This paper reports the experimental verification of concurrent backscatter streaming system comprising batteryless backscatter sensors and a software defined interrogator. The backscatter sensor is composed of a newly developed Radio Frequency Integrated Circuit (RFIC) and a commodity three axis microelectro mechanical system (MEMS) accelerometer. The concurrency is realized by allocating a dedicated subcarrier to each backscatter sensor, and using novel interference rejection signal processing in the interrogator. The communication protocol bases on ISO/IEC 18000-63 protocol with the extension of channel allocation and streaming control. The prototype system is evaluated in an experiment in where three backscatter sensors are installed on three emulated robotic mechanisms for wireless motion capture. It is confirmed that over-the-air subcarrier allocation and the concurrent capture of three robotic mechanism accelerations can be done despite the 10-4 order frequency instability of RFICs.