Coherent Multiantenna Receiver for BPSK-Modulated Ambient Backscatter Tags

Abstract

Ambient Backscatter Communication (AmBC) is an emerging communication technology enabling green Internet-of-Things deployments. The widespread acceptance of this paradigm is limited by the low Signal-to-Interference-Plus-Noise Ratio (SINR) of the signal impinging on the receiver antenna due to the strong direct path interference and unknown ambient signal. The adverse impact of these two factors can be mitigated by using non-coherent multi-antenna receivers, which are known to require a higher SINR to reach the Bit-Error-Rate (BER) performance of coherent receivers. However, considering the unknown ambient signal, unknown location of AmBC tags, and varying channel conditions, coherent receivers for AmBC systems are rarely studied in literature. In this paper, a coherent multi-antenna receiver, which requires no prior information of the ambient signal for decoding the Binary-Phase-shift-Keying (BPSK) modulated signal, is presented. The performance of the proposed receiver is compared with an ideal coherent receiver that has perfect phase information, and also with the performance of a non-coherent receiver, which assumes distributions for ambient signal and phase offset caused by the excess length of the backscatter path. Comparative simulation results show the designed receiver can achieve the same BER performance of the ideal coherent receiver with 1-dB more SINR, which corresponds to 5-dB or more gain with respect to non-coherent reception of On-Off-Keying modulated signals. Variation in the detection performance with the tag location shows that the coverage area is in the close vicinity of the transmitter and a larger region around the receiver, which is consistent with the theoretical results.

Optimum Multi-Antenna Ambient Backscatter Receiver for General Binary-Modulated Signal

“…Different markers representing different estimation methods: power iteration ( ), singular value decomposition ( ), and inverse of sample variance matrix ( ). The line with marker ( ) in (c) represent the coherent receiver in [11].…”

“…y|x . Adopting the same approach presented in Appendix of our previous work [11], we are ready to know that the test statistic follows Asymmetric Laplace distribution [28, ch. 3] with its PDF and CDF expressed as…”

“…Such fact causes the implementation of AmBC systems lacks flexibility and has uncertain computational complexity. To take binary phase shift keying (BPSK) as an example, its demodulator can achieve the same BER performance with up to 6 dB less SNR compared with OOK demodulator, and its optimum multi-antenna receiver obtaining all the SNR gain is a coherent receiver which is analyzed in work [11]. However, the optimum multi-antenna receivers for other binary modulations have not been studied.…”

A Simplified Multi-Antenna Receiver for General Binary-Modulated Ambient Backscatter Signal

“…Under hypothesis H 0 , Σ b H y|x0 = 1, the PDF of z g is given by Eq. (10). When H 1 is true, the common variance is (1 + σ 2 s κ 2 )/2.…”

“…The above receivers are noncoherent in nature. If the BD signal is demodulated coherently, however, a more complicated receiver is required [10].…”