Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
TITLE OF THE INVENTION
Deep and Robust Data Communication
NAME OF INVENTOR
Aryan Saed
DESCRIPTION OF THE INVENTION
AREA OF INVENTION
[0001] The present invention applies to the area of data communications.
Specifically the invention is
concerned with the modulation of signals, whereby the frequency, phase and/or
amplitude of a signal
are set by the data represented within it.
[0002] As is well known, data may be communicated by modulated waves. Such
waves may be
electromagnetic waves, typically at Radio Frequencies (RF) or at optical
frequencies, they may be
mechanical waves at sonic, subsonic and and ultrasonic frequencies, and/or
they may comprise
oscillations of voltage and/or current.
[0003] In prior art data modulation schemes and data division schemes, data
may be parceled and
allocated to streams (also called data channels) which are allocated to
frequencies as in FDM
(Frequency Division Modulation) or OFDM (Orthogonal Frequency Division
Modulation) schemes, or
to time slots as in TDM (Time Division Modulation) schemes, or to orthogonal
codes as in CDM
(Code Division Multiplexing), or a combination thereof.
DISCUSSION OF PRIOR ART
[0004] Main communications systems and protocols provide a distinct overhead
or initialization
channel so that transmitting stations and receiving stations can establish
connections or communicate
auxiliary data without disrupting their main payload channel.
[0005] Out-of-band signaling is commonly used for this purpose. Out-of-band
signaling generally
contains overhead & management data or synchronization signals separate from
the main data. In some
communication protocols, esp. optical networks, out-of-band signaling may
refer to additional frame
overhead embedded in the line data, thus requiring an increasing in the line
rate to maintain a payload
rate.
[0006] In computer peripheral protocols, out-of-band may refer to distinct and
separate electrical
connections or lanes that are used to send robust tones or patterns for device
recognition and rate
negotiation.
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[0007] High-speed interconnect protocols are commonly used between computers
and other computing
or storage devices. Examples of these protocols are PCIe (Peripheral Component
Interconnect ¨
Express), Small Computer System Interface (SCSI), Serial Attached SCSI (SAS),
and Serial ATA
(Serial Advanced Technology Attachment). During link initialization, it is
common to transmit protocol
primitives such as a fixed "ALIGN" bit-pattern and electrical idle, in an
on/off manner, for speed
negotiations, clock rate matching, and device recognition. Protocol primitives
such as synchronization
symbols or equalizer training symbols generally contain a repetitive pattern,
resulting in a Power
Spectral Density (PSD) profile that stands out from the rest of the signal
that carries data.
[0008] Patent US 9270373, "Transporting Data And Auxiliary Signals Over An
Optical Link" by
Zbinden e.a. describes the controlled activation and deactivation of two or
more optical channels of an
optical link. Auxiliary signals are transmitted by selectively enabling and
disabling two or more of the
optical channels and in which one or more auxiliary signals are received by
determining which ones of
the optical channels have been enabled and which ones of the optical channels
have been disabled.
[0009] Patent US 9712247 "Low Bit Rate Signaling With Optical IQ Modulators",
by Duthel describes
a low bit rate signaling data so that an optical receiver may identify the
optical transmitter port to which
it is connected, by decoding the average optical output power signal produced
by the transmitter, and
applying different transmit power levels, or different patterns of transmit
power levels, for different
channels.
[0010] Patent US 7283688 "Method, apparatus and system for minimally intrusive
fiber identification"
by Frigo, and related publications, describe a detectable unique signature
that is imparted on optical
signals propagating through a subject optical fiber or optical fiber path. The
signature comprises
polarization (i.e., the direction of the oscillating electric field);
frequency; and amplitude (the electric
field strength) or power (proportional to its square) and is subsequently
detected to identify an optical
fiber or path.
