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-
$m$
fading. We find that the diversity order achieves
$L$
for Rician fading and achieves
$L\min(m_{f}, Nm_{b})$
for Nakagami-
$m$
fading. Two receiving antennas
$(N = \hbox{2})$
can capture most of the receiving side gain regardless of the number of tag antennas
$L$
for Rician fading, and this is also applicable to Nakagami-
$m$
fading 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 (the
$K$
factor or the
$m$
parameter) of the forward link than that of the backscattering link.