Wireless Networks in Aircrafts

Over the last decade, wireless networking has become an increasingly popular alternative to the traditional wired networks. One area where wireless networks are of great practical use is the aviation industry. Since aircraft are positioned all over the world, there needs to be an efficient, cost-effective medium to provide data communication in the air. In this paper I will examine developments in aircraft wireless networks (AWN). Next, I will discuss the important research which has enabled wireless technology on airplanes, including services such as OnAir and Connexion by Boeing, which aim to satisfy the demands for in-flight Internet usage. In addition to being used for commercial purposes, the military relies on wireless networks to improve awareness and information-availability to warplanes. The development of AWNs for the military is most advanced in terms of standardization and popularity, but for the sake of brevity, this paper will only examine the commercial side of AWNs.

In this section, we examine previous and current research on AWNs. As mentioned previously, there is an ever-increasing demand for in-flight passenger communication. Therefore, the focus of most pre-existing research has been connecting passengers within an aircraft to the outside world. A common architecture for this process consists of three basic segments: an airplane, a satellite link, and a station located on the ground. On the airplane, a wireless access point can provide connectivity to both passengers and crew. The satellite link provides a connection to the station on the ground, which in turn is connected to the Internet.

The most useful research that is currently being conducted is concerned with finding a way to for AWNs to be more usable and efficient. The major issues in AWN research that I choose to examine are interoperability, interference, mobility, and quality of service.

Interoperability is the notion that different passengers will require different services. This requires the airline company to account for the use of multiple technologies. Two of the most important in-flight services under consideration are Internet and cellular phone connectivity. To provide these services, an airplane must have access points for receiving and transmitting both types of wireless signals. This is done via the satellite link with the ground station.

It is important for AWN specialists to account for and understand interference. It is imperative that in-flight networking does not interfere with the navigation and communication systems needed to safely and successfully operate the airplane. Personal electronic devices emit two kinds of radiation: intentional and spurious. Intentional emissions only transmit data in the allocated frequency bands of the device. Spurious emissions are unintentional and contribute to radio frequency noise. Spurious emissions are more significant in wireless devices. Therefore, if the power level of a spurious emission is high enough at a receiving frequency of aircraft instrumentation, it could possibly interfere with the operation of the airplane (Jahn, 2003, paragraph 12/14).

The large amounts of distance covered by the aircraft raise concerns about mobility and quality of service. Since the aircraft is moving at a rapid pace, the ground stations it communicates with must be able to handle this movement. As an airplane moves out of range of one ground station, it must connect with anew ground station in order to re-establish a path for network traffic. The ground station needs to be able to handle the routing and re-routing of nodes for each aircraft as they are connected and disconnected. This process of switching between satellites and/or ground stations can lead to degraded performance of the network. To combat this, efficient handover algorithms are imperative as airplanes move from one satellite coverage area to another.

A breakthrough research project in the implementation of AWNs was the WirelessCabin. This project was especially usually because it was actually tested on airplanes. The goal of the experiment was to develop a reliable architecture for in-flight wireless connectivity for passengers. The technologies considered for integration in this project included WLAN (IEEE 802.11) and Bluetooth. In the experimental system, a 3G piconet and an 802.11 WLAN were set up for passengers to use to connect to the Internet. In addition, passengers were able to create Personal Area Networks (PANs) for personal devices using Bluetooth. Ideally, all the devices would operate in one environment without the different wireless technologies interfering with each other. The experimental architecture consisted of three segments: cabin, transport, and ground. Network traffic was partitioned into four quality of service classes based on priority as related to real-time requirements. The ultimate test of this experimental system was a demonstration flight aboard an Airbus A340 aircraft in September 2004. During the flight, voice over IP and e-mail and web services were successfully demonstrated (Jahn, 2004, paragraph 9/12/15)

Another successful research project, the Aeronautical Telecommunications Network (ATN), developed by the International Civil Aviation Organization, was created to provide ground-to-ground and air-to-ground data communications services in the aviation industry. ATN is based on the seven-layer Open Systems Interconnection (OSI) model and is a private network with its own IP addresses and a procedure for providing network mobility for airplanes. The organization's solution to the problem of mobility included a large address space and backbone routers which would update information in the network. When an aircraft was in-range of a new access point, it would connect and the associated backbone router would pass the aircraft's network information back through the ATN backbone. Although ATN has been continuously developed for the past 15 years, it is used sparingly for services such as Air Traffic Services (ATS) and Airline Operation Communications (AOC) (Smith, 2001).

