We present BumbleBee, a novel backscatter system that creates ZigBee transmissions over productive Bluetooth Low Energy (BLE) carriers. In contrast to prior content-aware or non-productive backscatter, BumbleBee overwrites tag information independently on any ambient BLE. The backscattered signal is dominated by the tag information and compliant with commodity ZigBee radios. Since BLE signals are widespread, BumbleBee enables the vision of pervasive ZigBee backscatter communication. We prototype BumbleBee using commodity BLE transmitters, an off-the-shelf FPGA, and commodity ZigBee receivers. Through extensive experiments and field studies, we show that BumbleBee works universally with ambient BLE and commodity receivers. Further, when the signal strength is -80 dBm, BumbleBee has a throughput of 218 kbps and 204 kbps in the line-of-sight (LOS) and nonline-of-sight (NLOS) scenarios, respectively. The throughput improvement is up to 3x compared with the advanced non-productive backscatter system, Interscatter [1], and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$32\mathrm{x}$</tex> over the content-aware backscatter system, FreeRider [2]. The bit error ratio (BER) is below 1% when the tag-to-receiver distance is 20 meters. As the first ambient ZigBee backscatter system that works universally with commodity transceivers, we believe BumbleBee takes a crucial step towards pervasive ZigBee backscatter communication. 

BumbleBee: Enabling the Vision of Pervasive ZigBee Backscatter Communication

Divergent mechanisms governed by several laws in force in Indonesia continue to impede the implementation of decisions rendered by state administrative courts. As a result, issues about the nature of government autonomy, legal consciousness, leadership structures, and political determination arise in the context of regional autonomy. The employed research methodology is normative juridical research, which analyzes articles in the law on state administrative courts about the execution of state administrative court institutions' decisions to identify and formulate legal arguments. This study demonstrates discrepancies in how decisions are executed by state administrative tribunals in Indonesia and several challenges associated with their practical implementation. In order to address these challenges, four conceptual frameworks of executive authority have been developed to establish a mechanism for implementing administrative court rulings in a globalized environment. The evolution model of legal instruments for implementing decisions of state administrative courts, the defense model for various types of implementation such decisions, the law enforcement model for executing state administrative courts, and the execution model as a question vacate. 

The Compliance of Regional Autonomy with State Administrative Court Decisions

We present DanBlue, a commodity Bluetooth backscatter system that can take multi-frequency signals as excitations. Unlike all prior systems, DanBlue leverages ambient Bluetooth signals of various frequencies to backscatter in the standard Bluetooth-hopping way. To do so, we first introduce an edge proxy to identify uncontrolled ambient Bluetooth signals. Then, we design a wideband channel hopping to enable fast frequency shifts for low-power tags, empowering backscatter hopping much like active Bluetooth hopping. We prototype the DanBlue tag using off-the-shelf FPGAs and the DanBlue edge with commercial off-the-shelf (COTS) chips. Through comprehensive field studies, we show that DanBlue supports hopping from any-frequency Bluetooth excitations to any-frequency Bluetooth channels. Furthermore, the accuracy of frequency identification is as high as 99% with less than 7.1 ms latency. For the first time, we demonstrate DanBlue can emulate the Bluetooth protocol stack and seamlessly build connectivity with multiple active Bluetooth radios. We believe DanBlue is taking a crucial step forward on fully functioning battery-free Bluetooth. 

Dances with Blues: Harnessing Multi-Frequency Carriers for Commodity Bluetooth Backscatter

Human activity recognition (HAR) has become a hotspot. However, the existing HAR has some shortcomings, such as few recognized human activities, no identification, privacy leakage, and battery maintenance. Therefore, we design body RFID skeleton which fully senses the key features of human activity, and further propose human activity recognitions by taking advantage of RFID (privacy protection, identification, and battery-less maintenance). First, we devise RFID skeleton activity graph as human activity model. Second, we propose baseline RFID skeleton activity graph convolution network (FSCN) by using the graph convolution network (GCN), and FSCN classifies the RFID skeleton activity graph for human activity recognition. Third, to solve the tag response signal feature data over-smoothing and the different information aggregation degree in FSCN, we propose improved FSCN with the residual network (R-FSCN). Finally, we design the parallel RFID skeleton activity graph convolution network (PR-FSCN) for optimizing R-FSCN. Massive experiments show that PR-FSCN has comprehensive superiority to the existing HARs. As far as we know, this study is the first work that appropriately designs body RFID skeleton for HAR, and that successfully introduces GCN to investigate the new bound-RFID HAR with high recognition performance.

Body RFID Skeleton-Based Human Activity Recognition Using Graph Convolution Neural Network

