CLOSED LOOP OFDM SYSTEMS

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is one of the current research themes in the communication industry. OFDM has been a subject of theory for decades, but with the communication evolving at a rapid pace, newer dimensions are being achieved in terms of high data rate transmissions and quality-of-services offered. OFDM will have a significant role in the future in high data rate transmission links. Unlike the conventional FDM, OFDM makes use of sub-carriers that are orthogonal to their adjacent carriers. This orthogonality allows spectral over-lapping and thereby, increases the spectral efficiency. The Closed Loop OFDM Systems, successfully simulated using the Matlab2008a ®, is a pilot based approach for Additive White Gaussian Noise and Rayleigh Fading Noise channel characteristics with Binary Phase-Shift Keying and Quadrature Amplitude Multiplexing modulation/demodulation schemes. Orthogonal sub-carriers have been generated in software with the Discrete-Fourier Transforms computations using the Fast-Fourier Transform algorithms. Orthogonality principle reduces the Inter-Carrier Interference (ICI) but is also responsible for Inter-Symbol Interference (ISI). Cyclic Prefix, replica of end part of an IFFT symbol that is pre-fixed to the IFFT symbol not only mitigates ICI but also combats ISI. The report includes the Bit-Error-Rate (BER) versus Eb/No (in dB) plots that give the performance of the Closed Loop OFDM Systems. Tables illustrating the number of pilot carriers inserted into the transmitted data stream with respect to the variation in BER have also been prepared from the simulated data obtained.