Multi-booster em network for along string communications

Abstract

A device includes a first transceiver receptive of a first electromagnetic (EM) signal including data and a second transceiver configured to transmit a second EM signal including the data based at least in part on the first EM signal. A first temporal period associated with transmission of the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap. A method includes receiving a first EM signal including data and transmitting a second EM signal including the data based at least in part on the first EM signal, where a first temporal period associated with receiving the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

Description

65TEL-510229-WO-2_INT1024PCT MULTI-BOOSTER EM NETWORK FOR ALONG STRING COMMUNICATIONS CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of an earlier filing date from U.S. Provisional Application Serial No.63 / 635,885, filed April 18, 2024, the entire disclosure of which is incorporated herein by reference. TECHNICAL FIELD

[0001] Aspects of the present disclosure relate to an electromagnetic (EM) transmission repeater network and, more particularly, a multi-booster EM network for communications along a drill string. BACKGROUND

[0002] In the resource recovery and fluid sequestration industries, recovering hydrocarbons from subterranean zones may involve drilling wellbores.

[0003] Wellbores may be formed using surface-located drilling equipment which drives a drill string that eventually extends from the drilling equipment to the formation or subterranean zone of interest. In some cases, the drill string can extend thousands of feet or meters below the surface. The terminal end of the drill string may include a drill bit for drilling (or extending) the wellbore. Drilling fluid, in some cases in the form of a drilling “mud,” may be pumped through the drill string. The drilling fluid cools and lubricates the drill bit and also carries cuttings back to the surface. Drilling fluid may be used to control bottom hole pressure to inhibit hydrocarbon influx from the formation into the wellbore and potential blow out at surface.

[0004] Bottom hole assembly (BHA) refers to equipment at the terminal end of a drill string. In addition to a drill bit, a BHA may include elements such as, for example, an apparatus for steering the direction of the drilling (e.g., a steerable downhole mud motor or rotary steerable system), sensors for measuring properties of the surrounding geological formations (e.g., sensors for use in well logging), sensors for measuring downhole conditions as drilling progresses, one or more systems for telemetry of data to the surface, stabilizers, heavy weight drill collars, pulsers, and the like. The BHA may be advanced into the wellbore by a string of metallic tubulars (drill pipe).

[0005] Some drilling systems may include any of a wide range of mechanical / electronic systems in the BHA or at other downhole locations. Such65TEL-510229-WO-2_INT1024PCT mechanical / electronic systems may include active mechanical, electronic, and / or electromechanical systems capable of operating downhole. A downhole system may provide any of a wide range of functions including, without limitation, data acquisition, measuring properties of the surrounding geological formations (e.g., well logging), measuring downhole conditions as drilling progresses, controlling downhole equipment, monitoring status of downhole equipment, directional drilling applications, measuring while drilling (MWD) applications, logging while drilling (LWD) applications, measuring properties of downhole fluids, and the like. A downhole system may include or be connected to one or more systems for, for example, telemetry of data to the surface, collecting data by way of sensors (e.g., sensors for use in well logging) that may include one or more of vibration sensors, magnetometers, inclinometers, accelerometers, nuclear particle detectors, electromagnetic detectors, acoustic detectors, and others, acquiring images, measuring fluid flow, determining directions, emitting signals, detecting particles or fields, interfacing to other downhole equipment, sampling downhole fluids, and the like.

[0006] A downhole system may communicate a wide range of information to the surface by telemetry and / or receive a wide range of information from other systems which may be located at the surface and / or underground. Telemetry information can be invaluable for efficient drilling operations. For example, telemetry information may be used by a drill rig operator to make decisions about controlling and steering the drill bit to optimize the drilling speed and trajectory based on numerous factors, including legal boundaries, locations of existing wells, formation properties, hydrocarbon size and location, and the like. An operator may make intentional deviations from the planned path as applicable based on information gathered from downhole sensors and transmitted to the surface by telemetry during the drilling process. The ability to obtain and transmit reliable data from downhole locations allows for relatively more economical and more efficient drilling operations.

[0007] Some telemetry techniques include transmitting information by generating vibrations in fluid in the bore hole (e.g., acoustic telemetry or mud pulse (MP) telemetry) and transmitting information by way of electromagnetic signals that propagate at least in part through the earth (EM telemetry). Other telemetry techniques use hardwired drill pipe, fiber optic cable, or drill collar acoustic telemetry to carry data to the surface.

[0008] Advantages of EM telemetry, relative to MP telemetry, include generally faster data transmission rates, increased reliability due to no moving downhole parts, high resistance to lost circulating material (LCM) use, and suitability for air / underbalanced drilling. An EM telemetry system can transmit data without a continuous fluid column, which65TEL-510229-WO-2_INT1024PCT provides advantages for cases in which there is no drilling fluid flowing. This is advantageous when a drill crew is adding a new section of drill pipe, as the EM signal can transmit information (e.g., directional information) while the drill crew is adding the new pipe. Some disadvantages of EM telemetry include lower depth capability, incompatibility with some formations (for example, high salt formations and formations of high resistivity contrast), and some market resistance due to acceptance of older established methods. Also, as the EM transmission may be strongly attenuated over long distances through the earth formations, the amount of power involved in association with transmitting EM signals is relatively large in order for the EM signals to be detected at the surface. In some cases, the electrical power available to generate EM signals may be provided by batteries or another power source that has relatively limited capacity.

[0009] Improved systems for conveying data to and from downhole systems with, for example, higher data rates, reliable transmission at greater depths, or the like, are desired. SUMMARY

[0010] Embodiments of the present disclosure are directed to a device including: a first transceiver receptive of a first electromagnetic (EM) signal including data; and a second transceiver configured to transmit a second EM signal including the data based at least in part on the first EM signal, wherein a first temporal period associated with transmission of the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

[0011] Embodiments of the present disclosure are also directed to a communication system including: a set of devices, wherein a device of the set of devices includes: a first transceiver receptive of a first electromagnetic (EM) signal including data; and a second transceiver configured to transmit a second EM signal including the data based at least in part on the first EM signal, wherein a first temporal period associated with transmission of the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

[0012] Embodiments of the present disclosure are also directed to a method including: receiving a first electromagnetic (EM) signal including data; and transmitting a second EM signal including the data based at least in part on the first EM signal, wherein a first temporal period associated with receiving the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.65TEL-510229-WO-2_INT1024PCT

[0013] Further aspects supported by the present disclosure and features of example embodiments are illustrated in the accompanying drawings and / or described in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

[0015] FIG.1 is a diagram illustrating an example embodiment of a system in accordance with aspects of the present disclosure.

[0016] FIGS.2A, 2B, 2C, and 2D schematically illustrate a borehole string and an associated communication system in accordance with one or more embodiments of the present disclosure.

[0017] FIG.3 illustrates a block diagram of an example repeater node in accordance with one or more embodiments of the present disclosure.

[0018] FIGS.4A, 4B, and 4C illustrate block diagrams of example repeater nodes in accordance with one or more embodiments of the present disclosure.

[0019] FIG.5 illustrates an example of a gap sub in accordance with one or more embodiments of the present disclosure.

[0020] FIGS.6A and 6B illustrate block diagrams of a repeater node in accordance with one or more embodiments of the present disclosure. FIG.6C illustrates example waveforms associated with a repeater node in accordance with one or more embodiments of the present disclosure.

[0021] FIG.7A illustrates an example bipolar EM telemetry waveform in accordance with one or more embodiments of the present disclosure. FIG.7B illustrates an example modified unipolar waveform in accordance with one or more embodiments of the present disclosure.

[0022] FIGS.7C and 7D illustrate block diagrams of repeater nodes in accordance with one or more embodiments of the present disclosure. FIG.7E illustrates example waveforms associated with pulse shaping in accordance with one or more embodiments of the present disclosure.

[0023] FIGS.8A to 8D illustrate example waveforms associated with yielding and receiving a chopped waveform in accordance with one or more embodiments of the present disclosure. FIG.8E illustrates a block diagram of a repeater node capable of generating a chopped waveform in accordance with one or more embodiments of the present disclosure.65TEL-510229-WO-2_INT1024PCT

[0024] FIG.9 illustrates a block diagram of an example repeater node in accordance with one or more embodiments of the present disclosure.

[0025] FIG.10 illustrates a block diagram of an example repeater node in accordance with one or more embodiments of the present disclosure.

[0026] FIG.11 illustrates an example flowchart of a method in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0027] A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

[0028] According to one or more embodiments of the present disclosure, systems and techniques are described herein which support methods for EM telemetry of data, EM telemetry repeaters for downhole applications, methods for reducing or eliminating feedback in EM telemetry repeaters, electronic circuits for feedback reduction in EM telemetry systems, EM telemetry transceivers capable of simultaneous transmission and reception of EM telemetry signals, and gap subs for EM telemetry applications.

[0029] The systems and techniques described herein in accordance with one or more embodiments of the present disclosure include performing positive feedback reduction by modifying transmission of EM telemetry signals. In one or more embodiments, the systems and techniques support modifying the transmission by one or more of retransmitting data from received EM telemetry signals in transmitted signals that are out of phase with the received signals, retransmitting data from received EM telemetry signals in transmitted signals that are unipolar (e.g., signals having the form of a half-wave rectified sine wave), and retransmitting data from received EM telemetry signals in transmitted signals, in which the frequency or frequencies of the transmitted signals are different from a frequency or frequencies of the received EM telemetry signals.

[0030] In one or more embodiments, the systems and techniques described herein may include receiving EM telemetry signals by detecting the EM telemetry signals across a first electrically-insulating gap in a drill string and retransmitting data from the received EM telemetry signals by applying a modulated potential difference across a second electrically- insulating gap in the drill string, in which the second electrically-insulating gap is spaced apart from the first gap along the drill string. In some embodiments, respective filters (e.g.,65TEL-510229-WO-2_INT1024PCT bandpass filters) may be provided across the first electrically-insulating and / or the second electrically-insulating gap.

[0031] In one or more embodiments, prior to retransmitting received EM telemetry signals, the systems and techniques may include identifying a component of the received EM telemetry signals corresponding to feedback from transmitted EM telemetry signals, and further, subtracting from the received EM telemetry signals the identified component.

[0032] In one or more embodiments, the systems and techniques described herein may include retransmitting data from received EM telemetry signals using a waveform that is interrupted at a relatively high frequency (e.g., by chopping) and detecting the received EM telemetry signals in the interruptions.

[0033] According to one or more embodiments of the present disclosure, an EM signal repeater system as described herein supports simultaneous transmission by multiple repeater nodes. Each repeater node includes circuitry for reducing positive feedback (experienced at a receiver of the repeater node) associated with a signal transmitted from a transmitter of the same repeater node.

[0034] In one or more embodiments, reducing the positive feedback may be implemented using a “chopper” modulation technique. In an example, at the transmitter of a repeater node, the transmitted signal is generated through high frequency modulation (chopping / gating) of the signal to be transmitted.

[0035] In one or more additional and / or alternative embodiments, reducing the positive feedback may be implemented using background subtraction techniques at different frequencies. For example, a repeater node may include a level analyzer. A sample of a received signal at the receiver of the repeater node is transferred to a level analyzer included in the repeater node and subtracted from the received signal.

[0036] In one or more additional and / or alternative embodiments, reducing the positive feedback may be implemented through a continuous frequency mode supported by the repeater system and repeater nodes. For example, pulse shaping techniques supported by the repeater system may create gaps in a cycle that are utilized to receive the signal at a receiving repeater node.

[0037] In some aspects, the repeater nodes are capable of providing various information to other repeater nodes for determining operational frequencies for intercommunication. In one or more embodiments, the information includes formation property measurements. For example, each repeater node is capable of providing formation property measurements for a given location / depth, to other repeater nodes included in the65TEL-510229-WO-2_INT1024PCT repeater system. Receiver repeater nodes may process the formation properties and determine a target operational frequency and target transmission power level for transmitting (e.g., retransmitting) received EM telemetry signals.