Backscatter communication (BackCom) technology represents a low-cost and battery-free technology for Internet-of-Things (IoT) applications. One variant of BackCom, termed as ambient BackCom, which uses ambient signals to eliminate the need for a dedicated carrier source is more advantageous due to reduced system complexity and cost. Previous studies on ambient BackCom have primarily relied on amplitude modulation-based systems like ON&NDASH;OFF-keying (OOK) modulation, which achieved a maximum tag-to-receiver (Rx) distance of less than five meters. Alternatively, frequency-shift-keying (FSK)-based ambient BackCom systems have demonstrated improved distance, but with limitations. This work introduces an ambient broadcast frequency-modulation (FM) BackCom system utilizing in-band 2FSK-based modulation, designed to be compatible with both mono and stereo radio systems and extend communication distance. In order to successfully detect the backscatter 2FSK symbols, two pivotal technologies are employed: first, a quadrature demod-based in-phase/quadrature ( $I/Q$ ) sample processing method enhances the signal-to-interference-plus-noise ratio (SINR). This enhancement has been substantiated through theoretical analysis, simulations, and cable-connected experiments. Second, a moving window-based 2FSK demodulation strategy is implemented, exhibiting resilience to tag frequency instability. The proposed system significantly enhances the tag-to-Rx communication distance, achieving an impressive range of over 100 m, a considerable improvement over the current state-of-the-art. The performance of the proposed system is evaluated in both cable-connected and outdoor environments, achieving a maximum bit rate of 333 bits per second (bps) at a distance of 58 m and a maximum communication distance of 107 m at a bit rate of 200 bps.

FM Rider: Two-FSK Modulation-Based Ambient FM Backscatter Over 100 m Distance

This paper presents TiScatter, a timespan-based WiFi backscatter system that provides high-throughput communication with a single COTS receiver used. It outperforms the prior works that tradeoff between considerable data rate and practical deployment. To improve the data rate, TiScatter introduces a symbol-level times-pan modulation method that encodes tag data into the timespan between two modulated WiFi codewords in two successive WiFi packets. For decoding, TiScatter for the first time employs the injective feature between the checksum and the modulated codeword positions, which enables the demodulation of both the tag and original WiFi data using only one COTS receiver. This makes TiScatter more practical. Furthermore, we design TiScatter+ that shows these advantages while providing an even higher throughput under 802.11b excitations. We prototype our design, and comprehensive evaluations demonstrate that TiScatter shows a throughput over 100× higher than prior single-receiver backscatter systems like FS-Backscatter. It even has a better BER and throughput than the prior double-receiver backscatter systems like MOXcatter. Specifically, TiScatter provides 1) 2× higher peak throughput than MOXcatter and 2) an order of magnitude lower BER than MOXcatter with the presence of substantial interferences. In addition, TiScatter+ can deliver a throughput 3× higher than TiScatter under 802.11b ambient excitations. Our evaluation also confirms that TiScatter is generic and applicable to excitations under diverse WiFi standards (e.g., 802.11b/g/n).

Timespan-based Backscatter Using a Single COTS Receiver

Bidirectional links are widely adopted in many active radios to provide efficient data exchanges, e.g., WiFi and Bluetooth. However, they are underexplored for general-purpose backscatter communications. The downlinks of state-of-the-art Bluetooth backscatter systems are based on packet length modulation, which is inefficient and unreliable. In this paper, we propose BiBlue, a bidirectional Bluetooth backscatter system that uses an edge server to enable fast and reliable downlinks. Specifically, our edge server acts like a bridge that can translate commercial Bluetooth signals to Amplitude Shift Keying (ASK) signals. In addition, we design a reliable edge-to-tag link that adaptively decodes ASK signal under variance. Finally, we propose a low-power uplink design that enables connection-based bidirectional communication with commodity devices. We prototype BiBlue using FPGA and Software Defined Radio (SDR). Extensive experimental results demonstrate that BiBlue achieves more than 62x downlink throughput gains over FreeRider and meanwhile supports an 80 cm communication range of edge-to-tag with BER at around 1%. 

Bidirectional Bluetooth Backscatter with Edges

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. 

Heartbeating with LTE Networks for Ambient Backscatter

This paper presents the first symbol-level modu-lation technology for ZigBee backscatter communication. The developed backscatter tag, leveraging ambient ZigBee transmissions as radio frequency (RF) carrier excitation, conveys data by translating an excitation signal into a new ZigBee signal in neighboring ZigBee channels. This avoids the strong interference from the ambient excitation signals. The key enabling technique is a symbol-level codeword translation, which exploits square waves based on the difference between the excitation and tag data. A working prototype was successfully demonstrated to validate the modulation technology, which consists of two parts: an RF front-end circuit and an FPG A-based control circuit. Through extensive experiments and field studies, the evaluation shows that the bit error rates (BERs) can be controlled to be less than 0.1 when the communication distance is within 2 meters.

A Fine-grained Modulation Technology for ZigBee Backscatter Communication

Recently, using deep learning to achieve WiFi-based human activity recognition (HAR) has drawn significant attention. While capable of achieving accurate identification in a single domain (i.e., training and testing in the same consistent WiFi environment), it would become extremely tough when WiFi environments change significantly. As such, domain adversarial neural networks-based approaches have been proposed to handle such diversities across domains, yet often found to share the same limitation in practice: the imbalance between high-capacity of feature extractors and data insufficiency of source domains. This article proposes i-Sample, an intermediate sample generation-based framework, striving to tackle this issue for WiFi-based HAR. i-Sample is mainly designed as two-stage training, where four data augmentation operations are proposed to train a coarse domain-invariant feature extractor in the first stage. In the second stage, we leverage the gradients of classification error to generate intermediate samples to refine the classifiers together with original samples, making i-Sample also capable to be integrated into most domain adversarial adaptation methods without neural network modification. We have implemented a prototype system to evaluate i-Sample, which shows that i-Sample can effectively augment the performance of nowadays mainstream domain adversarial adaptation models for WiFi-based HAR, especially when source domain data is insufficient.

i-Sample: Augment Domain Adversarial Adaptation Models for WiFi-based HAR

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