U.S. patent application number 14/215617 was filed with the patent office on 2014-09-18 for network telemetry system and method.
This patent application is currently assigned to Xact Downhole Telemetry, Inc.. The applicant listed for this patent is Xact Downhole Telemetry, Inc.. Invention is credited to John-Peter van Zelm.
Application Number | 20140266769 14/215617 |
Document ID | / |
Family ID | 51525115 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140266769 |
Kind Code |
A1 |
van Zelm; John-Peter |
September 18, 2014 |
NETWORK TELEMETRY SYSTEM AND METHOD
Abstract
A telemetry system produces, transmits and receives signal sets
from network nodes, which correspond to transceiver stations.
Repeater scheduling and other interference mitigating techniques
are utilized to simultaneously transmit from multiple nodes with
minimized network degradation. Update interval/rate and network
throughput are thereby fixed regardless of the number of network
nodes and a network telemetry method is provided using the
system.
Inventors: |
van Zelm; John-Peter;
(Calgary, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xact Downhole Telemetry, Inc. |
Calgary |
|
CA |
|
|
Assignee: |
Xact Downhole Telemetry,
Inc.
Calgary
CA
|
Family ID: |
51525115 |
Appl. No.: |
14/215617 |
Filed: |
March 17, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61800063 |
Mar 15, 2013 |
|
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Current U.S.
Class: |
340/854.3 ;
367/81 |
Current CPC
Class: |
E21B 47/14 20130101;
E21B 47/12 20130101 |
Class at
Publication: |
340/854.3 ;
367/81 |
International
Class: |
E21B 47/12 20060101
E21B047/12; E21B 47/14 20060101 E21B047/14 |
Claims
1. A wireless telemetry network system, which includes: multiple
network nodes; a sensor associated with one or more of said nodes
and adapted for providing output comprising signal data
corresponding to an operating or status condition; a transmitter
associated with one of said nodes for propagating said signal data
between nodes; a receiver associated with one of said nodes for
receiving signals from other nodes; multiple network nodes adapted
for receiving said signal data; and said system being adapted for
transmitting telemetry signals across multiple network links
simultaneously.
2. A linear wireless telemetry network system for a well including
a wellbore structure extending subsurface downwardly from the
surface, which telemetry network system includes: multiple network
nodes distributed along the wellbore; at least one said node
including a sensor adapted for providing a signal data set output
corresponding to a downhole condition; a transmitter for
propagating said signal between nodes; a receiver for receiving
said signal from other nodes; and said system being adapted for
transmitting telemetry signals across multiple network links
simultaneously.
3. The telemetry system according to claim 2, which includes: said
telemetry signals being chosen from among the group comprising
acoustic, electromagnetic (EM), mud pulse (MP) and optical.
4. The telemetry system according to claim 2 wherein said signal
sets comprise orthogonal (low interference/cross-correlation)
signal sets assigned to network nodes so as to reduce interference
at adjacent nodes.
5. The telemetry system according to claim 4 wherein said telemetry
signals are located in multiple, minimally-interfering frequency
channels within a medium and/or separate mediums chosen from among
the group comprising acoustic, EM and MP.
6. The telemetry system according to claim 2 wherein: said nodes
have predefined separations (and therefore a signal propagation
associated attenuation level) and/or transmission power levels
adapted so as to maintain interference at receiver locations within
a tolerable range.
7. The telemetry system according to claim 6, which includes: an
update interval rate and network throughput being fixed regardless
of the number of network nodes.
8. The telemetry system according to claim 2, which includes: a
respective node including a transmitter and a receiver; and the
respective node simultaneously transmitting and receiving.
9. The telemetry system according to claim 8, which includes a
filter adapted to an approximation of the channel between the
respective node's transmitter and receiver.
10. The telemetry system according to claim 8, which includes said
receiver being adapted for receiving with mitigated
self-interference during transmission.
11. The telemetry system according to claim 9, which includes an
estimation function including: a transmitter-to-receiver intranode
channel providing an output; said adaptive filter having the signal
destined for transmission as a reference input; a summer receiving
outputs from said receiver channel and said adaptive filter; said
summer providing an error signal as a feedback output to said
adaptive filter; and said adaptive filter being adjusted so as to
minimize error signal.
12. The telemetry system according to claim 9, which includes a
receiver signal isolation function including: an estimated
intranode transmitter-to-receiver channel filter having the signal
destined for transmission as an input from the transmitter and
providing an output that is the estimated transmitter signal as
perceived by the receiver; a summer receiving inputs from said
adaptive filter and the receiver signal output that are
synchronized in time; and said summer providing an output
comprising the received signal with reduced transmitter signal
content.
