c. Separation between channels (also known as Guard Band) is small.
d. Allows large number of users to share information at the same time.
e. Interference between adjacent channels is theoretically negligible.
f. SCM can also be used to transmit digital voice and video at a high speed.
g. SCM system can be implemented for any RF Band (e.g. UHF, VHF etc..)
h. SCM supports frequency division duplex (FDD) paired bands with a difference
of few MHz between transmitting and receiving frequencies.
i. SCM supports TDMA as well as FDMA multiplexing techniques.
j. SCM can support spread spectrum frequency hopping techniques.
Because of above-mentioned inherent advantages, SCM when used in conjunction
with
FDMA or TDMA guarantees high-speed data transmission to multiple simultaneous
users.
When used in FDMA mode, each user is assigned a particular carrier frequency
to
transmit/receive their information. Therefore, since the bandwidth requirement
for a channel
to transmit (or receive) high.-speed data is low, hundreds or thousands of
channels can be
accommodated within a narrow spectral band. SCM in FDMA mode allows the user
to use the
channel 100% of the time.
When used in TDMA mode, multiple users share the common frequency band and
they
are required to transmit their information at different time slots within the
carrier. Data is
transmitted and received in bursts. These bursts are reassembled at the
receiver (or base station)
to provide continuous information. Since the data transmission speed is the
same as the carrier.
speed in SCM, this process of transmitting/receYving bursts of data appears
continuous.
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Like CDMA, the SCM method has negligible interference from adjacent channels.
But
CDMA performance decreases as the system approaches its capacity (i.e., as the
number of users
increase, each user must transmit more power). This creates a coverage problem
for CDMA.
Thus, CDMA requires a tradeoff between maximum capacity and maximum coverage.
The
SCM system performance does not decrease with an increase in the number of
users in a
multiple access system. This is because when the SCM system is used in FDMA
mode, each
user will have its own carrier, and when the SCM system is used in TDMA mode,
each user is
allowed to transmit/receive in its particular time slot only. Thus capacity
and coverage
problems in SCM are negligible.
A sinusoidal RF carrier is modulated for the transmission of digital binary
data streams
through the amplitude suppression of carrier wavelets, which are defined
between zero
crossover positions representing zero energy locations. This modulation is
accomplished when
the carrier is slightly amplitude modulated with a modulation signal that is
equal in frequency
to the carrier itself and the modulation always begins or ends upon the exact
zero voltage
crossing point of the RF cycle phase. The modulation is applied as a slight
shift of the
amplitude of any single cycle, each cycle representing a single bit of data. A
single cycle of RF
will either represent a"1 or "0" depending upon the amplitude of the cycle,
relative to other
adjacent cycles in the same carrier.
