The Tech Behind: “WiFi on Air” at 30,000 feet!

klm-wifi-logo-largeIt’s fascinating to see that many airlines in United States are offering “WiFi on Air” packages to the passengers. Most of the passengers are happily paying for such packages, maybe not as much for actual utility, as for the delight of texting their friends – “Guess where I’m texting from?!” The technology is still in the nascent stage, where you can complain about it being expensive and yet too slow. However, it is undoubtedly a big leap in technology. Let’s see how all of this works out for us at over 30,000 ft!

There are primarily two ways in which a WiFi communication network can be established within the high-flying airplanes.

Air To Ground Based Link: The first one is Air to Ground based, where an antenna is attached to the bottom of the plane to transmit and receive signals from ground based towers. The working is pretty much the same as cellular connections, however the operating frequency is 3GHz. The signal is transmitted from the plane to the nearest ground tower, which in turn relays the signal to the ground station. The ground station transmits the data to the ground tower which in turn relays the signal to the plane. There are almost 200 ground towers in USA that are dedicated to establish this communication network and more and more are coming up. The bandwidth for data is not that great, at 3.2 Mbps, that too not for each customer but for the entire plane! So limit yourselves to texting without any Voice over IP and video streaming applications. Such a communication system can be made more effective by using directional antennas on the plane for a more focused capturing of beam and thus, enhancing the bandwidth to 9.8 Mbps. It is but obvious, that such a system will cry out loud when the plane is flying over water bodies, as there will be no nearest tower to relay the signal to/from!

Satellite Based Link: The second one is Satellite Based network, where an antenna is attached to the top of the plane to transmit and receive the signals to the ground stations via satellites. The plane sends a request for data to the satellites, which communicates the same to the ground station. The ground stations sends the data for the requested web page to the satellite, which in turn relays the same to the plane. In this kind of a communication link we can achieve data rates from 10-30 Mbps. The operating frequency is in the Ku Band i.e. 12-18GHz. The satellites can take care of communication over Atlantic and Pacific ocean too!

It will be intriguing to see how this technology morphs into a more sophisticated form with higher data rates, more connectivity and availability at cheaper cost, in the coming time. The fear of hacking into the plane system is minimal with the differentiation of the operating frequency bands, however, the risk of opening up more an more communication links can’t be denied.


Missing Malaysia Flight 370: Technical Understanding of Tracking Airplanes

While we curse technology for not being able to track the Missing Malaysia Flight 370, everything  still remains a mystery. Failing attempts of the military in gathering any concrete information from the radar observations and air-control traffic management database, have made the situation worse. Being a wireless communication engineer, I was inquisitive to understand the air-ground communication and the scope of it failing this badly. In my first post, I talk of the former.

flowchartA Duplex (two way ) Telecommunication datalink between the aircraft and ground radio is a thing of 1980’s. What used to happen before that?  Well, there used to be a downlink (aircraft to ground radio) voice communication over the VHF Band, where the pilot could send verbal messages to ground station. VHF, for your information, is the very band in which you use the services of FM, Satellite TV and the most modern Digital Radios available today (ex. DRM). What used to happen before that? Well, there used to the Morse Code, where the pilot would look at a chart, spot the symbol that matches his problem and press over it, only with a hope that the circuit completes. What used to happen before that? You mean when the Wright brothers must have faced troubles in their flight? Unfortunately they had to rely on a gun shot in the air and if they fell short of bullets, then shouting at the peak of their voices was the only option.

Fortunately today, both Boeing and Airbus are equally (more or less) competent in adhering to the Aeronautical Telecommunication Network Protocol for Air Traffic Control Communications.  Let us try to understand the working of air- ground trans-reception through this simplified diagram I have made for you.

architectureThe communication system has two deployments: on the aircraft and on the ground.

On the aircraft, the system is composed of an Aircraft Management Unit and an Aircraft Control Display Unit. The management system is efficiently designed to take care of the trans-reception of digital messages, with or without the intervention of the pilot or the flight crew. It has an easy integration with the on board avionics and has a lot of engineering that goes into the automation and self detection, reporting to ground station and management of the flight failures.

On the ground, the system is made up of a centralized network of radio transceivers for analyzing the datalink messages. After demodulating and decoding the digital messages, they are routed to the various synchronized processors for specific performance analysis and counter measures to be taken, for ex. checking if the desired trajectory is being mapped, through the analysis of the navigation satellite data information sent from the aircraft.

Now comes the important part i.e. the network of communication. The first way is VHF, however it is line-of-sight dependent so you can’t rely on it for communication over oceanic regions. Second method is satellite communication, which can provide you a worldwide coverage. The third and the most recent advancement is HF, which allows you coverage over the polar regions. The aircraft system is intelligent enough to decide which of the three networks is to be chosen on the basis of the current positioning of the aircraft w.r.t ground station.

The flight that went missing is Boeing 777. Boeing, like Airbus, boasts of adhering to all the standards of aircraft-gound telecommunication protocols like ARACS, FANS and ATN.  My next post will talk about the scenarios in which such a system can fail. Follow the blog to stay tuned. I really hope we, I mean the radars, can trace the flight soon, provided it has really gone missing. There is still a strong possibility of concealed information which has been given to us by the military of China.