# Patent

## Title
Wireless exploration seismic system

## Abstract

Systems and methods for seismic data acquisition employing a dynamic multiplexing technique. The dynamic multiplexing technique may include advancing one or more modules in a seismic array through a multiplexing signature sequence in successive transmission periods. The multiplexing signature sequence may be random or pseudo-random. A shared multiplexing signature sequence may be used at all the modules in the seismic array. As such, modules belonging to a common collision domain may operate out of phase with respect to the shared multiplexing signature sequence.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority as a continuation-in-part to U.S. patent application Ser. No. 12/837,177 filed on Jul. 15, 2010 entitled “WIRELESS EXPLORATION SEISMIC SYSTEM,” which is a continuation of U.S. patent application Ser. No. 11/538,744 filed on Oct. 4, 2006 entitled “WIRELESS EXPLORATION SEISMIC SYSTEM” now U.S. Pat. No. 7,773,457 which claims priority to U.S. Provisional Application No. 60/724,271 filed on Oct. 7, 2005 and U.S. Provisional Application No. 60/821,217 filed on Aug. 2, 2006. The entire disclosures of the foregoing being are hereby incorporated by reference in their entirety as if set forth in full herein.


FIELD
The present disclosure relates to systems and methods seismic survey systems where the data signals from multiple sensors are transmitted by wireless means. In particular, the present disclosure relates to systems and methods that facilitate real time read out of a seismic survey system, even in the case of rapidly repeating vibrating energy sources, without backlogging of data or delay of the survey process.
BACKGROUND
Seismic surveys are often used by natural resource exploration companies and other entities to create images of subsurface geologic structure. These images are used to determine the optimum places to drill for oil and gas and to plan and monitor enhanced resource recovery programs among other applications. Seismic surveys may also be used in a variety of contexts outside of oil exploration such as, for example, locating subterranean water and planning road construction.
A seismic survey is normally conducted by placing an array of vibration sensors (accelerometers or velocity sensors called “geophones”) on the ground, typically in a line or in a grid of rectangular or other geometry. Vibrations are created either by explosives or a mechanical device such as a vibrating energy source or a weight drop. Multiple energy sources may be used for some surveys. The vibrations from the energy source propagate through the earth, taking various paths, refracting and reflecting from discontinuities in the subsurface, and are detected by the array of vibration sensors. Signals from the sensors are amplified and digitized, either by separate electronics or internally in the case of “digital” sensors. The survey might also be performed passively by recording natural vibrations in the earth.
The digital data from a multiplicity of sensors is eventually recorded on storage media, for example magnetic tape, or magnetic or optical disks, or other memory device, along with related information pertaining to the survey and the energy source. The energy source and/or the active sensors are relocated and the process continued until a multiplicity of seismic records is obtained to comprise a seismic survey. Data from the survey are processed on computers to create the desired information about subsurface geologic structure.
In general, as more sensors are used, placed closer together, and/or cover a wider area, the quality of the resulting image will improve. It has become common to use thousands of sensors in a seismic survey stretching over an area measured in square kilometers. Hundreds of kilometers of cables may be laid on the ground and used to connect these sensors. Large numbers of workers, motor vehicles, and helicopters are typically used to deploy and retrieve these cables. Exploration companies would generally prefer to conduct surveys with more sensors located closer together. However, additional sensors require even more cables and further raise the cost of the survey. Economic tradeoffs between the cost of the survey and the number of sensors generally demand compromises in the quality of the survey.
In addition to the logistic costs, cables create reliability problems. Besides normal wear-and-tear from handling, they are often damaged by animals, vehicles, lightning strikes, and other problems. Considerable field time is expended troubleshooting cable problems. The extra logistics effort also adds to the environmental impact of the survey, which, among other things, adds to the cost of a survey or eliminates surveys in some environmentally sensitive areas.
As a result, wireless acquisition units have been developed to do away with the burdensome nature of cables in such a system. For instance, U.S. Pat. No. 7,773,457, which is hereby incorporated in its entirety by reference as if reproduced herein, describes a system for performing a seismic survey using wireless acquisition units.
When conducting a survey using wireless data acquisition units, it may be advantageous to perform a wireless data read out from such units in real time. As such, survey verification may occur prior to the conclusion of the survey, and the cost and time associated with manual data retrieval of such units may be reduced or eliminated. However, when employing a real time data read out, the bandwidth usage of the wireless communication between modules must be carefully considered so as not to slow the speed at which the survey is conducted.
In turn, a multiplexing regime may be imparted to the wireless modules in the seismic survey so that multiple units within range of one another may simultaneously broadcast and receive data. Examples of such multiplexing regimes include time division, frequency division, code division, etc. For example, U.S. Pat. No. 7,773,457 describes employing multiplexing techniques in a “bucket brigade” type system to perform real time read out of data.
SUMMARY