[0038] In an example implementation, a repeater node may perform ongoing measurements of voltage and current applied across a transmission gap to calculate resistivity. In some embodiments, the repeater node is capable of performing measurements at specific time points / near real-time. In some examples, the repeater node may provide the measurements in real-time or near real-time to other repeater nodes, a downhole tool, and / or surface equipment. In some aspects, the repeater node may transmit the formation properties during a time frame dedicated for formation property transmissions (e.g., by the repeater node). Additionally, or alternatively, the repeater node may transmit the formation properties in a separate data package (e.g., a message) with a header corresponding to the repeater node.

[0039] In some examples, other repeater nodes (e.g., each repeater node in a repeater chain), the downhole tool, and / or the surface equipment may process the information (formation properties) to determine an optimized operational frequency and power level for transmitting data. In another example, the first repeater node (or first two repeater nodes) located at the top of a repeater chain (e.g., closest to the surface) may have an estimation of a target configuration for the repeater nodes of the repeater chain. The first repeater node (or first two repeater nodes) may provide a data packet including the target configuration information with adjacent repeater nodes, and based on the target configuration information, the adjacent repeater nodes may configure their respective receivers and transmitters.

[0040] In one or more additional and / or alternative embodiments, each repeater node includes circuitry and / or sensors based on which the repeater node may estimate location information (e.g., local position) of the repeater node. For example, a repeater node may determine the location information of the repeater node based on time of flight measurements of EM signals or mud pulse waves generated by the repeater node. In some aspects, each repeater node may transmit or share data indicative of the location information to other repeater nodes included in the repeater chain.

[0041] In one or more additional and / or alternative embodiments, the systems and techniques described herein support determining operational frequencies for intercommunication among repeater nodes using frequency sweeps. For example, a repeater node may perform frequency sweeps (e.g., based on a predetermined temporal schedule) during blank periods, and based on a result of the frequency sweeps, the repeater node65TEL-510229-WO-2_INT1024PCT (and / or other repeater nodes adjacent the repeater node) may determine a target operational frequency and / or a target operational power level for communication.

[0042] In one or more embodiments, the systems and techniques described herein support operation of the repeater chain according to a variable frequency mode or a continuous frequency mode.

[0043] As will be illustrated herein, the simultaneous node transmission of the repeater chain system supports a continuous stream of data and concurrent uplinking and downlinking at each repeater node. Some other repeater approaches use multi-frequency chirp modulation (e.g., non-continuous, time based, transmission of data) among repeater nodes and are unable to provide a continuous stream of data. In some examples, the bidirectional communication system supports autonomous drilling in a downhole system. The repeater node capabilities / techniques for mitigating positive feedback effects support increased data rates, increased depth of operation, and increased reliability.

[0044] In some aspects, as the repeater systems described herein may be implemented without multi-frequency chirp modulation among the repeater nodes, each repeater node may be implemented with reduced processing overhead, which supports a reduction in hardware / processor cost. For example, as the techniques described herein may be implemented with less processing complexity compared to other repeater system techniques (e.g., multi-frequency chirp modulation), the repeater system may be implemented with relatively lower end processors (e.g., reduced financial cost). In some examples, the repeater chain system may be implemented without decoder firmware used in other repeater node approaches.

[0045] Additionally, or alternatively, due to the reduction in processing complexity, less heat is generated and less power is consumed by the repeater nodes, which provides advantages with respect to power budgets, temperature tolerances, and device reliability in environments (e.g., downhole environment) where power and / or operating temperature may be of a concern. In some other aspects, the sharing of formation properties among repeater nodes supports effective drill control during a drilling operation, for example, as the drill progresses through different formations (e.g., real-time and / or near real-time adjustment to drill parameters according to formation changes). In some embodiments, based on the formation properties, a repeater node may determine a target operational frequency and / or a target operational power level for communication. In some aspects, transmitting at the target operational power level may support maximizing power efficiency.65TEL-510229-WO-2_INT1024PCT

[0046] Example aspects of the repeater nodes and repeater chains will further be described herein.

[0047] FIG.1 is a diagram illustrating an example embodiment of a system 100 for performing energy industry operations in accordance with aspects of the present disclosure. The system 100 supports a multi-booster EM network for communications along a borehole string 140.

[0048] The system 100 is configured to perform any suitable energy industry operation, such as, for example, a drilling operation, a stimulation operation, a measurement operation and / or a production operation. However, example aspects of communication techniques supported by the system 100 as described herein are not limited to energy industry operations and an associated downhole environment.

[0049] The system 100 includes a borehole 135 in a subsurface formation 130. A borehole string 140 (also referred to herein as a drill string) is disposed in the borehole 135 that penetrates the formation 130. The borehole 135 may be an open hole, a cased hole or a partially cased hole. In one embodiment, the borehole string 140 is a stimulation or injection string that includes a tubular, such as a coiled tubing, pipe (e.g., multiple pipe segments) or wired pipe, that extends from a wellhead at a surface location (e.g., at a drill site or offshore stimulation vessel).

[0050] As described herein, a “string” refers to any structure or carrier suitable for lowering a tool or other component through a borehole or connecting a drill bit to the surface, and is not limited to the structure and configuration described herein. The term "carrier" as used herein means any device, device component, combination of devices, media and / or member that may be used to convey, house, support or otherwise facilitate the use of another device, device component, combination of devices, media and / or member. Example non- limiting carriers include casing pipes, wirelines, wireline sondes, slickline sondes, drop shots, downhole subs, BHAs and drill strings.

[0051] In one embodiment, the system 100 is configured as a hydraulic stimulation system. As described herein, “hydraulic stimulation” includes any injection of a fluid into a formation. A fluid may be any flowable substance such as a liquid or a gas, and / or a flowable solid such as sand. In this embodiment, the borehole string 140 includes a stimulation assembly that includes one or more tools 150 or components to facilitate stimulation of the formation 130. Non-limiting examples of the tools 150 included in the borehole string 140 include a fracturing assembly (e.g., a fracture or “frac” sleeve device), a perforation assembly65TEL-510229-WO-2_INT1024PCT (e.g., shaped charges, torches, projectiles and other devices for perforating the borehole wall and / or casing), and isolation or packer subs.

[0052] One or more of the tools 150 may include suitable electronics or processors configured to communicate with a surface processing unit (e.g., a computing device 105) and / or control the respective tool 150 or assembly.

[0053] The system 100 includes surface equipment 110 for performing various energy industry operations. For example, the surface equipment 110 is configured for injection of fluids into the borehole 135 in order to, e.g., fracture the formation 130. In one or more embodiments, the surface equipment 110 includes an injection device such as a high pressure pump 115 in fluid communication with a fluid tank 120, mixing unit or other fluid source or combination of fluid sources. The pump 115 injects fluid into the borehole string 140 or the borehole 135 to introduce fluid into the formation 130, for example, to stimulate and / or fracture the formation 130. The pump 115 may be located downhole or at a surface location.

[0054] One or more flow rate and / or pressure sensors 125 may be disposed in fluid communication with the pump 115 and the borehole string 140 for measurement of fluid characteristics. The sensors 125 may be positioned at any suitable location, such as proximate to (e.g., at the discharge output) or within the pump 115, at or near the wellhead, or at any other location along the borehole string 140 or the borehole 135. The sensors described herein are exemplary, as various types of sensors may be used to measure various parameters.

[0055] A computing device 105 (e.g., computing device 105-a) may be disposed in operable communication with components such as sensors 125 located above the surface, the pump 115, and / or downhole components. For example, the computing device 105 may be in operable communication with sensors (e.g., pressure sensors, temperature sensors, vibration sensors, gas sensors, and the like) located below the surface and / or in the borehole string 140. In some examples, the computing device 105 may be in operable communication with a tool 150 (or multiple tools).

[0056] The system 100 supports communication between the computing device 105 and other devices of the system 100 via wired communication protocols, wireless communication protocols (e.g., electromagnetic (EM) signals, WiFi, Bluetooth™, ZigBee™, Ubiquiti™, 3G, 4G, 5G, LTE, and the like), and / or combinations including one or more of the foregoing.

[0057] The system 100 supports telemetry techniques capable of transmitting data from components located downhole to the surface and / or surface equipment 110. Non- limiting examples of the telemetry techniques include acoustic telemetry or mud pulse (MP)65TEL-510229-WO-2_INT1024PCT telemetry supportive of transmitting information by generating vibrations in fluid in the borehole 135, electromagnetic (EM) telemetry supportive of transmitting information by way of signals that propagate at least in part through the earth (e.g., through formations 130). Other non-limiting examples of telemetry techniques supported by aspects of the present disclosure include the use of hardwired drill pipe, fibre optic cable, or drill collar acoustic telemetry to carry data to the surface and / or surface equipment 110.

[0058] The system 100 may include one or more repeater nodes 170 supportive of communicating data along the borehole string 140 (e.g., up or down the borehole string 140). In one or more embodiments, the repeater nodes 170 may be implemented in the borehole 135 or a communication borehole (not illustrated) separate from the borehole 135. In some examples, the one or more repeater nodes 170 may provide functionality as wireless access nodes for repeating or relaying data from a tool 150 to the surface (e.g., to a computing device 105).

[0059] In one or more embodiments, the system 100 may include a chain of repeater nodes 170 spaced apart along the borehole string 140, and the chain of repeater nodes 170 may support repeating of data in a unidirectional (e.g., downhole to surface or surface to downhole) or bidirectional manner. For example, a repeater node 170 (or chain of repeater nodes 170) may support the communication of data between a computing device 105, a tool 150, and the like.

[0060] Accordingly, for example, the communication protocols and telemetry techniques supported by the system 100 enable communication between computing devices 105 (e.g., computing device 105-a, computing device 105-b, and the like) and downhole components.

[0061] The computing device 105 is configured to receive, store and / or transmit data generated from components (e.g., pump 115, fluid tank 120, sensors 125, and the like) included in the surface equipment 110 and / or downhole components (e.g., a tool 150, downhole sensors, and the like). The computing device 105 includes processing components configured to analyze received data (e.g., data received from the pump 115, fluid tank 120, sensors 125, a tool 150, and the like). The computing device 105 includes processing components configured to provide data (and / or control signals to other components of the system 100. The computing device 105 includes any number of suitable components, such as processors, memory, communication devices and power sources.

[0062] In accordance with one or more embodiments of the present disclosure, a data telemetry system is provided that supports the communication of data 165 along a borehole65TEL-510229-WO-2_INT1024PCT string 140 in either direction (e.g., upwards towards the surface, downwards towards the tool 150) by providing a chain of repeater nodes 170 spaced apart along the borehole string 140. The data 165 may be generated or provided by components (e.g., a computing device 105, surface equipment 110, a tool 150, or a repeater node 170) of the system 100.

[0063] FIG.2A illustrates schematically a borehole string 140 including a communication system 171 supportive of communicating data 165 to and from surface equipment 110 (and / or a computing device 105) by way of multiple repeater nodes 170 that are spaced apart along borehole string 140. The communication system 171 supports unidirectional (e.g., downhole to surface, or surface to downhole) and bidirectional data communication.

[0064] The communication system 171 supports the communication of signals carrying the data 165. In some examples, the data 165 may be generated by tool 150 and / or the repeater nodes 170, and the communication system 171 supports the transmission of the data 165 to surface equipment 110 (and / or computing device 105). The communication system 171 supports the transmission of other data (e.g., control signals) from the surface equipment 110 and / or computing device 105 to the tool 150 via the repeater nodes 170.

[0065] The signals may be EM telemetry signals generated using modulation techniques capable of encoding the data 165. Non-limiting examples of the modulation techniques include phase shift keying, quadrature phase shift keying (QPSK), binary phase shift keying (BPSK), amplitude phase shift keying (APSK), frequency-shift keying (FSK), quadrature amplitude modulation (QAM), 8 amplitude shift keying (8ASK), and the like. Aspects of the present disclosure are not limited thereto, and the communication system 171 may support communication techniques including any combination of changes in phase, amplitude, timing of pulses, and frequency suitable for communicating the data 165. Example aspects of frequencies used by the repeater nodes 170 in association with communicating the data 165 are later described herein.