13. The telemetry system according to claim 2, which includes: said
transmitter and said receiver operating in the same channel; said
received signals being isolated from each other; said receiver
being configured to receive with minimized self-interference during
transmission; and said control system including a function for
favoring a desired signal over an interferer signal.
14. The telemetry system according to claim 2 which includes: said
control system function coordinating network timing whereby a
desired signal precedes in time an anticipated, overlapping
interferer signal creating an interference-free time period at a
node for reception of a portion of the desired signal, thereby
allowing the node receiver to lock onto the desired signal.
15. The telemetry system according to claim 2, which includes:
multiple receivers within a node with signal outputs which are
phased and combined in such a manner to form a phased array that
gives rise to directional discrimination of incoming signals to
minimize interference from an undesired node transmissions arriving
from another direction.
16. The telemetry system according to claim 2, which includes:
multiple transmitters within a node with output signals phased in
such a manner so as to propagate outgoing signals in one direction
only and minimizing interference at another node.
17. The telemetry system according to claim 2, which includes: said
directional receivers being adapted to suppress undesired
interfering signals arriving at the receiver from one direction,
while receiving desired signals from another direction.
18. A method of transmitting acoustic telemetry signals in a well
including a wellbore structure extending subsurface downwardly from
the surface, which method includes the steps of: defining with said
structure a linear/daisy-chain network; providing multiple network
nodes positioned along said structure; transmitting said signals in
signal sets comprising orthogonal (low interference) signal sets
assigned to network nodes to reduce inter-node interference;
pre-defining node separations and/or transmission power levels;
predefining tolerable interference ranges for said receivers;
maintaining interference at receiver locations within tolerable,
predefined ranges through signal propagation attenuation; providing
a sensor associated with one or more of said nodes and adapted for
providing output comprising signal data corresponding to an
operating, status, or wellbore condition; providing a transmitter
associated with one of said nodes for propagating said signal data
between nodes; providing a receiver associated with one of said
nodes; receiving with said receiver signals from other nodes;
receiving said signal data with said multiple network nodes; and
transmitting telemetry signals across multiple network links
simultaneously.
19. The method according to claim 18, which includes the additional
step of: providing said well with a node located at said surface
and a bottom hole assembly (BHA) located at the bottom of said
well; providing sensors configured to monitor operating conditions
near or at the BHA; generating said signals with data corresponding
to said BHA operating stations; transmitting said BHA operating
condition data signals to said surface node; and exporting said BHA
operating condition data signals to a remote data processing system
configured to monitor operating conditions at said well.
20. The method according to claim 18, which includes the additional
step of generating said telemetry signals using a signal type
chosen from among the group comprising: acoustic; electromagnetic
(EM); mud pulse (MP); and optical.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority in U.S. Provisional
Application No. 61/800,063 for Increased Throughput Downhole
Network Telemetry System and Method, filed Mar. 15, 2013. This
application is related to U.S. Patent Applications Ser. No.
61/731,898 for Downhole Low Rate Linear Repeater Network Timing
Control System and Method, filed Nov. 30, 2012; and Ser. No.
61/799,588, for Robust Network Downhole Telemetry Repeater System
and Method, filed Mar. 15, 2013. All of the above applications are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to telemetry
apparatuses and methods, and more particularly to acoustic
telemetry increased throughput network systems and methods for the
well construction (drilling, completion) and production (e.g., oil
and gas) industries.
[0004] 2. Description of the Related Art
[0005] Acoustic telemetry is a method of communication used in the
well drilling, completion and production industries. In a typical
drilling environment, acoustic extensional carrier waves from an
acoustic telemetry device are modulated in order to carry
information via the drillpipe as the transmission medium to the
surface. Upon arrival at the surface, the waves are detected,
decoded and displayed in order that drillers, geologists and others
helping steer or control the well are provided with drilling and
formation data. In production wells, downhole information can
similarly be transmitted via the well casings.
[0006] The theory of acoustic telemetry as applied to communication
along drillstrings has generally been confirmed by empirical data
in the form of accurate measurements. It is now generally
recognized that the nearly regular periodic structure of drillpipe
imposes a passband/stopband structure on the frequency response,
similar to that of a comb filter. Dispersion, phase non-linearity
and frequency-dependent attenuation make drillpipe a challenging
medium for telemetry, the situation being made even more
challenging by the significant surface and downhole noise generally
experienced.
