Most works on intelligent reconfigurable surface (IRS)-assisted networks consider link-level simulations and do not address the upper protocol layers. This limitation becomes particularly relevant in practical systems like 802.11 Wi-Fi, where channel access is based on listen-before-talk (LBT) scheme, making conventional IRS scheduling strategies (time-division or centralized coordination) difficult to apply. Given these reasons, we shift the focus to random channel access based on carrier sense multiple access with collision avoidance (CSMA/CA) to explore how an IRS can be beneficial in such scenarios. We first discover that improving the SNR of links from stations (STAs) to an access point (AP) introduces the potential risk of hidden terminals among the STAs in the uplink. To analyze this, we introduce ns3IRS, a framework that integrates a model of an IRS into the ns-3 network simulator, which allows us to run the full WiFi stack within an IRS-assisted wireless network. We propose two solutions to mitigate the hidden terminal problem caused by the IRS also by assuring mutual carrier sensing: (i) splitting a single centralized IRS, or (ii) using additional small IRSs nearby the STAs – to create direct links among them, with the purpose of enabling mutual carrier sensing. Results show that these two solutions can improve the throughput compared to the traditional approach where virtual carrier sensing, i.e., CSMA/CA with Request-to-Send/Clear-to-Send (RTS/CTS), is used. For instance, for a system with four users, the proposed approaches improve the throughput from 25Mbit/s to around 35Mbit/s compared to the baseline scenario with RTS/CTS. Additionally, latency and jitter are decreased. However, as the number of users increases, achieving performance gains requires a larger IRS, since the gain scales with the number of reflecting elements, especially for the centralized IRS. In scenarios where scaling the IRS is impractical, CSMA/CA with RTS/CTS may become a more effective alternative.

We present ToFMD, a system that can passively detect the movement of an indoor device-free user by relying on the absorptions and reflections of WiFi signals off his body. Our system is of practical use as it is able to reuse existing deployed commodity 802.11 infrastructure networks. It is based on the observation that the movement of an user is altering the multipath characteristics of the wireless channel which leads to changes in the measured time-of-flight (ToF) between adjacent WiFi access points. The system can detect moving people at different places in the room, it is not necessary that the user blocks the line-of-sight (LOS) path. In contrast to other approaches, our system works with inexpensive single antenna WiFi systems without access to low-level parameters like channel state information (CSI). Instead the ToF between any pair of access points is estimated using the fine time measurement (FTM) protocol, which is standardized within IEEE 802.11. The movement is detected with the help of a one class support vector machine. As proof of concept, we implemented our system with ultra-low cost ESP32 microcontrollers. The evaluation shows that our solution outperforms traditional approaches using RSSI except for the scenario with user motion in adjacent rooms. If our system is installed in the same room as the user, it is able to detect its movement with an accuracy of at least 95 %.

Resilient wireless networks ensure that the network maintains functionality despite adverse conditions like hardware and software failures, adversarial jamming attacks, or environmental changes like wireless channel fading which can disrupt connectivity. We show that Cross-Technology Communication (CTC), which was developed to enable direct communication between otherwise incompatible radio technologies, can be utilized to improve the resilience in wireless networks. This is achieved by increasing the number of independent wireless links between adjacent wireless nodes as well as by the increase in communication distance resulting in increased path diversity. Results from our analysis reveal that the same level of resilience can be achieved with reduced number of radio interfaces per node while tolerating an order of magnitude higher node failure rate. Moreover, such CTC-enabled networks are more resilient to advanced technology-specific jamming attacks.

The recent move of the LoRa wireless technology towards the wider 2.4 GHz ISM spectrum band creates multiple opportunities for its broader usage in new IoT applications requiring larger data rates. However, this ISM band is already crowded with other wireless technologies like WiFi or Bluetooth, and cross-technology interference issues need to be considered. Moreover, the less favorable radio propagation properties in the 2.4 GHz band shorten the communication distance of LoRa transmissions and therefore make relaying necessary. Unfortunately, the direct usage of LoRa technology in a wireless mesh network is challenging due to the non-existent generic frame preamble and header, i.e. LoRa frames are not self-contained. This makes the dynamic adaptation of the modulation used by LoRa per link or even packet transmission challenging. We show in this paper that such limitation can be partially overcome by utilizing the macro spacial diversity provided by opportunistic routing (OR) protocols. In contrast to traditional routing OR selects a candidate set of nodes per hop along the path in the mesh network. Thus any temporal channel fading and local interference conditions will not result in a failed transmissions due to utilization of the spatial diversity provided by OR. The usage of OR achieves a much higher E2E packet delivery rate as well as lower E2E delay as compared to traditional routing while the overhead is reasonable. Moreover, with OR the same signal modulation can be used network-wide and its adjustment can be made on a long-term basis.