[0066] A PSK (phase-shift keying) encoding scheme may use a number of cycles (at a current frequency) to transmit each symbol. The number of cycles used to transmit each symbol may be varied. For example, in low-noise environments, the communication system 171 is capable of successfully transmitting (e.g., meet target transmission criteria) EM telemetry symbols using two cycles per symbol. In higher noise environments, the communication system 171 may be configured to use three cycles (or more) to transmit each symbol. In some implementations, the communication system 171 may select the number of cycles to be used to encode a symbol based on a measured signal-to-noise ratio (SNR).65TEL-510229-WO-2_INT1024PCT

[0067] The communication system 171 may include a series of repeater nodes 170 (EM telemetry repeaters) spaced apart along and capable of carrying data along borehole string 140, and the communication system 171 supports various modes of communication. For example, the communication system 171 supports an ‘echo’ mode in which each repeater node 170 receives and records a block of data (e.g., data 165) from one or more other repeater nodes 170.

[0068] After receiving the block of data, the repeater node 170 may retransmit the block of data. In some cases, the echo mode may introduce latency, since a repeater node 170 transmitting according to the echo mode transmits after having received a block of data, and data blocks are transmitted at spaced apart times to allow time for a repeater node 170 to retransmit the data of a given block of data before starting to receive data for the next data block. In a ‘continuous’ mode, each repeater node 170 may receive and transmit data simultaneously.

[0069] Modes of operation supported by the communication system 171 and the repeater nodes 170 can differ in the degree to which received signals are processed.

[0070] In some modes, a repeater node 170 may operate by decoding received signals to extract the data encoded in the received signals and optionally performing error correction using error correction information (e.g., parity or CRC information) encoded in the received signals. The repeater node 170 may then reencode and retransmit the received signals (including the extracted data). In some cases, reencoding and retransmission may introduce some latency, and a repeater node 170 may include circuits for decoding and encoding received data. In such example modes, the transmitted signal may differ from the received signal in various ways including, for example, frequency, data encoding scheme, and / or data content. Such differentiation between the received and transmitted signals may beneficially reduce feedback from the transmitted signal to the received signal and / or may be applied to adapt transmitted signals for improved reception in view of formation properties between a repeater node 170 and another repeater node 170 (e.g., a subsequent repeater node 170 included among the communication system 171). In some aspects, a repeater node 170 may include processing circuitry configured to detect whether data extracted from a received signal has been corrupted, and the repeater node 170 may transmit or refrain from transmitting the corrupted data.

[0071] In some modes of operation supported by the communication system 171, a repeater node 170 may refrain from decoding a signal and / or received data, and the repeater node 170 may instead characterize and retransmit the received data signal. For example, a65TEL-510229-WO-2_INT1024PCT repeater node 170 may detect a waveform (e.g., a cycle of a sine wave) in a received EM telemetry signal and recreate the waveform including features of the waveform (e.g., phase shifts) that encode data. In some embodiments, the repeater node 170 may recreate the waveform based on a priori knowledge of the nature of signals. In some cases, each repeater node 170 may be informed of the communication modality (or be capable of informing other repeater nodes 170 of the communication modality) through one or more signaling techniques.

[0072] In an example, the communication system 171 may be configured such that EM telemetry signals being transmitted by repeater nodes 170 are sine waves of a given frequency or frequencies. A repeater node 170 may be configured to search for such sine waves in received signals. Such example communication modes can have the advantage of reduced latency. In such modes, for example, a repeater node 170 may recreate the waveform (e.g., sine waves) such that the recreated waveform is substantially the same as (or different in part from) the waveform detected in the received signal. For example, the waveform of a signal transmitted by a repeater node 170 may be configured to differ from the waveform of a signal received by the repeater node 170 with respect to frequency, number of cycles per bit, and / or other suitable parameters supportive of the techniques described herein.

[0073] According to one or more embodiments of the present disclosure, a repeater node 170 may be configured to operate in a single mode described herein. In one or more additional and / or alternative embodiments, the repeater node 170 may be switchable or reconfigurable to operate in two or more different modes described herein. In some embodiments, repeater nodes 170 of the communication system 171 are configured for unidirectional communication (e.g., transmitting data in an uphole direction or transmitting data in a downhole direction) or for bidirectional operation. The communication system 171 may be implemented using repeater nodes 170 of any suitable mode or configuration described herein.

[0074] Referring to the example of FIG.2A, six transmission frequencies are used. Three transmission frequencies F1D, F2Dand F3Dare used for data transmission in the downhole direction and three transmission frequencies F1U, F2U and F3U are used for data transmission in the uphole direction. In an example, the repeater nodes 170 may cycle among the transmission frequencies moving along borehole string 140 such that, for example, each repeater node 170 may respectively transmit according to a subsequent transmission frequency. The receiver 305 of each repeater node 170 is configured to receive signals according to a downhole transmission frequency used by an adjacent repeater node 17065TEL-510229-WO-2_INT1024PCT located in a direction uphole of the repeater node 170. The receiver 305 of each repeater node 170 is configured to receive signals according to an uphole transmission frequency used by an adjacent repeater node 170 located in a direction downhole of the repeater node 170.

[0075] Other embodiments supported by aspects of the present disclosure include using different quantities of transmission frequencies. For example, FIG.2B illustrates an example in which four transmission frequencies are used. Two transmission frequencies F1D, F2Dare used for data transmission in the downhole direction and two transmission frequencies F1U, F2U are used for data transmission in the uphole direction.

[0076] FIG.2C illustrates an example implementation in which four transmission frequencies F1, F2, F3 and F4 are used for both data transmission in the downhole direction and data transmission in the uphole direction. Accordingly, for example, FIGS.2A through 2C illustrate examples of a variable frequency mode supported by the communication system 171, example aspects of which are later described herein.

[0077] FIG.2D illustrates an example implementation of a continuous mode supported by the communication system 171. In an example of the continuous mode, a continuous frequency F1 is used for data transmission in the uphole direction and a continuous frequency F2 is used for data transmission in the downhole direction. Example aspects of the continuous mode are later described herein.

[0078] In some embodiments, the communication system 171 supports reconfiguration of the frequencies at which repeater nodes 170 receive and / or transmit signals while the repeater nodes 170 are downhole. Each repeater node 170 (or a subset of the repeater nodes 170) may monitor (in real-time) factors such as, for example, properties of the earth formation surrounding the repeater node 170, power constraints, signal levels, or the like. Based on the factors, each repeater node 170 may dynamically configure the frequencies at which the repeater node 170 receives and / or transmits signals. In some embodiments, based on the factors, each repeater node 170 may dynamically configure the power level at which the repeater node 170 transmits signals. For example, in response to a repeater node 170 detecting a high resistivity of an earth formation, the repeater node 170 may adjust (e.g., reduce) the receiving and / or transmitting frequency.

[0079] Additionally, or alternatively, the repeater node 170 may provide data indicating the high resistivity of the earth formation to one or more other repeater nodes 170 (e.g., by broadcasting the data, directly transmitting the data, or the like). Based on the data, the other repeater node(s) 170 may dynamically configure the frequencies at which the other65TEL-510229-WO-2_INT1024PCT repeater node(s) 170 receives and / or transmits signals. In some embodiments, the repeater nodes 170 may exchange collected real-time data with other repeater nodes 170.

[0080] FIG.3 illustrates a block diagram 300 of a repeater node 170 in accordance with one or more embodiments of the present disclosure.

[0081] As shown in FIG.3, repeater node 170 includes an EM telemetry receiver 305, an EM telemetry transmitter 315, and electronic circuitry 310 (also referred to herein as electronics). The receiver 305, electronic circuitry 310, and transmitter 315 may be electrically coupled via one or more busses included in the repeater node 170. The electronic circuitry 310 may receive data from the receiver 305 and control the transmitter 315 to retransmit the received data. In some aspects, the repeater node 170 may retransmit the received data, with or without modifying the data.

[0082] In one or more embodiments, the receiver 305 may be a standalone receiver circuit, and transmitter 315 may be a standalone transmitter circuit. In one or more additional and / or alternative embodiments, receiver 305 and transmitter 315 may be integrated in a single transceiver. In one or more additional and / or alternative embodiments receiver 305 may be implemented in a first transceiver (e.g., transceiver 905 of FIGS.9 and 10), and transmitter 315 may be implemented in a second transceiver (e.g., transceiver 915 of FIGS.9 and 10).

[0083] Non-limiting examples of modifying the received data as supported by a repeater node 170 are described herein. The repeater node 170 supports modifying received data in accordance with one or more of the examples described herein. In one or more embodiments, the repeater node 170 may modify the received data by correcting one or more errors in the received data using, for example, error correction codes included in the data. In one or more additional and / or alternative embodiments, the repeater node 170 may add, to the received data, data identifying the repeater node 170, data from sensor(s) integrated with or connected to repeater node 170, and / or temporal information (e.g., a time stamp) associated with the received data.

[0084] In one or more additional and / or alternative embodiments, the repeater node 170 may reduce the size of the received data, for example, by applying data compression operations and / or reducing a resolution of the received data. In one or more additional and / or alternative embodiments, the repeater node 170 may modify a data format of the received data. In one or more additional and / or alternative embodiments, the repeater node 170 may reorder data included in a received signal prior to retransmitting the data in a subsequent signal, for example, to prioritize certain data over other data.65TEL-510229-WO-2_INT1024PCT

[0085] In accordance with one or more embodiments of the present disclosure, the communication system 171 supports a continuous mode in which repeater nodes 170 are configured to simultaneously transmit and receive signals carrying data (e.g., such that respective temporal periods associated with transmitting the signals at least partially overlap). In one or more embodiments, the continuous mode may be facilitated by using separate respective antenna elements (e.g., separate electrically-insulating gaps 144 (later illustrated at FIG.4A) in the borehole string 140) for transmitting and receiving. In one or more additional and / or alternative embodiments, the communication system 171 may facilitate the continuous mode through one or more anti-feedback schemes as discussed herein.

[0086] In some example embodiments described herein, a repeater node 170 may receive and retransmit a continuous modulated signal in real-time. In some embodiments, the repeater node 170 may refrain from decoding the signal and / or refrain from extracting data from the signal. In some embodiments, the repeater node 170 may modify (e.g., clean up) a received signal before retransmitting the signal. For example, for cases in which the received signal is of a particular form (e.g., a sine wave of a known frequency with phase shifts that encode data) known by the repeater node 170, the repeater node 170 may recreate (from the received signal) a signal that has the known form of the received signal. In an example, the repeater node 170 may recreate a received signal by fitting a sinusoid of the known frequency to the received signal and locating phase changes in the received signal.

[0087] The communication system 171 may support implementations in which the transmission and receiving frequencies at a repeater node 170 are the same or different. The transmission and receiving frequencies may be selected based on one or more criteria.

[0088] In an example, for a signal to be transmitted by one repeater node 170 and received at another repeater node 170, the repeater node 170 may transmit the signal according to a frequency which mitigates the amount of signal attenuation of the transmitted signal (e.g., due to distance and / or formations between the repeater nodes 170), such that the transmitted signal may be successfully received at the other repeater node 170.

[0089] For example, EM signals tend to be attenuated as they propagate through earth formations. In general, the attenuation increases with frequency and / or depth of operation. The repeater node 170 may transmit the signal according to a target power level and a target transmission frequency (e.g., a low enough frequency) such that the signal to noise ratio (SNR) of the signal, as received at a subsequent repeater node 170 along the borehole string 140, is equal to or greater than a target SNR.65TEL-510229-WO-2_INT1024PCT

[0090] In one or more embodiments, the repeater node 170 transmitting a signal may configure the transmission frequency based in part on one or more factors including, but not limited thereto, the distance between repeater nodes 170, the nature (e.g., properties) of the earth formations through which borehole string 140 passes, the efficiency of the coupling of signals from transmitters 315 (of the repeater node 170 and / or other repeater nodes 170) into the borehole string 140 and earthen formations, the available transmission power of the transmitters 315 (of the repeater node 170 and / or other repeater nodes 170), the sensitivity of receivers 305 (of the repeater node 170 and / or other repeater nodes 170), and any electrical noise present.

