1. Data transmission characterization with underwater copper link
Paris, October 15, 2008
Data transmission characterization with underwater copper link
F. Gensolen
CPPM electronics group

2. Summary
Objective:
>> study the behavior and performances of the state of the art underwater copper cables and connectors for high speed data transmission (gigabit),
>> characterize both on the table and under pressure (in situ).
Actions :
>> Define the state of the art underwater copper links (including connectors)
>> Build the setups to characterize these copper links :
1. Impedance profile along the link (cable + connectors) + average impedance
2. S-Parameters
4. Real data transmission test
5. Characterization of the data transmission (BER, eye diagram, jitter)
The measurements we target in order to characterize the quality of the link and the quality of the data transmission are the following:

3. Copper link state of the art
MacArtney Ethernet Instrumentation cable (Seacon unavailable)
1 bar
200 bar
600 bar

4. MacArtney P-31000 cable specs
Not state of the art cable but a good opportunity to start tests

5. Impedance measurements
Instrument and setup
One important parameter to transmit electrical data correctly is the impedance.
We have measured the impedance profile along the connection (including connectors and cable) during a pressure cycle from 1 to 310 bar.
The setup has been installed at Ifremer Brest (France).
Antares like connectors

6. Impedance profile Results for a first pressure cycle from 1 to 310 bar
As the cable length remains the same during the experiment, it shows that the propagation time depends on the pressure !..

7. Average impedance variations
Results for a first pressure cycle from 1 to 310 bar bar)
The cable impedance changes with pressure !..

8. S-parameters
Setup
Important insights into the cable behavior can be achieved through frequency domain analysis in addition to a characterization in the time domain.

9. S-parameters
First measurements up to 100 MHz

10. Data transmission test
Setup
In order to characterize the data transmission over this cable and connectors, we have carried out a real data transmission using :
>> TI board based on TLK2501 serdes as a pseudo-random generator with a BIST test mode (from 600 Mbps up to 2.5 Gbps)
>> NS DriveCable board with buffer and equalizer (150 Mbps up to 1.5 Gbps).

11. Data transmission test
Specifications of critical components (buffer and equalizer)
Buffer (DS15BA101)
Equalizer (DS15EA101)
Gbps (mW)
142
198
Timing
Transition time low >> high
typ / max (ps)
120 / 220
100 / 220
Transition time high >> low
Total Gbps (typ)
26 ps
0.25 UI = 166 ps (cat 5e, 25m)
Maximum cable loss
MHz

12. Data transmission test
Setup

13. Data transmission test
Data transmission 800 Mbps with 50 m of P cable

14. Data transmission characterization
Setup
In order to have an indication of the performance margin of the data transmission (bit error rate, total jitter, eye opening..) we use the Lecroy SDA11000 serial data analyser to characterize signals coming out of the cable.
The setup includes :
>> TI board based on TLK2501 serdes as a pseudo-random generator (from 600 Mbps up to 2.5 Gbps)
>> NS DriveCable board with buffer and equalizer (150 Mbps up to 1.5 Gbps)
>> LeCroy SDA11000 serial data analyzer.
Digital pattern generator
HP-81110
Buffer
Serial data analyzer
Clock
LeCroy
SDA11000
DriveCable
TLK2501
Equalizer

15. Data transmission characterization
Example of Gbps with standard coaxial cable
Eye diagram
Jitter amplitude vs. time
Jitter dispersion
BER (bathtub curve)

16. Summary of measurements
Measurements for copper link characterization :
1>> Impedance profile along the underwater link (cable + connectors)
and average impedance of the cable
2>> S-Parameters
3>> Real data transmission tests
4>> Characterization of the data transmission (BER, eye diagram, jitter)
Physical
modeling
for simulations
Data
transmission
characterization

17. Conclusions
1>> MacArtney Instrumentation cable with connectors is the state of the art copper link available
>> purchased and waiting for them (December)
2>> First pressure measurements on the P MacArtney underwater cat 5 copper cable showed that characteristics changed with pressure
3>> All the electronic and instrumental setups are ready for a complete characterization of the links, both on the table and in hyperbaric tank (January).