Spectrum load balancing as a medium access control in a multiuser OFDM based cognitive radio systems

In the era of ever increasing demands on wireless communications the requirement of additional spectrum usage to support various Quality of Services (QoS) has been the prior interest for various Research communities. The utilization of the unlicensed spectrum is reaching its limits and various regulatory changes to provide the licensed spectrum has been complex and time consuming.;Radios designed for efficient usage of shared spectrum and not causing significant interference to the licensed ones are referred to be cognitive or spectral agile known to be intelligent radios. These radios are used to identify the unused spectrum and assign the subcarriers effectively and load the bits adaptively according to the channel state information provided to the user by the system.;In this thesis we consider sub-carrier and bit allocation for multiuser OFDM based cognitive radios. In general sub-carrier and bit allocation are carried out in two steps; first the sub-carrier allocation is performed using various optimization techniques followed by bit loading. This work includes the study and implementation of Spectrum load Smoothing and Spectrum Load balancing as cognitive medium access for sub-carrier allocations in conjunction with multiuser diversity. For the bit allocation we employ single user bit loading algorithm. We analyze these two approaches in terms of Number of Iterations, BER performance and SNR ratio.