SER of Orthogonal Space–Time Block Codes Over Rician and Nakagami- m RF Backscattering Channels

The multiple-input–multiple-output (MIMO) radio-frequency (RF) identification system applies the RF backscattering principle, and its physical channel exhibits a special kind of cascaded structure different from conventional wireless channels and other cascaded channels (e.g., the keyhole MIMO channel). In this paper, we provide a general formulation to study orthogonal space–time block codes (OSTBCs) for RF backscattering with different fading assumptions and then analytically study the symbol-error-rate (SER) performances for this channel under Rician fading and Nakagami-mfading. We find that the diversity order achievesLfor Rician fading and achievesLmin(mf, Nmb)for Nakagami-mfading. Two receiving antennas(N = 2)can capture most of the receiving side gain regardless of the number of tag antennasLfor Rician fading, and this is also applicable to Nakagami-mfading if the two links of the cascaded structure have similar channel conditions. More interestingly, we show that the performance of the this channel is more sensitive to the channel condition (theKfactor or themparameter) of the forward link than that of the backscattering link.