Receiver Architectures for OFDMA Systems with Subband Carrier Allocation

Abstract:
OFDM systems are very sensitive in phase noise and frequency dispersion. Thus, time and frequency synchronization tasks are very crucial for the proper signal recovery in the receiver. The difficulties and challenges are multiplied if we consider a multiuser OFDM system (OFDMA) where the subcarriers are shared between different users. The receiver has the task to choose optimal sampling instants and to align the subcarrier frequencies of an OFDM symbol that contains signals from multiple users. In this study the use of filter banks is considered in order to reduce Intercarrier interference in such a system and simplify the synchronization procedures that must take place. The proposed schemes are applicable to adjacent subcarrier permutation OFDMA systems where users are separated in bands of adjacent subcarriers. In order to achieve low processing load, techniques of multirate signal processing are adopted. The DFT-polyphase filters are the basic elements of the processing chain. Moreover the filtering procedure is preferred to be divided in multiple stages. The computational workload for each structure is determined and some measures for the reduction of the computational burden are presented.