It has been recognized that a dynamic multiplexing technique, wherein the multiplexing signature used to multiplex a signal is varied at different time periods, may be provided for use in systems such as those described in U.S. Pat. No. 7,775,457. For example, when using frequency division multiplexing, regulatory bodies such as the Federal Communication Commission in the United States may enforce regulations requiring that no single frequency may be used by a module for longer than a set duration. As such, a dynamic multiplexing technique may allow for operation in such cases where static multiplexing is not feasible.
When employing such a dynamic multiplexing technique, a random or pseudo-random multiplexing regime may be employed wherein each unit uses a different random multiplexing signature during successive transmission periods. However, with multiple units using a random or pseudo-random multiplexing signature, two units may simultaneously attempt to use the same multiplexing signature to transmit data. In such instances, a data collision may occur and the units may each be required to retransmit the data which was subject to the collision. These retransmissions may reduce the bandwidth of the system, which may slow the survey. This may add additional time and cost to the survey, and is thus preferably avoided. For example, in the case of two units operating within a common collision domain, it has been found that the bandwidth of the system may decrease by between 3%-5%. This may add additional time and cost to the survey, and is thus preferably avoided. As the number of units within a collision domain increases, the problem is exacerbated and the bandwidth can deteriorate much more than the amount listed above.
Accordingly, a first aspect includes a method for use in seismic data acquisition. The method includes disposing, in series, a plurality of seismic data acquisition modules that are operative to wirelessly communicate acquired seismic data. The acquisition modules define a wireless serial data transfer path for relaying data from upstream acquisition modules to downstream acquisition modules and a data collection unit. The method further includes assigning a first acquisition module in said serial data transfer path a first multiplexing signature sequence. In successive transmission periods, the first acquisition module advances sequentially through a first plurality of multiplexing signatures of the first multiplexing sequence. The method further includes assigning a second acquisition module in said serial data transfer path a second multiplexing signature sequence. In successive transmission periods, the second acquisition module advances sequentially through a second plurality of multiplexing signatures of the second multiplexing sequence.
A number of feature refinements and additional features are applicable to the first aspect. These feature refinements and additional features may be used individually or in any combination. As such, each of the following features that will be discussed may be, but are not required to be, used with any other feature or combination of features of the first aspect.
For example, in one embodiment, the method may further include first transmitting, using a first multiplexing signature of the first plurality of multiplexing signatures, seismic data from the first acquisition module to at least one downstream acquisition module and second transmitting, using a second multiplexing signature from the second plurality of multiplexing signatures, seismic data from the second acquisition module to at least one downstream acquisition module.
In an embodiment, the first multiplexing signature sequence and the second multiplexing signature sequence may be a random sequence of multiplexing signatures. In turn, the method may further include detecting when the first multiplexing signature used in the first transmitting is the same as the second multiplexing signature used in the second transmitting. The method may also include first retransmitting, using the next multiplexing signature from the first multiplexing signature sequence, seismic data from the first acquisition module to at least one downstream acquisition module and second retransmitting, using the next multiplexing signature from the second multiplexing sequence, seismic data from the second acquisition module to at least one downstream acquisition module.
In one embodiment, the first multiplexing signature may be different than the second multiplexing signature. Additionally, at least a portion of the first transmitting and at least a portion of the second transmitting may occur during a common transmission period. In an embodiment, the first multiplexing signature sequence and the second multiplexing signature sequence may be the same pseudo-random sequence of multiplexing signatures. Furthermore, the first acquisition module and the second acquisition module may operate out of phase with respect to the shared pseudo-random sequence of multiplexing signatures. In one embodiment, the multiplexing signatures comprise a plurality of different frequencies.
In yet another embodiment, the method includes assigning the first multiplexing signature sequence to a third data acquisition module. The first and third acquisition modules may be positioned in the serial transmission path at first and second locations. A distance between the first and second locations may be greater than a transmission range of the first and third acquisition modules.
A second aspect includes a method for use in seismic data acquisition. The method includes disposing a plurality of seismic data acquisition modules in an array. Each seismic data acquisition module is operative to wirelessly communicate with at least one other seismic data acquisition module in said array to define at least a first serial data transmission path. Additionally, the method includes assigning each of said plurality of seismic data acquisition modules in said first serial data transmission path a multiplexing signature sequence for use in transmitting said seismic data. At least one multiplexing signature is assigned to first and second seismic data acquisition modules in said first serial data transmission path during a first common transmission period. The method also includes, during the first common transmission period, transmitting seismic data from said first and second seismic data acquisition units using said at least one multiplexing signature. Also, the method includes advancing the first and second seismic data acquisition modules in the multiplexing signature sequence such that the first and second seismic data acquisition modules are assigned at least one different multiplexing signature during a second common transmission period.