So far we have looked at previous research which focused on AWNs. This research is directly correlated to the commercial airline industry's desire to provide Internet connections to passengers while in flight. In the next section, we examine some of the services which are currently used in industry.

Up until recent years, passenger aircraft seemed to be a parallel universe, where the public could not receive Internet connectivity or the services that are offered on the ground (VoIP, etc.). Recent efforts by leaders in the airline industry have started to change this trend. Early on, service offerings were limited by data transfer rates and only used seat-back interfaces. As expected, this practice proved to be unprofitable because the real demand was for high-bandwidth services on passenger's personal electronic devices. In this section we discuss the satellite system owned by Inmarsat which is currently offering in-flight services and is currently developing future services. In addition, we discuss the current market leader in passenger communication services, Connexion by Boeing, which does not use Inmarsat.

There are multiple options for satellite service providers, including Iridium and Globalstar, but the biggest player in satellite communication for commercial aircraft is Inmarsat, an international company which operates a total of 11 satellites. The most widely available of Inmarsat's aeronautical services is Swift64, which offers up to 64 kbps per channel, 6.67 times faster than any of their other services. Swift64 terminals can offer up to 4 channels, thus increasing the data rate to 256 kbps per terminal. Effective data acceleration techniques can boost the data rate close to 0.5 Mbps (Aeronautical, 2005). Another widely praised service offered by Inmarsat is the Broadband Global Area Network (BGAN), which offers up to 492 kbps and can be used to support Internet services. To support this service, Inmarsat has three satellites, one over each major ocean (Pacific, Atlantic, and Indian) (Inmarsat, 2005).

OnAir, a joint venture between Airbus and SITA INC, claims shared data rates of up to 864 kbps. The service will allow in-seat telephony, text messaging, and Internet and will be offered on both Boeing and Airbus aircraft sometime in 2007 (OnAir, 2006).

The first company to market in-flight passenger was Boeing. Implemented in 2004, Connexion by Boeing offers a high-speed two-way Internet connection and global TV. These services are provided on multiple partner carriers on both Boeing and Airbus aircraft (Connexion, 2004). Each transponder provides data transfer rates of 5 Mbps download and up to 1 Mbps upload. Each aircraft may carry multiple transponders, thus increasing data transfer rates to up to 20 Mbps download. Upload capacity per aircraft is capped at 1 Mbps. The service is much like that in a Web cafe, with passengers gaining access to the Internet through a high-speed wireless network. The system, which is also used by executive jets as well as oil rigs and vessels at sea, bounces the Internet connection off a series of satellites (Crampton, 2006, paragraph 5).

In an interesting and questionable move, Boeing decided (in mid-August 2006) to discontinue its Connexion service (Crampton, 2006, paragraph 2). The company cited the lack of demand for the service as the reason for its discontinuation, claiming "the market for this service has not materialized as had been expected" (Boeing, 2006, paragraph 2). Experts maintain, however, that in-flight Internet connectivity is seen by business travelers as an absolute necessity. Boeing's failure might be rooted in the pricing of the service at $9.95 per hour or $26.95 for an entire flight.

Despite Boeing's decision to drop out of the in-flight WiFi market, Airbus plans to continue development and deployment of their much-anticipated OnAir service. "We are full speed ahead with deploying wireless Internet on board our aircraft," says Justin Dubon, an Airbus spokesman (Crampton, 2006, paragraph 16).

AWNs continue to be an area of great interest and development, particularly in commercial aviation. This is driven by passenger demand for in-flight entertainment and communication services. While Connexion by Boeing seems to be disappearing, it was a pioneer for the industry, as it was the first in the airline market to offer services with which passengers could use their own personal electronic devices. Now, the Airbus service OnAir seems poised to take advantage of a traveler's necessity to stay connected with the outside world, even in-flight.

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