Tuesday 2nd Sep 2014
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‘Modification in Turbo Codes Reduces Error up to 1000 Times’

Face-to-Face

ENGINEER MOHAMMAD SALIM, Associate Professor and Head of Department of Electronics and Communications in Malaviya National Institute of Technology (MNIT), Jaipur and Secretary Jamaat-e-Islami Hind, talks about the upcoming 4G mobile communication technology and its salient features. In an interview with KAMRAN SHAHID ANSARI, he reveals his contribution to reducing the error levels by making some modifications in the turbo codes which can improve its performance on wireless fading channels.

Please acquaint us with the journey from 1G to 2G to 3G.

See 1G was basically based on analog system and it never came to India. However before 1G there was another technology; some call it 0G, however the term 0G was never used to refer to that technology. 1G was not cellular and used to employ old kinds of transmitters and receivers and was used only by military. It never came into public domain and remained confined only to the governments. It was mainly used in the United States and Europe and was used for voice communications.

Later with the advancement in technology, 2G came into existence which had excellent improvement over the data speed. The main reason for such increase and improvement in speed was because of the digitalisation of the system from the earlier used analog system. Digital system is all about breaking the signals in digits i.e. in 0 and 1 form or high or low form.

Another important improvement in 2G was that it reduced the errors to a very significant level and along with that reduced the power as well. Short Messaging Service (SMS) that was not available in 1G was introduced in 2G; hence it was both audio as well as short messages.

Next in-between 2G and 3G there is another stage which is sometimes referred to as 2.5G. Right now it is the 2.5G which is in vogue and the majority of us are using this technology. It is a little advanced version of 2G and has slight improvement in speed and errors. The latest that has been introduced is the 3G technology and besides the fact that it has been standardised it is not very popular and the users are very less. The reason for which can be the high cost related to it. Another thing is that 3G technology requires the mobile handset as well as the SIM card which is compatible with the technology. The maximum data rate that has been achieved in 3G wireless technology is 1 Mbps.

 

How 4G is different and improved from the rest of the technologies?

The most important achievement of 4G is that the data rate or speed which in the earlier technologies was limited to 1Mbps has reached 1 Gbps. This much speed of data transfer enables the user to see videos without any buffering. Hence the live transmission of any event can be seen without any disturbance or buffering aspect. In technical terms we say that we are seeing the data in ‘real-time’. Another improvement of 4G technology is the interportability. Interportability is a technology which enables the user to move anywhere in the world with the same connection without even the need to activate it. Whether the user is on roaming or international roaming or local, it makes no difference in the connectivity and the user enjoys uninterrupted network connection. Another advantage of interportability is that unlike mobile portability, where one can subscribe to a different service provider without changing the phone number, there is in fact no need to subscribe to any service provider as the technology automatically will start catching the signal which would be most powerful in the area.

In 4G, audio, video, data, MMS services and GPS all will be integrated.

 

In your research work you have suggested improvements over error control codes. Please elaborate on that.

In every system we have error control codes. Turbo codes are the most powerful codes whose very primary version was used in 3G and now in 4G it is the most advanced version of the turbo codes that has been used. Modifications in turbo codes can reduce error level up to 1000 times, which is in fact a great achievement of 4G technology. Earlier we reduced the error level to 100000 level but now with the modification in the turbo codes we have reduced it further to 100000000 times.

If we talk in technical terms, it is basically about reshuffling the codes at the transmitting end and then decoding the data at the receiving end by devising an algorithm. For this purpose, I designed a new interliver, which is very simple in its design, yet counters all the problems with great efficiency. As we know that noise comes into the data while its transmission, hence before transmitting data is shuffled and reshuffled in order to ‘fool the channel’ (in lay man terms), and as we are equipped with the algorithm to decode it at the end, we receive the signal with much lesser amount of distortion.

 

What are fading wireless channels?

As we are sitting in this room, there are ‘n’ number of signals entering this room, which in turn are connecting mobile phones. However a nullifying effect comes into picture as the signals that are entering are coming after traversing diverse paths. Some are coming directly to our phones without any obstacle in between; some are undergoing one reflection and some many, hence when they reach the mobile phones, they nullify each other. This nullifying effect is referred to as fading wireless channels.

 

Is this technology being used anywhere in the world? If not, when can we expect its launch?

This technology has not entered into public domain in any part of the world. However it is in experimental phase in the United States. As per my knowledge, I anticipate that it will hit the market in another 4 to 5 years, or may be earlier, and it will be full-fledged with proper standardisation norms.



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