A number of feature refinements and additional features are applicable to the second aspect. These feature refinements and additional features may be used individually or in any combination. As such, each of the following features that will be discussed may be, but are not required to be, used with any other feature or combination of features of the second aspect.
For instance, in one embodiment the multiplexing signature sequence may be a random sequence of multiplexing signatures. Additionally, the method may also include detecting a data collision between the first and second seismic data acquisition unit during the first common transmission period and retransmitting the seismic data during the second common transmission period using the at least one different multiplexing signature.
In an additional embodiment, the multiplexing signature sequence may be a pseudo-random sequence. The multiplexing signature sequence for the first seismic data module and the second seismic data module may be the same. As such, the first seismic data module and the second seismic data module may be out of phase with respect to the multiplexing signature sequence.
A third aspect includes a system for use in seismic data acquisition. The system includes a plurality of seismic data acquisition modules, disposed in series, that are operable to wirelessly communicate acquired seismic data. The acquisition modules define a wireless serial data transfer path for relaying data from upstream acquisition modules to downstream acquisition modules and a data collection unit. The system further includes a first acquisition module in said serial data transfer path for transmitting seismic data using a first multiplexing signature from a first multiplexing signature sequence during a first transmission period. The first acquisition module advances through the first multiplexing signature sequence in successive transmission periods. Additionally, the system includes a second acquisition module in the serial data transfer path for transmitting seismic data using a second multiplexing signature from a second multiplexing signature sequence during the first transmission period. The second acquisition module advances through said second multiplexing signature sequence in successive transmission periods. The first multiplexing signature and said second multiplexing signature are different during the first transmission period.
A number of feature refinements and additional features are applicable to the third aspect. These feature refinements and additional features may be used individually or in any combination. As such, each of the following features that will be discussed may be, but are not required to be, used with any other feature or combination of features of the third aspect.
In one embodiment, the first multiplexing signature sequence and said second multiplexing signature sequence may be a common pseudo-random sequence of a plurality of frequencies. The first acquisition module and said second acquisition module may be out of phase with respect to the common pseudo-random sequence.
In another embodiment, the system may include a third acquisition module in said serial data transfer path for transmitting seismic data using the first multiplexing signature from the first multiplexing signature sequence during the first transmission period. The third acquisition module may advance through said first multiplexing signature sequence in successive transmission periods. Additionally, the first acquisition module and third acquisition module may be at a first location and a second location. The first location and second location may be separated by a distance greater than the transmission range of the first and third acquisition module. In this regard, the first and third module may be in phase with respect to the common pseudo-random sequence.
Furthermore, a number of feature refinements and additional features are applicable to any of the foregoing aspects. These feature refinements and additional features may be used individually or in any combination. As such, each of the following features may be, but are not required to be, used with any other feature or combination of features of the foregoing aspects.
For example, the multiplexing sequence for the one or more modules described above may reside in non-volatile storage at each unit. That is, the multiplexing sequence may be stored locally in a memory of the module. Alternatively or additionally, the multiplexing sequence may be transmitted among units (e.g., from a base unit to individual units disposed in the array). In this regard, the multiplexing sequence may be updated or modified during a survey. The transmitted sequence may in turn be stored in memory once received at the module.
In addition, the modules may comprise a seismic array. The seismic array may be of any appropriate configuration. For example, the modules of any of the foregoing aspects may be arranged in lines to communicate to a base station. The modules may transmit to an adjacent module in the line or the modules may transmit to a non-adjacent module. As such, each module may communicate sequentially down the line to the base station or each module may jump adjacent modules and transmit to non-adjacent downstream modules.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of an embodiment of a seismic survey area.
FIGS. 2A and 2B are schematic view of a first and a second wireless acquisition unit pair employing frequency division multiplexing to transmit seismic data.
FIGS. 3-6 are charts graphically depicting the respective relative portion of a first and second acquisition unit pair at different transmission periods.
FIG. 7 is a flow chart depicting an embodiment of a process for avoiding data collisions.
FIG. 8 is a flow chart depicting another embodiment of a process for avoiding data collisions.
FIG. 9 is a schematic view of another embodiment of a wireless array.
FIG. 10 is a schematic view of a portion of an embodiment of a wireless array shown in three different instances of operation.
FIG. 11 is a schematic view of yet another embodiment of a wireless array.
FIG. 12 is a schematic view of a wireless array shown at various instances of operation.
FIG. 13 is a schematic view of still another embodiment of a wireless array.



