Optimal 4QAM backscatter modulation for passive UHF CRFID tags.

With the development of the Internet of Things (IoT), the amount of transmitted data is getting huge. Traditional passive UHF CRFID Tag currently adopts 2ASK or 2PSK backscatter modulation, and each symbol conveys 1 bit of information. Still, this modulation has the problems of low throughput, poor real-time, and low energy utilization. This paper proposes an optimal 4 Quadrature Amplitude Modulation (4QAM) backscatter scheme at 920 MHz, which can increase the throughput and simultaneously improve energy utilization. In this optimal scheme, the reflection coefficient modulus | Γ | is closely related to the energy. The low power of the passive tag requires that the modulation circuit's design consider how to choose | Γ | o p t (optimal reflection coefficient modulus). Therefore, we build the energy model of CRFID to explore the | Γ | o p t at different symbol rates and use the | Γ | o p t to design a more reasonable constellation diagram for passive tags. Finally, this paper analyzes the decoding of multinary backscatter signals, and an improved Kmeans algorithm can solve the cluster offset problem at high symbol rates. After experiments, | Γ | o p t is around 0.67, the maximum throughput of 4QAM backscatter modulation can reach 16 Mbit/s, and the power consumption is 4.38 mW. Compared with the traditional binary modulation, the tag in this paper can double the throughput at the same symbol rate. [ABSTRACT FROM AUTHOR]