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WiFi on trains | Advantages of WiFi at metro stations and rail tunnels

This article covers possible wifi network architectures used to provide internet service on board trains. It covers benefits or advantages of wifi on trains including working of wifi rail architectures for moving trains, covered metro stations and rail tunnels. The article mentions Wi-Fi on rail products and solutions providers or vendors.

Introduction: WiFi is very common across the world. It allows us to connect our smart devices with the internet wirelessly. It uses electro-magnetic radio waves at various frequencies viz. 2.4 GHz, 5 GHz and 6 GHz as per supported WLAN chips. In order to allow increased data rates and enhanced coverage, various WLAN standards have been developed. The WLAN follows IEEE standards which include 802.11b, 11a, 11g, 11n, 11ac, 11ax, 802.11be etc. The WiFi network is usually used for higher data rates with limited coverage and mainly developed to support devices inside buildings, offices, railway stations, airports, trains etc.

Initially WLAN (Wireless Local Area Network) standards have been developed to support smart devices at lower mobility. IEEE 802.11ax version supports higher mobility to allow internet access in vehicular bound devices using wifi hotspots. Cellular technologies follow 3GPP or ETSI standards and are mainly targeted for use in outdoor environments for high speed moving vehicles. Cellular standards include 2G (GSM), 3G (UMTS or CDMA), 4G (WiMAX, LTE) and 5G NR (New Radio). WiFi service is provided by installing 802.11 AP (Access Point) called WiFi Router. Cellular service is provided by installing Cell tower along with backbone infrastructure for PSTN/PSDN interfacing. Satellite network provides connectivity in remote areas where cellular towers are not available or not feasible to be installed in rural and hilly terrain regions. Satellite offers much wider coverage of the Earth due to its location at very high altitude above the Earth.

For railway, specific cellular standards have been developed which include GSM-R and LTE-R with following specifications. Following table mentions main features of wifi and cellular standards (GSM-R, LTE-R and 5G NR).

Features WiFi-6/6E (IEEE 802.11ax) Cellular (GSM-R) Cellular (LTE-R) Cellular (5G NR)
Frequency 2.4 GHz, 5 GHz, 6 GHz 876 to 880 MHz, 912 to 925 MHz 450, 800, 1400 MHz 3.5, 28, 34, 66 GHz
Channel Bandwidth 20 to 160 MHz 0.2 MHz 1.4 to 20 MHz 1.25 to 400 MHz
Data rate i.e. throughput 600 Mbps (80 MHz, 1 Spatial Stream-SS), 9.6 Gbps (160 MHz, 8 SS) 172 Kbps per channel 50/10 Mbps 4 Gbps per channel
Mobility 300 Km/h 350 Km/h 500 Km/h 500 Km/h

Table-1 Comparison of WiFi and Cellular technologies

There are different bands used in satellite communication network viz. L band (1-2 GHz), C band (3700-4200 MHz in downlink and 5925-6425 MHz in uplink), Extended-C band, Ku band (11.7-12.7 GHz in downlink, 14-14.7 GHz in uplink) and Ka band (18.8-19.3 GHz in downlink, 28.6-29.10 GHz in uplink). Most commonly used satellite transponder bandwidths are 36 MHz and 72 MHz. These entire bandwidths are used for multiple voice/data calls by ground station users based on various multiple access techniques.

WiFi network architecture at Home

The simple WiFi system consists of one WiFi router at home which is connected with ISP (Internet Service Provider) on one side and with WiFi Clients (i.e. Stations) on the other side. Usually cable modem or suitable modem is required based on technologies used by ISP to interface with WiFi router as shown. Over the years various technologies are used by ISP to provide internet service to the users which include dial up internet, ADSL/SDSL, Cable internet, ISDN, Ethernet, fiber optic, satellite, WiFi and cellular broadband.

wlan, WiFi architecture
Figure-1 WiFi network architecture at Home

WiFi router allows multiple wifi compliant smart devices to share single internet connection. Hence more than one people can use the single high speed internet comfortably and affordably.