DETAILED DESCRIPTION
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that it is not intended to limit the invention to the particular form disclosed, but rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the claims.
FIG. 1 shows one possible configuration of a seismic data acquisition system 100 in accordance with an embodiment of the present invention. The seismic acquisition system 100 may include all or any of the features described in U.S. Pat. No. 7,773,457. For example, a number of remote modules 101 may be arranged in lines as is done with previous wired systems, except that there is no physical connection between the remote modules 101. Base station modules 102 are provided which may be connected to a central control and recording system 103 by Ethernet, fiber optic, or other digital data link or a wireless substitute. Example radio links operating on frequencies F1 to F12 are indicated by arrows. Note that for improved data rate, each radio link in the illustrated embodiment leaps past the nearest remote module to the next module closer to the base station. Other radio transmission paths are possible, including direct to the nearest remote module, leaping multiple modules, or in the case of an obstruction or equipment fault, past a defective remote module or even across to another line or any other logical path that establishes a communication flow. The central control and recording system 103 may be a notebook computer or larger equivalent system. In the various implementations of a wireless acquisition system described above, each of the wireless modules being controlled by a single base station may be referred to as a line segment. This line segment may be further divided into one or more subnets. Each subnet may comprise an independent serial data transfer path in a line segment. In this regard, and as shown in FIG. 1, a base station unit 102 may be disposed such that a portion of the line segment are arranged on opposite sides of the base station. That is, the base station may reside at a point within the line segment. The portions on either side of the base station of the line segment may be symmetric or may not be symmetric. The portions of the line segment on either side of the base station may each comprise a subnet such that each module transmits to an adjacent module rather than the embodiment depicted in FIG. 1 wherein each module transmits to a non-adjacent module nearer the base station. Furthermore, each portion of the line segment on either side of the base station may comprise multiple subnets as shown wherein modules transmit to non-adjacent modules. In this regard, modules may be interleaved such that there is more than one subset in a line segment.
For example, with additional reference to FIG. 9, each module 101 may communicate with an adjacent module such that no modules are skipped. FIG. 10 shows a similar configuration as shown in FIG. 9, wherein each module 101 transmits to an adjacent module. FIG. 10 shows a portion of a line segment in various instances in time (T1, T2, and T3). At each successive time interval, different modules may transmit data (e.g., appending acquired seismic data to the transmission) such that the data is in turn passed down the line segment to a base station 102. A full array of this sort is shown in FIG. 11. Note that either side of a line segment may each comprise a subnet of modules. The base stations 102 may receive a transmission from a respective one of the different subnets in different transmission cycles. In this regard, and as illustrated in FIG. 12, a number of subnets may be provided that may transmit data back to a base station 102. The number of subnets may correspond on the number of cycles required for each subnet to subsequently transmit data to the base station 102. Alternatively, as shown in FIG. 13, base stations 102 may be provided with multiple radios to receive transmissions from more than one subnet at the same time. In this regard, for an embodiment wherein the base station unit interrupts the line segment and is positioned therein, the base station unit may have multiple radios operative to receive the data multiple subnets at the same time. Alternatively, the subnets may transmit to the base station in alternating time periods such that each subnet transmits data to the base station at different periods as shown in FIGS. 10-12.
In this regard, any given one of the remote modules 101 may be positioned within transmission range of one or more other remote modules. Accordingly, collision domains (e.g., areas having the potential for interference or crosstalk between modules) are introduced into the system. Each module may have a unique collision domain wherein potential interference with other modules may occur. One or more multiplexing techniques may be used to reduce the potential for collisions of transmitted seismic data in the data acquisition system. For instance, each of the remote modules 101 transmitting data may do so on one of a plurality of different frequency ranging from F1 to F12 as represented in FIG. 1. In this regard, even if all the transmissions occur during a common transmission period, use of the different frequencies allow for the simultaneous transfer of seismic data with reduced potential for data collisions. Accordingly, modules receiving data may only listen for the particular frequency such that other seismic data transferred at a different frequency is not received.
Other multiplexing techniques may also be used. For example, each of the remote modules 101 may use a different code in a code division multiplexing technique. Further still, each module 101 may transmit in a different discrete time period in a time division multiplexing technique.
