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SpaceTime/SpaceFrequency Block Coded OFDM with Diagonalized Maximum Likelihood Decoder (ST/SFOFDM with DMLD)
Hiroshi KANEMARU Tomoaki OHTSUKI
Publication
IEICE TRANSACTIONS on Communications
Vol.E87B
No.7
pp.20342039 Publication Date: 2004/07/01
Online ISSN:
DOI:
Print ISSN: 09168516 Type of Manuscript: LETTER Category: Wireless Communication Technology Keyword: STBC, STOFDM, SFOFDM, DMLD,
Full Text: PDF>>
Summary:
Recently, SpaceTime Block Coded OFDM (STOFDM) that applies SpaceTime Block Code (STBC) to OFDM has been proposed. SpaceFrequency Block Coded OFDM (SFOFDM) has been also proposed where the block codes are formed over the space and frequency domain. STOFDM and SFOFDM are known as the schemes that achieve good performance over the multipath fading environments and the fast fading environments, respectively. For the systems with two transmit antennas, the orthogonal conditions required to separate the received signals are that in STOFDM, the frequency responses of the consecutive two OFDM symbols are almost identical and that in SFOFDM, the frequency responses of the adjacent two subcarriers are almost identical. In practical fading environments, however, these conditions of the orthogonality sometimes cannot be satisfied. In those environments, the received signals cannot be well separated and the performances are degraded. Recently, the diagonalized maximum likelihood decoder (DMLD) of new zeroforcing (ZF) type was proposed for the spacetime block coded single carrier QPSK system to maintain the orthogonality of STBC under the fast fading environments and the flat fading environments, where the channel separation in DMLD is performed by the ZF algorithm using two receive signals at time index 2n, 2n+1 (Space Time Code: STC) or two subcarriers (Space Frequency Code: SFC). Note that the matrix generated after the channel separation is not an identity matrix but the matrix proportional to an identity matrix. We show that ST/SFOFDM with DMLD outperform ST/SFOFDM in terms of Bit Error Rate (BER).

