Symbol synchronization for downhole OFDM telemetry
US8749400B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | Aug 18, 2008 |
| Grant date | Jun 10, 2014 |
| Priority date | — |
| Expiry date | Jan 16, 2033 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L2025/03414
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
Enhanced symbol synchronization methods suitable for use in narrowband orthogonal frequency division multiplexed (OFDM) telemetry systems. In at least some embodiments, a logging while drilling (LWD) tool assembly communicates with the surface using low frequency electromagnetic (EM) signals. The telemetry transmitter employs OFDM modulation to fully exploit the narrow range of available bandwidth, resulting in signals that have relatively long frames. At the surface a receiver digitizes the receive signal and applies an enhanced symbol synchronization technique to identify frame boundaries before demodulation is attempted. The enhanced symbol synchronization technique employs a pulse train filter to clean up a cyclic prefix correlation signal that otherwise behaves badly in the narrowband regime. The improved timing information from the enhanced symbol synchronization significantly reduces the error rate in the demodulated signal.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.