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

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:

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

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

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

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 !..

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

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.

S-parameters First measurements up to 100 MHz

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).

Data transmission test Specifications of critical components (buffer and equalizer) Buffer (DS15BA101) Equalizer (DS15EA101) Power @1.25 Gbps (mW) 142 198 Timing Transition time low >> high typ / max (ps) 120 / 220 100 / 220 Transition time high >> low Total jitter @1.5 Gbps (typ) 26 ps 0.25 UI = 166 ps (cat 5e, 25m) Maximum cable loss 35 dB @ 750 MHz

Data transmission test Setup

Data transmission test Data transmission OK @ 800 Mbps with 50 m of P-31000 cable

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

Data transmission characterization Example of results @2 Gbps with standard coaxial cable Eye diagram Jitter amplitude vs. time Jitter dispersion BER (bathtub curve)

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

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-31000 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).