Interference-Free Transmission for Near-Field Communication with Unlimited Antennas

Extra large-scale (XL) multiple-input multiple-output (MIMO) is a potential key technology for the sixth-generation (6G) mobile communication systems. An important conclusion in the early literature is that intra-cell interference vanishes when the number of base station (BS) antennas tends to infinity under the far-field channel assumption. However, as the number of antennas increases, users may fall in the near, Fresnel, and far fields. In this paper, we check whether intra-cell interference still vanishes by investigating the correlation among near-field, Fresnel-field and far-field user channels, and find that the channel of a near-field user does not have asymptotic orthogo-nality with another user in any field. To achieve interference-free transmission, we further propose a novel antenna allocation and power control scheme. Our numerical results show that when the number of antennas is large enough, this transmission scheme can achieve the same performance as the ideal case without any interfering user.