Sustainably solar and wind powered wireless networking for Internet café at the Big Green Gathering (BGG) Festival, July 2002

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Teepees and young lad with laptop.

At the Big green Gathering (BGG), held at Fernhill Farm in Compton Martin, Somerset, UK, from 21-25 July 2002, Psand.net ran a truly mobile, sustainably powered satellite wireless network. This page attempts to cover what we did, how we did it, and some of the lessons learnt.

Thanks to DC-Sat.Net for loan of the satellite hardware and advice, and also to Groovy Movie for providing enough solar power to make it possible.

Overview

Connection to the Internet was made using a bi-directional microwave satellite link, with a 90 cm dish mounted on top of an ex-TVS (Television South and South East) microwave links vehicle. This connection was then shared out via a modified Apple Airport Basestation. The Airport Basestation's wireless signal was augmented using a quarter wave omni-directional antenna placed at the top of a mast on the vehicle.

Network diagram for the network.
Network diagram for the wireless network.

Public access terminals were provided at the festival; a Mac iBook, two Mac PowerBooks, and two Dell Inspirons. The Macs were running OS X 10.1, one Insipron Windows XP and the other Debian GNU/Linux running X. This gave visitors a choice of operating systems with which to feel at home, and a chance to compare them. Two other visitors to the festival brought laptops and wireless cards and were able to share the Internet connection. We were fortunate to have the Laguna Blu Cafe (also solar powered) as a venue, providing outdoor seating under umbrellas, and a choice of coffee and tasty cakes!

The Laguna Blu Cafe.
The Laguna Blu Cafe, with five laptops running.

Power for the network and laptops for the whole event was to be provided by solar power from the Sun, but in reality, there was not enough bright sunlight over the five days to run solely on a single solar panel mounted on the vehicle roof (86 Watts max), so we used power supplied by Groovy Movie's bank of solar panels. This also allowed us to charge some of the various laptops we were using, and provide over 2 hours of public access daily. When the lack of sunlight meant that we could only run the connection, but not charge the laptops. we borrowed a pedal generator and used that to produce power to charge one laptop at a time, whilst in use.

The event was technically successful, and proved to be very popular and thought-provoking to visitors and spectators. The uses for the network were diverse, although e-mail was the most popular of the available services.

The only real problem was the shortage of power. This could easily be rectified by the use of more solar panels, better weather, or more use of diverse sustainable power sources, such as wind and pedal. Unfortunately due to a lack of space, imposed by Health and Safety requirements, we were unable to use a wind generator during the event.

The satellite connection

We used the Astra 1H satellite to provide internet connectivity. This transmits and receives signals via the Astra Broadband Interactive Hub in Betzdorf, Luxembourg, which acts as ISP (Internet Service Provider), giving us 17 fixed IP (Internet Protocol) addresses.

The satellite hardware.
The satellite dish mounted on top of a vehicle.

The uplink is in the 29.5 to 30.0 GHz (Ka band) and has a throughput of 384 Kbps, and the downlink is 12.7 GHz (Ku band), with a throughput of 1 Mbps (capable of 6 Mbps on request). Ping time is around 650 ms.

It was required that we obtain a licence for the uplink for the duration of the festival and for this we supplied Astra with the GPS co-ordinates for the location.

The IP address of the satellite indoor unit was 10.251.144.30

Using the satellite hardware

The vehicle rooftop.
The roof of the vehicle during set-up, showing the satellite hardware, solar panel and antenna mast.

There are major health considerations when setting up the transmit hardware. The beam from the dish is approximately 1 metre wide and has an elevation of 30 degrees above the horizon at around 161 degrees (19 degrees East of South). For this reason, we aligned the vehicle so that the dish could go in one corner of the roof, where nobody could pass in front of it, checking that no other obstructions were near the path of the beam. This is crucial. We then jacked the truck body up on four jacks, one at each corner, just enough to start lifting the weight of the box off the springs, until no discernable sway could be felt.

The truck used has a solid, walkable, flat roof. We placed a SAT 5/B mount (from Eurosat in Bristol Tel: 0044 1454 616479) in the southerly corner of the roof, and clamped it down with two scaffold poles crossing the truck roof. The satellite hardware was then clamped to this and the alignment and configuration done. The alignment is performed by fine-tuning the satellite dish to maximise the signal strength received from one of the television channels carried by the Astra satellite.

Aligning the satellite dish.
Aligning the satellite Dish.

Spectrum analyser.
Spectrum analyser used to align the satellite dish, showing the regular spiky digital signals on the left and messier analogue signals to the right, all coming from the Astra satellite.

