Bidirectional Cross-technology Communication (CTC) between WiFi and BLE demonstrates a wide range of applications prospects, such as temperature/humidity monitoring in smart home, LE-Audio relaying by WiFi APs, etc. However, existing CTC techniques between WiFi and BLE only support one-way transmission and are unable to be implemented on Commercial Off-The-Shelf (COTS) devices. This paper proposes BiCross, a bidirectional CTC scheme between WiFi and BLE which requires only software update on COTS devices. In essence, BiCross first presents a channel-specific symbol mapping technique to support all-channel reliable downlink CTC for BLE channel hopping. Then, BiCross leverages the spectrum scan capacity of WiFi Network Interface Cards (NICs) and analyzes the spectral characteristics of BLE frames to achieve uplink CTC. Finally, BiCross solves the problem of discontinuous and uncertain interval of spectrum analysis on commodity WiFi NICs through the design of BLE payload symbols and CRC-based error correction. The evaluation results demonstrate that BiCross achieves high reliability (downlink FRR > 95%, uplink FRR > 90%) and high throughput (downlink 854kbps, uplink 732kbps), and we showcase the application of BiCross on temperature acquisition in smart home scenario.

Bluetooth audio, as a common application in our daily life, faces a major challenge due to its limited transmission range in meeting users' demands. Traditional solutions, such as using high-power Bluetooth transmitters, require hardware upgrades that are neither cost-effective nor energy-efficient. This work introduces WiLE-Audio, a novel approach that extends Low Energy Audio (LE Audio) coverage through physical-layer cross-technology communication (CTC) from WiFi to Bluetooth Low Energy (BLE). We first present a novel symbol mapping technique from WiFi DQPSK to BLE GFSK symbols, which enables all-channel and reliable CTC to support Bluetooth channel hopping. Then, to implement CTC to commodity WiFi Network Interface Card (NIC), we present a real-time reverse scrambling method that dynamically calculates the payload of WiFi packets at the NIC driver. Finally, to align with the strict time window requirements of the BLE receiver, we design a precise timing strategy and a priority scheduling mechanism at the WiFi transmitter, effectively mitigating timing offsets due to Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and queue management. These systematic innovations allow WiLE-Audio to be easily implemented into existing commercial WiFi and BLE devices with only a simple software upgrade on the WiFi side. Furthermore, using existing WiFi infrastructures, WiLE-Audio enables the relaying of Bluetooth Low Energy Audio (LE-Audio) and the roaming of BLE receiver at any WiFi-covered location. We implement WiLE-Audio on commercial WiFi and BLE devices, and conduct extensive evaluations across various scenarios. Experimental results demonstrate that WiLE-Audio extends the transmission distance of LE Audio by 2× in single-hop mode and at least 2.6× in two-hop roaming mode. This work provides a cost-effective and scalable solution for enhancing Bluetooth audio coverage, providing a promising prospect for whole-house or even whole-building LE Audio listening.

Bluetooth audio faces a major challenge due to its limited transmission range in meeting users' demands. This work introduces WiLE-Audio, a novel approach that extends Low Energy Audio (LE Audio) coverage through cross-technology communication (CTC) from WiFi to BLE. We first present a novel symbol mapping technique to enable all-channel and reliable CTC. Then, we present a real-time reverse scrambling method to implement CTC to commodity WiFi devices. Finally, we design a precise timing strategy and a priority scheduling to align with the strict time window requirements of the BLE receiver. These systematic innovations allow WiLE-Audio to be easily implemented into existing commercial devices with only a simple software upgrade on the WiFi side. Furthermore, we achieve seamless switching between Bluetooth classic audio and WiLE-Audio, thus supporting whole-house audio roaming. We implement our work on commercial WiFi and BLE devices and demonstrate that WiLE-Audio extends the transmission distance of LE Audio more than 2×.

Data uploading applications in wireless networks may suffer from the degrade of Quality of Experiences (QoEs), due to the untimely adjustment of congestion window (cwnd) in face of the rapid change of wireless channel. To mitigate this problem, we analyzed the relationship between the NIC driver queue length at the wireless sender and the end-to-end transmission performances, and found a strong correlation between them, since the bottleneck mostly occurs at the wireless link. Based on this observation, we designed QCC, a congestion control algorithm that adjusts cwnd according to the residual queue length after each round of NIC transmission. Since obtaining congestion information locally at the sender leads to a much shorter feedback path than waiting for the end-to-end ACK feedback, QCC can track the time-varying wireless links much faster and more accurately. In addition, QCC also presents adaptive slow start mechanism and MAC layer-assisted fast recovery mechanism, both of which make efficient use of residual queue length to further improve transmission performances. Experiment results on both real-world Wi-Fi and cellular networks reveal that QCC can achieve at least 2.36X lower delay than that of BBR while ensuring 98.5% throughput of BBR.

