Multi-Access Point Collaboration (MAPC) envisioned in future Wi-Fi standards has the potential to provide reliable connectivity for time-critical IoT applications. The joint transmission (JT) concept strengthens the signals at the station transmitted from distributed APs, increasing its resilience against interference and multi-path fading to improve reliability and latency performance. There is no commercially available WiFi device capable of doing this since individual APs must be synchronized for time, RF carrier and packet data, and are required to share the medium access with each other. We present an experimental study of distributed dual-AP Wi-Fi network prototype with SDR platforms with openwifi. By synchronizing the clock source, packet transmission control and data, we demonstrate a successful constructive overlap of transmitted WiFi signals at the receiver from distributed APs. Specifically, we observe a 6 dB received signal power gain and a 4.4 dB SNR improvement from the decoded packets with two APs compared to a standalone transmission in the experiment.

Field-Programmable Gate Array (FPGA)-based Software-Defined Radio (SDR) is well-suited for experimenting with advanced wireless communication systems, as it allows to alter the architecture promptly while obtaining high performance. However, programming the FPGA using a Hardware Description Language (HDL) is a time-consuming task for FPGA developers and difficult for software developers, which limits the potential of SDR. High-Level Synthesis (HLS) tools aid the designers by allowing them to program on a higher layer of abstraction. However, if not carefully designed, it may lead to a degradation in computing performance or significant increase in resource utilization. This work shows that it is feasible to design modern Orthogonal Frequency Division Multiplex (OFDM) baseband processing modules like channel estimation and equalization using HLS without sacrificing performance and to integrate them in an HDL design to form a fully-operational FPGA-based Wi-Fi (IEEE 802.11a/g/n) transceiver. Starting from no HLS experience, a design with limited overhead in terms of latency and resource utilization as compared to the HDL approach was created in less than one month. The FPGA design generated by HLS achieved the same performance as compared to its HDL counterpart when deployed on a System-on-Chip (SoC)-based SDR, as verified by a professional wireless connectivity tester.

Due to the increasing volume of data generated by sensors in modern cars, the need for high data rate links rises in vehicular networking. A promising way to achieve this is using mmWave communications, although beamforming is needed to overcome the high propagation losses at these frequencies. In addition, relaying might be needed to extend the coverage to larger distances for the delivery of a message in a specific geographical area, called geocasting. Moreover, reaching multiple receivers at once via multicasting can be achieved by using a wider antenna beamwidth, which comes at the cost of transmission range, while spatial sharing can be exploited using narrow beams. This paper investigates if using multicasts is beneficial for routing and scheduling of mmWave geocasts that need to be delivered before a timeout. We consider a non-time-slotted system with realistic antenna model and multiple data rates, for which we seek an optimal solution by modeling it as a mixed-integer linear program. Our numerical evaluations show that using multicasts is especially advantageous in scenarios with multiple highway lanes. Furthermore, we devise a heuristic algorithm that efficiently finds a route and creates a transmission schedule for a geocast. Several methods to include multicast links are evaluated, of which some consistently outperform the unicast-only method.

Software Defined Radio (SDR) platforms are valuable for research and development activities or high-end systems that demand real-time adaptable wireless protocols. While low latency can be achieved using the dedicated digital processing unit of a state-of-the-art SDR platform, its Radio Frequency (RF) front-end often poses a limitation in terms of turnaround time (TT), the time needed for switching from the receiving to the transmitting mode (or vice versa). Zero Intermediate Frequency (ZIF) transceivers are favorable for SDR, but suffer from self-interference even if the device is not currently transmitting. The strict MAC-layer requirements of Time Division Duplex (TDD) protocols like Wi-Fi cannot be achieved using configurable ZIF transceivers without having to compromise receiver sensitivity. Using a novel approach, we show that the TT using the AD9361 RF front-end can be as low as 640 ns, while the self-interference is at the same level as achieved by the conventional TDD mode, which has a TT of at least 55 μs. As compared to Frequency Division Duplex (FDD) mode, a decrease of receiver noise floor by about 13 dB in the 2.4 GHz band and by about 4.5 dB in the 5 GHz band is achieved.