[0011] In Pulse Position Modulation (PPM) of the prior art, data is
communicated by transmitting a
pulse in one of many temporal positions. This type of modulation is the basis
of hydraulic semaphore
systems where electrical or radio wave communications are not practical. For
instance, in Measurement
While Drilling (MWD), water or oil pressure fluctuations are employed to
signal information about a
drill unit deep underground to a driller above ground, where the information
includes the reading of an
analog sensor such as including the severity of vibration of a drill head, or
battery life status, or a
gyroscope position and magnetic heading for directional drilling. The position
of the pulse is
commonly a coded representation of the data to be communicated. PPM is also
used for the control of
actuators in Radio Controlled vehicles, where it is attractive due to its
simplicity, since the position of
the pulse relative to a predetermined range can be made analogous to a desired
actuator setting relative
to a maximum. To ease the symbol timing, Differential Pulse Position
Modulation places each pulse
relative to the previous, and the receiver measures the difference in the
timing position of successive
pulses. PPM is a sparse code, because the transmission is mostly idle: the
time span during which a
pulse. or "mark", occurs, during which typically a RF carrier or a high signal
level is transmitted, is
substantially less than the time spans during which its enveloping idle/quiet,
or "space", occurs.
[0012] In wireless communications, overhead information is included in the
communication data-frame
that is sent between stations. The overhead is sometimes modulated at a lower
order, so that it may be
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reliably decoded if the connection between the stations is poor, for instance
due to interference, multi-
path fading, or heavy signal attenuation. Examples are the headers employed in
protocols for cellular
communications, such as 4th Generation Long Term Evolution (LTE-4G), and
wireless home
networking protocols such as WiFi (IEEE 802.11a/b/n/g/ac). As part of
cognitive radio protocols and
wireless medium sharing and co-existence, devices may yield their
transmission, using deliberate idles,
back-offs, or gaps, in order to enable other wireless stations of the same or
a different protocol to
coexist within a same frequency channel or band. In wireless communications it
is also common to
include a random back-off transmission gap in the case of a Carrier Sense
Multiple Access ¨ Collision
Avoidance (CSMA-CA) scheme such as in Ethernet and WiFi, and in the case of a
Time Domain
Duplex communication there is commonly a Transmitter or Receiver Turn Around
Gap (TTG, RTG)
between Physical Layer frames, to allow switching of RF circuitry in cellular
protocol devices. Most
wireless communications protocols, including LTE and WiFi include preambles in
their Physical
Layer frames. These preambles contain pre-defined signatures with power
spectral densities that stand
out from the data portion of the frame, and they have good auto- and cross-
correlation properties so that
a receiver can recognize the beginning of a burst, perform timing and
frequency synchronization and
train its equalizers, even in communication channels that are noisy and that
have heavy multi-path
fading.
[0013] Publication Vvr0/2013/112983, "Dynamic Parameter Adjustment For LTE
Coexistence", by
Bala e.a., describes the use of coexistence gaps to share a channel in a
dynamic shared spectrum.
During negotiated transmission gaps, stations of one protocol, e.g. LTE,
remain silent so that stations of
a second protocol can communicate and coexist in the same frequency band or
channel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 illustrates a QPSK data transmission with 2 gaps.
Figure 2 shows the corresponding gapping signal which forms the auxiliary
channel.
Figure 3 and 4 show an OFDM transmission with gaps.
DETAILED DESCRIPTION
[0015] In the present invention data may be parceled and allocated to one or
more main data channels
as in the prior art, and additionally to one or more auxiliary data channels.
[0016] Thc auxiliary channel may contain auxiliary data which would be
transmitted at a lower average
rate than the main data.
[0017] As a non limiting example, in the present invention a data burst
comprised of 8 symbol slots
contains 7 QPSK symbols and one gap symbol, for a total of 8 symbols. The
position of the gap codes
3 bits, since there are 8 positions available for the gap. Each QPSK symbol
contains 2 main bits. Thus
each burst contains 3 bits of auxiliary data plus 14 bits of main data. The
auxiliary data is transmitted at
a rate of 3 bits per burst period. The main data is transmitted at a rate of
14 bits over the same burst
period.
