Towards 5G-advanced NR-unlicensed systems: Physical layer design and performance

In the pursuit of a highly reliable and low-latency-enabled 5G-advanced new radio unlicensed (NR-U) system, addressing the challenge of high error rates and high signaling overhead transmissions remains key to improving network performance. In this context, to reduce error rates, mechanisms such as retransmissions can be employed. However, performing multiple retransmissions comes at the cost of utilizing extra transmission resources, which in turn affects the spectral efficiency of the network. This would further necessitate proper scheduling to alleviate resource wastage and undesirable collisions during data transmission. In this article, we provide an overview of the design specifications of the long-term evolution-license assisted access (LTE-LAA) technology and the prospective enhancements to enable NR-U operation in bands beyond 7 GHz. Additionally, we examine the configurations of selected design features to enable NR-U scheduling. Specifically, we illustrate the benefits and the limitations of the choice of the switching pattern under the frame structure, the feedback value type under the hybrid automatic repeat request (HARQ) procedure, and the timing parameters under the radio link control (RLC) layer. Besides, we present simulation results to depict the impact of the configurations mentioned above on the performance of NR-U.