[0091] In some EM telemetry applications where a downhole EM transmitter transmits directly to the surface from a location deep in a wellbore, transmission frequencies are typically set to 20 Hz or lower because of the strong attenuation at higher frequencies. In some embodiments of the present invention, repeater nodes 170 are spaced closely enough together to allow the practical use of frequencies higher than 20 Hz. For example, repeater nodes 170 are spaced apart by distances of 30 m to 600 m in some embodiments. In such cases, frequencies of up to at least a few hundred Hz or a few kHz may be practical.

[0092] According to one or more embodiments of the present disclosure, additional factors may be considered where different transmission and receive frequencies are used. In an example, the communication system 171 may select or configure the transmission and receive frequencies for a repeater node 170 to be non-interfering. For example, the communication system 171 may support selecting (e.g., by a repeater node 170) the transmission and receive frequencies to differ such that a repeater node 170 may filter the transmission frequency out of a received signal (of a given receive frequency), while avoiding implementations in which the receive frequency is close to a harmonic frequency of the transmission frequency (or vice versa).

[0093] Additionally, or alternatively, the communication system 171 may support configuring and utilizing transmission frequencies and / or receive frequencies based on the direction (e.g., downhole, uphole) in which data is being transmitted. Additionally, or alternatively, the communication system 171 may support utilizing and configuring transmission frequencies and / or receive frequencies based on the depths at which repeater nodes 170 are operating. Additionally, or alternatively, the communication system 171 may support utilizing and configuring transmission frequencies and / or receive frequencies based on formation properties measured by the repeater nodes 170.65TEL-510229-WO-2_INT1024PCT

[0094] In some cases, attenuation of EM telemetry signals can be advantageous, as the attenuation may reduce the likelihood of interference between repeater nodes 170 using the same transmission frequencies, for example, for cases in which the repeater node 170 are spaced apart by a distance supportive of reducing the interference. Accordingly, for example, the communication system 171 supports reusing the same transmission frequency (or frequencies) for parts of the borehole string 140 in which the distance between repeater nodes 170 (e.g., between two repeater nodes 170) is such that the potential for interference is mitigated due to attenuation of the signals transmitted by the repeater nodes 170.

[0095] As described herein, the techniques described herein support controlling positive feedback at a repeater node 170. For example, since the receiver 305 of a repeater node 170 is located relatively close to the transmitter 315 of the same repeater node 170, the amplitude (at the receiver 305) of the signal transmitted by transmitter 315 is typically several orders of magnitude greater than the amplitude of signals received at the receiver 305 from other repeater nodes 170.

[0096] In an example, at the receiver 305 of a repeater node 170, the amplitude of an EM signal transmitted from the transmitter 315 of the repeater node 170 may be at least thousands of times larger than the amplitudes of signals received at the receiver 305 from adjacent repeater nodes 170. For example, for a repeater node 170, the transmitter 315 may generate and transmit signals having an amplitude of 50 volts, while the amplitudes of signals received at the receiver 305 from other repeater nodes 170 may be in the millivolts or microvolts. In some embodiments, for a repeater node 170, the transmitter 315 may generate and transmit signals having an amplitude of 36 volts. It is to be understood that the amplitudes described herein are examples, and the transmitter 315 may be configured for generating and transmitting signals of a suitable amplitude supportive of transmission efficiency described herein.

[0097] In some cases, problems associated with positive feedback described herein can be especially severe when the transmitter 315 and the receiver 305 of a repeater node 170 are both connected across the same gap of a borehole string 140. In this case, potential differences caused by the output signal of the transmitter 315 are applied directly to the input of the receiver 305. Additionally, for cases in which the transmitter 315 and the receiver 305 of a repeater node 170 are connected across different respective gaps of a borehole string 140 as described herein, positive feedback due to the transmitter 315 may still impact the receiver 305 (e.g., potentially overload input circuits of the receiver 305). Accordingly, for example, excessive positive feedback at the receiver 305 may result for cases in which the output of the65TEL-510229-WO-2_INT1024PCT transmitter 315 is directly connected to the input of the receiver 305 and for cases in which the output of the transmitter 315 is transmitted back to the input of the receiver 305 through earth formations that surround the input of the receiver 305.

[0098] According to one or more embodiments of the present disclosure, the systems and techniques described herein address the problems associated with the output of the transmitter 315 feeding back to the input of the receiver 305 by providing and controlling a switch (e.g., switch 312 later described with reference to FIG.4C) capable of disconnecting the input of the receiver 305 according to one or more criteria. As later described herein, the systems and techniques described herein further support implementations using the switch such that the reception and transmission of signals at a repeater node 170 is not simultaneous and / or partially overlaps.

[0099] According to one or more embodiments of the present disclosure, techniques are described for mitigating the problems described herein in which a receiver 305 of a repeater node 170 is impacted by positive feedback due to signals being transmitted by the transmitter 315 of the same repeater node 170. The techniques may include connecting the receiver 305 across a gap in borehole string 140 and connecting the transmitter 315 across a different gap in borehole string 140. The gaps may, for example, each be provided by a gap sub 500 later described with reference to FIG.5. In some embodiments, two or more gaps may be provided by the same gap sub.

[0100] FIG.4A illustrates an example case of a repeater node 170-a in which input terminals 320-a and 320-b of receiver 305 are connected across a gap 144-a and output terminals 360-a and 360-b of transmitter 315 are connected across a gap 144-b that is spaced apart from gap 144-a. In an example in which data transmissions are primarily in the downhole-to-uphole direction, gap 144-a may be downhole from gap 144-b.

[0101] Each of gaps 144-a and 144-b provides electrical insulation between adjacent electrically conductive parts 142 of borehole string 140 (also referred to herein as electrically conductive sections of borehole string 140). In the example of FIG.4A, gap 144-a electrically insulates parts 142-a and 142-b of borehole string 140 from one another while maintaining the mechanical integrity of borehole string 140, and gap 144-b electrically insulates parts 142-b and 142-c of borehole string 140 from one another while maintaining the mechanical integrity of borehole string 140.

[0102] As illustrated at FIG.4A, the repeater node 170-a may include a filter 311 connected across gap 144-a. In an example, a pass band frequency of the filter 311 may correspond to the transmission frequency of transmitter 315. Filter 311 may reduce65TEL-510229-WO-2_INT1024PCT amplitudes of signals (e.g., signals transmitted by transmitter 315) as received at receiver 305 and / or amplitudes of electrical noise present in signals received by receiver 305, thereby enabling the transmission of signals from transmitter 315 at higher power / higher amplitude and improving the distance over which signals transmitted by transmitter 315 can be detected by other repeater nodes 170.

[0103] FIG.4B illustrates an example embodiment of a repeater node 170-b further including a data bus 490 which carries data to transmitter 315. The repeater node 170- b may include aspects of other example repeater nodes 170 described herein, and repeated descriptions of like elements are omitted for brevity. For example, repeater node 170-b includes data bus 490 in addition to the features described with reference to repeater node 170-a.

[0104] The example aspects described with reference to FIG.4B support increasing the distance between gaps 144-a and 144-b, which may further reduce unwanted pickup at receiver 305 of signals transmitted by transmitter 315. In some embodiments, the data bus 490 may carry (from the receiver 305) data to be transmitted to transmitter 315.

[0105] Data bus 490 may include any suitable data bus such as, for example, a controller area network (CAN) BUS. In an example embodiment, data bus 490 may be a differential CANBUS. In the example illustrated at FIG.4B, electronic circuitry (not illustrated) including interfaces for data bus 490 are integrated with receiver 305 and transmitter 315. Where a data bus 490 is provided, data bus 490 may carry data which has been extracted from a received signal. The transmitter 315 may reencode the data and transmit a signal comprising the data.

[0106] In the example of FIG.4B, receiver 305 and transmitter 315 may be housed in separate housings 317-a and 317-b. In another example, the repeater node 170-b may be implemented without the housings 317-a and 317-b.

[0107] In another example, the data may be a digitized version of the received signal. For example, electronic circuitry 310 associated with receiver 305 may include an analog to digital converter that samples the received signal at a sampling frequency. Electronic circuitry 310 associated with transmitter 315 may then control transmitter 315 to transmit a replica of the received signal. The replica may, for example, be an amplified version of the received signal. In an example, the transmitter 315 (and / or electronic circuitry 310) may generate the replica of the received signal by processing the received signal. In one or more embodiments, processing of the received signal may include phase shifting and / or cleaning up of the received signal.65TEL-510229-WO-2_INT1024PCT

[0108] Data bus 490 may be a wired or wireless communication bus. For example, data bus 490 may include a wireless interface which may include wireless interfaces such as, for example, WiFi, Bluetooth™, ZigBee™, Ubiquiti™, 3G, 4G, 5G, LTE, or the like.

[0109] In another example embodiment, data bus 490 may be replaced with an analog connection which carries the received signal in analog form. For example, data bus 490 may support communication of analog signals between receiver 305, electronic circuitry 310, and transmitter 315. In one or more embodiments, data bus 490 may support transmission and reception of digital and / or analog signals.

[0110] The communication system 171 supports multiple gaps 144 for use by a repeater node 170, and the gaps 144 may be implemented by a single drill string component or gap sub 500 in some embodiments, example aspects of which are later described herein.

[0111] FIG.4B illustrates an example implementation further including an electrically insulating gap 144-c. When gap 144-c is present, receiver 305 has input terminals 320-a and 320-b connected at different respective sides of gap 144-a, transmitter 315 has output terminals 360-a and 360-b connected at different respective sides of gap 144-b, and gap 144-c is provided in borehole string 140 between gaps 144-a and 144-b. Gap 144-c electrically isolates input terminals 320-a and 320-b of receiver 305 from output terminals 360-a and 360-b of transmitter 315.

[0112] Gap 144-c, illustrated in the examples of FIG.4B, FIG.4C, and FIG. 5, may support increased feedback reduction as described herein.

[0113] In some aspects, as illustrated at FIG.4C, the systems and techniques described herein support implementing one or more switches 312, and by opening or closing the switches 312, the communication system 171 may adjust the length of drill pipe (e.g., the effective length of an electrically conductive part 142) that is electrically connected to either side of a gap 144. For example, by implementing switches 312 at one or more gaps 144, the systems and techniques described herein may controllably increase or decrease the length of drill pipe that is electrically connected to either side of a gap 144.

[0114] In some examples, increasing the length of drill pipe that is electrically connected to either side of a gap 144 may provide increased efficiency associated with transmitting EM signals (e.g., due to reduced transmission power at a transmitter 315, an associated reduction in feedback experienced at a receiver 305, and resultant effects). In some other examples, where separate gaps 144 (e.g., 144-b and 144-a) are used for transmission and reception of EM telemetry signals, practical considerations (e.g., due to spacing, target65TEL-510229-WO-2_INT1024PCT performance criteria, or the like) may involve maintaining the length of conducting drill pipe between gaps 144-b and 144-a to be relatively short, and some gap subs 500 and repeater node 170 configurations may be implemented without gap 144-c.

[0115] In some embodiments, the effective length of drill pipe connected to a transmitter 315 connected across a gap 144-b may be increased by providing an electrical switch 312 that can selectively electrically connect the conductive sections 142 (e.g., conductive part 142-a, conductive part 142-b2) of borehole string 140 on either side of an adjacent gap 144-a (across which the corresponding receiver 305 may be connected). In an example, repeater node 170-c includes a switch 312 that is connected across gap 144-a and controllable by electronic circuitry 310.

[0116] According to one or more embodiments of the present disclosure, the communication system 171 supports controlling the creation of a short circuit across gap 144- a (e.g., using switch 312) while refraining from interfering with detecting signals at receiver 305. For example, the communication system 171 provides a repeater system configured to transmit data in spaced apart bursts through the use of switch 312. In some aspects, transmission of the data in spaced apart bursts provides improved transmission efficiency.

[0117] In an example, with reference to FIG.4C, repeater node 170-c may transmit a burst of data while maintaining switch 312 in an ON state (a closed state). The repeater node 170-c may then receive a burst of data from another repeater node 170 while maintaining switch 312 in an open state. The repeater node 170-c may again set switch 312 to the closed state to improve transmission efficiency, retransmit the burst of data (while maintaining switch 312 in the closed state), and subsequently return switch 312 to the open state so that receiver 305 can monitor for the next burst of data to be received and retransmitted.

