Performance bounds for multipath-assisted indoor localization on backscatter channels

In this paper, we derive the Cramer-Rao lower bound (CRLB) on the position error for an RFID tag localization system exploiting multipath on backscatter radio channels. The backscatter channel is modeled with a hybrid deterministic/stochastic channel model. In this way, both the geometry of the deterministic multipath components (MPCs) and the interfering diffuse multipath are taken into account. Computational results show the influence of the room geometry on the bound and the impact of the diffuse multipath. Time reversal (TR) processing on the uplink channel is analyzed using the deterministic MPCs to overcome the degenerate nature of the backscatter channel. The CRLB shows the potential gain obtained from TR processing as well as its strong dependence on the geometry. Such TR processing has been proposed for TX waveform adaptation in the perception-action cycle of a cognitive radar. The results of this paper illustrate that it can indeed influence beneficially the measurement noise of the received signal, yielding control over the localization system.