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SwissEx:WifiFrom SwissExperimentWifi
Long distance Wifi Links
In order to get the data to a point where coverage is available, or in high data rate cases, where HSPA or UMTS coverage is available, SLF are developing and trialling a multi-hop wifi link. This link is to be mobile enough that it can be deployed in the event of a short term experiment to allow real-time data transfer. Davos Radar data linkWifi equipment such as that described below is in operational use to retrieve data from the LTE Radar and to link the radar to the internet so that it can be remotely operated from anywhere in the world. Such equipment allows the high data rates required to return the data (not currently achievable using mobile networks) as well as being operable in any area regardless of the mobile telephony infrastructure. The link currently operates over a 2.6km stretch, providing data rates of approx. 16Mbits/s. This initially seems to be regardless of weather conditions, although performance plots will be posted here as they become available. The network scenario is shown below:  This network is attached to the radar at one end and the server PC at the valley end. The server is connected (on a second network card) to the internet. Data is regularly transferred from the radar to the server PC, where it is stored. As internet data upload rates do not currently suffice to transfer this amount of data continuously, certain periods of interest will be picked out of this data set for further processing. Hydrosys in-field mobile device coverageThe next step in SwissEx/Hydrosys's wifi developments will be to interface the current data transfer setup to a sector antenna. This will provide the wifi coverage required by Hydrosys mobile devices on the Dorfberg fieldsite. The step after this will be to interface it with 3G technologies and power it by a solar panel. The wifi equipment, together with the sector antenna will then be mounted on the ridge above the Hydrosys La Fully fieldsite in order to provide wifi coverage on the glacier for the mobile devices. Davos Test NetworkEngineers at SLF are building a test network to demonstrate this capability: SLF's test network will transfer data to and from the Wannengrat field site. A long term test will provide information on the stability of the network during wide ranging meteorological conditions. This network will transfer data to the home of some ex-SLF employees, who serve as the hosts of the Davos network nodes. From here, data will be transferred over 3G network technologies to a server at WSL, Birmensdorf (Zurich), where GSN has access to. The Hardware The test network consists of several ALIX PC boards as shown below: Davos: Alix2d2 with two Compex WLM54sag23 miniPCI wifi cards. Both of these wifi cards are running at 2.4GHz. One card is to supply a wireless internet connection for the host family and the other is to transfer data to and from the roof network node. SLF engineers are currently completing the connection to the Birmensdorf server from this router using a Sierra Wireless Compass 885 USB modem Davos Roof: Alix3d1 in an outdoor enclosure with two Compex WLM54sag23 miniPCI wifi cards, one to receive/send signals from/to the Davos node at 2.4 GHz and one to transmit to the Wannengrat node on 5.8GHz using a 27dBi Grid Antenna Wannengrat: Alix 2d3 with one Compex WLM54sag23 miniPCI wifi card connected to a 27dBi Grid Antenna situated at the Wan3 Meteostation. 5.8GHz was chosen as the long distance transmission frequency as this frequency, although generally attenuated more, is less absorbed by precipitation - something which has to be taken into account in the alps. For most purposes, Mikrotik RouterOS was used to reduce setup time. However, for other purposes, such as the connection of the USB modem, installation of Voyage Linux is required.
The test set up is as shown below:
The network functions as a bridge, allowing direct access to all three LAN inputs at Wannengrat from the Davos end. More details and images to follow. Contact: Nicholas Dawes
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