[0118] The example switching techniques described with reference to FIG.4C eliminates feedback from transmitter 315 to the corresponding receiver 305 by causing transmissions and receptions of data at the repeater node 170-c to occur at different times. Use of a switch 312 as described herein may support increased distances between repeater nodes 170 along a borehole string 140, while maintaining transmission efficiency (e.g., achieving a target transmission power and / or a target transmission frequency (for example, a low enough frequency) supportive of a target SNR, a target transmission rate, or the like).

[0119] With reference to FIGS.4A through 4C, in some embodiments, gaps 144-a and 144-b used by a repeater node 170 (e.g., repeater node 170-a, repeater node 170-b) are spaced apart along borehole string 140 from one another by a distance equal to about 1065TEL-510229-WO-2_INT1024PCT meters. In some example embodiments, gaps 144-a and 144-b may be spaced apart along borehole string 140 from one another by a distance of about 30 meters. In some embodiments, the distance between gaps 144-a and 144-b may be selected and / or modified to achieve a target amount of positive feedback at receiver 305.

[0120] Optionally, the frequency band of a wireless interface and / or the distance between gaps 144-a and 144-b may be adaptively altered to sustain reliable communication (e.g., based on data rate, signal integrity, SNR, and the like) between receiver 305 and transmitter 315.

[0121] According to one or more embodiments of the present disclosure, the repeater nodes 170 further support adaptively varying distances between gaps 144 through one or more switches 312. In an example implementation, the systems and techniques described herein may include preconfiguring the communication system 171 such that the spacing between repeater nodes 170 is set up for worst-case scenarios. For example, the respective distances between repeater nodes 170 may be fixed in accordance with worst-case scenarios (e.g., worst-case attenuation due to worst-case or predicted formation properties).

[0122] In an example, the amplitude of a signal received at a repeater node 170 may be relatively high due to formation properties which permit the propagation of the signal with relatively minimal attenuation of the transmitted signal. In this case, a switch 312 at the receiver 305 of the repeater node 170 and another switch 312 (not illustrated) at the transmitter 315 of the repeater node 170 may be utilized (e.g., switched ON or to the closed state) to bypass the repeater node 170 completely and save power for the bypassed repeater node 170. For example, the repeater node 170 may remain in an idle mode. Once the EM friendly formation is passed (e.g., the location of the repeater node 170 with respect to the surface changes during a drilling operation), the repeater node 170 may resume a standard operational mode (e.g., in which the switches 312 are switched OFF or to the open state).

[0123] FIG.5 illustrates an example of a gap sub 500 in accordance with one or more embodiments of the present disclosure.

[0124] With reference to FIG.5, the communication system 171 may support EM telemetry through using parts of the borehole string 140 as an antenna. For example, the borehole string 140 may be divided into multiple (e.g., two, three, or more) conductive sections by including an insulating joint or connector (a gap sub 500) in the borehole string 140. The gap sub 500 may be placed at the top of a bottom hole assembly such that metallic drill pipe in the borehole string 140 above the BHA serves as one antenna element and metallic sections in the BHA serve as another antenna element.65TEL-510229-WO-2_INT1024PCT

[0125] The communication system 171 supports transmission of EM telemetry signals by applying electrical signals between the two antenna elements. In some cases, the EM telemetry signals include very low frequency AC signals (e.g., about 1 Hz to 32 Hz) applied in a manner that codes information for transmission to the surface. In some examples, the communication system 171 may utilize lower frequency signals (e.g., about 1 Hz to 32 Hz and / or other suitable frequencies for preventing or mitigating signal attenuation), as lower frequency signals are less susceptible to attenuation compared to relatively higher frequency signals. The electromagnetic signals may be detected at the surface, for example by measuring electrical potential differences between the borehole string 140 or a metal casing that extends into the ground and one or more ground rods. In some other examples, the communication system 171 may use relatively higher frequency signals (e.g., frequencies of up to at least a few hundred Hz or a few kHz) based on the spacing between repeater nodes 170.

[0126] Gap sub 500 includes a tubular section 510 having a bore 520 configured with fittings that support coupling section 510 in line into borehole string 140. For example, the gap sub 500 includes tool joints 530-a and 530-b. Tool joint 530-a includes a threaded box end, and tool joint 530-b includes a threaded pin end. The threads of tool joints 530-a and 530-b may, for example, include threads which satisfy American Petroleum Institute (API) standard specifications.

[0127] Gap sub 500 includes a gap 144-b spaced longitudinally apart from a gap 144-a. Each of gaps 144-b and 144-a provides electrical insulation between electrically- conductive parts 142 of section 510 on either side of the gaps 144. In the example illustrated at FIG.5, gap 144-b electrically insulates electrically-conductive part 142-c (which includes tool joint 530-a) from electrically conductive part 142-b1, and gap 144-a electrically insulates electrically-conductive part 142-b2 from electrically-conductive part 142-a (which includes tool joint 530-b). Accordingly, for example, the gaps 144 described herein further support isolating repeater nodes 170 from each other.

[0128] In an example, output terminals 360-a and 360-b of a transmitter 315 of a repeater node 170 described herein may be connected across one of gaps 144-b and 144- a, and input terminals 320-a and 320-b of a receiver 305 of the repeater node 170 may be connected across the other one of gaps 144-b and 144-a.

[0129] Some embodiments may provide three (or more) electrically-insulating gaps 144 in association with a repeater node 170. In some aspects, providing at least one additional gap 144 (e.g., gap 144-c as illustrated at FIGS.4B, 4C, and 5) between gaps used65TEL-510229-WO-2_INT1024PCT by a receiver 305 and a transmitter 315 in a repeater node 170 may support the further reduction of feedback by permitting the transmitter 315 and receiver 305 to use different references.

[0130] FIG.6A illustrates an example of a repeater node 170-d in accordance with one or more embodiments of the present disclosure. FIG.6A illustrates example feedback mitigation strategies which may be implemented additional and / or alternative to other feedback mitigation strategies described herein. The repeater node 170-d of FIG.6A may adaptively subtract a signal 641-b from an input signal 641-a received by receiver 305, based on a signal 651 to be amplified and output by the corresponding transmitter 315.

[0131] Referring to FIG.6A, transmitter 315 includes an amplifier 625 (also referred to herein as amplification circuitry) connected to receive a signal 651. The signal 651 may be a modulated signal provided by receiver 305 including encoded data (e.g., as encoded by modulation) to be transmitted. Signal 651 is amplified by amplifier 625 to yield an amplified signal 691 across output terminals 360-a and 360-b. Output terminals 360-a and 360-b are electrically connected to portions of borehole string 140 on either side of a gap 144-b.

[0132] Receiver 305 includes input terminals 320-a and 320-b electrically connected to portions of borehole string 140 on either side of a gap 144-a. Output terminals 360-a and 360-b and receiver input terminals 320-a and 320-b may be connected across multiple different gaps 144 (e.g., gaps 144-b and 144-a of a dual gap sub as shown in FIG.5) as illustrated in the example of FIG.6A. Additionally, or alternatively, in some non-limiting implementations, output terminals 360-a and 360-b and receiver input terminals 320-a and 320-b may be connected across the same gap 144.

[0133] Input terminals 320-a and 320-b are connected to provide a signal 641- a to signal processing components 670. Signal processing components 670 may perform functions such as amplifying and bandpass filtering. Signal processing components 670 includes a subtraction circuit 680. Subtraction circuit 680 subtracts from signal 641-a a feedback cancellation signal 641-b that is based on signal 651 input to the amplifier 625. Feedback cancellation signal 641-b may, for example, be signal 651 or may be generated by applying signal processing such as one or more of amplifying, time shifting and filtering to input signal 651.

[0134] An output from signal processing component 670 is passed to transmitter 315. As described herein, signal processing component 670 is configured to65TEL-510229-WO-2_INT1024PCT effectively reduce or eliminate, from signal 641-a, a component of signal 641-a corresponding to feedback from the signal 691 transmitted by transmitter 315.

[0135] In one or more embodiments, the processing of signals 641-a and 641- b upstream from subtraction circuit 680 is selected such that the subtraction performed by subtraction circuit 680 effectively reduces or eliminates (from signal 641-a) a component of signal 641-a corresponding to feedback from the signal 691 transmitted by transmitter 315. In an example, the subtraction circuit 680 may include a filter 672. Filter 672 may be a band- pass filter configured to pass the signal 691 output by transmitter 315. For example, the band- pass frequency of filter 672 may correspond to the transmission frequency associated with the signal 691.

[0136] The signal processing component 670 supports adaptive feedback cancellation. In some embodiments, for example, where the signal 691 output by transmitter 315 is intended to be an amplified version of the same signal received from another repeater node 170, the signal processing component 670 may measure (e.g., at level analysis block 671-b) the level of the signal 641-a received at receiver 305 and the level of the signal 691 output by transmitter 315. In an example, the signal processing component 670 (e.g., at level analysis block 671-b) may determine, based on the measurements, a level of the signal to be subtracted by subtraction circuit 680.

[0137] Level adjust block 671-a may generate a feedback cancellation signal 641-b based on the level of signal 641-a (e.g., as measured by level analysis block 671-b) and the level of signal 651 (e.g., as measured by level adjustment block 671-a). Accordingly, for example, the receiver 305 may provide a signal 651 to the transmitter 315, and the properties of the signal 651 may support the mitigation or elimination of feedback from transmitter 315 to the receiver 305.

[0138] In one or more embodiments, the nature of the signal transmitted by transmitter 315 is identifiable or measurable by subtraction circuit 680 (e.g., from signal 651). Subtraction circuit 680 is configured to identify or measure signal 641-a. Aspects of the present disclosure support configuring the subtraction circuit 680 for monitoring and measuring signal 641-a to determine if a feedback component (which matches the pattern specified by signal 651) is present.

[0139] In an example, in response to determining the feedback component is present in signal 641-a, subtraction circuit 680 may adjust the generation of the signal 651 (e.g., by increasing the gain of the signal 651), until the feedback component is effectively65TEL-510229-WO-2_INT1024PCT cancelled. In another example, in response to determining the feedback component is not present in signal 641-a, subtraction circuit 680 may maintain the signal 651.

[0140] In one example embodiment, subtraction circuit 680 includes a data processor (e.g., implemented at level adjustment block 671-a). The data processor may be programmed to compare received signal 641-a to input signal 651. Based on the comparison, the data processor may adjust a gain and / or other processing parameters applied to signal 651, before subtracting the processed signal 651 from the received signal 641-a. The subtraction may be performed either in the digital domain or in the analog domain.

[0141] FIG.6B illustrates another example configuration of a repeater node 170-e in accordance with one or more embodiments of the present disclosure. The repeater node 170-e includes aspects of the repeater node 170-d described with reference to FIG.6B, and repeated descriptions of like elements and supported features are omitted for brevity.

[0142] FIG.6B further illustrates transceiver circuitry 685 at receiver 305. Transceiver circuitry 685 is configured to transmit signal 651 to transmitter 315. FIG.6B further illustrates input terminals 320-a1 and 320-a2, which include aspects of input terminal 320-a described herein. FIG.6B further illustrates output terminals 320-b1 and 320-b2, which include aspects of input terminal 320-b described herein.

[0143] Aspects of receiver 305 and / or transceiver circuitry 685 may be implemented by signal processing component 670 described with reference to FIG.6A. Aspects of the signal processing component 670 described herein may be implemented by a software / firmware process. Additionally, or alternatively, aspects of the signal processing component 670 may be implemented by hardware.

[0144] FIG.6C illustrates example waveforms corresponding to signal 641-a received at receiver 305 and amplified signal 691 as output by transmitter 315.

[0145] With reference to FIGS.6B and 6C, and as supported by aspects of the present disclosure, the background subtraction techniques described herein may be implemented at different frequencies. The background subtraction techniques may be implemented with less complexity compared to some other filtering schemes, may be implemented without restrictions on operational frequencies due modulation scheme bandwidth, and may effectively prevent or mitigate saturation at the receiver 305.

