We present HEScatter, a high-efficiency ambient backscatter system that simultaneously improves carrier, power, and transmission efficiency. To improve carrier efficiency, we choose cellular signal as the carrier due to its continuous transmission nature. Specifically, to ensure low power, we design low-power periodic template matching based on the periodicity of cellular signals to trade time for synchronization accuracy. Further, we calibrate the drift introduced by Sampling Frequency Offset (SFO) to increase carrier utilization. In addition, we exploit Reference Signal (RS)-based demodulation to demodulate tag and ambient data from backscattered signals alone in various traffic patterns for efficient transmission. We prototype HEScatter using off-the-shelf FPGAs and SDRs. Extensive experiments show that HEScatter performs well in carrier utilization, power consumption and data transmission. The carrier utilization rate of HEScatter is as high as 99.97%, which is 3.0x higher than the counterpart of SyncLTE. In end-to-end transmission, the energy efficiency of HEScatter is 1.6x and 19.2x higher than LScatter+ and SyncLTE, while LScatter suffers from transmission failures. We also demonstrate the high transmission efficiency of HEScatter, as its aggregate goodput is 1.5x and 3.8x better than LScatter+ and SyncLTE respectively.

Ambient LTE backscatter is a promising way to enable ubiquitous wireless communication with ultra-low power and cost. However, modulation in previous LTE backscatter systems relies heavily on the original data (content) of the signals. They either demodulate tag data using an additional receiver to provide the content of the excitation or modulate on a few predefined reference signals in random ambient LTE traffic.This paper presents CABLTE, a content-agnostic backscatter system that efficiently utilizes uncontrolled LTE PHY resources for backscatter communication using a single receiver. Our system is superior to prior work in two aspects: 1) Using one receiver to obtain tag data makes CABLTE more practical in real-world applications, and 2) Efficient modulation on LTE PYH resources improves the data rate of backscatter communication. To obtain the tag data without knowing the ambient content, we design a checksum-based codeword translation method. We also propose a customized channel estimation scheme and a signal identification component in the backscatter system to ensure our accurate modulation and demodulation. Extensive experiments show that our CABLTE provides maximum tag throughput of 22 kbps, which is 3.67x higher than the content-agnostic system CAB and even 1.38x higher than the content-based system SyncLTE.

Different from intermittent ISM signals like Bluetooth and WiFi, LTE signals are continuous in time and more pervasive in space, which makes them suitable carriers for ambient backscatter systems. However, due to the continuous LTE traffic and complex frame structures, existing ambient backscatter systems, such as HitchHike and LScatter, cannot reliably backscatter LTE signals in a standard-compatible way. We observe that the primary cause of their failures is that tags cannot accurately synchronize with LTE excitations. To address this issue, we propose SyncLTE, an LTE backscatter system that achieves high-accuracy synchronization and standard-compatible backscatter communication. The key novelty is a new tag design that uses the periodicity of LTE signals for synchronization and provides a customized single-symbol modulation scheme for LTE carriers. Our design is prototyped using FPGAs, SDR LTE eNBs and UEs. Comprehensive experiments have been done in various scenarios, including LoS, NLoS, indoor and outdoor. Results show that SyncLTE is 22.4x and 7.4x better than LScatter and Multiscatter in terms of the 80th percentiles of synchronization errors. Also, SyncLTE can deliver throughputs of up to 200 bps using BPSK and 400 bps using QPSK while other systems suffer from failures.

The continuous and ubiquitous nature of LTE traffic makes it advantageous as a backscatter carrier. However, existing backscatter works ignore the importance of being LTE-like, resulting in incompatibility with the standard and inability to access LTE services. We observe that achieving LTE-like requires a service initiation mechanism, that is, paging and accurate downlink synchronization. To this end, we present LTElike, a novel backscatter design that can page tags to initiate LTE service requests. Specifically, we page our tag using the form of amplitude modulation, enabling the ultra-low-power tag to receive paging and wake up. Further, we design an accurate synchronization strategy combining detection and template matching based on correlation, which improves the accuracy to single symbol level. We prototype LTElike using FPGAs, SDR LTE eNBs and UEs. The evaluation results show that the paging identification rate is as high as 100%, and the mean synchronization error of LTElike is 17x better than the counterpart of LScatter.

Recently, backscatter technology has attracted much interest in wireless communication due to its novel low-cost and battery-free design. Since Bluetooth Low Energy (BLE) was born to be low energy consumption, great efforts have been made in BLE-based backscatter systems, like FreeRider, RBLE. In this paper, we present BonusBlue, a BLE backscatter system that enables high-goodput communication with commercial BLE devices. BonusBlue tag generates BLE packets by modulating data on excitation signals and set up a data connection with BLE receiver using a state machine, thus achieving a high-goodput communication link. We present this state machine design and build a prototype of our tag using an FPGA, and evaluate its performance with BLE devices. Our evaluation shows that the backscatter tag can build a robust data connection link with commodity BLE device in the guidance of our state machine and transmit tag data on this link. Experimental results show that our backscatter system can achieve a goodput of up to 16.9 kbps.