The Argenia SilverHawk and SilverFox controllers each have two generic 20 pin sockets that can support several types of wireless solutions. The supported technologies are:
Frequency Hopper Spread Spectrum (902 MHz and 2.4GHz)
Cellular LTE CAT 1 and NB
Digital Mesh at 2.4 GHz
Wifi 2.4 GHz
This paper will discuss these technologies and how they are applied to the Argenia Line of railway specific communication solutions.
Radios operate on the principle that they emit radio frequency energy at a specific frequency and the receiver which is tuned to the same frequency, can receive the signal. In this simple scheme, noise at that frequency can interrupt and totally destroy the integrity of the connection. This would be disastrous for a railway signaling system or any type of vital control operating over wireless channels.
The industry has developed many techniques to combat the interference issue.
This type of radio uses 49 discrete channels in an allocated band and can switch in a series of hops from one channel to another. As long as the receiver knows the same hop sequence, they are easily synchronized so they hop together. Any noise source on a channel blocks that channel, but hopping to another channel occurs simultaneously so the data can be re-transmitted. Several radios may operate in the same band as long as they use a different hopping sequence. There will be some collisions however but communications still get through on the good channels. It would be very unlikely that noise could block all channels at the same time.
Argenia uses FHSS radios for distance up to 4 miles in a stationary Line of Site (LOS) transmission. For vital signalling, we also use two simultaneous radios operating on different hopping sequences. If the probability of losing one channel is 0.1, then the probability of losing both at the same time is 0.01. Then, even if we lose one packet, the next packet is re-transmitted in 0.25 seconds later. A complete loss of data for 5 seconds is considered a dropout and occurs in the vicinity of once per year. On a drop-out, the system would fail-safe, but recover when either radio receive a good packet.
Each radio must use separate antennae and separate towers so a different Line of Site is achieved.
The 902 Mhz radios can emit power at 1 watt so distance of up to 30 miles is possible with good high gain antenna. The 2.4GHz radios are limited to 125 mw and are good to about 4 miles.
Our FHSS radios is used for mobile on-board system and uses a search function where the radios constantly look for better connections and will automatically connect to the best source. This allows the train to automatically connect to each station as the train progresses along its route.
Mesh Radio Technology
This is an incredibly robust network where a lot of radios operate in a limited area, say a railway yard. Frequent movement of trains will block some of the direct LOS paths between antennae, The mesh idea works by having radio software turning every radio into a repeater for the others, creating many different LOS paths. The network software is constantly polling its nodes to determine which radio can connect to others. When a packet is presented by the users system, the radio network already knows how to get to the destination. If any radio losses its first choice receiver, it will use an alternative. The network is constantly re-evaluating and healing broken links. The more nodes on the network the more transmission paths are available.
The repeaters can be simple radios which sit on the RF network and create transmission paths.
The MESH is not ideal for a linear system, such as for a wayside controller along a track. This would allow a direct path between radios but not many alternates. Using a repeater on top of a nearby building and repeaters on trains help create additional paths needed for more reliable networking.
Th Argenia WiFi module provides all the standard functions of any WiFi node. Generally, WiFi is good to connect to a nearby PC and is not used for long distance connections, although up to 1 mile is possible with good LOS and good antennae.
Some railway solutions are made with Wifi Max where additional RF power increases the range of the nodes.
With two general purpose sockets available on the SilverHawk and SilverFox controllers, a wide choice of wireless options are available. The SafeNet Operating system embedded in the controllers assures transparent deliver of data over a variety of networks. For land based communications, the RS485 serial outputs of the controllers can interface directly to fiber-optic transceiver to create fiber networks with spans up to 80 km per segment.
Argenia has significant field experience with various wireless technologies and can assist in designing the proper network for your application.
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