[0146] In an example, a sample of signal 641-a received at the receiver 305 is transferred to the level analysis block 671-b, and the level analysis block 671-b subtracts the sample from the signal 641-a.65TEL-510229-WO-2_INT1024PCT

[0147] The filter 672 is a bandpass filter applied to the frequency of signal 641-a, which the receiver 305 expects to receive from another repeater node 170. As shown in FIG.6C, the receiver 305 expects to receive the 641-a while the signal 691, which is transmitted by 315, will also be seen by receiver 305 due to positive feedback. Accordingly, for example, the techniques described herein include tuning the level analysis block 671-b to the signal frequency and amplitude of signal 641-a in the software / firmware. The result is subtracted from the signal across the gap 144-a (Rx gap) to extract the 641-a.

[0148] In one or more embodiments, the techniques may further apply a 180 degree phase shift to the signal 691 to enhance efficiency, example aspects of which are later described herein.

[0149] According to one or more embodiments of the present disclosure, the systems and techniques described herein support techniques for reducing feedback by altering a signal 791 transmitted by transmitter 315, example aspects of which are described with reference to FIGS.7A through 7E.

[0150] FIG.7A illustrates a waveform of a signal 791-a. In the example of FIG.7A, the waveform is a sine wave. Signal 791-a may be modulated to carry data, for example, by a phase shift keying scheme.

[0151] FIG.7B illustrates a waveform of a modified signal 791-b having a single polarity (also referred to herein as a modified unipolar waveform). In an example, signal 791-b is a positive polarity half of signal 791-a. Example aspects of generating the signal 791-b are described with reference to FIG.7C.

[0152] Repeater node 170-f illustrated at FIG.7C may generate signal 791-b by half-wave rectification of input signal 751. For example, repeater node 170-f may include a half-wave rectifier (not illustrated) coupled to or integrated with transmitter 315 or electronic circuitry 310. The half-wave rectifier may be configured for permitting or passing the top half (positive half) of the input signal 751, prior to generating signal 791-b based on the input signal 751. Additionally, or alternatively, the half-wave rectifier may be configured for permitting or passing the top half (positive half) of the input signal 791, prior to transmitting signal 791-b.

[0153] In some aspects, by transmitting signal 791-b, feedback from transmitter 315 to receiver 305 may be reduced. In one or more embodiments, the communication system 171 (and repeater node 170-f) support applying one or more phase shift keying modulation schemes unaltered on the signal 791-b.65TEL-510229-WO-2_INT1024PCT

[0154] The communication system 171 (and repeater node 170-f) support the ability to transmit data in a unipolar mode. In some aspects, transmitting data in the unipolar mode may be implemented to continue data transmission in the case where one half of a bipolar transmission circuit (e.g., an H-bridge circuit) experiences a failure. In some embodiments, the transmitter 315 of repeater node 170-f may be capable of both a mode where bipolar data (e.g., a full sine wave with some type of phase shift keying) is transmitted and a unipolar mode.

[0155] In an example, the transmitter 315 may switch automatically to the unipolar mode in response to detecting a failure of one half of the bipolar transmission circuit (e.g., the H-bridge circuit). For example, in response to detecting a failure of one half of the bipolar transmission circuit (e.g., H-bridge circuit configured for permitting or passing the bottom half (negative half) of the signal 791-a), the transmitter 315 may switch automatically to the unipolar mode and disable the half associated with the detected failure, while continuing to generate and output a signal corresponding to the remaining half (e.g., positive half) of the signal 791-a.

[0156] In one or more embodiments, the repeater node 170-f may support automatically adjusting (e.g., increasing, decreasing) the amplitude of the signal 791-b. The signal 791-b may be referred to herein as a unipolar signal or a modified signal.

[0157] In one or more additional and / or alternative embodiments, the repeater node 170-f may reduce feedback by controlling transmitter 315 to transmit signals (e.g., signal 791) that are out of phase with a signal 741-a being received at the receiver 305. Examples of transmitting signals that are out of phase with a signal 741-a are later described with reference to FIG.7E.

[0158] In an example, the repeater node 170-f may process a signal 741-a received at the receiver 305 to determine a phase of the signal 741-a. In some examples, the repeater node 170-f may process the signal 741-a using processing circuitry or firmware implemented at the receiver 305 or electronic circuitry 310. The repeater node 170-f may control the transmitter 315 such that peaks of the transmitted signal 791 are out of phase (e.g., by approximately 90 degrees, 180 degrees, or the like) with peaks of the signal 741-a.

[0159] The receiver 305 may include circuitry capable of detecting the phase difference between signal 791 and signal 741-a, and for example, rejecting the signal component of signal 791 based on the phase difference. Accordingly, for example, the techniques described herein support exploiting phase differences between the signal 791 and65TEL-510229-WO-2_INT1024PCT the signal 741-a to reject the component of signals (e.g., signal 791) received at the receiver 305 that correspond to feedback from transmitter 315.

[0160] In one or more additional and / or alternative embodiments, with reference to repeater node 170-f illustrated at FIG.7C, transmitter 315 may be configured to generate output signals that are 180 degrees out of phase with the signals received by the corresponding receiver 305. In the example of FIG.7C, transmitter 315 and receiver 305 are connected to the borehole string 140 such that the polarity of the output terminals 360 of the transmitter 315 is the reverse of the polarity of the input terminals 320 of the receiver 305.

[0161] For example, input terminals 320-a and 320-b of receiver 305 are connected across gap 144-a, such that input terminal 320-b (negative input terminal) is connected to conductive part 142-b of borehole string 140. Output terminals 360-a and 360-b are connected across gap 144-b, such that output terminal 360-b (negative input terminal) is connected to conductive part 142-b. Accordingly, for example, receiver 305 and transmitter 315 are connected such that, based on the common reference point (conductive part 142-b of borehole string 140 between gaps 144-b and 144-a) input terminals 320-a and 320-b of receiver 305 are opposite in polarity to output terminals 360-a and 360-b of transmitter 315.

[0162] In one or more embodiments, electronic circuitry 310 may provide electrical isolation between receiver 305 and transmitter 315. The electrical isolation may be provided by a component 708 such as, for example, a capacitor, transformer, or optical isolator that carries received signals from receiver 305 to transmitter 315. The phasing provided by a repeater node 170 (e.g., repeater node 170-f) described herein may advantageously support a higher transmission gain without excessive feedback.

[0163] In the example configuration illustrated at FIG.7C, the direction of current flow 710-b caused by transmitter 315 at the part 142-c of borehole string 140 (located on the side of gap 144-b away from gap 144-a) is the same as the direction of current flow 710-a at the part 142-a of borehole string 140 (on the side of gap 144-a away from gap 144- b). The current flow 710-a is caused, for example by an adjacent repeater node 170 or another EM signal transmitter.

[0164] In examples in which transmitter 315 is controlled by the repeater node 170-f to immediately transmit signal 791 in response to receipt of the signal 741-a at receiver 305 (e.g., repeat the signal 741-a), the current flows 710-b and 710-a which are in the same direction reinforce the transmission of EM telemetry signals (e.g., signal 791) along borehole string 140, thereby improving reception of the signals further along borehole string 140.65TEL-510229-WO-2_INT1024PCT

[0165] FIG.7D illustrates an example of a repeater node 170-g including electronic circuitry 310 capable of generating output signals 791 for transmitter 315 that are 180 degrees out of phase with the signals 741-a received by receiver 305.

[0166] As illustrated at FIG.7D, signals 741-a received by receiver 305 may be forwarded (with or without further processing by the receiver 305) to electronic circuitry 310. Electronic circuitry 310 may generate, using based on signal 741-a, output signal 791 that is 180 degrees (or about 180 degrees) out of phase with signal 741-a. Electronic circuitry 310, may, for example, include processors programmed with preloaded firmware to generate signal 791 based on received signal 741-a. In such example embodiments, receiver 305 and transmitter 315 may be connected across gaps 144-a and 144-b such that the polarities of output terminals 360 are the same or different as the polarities of input terminals 320.

[0167] FIG.7E is an example illustrative of pulse shaping supported by aspects of the present disclosure. The pulse shaping techniques described herein support the continuous transmission mode for the repeater nodes 170 of the communication system 171.

[0168] According to one or more embodiments of the present disclosure, the communication system 171 supports pulse shaping to create some gaps in one cycle that are utilized to receive a signal B (e.g., signal 641-a, signal 741-a) at receiver 305 of a repeater node 170. With reference to the example illustrated at FIG.7E, signal C (e.g., signal 691, signal 791) is the signal transmitted by the transmitter 315 without pulse shaping described herein, signal A is the signal transmitted by the transmitter 315 with pulse shaping applied, signal B is the signal expected to be received at receiver 305 (and generated by an adjacent repeater node 170).

[0169] As shown in the example of FIG.7E, the operational frequency of signal A is the same as the operational frequency of signal B. Signal A is produced by shaping (e.g., reducing the width of) sine wave pulses of signal C, which provides temporal windows 795 to receive the signal B. Further, for example, a phase shift of about 180 degrees is implemented between signal A and signal B in accordance with the techniques described herein. The phase shift of 180 degrees as introduced mitigates or eliminates opportunities for interference between signal A and signal B.

[0170] FIGS.8A through 8E are described with reference to techniques supported by the communication system 171 for reducing positive feedback at receivers 305 of repeater nodes 170. The feedback reduction techniques described herein with reference to FIGS.8A through 8E may be applied to both the variable frequency transmission mode and the continuous frequency mode described herein.65TEL-510229-WO-2_INT1024PCT

[0171] FIG.8A illustrates an example signal 810 to be transmitted by a repeater node 170-h illustrated at FIG.8E. Signal 810 has a frequency F1. Repeater node 170-h includes a modulator 860 capable of gating signal 810 by a square wave 820 (of FIG. 8B, for example, a clock signal) having a frequency F2 >> F1 to yield a chopped signal 830 (of FIG.8C), which is transmitted by transmitter 315.

[0172] In accordance with example aspects of the present disclosure, since the amount in which a transmitted signal is attenuated when propagating through earth formations increases according to frequency of the transmitted signal, the earth formations act as a low-pass filter. For example, by the time the signal 830 transmitted by the repeater node 170-h reaches the next repeater node 170, the high frequency component of the signal 830 (corresponding to the ‘chopping’) will typically be filtered out. That is, for example, due to the filtering out of the high frequency component, the signal 840 (illustrated at FIG.8D) received at the next repeater node 170 will effectively be the same as the signal that would have been received had the signal 810 been transmitted without being ‘chopped.’

[0173] With reference to FIG.8E, in some embodiments, receiver 305 is controlled to sample received signals at times when the transmitted signal (e.g., 830) is OFF (e.g., logic level zero). For example, the received signals may be sampled at frequency F2. Sampling may optionally be controlled by modulator 860 based on the frequency F2 of square wave 820.

[0174] The techniques described herein with reference to FIGS.8A through 8E support generating a signal 810 (an ‘unchopped’ signal) and then chopping the signal 810 using square wave 820 (e.g., a clock, a chopping waveform). In other embodiments, the repeater node 170-h may generate signal 830 (having a chopped waveform) from signal 810 through a synthesis operation performed by a programmed data processor.

[0175] Referring to FIG.8E, repeater node 170-h includes a signal processing block 850 (also referred to herein as an analysis / reconstruction block) coupled to an output of receiver 305. The signal processing block 850 may process signal 805 to generate signals 810 to be transmitted to the next repeater node 170. Signal 810 may be chopped (modulated) by modulator 860 based on the frequency of square wave 820. Modulator 860 may, for example, include an electrically-operated switch.

[0176] In some aspects, the square wave 820 based on which the modulator 860 ‘chops’ or modulates the signal 810 may be a clock signal generated by the modulator 860. In one or more additional and / or alternative embodiments, the clock signal may be generated by clock 818 and synchronized with modulator 860.65TEL-510229-WO-2_INT1024PCT

[0177] In some aspects, the signal 810 controls receiver 305 to block or not process input signals except when modulator 860 is OFF. In an example, blocking or not processing input signals except when modulator 860 is OFF may mitigate the positive feedback scenario, such that the received signal (at receiver 305) is interpolated during the off / quiet time of the chopping modulation (by the modulator 860) which involves the modulator clock feedback to the receiver 305. Modulator 860 provides signal 830 (modulated signal) to transmitter 315.

