摘要 |
The invention relates to apparatus, methods, processor control code and signals for channel estimation in MIMO (Multiple-input Multiple-output) OFDM (Orthogonal Frequency Division Multiplexed) communication systems. <??>An OFDM signal is transmitted from an OFDM transmitter (1000) using a plurality of transmit antennas but has one or more nulled subcarriers, corresponding to windowing in the frequency domain. The OFDM signal is adapted for channel estimation for channels associated with said transmit antennas by the inclusion of orthogonal training sequence data (1014c) in the signal from each said antenna. The training sequence data (1014c) is derived from substantially orthogonal training sequences for each said transmit antenna, the training sequences being constructed based upon sequences of values <DF>X<m> k = exp (-j 2 pi k m /M) </DF> where k indexes a value in a said sequence, m indexes a transmit antenna, and M is the number of transmit antennas. Embodiments of these techniques provide training sequences that are more robust to, inter alia, nulled subcarriers. <IMAGE>
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