Performance of Battery-free BackCom in Uplink NOMA Systems with Joint Detection

In this paper, a framework for the performance evaluation of uplink Non-Orthogonal Multiple Access (NOMA) Backscattering Communication (BackCom) systems is proposed. A two-nodes bi-static scenario is considered, where the communication is affected by multi-path on both the forward and the backscattering links. The battery-free nature of the nodes is explicitly included in the model by introducing a node's activation power threshold. A power-domain NOMA approach is enforced, where multiplexing of interfering signals is performed by assigning a specific reflection coefficient to each node, based on Channel State Information (CSI) at the receiver. Moreover, two relevant detection schemes, namely the Successive Interference Cancellation (SIC) detector and the minimum distance joint detector (JD), are considered. Performance is evaluated in terms of average Bit Error Rate (BER) and aggregate successful decoding probability. Extensive simulations results examine the interplay among powering condition, reflection coefficients selection and interference rejection efficiency, and show a performance improvement offered by joint detection over SIC. Finally, a comparison with state-of-the-art performance evaluation is included.