Extremely large-scale array (XL-array) is envisioned to achieve super-high spectral efficiency in future wireless networks. Different from the existing works that mostly focus on the near-field communications, we consider in this paper a new and practical scenario, called mixed near- and far-field communications, where there exist both near- and far-field users in the network. For this scenario, we first obtain a closed-form expression for the inter-user interference at the near-field user caused by the far-field beam by using Fresnel functions, based on which the effects of the number of BS antennas, far-field user (FU) angle, near-field user (NU) angle and distance are analyzed. We show that the strong interference exists when the number of the BS antennas and the NU distance are relatively small, and/or the NU and FU angle-difference is small. Then, we further obtain the achievable rate of the NU as well as its rate loss caused by the FU interference. Last, numerical results are provided to corroborate our analytical results.

翻译：超大规模阵列（XL-array）被设想为在未来无线网络中实现超高频谱效率。与现有工作多聚焦于近场通信不同，本文考虑一种新颖且实际的场景——混合近远场通信，即网络中同时存在近场与远场用户。针对该场景，我们首先利用菲涅尔函数推导出远场波束对近场用户造成用户间干扰的闭式表达式，进而分析基站天线数、远场用户角度、近场用户角度及距离的影响。研究表明：当基站天线数与近场用户距离较小时，和/或近场与远场用户角度差较小时，会产生强干扰。随后，我们进一步求得近场用户的可达速率及其因远场干扰导致的速率损失。最后，通过数值结果验证了理论分析的有效性。