Contents
Spread Spectrum Technology
by
Neelesh Pataodi(02D07025)
Maringanti Anirudh (02D070130)
Vivek Patel (02007028)
Abstract:
A majority of present day communication systems involve transmission of data through electromagnetic waves. Due to presence of a large number of such waves they have to be transmitted in such a way that interference losses, transmission losses be minimum and the privacy of the data be maintained. There are a lot of techniques for such transmission. Conventional radio signals are generally amplitude or frequency modulated to allow easy transmission. However newer advanced systems do not rely on this technique because it limits the scope of such systems. Here we are going to talk about Spread Spectrum technology which is used by such systems for signal transmission. Spread Spectrum has many advantages over the other systems especially in terms of security and interference losses. The presentation briefly talks about the main basic concept behind the technique and its application. We plan to give an overview to how signals are transmitted in this technique and the basic system requirements. There are few many other techniques in SS technology but we have mainly focused on Direct Sequence Spread Spectrum technique as it is used in CDMA- the technology behind the success of mobile phones.Introduction:
Consider a city like Mumbai. It has more than a million mobile phone users, more than a dozen radio stations, TV stations in addition to other local radio systems. How is it that all these signals do not interfere and mess up the data transmitted? How is it possible that the data sent is not tampered or lost? Tough question? The answer lies in the technology used in transmitting signals. Though some systems still use the traditional techniques like Amplitude Modulation and Frequency Modulation, newer and far more advanced systems like mobile phones and wireless networks use Spread Spectrum (SS) technology.So what is SS technology?
Spread Spectrum technology was a technique used mainly by the military and was developed in the 1930’s by the US. Its main advantages were that it was difficult to decode. Moreover it looked like any noise signal and was difficult to recognize as well. However the eighties and nineties saw a remarkable growth in communications especially in the wireless networking and mobile technology. The main requirement of these systems was minimal transmission data loss and privacy. With SS technology one could not only guarantee this but also got many more other advantages including that of security. SS also allows one to use code division multiplexing for Code Division Multiple Access (CDMA). Multiple access is much more easier with SS technology.The two main types of SS techniques are:
a) Direct Sequence
b) Frequency Hopping
In this presentation we are going to look at Direct Sequence Spread Spectrum in a broader sense and try to appreciate the theory and working behind this technique.
MOTIVATION:
In the past half a year or more the number of mobile phone users has increased dramatically in our institute. It is quite amazing that there could more than a few thousand users in and around the campus at any time and who are able to send receive signals without any problem. So when we were asked to do an application presentation on Signals and Systems we chose this topic because we thought it will be nice of we could present the idea and the theory behind the transmission of these signals in a simple way so that people can appreciate their mobiles better and not view it as a technological marvel whose working is beyond their understanding. Though we thought that the technology is way beyond our understanding we have realized that the technology uses concepts that we have learnt in our course and the basic foundations on which the theory is built can be explained. Our presentation is not complete analysis of the working of the system. There are many more techniques and considerations involved which we have avoided because it involved concepts beyond our scope under the present circumstances.
