The demonstration scenario, illustrated in Figure 1, is composed of a Primary User (PU) transmitting to a Primary Base Station (BS) and two Secondary Users (SU1 and SU2) transmitting to a Secondary Base Station. Since all users will utilize the same frequency and be transmitted at the same time, the two Secondary Users (SU1 and SU2) will be perceived as interference by the Primary BS.
The precoding and decoding algorithms were implemented in Xilinx System Generator environment for later compilation and deployment to the FPGA kits, as cn be seen in the next figure.
The Tx block is comprised by a Precoding and Framing part, OFDM engine and UE demultiplexer. The first part pre-codes all users data, introduces pilots for channel estimation and serializes the information. Such serializer is a resource saving technique that allows the usage of a single OFDM Tx Engine. Then, the UE demultiplexer receives the modulated information and feeds it to the correct transmitting antennas for Over-The-Air transmission.
The algorithm running on the Base Station side is responsible for channel estimation recurring to the sent pilots, data demodulation with the OFDM Rx Engine, as well as, estimating the PU data with the decoding algorithm.
The MU-MIMO OFDM had such a frame structure. The sent payload is represented by the white tiles that are common in all users, each being an interference to each other. In the end the decoding will be responsible of recovering the original data.
