MIMO-OFDM spatial multiplexing technique implementation for GNU radio

Multiple-Input Multiple-Output (MIMO) is a wireless technology allowing a significant increasing of the throughput without the extension of the bandwidth but by means of the use of multiple antennas both in transmission and reception. Currently, Orthogonal Frequency Division Multiplexing (OFDM) is used in conjuction with MIMO to achieve better performance. With OFDM, instead of a single carrier, the main signal is split in a sub-set of independently modulated signals on orthogonal sub-carriers. In this paper, we provide a description of our MIMONet SDR platform for network-level exploitation of MIMO technology. We present the implementation of our OFDM transceiver, developed following the structure of IEEE 802.11n standard and implementing one of the most powerful MIMO technique: spatial multiplexing. In this technique, two (or more) different data streams are simultaneously transmitted over two (or more) antennas. Starting from the original GNU Radio code, we modified and added blocks to achieve a complete implementation of MIMO-OFDM spatial multiplexing. We added some features, such as the concatenation of Forward Error Correction (FEC) in the packet construction, and the use of pilot sub-carriers for channel estimation. We also developed a new synchronization algorithm derived by extending the Van de Beek algorithm to the MIMO setting. We build the framework of the standard IEEE 802.11n. In particular, we put all the preambles needed for synchronization and channel estimation. We have also designed and implemented a fine grained signal-to-noise ratio (SNR) estimation, bit error rate (BER) and packet error rate (PER) computations, that allow us to evaluate the channel conditions and validate performance of the software implementation.