In this regard, different multiplexing regimes may be applied to a wireless acquisition unit system such as the one shown in FIG. 1. As used herein, a multiplexing regime refers to the type of multiplexing used. As such, a multiplexing regime may be, but is not limited to, frequency division multiplexing, code division multiplexing, time division multiplexing or other appropriate multiplexing techniques. A multiplexing regime may employ a plurality of unique multiplexing signatures. The multiplexing signature is a unique parameter assigned to each of the remote modules. As such, in the example provided in FIG. 1, the plurality of frequencies F1-F12 each represent a unique multiplexing signature. Other multiplexing signatures may also be provided, such as different codes for use in code division multiplexing or different discrete time periods for use in time division multiplexing.
In addition to the static multiplexing technique depicted in FIG. 1 wherein each module in a collision domain employs a static multiplexing signature for transmission of data, a dynamic multiplexing regime may be employed in such a system 100. This may allow for use of the system in jurisdictions where regulatory bodies prevent the use of a single constant frequency by any particular device for longer than a set duration. As such, these units may frequency hop (i.e., change frequencies) after the unit operates at a particular frequency for a predefined duration. As such, these units may include a random or pseudo-random sequence of multiplexing signatures. The unit may randomly hop frequencies in successive transmission periods such that no single frequency is used longer than the predefined duration. This type of random frequency hopping may be employed by each of the modules in a system.
For instance, the system shown in FIG. 1 may employ such a random frequency hopping technique. As such, each of the frequencies shown F1-F12 may actually be a random or pseudo-randomly generated frequency. These random or pseudo-random frequencies may be bounded at upper and lower ends and may include a number of discrete frequencies that are defined within a range of operating frequencies. In successive transmission periods, each remote module 101 may randomly hop to another random frequency.
One such embodiment of a frequency hopping technique may be Frequency Hopping Spread Spectrum (FHSS). In an FHSS system, the initiating party sends a request via a predefined frequency or control channel to the receiving party. The receiving party may return an index number to the initiating party. The initiating party may uses the index number to determine one or more frequencies (e.g., a pseudo-random sequence of frequencies to use). In turn, the initiating party may send a synchronization signal on the first frequency in a predetermined sequence. This synchronization signal may synchronize the transmission periods of the module and serve as an acknowledgement to the receiving party that the initiating party has correctly determined the frequency sequence. In turn, data may be transmitted with both the initiating and receiving party hopping frequencies in the predefined sequence in successive transmission periods.
However, this random frequency hopping introduces a collision domain into the system because two modules may randomly employ the same multiplexing signature such that a data collision occurs. It has been estimated that the occurrence of two modules hopping to the same random frequency may reduce the bandwidth of a system by 3% to 5%. This is because once a data collision occurs, each module may hop to another random multiplexing signature in the multiplexing regime and retransmit the data, effectively losing one duty cycle for each of the colliding modules.
Accordingly, another embodiment of a dynamic multiplexing regime may include assigning a shared pseudo-random multiplexing signature sequence to each of the modules in a system. In this regard, each module in the system may be assigned an identical multiplexing signature sequence. This shared pseudo-random multiplexing signature sequence may include a sequence of frequencies, codes, or other different multiplexing signatures. By using an identical multiplexing signature sequence, the potential for two modules randomly hopping to the same multiplexing signature may be reduced by controlling the phase of each module with respect to the multiplexing signature sequence. Stated differently, the modules within a collision domain may operate out of phase from each other with respect to the multiplexing signature sequence. As each of the modules may advance through the shared multiplexing signature sequence at the same rate (e.g., one multiplexing signature per transmission cycle), once modules within a given collision domain become out of phase from one another, the occurrence of data collisions may be minimized while still achieving a dynamic multiplexing environment.
This concept is further demonstrated with reference to FIG. 2A, which depicts a first seismic acquisition unit pair 200 and a second seismic acquisition unit pair 300. The first seismic acquisition unit pair 200 shares a collision domain with the second seismic acquisition unit pair 300 such that without a multiplexing technique, transmission between the first seismic acquisition unit pair 200 and the second seismic acquisition unit pair 300 may result in a data collision or crosstalk between the pairs. In this regard, the first seismic acquisition unit pair 200 may be within transmission range of the second seismic data acquisition unit pair 300. However, as shown in FIG. 2A, a first seismic acquisition unit 210 transmits to a second seismic acquisition unit 220 using a first frequency F1. At the same time, a third seismic acquisition unit 310 may transmit to a fourth seismic acquisition unit 320 using a second frequency F2. As such, crosstalk and/or data collisions are avoided and each seismic acquisition unit pair transmits data without interference using a unique multiplexing signature.