With the development of wireless communications (e.g., WiFi 6 and 5G), more and more high-bandwidth networks are emerging in our daily life. However, due to the limited speed of the slow start phase in congestion control algorithms, the high-bandwidth links may not be fully utilized, which will degrade the Quality of Service (QoS). The reason is, since the available link capacity is unknown until the link is fully occupied, the sender has to gradually increase the congestion window (cwnd) from a small initial value, causing the link to be underutilized, until a packet is dropped or a congestion signal is detected. Especially, for a short flow, the transmission is often finished before the link capacity is reached, leading to the waste of available bandwidth. To better exploit the high bandwidth links, this paper proposes FBE (Fast Bandwidth Estimation without Filling up the Bottleneck Link), by leveraging the effective ACK's returning rate to estimate the bottleneck link capacity. More specifically, instead of sending out any additional probe packets, FBE uses the ACK rates from the first two RTT rounds to quickly estimate the bandwidth during slow start phase. Since the original ACK rate is significantly lower than the available link bandwidth due to the exhaustion of send window, and the competing flows also have an impact on the ACK rate, FBE elaborates the ACK interval compensation algorithm to refine the ACK intervals to reflect the link rate, and then updates cwnd to a suitable size. To address the challenge of inaccurate bandwidth estimation, especially for rapidly changing wireless link, FBE dynamically adjusts cwnd according to the feedback of driver queue length after the bandwidth estimation. Experiments in real WiFi and LTE networks show that FBE reduces the slow start convergence time by 54.8% and 53.5% compared to CUBIC and BBR with traditional slow start, respectively. And when transferring short flows (512KB in size), FBE reduces the flow completion time by 40.4% and 43.8% compared to CUBIC and BBR, respectively.

Data upload applications such as streaming of live videos and cloud services bring convenience to our lives. However, the Quality of Experience in wireless networks is often unsatisfactory. One of the reasons is, wireless communication is vulnerable to unpredictable factors such as rapid change of channel and competition of channel resources, leading to hysteresis and inaccuracy when performing a congestion control algorithm. To mitigate this problem, we analyzed the relationship between the real-time length of the NIC driver queue at the sender and the end-to-end transmission performances, and found a strong correlation between them. The reason is, when the wireless link is the first hop of data upload, the bottleneck mostly occurs at this hop, thus causing the accumulation of packets on the NIC driver queue. Based on this observation, we designed QCC, a congestion control algorithm that adjusts the congestion window (cwnd) according to the residual queue length after each round of NIC transmission. Specifically, the cwnd will be quickly reduced when this queue length is large to mitigate congestion, and gradually increased when it is small to increase link utility. By this means, QCC can track the time-varying wireless links quickly and accurately to achieve both high throughput and low latency. We evaluate QCC on both real-world Wi-Fi and cellular network implementations. Our experiment results reveal that QCC can achieve 2.04X lower delays than that of BBR while ensuring the similar link utilization rate as BBR (99% of BBR's throughput).

Recent advances on Physical-layer Cross-Technology Communication (PHY-CTC) have achieved high throughput direct communication across different wireless technologies. These PHY-CTC works are commonly achieved by emulating the target signal waveform of the receiver. However, signal emulation suffers from inherent unreliability due to imperfect emulation, and it only supports few communication channels. When applied in WiFi to Bluetooth Low Energy (BLE) scenario, it will face two challenges: i) a BLE receiver can not tolerate any bit error in a frame, while emulation errors are easy to appear; and ii) the BLE device performs channel hopping while most BLE channels are unavailable for emulation based CTC.To address these challenges, we present WiBle, a high reliable and all-channel supporting PHY-CTC from WiFi to BLE. The key technical insight of WiBle is symbol transition mapping: When a symbol is transmitted by a WiFi sender and flows into a BLE receiver, it will leave some unique signatures which can be leveraged to extract information. More specifically, it is observed that the phase shifts of BLE received signal can be mapped to the transitions of WiFi symbols. Therefore, by carefully selecting the symbols at the WiFi sender, we can generate the desired phase shifts for correct BLE GFSK demodulation and achieve reliable CTC. Evaluation results on both USRP and commodity chip show that WiBle outperforms state-of-the-art CTCs by higher reliability (> 95% frame reception ratio), wider channel coverage (supporting all 40 BLE channels), and higher throughput (974.3Kbps), under a full range of configurations including indoor/outdoor and LoS/NLoS settings.

Cross-technology Communication (CTC) is a promising paradigm for efficient coordination and cooperation among heterogeneous wireless technologies. Recent advances in physical-layer CTC (PHY-CTC) approaches the standards' maximum transmission rate by exploring PHY-layer signal features. However, due to the lack of reliable feedback, current PHY-CTC technologies can hardly ensure transmission reliability. This paper presents RAP (Reliable Acknowledged PHY-CTC), a bidirectional CTC design with reliable PHY-CTC feedback. First, we present a novel PHY-CTC technique to efficiently establish a reliable feedback channel (e.g., ACKs or NACKs). Then, based on the feedback, we propose a joint intra-packet coding and inter-packet coding scheme to improve the reliability of CTC. Finally, we present an on-demand data (re)transmission scheme to support unicast, multicast and broadcast more efficiently. We implement and evaluate RAP on USRP N210 with IEEE 802.11g PHY (WiFi) and commodity ZigBee devices. The experiment results show RAP achieves reliable data transmission (>99% packet reception rate (PRR)) and high throughput (over 35kbps) under a wide range of scenarios.

Recent advances on physical-layer Cross-Technology Communication (PHY-CTC) achieve high throughput direct communication across different wireless technologies, by emulating the standard waveform of the receiver. However, this signal emulation method faces the challenges of inherent unreliability due to the imperfect emulation. Therefore, it's not suitable to achieve PHY-CTC from WiFi to BLE, since a BLE receiver can not tolerate any bit error in preamble checking when receiving a BLE frame. We present NBee, the first WiFi to BLE physical-level CTC. The key insight lies in Narrow-Band Decoding, i.e., 22MHz bandwidth WiFi (802.11b) signal can be correctly decoded at the BLE RF front-end with only 1MHz bandwidth, if the WiFi payload bits are selected by a specific pattern. More specifically, NBee leverages the unique signatures in the WiFi signal distorted by 1MHz Low Pass Filter (LPF) at BLE to extract information. Evaluation results on commodity BLE chips show NBee can achieve 1Mbps CTC with 95% packet reception rate (PRR), 3400x faster than the state-of-art CTC from WiFi to BLE.