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How Users Access Internet on Board?

Wi-Fi

Deploying a WLAN such as Wi-Fi within the train is the approach chosen unanimously by all deployed solutions [1,2]. The deployment of a wired Ethernet network could be considered. However, it causes very high installation costs, especially since it requires equipment of all “connected trains” [3]. Rewiring may also be needed every time the train is reconfigured. In addition, it is generally accepted that replication concept of Wi-Fi access points within the train is not only the best technical solution to create “connected trains”, but also the ideal client interface [1]. Wi-Fi is a well-known technology with unlicensed bands, easy to roll out and cost effective. The different standards of Wi-Fi IEEE 802.11 are reminded in the Table 2.1.

IEEE 802.11n allows achieving theoretical throughput up to 450 Mbps on each available band (2.4 and 5 GHz). It improves the previous standards: IEEE 802.11a on the 5 GHz band, and IEEE 802.11b and IEEE 802.11g on the 2.4 GHz band by the following enhancements:

  • • The standard relies on the Multiple Input Multiple Output (MIMO) technology;
  • • The aggregation of channels allows increasing the bandwidth to 40 MHz, instead

of 20 MHz for previous standards.

In [3], two different topologies are studied in order to construct the network on board train using Wi-Fi technology. The wireless coverage in a single carriage is easily achieved via an Access Point (AP) by using IEEE 802.11a. The issue is the wireless distribution network, whose goal is to interconnect the different carriages. The first topology consists in linking the different cars with IEEE 802.11b via external directive antennas. The second topology is based on the assumption that the access network (IEEE 802.11a in each carriage) is also used as a distribution network between the different carriages. The paper concludes that these propositions still have to be tested by real experiments.

Finally, the last Wi-Fi standard developed from 2011 to 2013 was approved in January 2014, the so-called IEEE 802.11ac. It uses the 5GHz band exclusively. Theoretical throughput of 500 Mbps can be reached and up to 7 Gbps by using multiplexing and MIMO techniques. The main drawback of this new standard is

Table 2.1 Main standards of the Wi-Fi IEEE 802.11

Standard

Standardization

Frequency

Theoretical throughput

IEEE 802.11a

1999

5 GHz

54 Mbps

IEEE 802.11b

1999

2.4 GHz

11Mbps

IEEE 802.11g

2003

2.4 GHz

54 Mbps

IEEE 802.11n

2009

2.4/5 GHz

450 Mbps

IEEE 802.11p

2010

5.85-5.925 GHz

/

that terminals have to be specifically designed for this new technology. However, equipped terminals can support 802.11n standard (but not a, b and g ones).

Some researches investigate also very recent technologies, such as the new IEEE 802.11ad, or WiGig (at 60 GHz), and the Li-Fi. They are presented in the following.

 
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