Spectral Efficiency Considerations in 6G Networks

As wireless connectivity continues to evolve toward 6G, the demand to efficiently deliver higher throughput, lower latency, and improved reliability increases. Efficiency has been traditionally quantified in terms of spectral efficiency (SE) and energy efficiency (EE). Herein, a new radio access technology (RAT) system metric, radio resource utilization efficiency (RUE), is introduced. RUE measures the efficiency with which the considered RAT utilizes available radio resources (spectrum, access methods, time slots, and data symbols) to meet future 6G demands for downlink (DL) and uplink (UL) transmissions. The performance of typical cellular and cell-free massive multiple-input multiple-output (MIMO) deployments is compared to demonstrate the need for considering RUE when designing 6G networks. Factors influencing SE are investigated across three categories: 5G infrastructure, practical limitations (such as channel matrix rank deficiency) and implementation losses (signal-to-interference-plus-noise ratio degradation). For the example RAT configuration, 5G infrastructure yields a DL-RUE of 47% and UL-RUE of 40%, revealing significant room for improvement when defining 6G. Practical limitation assumptions are based on 5G single-user MIMO and multiuser MIMO measurements conducted in commercialized deployments. The resulting SE losses are characterized to offer guidance for advanced algorithms employing machine learning–based techniques. The benefits of increasing transmission bandwidth from 100 MHz to 1.6 GHz are also demonstrated, and a next-generation radio access network architecture that can support 6G and artificial-intelligence-enabled radio access networks is described.