[0007] Drillstring acoustic telemetry systems are commonly designed
with multiple transceiver nodes located at spaced intervals along
the drillstring or wellbore. The nodes can be configured as signal
repeaters as necessary. Acoustic telemetry networks can function in
a synchronized fashion with the operation of the nodes and repeater
nodes and other system components. Data packets consisting of
downhole sensor data were relayed node to node, in a daisy chain or
linear fashion, typically beginning from a node located in the
borehole apparatus (BHA), through the network to a destination,
usually the surface receiver system. For purposes of minimizing
interference between nodes, the data packets were transmitted
(typically up-string) using time division multiplexing (TDM)
techniques. Maximizing data packet transmission speed and
throughput are objectives of drillstring telemetry systems and
methods. For a discussion of a repeater network for these
applications, see co-pending U.S. Patent Application Ser. No.
61/731,898.
[0008] When exploring for oil or gas, and in other drilling
applications, an acoustic transmitter can be placed near the BHA,
typically near the drill bit where the transmitter can gather
certain drilling, wellbore, and geological formation data, process
this data, and then convert the data into a signal to be
transmitted uphole to an appropriate receiving and decoding
station. In some systems, the transmitter is designed to produce
elastic extensional stress waves that propagate through the
drillstring to the surface, where the waves are detected by
sensors, such as accelerometers, attached to the drillstring or
associated drilling rig equipment. These waves carry information of
value to the drillers and others who are responsible for steering
the well. Examples of such systems and their components are shown
in: Drumheller U.S. Pat. No. 5,128,901 for Acoustic Data
Transmission through a Drillstring; Drumheller U.S. Pat. No.
6,791,470 for Reducing Injection Loss in Drillstrings; Camwell et
al. U.S. Pat. No. 7,928,861 for Telemetry Wave Detection Apparatus
and Method; and Camwell et al. U.S. Pat. No. 8,115,651 for Drill
String Telemetry Methods and Apparatus. These patents are
incorporated herein by reference.
SUMMARY OF THE INVENTION
[0009] In the practice of the present invention, a network is
configured with multiple nodes using the acoustic transmission
channel simultaneously, i.e., "multiplexing" the channel. Network
throughput is thus decoupled from the number of nodes and
performance increases accordingly. Internode interference can be
controlled by one or more methods, including the following: [0010]
Node transmission timing: nodes transmitting at separate times.
Current (prior art) method which tends to be relatively
inefficient. E.g., time division multiplexing (TDM). [0011]
Attenuation where nodes transmit at the same time and interference
is suppressed by differences in propagation distance and associated
path loss (signal attenuation). [0012] Frequency differentiation
where nodes transmit simultaneously on different frequencies
whereby interference is suppressed by the frequency separations and
associated filtering. [0013] Signal orthogonality with nodes
transmitting at the same time but interference being suppressed by
the orthogonal relationship of the signal sets. [0014] Directional
transmitter and receiver configurations, with nodes tuned to
transmit in the direction of the desired destination node or
receive in the direction of the originating node, thereby
minimizing interference within the network.
[0015] Other objects and advantages of the present invention will
be apparent from the following description. Detailed descriptions
of exemplary embodiments are provided in the following sections.
However, the invention is not limited to such embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagram of a typical drilling rig, which can
include an acoustic telemetry system with a downhole serial network
embodying an aspect of the present invention.
[0017] FIG. 2 is a fragmentary, side-elevational and
cross-sectional view of a typical drillstring, which can provide
the medium for acoustic telemetry transmissions for the present
invention.
[0018] FIG. 3 is a schematic diagram of a prior art linear network
timing control system with nodes transmitting sequentially at
different times, following a time division multiplexing (TDM)
approach
[0019] FIG. 4 is a schematic diagram of a path loss attenuation
isolation system with a two-node gap transmission schedule.
[0020] FIG. 5 is a schematic diagram of a path loss attenuation
isolation system with a one-node gap transmission schedule.
[0021] FIG. 6 is a schematic diagram of a path loss attenuation
isolation system wherein nodes transmit and receive
simultaneously.
[0022] FIG. 7 is a schematic diagram of a configuration whereby a
node is adapting a filter to estimate the channel between the
node's transmitter and receiver.
[0023] FIG. 8 is a schematic diagram showing receiver signal
isolation from the transmitter signal.
