2, 4, and 8 antenna configurations are also supported. The MS is required to have two receive antennas as a minimum. The layer-to-stream mapping is performed by the MIMO encoder. The MIMO encoder is a block processor that operates on M input symbols at a time. The input to the MIMO encoder is an M X 1 vector S = [S1,S2,...,SM] where Si is the ith symbol within the input block. The layer to stream mapping of the input symbols is done starting with the spatial dimension. The output of the MIMO encoder is an Ns X Nf matrix given by X = S(s) which serves as the input to the precoder block where Ns denotes the number of streams, Nf is the number of sub-carriers occupied by one MIMO resource block, X is the output matrix of the MIMO encoder, S is the input vector, and S(s) is the MIMO encoder trans- formation matrix. The output of the MIMO encoder can be described as: (10-48) For SU-MIMO transmissions, the spatial rate is defined as in R = MINf. For MU-MIMO trans- missions, the spatial rate per layer R is equal to 1 or 2. There are four MIMO Encoder Formats (MEF) specified in the IEEE 802.16m as follows: Space-frequency block coding; Vertical encoding; Horizontal or multi-layer encoding; Conjugate Data Repetition (CDR). In SU-MIMO, MIMO encoding would allow the use of spatial multiplexing and transmit diversity transmission schemes. Spatial multiplexing MIMO employs vertical encoding within a single layer (codeword). Transmit diversity utilizes either vertical encoding with a single stream or space- frequency block coding. In MU-MIMO, horizontal or multi-layer encoding is used at the base station, while up to two streams can be transmitted to each mobile station. For open-loop transmit diversity with SFBC encoding, the input to the MIMO encoder is represented by 2 X 1 vector S = [S1 S2]t. The MIMO encoder generates the 2 X 2 SFBC matrix as follows: (10-49) The SFBC output matrix occupies two consecutive sub-carriers. For open-loop transmit diversity with CDR encoding, the input to the MIMO encoder is represented by a 1