OLPC France's long distance Wi-Fi installation in Nosy Komba


The OLPC deployment in Antitourna, Nosy Komba is located in the island of Nosy Komba, between the island of Nosybé and the « great island » of Madagascar. The OLPC deployment done by OLPC France consists of 160 XOs + 1 XS installed in the primary school of the village of Antitourna. This village is located one-hour away (by boat) from the city of Hell-Ville in Nosybé.

The GPS coordinates of the Antitourne school is : 13°27'03.50'' S, 48°21'34'' E and the the GoogleEarth KMZ file can be found here. Pictures of the deployment are available in this and that blog post and on OLPC France's Flickr page.

Architecture of the long distance wifi deployment

After the deployment of the XS server at the Antitourna school, OLPC France decided to find a way to connect the school to Internet with an affordable and reliable solution operated by a local team in Nosybé / Nosy Komba area.

Internet connexions in the island of Nosy Komba are currently (Sept 2011) only wireless solutions (VSAT-IP, WiMAX, 2.5/3G usb dongle) that either are costly and latency intensive (vsat, wimax) or non-reliable in terms of bit rate (2.5/3g).

However Madgascar has a pretty good DSL coverage through the national ISP Telma and proposed a DSL subscription (512k or 1M downlink) in Hell-Ville (on the island of Nosybé) with a reliable throughput due the optical fiber connecting Madagascar to the African optical loop (sometimes hybrided with long distance wireless connexions in the 21GHz band).

The targetted architecture was then to connect the Antitourna school to a DSL wired connexion in Hell-Ville even if the GPS coordinates from the school indicates no direct line-of-sight with Hell-Ville (cf the KMZ file indicating the 2 points of connexion).

The island of Nosy Komba is like a mountain in the sea with a stip up-hill path to the top. A point of relaying for the wireless signal was then identified with 2 direct lines-of-sight to Hell-Ville and to Antitourna primary school. Below is the global architecture of the Internet connexion:

On the school, a normal Internet access architecture was configured with a switch connected to the receiving UBNT Airgrid5 and to the XS server as Internet Gateway for the local wireless network and the local services for the XOs. The XS has 2 network interfaces (one for Internet and one to the local wireless router in bridge mode to serve connectivity to the XOs).

The main devices used to set-up the long shot wifi in the 5GHz band was Ubiquity Airgrid5, below is a picture with the 27dBi antenna and the active head with the router inside, powered by PoE (Power over Ethernet).

Technical details of the deployment

Location Hardware Power supply
Hell-Ville high point DSL router (Zyxel)
UBNT Airgrid5
PoE (UBNT passive injector 220-to-5V)
1 UBNT requires less than 5W under
Nosy Komba wireless relay 2 x UBNT Airgrid5
DIY-made RJ45 female-to-female connector between the 2 UBNT
50W/12V solar panel (Femtoni SS50 2.78A )
Solar charge controller (Steca Solsum 6.6F 12/24V, 6A)
3 x 12v batteries (intact block-power BP 12-7.0, 7.0Ah, 1.75V/cell@ 20°)
12V/5V DC-DC converter (for the UBNT passive PoE injector)
crepuscular relay for night power switching
Antitourna school 1 UBNT Airgrid5
1 Switch
1 FON 2200 (main)
1 wireless router (back-up)
250W solar panel (used for XOs also)
12V/220V DC-AC converter
APC for the technical room (XS, wireless router)

The final pole installation at Nosy Komba Relay.

The video-conf with the Antitourna school during Sugar Camp #2 in Paris.

Note: You can also download this report as in a PDF version.

Xavier Carcelle is OLPC France's wireless networking guru.


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