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A successive intercarrier interference reduction algorithm for OFDM systems
 Proc. IEEE Int. Conf. Commun
, 2007
"... Abstract — In a rapidly fading environment, Doppler spread caused by user mobility destroys the orthogonality among OFDM subcarriers, resulting in intercarrier interference. In this paper, a low complexity ICI reduction algorithm which can be applied to QAM signal constellations is proposed. A combi ..."
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Abstract — In a rapidly fading environment, Doppler spread caused by user mobility destroys the orthogonality among OFDM subcarriers, resulting in intercarrier interference. In this paper, a low complexity ICI reduction algorithm which can be applied to QAM signal constellations is proposed. A combinatorial optimization problem for ICI suppression is formulated and then relaxed to a quadratic programming problem. A successive method is then utilized to deduce a sequence of reducedsize QP problems, which is solved by limiting the search in the 2dimensional subspace spanned by its steepestdescent and Newton directions to reduce the computational complexity. Furthermore, a lowbit descent search is employed to enhance the system performance. The proposed algorithm is shown to provide excellent performance with low computational complexity. I.
“14ch072853369780123744838 ” — 2011/3/9 — 22:03 — page 285 — #1 CHAPTER
"... parallel data transmission in the frequency domain and mainly owes its success to the easy equalization for linear timeinvariant (LTI) frequencyselective channels. In OFDM systems, the data symbol stream is split into L parallel flows, which are transmitted on equispaced frequencies called subcar ..."
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parallel data transmission in the frequency domain and mainly owes its success to the easy equalization for linear timeinvariant (LTI) frequencyselective channels. In OFDM systems, the data symbol stream is split into L parallel flows, which are transmitted on equispaced frequencies called subcarriers, each one characterized by a transmission rate that is 1/L times lower than the original data rate. This is obtained by splitting the original data stream into multiple blocks, which are transmitted in consecutive time intervals, where each symbol of a block is associated to a specific subcarrier. This frequencydomain multiplexing can be efficiently performed by means of fast Fourier transform algorithms. Due to the use of orthogonal (equispaced) subcarriers, OFDM systems with LTI frequencyselective channels avoid the socalled intercarrier interference (ICI) among the data symbols of the same OFDM block. Differently from conventional frequencydivision multiplexing, a frequency overlapping among the spectra associated to different substreams is permitted, resulting in a significant reduction of the bandwidth requirements. Moreover, for LTI frequencyselective channels, the absence of ICI allows an easy channel equalization, which can be performed on a persubcarrier basis by means of scalar divisions. The intersymbol interference (ISI)1 among data symbols of different OFDM blocks, induced by multipath propagation, is avoided by a suitable cyclic extension of each OFDM block, usually