MIMO (Multiple-Input Multiple Output) antenna systems have been a part of mobile technology standards for many years but have not been deployed to any great extent so far, thanks to the combination of several limiting factors. These factors include space constraints, particularly for sub 1 GHz frequencies, at the base station and in the user equipment (UE) or handset and the computational overhead required for frequency division duplex (FDD) systems – the most prolific LTE access technology. These and other challenges including fronthaul capacity, cost and power have helped limit MIMO for the most part to simple 2x2 MIMO deployments.
However, as LTE continues to evolve to more advanced versions such as LTE-Advanced, LTE-Advanced Pro and Gigabit LTE encapsulated in the 3GPP Standards, we expect that MIMO will become an increasingly important part of the mobile network operators’ (MNOs) options in the evolution to 5G. Under continuous pressure to boost data throughput MNOs will first upgrade to 256 QAM and/or refarm spectrum. MIMO will be next since adding antennas is a less costly way to densify the network than building a new cell site and erecting a tower.
While MIMO has not delivered on its promises so far, we are left in no doubt that the technology will become a foundational building block for mobile networks in the evolution to 4G/5G and advanced antenna systems will receive increasing attention and R&D by both vendors and MNOs. Advanced antenna systems including complex passive antennas and large scale active antennas will become part of the roadmap to advanced LTE and 5G.