The Channel Capacity of General Complex-Valued Load Modulation for Backscatter Communication


Gregor Dumphart, Johannes Sager, and Armin Wittneben


IEEE Wireless Communications and Networking Conference (WCNC), Austin, TX, USA, pp. 1-6, Apr. 2022.

DOI: 10.1109/WCNC51071.2022.9771646

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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.


load modulation, backscatter communication, RFID, ambient backscatter, channel capacity, achievable rate, low energy communication, passive communication


Awarded the Best Paper Award of the IEEE Wireless Communications and Networking Conference, Track 1: Physical Layer and Communication Theory.

Presentation slides are found HERE.
Conference presentation video is found HERE.
Journal paper is found HERE.

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