[0018] In accordance with the preferred embodiment, gapping involves idling
(zeroing) the transmit
signal over time periods as determined by the data in the auxiliary channel.
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[0019] A non-limiting example of such an idling scheme is OOK (On-Off Keying).
Thus, by sensing
the power of the received signal, a receiver may decode the OOK back to
corresponding auxiliary data
values.
[0020] In the preferred embodiment, when using 00K, the main data is
transmitted during the On
phase of the 00K. This phase may also be called the "Mark" phase. The signal
transmitted in the ON
phase contains phase and/or amplitude signals modulated by the main data. The
timing and thus
temporal positioning of the OFF phase indicates the auxiliary data. The OFF
phase may be called the
"Space" phase. Timing of the OFF phase may be relative to the start of a
burst, or to the start or end of
the previous OFF phase, or relative to other events embedded in the signal, or
relative to an absolute
timing reference such as a network referenced clock.
[0021] Thus the main data may be transmitted using schemes of prior art
modulation, such as TDM
(Time Division Multiplexing), FDM (Frequency Division Multiplexing), OFDM
(Orthogonal
Frequency Division Multiplexing), CDM (Code Division Multiplexing) etc... with
prior art symbol
modulation such as nPSK (Phase Shift Keying), PAM (Pulse Amplitude
Modulation), QAM
(Quadrature Amplitude Modulation) etc.. The auxiliary data is transmitted by
gapping the main data
transmission at the transmitter. Since gapping occurs at the transmitter, no
data is lost. Main data
transmission may be suspended during a gap symbol and continued after the gap.
[0022] In the preferred embodiment, a gap location code is used to control the
On/Off Keying. As a
non-limiting example, a value of 0 to 15 is calculated from a group of 4 bits,
each value uniquely
mapping to one of the 4-bit permutations. A bit permutation "0000" yields a
value of 0, "0001" yields a
value of 1, "0010" a value of 2 etc.. in a binary fashion until "1111" which
yields IS. Then this value,
as determined by the permutation to be transmitted, determines the location of
a gap in a transmission
burst.
[0023] In accordance with the above non-limiting example, gapping is applied
as follows to an OFDM
transmission. For binary auxiliary data "0011" symbol 3 of an OFDM burst
transmission is idled. Thus,
under poor channel conditions, when OFDM receptions of the main data channels
are not successful, a
power detector may be used to decode the auxiliary channel.
[0024] The present invention also provides for gapping with a higher
indication order. It can be said
that OOK entails gapping with a simple first order gap, an idle or zeroing.
Higher order indication may
involve additionally adjusting the duration of the gap period depending on the
data. For instance the
location of a gap is determined by a 4 bit permutation of auxiliary data, as
in the example above, and
the length of the gap is determined by an additional bit of auxiliary data.
[0025] A single gap positioned in one of N slots entails a I in N code. The
present invention may
involve more than one gap per burst. Thus the auxiliary channel may employ M
gaps out of N slots,
which entails an M in N code. The number of bits thus coded may be calculated
as 1og2(N choose M).
For instance a 1 in 8 code encodes 8 values and thus 3 bits per burst, whereas
a 2 in 8 code encodes 28
values and thus almost 5 bits.
[0026] In addition to setting the gap position based on the auxiliary data,
also the duration of the gap
may be set based on the auxiliary data, so that in combination more auxiliary
data is transmitted in a
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burst.
[0027] Reception of auxiliary channel is thus valuable when reception of the
main channel is not
possible. This is useful in situations where the communications channel is
temporarily faded or
interfered and data rate adaptation to a more robust coding and modulation
scheme has not yet been
applied by the transmitter. Applications include Machine-to-Machine
communications as part of the
Internet-of-Things.
[0028] This is also useful in situations where acknowledgements or data rate
feedback from the
receiving station back to the transmitting station are temporarily or
permanently not possible.
