[简介] 下一代多址技术将突破以正交性为基础的设计原则，通过非正交性的设计和更先进的信息处理技术获得更高的谱效和能效。针对海量随机接入与非正交多址（NOMA）面临的不同挑战，认为不同的接入方法与接收机设计可大幅提升大规模接入与数据传输的效率。此外，人工智能、大规模多输入多输出（MIMO）和多基站协作等技术的蓬勃发展也为下一代多址技术的发展提供了新的可能。

[简介]算力需求提升带动网络带宽成倍提速，数据中心能耗呈指数型增长。针对低功耗、高带宽的技术需求，硅光、共封装光学（CPO）等技术有望成为长期解决方案。硅光芯片采用光互联，叠加CPO技术，将光引擎与交换芯片共同封装，在速率提高的同时大大缩减功耗。液冷技术、线性驱动可插拨光模块（LPO）、相干技术及薄膜铌酸锂等技术成为光模块优化主要新趋势。LPO在高线性度跨阻放大器（TIA）/驱动芯片厂商大力推动下或可快速落地。相干精简版解决方案在数据中心2 km以内传输距离方面拥有竞争性。

[Introduction] Extremely large-scale multiple-input multiple-output (XL-MIMO) and terahertz (THz) communications are pivotal candidate technologies for supporting the development of 6G mobile networks. However, these techniques invalidate the common assumptions of far-field plane waves and introduce many new properties. To accurately understand the performance of these new techniques, spherical wave modeling of the near-field communications needs to be applied for future research. Hence, the investigation of near-field communication holds significant importance for the advancement of 6G, which brings many new and open research challenges in contrast to conventional far-field communication. In this paper, we first formulate a general model of the near-field channel and discuss the influence of spatial nonstationary properties on the near-field channel modeling. Subsequently, we discuss the challenges encountered in the near field in terms of beam training, localization, and transmission scheme design, respectively. Finally, we point out some promising research directions for near-field communication.

[Introduction] Extremely large-scale hybrid reconfigurable intelligence surface (XL-HRIS), an improved version of the RIS, can receive the incident signal and enhance communication performance. However, as the RIS size increases, the phase variations of the received signal across the whole array are nonnegligible in the near-field region, and the channel model mismatch, which will decrease the estimation accuracy, must be considered. In this paper, the lower bound (LB) of the estimated parameter is studied and the impacts of the distance and signal-to-noise ratio (SNR) on LB are then evaluated. Moreover, the impacts of the array scale on LB and spectral efficiency (SE) are also studied. Simulation results verify that even in extremely large-scale array systems with infinite SNR, channel model mismatch can still limit estimation accuracy. However, this impact decreases with increasing distance.