FIG. 2B depicts the same first seismic acquisition unit pair 200 and second seismic acquisition unit pair 300 shown in FIG. 2A. However, as shown in FIG. 2B, the transmission between the first seismic acquisition unit 210 and the second seismic acquisition unit 220 as well as the transmission between the third seismic acquisition unit 310 and the fourth seismic acquisition unit 320 uses a common frequency F3. The result would be a data collision such that the data transmitted between each of the unit pairs 200 and 300 may be subject to a collision. In turn, neither the second seismic acquisition unit 220 nor the fourth seismic acquisition unit 320 may accurately receive the data intended for the respective modules. This is an example of a situation where in prior systems, each unit pair would in turn randomly hop within a random sequence and retransmit the data attempted to be transmitted in FIG. 2B.
Such an instance is also depicted in FIG. 3. FIG. 3 includes a chart 400 depicting the frequency at which the first unit pair 100 and a second unit pair 200 are operating. A sequence of pseudo-random frequencies 410 are represented in the middle column of the table 400 and include frequencies f0 through fn. Any number of unique multiplexing signatures may be used. In addition, while f0-fn are numbered consecutively, the pseudo-random frequencies may not be consecutively arranged and may jump to different (i.e., higher and lower frequencies) in the spectrum without limitation. That is, the order of f0-fn does not necessarily indicate an increase or decrease in frequencies, but rather each subsequent frequency or multiplexing signature in the sequence may be random. As shown, both the first unit pair 100 and the second unit pair 200 are operating using a common frequency f0. This corresponds to the situation shown in FIG. 2B where a collision may occur.
In one particular embodiment, a total of sixty-four different multiplexing signatures may be employed in order to transmit data between modules. For example, these sixty-four multiplexing signatures may comprise different frequency signatures residing in the 2.4 GHz band. Additionally, fifteen multiplexing signatures may be used that are dedicated to deployment, formation, and wake-up system functions. In this regard, these fifteen multiplexing signatures may be used in a configuration mode in order to order and establish the array.
In accordance with the present invention, rather than having each of the first unit pair 100 and second unit pair 200 randomly sequence among the pseudo-random frequency signature sequence upon occurrence of a collision, the second unit pair 200 is advanced out of turn in the frequency sequence 410. The first unit pair 100 may maintain its position in the frequency sequence 400 while the second unit pair 300 is advanced. As such, the modules may operate as depicted in FIG. 4, wherein the first unit pair 200 operates at fo while the second unit pair 300 operates at f1. Alternatively, the first unit pair 200 may be advanced by a single step in the sequence and the second unit pair 300 may be advanced further out of turn (e.g., by two frequencies). As such, a retransmission of data may occur such that no data collision occurs. Additionally, the first unit pair 200 is now out of phase from the second unit pair 300 with respect to the frequency sequence 410.
Furthermore, upon successive transmission periods, such as the one shown in FIG. 5, the first unit pair 200 and second unit pair 300 may advance at the same rate through the frequency sequence so as to stay out of phase with respect to the common frequency sequence 410 shared between the first unit pair 200 and the second unit pair 300. This may continue until the time period shown in FIG. 6 wherein the first unit pair 200 remains on the last frequency fn in the frequency sequence 410 while the second unit pair 300 recommences from the beginning of the frequency sequence 410. In turn, once one of the unit pairs is advanced out of sequence different than the other unit pair, the unit pair will remain on different multiplexing signatures in the pseudorandom sequence and thus avoid data collisions.
In this regard, rather than the ongoing potential of data collisions when using a purely random multiplexing signature hopping technique, the foregoing allows the wireless acquisition units to hop to different multiplexing signatures without the potential for data collisions so long as the units in a given collision domain remain out of phase from one another. The manner in which unit pairs are set to be out of phase from one another may vary in different embodiments. For instance, the collision domain for each individual module may be manually analyzed and respective collision domains may be determined for each acquisition unit. In turn, acquisition units identified as belonging to a common collision domain may be set such that each unit in the collision domain initiates operation out of phase with respect to each other unit in the collision domain. Based on this information, the modules are manually set to be out of phase from one another. This manual setting of the modules out of phase from one another may occur at the deployment or set up of the modules.
Alternatively, a collision detection method may be employed such that the modules begin communicating according to the sequence. Only when a collision is detected do the two colliding modules act in accordance with the foregoing such that one of the modules is advanced out of phase from the other. This out of phase advancement of one module may result in the module advancing a single point or may randomly advance through the sequence to a different point than the other colliding module. As such, a learning protocol may be employed such that the modules in the collision domain identify a collision and learn to settle into the multiplexing signature sequence such that each module in the collision domain is out of phase.