Once the connection was up and running both ways, we needed to change the TCP window sizes to allow full speed file transfer.

The wireless network

The wireless network was implemented using 802.11b, a public, unlicensed band between 2.4 and 2.45 GHz. Bandwidth is rated at 11 Mbps and after packet handling can achieve throughputs of up to around 6 Mbps

The satellite Indoor Unit was connected via category 5 Ethernet to the LAN port on an Apple Airport Basestation (Apple's UFO-like wireless hub and router). Despite the Airport Basestation's lovely design and functionality, it has no external connection for extended range antennae. Modifications had to be made, which involved removing the Torx bolts in the bottom of the Airport Basestation, taking the casing apart and finding the external antenna connection on the internal PCMCIA card, just visible in a gap in the shielding inside. We drilled a hole in the top of the Airport Basestation casing and passed a standard pigtail connector through, plugging it into the PCMCIA card. We re-assembled the case. The pigtail then terminated in an N-type socket connector.

Modified Airport Basestation.
The modified Airport Basestation, showing N-type pigtail attached.

A 6 metre N-type cable (URM67, signal loss of around 0.3 dB per metre) took the radio signal from the Airport Basestation up to the top of the mast on the vehicle at 5.5 metres from the ground. Here a homemade quarter wave omnidirectional antenna was used to achieve a much larger radio cell than would be possible with just the Airport Basestation. A line of sight to this antenna was then possible from almost all of the festival site, even over the top of a double-decker bus that was parked nearby to the transmitting mast.

Quarter wave omnidirectional antenna
Homemade quarter wave omni-directional antenna for 2.4 GHz mounted on top of the vehicle mast.

The IP address of the Airport Basestation was fixed at 10.251.144.28 with default gateway set to 10.251.144.30 (IP of the satellite indoor unit), Netmask 255.255.255.240. DNS (Dynamic Name Service) for the Airport Basestation was set to 212.56.224.20/194.164.97.10. The Airport Basestation then handed out IP leases over DHCP (Dynamic Host Configuration Protocol) within the range 10.0.1.2 to 10.0.1.200 and it's 'LAN side' IP was 10.0.1.1, hence for a client machine running DHCP:

IP10.0.1.x
Gateway10.0.1.1
Netmask255.255.255.0

We used channel 11, with WEP (wireless Encryption Protocol) turned off, and set the Airport Basestation to high density. There are some screenshots of the Airport Basestation configuration here.

A Dell Inspiron with a Dell TrueMobile 802.11b card could still receive a signal at over 250 metres away (6 dB signal to noise, very low but still useable). By augmenting the 802.11 card with a range extending antenna, it would be possible to obtain a good connection almost everywhere within the festival perimeter.

Notes

Keeping the network alive with Solar Power

The power to run the Internet connection and wireless network came from the sun alone. This involved using a bank of solar panels, facing south, at an elevation of around 50 degrees from the horizon. The current from these was fed down high current cabling into a battery bank, via a diode, which stops current being passed back to the panels at night, and via a regulator, which monitors the DC Voltage of the battery bank and prevents the batteries from becoming damaged by overcharging.

The charge stored in the battery bank is then fed via fused distribution to an inverter. This converts the 12 Volt DC to 230 Volt AC to run normal mains appliances. We only had two appliances to run to keep the network alive - the satellite Indoor Terminal and the Airport Basestation.

Circuit diagram for the solar charging and inverting.
The solar charging and inverting circuit.

Notes

Charging the laptops while in use with Pedal Power

The power to charge the laptops came from a pedal generator. This had been made from an old bike chopped up and welded to a standing frame. The peddles then turned a fly wheel via a chain. The fly wheel powered a car alternator via a large belt. The alternator output was connected to a leisure battery, and the windings excited by connecting to the 12 Volt DC of the battery (normally a car connects these via the igntion switch). Once spinning, the alternator pulled the battery up to around 12.5 Volt whilst pedalling comfortably. A volt meter was visible to help pace pedalling speed.

The pedal generator.
The pedal generator running one laptop.

The 12 Volt DC generated was then treated in exactly the same way as the solar battery power and converted via an inverter to 230 Volt AC. One laptop at a time was then plugged directly into the inverter.

Circuit diagram for the pedal charging and inverting.
The pedal charging and inverting circuit. The windings switch should be closed whilst pedalling.

This allowed us to run an iBook and a Powerbook simultaneously without any other external supply, and prevent the battery from losing charge, providing there was a steady stream of pedal-generated power.

Notes

Lessons learnt

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Copyleft

Author: Dave Gough

Copyright (c) 2002 Psand Limited. Permission is granted to copy, distributed and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

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