[0024] FIG. 9 is a schematic diagram of an increased-rate linear
telemetry network scheduling system using orthogonal signal
sets.
[0025] FIG. 10 is a schematic diagram of another increased rate
linear telemetry network scheduling system using orthogonal signal
sets combined with simultaneous transmission and reception.
[0026] FIG. 11 is a schematic diagram showing an example of
multi-node transmission in an along-string measurement (ASM)
configuration with varying/accumulating node payloads.
[0027] FIG. 12 is a schematic diagram illustrating a node receiving
a portion of a desired signal transmission during an
interference-free period.
[0028] FIG. 13 is a schematic diagram showing a system using
directional transceivers to suppress intra-node interference and
increase network throughput.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] In the following description, reference is made to "up" and
"down" waves, but this is merely for convenience and clarity. It is
to be understood that the present invention is not to be limited in
this manner to conceptually simple applications in acoustic
communication from the downhole end of the drillstring to the
surface.
I. Drilling Rig, Drillstring and Well Environment
[0030] Referring to the drawings in more detail, the reference
numeral 2 generally designates a high throughput network system
embodying an aspect of the present invention. Without limitation on
the generality of useful applications of the system 2, an exemplary
application is in a drilling rig 4 (FIG. 1). For example, the rig 4
can include a derrick 6 suspending a traveling block 8 mounting a
kelly swivel 10, which receives drilling mud via a kelly hose 11
for pumping downhole into a drillstring 12. The drillstring 12 is
rotated by a kelly spinner 14 connected to a kelly pipe 16, which
in turn connects to multiple drill pipe sections 18, which are
interconnected by tool joints 19, thus forming a drillstring of
considerable length, e.g., several kilometers, which can be guided
downwardly and/or laterally using well-known techniques.
[0031] The drillstring 12 can terminate at or near a bottom-hole
(borehole) apparatus (BHA) 20, which can be at or near an acoustic
transceiver node (Primary) Station 0 (ST0). Other rig
configurations can likewise employ the present invention, including
top-drive, coiled tubing, etc. FIG. 1 also shows the components of
the drillstring 12 just above the BHA 20, which can include,
without limitation, a repeater transceiver node 26 (ST1) and an
additional repeater transceiver node 22 (ST2). An upper, adjacent
drillpipe section 18a is connected to the repeater 22 and the
transmitter 26. A downhole adjacent drillpipe section 18b is
connected to the transmitter 26 and the BHA 20. A surface receiver
node 21 is located at the top of the drillstring 12 and is adapted
for receiving the acoustic telemetry signals from the system 2 for
further processing, e.g., by a processor or other output device for
data analysis, recording, monitoring, displaying and other
functions associated with a drilling operation.
[0032] FIG. 2 shows the internal construction of the drillstring
12, e.g., an inner drillpipe 30 within an outer casing 32.
Interfaces 28a, 28b are provided for connecting drillpipe sections
to each other and to the other drillpipe components, as described
above. W.1 illustrates an acoustic, electromagnetic or other energy
waveform transmitted along the drillstring 12, either upwardly,
downwardly, or laterally (in the case of horizontal wells). The
drillstring 12 can include multiple additional repeater transceiver
nodes 22 at intervals determined by operating parameters such as
optimizing signal transmission and reception with minimal delays
and errors. The drillstring 12 can also include multiple sensors
along its length for producing output signals corresponding to
various downhole conditions.
[0033] Data packets contain sensor or node status data and are
transmitted from the primary node (e.g., ST0, typically the deepest
node) and relayed from node-to-node in a daisy-chain (herein
interchangeably referred to also as linear or serial) fashion to
the surface receiver (Surface Rx) 21, which is generally located at
or near the wellhead. The data packets include sensor measurements
from the BHA 20 and other sensors along the drillstring 12. Such
data packet sensor measurements can include, without limitation,
wellbore conditions (e.g., annular/bore/differential pressure,
fluid flow, vibration, rotation, etc.). Local sensor data can be
added to the data packet being relayed at each sensor node, thus
providing along-string-measurements (ASMs).
[0034] A single node functions as the master node (e.g., ST0) and
is typically an edge node at the top or bottom of the drillstring
12. The master node monitors well conditions and sends data packets
of varying type and intervals accordingly.