Applications include military probes and sensors, deep space communications,
and telemetry for MWD
(Measurement While Drilling)
[0029] Figure 1 illustrates a data transmission in accordance with an
embodiment of the present
invention. The figure shows a QPSK (4-phase, quadrature phase shift keying)
transmission of
sinusoidal signal. As is well known in the art, a QPSK symbol is an
oscillation at a specific frequency
at one of 4 phases, each phase representing the value of one pair of data
bits. The symbol period is
0.25s. The transmission begins with a 0.25s gap, which is an idle (zero,
silent) transmission. Then
follow 3 QPSK symbols, followed by another gap.
[0030] Figure 2 shows the corresponding gapping signal which forms the
auxiliary channel. A signal
level of 0 denotes a gap. Thus gaps are located at several positions: a first
at Os to 0.25s, a second gap
at Is to 1.25s, a third at 1.5s to 1.75s, a fourth at 5.25s to 5.5s. The first
and third may be used for
synchronization and may be used to separate the second and fourth gaps as
auxiliary data from a data
TYPE indicator (spanning 4 symbol slots from 0.5s to 1.5s) and a data VALUE
indicator (spanning 16
slots form 2s to 6s) in a TYPE/VALUE field of a data structure for the
auxiliary channel. The gap for
TYPE is in slot 2 indicating the data type the field (e.g. a temperature
reading) , and the gap for
VALUE is in slot 13, indicating the temperature value of the reading.
[0031] Figure 3 and 4 show an OFDM transmission with gaps. Figure 4 shows two
bursts of an OFDM
main communication signal and figure 3 shows an on-off signal to highlight the
position of gaps in
accordance with the present invention: where the on-off signal is "high" the
OFDM main
communication signal is being transmitted, and where the on-off signal is
"low" the OFDM main
communication signal is ceased. The first burst occurs from 0.5 to 2.5s, then
there is a 0.5s separation,
followed by the second burst which occurs from 3s to 5s. Here, the OFDM symbol
period is 0.25s for
both bursts, and both bursts are 8 symbols (2s) in length. In accordance with
one aspect of the
invention, each symbol in a burst is assigned a unique index: the first symbol
has index 0, the second
symbol has index 1 etc.. until the last symbol which has index 7. From the
auxiliary data, portions of 3
bits of auxiliary data are transmitted in subsequent bursts, by uniquely
selecting one of the 8 symbols to
represent the 3 bits in a burst. This is easily accomplished by calculating a
3 bit binary value from the 3
auxiliary bits and selecting the corresponding symbol. The gap of the first
burst occurs from ls to
1.25s, which is in the 3 symbol (having symbol index 2) of the burst, which
corresponds to a bit
permutation of "010" for the transmitted portion of auxiliary data. Thus, each
burst contains a gap, and
the location of the gap within the burst represents the value of a portion of
transmitted auxiliary data.
Analogously, the gap of the second burst occurs from 4.25s to 4.5s, which is
in the 6th symbol (having
symbol index 5) of the burst, which corresponds to a bit permutation of -101"
for the transmitted
portion of auxiliary data. It should be clear to a person skilled in the art
that the selection of the symbol
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period, the length of the burst, and the type of symbol are examples to
illustrate the transmission of
auxiliary data by transmitting gaps in lieu of modulation symbols of the main
signal.
[0032] In alternative embodiments, the symbols contain higher order modulated
signals, such as
OFDM symbols. Moreover, the symbols may occupy only a sub-band (a sub-
division) of the
transmission frequency band width. For instance, in a sonic transmission over
a pressure wave channel
that is 10KHz wide, symbols may occupy a sub-band that is 500Hz wide, centered
at 1KHz.
[0033] In alternative embodiments the gap may constitute a transmission of a
tone, or other signal at a
frequency generally outside the frequency band of the data symbols. This may
allow transmission of
data in a different frequency sub-band of the communication channel. For
instance, where data symbols
occupy a sub-band that is 500Hz wide centered at 1KHz, during the gap data
symbols are transmitted in
a different sub-band that is 500Hz wide centered at 2KHz.
