SRGanalystsconductedtestsofT-Mobile's2.5GHznetworkinSouthernCalifornia,whereEricssonistheinfrastructuresupplier.Theirconclusionsshowasignificantcapacityincrease(over50%)inthepresenceofMU-MIMOcomparedtosingle-userMIMO,alsoknownasSU-MIMO.ThisisespeciallyrelevantforhisFixedWirelessAccess(FWA)businessatT-Mobile.

For SRG`s tests, T-Mobile furnishedlogistical assist, consisting ofphones, SIMs and steeringon whereinto discover amassivecluster of cells helpingMU-MIMO with 10 Gbps backhaul. Neither T-Mobile nor Ericsson furnishedeconomicassistfor the study. The analysts used industrialsmartphones OnePlus 10 Pro and the Samsung Galaxy S22, in addition topre-industrialCPEs from Arcadyan. Spirent Communications and Accuver Americas furnishedtake a look atand sizetools.

SRG Presidentand founder Mike Thelander said his companygaveT-Mobile and Ericsson abriefpresentationaheadofthe report'srelease,notingthat T-Mobile has MU-MIMO capabilitiesnationwide.,revealedthattheSounding Reference Signal (SRS) Technologyisimplemented.Iamusing Ericsson equipment.Thereareplanstorollout similar functionality onNokia 2.5GHzsites by mid-2023.He pointedoutthat not all smartphones support hisSRS, butSRG believes the featureispresentonthe carrierFWA CPEand at least oncertain ofhisiPhone models.

Last year, Thelander encountered MU-MIMO in the Verizon band n77 (C-band) Ericsson network in Minneapolis. Verizon confirmed to SRG that it is evaluating the technology, Thelander said. “There’s clearly interest from all operators. I don’t know where Verizon’s at in terms of deploying it” or testing it, he said. Both T-Mobile and Verizon use Ericsson and Nokia 5G gear; Verizon also uses Samsung. 

“If an operator can increase their network capacity by 50% through a basic software upgrade, that’s a no brainer,” he said. “That’s why it’s so compelling.”

There are different ways of implementing MU-MIMO. What Ericsson is doing is based on technology called SRS and Thelander equated it to a game of Marco Polo in a swimming pool.

“This is a similar concept whereby the phone is transmitting signals in the uplink. Those signals allow the base station to figure out where that mobile phone is,” and it can precisely send data to it and use the same resource block to send data to another phone, he said. It works best in a low-mobility situation, which is where FWA operates.

SRG included some insights based on its observations while testing and analyzing the study results that are unrelated to MU-MIMO. “The Reader’s Digest version is that T-Mobile is currently evaluating a new configuration for its TDD frame structure which will allow it to increase downlink capacity/downlink data speeds,” the report notes.

Thelander also explained the meaning behind the illustration on the cover of the MU-MIMO report. It shows a Spider-Man character shooting signal beams aimed at Doctor Octopus, who has four “arms” and each one is holding a phone. Two beams of light are coming from the base station to each phone, and these beams represent data streams, tallying up to eight.

With SU-MIMO, each network resource can be re-used up to four times. The terms “4x4 MIMO” and “4-layer MIMO” refer to one network resource being re-used four times, and there’s a theoretical quadrupling of the throughput over a single network resource, he said.

MU-MIMO is conceptually similartoSU-MIMO, but “the difference is that onenetwork resource can be shared bymultiple phones,” he said, theoreticallyallowingeightphonestosharethe same network resource at the same time. IaddedthatyoucanconnecttodifferentphoneswithThiseffectively doublesthe capacity of the network, makingcapacity criticalwhen it comes to FWA. Both T-Mobile and Verizon claimtheyaretaking steps to ensure thathisFWAusers,whoonaverageusemoredatathantheircellphonecustomers,don'trun out of capacity.But the question of capacity and how much wecan delivercomesup againandagain.Especiallywhen thereisn'tmuchmid-band 5G spectrum in the pipeline,it'snosurprisethatcarriersareattheirdisposaltousewhatevertoolstheycantoincreasecapacity."Forthings like fixed wireless access,whichconsumesa lot of data,it'sa great wayfor operatorsto increasethe overall capacity oftheir networks,"saidThelander.