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Article
MIMO for 3GPP L2 RAN Developer
by
Samir Amberkar
(published on 10-Jun-2023)
MIMO is (almost) a baseline feature for 5G NR.
Most of the commercial UE implementations will support it.
As there is considerable amount of (mathematical) theory around the concept,
novice 3GPP protocol stack developers sometimes find it difficult to comprehend it.
This article provides simplified initial understanding of MIMO from 3GPP 5G NR point of view.
It is assumed that the reader has basic understanding of 3GPP LTE or 5G NR PHY procedures.
In simple terms, Channel represent signal conditions.
From theory of view, it is a mathematical representation.
Often confused with or compared with physical antennas,
Antenna port is actually a virtual or logical representation.
Signals are said to be coming from two different antenna ports when they experience two different channels (signal conditions).
In other words, when signals are transmitted over two different antenna ports, they will supposedly experience two different channels.
As the name suggests, MIMO consists of multiple transmit and multiple receive antennas -
more accurately, antenna ports.
Below is an example of MIMO system with two transmit antenna ports and two receive antenna ports.
Fig "2x2 MIMO"
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