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In OFDM, IFFT and cyclic prefix to avoid the circular convolution aliasing are usually used to ensure the orthogonality for all subchannels, while FBMC only requires orthogonality with adjacent subchannels. In order to fully exploit channel bandwidth, modulations in the subchannels must adapt to the neighbor orthogonality constraint, so Offset Quadrature Amplitude Modulation (OQAM) is used for this purpose. Frequency selective filter is accomplished by using longer and spectrally well-shaped prototype filters, and because of frequency selective filter, the sidelobe levels are lower comparing to OFDM. Combination of filter banks and OQAM modulation result in no need for guard time or cyclic prefix like OFDM, leading to higher bandwidth efficiency. In general, this technique is called Filter Bank Multicarrier (FBMC) technique.
In FBMC system, the transmitter is called synthesis filter bank. We can get an intuitive algorithm, implemented by Inverse Discrete Fourier Transform. Then, the receiver is called analysis filter bank, implemented by using Discrete Fouier Transform. Filter banks consists of Polyphase Network (PPN) filter and FFT processor, we. Because the condition of the system speed demand is not fast, we choose the memory-based IFFT/FFT processor. Finally, PPN filter and IFFT/FFT processor are combined in transmitter and receiver.
This dissertation presents a reconfigurable homogeneous memory-based FFT processor architecture. Specifically, this thesis reinvestigates a radix-2 FFT algorithm and rearranges an alternative signal flow graph (SFG) from conventional SFGs. By developing the alternative SFG, this thesis proves that the altered permutation of input data can maintain the original functionality of FFT computation. Consequently, the alternative SFG is readily realized as the architecture of homogeneous parallel structure with multiple processing elements to increase throughput. However, the proposed design retains the advantage of a small area for the memory-based architecture, and achieves the goals of fast operation and ease of control. | en_US |