As the Open Radio Access Network (O-RAN) paradigm is transforming the cellular landscape, third-party Extensible Applications (xApps) deployed in the Near-Real-Time RAN Intelligent Controller will play a critical role in facilitating next-generation cellular networks. Such networks will rely heavily upon robust data-driven Artificial Intelligence and Machine Learning(AI/ML) solutions that can perform fine-grained RAN control at the millisecond timescale. As xApps represent the point of contact between these advanced AI/ML solutions and the RAN itself, understanding these important O-RAN applications is essential for researchers in the wireless domain and will be critical to the full-scale integration of AI/ML into the next generation of cellular networks. Motivated by a lack of relevant and up-to-date surveys on this topic, we provide a comprehensive overview of xApps, including important background information, current xApp development techniques, a discussion of xApps and AI/ML, state-of-the-art use cases, vulnerabilities in the xApp architecture, and other critical research challenges. We summarize the plethora of available information on this topic by highlighting the keyissues and presenting a cohesive message that provides the necessary back-ground to the reader and isolates the critical research issues that currently remain unaddressed. As such, this survey is a one-stop-shop for researchers seeking a solid grasp of the state-of-the-art and a clear outline of the central research challenges relevant to xApps in cellular networks.

Despite the success of Test-time adaptation (TTA), recent work has shown that adding relatively small adversarial perturbations to a limited number of samples leads to significant performance degradation. Therefore, it is crucial to rigorously evaluate existing TTA algorithms against relevant threats and implement appropriate security countermeasures. Importantly, existing threat models assume test-time samples will be labeled, which is impractical in real-world scenarios. To address this gap, we propose a new attack algorithm that does not rely on access to labeled test samples, thus providing a concrete way to assess the security vulnerabilities of TTA algorithms. Our attack design is grounded in theoretical foundations and can generate strong attacks against different state of the art TTA methods. In addition, we show that existing defense mechanisms are almost ineffective, which emphasizes the need for further research on TTA security. Through extensive experiments on CIFAR10-C, CIFAR100-C, and ImageNet-C, we demonstrate that our proposed approach closely matches the performance of state-of-the-art attack benchmarks, even without access to labeled samples. In certain cases, our approach generates stronger attacks, e.g., more than 4% higher error rate on CIFAR10-C.

Emerging applications require mobile devices to continuously execute complex deep neural networks (DNNs). While mobile edge computing (MEC) may reduce the computation burden of mobile devices, it exhibits excessive latency as it relies on encapsulating and decapsulating frames through the network protocol stack. To address this issue, we propose PhyDNNs, an approach where DNNs are modified to operate directly at the physical layer (PHY), thus significantly decreasing latency, energy consumption, and network overhead. Conversely from recent work in Joint Source and Channel Coding (JSCC), PhyDNNs adapt already trained DNNs to work at the PHY. To this end, we developed a novel information-theoretical framework to fine-tune PhyDNNs based on the trade-off between communication efficiency and task performance. We have prototyped PhyDNNs with an experimental testbed using a Jetson Orin Nano as the mobile device and two USRP software-defined radios (SDRs) for wireless communication. We evaluated PhyDNNs performance considering various channel conditions, DNN models, and datasets. We also tested PhyDNNs on the Colosseum network emulator considering two different propagation scenarios. Experimental results show that PhyDNNs can reduce the end-to-end inference latency, amount of transmitted data, and power consumption by up to 48×, 1385×, and 13×while keeping the accuracy within 7% of the state-of-the-art approaches. Moreover, we show that PhyDNNs experience 4.3 times less latency than the most recent JSCC method while incurring in only 1.79% performance loss. For replicability, we shared the source code for the PhyDNNs implementation.

This work reveals a critical vulnerability of the Wi-Fi standard that if unaddressed, might lead to serious security issues and compromise the performance of several billions of Wi-Fi devices. Specifically, this paper introduces and validates with commercial off-the-shelf Wi-Fi devices a new Beamforming Report Eavesdropping Attack (BREAK), which leverages the MU-MIMO channel estimation procedure used by Wi-Fi to decrease the throughput of the entire network without being detected. Through rigorous mathematical optimization, we compute the poisoned feedback that a BREAK adversary eavesdropping the feedback angles needs to send to the access point to reduce the throughput of legitimate users. Through extensive experimental evaluation with Beamformee commercial Wi-Fi routers and smartphones in multiple network configurations, we show that through BREAK, an adversary may victim beamforming feedback angles decrease the throughput at legitimate stations by 65% modifying only about 17% of its feedback without being detected. For replicability, we shared the code implementing the attack together NDP for channel sounding with the modified firmware to be used at the adversary node.

In this paper, we present m3MIMO a mmWave fully-digital multi-user multi-input multi-output (MU-MIMO) testbed for advanced wireless research. m3MIMO operates in the 57-64 GHz frequency range and supports up to 1 GHz of bandwidth enabling large data multiplexing in the frequency domain through orthogonal frequency-division multiplexing (OFDM). The testbed features three custom-designed Zynq UltraScale+ RFSoC-based Software Defined Radios (SDRs) empowered with the Pi-Radio fully digital transceivers. Two of these SDRs support eight transmit and receive streams each (8 × 8 MIMO), while the third SDR supports up to four channels. m3MIMO supports three different communication modes: (i) point-to-point (P2P) transmissions; (ii) single-user multi-input multi-output (SU-MIMO), where multiple streams are transmitted to a single end-device; and (iii) MU-MIMO, where two devices are simultaneously served by a single transmitter. To showcase the m3MIMO's versatility, we present two research use cases: tracking-based beamforming and mmWave-based sensing. We will open-source the m3MIMO code along with the relevant use-case datasets, facilitating further analysis.