One example of a process 700 for performing such a dynamic multiplexing technique is shown in FIG. 7. The process 700 may include assigning 710 a multiplexing signature sequence to a first and a second module. The process 700 may further include transmitting 720 seismic data from the first and the second module using at least one multiplexing signature at each one of the first and second module. In this regard, the first and second module may operate using a common multiplexing signature. In this regard, a collision may be detected 730. Upon detection 730 of a collision, the process 700 may include offsetting 740 one of the first or second modules such that the first and second module are out of phase from each other with respect to the multiplexing signature sequence as discussed above with regard to FIGS. 4-6.
After offsetting 740 at least one of the first and second modules within the multiplexing signature sequence, the offset module may transmit 750 and index number to a corresponding receiving unit. In this regard, the transmitting 750 of the index number to the corresponding receiving unit may allow the corresponding receiving unit to similarly advance in the multiplexing signature sequence such that the receiving unit corresponding to offset module is in sync with the offset module. In this regard, the process 700 may include modifying 716 the receiving unit to operate at the same multiplexing signature sequence as the offset module.
In this regard, the process 700 may include retransmitting 770 data subject to the data collision with the first and second modules being out of phase within the multiplexing signature sequence. The process 700 may include continuing to transmit 780 data from the first and second module when the first and second modules are out of phase with respect to the multiplexing signature sequence.
An alternative embodiment of a process 800 from deploying a dynamic multiplexing technique as shown in FIG. 8. The process 800 may include manually offsetting a first and second module in an identified collision domain to be out of phase prior to the occurrence of a new transmission. In this regard, the process 800 may occur at the start up or the deployment of the units such that there is no data transmission prior to the modules being manually set to be out of phase. In this regard, the process 800 may include assigning 810 a multiplexing signature sequence to the first and second module. The process 800 may further include offsetting 820 at least one of the first and second modules within the multiplexing signature sequence such that the first and second modules are out of phase from one another with respect to the multiplexing signature sequence. Again, the offsetting 820 of the modules may be manually achieved based at least partially on identified collision domains within the array.
The process 800 may further include transmitting 830 and indexing number from a respective one of the first and second modules to corresponding receiving units. The transmitting 830 of an indexing number may allow the transmitting and receiving unit to become synchronized such that corresponding receiving units are in synch with the first and second module with respect to the multiplexing signature sequence. The method 800 may further include transmitting 840 seismic data from the first module and the second module using a multiplexing signature sequence such that the first module and the second module are out of phase with respect to the shared multiplexing signature sequence. The process 800 may continue transmitting 850 from the first and second module such that the first and second modules remain out of phase and the occurrence of data collisions is reduced.
Based on the foregoing, it will be understood that for a given number of modules in a collision domain, there may be at least a corresponding number of unique multiplexing signatures such that each of the modules may in turn occupy a point in the sequence out of phase from the other modules. Based on this, the design of the survey may be modified such that on appropriate number of multiplexing signatures may be made available based on the number of modules in a given collision domain.
While described herein as using frequencies, the same principle may also be applied wherein the multiplexing signature sequence includes different codes applied to the data and transmitted using code division multiplexing. In this regard, the sequence may be pseudorandom may include a random code generator.
In addition, the wireless modules described herein may be location aware. In this regard, and as described in U.S. Pat. No. 7,773,457, the modules may have components that are operative to obtain location data for the module. A module which has obtained location data may transmit its location data to another module in the array which has yet to locate itself. In this regard, the location data transmitted from the location aware module to the locating module may be used by the locating module to acquire a location. For instance, when a GPS module is provided to obtain location data, ephemeris data of a wireless module which is used to acquire a GPS location may be provided to another module which is yet to acquire a location data from a satellite. In this regard, the ephemeris data may be used by the locating wireless module to obtain location data. This may improve the locating modules ability to require satellite location data. For instance, the time required to acquire a satellite fix may be reduced such that the modules may be deployed and located faster.
Additionally, while the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character. For example, certain embodiments described hereinabove may be combinable with other described embodiments and/or arranged in other ways (e.g., process elements may be performed in other sequences). Accordingly, it should be understood that only the preferred embodiment and variants thereof have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.

