Mohammad Zavid Parvez; Md. Abdullah Al Baki MEE10:12, pp. 67. ING/School of Engineering, 2010.
High data rate wireless access is demanded by many applications. Usually, more bandwidth is required for higher data rate transmission in any of the system. With promising technology and ever-increasing wireless devices, the spectrum is becoming scarcer day by day. In this case, using Orthogonal Frequency Division Multiplexing (OFDM) and Cognitive Radio (CR) for spectrally efficient transmission are an alternative solution.
OFDM is a bandwidth efficient multicarrier modulation where the available spectrum is divided into subcarriers, with each subcarrier containing a low rate data stream. OFDM has gained a tremendous interest in recent years because of its robustness in the presence of severe multipath channel conditions with simple equalization, robustness against Inter-symbol Interference (ISI), multipath fading, in addition to its high spectral efficiency. However, the Peak-to-Average Power Ratio (PAPR) is a major drawback of multicarrier transmission system such as OFDM.
CR can be defined as an intelligent wireless system that is always alert about its surrounding environment through sensing and should have ability to dynamically adjust its radio operation parameters. The CR demands that the physical layer (PHY) needs to be adaptable and flexible.
For flexibility and adaptability, the OFDM is an attractive candidate for CR systems. This dissertation proposes a novel non-contiguous OFDM (NC-OFDM) technique, where the implementation achieves high data rates of non-contiguous subcarriers while simultaneously avoiding any interference to the transmissions.
In this dissertation we apply different modulation techniques to reduce high PAPR for non-contiguous bands spectrum of OFDM based CR. The simulation results for PAPR reduction shows that higher modulation techniques are better compared to lower modulation techniques.