II. Prior Art Acoustic Repeater Scheduling
[0035] FIG. 3 shows the operation of a prior art linear telemetry
network scheduling configuration where node transmissions are
scheduled for separate non-overlapping time windows in order to
prevent inter-node interference and the associated degradation in
link performance (reliability and range). This constitutes time
division multiplexing (TDM) channel management. However, the update
interval increases with the number of nodes, whereby the network
throughput decreases. For example, with a five-node, 20 bits per
second (bps) transmission link rate system, neglecting guard and
signal propagation times, the effective data rate (network
throughput) is approximately (20 bps)/(5 nodes)=4 bps, while in a 2
node network, the network throughput is approximately (20 bps)/(2
nodes)=10 bps.
III. Multiplexing Acoustic Transmission Channels
[0036] Preferably multiple nodes are configured for using the
acoustic transmission channels at the same time, i.e.,
"multiplexing" the drillstring channel. Multiplexing, with multiple
nodes transmitting simultaneously, decouples network throughput
dependency on the number of nodes, and increases performance.
However, if not mitigated, multiple nodes transmitting
simultaneously will lead to inter-node interference and an
associated degradation in link performance. One or more of the
following methods can be implemented to control internode
interference during multi-node transmission: [0037] Signal
attenuation, with nodes transmitting simultaneously and
interference being suppressed by differences in propagation
distance and associated path loss, and perhaps further optimized
through adjustment of node transmission power level. [0038]
Frequency separation with nodes transmitting simultaneously but on
different frequencies whereby interference is suppressed. [0039]
Signal orthogonality, with nodes transmitting at the same time and
interference being suppressed by low correlation between signals
within allowable signal set. [0040] Directional transmitter and
receiver configurations, with nodes tuned to transmit in the
direction of the desired destination node or receive in the
direction of the originating node, thereby minimizing interference
within the network.
IV. Isolation Via Path Loss Attenuation
[0041] FIG. 4 shows a 2-node gap multiplexing scheduling
configuration. Interfering transmissions are mitigated by physical
separation (e.g., 2-node gap). This configuration is applicable to
electromagnetic pulse systems as well as acoustic, and is further
applicable to downlink, uplink and bi-directional networks.
Interfering transmissions are mitigated by physical separation and
associated signal propagation path loss: 3-link propagation path
loss attenuation (desired) versus 1-link propagation path loss
attenuation (interference). Additional interference minimization
can be achieved through adjustment of the transmitter output power
levels to minimize interference at one location, while providing
sufficient signal power at the desired node receiver. Update
interval/rate and network throughput are thus fixed regardless of
the number of network nodes. Only latency increases with node
number.
[0042] The interference between nodes can be further managed by
coordinating network timing in such a manner that, while multiple
node transmissions overlap in time, the desired signal precedes the
anticipated interferer signal such that a sufficient portion of the
desired signal experiences no interference allowing the receiving
node to achieve more reliable signal detection, timing and phase
recovery, and decoding once the interfering node begins
transmission and signals overlap. This method allows the receiver
to favour the desired signal over the interferer. See, e.g., FIG.
12, which is discussed below.
[0043] FIG. 5 shows a 1-node gap multiplexing scheduling
configuration wherein multiple nodes are transmitting at the same
time. This configuration is more aggressive than the 2-node gap
configuration shown in FIG. 4, having less interference
suppression. Interfering transmissions are mitigated by physical
separation and associated path loss: 1-link path loss attenuation
(desired) versus 2-link path loss attenuation (interference).
Update interval/rate and network throughput are thus fixed
regardless of the number of network nodes. Only latency increases
with node number.
[0044] FIG. 6 shows scheduling with an update rate which can be
fixed at approximately 2t.sub.tx, for example, regardless of the
number of nodes. Only latency increases with node number. The
receiver must be able to operate during self-transmission, without
being excessively degraded by self-interference. This can be
accomplished by assigning non-interfering frequency or orthogonal
signal sets to the transmitter and receiver. If the transmitter and
a receiver operate in the same channel (time, frequency), or
further interference suppression is desired, high-power interfering
self-transmission signals can be isolated from received signals
through channel estimation techniques, as described below.
[0045] FIG. 7 shows a "receive-while-transmitting" configuration
wherein an estimating function with a feedback loop is used to
estimate the in-node transmitter to receiver channel. A transmitter
(e.g., a piezo-electric stack, in the case of acoustics) to
receiver (accelerometer, in the case of acoustics) channel
estimation is shown, using an adaptive filter to emulate the
intra-node channel. FIG. 8 shows how the estimated intra-node
channel can be used to suppress self-interference. Specifically, by
applying an estimated channel filter to the known transmitted
signal (as derived in FIG. 7), to translate the signal to how the
receiver would perceive it, and subtracting it from the composite
receive signal (self-interference from transmitter+desired receive
signal originating from another node) to provide output
corresponding to the desired receive signal only.
