Achieving MIMO performance with single-antenna radios

Multiple-antenna systems have been shown to provide significant performance improvements over single-antenna systems. Theoretical analysis, simulation and experimental testing corroborate improvements in capacity and transmit power/energy savings. Unfortunately, co-located MIMO radios have numerous disadvantages compared to single-antenna radios; such as more complex RF and modem signal processing, inability to provide sufficient antenna spacing for soldier communication frequencies, increased radio size form factors and higher digital hardware power requirements. In this work, we propose to use simple and low cost single-antenna radios in “distributed groups” to form MIMO virtual arrays. Virtual arrays are created by “clusters” of single-antenna transmitters and receivers, respectively, each of which work cooperatively together and can be shown to provide many of the benefits of co-located MIMO systems. We used a 2×2 USRP-based MIMO OFDM system to perform field measurements with the objective to determine throughput and capacity performance compared to SISO OFDM. We compared performance by changing channel propagation environment, antenna spacing, RF frequency and propagation distance. In some channel environments, throughput gains (TPG) of 2X were found with range gain (RNG) of 2X compared to the same SISO OFDM system. We found that optimal antenna spacing may be environment dependent, which motivated us to develop a more general distributed MIMO system approach that could be utilized for field measurements in nearly any configuration desired. Subsequently, we developed a 2-transmit and (1-4)-receive distributed OFDM MIMO model suitable for single-antenna radios, with simulations that support a RNG of between 2.25X and 5.5X.