A massive MIMO terminal concept based on small‐size multi‐mode antennas

In this tutorial, a novel variation of massive multiple‐input multiple‐output (MIMO) is proposed, dubbed multi‐mode massive MIMO. A key feature is an advanced antenna design suitable for small‐scale user terminals like smartphones. Unlike traditional antenna layouts employing a single‐antenna port per antenna element, multiple orthogonal modes shall be excited on a conductive body, like the printed circuit board. This antenna conception is motivated by the theory of characteristic modes for conductive bodies. Each mode can be assigned with an individual antenna port, and all antenna ports can be fed independently. In conjunction with suitable baseband processing, unique features, such as single‐mode beamforming, can be exploited. Most importantly, some bottlenecks of conventional massive MIMO in conjunction with single‐antenna terminals like single‐stream processing on the uplink and pilot contamination on the downlink can be improved. Performance results for a three‐port prototype multi‐mode antenna support the feasibility of the proposed concept. The terminal concept is suitable in context of the upcoming fifth mobile radio generation (5G) and for ultra‐fast (100 Gbps) wireless internet access among other applications.