# Research on Key Technologies of 260 \({}^{\circ}\)C/210 MPa Ultra-Deep Logging Equipment
## 3 Research on Key Technologies of Ultra-High-Temperature and High-Pressure Logging
### Data Transmission over Ultra-Long Cables  
The high-reliability data transmission system for 10,000 m cables overcomes the communication challenges of a 15,000 m ultra-long seven-core cable, achieving an uplink data rate of \(\geq\)200 kbps and a downlink command rate of \(\geq\)20 kbps. For the measurement of ultra-long cable characteristics, the attenuation characteristic parameters of 6500 m and 13,000 m seven-core cables were measured, and the actual measurement data and attenuation curves are shown in Table 1 and Figure 12. Based on these data, the following conclusion was drawn: the usable cable bandwidth frequency for the 13,000 m ultra-long cable is a maximum of 100 kHz. The measurement waveform is shown in Figure 13. The green signal represents the 100 kHz, 4 Vpp input waveform at the cable's input end, the blue signal represents the output waveform at the cable's output end, and the center line represents the Fast Fourier Transform (FFT) frequency amplitude waveform. The attenuation test comparison data indicated that over the 13,000 m ultra-long cable, the receiving end of 1 kHz signal is 1200 mV, while t the receiving end of 90 kHz signal is 50 mV. The amplitude ratio of the two signals is 24 times. In addition, the group delay at the receiving end of the 90 kHz signal is quite large, which may lead to signal distortion or delay. When the frequency is further increased, the frequency and phase of the received signal cannot be resolved through FFT algorithm. To ensure reliable data transmission within this frequency band, the following key technologies are utilized: time-division half-duplex working mode, RS forward error correction coding and decoding technology, frequency pre-emphasis technology, real-time modulation constellation allocation technology, PID synchronization for clock signals, and channel characteristic evaluation statistics. Time-Ddivision half-duplex working mode The original megabit remote transmission system used a frequency-division full-duplex mode, where uplink data and downlink commands were transmitted simultaneously along the cable. This required isolating the uplink data and downlink commands in frequency. Downlink commands used a cable bandwidth of 2-18 kHz, uplink data used 40-205 kHz, and the 18-40 kHz frequency band was left unused for isolation. For the 15,000 m ultra-long cable, the communication signal frequency range was 4-100 kHz. The transmission mode has been modified to a half-duplex time-division transmission mode, utilizing the 18-40 kHz bandwidth. This way, during any unit of time, either data or commands can use the entire cable bandwidth exclusively, increasing the bandwidth utilization and effectively improving the data transmission rates and quality. RS forward error correction program design In the previous generation of telemetry systems, RS forward error correction (FEC) processing was used for uploading data. However, since the FPGA's used downhole (Field-Programmable Gate Array) was an ACTEL high-temperature-resistant device, and the company did not provide a free RS decoder IP core, the downlink commands lacked forward error correction functionality and only had CRC checksum functionality. This meant that it could only detect errors but not correct them, resulting in a higher bit error rate for command reception when the cable was long [13], and a significant loss of downlink commands. To improve the accuracy of the downlink telemetry command reception, an RS(24,16) decoder was designed within the ADSP21060 chip of the downhole telemetry  
Frequency pre-emphasis technology  
Given the inherent characteristics of seven-core cables, which exhibit varying attenuation properties for OFDM high-frequency signals--specifically, lower attenuation at lower frequencies and higher attenuation at higher frequencies--pre-emphasis processing has been designed for both downhole and surface modulation signals to compensate for the frequency-dependent attenuation.