Life in the AtacamaCarnegie Mellon Communications Testing Michael Wagner Dominic Jonak Robotics Institute July 28, 2003

Life in the AtacamaCarnegie Mellon VHF Testing Purpose VHF communications are very dependent on noise and soil properties Pittsburgh region has numerous transmitters, the desert’s radio environment is quite different Pittsburgh and Atacama are geologically distinct Understand tradeoffs to design a very long-range, intermittent comm solution for subsequent years

Life in the AtacamaCarnegie Mellon VHF System Operates on 144 – 148 MHz licensed band Very long range, non-line of sight Tested connectivity between stations at 9600 bps ModemRadio Amplifier (25 W) Omni-Antenna 6 dBi Remote (truck) Modem Radio (50 / 10 W) Yagi Antenna 7.8 dBi Base RS-232

Life in the AtacamaCarnegie Mellon April 27 April 25 April 26 Ops Tent / Antenna 4.2 km 1.4 km 8.7 km 20.1 km 9.7 km VHF Connectivity Tests April 25 – 27 “Green Hills” Salt Mine

Life in the AtacamaCarnegie Mellon April 25: Links Established 20 m Link established

Life in the AtacamaCarnegie Mellon April 26 “Green Hills”: Links Failed 150 m Good voice, But link failed

Life in the AtacamaCarnegie Mellon April 27: Mixed Results Link successful at low power Link failed at high power Salar – no data in DEM 70 m

Life in the AtacamaCarnegie Mellon April 27: Link Failed 110 m Link failed

Life in the AtacamaCarnegie Mellon VHF Testing Conclusions The VHF comm system tested is capable of supporting intermittent, low data rate connections at ranges on the order of 10 km Much further range (>20 km) is likely with: A higher antenna mount (~20 ft) A higher-gain antenna (~13 dBi) Automated pointing at base camp (only 10 deg accuracy required) Comm-based mission planning onboard robot – based on LOS results from tests

Life in the AtacamaCarnegie Mellon 900 MHz Testing Purpose Understand suitability of 900 MHz system for a wireless Ethernet replacement Longer range, but lower data rates

Life in the AtacamaCarnegie Mellon 900 MHz System Good theoretical range (> 10 km), but dependent on line of sight Tested connectivity between robot and base at bps System can operate at 9600 to 115,200 bps Radio Modem Omni-Antenna 5 dBi Remote (Hyperion) Radio Modem Omni-Antenna 3 or 8 dBi Base RS-232

Life in the AtacamaCarnegie Mellon 900 MHz Link Continuity Example Base Station – Rover path during test Comm dropout >1 sec 170 s <5 s 42 s

Life in the AtacamaCarnegie Mellon 900 MHz Testing Conclusions Several advantages over 2.4 GHz Small 3 dBi antenna matched range of high-gain 2.4 GHz antennas, 8 dBi antenna should do far better Smaller antenna means less panel shadowing / mechanism interference Directionality still very important Did not collect enough data to determine relationship between distance and data rate Future 900 MHz systems should have: Very tall antenna mounts or well-placed repeaters Directional antennas with automated antenna pointing Comm-based mission planning onboard robot

Life in the AtacamaCarnegie Mellon 2.4 GHz Description Moderate range (few km), but extremely dependent on line of sight Tested connectivity between robot and base from 1 to 11 Mbps Radio Modem / Bridge Omni-Antenna 15 dBi Remote (Hyperion) Ethernet Radio Modem / Bridge Omni or Grid Antenna 15 or 24 dBi Base Ethernet Radio Modem / Bridge Omni-Antenna 8.5 dBi Repeater Ethernet

Life in the AtacamaCarnegie Mellon 2.4 GHz Conclusions Needed to reposition repeater station very frequently, sometimes 3 or 4 times per day Repeater movements would interrupt operations for 20 – 60 minutes Automatically-maintained network maps were not reliable

Life in the AtacamaCarnegie Mellon Telemetry Log Volume Collected telemetry logs over entire expedition Includes gigabytes of inter-process messages, commands and telemetry Does not include science data Analyzed the contents of logs over 10 days Over 2.5 million messages logged Over 3 GB of data logged

Life in the AtacamaCarnegie Mellon Telemetry Log Composition 10 Most Common Messages Inadvertently 5 Hz

Life in the AtacamaCarnegie Mellon Telemetry Log Composition Size of 10 Largest Messages 2401 MB 555 MB

Life in the AtacamaCarnegie Mellon Telemetry Log Composition Size of 8 Next Largest Messages (Excluding imageMsg and lolCompImageMsg) 1152 ~2 Hz 46 MB 30 MB 16 MB 18 MB

Life in the AtacamaCarnegie Mellon Telemetry Manager Improvements Must operate over low-bandwidth, intermittent communications link How to prioritize data for remote operators? Consider what tasks remote operators need to do Provide only the data that enables these tasks For instance, if pitch angle limits exceeded, return recent rover pose and terrain maps to assist recovery Will require that the TM cooperate with other software modules