Code-division multiple-access (CDMA) wireline telemetry system

• US 20040085988A1
• Filed: 11/06/2002
• Published: 05/06/2004
• Est. Priority Date: 11/06/2002
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Schultz, Roger L., Murali, Beegamudre N., Gardner, Wallace R., Prammer, Manfred G.
• Granted Patent: US 7,061,932 B2
• Time in Patent Office: Days
• US Class Current: 370/441
• CPC Class Codes: E21B 47/13 by electromagnetic energy, e.g. radio frequency
• CPC Class Codes: H04B 1/707 using direct sequence modulation

Abstract

A downhole telemetry system employing code division multiple access (CDMA) is disclosed. In one embodiment, the downhole telemetry system comprises one or more downhole transmitters and an uphole receiver. Each of the downhole transmitters transmits a corresponding uplink signal which is generated using amplitude modulation of corresponding code word signals. The code word signals are orthogonal to each other, and the transmitters may be configured to adjust the timing to assure synchronous arrival of the various uplink signals at the receiver. Each of the transmitters may be allocated a different number of code words when it is desired to allow for unequal bandwidth requirements. Such allocation is preferably dynamic. Additional modulation techniques may be employed with CDMA, including frequency division multiplexing, time division multiplexing, and frequency re-use. In the preferred embodiment, the uplink signals are transported over a multi-conductor wireline cable, but other physical channels are also contemplated.

Claims

1. A downhole telemetry system that comprises:

a first downhole transmitter that transmits a first uplink signal, wherein the first uplink signal is generated using amplitude modulation of a first uplink data stream onto a first code word signal; and

a second downhole transmitter that transmits a second uplink signal, wherein the second uplink signal is generated using amplitude modulation of a second uplink data stream onto a second code word signal, wherein the first and second code word signals are orthogonal; and

an uphole receiver that receives a composite uplink signal including the first and second uplink signals in combined form, wherein the receiver is configured to extract the first and second uplink data streams from the composite uplink signal.

2. The downhole telemetry system of claim 1, wherein the first and second downhole transmitters are configured to adjust timing of the first and second code word signals, respectively, so as to provide synchronization of the first and second uplink signals at the uphole receiver.

3. The downhole telemetry system of claim 1, further comprising:

additional downhole transmitters that each transmit corresponding uplink signals, wherein the corresponding uplink signals are generated using amplitude modulation of corresponding uplink data streams onto corresponding code word signals, wherein the code word signals are mutually orthogonal.

4. The downhole telemetry system of claim 1, wherein second uplink signal is further generated using amplitude modulation of a third data stream onto a third code word signal, wherein the third code word signal is orthogonal to the first and second code word signals.

5. The downhole telemetry system of claim 1, wherein the second downhole telemetry transmitter is configured to use a programmable number of code word signals to generate the second uplink signal.

6. The downhole telemetry system of claim 1, further comprising a surface unit coupled to the uphole receiver and coupled to a uphole transmitter, wherein the surface unit is configured to dynamically assign code words to downhole transmitters, and wherein the surface unit is configured to communicate that assignment to the downhole transmitters via the uphole transmitter.

7. The downhole telemetry system of claim 1, wherein the code word signals are based on Walsh codes.

8. The downhole telemetry system of claim 1, wherein the first uplink signal is further generated by upconversion using a first carrier signal.

9. The downhole telemetry system of claim 8, wherein the second uplink signal is further generated by upconversion using a second carrier signal having a frequency different from that of the first carrier signal.

10. The downhole telemetry system of claim 8, further comprising:

a third downhole transmitter that transmits a third uplink signal, wherein the third uplink signal is generated using amplitude modulation of a third uplink data stream onto a third code word signal, wherein the first and third code word signals are substantially identical,

wherein the third uplink signal is further generated by upconversion using a third carrier signal having a frequency equal to that of the first carrier signal, wherein said third carrier signal is ninety degrees out of phase with the first carrier signal.

11. The downhole telemetry system of claim 1, further comprising:

a third downhole transmitter that transmits a third uplink signal, wherein the third uplink signal is generated using amplitude modulation of a third uplink data stream onto said a third code word signal, wherein said first and third code word signals are based on the same code word, wherein said first and third uplink signals are nonzero only at different times.

12. The downhole telemetry system of claim 1, wherein the downhole transmitters are coupled to the uphole receiver via a multi-conductor logging cable which carries composite uplink signal in one of a set of orthogonal transmission modes to the uphole receiver.

13. The downhole telemetry system of claim 1, wherein the downhole transmitters are each coupled to a logging cable via corresponding transformers, and wherein the logging cable transports the composite uplink signal to the uphole receiver.

14. The downhole telemetry system of claim 1, wherein the downhole transmitters are each coupled to a logging cable in an impedance-divider configuration, and wherein the logging cable transports the composite uplink signal to the uphole receiver.

15. The downhole telemetry system of claim 1, wherein the first uplink signal is protected against burst errors by interleaving.

16. The downhole telemetry system of claim 1, wherein the first uplink signal is protected against errors by error correction coding.

17. The downhole telemetry system of claim 1, wherein the first and second transmitters are contained within different tools of a wireline sonde.

18. The downhole telemetry system of claim 1, wherein the first and second transmitters are contained within different logging-while-drilling tools of a drillstring.

19. The downhole telemetry system of claim 1, wherein the second downhole transmitter generates a third uplink signal using amplitude modulation of a third uplink data stream onto said second code word signal, wherein the second downhole transmitter upconverts the second uplink signal using a first carrier signal having a given frequency, and wherein the second downhole transmitter upconverts the third uplink signal using a second carrier signal having said given frequency, wherein the second carrier signal is orthogonal to the first carrier signal.

20. A method of transmitting uplink data, the method comprising:

modulating each of multiple orthogonal code words with corresponding amplitudes that represent uplink data; and

transmitting the modulated orthogonal code words to a surface receiver.

21. The method of claim 20, wherein said multiple orthogonal code words include at least three code words.

22. The method of claim 21, wherein said modulating is performed downhole.