This paper studies achievable information rates of backscatter communication systems where the tag performs load modulation with a freely adaptable passive termination. We find that the complex phasor of the tag current is constrained to a disk and that the capacity problem can therefore be described with existing results on peak-power-limited quadrature channels. This allows us to state the channel capacity and the capacity-achieving distribution of the load impedance, which is described by non-concentric circles in the right half-plane. For the low-SNR case (SNR < 4.8 dB) we find that channel capacity is achieved by a purely reactive load with Cauchy-distributed reactance. The exposition is based on a system model that abstracts all relevant classes of backscatter communication systems, including RFID. To address practicality, we construct a symbol alphabet that allows for a near-capacity information rate of more than 6 bit per load-switching period at reasonably high SNR. We also find that the rate hardly decreases when typical value-range constraints are imposed on the load impedance.
翻译:本文研究后向散射通信系统的可实现信息率,其中标记进行负载调节并自由调整被动终止。 我们发现标记流的复杂散射器被限制在磁盘上,因此能力问题可以用最高功率限制的二次曲线频道的现有结果来描述。 这使我们能够说明频道的容量和负载阻力的获得能力分布,右半空的非中心圈描述的负载阻力分布。 对于低SNR案件(SNR < 4.8 dB),我们发现频道能力是通过纯粹的反应式负载和卡苏尔分散反应来实现的。 解析基于一个系统模型,该模型将所有相关类别的后向散射通信系统(包括RFID)进行摘要介绍。 为解决实用性,我们制作了一个符号字母,允许在合理的高SNR中,每负载开关期近6位以上的信息速率。 我们还发现,当对负载阻力施加典型的数值限制时,这种速率几乎没有下降。