Downhole communications using selectable frequency bands

1. A system that is usable to improve wireless communications transmitted through a wellbore in a subterranean formation, the system comprising:

a first transceiver that is positionable external to a casing string in the wellbore for wirelessly transmitting data via a signal within a frequency band, wherein the first transceiver comprises:

a processing device; and

a memory device that includes instructions executable by the processing device for causing the processing device to:

receive one or more sensor signals from one or more sensors;

determine a fluid property of a fluid in the wellbore based on the one or more sensor signals;

determine a property of a subterranean formation based on the one or more sensor signals;

select the frequency band based on the fluid property and the property of the subterranean formation by consulting a lookup table in which a plurality of fluid properties and a plurality of subterranean formation properties are mapped to a plurality of frequency bands; and

a second transceiver that is positionable externally the casing string and operable to receive the signal.

2. The system of claim 1 , wherein the first transceiver is operable to transmit the data via the signal and via another signal within another frequency band substantially simultaneously.

3. The system of claim 1 , wherein the fluid comprises a combination of a wellbore servicing fluid and a formation fluid.

4. The system of claim 1 , wherein the lookup table includes a first lookup table, and wherein the memory device further includes instructions that are executable by the processing device for causing the processing device to:

receive a wireless transmission via a communications device;

detect a signal-to-noise ratio of the wireless transmission; and

determine the fluid property and the property of the subterranean formation based on the signal-to-noise ratio by consulting a second lookup table stored in the memory device in which the plurality of fluid properties and the plurality of subterranean formation properties are mapped to a plurality of signal-to-noise ratios.

5. The system of claim 1 , wherein the lookup table further comprises a plurality of casing string properties mapped to the plurality of frequency bands, and wherein the first transceiver is operable to select the frequency band based on a casing-string property.

6. The system of claim 5 , wherein the memory device further comprises instructions that are executable by the processing device for causing the processing device to:

determine the casing-string property based on the one or more sensor signals, the casing-string property comprising a conductivity or a geometry of the casing string; and

select the frequency band based on the casing-string property by consulting the lookup table.

7. The system of claim 1 , wherein the fluid property comprises a first conductivity of the fluid and the property of the subterranean formation comprises a second conductivity of the subterranean formation.

8. The system of claim 1 , wherein the frequency band is selected by the first transceiver in order to increase a transmission distance associated with the signal, increase a transmission efficiency associated with the signal, increase a data throughput associated with the signal, reduce interference between the signal and another wireless signal, or increase a signal-to-noise ratio associated with the signal.

9. A communication system that is positionable in a wellbore, the communication system comprising:

a first transceiver that is positionable external to a casing string in the wellbore for wirelessly transmitting a signal in a frequency band, wherein the first transceiver comprises:

a processing device; and

a memory device that includes instructions executable by the processing device for causing the processing device to:

receive one or more sensor signals from one or more sensors;

determine a fluid property of a fluid in the wellbore based on the one or more sensor signals;

determine a property of a subterranean formation based on the one or more sensor signals;

select the frequency band based on the fluid property and the property of the subterranean formation by consulting a lookup table in which a plurality of fluid properties and a plurality of subterranean formation properties are mapped to a plurality of frequency bands; and

a second transceiver that is positionable external to the casing string for receiving the signal, extracting data from the signal, and relaying the data to a third transceiver using another frequency band.

10. The communication system of claim 9 , wherein the first transceiver is operable to transmit the signal in the frequency band and in a different frequency substantially simultaneously.

11. The communication system of claim 9 , wherein the fluid comprises a combination of a wellbore servicing fluid and a formation fluid.

12. The communication system of claim 9 , wherein the lookup table includes a first lookup table, and wherein the memory device further includes instructions that are executable by the processing device for causing the processing device to:

receive a wireless transmission via a communications device;

detect a signal-to-noise ratio of the wireless transmission; and

determine the fluid property and the property of the subterranean formation based on the signal-to-noise ratio by consulting a second lookup table stored in the memory device in which the plurality of fluid properties and the plurality of subterranean formation properties are mapped to a plurality of signal-to-noise ratios.

13. The communication system of claim 9 , wherein the lookup table further comprises a plurality of casing string properties mapped to the plurality of frequency bands, and wherein the first transceiver is operable to select the frequency band based on a casing-string property.

14. The communication system of claim 13 wherein the memory device further comprises instructions that are executable by the processing device for causing the processing device to:

determine the casing-string property based on the one or more sensor signals, the casing-string property comprising a conductivity or a geometry of the casing string; and

select the frequency band based on the casing-string property by consulting the lookup table.

15. The communication system of claim 9 , wherein the fluid property comprises a first conductivity of the fluid and the property of the subterranean formation comprises a second conductivity of the subterranean formation.

16. A method usable to improve wireless communications in a wellbore, the method comprising:

receiving, by a first transceiver that is external to a casing string, one or more sensor signals from one or more sensors operable to detect a fluid property of a fluid in the wellbore and a property of a subterranean formation;

determining, by the first transceiver, the fluid property of the fluid based on the one or more sensor signals;

determining, by the first transceiver, the property of the subterranean formation based on the one or more sensor signals;

selecting, by the first transceiver, a frequency band based on the fluid property and the property of the subterranean formation by consulting a lookup table in which a plurality of fluid properties and a plurality of subterranean formation properties are mapped to a plurality of frequency bands; and

wirelessly transmitting, by the first transceiver, data via a signal within the frequency band to a second transceiver.

17. The method of claim 16 , wherein the frequency band is a first frequency band, and further comprising:

transmitting, by the first transceiver, the signal in both the first frequency band and a second frequency band substantially simultaneously.

18. The method of claim 16 , wherein the lookup table comprises a first lookup table, and further comprising:

receiving a wireless transmission, via a communications device;

detecting a signal-to-noise ratio of the wireless transmission; and

determining the fluid property and the property of the subterranean formation based on the signal-to-noise ratio by consulting a second lookup table in which a plurality of signal-to-noise ratios are mapped to the plurality of fluid properties and the plurality of subterranean formation properties.

19. The method of claim 16 , further comprising:

determining a conductivity or a geometry of the casing string based on a sensor signal; and

selecting the frequency band based on the conductivity or the geometry of the casing string by consulting the lookup table, wherein the lookup table further comprises a plurality of casing string properties mapped to the plurality of frequency bands.

20. The method of claim 16 , wherein the frequency band is selected by the first transceiver in order to increase a transmission distance associated with the signal, increase a transmission efficiency associated with the signal, increase a data throughput associated with the signal, reduce interference between the signal and another wireless signal, or increase a signal-to-noise ratio associated with the signal.