AraRACH: Enhancing NextG Random Access Reliability in Programmable Wireless Living Labs

TL;DR

AraRACH addresses the reliability of the 5G random access procedure in outdoor, field-deployed, open-source RAN testbeds by eliminating reliance on special RA slots and instead using full downlink and uplink slots for msg2 and msg3. The authors integrate AraSDR hardware with RF frontends (PA/LNA) into the OpenAirInterface stack, modifying scheduling so that msg2 is placed in the last DL slot and msg3 in a subsequent UL slot, while expanding available symbols to improve robustness. Through real-world experiments in a large rural living-lab, they show that longer symbol durations significantly increase RA success, achieving 90–100% success in obstructed environments when at least nine symbols are used for msg3, and demonstrate detection and decoding improvements across LoS and non-LoS scenarios. The work demonstrates a scalable path for reliable, end-to-end, open-source 5G/NextG experimentation on large outdoor testbeds and informs design choices for future programmable RAN research.

Abstract

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.

Figures (11)

• Figure 1: RF Frontend Control using GPIO Signal in OAI
• Figure 2: Contention-Based Random Access Procedure in 5G
• Figure 3: TDD UL/DL Common Configuration
• Figure 4: msg2 Scheduling in a Special Slot
• Figure 5: GPIO Control Signal Switching in OAI gNB