Methods and apparatus for circulation transmissions for OFDM-based MIMO systems
View Patent ↗System performance in wireless communication is improved by increasing diversity in time, space and frequency. In OFDM-based MIMO systems in which the number of antennas M is greater then the number of simultaneously transmitted OFDM symbols N, circulation transmissions according to the present invention improve signal diversity. In symbol-based circulation transmission, N antennas are chosen from the M available antennas to transmit the N OFDM symbols. In subcarrier-based circulation transmission, M output OFDM symbols are composed from the QAM-mappled samples of the N input OFDM symbols. These M output OFDM symbols are then transmitted from the M antennas simultaneously.
1. A method of transmitting N.sub.OFDM input OFDM symbols in an OFDM-based MIMO system including M transmission antennas, wherein N.sub.OFDM≦M and wherein each of the M antennas has N.sub.SC subcarriers and each of the N.sub.OFDM input OFDM symbols has N.sub.SC QAM-mapped samples corresponding to the N.sub.SC subcarriers, the method comprising:
forming M output OFDM symbols from the QAM-mapped samples of the N.sub.OFDM input OFDM symbols, wherein each of the M output OFDM symbols has N.sub.SC QAM-mapped samples corresponding to the N.sub.SC subcarriers and wherein each of the M output OFDM symbols includes a plurality of QAM-mapped samples from each of the N.sub.OFDM input OFDM symbols;
forming
N
Pattern
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N
OFDM
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=
M
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N
OFDM
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distinct combinations of N OFDM of
the M output OFDM symbols; and
forming a sequence of N SC elements wherein each element is one of the N Pattern distinct combinations and assigning a combination pattern to the subcarrier according to the sequence designated as P(s)=[floor(s/N pattern )+(s mod N Pattern )] mod N pattern wherein s =0, 1, 2, . . . , N SC −1 is the subcarrier number.
2. The method as recited in claim 1 , wherein forming M output OFDM symbols further comprising: for each of the N.sub.SC subcarriers, choosing N.sub.OFDM of the M output OFDM symbols; assigning the N.sub.OFDM QAM-mapped samples of the N.sub.OFDM input OFDM symbols to the N.sub.OFDM chosen output OFDM symbols; and assigning a zero QAM-mapped sample to the M−N.sub.OFDM remaining output OFDM symbol.
3. The method as recited in claim 1 , including designating the sequence as P(s)=[N shift *floor(s/N carrier )+N offset *(s mod N carrier )] mod N partial , where N carrier defines the number of subcarriers grouped together, N shift and N offset define the shift of the groups and the pattern numbers to be selected from all possible patterns, and N partial defines a set of periodic patterns that includes at least a partial number of patterns from all possible patterns.