Artificial Rich Scattering-Assisted MIMO Systems Using Passive Backscatter Devices

Reconfigurable intelligent surfaces (RIS) are emerging as a promising technology for the future 6G networks. One of the challenges of IRS systems is that they require feedback control which in turn means that they have to have receiver and microcontroller that consume power. In this paper, we propose to use passive chipless backscatter devices to shape the channel between the transmitter and the receiver. We propose a novel artificial rich scattering (ARS)-assisted MIMO system, that uses passive chipless backscatter devices to shape the channel covariance matrix by increasing its rank even if the direct transmission channel has strong line-of-sight (LoS) component. In particular, we conduct a large system analysis and show that the achievable rate is independent of the phase shift matrix at the backscattering nodes. Moreover, by introducing large number of passive scattering elements in the system, we can improve the system capacity even with the presence of strong LoS component in MIMO channel. We also consider the case of ARS-assisted MISO case when the channel state information (CSI) is available at the transmitter side and derive tight lower bound on the ergodic rate.