The rapid evolution of wireless technologies has intensified interest in open and fully programmable radio access networks for whole-stack research, innovation, and evaluation of emerging solutions. Large-scale wireless living labs, such as ARA, equipped with real-world infrastructure play a vital role in this evolution by enabling researchers to prototype and evaluate advanced algorithms for next-generation wireless systems in outdoor and over-the-air environments benefiting from real-world fidelity and end-to-end programmability. However, at the core of this innovation is the performance in terms of coverage and reliability of these wireless living labs. For instance, interfacing power amplifiers and low noise amplifiers with software-defined radios (SDRs) for experimenting outdoors introduces issues in random access procedure—a process crucial in establishing connectivity between user equipment (UE) and the core network in 5G and 6G systems. Therefore, to ensure seamless connectivity and reliable communications in open-source 5G software stacks such as OpenAirInterface (OAI), we propose a slot-based approach to the 5G random access procedure leveraging full downlink (DL) and uplink (UL) slots instead of using special or mixed slots. We highlight how this approach achieves reliable 5G connectivity over 1 mile—the longest communication range that has been achieved so far in real-world settings using open-source 5G software stacks and the Universal Software Radio Peripheral (USRP) SDRs. We also demonstrate that, in a highly obstructed environment such as an industrial setting, we can increase the probability of a successful random access procedure to 90%–100% when we use at least 9 OFDM symbols to transmit msg2 and msg3.

Wireless innovation can significantly benefit from having access to real-world, over-the-air (OTA) living labs for open-source prototyping and field evaluation of emerging, state-of-the-art solutions. However, the existing open-source 5G testbeds are either confined to controlled indoor environments, or they use commercial-off-the-shelf (COTS) user equipment (UEs) only without supporting software-defined-radio (SDR) UEs, thus lacking real-world fidelity or end-to-end programmability from UEs to gNBs and core networks. To fill the gap, we develop and deploy AraSDR that, as an integral element of the ARA Platform for Advanced Wireless Research (PAWR) on rural broadband, serves as a first-of-its-kind outdoor living lab supporting end-to-end, fully-programmable 5G experiments with SDR UEs and base stations (BSes) in real-world rural settings. AraSDR deploys in agriculture farms and rural cities NI N320 and B210 as the BS and UE SDRs respectively, and it employs low-cost, performant custom RF front-ends with power amplifiers (PAs) and low-noise amplifiers (LNAs) to boost the transmit and receive signals for extended cellular coverage. To enable real-world SDR-based experiments with open-source 5G stand-alone (SA) TDD cellular operations, we address the challenges of reliable control signaling, precision timing of the transmission/reception mode of RF front-ends, as well as transmission and reception gain control. We develop the software control framework to support remote experiments with streamlined workflows and to enable container-based experiment portability and reproducibility. Using OpenAirInterface (OAI) as an example open-source 5G software platform, we demonstrate the capability of AraSDR in supporting real-world, OTA 5G experiments.

ARA is an at-scale Platform for Advanced Wireless Research (PAWR), specifically tailored to the unique community, application, and economic context of rural regions. It features the first-of-its-kind real-world implementation of long-distance, high-capacity wireless backhaul and access systems spanning over 30 km in diameter. Leveraging both software-defined radios and programmable Commercial Off-The-Shelf (COTS) systems, ARA orchestrates the wireless resources alongside the networking and compute resources for enabling end-to-end experiments involving user equipment, base stations, edge computing, and cloud infrastructure. Such an integration facilitates the coevolution of rural-focused wireless innovation and applications, while helping to advance the frontiers of advanced Next-G wireless systems such as Open RAN. As of summer 2024, ARA is publicly accessible with 7 base stations (BSes) and over 30 user equipment (UEs). In this demo, we share advanced wireless research experiments enabled by ARA, involving MU-MIMO in TV White Space (TVWS) bands, long-range mmWave and microwave backhaul communications, and open-source 5G NR protocol stacks such as srsRAN and OpenAirInterface (OAI).

Time synchronization is a critical component in network operation and management, and it is also required by Ultra-Reliable, Low-Latency Communications (URLLC) in next-generation wireless systems such as those of 5G, 6G, and Open RAN. In this context, we design and implement AraSync as an end-to-end time synchronization system in the ARA wireless living lab to enable advanced wireless experiments and applications involving stringent time constraints. We make use of Precision Time Protocol (PTP) at different levels to achieve synchronization accuracy in the order of nanoseconds. Along with fiber networks, AraSync enables time synchronization across the AraHaul wireless x-haul network consisting of long-range, high-capacity mmWave and microwave links. In this paper, we present the detailed design and implementation of AraSync, including its hardware and software components and the PTP network topology. Further, we experimentally characterize the performance of AraSync from spatial and temporal dimensions. Our measurement and analysis of the clock offset and mean path delay show the impact of the wireless channel and weather conditions on the PTP synchronization accuracy.

As the Platform for Advanced Wireless Research (PAWR) in rural broadband, the ARA wireless living lab features the deployment of first-of-its-kind wireless access and backhaul platforms in real-world agriculture and rural settings, and preliminary experiments have demonstrated very promising results, e.g., up to 3.2 Gbps wireless access throughput and more than 10 Gbps throughput across a wireless backhaul link of over 10 km. ARA is expected to be publicly released for broad community use starting in September 2023. Through this demo, we plan to share, for the first time, with the wireless research community the transformative research experiments enabled by ARA. To stimulate discussion and community participation, we will demonstrate a few example experiments ranging from MU-MIMO in TV White Space (TVWS) bands to long-range mmWave and microwave backhaul communications, as well as open-source 5G NR protocol stacks such as srsRAN and OpenAirInterface.

Millimeter waves (mmWaves) are considered as promising candidates for high bandwidth and high data rate transmission in 5G and beyond cellular networks. However, such high frequencies require directional transmission due to their inherent path loss and sensitivity to blockage. With directional transmission, it is difficult to locate a Mobile User (MU) in a cell which leads to mis-detections and delayed Initial Access (IA). In this paper, we propose a novel IA scheme that leverages the Channel State Information (CSI) to search sectors. Our scheme searches the sectors in the descending order of channel quality and, thus, named the Sorted Search Scheme (SSS). We argue that our CSI-based approach reduces the latency of IA in 5G and beyond networks and show that SSS has a low Mean Detection Latency (MDL) while maintaining the Mis-detection Probability (MDP) of the benchmark Exhaustive Search Scheme (ESS). Further, the analytical expressions of MDP and MDL are derived for all fading scenarios. Numerical simulation show that our SSS reduces the MDL by 16%, thereby making it useful for low-latency applications. It is also shown that even partial or imperfect CSI can reduce the MDL.