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讨论的启动，有必要仔细量化已部署的5G网络相比4G通过更高阶调制、波束赋形和MIMO等增强技术实际实现的光谱效率增益。这将为未来蜂窝系统设计提供参考，特别是在平衡带宽与传播特性的中频段。与4G类似，5G同样使用低频段（<1 GHz）和中频段（1-6 GHz）频谱，因此对比这两个频段的4G与5G性能，有助于洞察如何实现进一步提升。本研究聚焦一个关键问题：5G相比4G的性能提升主要源于带宽增加，还是其他增强技术起到重要作用？若后者成立，在何种条件下生效？为此，我们在芝加哥和明尼阿波利斯市范围内对低频段和中频段部署的4G与5G蜂窝网络进行测量，并仔细量化5G各项技术改进对吞吐量性能提升的贡献。分析表明：（i）当前5G相比4G的吞吐量提升主要受限于更宽的信道带宽（包括单信道与信道聚合）；（ii）除更宽信道外，5G吞吐量提升还需更优的信号条件，这可通过中频段更密集的基站部署和/或波束赋形实现；（iii）实际环境中的信道秩极少支持4×4 MIMO的全部4层传输；（iv）MU-MIMO及1024-QAM等高级功能尚未广泛部署。这些观测与结论提示我们：设计下一代蜂窝系统时应考虑更宽的信道（或许通过改进信道聚合）以及采用更多波束的密集部署方案。