US operators are evaluating a new method for tackling propagation challenges in mmWave, which are regarded as a key barrier to 5G commercialisation.
While mmWave offers more bandwidth for operators to drastically increase speed and capacity, it is also notorious for its poor propagation characteristics. But where operators can crank up the transmit power on base stations to extend signals, mobile devices must limit transmit power to preserve battery life.
In an interview with Mobile World Live, Farooq Khan, CEO of US wireless infrastructure start-up Phazr (pictured, left), explained the power difference translates to a huge disparity in coverage and performance in the up and downlinks of mmWave systems.
The limited transmit power in devices threatens to handicap mmWave coverage in the uplink and would require operators to build ultra-dense networks to compensate.
But Khan said operators are evaluating the use of sub-6GHz spectrum for the uplink because the lower frequency spectrum requires less transmit power to achieve the same coverage as mmWave.
“The industry is slowly coming to the realisation that probably mmWave on the uplink is not viable,” Khan said. Using the combination of mmWave and sub-6GHz makes “downlink and uplink coverage symmetric,” he explained.
Khan noted the approach would also reduce the number of cell sites required by ten-times compared with attempting to deliver the same coverage in mmWave alone.
The executive said Phazr is working with three of the country’s four top operators on trials as it pushes toward launching a commercial product combining the technologies in 2019.
The company recently filed for permission from the US Federal Communications Commission (FCC) to conduct a new round of tests using the 24GHz, 28GHz and 37GHz to 40GHz bands alongside 3.5GHz. Khan said the selection of those bands was driven by both operator interest and regulatory action.
“We have done 28GHz and 39GHz trials with the US carriers. But now, since the FCC is going to auction 24GHz spectrum and one of the carriers does not own mmWave spectrum, they are very interested in bidding for that spectrum” and assessing its performance.
Though Khan wouldn’t confirm which operators Phazr is working with, FCC filings show the company had collaborated with Verizon in the past. Meanwhile, Sprint is the only top US operator without substantial mmWave assets, though in a recent conference call, executives referred to mmWave as “an important part of our strategy going forward.”
There is also a connection to AT&T: some of Phazr’s initial funding came from FiberTower, which was recently acquired by the operator.
Khan noted “a lot” of Phazr’s customers are looking to deploy 5G New Radio in sub-6GHz spectrum at the end of 2019. The 3.5GHz band is of particular interest since it may become available sooner than refarmed LTE spectrum and offers wider channel bandwidth, he said.