[0178] In one or more embodiments, the frequency and / or the duty cycle of the square wave 820 may be selected to achieve a target reproduction accuracy of signals received at receiver 305 while maintaining a target quality of signals transmitted by transmitter 315 (e.g., such that a signal 840 received at a receiving repeater node 170 matches a signal 810 produced by a transmitting repeater node 170).

[0179] As described with reference to FIGS.8A through 8E, the techniques described herein support receiving and transmitting any wave shape at any frequency, by using a high frequency modulated signal that is multiplied by the transmitted signal. That is, for example, the resulting wave shape and frequency may be selected by the repeater node 170-h based on the low-pass filter formation-dependent properties of the earth and distance between repeater nodes 170. In some embodiments, the applied modulation frequency (e.g., frequency F2) may be substantially or significantly higher than the transmission frequency (e.g., frequency F1) as described herein. Using the techniques described herein, the receiver 305 and transmitter 315 of a repeater node 170 are active at synchronized and opposite times, and positive feedback due to transmissions from the transmitter 315 are mitigated or eliminated.

[0180] It can be appreciated from the examples described herein that some embodiments advantageously permit a repeater node 170 to simultaneously receive signals encoding data and to retransmit the data in those signals. The data may be encoded using a continuous modulation scheme. In some aspects, the continuous mode (continuous modulation scheme) described herein may be implemented without pausing or stopping transmissions to receive data and / or without pausing or stopping reception of data so as to transmit data.

[0181] According to one or more embodiments of the present disclosure, the receiver 305 and transmitter 315 of the example repeater nodes 170 described herein may be dedicated receivers and transmitters, respectively. In one or more additional and / or alternative embodiments, the receiver 305 and transmitter 315 may be implemented by65TEL-510229-WO-2_INT1024PCT transceivers. Example aspects of implementations utilizing transceivers for receiving and transmitting signals are described with reference to FIGS.9 and 10.

[0182] FIG.9 illustrates a block diagram 900 of a repeater node 970 configured for bidirectional communication of data in accordance with one or more embodiments of the present disclosure. The repeater node 970 includes aspects of a repeater node 170 (e.g., any of 170-a through 170-h) described herein, and repeated descriptions of like elements and like features (e.g., operational modes) are omitted for brevity.

[0183] With reference to FIG.9, repeater node 970 includes EM transceivers 905 and 915 electrically coupled to electronic circuitry 910 (also referred to herein as electronics). Transceivers 905 and 915 each may receive and / or transmit EM telemetry data. Electronic circuitry 910 is configured to receive received data from transceivers 905 and 915 and to control transceivers 905 and 915 to retransmit the received data. The received data may be retransmitted with or without modification in accordance with the example techniques described herein.

[0184] FIG.10 illustrates a block diagram 1000 of a repeater node 970 supportive of bidirectional communication in accordance with one or more embodiments of the present disclosure.

[0185] Referring to FIG.10, terminals 920-a and 920-b of transceiver 905 are connected across a gap 144-a and terminals 960-a and 960-b of transceiver 915 are connected across a gap 144-b. In one or more embodiments, the repeater node 970 may include filters 911-a and 911-b respectively connected across gaps 144-a and 144-b. Filters 911-a has a pass band corresponding to the transmission frequency of transceiver 915, and filter 911-b has a pass band corresponding to the transmission frequency of transceiver 905.

[0186] Filter 911-a may reduce amplitudes of signals (e.g., signals transmitted by transceiver 915) as received at transceiver 905 and / or amplitudes of electrical noise present in signals received by transceiver 905, thereby enabling the transmission of signals from transceiver 915 at higher power / higher amplitude and improving the distance over which signals transmitted by transceiver 915 can be detected. Similarly, for example, filter 911-b may reduce amplitudes of signals (e.g., signals transmitted by transceiver 905) as received at transceiver 915 and / or amplitudes of electrical noise present in signals received by transceiver 915, thereby enabling the transmission of signals from transceiver 905 at higher power / higher amplitude and improving the distance over which signals transmitted by transceiver 905 can be detected by other repeater nodes 970.65TEL-510229-WO-2_INT1024PCT

[0187] In one or more embodiments, the filters 911 may be bandpass filters implemented in hardware or firmware / software. In an example in which gap 144-a is downhole from gap 144-b, uplink data may be received at transceiver 905 and retransmitted by transceiver 915, and downlink data may be simultaneously received at transceiver 915 and retransmitted by transceiver 905.

[0188] The communication system 171 described herein supports carrying data by way of a sequence of repeater nodes. The communication system 171 supports providing temporal information indicating the amount of time for any particular item of data to be transmitted from its origin downhole to the surface (e.g., latency of the data), for example, based on a real-time clock at the downhole system from which the data originates. In an example, the downhole system may include a timestamp with data when the data is transmitted. The time stamp may be compared to a current time as measured by a real-time clock at surface equipment 110 when the data is received at the surface equipment 110.

[0189] Aspects of the communication system 171 further support providing information based on which surface equipment 110 or computing device 105 may determine causes of latency associated with transmitting data from downhole to surface (and / or latency associated with transmitting data from surface to downhole).

[0190] For example, additional or alternative to providing a time stamp at the origin of data (or data packet), each repeater node (e.g., repeater node 170, repeater node 970) through which data passes may track the latency introduced by that repeater node in association with retransmitting the data. The repeater node may provide, with the data, an indication regarding the latency introduced by the repeater node. In one or more embodiments, the repeater node may provide the indication in the form of a time stamp from a real-time clock at the repeater node. In one or more additional and / or alternative embodiments, the indication may include a temporal value of the introduced latency. In one or more additional and / or alternative embodiments, the indication may include a temporal value corresponding to a deviation from a typical latency introduced by the repeater node.

[0191] In response to receiving a data packet from the repeater chain of the communication system 171, the surface equipment 110 or computing device 105 may compile and provide the latency information to an operator (e.g., via a display at the surface equipment 110 or the computing device 105). Additionally, or alternatively, the surface equipment 110 and / or the computing device 105 may process the latency information to identify problems associated with excessive latency introduced by individual repeater nodes.65TEL-510229-WO-2_INT1024PCT

[0192] According to one or more embodiments of the present disclosure as described herein, an EM repeater-like system has been disclosed. In some aspects, instead of receiving an EM transmission from an adjacent repeater node and re-transmitting, the repeater-like system may work together as a whole by simultaneously boosting the signal transmitted from a measurement-while-drilling (MWD) EM telemetry system connected to the BHA. The systems and techniques described herein support obtaining a more reliable EM signal, particularly in deeper wells than historically possible and / or wells with EM unfriendly zones. An EM transmission system network spaced out throughout a drill string as described herein is different from some other approaches to EM telemetry.

[0193] For example, wells are being drilled in deeper zones than ever before and in many EM unfriendly zones. The techniques described herein mitigate issues with poor and intermittent EM telemetry which may negatively impact drilling.

[0194] In accordance with one or more embodiments of the present disclosure, the techniques described herein support boosting the EM signal along the drill string at EM network nodes (all the way from the MWD EM telemetry tool), thereby increasing the received signal level of the EM transmission at the surface, and further, increasing the SNR and EM decoding success rate.

[0195] The techniques described herein provide advantages in that the multi- boosting network may be implemented with significantly less processing overhead, reduced complexity for hardware design, and shorter development time compared to other implementations using a repeater (e.g., compared to echo cancellation processing algorithms involving computer level software processing).

[0196] According to one or more embodiments of the present disclosure, the systems and techniques described herein address complications associated with the transmission of EM signals to a repeater in a continuous signal chain fashion. In one or more embodiments, the systems and techniques described herein may involve a triple gap sub and other modulation schemes as a way to circumvent feedback from saturating the repeater receiver input circuitry. Example aspects of a phasing approach described herein not only allow a higher gain before feedback saturation is achieved, but also directs EM current in the same direction as the lower repeaters or BHA transmission current. The techniques described herein support constructive superposition of the EM signal instead of the destructive cancellation of the signal seen with the dual gap sub using a common reference for the receiver and transmitter subsections. The systems and techniques described herein may be65TEL-510229-WO-2_INT1024PCT implemented using a dual gap sub but the effect would be even easier to control using the triple gap sub arrangement.

[0197] In some embodiments, the systems and techniques described herein include a receiver / transmitter amplification scheme of a repeater, in which the reference point with respect to each subsection is 180 degrees out of phase. Such example techniques may be implemented using an isolation scheme such as, for example, capacitive or transformer isolation between the receiver and transmitter sub sections of the repeater. The systems and techniques described herein support continuous transmission in a repeater setup in combination with one or more techniques for circumventing feedback. The systems and techniques described herein support a repeater system having improved reliability and decreased overall cost.

[0198] FIG.11 illustrates an example flowchart of a method 1100 in accordance with one or more embodiments of the present disclosure. The method 1100 is an example computer-implemented method that may be implemented by the example aspects of a system 100, a communication system 171, a repeater node 170, and / or a computing device 105 as described herein.

[0199] At 1105, the method 1100 includes receiving a first EM signal including data.

[0200] At 1110, the method 1100 includes transmitting a second EM signal including the data based at least in part on the first EM signal. In some aspects, a first temporal period associated with receiving the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

[0201] In the descriptions of the flowcharts herein, the operations may be performed in a different order than the order shown, or the operations may be performed in different orders or at different times. Certain operations may also be left out of the flowcharts, one or more operations may be repeated, or other operations may be added to the flowcharts.

[0202] In the descriptions of the flowcharts herein, the operations may be performed in a different order than the order shown, or the operations may be performed in different orders or at different times. Certain operations may also be left out of the flowcharts, one or more operations may be repeated, or other operations may be added to the flowcharts.

[0203] Set forth below are some embodiments of the foregoing disclosure:65TEL-510229-WO-2_INT1024PCT

[0204] Embodiment 1. A device comprising: a first transceiver receptive of a first electromagnetic (EM) signal comprising data; and a second transceiver configured to transmit a second EM signal comprising the data based at least in part on the first EM signal, wherein a first temporal period associated with transmission of the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

[0205] Embodiment 2. The device as in any prior embodiment, wherein the second transceiver is configured to generate the second EM signal by modulating a data signal comprising the data based on a second frequency greater than a first frequency associated with the first EM signal.

[0206] Embodiment 3. The device as in any prior embodiment, wherein the second frequency is at least ten times the first frequency.

[0207] Embodiment 4. The device as in any prior embodiment, wherein the first transceiver comprises a bandpass filter configured based on a frequency associated with the second EM signal.

[0208] Embodiment 5. The device as in any prior embodiment, wherein: the second transceiver is receptive of a third EM signal comprising second data; and the first transceiver is configured to transmit a fourth EM signal comprising the second data based at least in part on the first EM signal, wherein a third temporal period associated with transmission of the third EM signal and a fourth temporal period associated with transmitting the fourth EM signal at least partially overlap.

[0209] Embodiment 6. The device as in any prior embodiment, wherein the first temporal period, the second temporal period, the third temporal period, and the fourth temporal period at least partially overlap.

[0210] Embodiment 7. The device as in any prior embodiment, further comprising: a switch coupled to input terminals of the first transceiver, wherein the device is configured to control the switch in association with connecting at least one input terminal of the first transceiver to a first conductive portion of a borehole string, and wherein at least one output terminal of the second transceiver is electrically coupled to a second conductive portion of the borehole string.

[0211] Embodiment 8. The device as in any prior embodiment, wherein a second polarity of the second EM signal is different from a first polarity of the first EM signal.65TEL-510229-WO-2_INT1024PCT

[0212] Embodiment 9. The device as in any prior embodiment, wherein the second EM signal comprises a unipolar waveform.

[0213] Embodiment 10. The device as in any prior embodiment, wherein: the second transceiver is configured to modify a pulse shape of the second EM signal; and the first transceiver is configured to receive the first EM signal based on a temporal window associated with the modified pulse shape of the second EM signal.

[0214] Embodiment 11. The device as in any prior embodiment, wherein the second transceiver is configured to delay transmission of the second EM signal such that a phase difference between the first EM signal and the second EM signal is greater than 0 degrees.

