Transmit Diversity and Spatial Multiplexing for RF Links Using Modulated Backscatter

A new multi-antenna or multiple-input-multiple-output (MIMO) configuration is introduced for RF modulated backscatter in a multipath environment. RF modulated backscatter is used by semipassive RF tags to transmit without a power amplifier, and is therefore appropriate for applications with extreme power constraints such as sensor communications, electronic shelf tags, electronic toll collection, and container identification. Channel information is used by the interrogator transmitter to provide transmit diversity. Multiple reflection antennas are used by the RF tags to reflect according to different data streams. Multiple interrogator receiver antennas provide multi-stream detection capability. Simulations show that range can be extended by a factor of four or more in the pure diversity configuration and that backscatter link capacity can be increased by a factor of ten or more in the spatial multiplexing configuration.