[0034] The aforementioned gapping with optional sub-banding per the present
invention applies
equally to RF signals. For instance a 20MHz WiFi transmission may be divided
into an upper 10MHz
and a lower 10MHz, and auxiliary signaling occurs by switching transmissions
between the two.
[0035] In alternative embodiments the gap may have a duration of multiple
whole symbols (e.g. one of
2 or 3 symbol periods etc..) or a fractions of a symbol (e.g. one of 0.5 or
0.25 or 0.75symbo1 period), or
a combination of the two (e.g. one of 1 or 1.25 or 1.5 or 1.75 Symbols). The
set of allowable durations
may be adjusted based on the receiver requirements and the communication
channel conditions such as
distortion, noise and interference. Generally, the worse the channel
conditions are, the longer of a gap
may be required to reliably distinguish between a gap symbol and an ordinary
modulated symbol.
[0036] In alternative embodiments, the auxiliary data channel which determines
the position of the gap
may instead determine the start time of a burst rather than the location of a
gap within it. As a non-
limiting example, instead of transmitting a gap in slot 5 to represent a data
value of 5, the spacing
between two bursts is set to 5 gap periods. Thus a data value in the range 0
to 7 (8 values, 3 bits) may
be communicated in the auxiliary channel by spacing two bursts respectively in
the amount of 0 to 7
gap periods. Alternatively a fixed base spacing of for instance 2 gap periods
may be included thus
spacing two bursts respectively in the amount of 2 to 9 gap periods thus
providing a minimum of 2 gap
periods regardless the auxiliary data.
[0037] In alternative embodiments a burst or portion thereof is transmitted at
a predetermined set of
frequencies, and a different burst or a different portion thereof is
transmitted at a different
predetermined set of frequencies. The choice between the first set and second
set is determined by the
auxiliary channel data. As a non-limiting example, an auxiliary data sequence
of "101" may imply the
transmission using frequency sets A, B then A. A first burst is transmitted at
frequencies of set A, the
following burst is transmitted at frequencies of set B, and the third burst is
transmitted at frequencies
of set A.
[0038] As non limiting examples, these frequency sets may be odd/even
groupings of OFDM
subcarriers, or High/Low FDM frequency sub-bands.
[0039] A receiver in accordance with the present invention includes a detector
to determine the length
and or location of the gaps at specified and predetermined frequencies. This
may be accomplished by
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comparing the received signal within the transmission sub-band against a
suitable OOK threshold. The
threshold is ideally placed between the expected receive power for symbol
periods that contain symbol
signals, and the expected receive power in idle symbols. The latter power
level is chiefly determined by
receiver "background" noise and/or interference when there is no transmission.
The threshold may be
adapted during reception based on fluctuating receive signal, noise and
interference power levels.
The receiver may measure the receive power using a band pass filter or
equivalent, in digital and/or
analog form, to minimise out-of-band noise, signals and interference.
Alternatively the output of an
FFT operation commonly used in OFDM demodulators may be used to determine the
power level of an
individual symbol.
[0040] Thus the present invention provides a more robust auxiliary channel for
a more reliable transfer
of critical data on top of the main data.
[0041] Applications of the present invention include but are not limited to:
I. Communication of signals in temporarily heavy fading RF channels
(wireless links), where user
safety demands the reliable communication of critical data as in vehicle-to-
vehicle
communications, robot communications, and machine-to-machine communications.
2. Communication of signals in temporarily heavily distorted and disturbed
sonic (acoustic)
channels in production tubing (pipe) or drill pipe in oil & gas exploration
and exploitation
3. Communication of deep space signals by optical means such as laser, or
RF
4. Areas where bi-directional communications used for acknowledgements and
rate adaptation are
expensive or slow, and a robust uni-directional backup channel is required,
such as in uplink
-only drilling applications, or in downlink-only space applications or in
broadcast-only multi-
user applications.
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