This paper presents an in-depth analysis of the Listen-Before-Talk (LBT) procedures required for cellular technologies operating in the unlicensed spectrum. We specifically investigate the 5G New Radio Unlicensed Standalone (NR-U SA) design under the most recent 3GPP standard-compliant Type 1 Channel Access Procedure (CAP). We highlight and address key challenges in adapting the asynchronous Type 1 CAP (i.e., load-based CAP) to NR-U’s synchronous slot-based framework and propose the Scheduled Type 1 CAP, which introduces a novel scheduling mechanism and implementation of additional sensing to facilitate seamless integration. We carry out our performance evaluation using a full-stack end-to-end network simulator and construct a realistic 3GPP-compliant coexistence scenario in which 5G NR-U SA and Wi-Fi networks operate indoors in unlicensed sub-7 GHz bands. The users of the 5G NR-U SA and Wi-Fi networks demand eXtended Reality applications. Through an extensive evaluation study, we analyse the interplay between the NR-U numerologies and the CAPs used in shared channel access and evaluate their impact on the end-to-end performance of both technologies by considering various quality of service metrics. The results reveal some of the main pitfalls of the LBT procedure defined by 3GPP in TS 37.213 and demonstrate the clear advantages of the proposed Scheduled Type 1 CAP. Our work provides valuable insights into CAPs for shared spectrum, proposes standard-compliant solutions, and lays the groundwork for future research by introducing a pioneering open-source network simulation platform for evaluating NR-U SA coexistence scenarios with the Scheduled Type 1 CAP.

We assess the performance of two distinct functional splits based on latency/latency variation and mapping efficiency, both individually and in unison. By considering hardware-offloading possibilities for a low-layer split (especially a pre-resource mapper split) using an option-6 software-based local thermal equilibrium split as an example, we show how data rate, Ethernet frame size and, in general, traffic generation characteristics will be very important aspects in the design of the future Ethernet mapping function. Then, an integrated Ethernet fronthaul with legacy and new/evolved split functionality operating at 100 Gb/s link rate is presented with the state-of-the art sub-100-ns latency variation for a timing-protocol flow. This is achieved through the application of a gap-filling aggregator, used for the first time in such a mobile fronthaul application.

An Opnet model of a time-aware shaper (TAS) based on the IEEE 802.1Qbv standard is presented. The TAS model is assumed to be the scheduling entity in an Ethernet-based fronthaul network, comprising of Ethernet switches. The fronthaul transports different traffic flow types as envisioned in next generation Radio Access Networks (RANs), including those for a timing protocol (based on the precision time protocol) and those from the implementation of different RAN functional subdivisions. The performance of the TAS is compared to that of a strict priority regime and is quantified through the frame delay variation of the high priority traffic when this contends with lower priority traffic. The results show that with the TAS implementation, contention effects can be overcome and frame delay variation (frame jitter) can be removed. Timing instability in the significant events of the scheduler is considered and a solution to overcome this issue is proposed.

A testbed implementation for an Ethernet fronthaul transporting signals arising from a long-term evolution (LTE) functional subdivision ("split") at the media-access control (MAC)/physical layer (PHY) interface is presented. Based on open LTE base station software, the testbed demonstrates significant data rate reductions compared to current fronthaul implementations that rely on In- phase and Quadrature radio sample transportation and data rates that scale with cell load. All generated traffic flows are clearly distinguishable using appropriate packet headers. A selection of test cases and their corresponding results are presented to demonstrate the operation of the fronthaul and the performance of individual flows in terms of data rates and overheads.