Forward Error Correction for MWD Acoustic Telemetry
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Solution Overview
Problem
Current MWD communication systems face challenges in reliably transmitting data from a downhole location to an uphole location due to the banded nature of the acoustic channel in drill strings, where stop-bands severely attenuate signals, and there is no mechanism for communication from the uphole to the downhole, hindering dynamic adaptation of data transmission.
Innovation Solution
Applying forward error correction (FEC) codes to data and modulating it into multiple sub-bands with spaced apart center frequencies for concurrent transmission over a banded communication channel, allowing data to be transmitted across both pass-bands and stop-bands, even when the frequency-domain locations of pass-bands are uncertain or changing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If acoustic telemetry is used to communicate MWD information through the drill string, then data transmission from downhole to uphole is enabled, but the banded nature of the acoustic channel with stop-bands causes severe signal attenuation and unreliable communication
Solution Approach 1:
The patent segments the data transmission into multiple frequency sub-bands, distributing data across multiple channels. This allows the system to bypass stop-bands by transmitting different portions of data through different frequency paths, thereby overcoming the attenuation problem and improving communication reliability
Solution Approach 2:
The system dynamically changes transmission parameters including frequency selection and power allocation based on channel conditions. By adapting transmission frequency away from stop-bands and adjusting power levels, the system maintains reliable communication despite the banded nature of the acoustic channel
2Reliability
If forward error correction codes are applied to data before transmission, then data can be decoded at the receiver even when portions are transmitted into stop-bands, but the device complexity increases
Solution Approach 1:
The patent applies forward error correction encoding to the data before transmission, preparing the data in advance to withstand potential losses. This preliminary action ensures that even if portions of data are attenuated in stop-bands, the receiver can still reconstruct the original information, improving reliability despite the added encoding complexity
3Adaptability or versatility
If data is modulated into multiple sub-bands with spaced apart center frequencies for concurrent transmission, then data can be transmitted across both pass-bands and stop-bands, but the device complexity increases
Solution Approach 1:
The patent divides the data stream into multiple sub-bands with spaced apart center frequencies, allowing concurrent transmission across different frequency channels. This segmentation enables the system to utilize both pass-bands and navigate around stop-bands, improving adaptability to the banded acoustic channel despite increased modulation complexity
Solution Approach 2:
The system transitions from single-frequency transmission to multi-frequency sub-band transmission, adding a frequency dimension to the communication. This dimensional expansion allows data to be transmitted across multiple frequency paths simultaneously, enhancing channel utilization and adaptability
Data Source
AI summary
A communication method is provided for a communication system comprising a transmitter and a receiver. The method involves communicating data from the transmitter to the receiver over a banded communication channel. The method comprises: applying a forward error correction, FEC, code to data to be transmitted to obtain FEC-encoded data; assigning the FEC-encoded data into a plurality of sub-channels; modulating the data from each of the plurality of sub-channels into a corresponding one of a plurality of sub-bands, the plurality of sub-bands having spaced apart center frequencies; and concurrently transmitting the data from the plurality of sub-bands onto a banded communication channel, the banded communication channel comprising one or more pass-bands and one or more stop-bands.