Synchronization of OFDM systems

OData support
Supervisor:
Szombathy Csaba Zoltán
Department of Broadband Infocommunications and Electromagnetic Theory

Telecommunication and broadcast devices make an increasing use of orthogonal frequency multiplexing (OFDM). Despite it's advantages this method has it's own drawbacks e.g. a very accurate synchronization is required for it to operate properly.

Any transmission error can be compensated if we know the value of the error exactly. For this, we need the error to be detected and it's value to be estimated. This task is done by the estimators of these errors.

In this paper I give an overview of the structure of an OFDM system and I examine the transmission errors and their mathematical model. Then I present several possible methods of error estimation and compensation.

The IEEE802.11a is a popular OFDM-based system, which provides wireless network capabilities for notebook computers. I compare two methods for carrier frequency offset estimation applied to this wireless communication system. The former is a classical one \cite{paperMoose} the latter have been presented recently. The two algorithms work in fundamentally different ways and their need for computing power is different. The point of my study is to compare the efficiency of the new method to the old one, which is acting as a reference.

First I developed a computer-based model of the signal to be analyzed in Matlab environment. Then I developed the procedures implementing the two methods. Using these models I simulated the operation of the methods as a function of different signal-to-noise ratios and I examined the statistical properties of their output data.

Then I compared the properties of the methods. First the mean and the standard deviation of the estimator's output versus the signal-to-noise ratio at a given frequency offset was estimated, then the estimated value of the error versus the exact value of the error at different signal-to-noise ratios was determined.

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