## Claims

1. A method for use in seismic data acquisition, comprising the steps of:
disposing, in series, a plurality of seismic data acquisition modules that are operative to wirelessly communicate acquired seismic data, wherein said acquisition modules define a wireless serial data transfer path for relaying data from upstream acquisition modules to downstream acquisition modules and a data collection unit;
assigning a first acquisition module in said serial data transfer path a first multiplexing signature sequence, wherein in successive transmission periods, the first acquisition module advances sequentially through a first plurality of multiplexing signatures of the first multiplexing sequence; and
assigning a second acquisition module in said serial data transfer path a second multiplexing signature sequence, wherein in successive transmission periods, the second acquisition module advances sequentially through a second plurality of multiplexing signatures of the second multiplexing sequence;
wherein the first acquisition module and the second acquisition module are spatially distributed with respect to said wireless serial data transfer path, and wherein said first acquisition module advances from a first multiplexing signature to a second multiplexing signature within said first multiplexing signature sequence at substantially the same time as said second acquisition modules advances from a third multiplexing signature to a fourth multiplexing signature within said second multiplexing signature sequence.

2. The method according to claim 1, further comprising:
first transmitting, using the first multiplexing signature of the first plurality of multiplexing signatures, seismic data from the first acquisition module to at least one downstream acquisition module; and
second transmitting, using the third multiplexing signature from the second plurality of multiplexing signatures, seismic data from the second acquisition module to at least one downstream acquisition module.

3. The method according to claim 2, wherein the first multiplexing signature sequence and the second multiplexing signature sequence comprise a random sequence of multiplexing signatures.

4. The method according to claim 1, wherein the first multiplexing signature is the same as the third multiplexing signature.

5. The method according to claim 2, wherein at least a portion of the first transmitting and at least a portion of the second transmitting occur simultaneously during a common transmission period.

6. The method according to claim 5, wherein the first multiplexing signature sequence and the second multiplexing signature sequence comprise the same pseudo-random sequence of multiplexing signatures.

7. The method according to claim 6, wherein the first acquisition module and the second acquisition module operate in phase with respect to the shared pseudo-random sequence of multiplexing signatures.

8. The method according to claim 7, wherein the multiplexing signatures comprise a plurality of different frequencies.

9. The method according to claim 7, further comprising:
assigning the same pseudo-random signature sequence to a third data acquisition module, wherein the third data acquisition module is spatially distributed with respect to the first and second data acquisition module;
wherein the third data acquisition module advances in the same pseudo-random sequence at the same time as the first and second acquisition modules advance in the same pseudo-random sequence.

10. A method for use in seismic data acquisition, comprising:
disposing a plurality of seismic data acquisition modules in an array, wherein each seismic data acquisition module is operative to wirelessly communicate with at least one other seismic data acquisition module in said array to define at least a first serial data transmission path;
assigning each of said plurality of seismic data acquisition modules in said first serial data transmission path a multiplexing signature sequence for use in transmitting said seismic data;
during a first common transmission period, transmitting seismic data from a first data acquisition module in said first serial data transmission path using a first multiplexing signature and transmitting seismic data from a second seismic data acquisition module in said first serial data transmission path using a second multiplexing signature, wherein at least a portion of the transmitting from the first data acquisition module during the first common transmission period and at least a portion of the transmitting from the second data acquisition module during the first common transmission period occur simultaneously; and
advancing said first and second seismic data acquisition modules in their respective multiplexing signature sequences at substantially the same time such that said first seismic data acquisition module is assigned a third multiplexing signature and said second seismic data acquisition module is assigned a fourth multiplexing signature, wherein said third multiplexing signature is different than said first multiplexing signature and said fourth multiplexing signature, and said fourth multiplexing signature is different than said second multiplexing signature and said third multiplexing signature;
during the second common transmission period, transmitting seismic data from said first data acquisition module using said third multiplexing signature and transmitting seismic data from said second seismic data acquisition module using said fourth multiplexing signature, wherein at least a portion of the transmitting from said first data acquisition module during the second common transmission period and at least a portion of the transmitting from the second data acquisition module during the second common transmission period occur simultaneously.

11. The method according to claim 10, wherein the multiplexing signature sequences are random sequences of multiplexing signatures.

12. The method according to claim 10, wherein the multiplexing signature sequence is a pseudo-random sequence.

13. The method according to claim 12, wherein the multiplexing signature sequence for the first seismic data module and the second seismic data module is the same.

14. The method according to claim 13, wherein the first seismic data module and the second seismic data module are out of phase with respect to the multiplexing signature sequence.

15. The method according to claim 1, wherein the first acquisition module and the second acquisition module are positioned in non-overlapping collision domains.

16. The method according to claim 15, wherein the first acquisition module and the second acquisition module are spaced apart by a distance greater than the transmission range of either the first or second acquisition module.

17. A method for use in seismic data acquisition, comprising the steps of:
disposing, in series, a plurality of seismic data acquisition modules that are operative to wirelessly communicate acquired seismic data, wherein each of said acquisition modules receives data from only one upstream acquisition module and transmits data to only one downstream acquisition module thereby defining a serial data transfer path;
first transmitting seismic data from a first acquisition module in said wireless serial data path to a first downstream acquisition module in said wireless serial data path; and
second transmitting seismic data from a second acquisition module in said wireless serial data path to a second downstream acquisition module in said wireless serial data path;
wherein at least a portion of the first transmitting and second transmitting occur simultaneously, and wherein interference between said first and second transmitting is avoided by using a unique multiplexing signature at the said first acquisition module and said second acquisition module, respectively.