The invention discloses a decoding method of a cyclic space-time code based on
affine projection in a downlink multi-user multi-input multi-output
system which comprises a first step of decomposing a channel matrix into a formula described in the specification, performing polar
decomposition on two symbols described in the specification and obtaining a formula 2described in the specification, wherein P (Q) is
unitary matrix of the NM*1 (NM*(M-1)), a C1 (C2) is a
positive definite matrix of 1*1 ((M-1)* (M-1)), defining a U to be a subspace formed by column vectors of the P, wherein the V is a subspace formed by column vectors of the Q, a second step of projecting a matrix described in the specification on the U along the V and obtaining an
affine projection of the matrix, wherein the
affine projection is a formula 3 described in the specification, substituting the matrix to the formula 3, carrying out simplification and obtaining formula 4 described in the specification, wherein another symbol is equal to a formula 6, a third step of using a P<H> for multiplying the formula 4 to obtain a formula 5 described in the specification, a fourth step of obtaining information of a first user through maximum likelihood decoding. The decoding method of the cyclic space-time code based on the affine projection has the advantages that under the condition that a sending end doesn't know channel status information, an affine
projection method is used and interference information among multiple users in a downlink multi-user
multiple input multiple output
system can be removed, through the utilization of the cyclic time-space code, information of each user is enabled to pass through all information channels, and therefore spatial diversity is ensured, and information of sending signals of a sending end is recovered accurately.