This paper proposes a practical method for the definition of multiple communication modes when antennas operate in the near-field region, by realizing ad-hoc beams exploiting the focusing capability of large antennas. The beamspace modeling proposed to define the communication modes is then exploited to derive expressions for the number of communication modes (i.e., degrees of freedom) in a generic setup, beyond the traditional paraxial approximation, together with closed-form definitions for the basis set at the transmitting and receiving antennas for several cases of interest, such as for the communication between a large antenna and a small antenna. Numerical results indicate that quasi-optimal communication can be obtained starting from focusing functions. This translates into the possibility of a significant enhancement of the channel capacity even in line-of-sight channel condition without the need of resorting to optimal but complex phase/amplitude antenna profiles as well as intensive numerical simulations. Traditional results valid under paraxial approximation are revised in light of the proposed modeling, showing that similar conclusions can be obtained from different perspectives.
翻译:本文提出在近地天线在近地区域运作时,利用大型天线的聚焦能力,实现特别光束,从而界定多通信模式的实用方法,然后利用拟议用于界定通信模式的波束模型,在除传统的准轴近似光谱外的通用设置中,为通信模式(即自由度)的数量进行表达,同时为若干感兴趣的情况,如大型天线和小型天线之间的通信,为传输和接收天线所设定的基础提供封闭式定义。数字结果显示,从聚焦功能开始,可取得准最佳通信。这转化成即使在直线通道条件下也有可能大大增强频道能力,而不必采用最佳但复杂的阶段/光度天线剖面图以及密集的数字模拟。根据拟议的模型,对在偏地光线下有效的传统结果进行了修订,表明可以从不同角度得出类似的结论。