As the demand for wireless connectivity continues to soar, the fifth generation and beyond wireless networks are exploring new ways to efficiently utilize the wireless spectrum and reduce hardware costs. One such approach is the integration of sensing and communications (ISAC) paradigms to jointly access the spectrum. Recent ISAC studies have focused on upper millimeter-wave and low terahertz bands to exploit ultrawide bandwidths. At these frequencies, hybrid beamformers that employ fewer radio-frequency chains are employed to offset expensive hardware but at the cost of lower multiplexing gains. Wideband hybrid beamforming also suffers from the beam-split effect arising from the subcarrier-independent (SI) analog beamformers. To overcome these limitations, this paper introduces a spatial path index modulation (SPIM) ISAC architecture, which transmits additional information bits via modulating the spatial paths between the base station and communications users. We design the SPIM-ISAC beamformers by first estimating both radar and communications parameters by developing beam-split-aware algorithms. Then, we propose to employ a family of hybrid beamforming techniques such as hybrid, SI, and subcarrier-dependent analog-only, and beam-split-aware beamformers. Numerical experiments demonstrate that the proposed SPIM-ISAC approach exhibits significantly improved spectral efficiency performance in the presence of beam-split than that of even fully digital non-SPIM beamformers.
翻译:随着对无线连接的需求持续攀升,第五代及以上的无线网络正在探索新的方法来有效利用无线频谱并降低硬件成本。一种方法是将感知和通信(ISAC)范式集成,以共同访问频谱。最近的ISAC研究集中在上部毫米波和低太赫兹频段中,以利用超宽带宽。在这些频率上,采用较少射频链的混合波束形成器以抵消昂贵的硬件成本,但代价是较低的复用增益。宽带混合波束形成器还受到来自子载波独立(SI)模拟波束形成器的波束分裂效应的影响。为了克服这些限制,本文介绍了一种空间路径索引调制(SPIM)ISAC结构,通过调制基站和通信用户之间的空间路径传输附加信息比特。我们首先通过开发考虑波束分裂的算法来估计雷达和通信参数,设计SPIM-ISAC波束形成器。然后,我们建议采用一系列混合波束形成技术,例如混合、SI、子载波相关的仅模拟和考虑波束分裂的波束形成器。数值实验表明,在波束分裂存在的情况下,所提出的SPIM-ISAC方法展现出比非SPIM波束形成器显著提高的频谱效率性能。