As discussions around 6G begin, it is important to carefully quantify the spectral efficiency gains actually realized by deployed 5G networks as compared to 4G through various enhancements such as higher modulation, beamforming, and MIMO. This will inform the design of future cellular systems, especially in the mid-bands, which provide a good balance between bandwidth and propagation. Similar to 4G, 5G also utilizes low-band (<1 GHz) and mid-band spectrum (1 to 6 GHz), and hence comparing the performance of 4G and 5G in these bands will provide insights into how further improvements can be attained. In this work, we address a crucial question: is the performance boost in 5G compared to 4G primarily a result of increased bandwidth, or do the other enhancements play significant roles, and if so, under what circumstances? Hence, we conduct city-wide measurements of 4G and 5G cellular networks deployed in low- and mid-bands in Chicago and Minneapolis, and carefully quantify the contributions of different aspects of 5G advancements to its improved throughput performance. Our analyses show that (i) compared to 4G, the throughput improvement in 5G today is mainly influenced by the wider channel bandwidth, both from single channels and channel aggregation, (ii) in addition to wider channels, improved 5G throughput requires better signal conditions, which can be delivered by denser deployment and/or use of beamforming in mid-bands, (iii) the channel rank in real-world environments rarely supports the full 4 layers of 4x4 MIMO and (iv) advanced features such as MU-MIMO and higher order modulation such as 1024-QAM have yet to be widely deployed. These observations and conclusions lead one to consider designing the next generation of cellular systems to have wider channels, perhaps with improved channel aggregation, dense deployment with more beams.

翻译：随着6G相关讨论的兴起，有必要通过量化分析5G网络相较4G在更高阶调制、波束赋形及MIMO等增强技术方面实际实现的频谱效率提升。这一研究将为未来蜂窝系统设计提供重要参考，尤其针对兼具带宽与传播优势的中频段。与4G类似，5G同样采用低频（<1GHz）与中频段（1-6GHz）频谱资源，因此对比二者在这些频段的性能表现，可揭示未来优化方向。本研究聚焦核心问题：5G相较4G的性能提升主要源自带宽扩展，还是其他增强技术发挥了关键作用？若后者成立，又需满足何种条件？为此，我们在芝加哥与明尼阿波利斯市范围内对部署于低频与中频段的4G/5G蜂窝网络进行全城测量，系统量化5G技术各项改进对吞吐量性能的贡献。分析表明：（i）当前5G相较4G的吞吐量提升主要得益于更宽的信道带宽（包括单信道与信道聚合），（ii）除更宽信道外，5G吞吐量提升需依赖更优信号条件，这可通过中频段更密集的基站部署及/或波束赋形技术实现，（iii）实际环境中信道秩难以支撑完整的4层4x4 MIMO，（iv）MU-MIMO与1024-QAM等高阶调制等先进特性尚未广泛部署。上述发现启示我们，下一代蜂窝系统设计应着眼于更宽信道（可结合改进型信道聚合技术）与更密集的多波束部署方案。