[0215] Embodiment 12. The device as in any prior embodiment, wherein: the first transceiver is configured to provide a signal to the second transceiver based on the first EM signal and a level analysis of the first EM signal; and the second transceiver is configured to amplify the signal, wherein the second EM signal comprises the amplified signal.

[0216] Embodiment 13. The device as in any prior embodiment, wherein the device is configured to: measure one or more properties of a formation, receive data indicating the one or more properties of the formation, or both; and configure a second frequency associated with transmitting the second EM signal based at least in part on the one or more properties.

[0217] Embodiment 14. A communication system comprising: a set of devices, wherein a device of the set of devices comprises: a first transceiver receptive of a first electromagnetic (EM) signal comprising data; and a second transceiver configured to transmit a second EM signal comprising the data based at least in part on the first EM signal, wherein a first temporal period associated with transmission of the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

[0218] Embodiment 15. The communication system as in any prior embodiment, wherein the second transceiver is configured to generate the second EM signal by modulating a data signal comprising the data based on a second frequency greater than a first frequency associated with the first EM signal.

[0219] Embodiment 16. The communication system as in any prior embodiment, wherein the first transceiver comprises a bandpass filter configured based on a frequency associated with the second EM signal.65TEL-510229-WO-2_INT1024PCT

[0220] Embodiment 17. The communication system as in any prior embodiment, wherein: the second transceiver is receptive of a third EM signal comprising second data; and the first transceiver is configured to transmit a fourth EM signal comprising the second data based at least in part on the first EM signal, wherein a third temporal period associated with transmission of the third EM signal and a fourth temporal period associated with transmitting the fourth EM signal at least partially overlap.

[0221] Embodiment 18. The communication system as in any prior embodiment, wherein a second device of the set of devices comprises: a third transceiver receptive of a third EM signal comprising the data; and a fourth transceiver configured to transmit a fourth EM signal comprising the data based at least in part on the first EM signal, wherein: a first frequency associated with the first EM signal is different from a third frequency associated with the third EM signal; and a second frequency associated with transmitting the second EM signal is different from a fourth frequency associated with transmitting the fourth EM signal.

[0222] Embodiment 19. The communication system as in any prior embodiment, wherein a second device of the set of devices comprises: a third transceiver receptive of a third EM signal comprising the data; and a fourth transceiver configured to transmit a fourth EM signal comprising the data based at least in part on the first EM signal, wherein: a first frequency associated with the first EM signal is equal to a third frequency associated with the third EM signal; and a second frequency associated with transmitting the second EM signal is equal to a fourth frequency associated with transmitting the fourth EM signal.

[0223] Embodiment 20. A method comprising: receiving a first electromagnetic (EM) signal comprising data; and transmitting a second EM signal comprising the data based at least in part on the first EM signal, wherein a first temporal period associated with receiving the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

[0224] According to one or more embodiments of the present disclosure, the techniques described herein relate to a method for repeating an EM telemetry signal, the method including: receiving a first EM telemetry signal encoding data and transmitting a second EM telemetry signal encoding the data wherein: transmitting the second EM telemetry signal includes inserting interruptions in the second EM telemetry signal at a frequency significantly higher than a frequency of the first EM telemetry signal; and receiving the first EM telemetry signal includes detecting the first EM telemetry signal during the interruptions.65TEL-510229-WO-2_INT1024PCT

[0225] In some aspects, the techniques described herein relate to a method wherein the second EM telemetry signal is a replica of the first EM telemetry signal.

[0226] In some aspects, the techniques described herein relate to a method wherein inserting interruptions is performed at a frequency at least ten times a frequency of the first EM telemetry signal.

[0227] In some aspects, the techniques described herein relate to a method wherein inserting the interruptions is performed at a frequency at least fifty times a frequency of the first EM telemetry signal.

[0228] In some aspects, the techniques described herein relate to a method including receiving the first EM telemetry signal using a receiver and opening a switch to disconnect the receiver at times outside of the interruptions.

[0229] In some aspects, the techniques described herein relate to a method wherein inserting the interruptions includes chopping the second EM telemetry signal with a square wave chopping signal.

[0230] In some aspects, the techniques described herein relate to a method wherein receiving the first EM telemetry signal includes measuring an electrical potential across an electrically-insulating gap in a drill string during some or all of the interruptions.

[0231] In some aspects, the techniques described herein relate to a method wherein measuring the electrical potential includes sampling the electrical potential using an analog to digital converter.

[0232] In some aspects, the techniques described herein relate to a method including processing a plurality of samples acquired by the analog to digital converter, wherein the processing includes detecting a waveform corresponding to the first signal by performing a correlation between a plurality of samples and a prototype waveform.

[0233] In some aspects, the techniques described herein relate to a method including receiving the first EM telemetry signal by monitoring a potential difference across a first electrically insulating gap in a drill string and transmitting the second EM telemetry signal by imposing a potential difference across a second electrically-insulating gap in the drill string spaced apart from the first electrically-insulating gap.

[0234] In some aspects, the techniques described herein relate to a method including transmitting the second EM telemetry signal with a polarity opposite to the first EM telemetry signal.

[0235] In some aspects, the techniques described herein relate to a method wherein: receiving the first EM telemetry signal is performed by a receiver located near the65TEL-510229-WO-2_INT1024PCT first electrically insulating gap; transmitting the second EM telemetry signal is performed using a transmitter located near the second electrically insulating gap; and the method further includes digitizing information characterizing the first EM telemetry signal at the receiver, carrying the digitized information to the transmitter by a data bus extending along a drill string and using the digitized information at the transmitter to generate the second EM telemetry signal.

[0236] In some aspects, the techniques described herein relate to a method wherein the first and second electrically insulating gaps are separated by a distance of at least 8 meters.

[0237] In some aspects, the techniques described herein relate to a method wherein the second EM telemetry signal is a unipolar signal.

[0238] In some aspects, the techniques described herein relate to a method wherein a waveform of the second EM telemetry signal is a half-wave rectified sine wave.

[0239] In some aspects, the techniques described herein relate to a method wherein a frequency of the second EM telemetry signal is different from a frequency of the first EM telemetry signal.

[0240] In some aspects, the techniques described herein relate to a method wherein the data is encoded in the first EM telemetry signal at least in part by phase shift keying.

[0241] In some aspects, the techniques described herein relate to a method wherein the data includes one or more error checking codes and the method includes processing the received first EM telemetry signal to recover the data and checking the data using the error checking codes.

[0242] In some aspects, the techniques described herein relate to a method including discarding the data without encoding the data in the second EM telemetry signal in response to determining, based on checking the data, that the data is corrupted and unrecoverable.

[0243] In some aspects, the techniques described herein relate to a method wherein the second EM telemetry signal is delayed relative to the first EM telemetry signal by no more than one cycle at a frequency of the first EM telemetry signal.

[0244] In some aspects, the techniques described herein relate to an apparatus including one or more features, a combination of the one or more features, or a sub- combination of the one or more features as described herein.65TEL-510229-WO-2_INT1024PCT

[0245] In some aspects, the techniques described herein relate to a method including one or more steps, one or more acts, a combination of the one or more steps and / or the one or more acts, or a sub-combination of the one or more steps and / or the one or more acts as described herein.

[0246] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Further, it should be noted that the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “about”, “substantially” and “generally” are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” and / or “substantially” and / or “generally” can include a range of ± 8% of a given value.

[0247] The teachings of the present disclosure may be used in a variety of well operations. Illustrative well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water flooding, cementing, etc.

[0248] Unless the context clearly requires otherwise, throughout the description and the claims, the terms “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The terms “connected”, “coupled”, or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof. The terms “herein,” “above,” “below,” and words of similar import, when used to describe this specification shall refer to this specification as a whole and not to any particular portions of this specification. The term “or,” in reference to a list of two or more items, covers all of the following interpretations of the term: any of the items in the list, all of the items in the list, and any combination of the items in the list. The singular forms “a,” “an,” and “the” also include the meaning of any appropriate plural forms.

[0249] Terms that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”,” “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present) depend on the specific orientation of the apparatus described and illustrated. The subject65TEL-510229-WO-2_INT1024PCT matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

[0250] In some embodiments, the invention may be implemented in software. For greater clarity, “software” includes any instructions executed on a processor, and may include (but is not limited to) firmware, resident software, microcode, and the like. Both processing hardware and software may be centralized or distributed (or a combination thereof), in whole or in part, as known to those skilled in the art. For example, software and other modules may be accessible via local memory, via a network, via a browser or other application in a distributed computing context, or via other means suitable for the purposes described above.

[0251] Where a component (e.g., a circuit, module, assembly, device, drill string component, drill rig system, etc.) is referred to herein, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component or any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

[0252] Specific non-limiting examples of systems, methods and apparatus have been described herein for purposes of illustration. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and / or acts with equivalent features, elements and / or acts; mixing and matching of features, elements and / or acts from different embodiments; combining features, elements and / or acts from embodiments as described herein with features, elements and / or acts of other technology; and / or omitting combining features, elements and / or acts from described embodiments.

[0253] It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.65TEL-510229-WO-2_INT1024PCT

[0254] While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited.

Claims

65TEL-510229-WO-2_INT1024PCT CLAIMS What is claimed is:

1. A device characterized by: a first transceiver receptive of a first electromagnetic (EM) signal characterized by data; and a second transceiver configured to transmit a second EM signal characterized by the data based at least in part on the first EM signal, wherein a first temporal period associated with transmission of the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

2. The device of claim 1, wherein the second transceiver is configured to generate the second EM signal by modulating a data signal comprising the data based on a second frequency greater than a first frequency associated with the first EM signal.

3. The device of claim 2, wherein the second frequency is at least ten times the first frequency.

4. The device of claim 1, wherein the first transceiver comprises a bandpass filter configured based on a frequency associated with the second EM signal.

5. The device of claim 1, wherein: the second transceiver is receptive of a third EM signal comprising second data; and the first transceiver is configured to transmit a fourth EM signal comprising the second data based at least in part on the first EM signal, wherein a third temporal period associated with transmission of the third EM signal and a fourth temporal period associated with transmitting the fourth EM signal at least partially overlap.

6. The device of claim 5, wherein the first temporal period, the second temporal period, the third temporal period, and the fourth temporal period at least partially overlap.

7. The device of claim 1, further comprising: a switch coupled to input terminals of the first transceiver, wherein the device is configured to control the switch in association with connecting at least one input terminal of the first transceiver to a first conductive portion of a borehole string, and wherein at least one output terminal of the second transceiver is electrically coupled to a second conductive portion of the borehole string.65TEL-510229-WO-2_INT1024PCT 8. The device of claim 1, wherein a second polarity of the second EM signal is different from a first polarity of the first EM signal.

9. The device of claim 1, wherein the second EM signal comprises a unipolar waveform.

10. The device of claim 1, wherein: the second transceiver is configured to modify a pulse shape of the second EM signal; and the first transceiver is configured to receive the first EM signal based on a temporal window associated with the modified pulse shape of the second EM signal.

11. The device of claim 1, wherein the second transceiver is configured to delay transmission of the second EM signal such that a phase difference between the first EM signal and the second EM signal is greater than 0 degrees.

12. The device of claim 1, wherein: the first transceiver is configured to provide a signal to the second transceiver based on the first EM signal and a level analysis of the first EM signal; and the second transceiver is configured to amplify the signal, wherein the second EM signal comprises the amplified signal.

13. The device of claim 1, wherein the device is configured to: measure one or more properties of a formation, receive data indicating the one or more properties of the formation, or both; and configure a second frequency associated with transmitting the second EM signal based at least in part on the one or more properties.

14. A communication system characterized by: a set of devices, wherein a device of the set of devices characterized by: a first transceiver receptive of a first electromagnetic (EM) signal characterized by data; and a second transceiver configured to transmit a second EM signal characterized by the data based at least in part on the first EM signal, wherein a first temporal period associated with transmission of the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

15. A method characterized by: receiving a first electromagnetic (EM) signal characterized by data; and65TEL-510229-WO-2_INT1024PCT transmitting a second EM signal comprising the data based at least in part on the first EM signal, wherein a first temporal period associated with receiving the first EM signal and a second temporal period associated with transmitting the second EM signal at least partially overlap.

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