[0046] FIG. 9 shows an increased rate repeater scheduling
configuration assigning orthogonal (i.e., low-interference) signal
sets (indicated by .alpha., .beta.) to transmitter and receiver
nodes, thereby allowing multiple signals in respective channels
simultaneously, increasing the update rate and the effective data
rate. The signal sets can be reused once interference nodes are
sufficiently separated to ensure adequate interference isolation.
The update interval, t.sub.update, is fixed at .about.2t.sub.tx,
regardless of the number of repeaters and only latency increases.
The concept is the application of orthogonal multiple access
techniques to increase channel efficiency (e.g., CDMA--Code Domain
Multiple Access, FDMA--Frequency Domain Multiple Access, OFDM
--Orthogonal Frequency Domain Multiplexing, etc.) as an alternative
to the relatively inefficient TDM (Time Division Multiplexing)
methods.
[0047] Examples of low-interference signal sets include: signals of
non-overlapping frequencies (Frequency Division Multiplexing
(FDM)), which can be contiguous frequency blocks (e.g., different
passbands) or interleaved blocks (e.g., OFDM); signals of low
cross-correlations, such as up/down, linear/exponential chirps,
pseudorandom noise (PRN) sequences (Code Division Multiplexing
(CDM)), e.g., Walsh codes, Hadamard, etc.; and signals transmitted
on separate, isolated mediums (channels): acoustic, electromagnetic
pulse, and mud pulse (MP); and propagation modes (e.g., axial,
longitudinal and spiral).
[0048] FIG. 10 shows orthogonal signal sets combined with
simultaneous transmit and receive, to providing an update rate,
t.sub.update, fixed at .about.t.sub.tx, regardless of the number of
nodes whereby only latency increases with node number. Node
receivers are able to operate during transmission with minimized
intra-node (self) interference due to transmitter-receiver signal
orthognality, as previously discussed. If the transmitter and the
receiver operate in the same channel, high-power interfering
self-transmission signals can be isolated from received signals
through channel estimation techniques, as described below.
[0049] FIG. 11 is a schematic diagram showing an example of an
along-string measurement (ASM) configuration with
varying/accumulating node payloads and signal propagation
interference isolation.
[0050] FIG. 12 shows signal transmission scheduling refinement
whereby a desired transmission (e.g., from M2 T.sub.x to M2
R.sub.x) precedes an interfering transmission (e.g., from M1
T.sub.x to M2 R.sub.x), creating a short period of
interference-free reception of the desired signal. This
interference-free period improves signal detection, timing and
phase recovery, effectively allowing the receiver (e.g., M2
R.sub.x) to "lock" onto the desired signal, and generally improve
link robustness.
[0051] FIG. 13 shows a system with directional transceivers for
interference suppression. The node receivers are tuned to receive
upwardly-traveling signals and to suppress/reject
downwardly-traveling signals. This can be accomplished by equipping
an acoustic node with multiple transmitters and receivers, and
phasing their outputs such that directional transmission or
reception is achieved (e.g., transmissions propagate only uphole
and receivers only detect signals originating from downhole, and
vice-versa). The details of such an operation would be known to one
versed in antenna beam forming techniques, and as such will not be
elaborated in this text. Receive and transmit directionality can be
exploited together, or individually, to suppress interference
between nodes, enabling multiple nodes to transmit at the same
time. Remaining interference is separated by a two-node gap.
[0052] The configurations described above have advantages of
preserving multi-hop repeater network throughput, which is
fundamentally related to channel multiplexing (reuse) efficiency.
Multiple nodes must share the channel, reducing system throughput
proportionally to the number of nodes in a system. For example, a
five-node system capable of 40 bits-per-second (bps) has a maximum
throughput of only 40 bps/5 nodes=8 bps, neglecting guard and
signal propagation times, while a two-node system has a maximum
throughput of 40 bps/2 nodes=20 bps. All multi-hop linear telemetry
systems will encounter the same limitation, including
electromagnetic (EM) systems.
[0053] It is to be understood that the invention can be embodied
and combined in various forms, and is not to be limited to the
examples discussed above. The range of components and
configurations which can be utilized in the practice of the present
invention is virtually unlimited.
* * * * *