Backscatter Communications Over Ambient OFDM Signals Using Null Subcarriers

Abstract

In recent years, ambient backscatter communications have gained a lot of interest as a promising enabling technology for Internet-of-Things and green communications. In ambient backscatter communication systems, battery-less devices are able to transmit information by backscattering ambient RF signals generated by legacy communication systems such as digital TV broadcasting, Wi-Fi, or cellular. This paper is concerned with ambient backscatter communications over legacy cellular OFDM signals. We propose a novel modulation scheme that allows backscattering devices to take advantage of the spectrum structure of ambient OFDM symbols to transmit information. We analyze the error performance of the proposed scheme, provide an exact expression for the error probability, and validate our analysis using Monte-Carlo simulation. We investigate the effects of varying the OFDM symbol size and maximum channel delay spread on the error performance. Our numerical results show that the proposed technique outperforms other techniques available in the literature for backscatter communication over ambient OFDM signals in different scenarios.

Challenges in Resource-Constrained IoT Devices: Energy and Communication as Critical Success Factors for Future IoT Deployment

“…As the interrogator has different purposes, it is not possible to control its stability, strength, or availability. It also needs to take into consideration the modulation (if any) of the source signal, i.e., using ASK modulation in a source signal with amplitude variation can make the backscatter communication unreadable [ 24 , 25 ].…”

Polarization Conversion-Based Ambient Backscatter System

“…The strong direct path signal appears as an interference to the AmBC demodulator. Several techniques have been pro-posed to mitigate the impact of the direct path interference, such as using long symbol duration to improve the signal-tonoise-plus-interference ratio (SINR) of the scattered signal at the receiver, shifting the backscattered signal to a different frequency band [18], [19] and using multiple receiver antennas [20]- [22]. More recently, hybrid beamforming techniques, machine-learning assisted detection approaches together with coding schemes have been applied to AmBC systems to promote the applications of AmBC in practice [15], [16].…”

“…In [25], [26] a multi-hop protocol was proposed, in which each of the backscatter devices in the multi-hop-chain between the transmitter and receiver shift the frequency further. In [18], [19], partial shift of the spectrum was proposed for Orthogonal Frequency Division Multiplexed (OFDM) ambient signals, such that the scattered component would appear in the null carriers of the ambient signal. The drawback of these frequency shifting approaches is that they assume that there is interference free spectrum white space available where the scattered component can be shifted.…”

Hybrid Beamformer Design for High Dynamic Range Ambient Backscatter Receivers

“…Most recently, authors in [15], [23]- [25] considered the ambient orthogonal frequency-division multiplexing (OFDM) modulated signals transmitted by the legacy systems. In [15], the ML rule was applied to obtain the ML decision regions to minimize the BER.…”

“…Exploiting the repeating structure of the ambient OFDM signals and the test statistics, [23] has proposed a receiver design to cancel out the direct-link interference generated by the legacy transmitter. In [25], a noncoherent backscatter communication technique over ambient OFDM signals has been proposed by using null subcarriers. In addition, the successive cancellation technique can be applied to jointly decode the legacy system and backscatter system information for a co-located legacy and backscatter receiver [14].…”