WiFi router comes with ethernet ports. Hence desktop computers or laptops with 10/100/1000 Mbps LAN devices can easily be interfaced with these ports using ethernet cables. WiFi hotspots are installed using wifi routers at shopping malls, railway stations, airports, businesses to provide internet service to customers or passengers. These wifi routers are connected with ISP.

Wifi network for moving train | How it works

Internet requires connectivity with ISP through various wired or wireless technologies. When train is moving at higher or lower speeds wired technologies are not feasible to be used. Hence cellular or satellite technologies are essential to provide internet connectivity using EM (Electro-Magnetic) waves to the train passengers.

Architecture of WiFi on Trains
Figure-2 WiFi architecture for on board trains

Each train compartments are equipped with one or multiple WiFi routers or APs. All these APs are connected to multi port gigabit switch using ethernet cables. Multimedia Server is connected to gigabit switch using ethernet cable to help in configuration and monitoring of all the APs and gateway. The WAN gateway is the device which provides connectivity between APs inside train and outside network (cellular or satellite). Gateways use specially designed rail antennas on roof of the train for this purpose. Based on the user requirements, multiple WAN gateways are installed in the trains.

MOXA Inc. offers solutions for onboard wifi broadband access and seamless train to ground communications as per following table.

MOXA Solutions for WiFi on Train
WiFi Access Point as per 802.11n
Model AWK-3131A-M12-RCC
Gigabit 12 port switch
Model TN-G6512
WAN Gateway
Model UC-8580/UC-8540
Media server
Model V2400A

Table-2 MOXA Products

Fluidmesh Networks offers solutions for commercial rail and passenger rail systems. It has products for intra-train solutions and train to ground communications. The company has been acquired by Cisco in July, 2020.

Fluidmesh Networks Solutions for WiFi on Train
Wireless bridges for intra-train solutions for throughput up to 500 Mbps. Gateway , models FM1000GWY and FM10000GWY Fluidmesh 4500 MOBI wireless broadband for fast moving vehicles Long range wireless bridges (Model Fluidmesh 1300 OTTO) Wireless backhaul called VOLO

Table-3 WiFi Solutions for Train by Fluidmesh Networks

WiFi/Cellular architecture for covered metro stations and rail tunnels

It is challenging to provide internet connectivity on trains when they are in underground stations or covered metro stations or in tunnels. There are many approaches which can be used for these scenarios. Initially repeater based solutions have been used in tunnels. In this approach, series of repeaters are used between APs mounted on two ends of the rail tunnel. These WLAN APs are connected with cellular tower available on the track side.

WiFi Cellular Architecture for Tunnel Rail System
Figure-3 WiFi/Cellular architecture for covered metro stations and rail tunnels

The other approach is under development which uses latest 5G NR cellular system. In this system, 5G NR RRUs and BBUs are connected together using Optical Fiber Cables (OFCs) and Optical to RF and RF to Optical converters as shown. Number of WLAN APs are also installed inside the rail tunnels or Capsules in hyperloop technology. These Multiple WLAN APs are connected together using OFC.

Advantages of WiFi on board trains

Following are the generic benefits or advantages of wifi on board trains:
➨The WiFi service allows passengers to be connected with their friends and relatives during journey.
➨Business personnel can continue their work while sitting in the trains.
➨The service is almost free and hence passengers can pass time by watching movies and listen to their favourite songs.
➨The train accidents or minor faults in the trains can easily be notified from remote hilly locations to their controlling stations located miles away.
➨The technology provides real time train control.
➨It makes it easy to have safety related applications such as CCTV streaming, door clearance, mission critical voice and passenger information systems.

The complete solutions are very expensive to be installed on all the trains. The benefits and drawbacks of the system largely depend upon specific technologies used for providing the internet service in the train. Reader can derive the same based on different train bound technologies such as ethernet, wifi, cellular, satellite etc. Refer advantages and disadvantages of WiFi 802.11ax, Cellular network and Satellite internet for more information and to know their respective merits and demerits.



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