Massive MIMO will come into its own in 5G deployments, but some operators plan to use it to bolster their 4G macro networks too. One of those is Sprint, which said it could boost sector capacity in its 2.5 GHz LTE network to 6Gbps using 64×64 MIMO antenna arrays combined with other technologies such as 256QAM modulation.
Shortly before his resignation was announced last month, Sprint’s first ever COO, Günther Ottendorfer, told the Next-Gen Wireless Networks Summit: “We are investing a lot of work into massive MIMO.”
Currently Sprint reaches gigabit LTE speeds, he said, by using about 60 MHz of spectrum with 2×2 MIMO and 64QAM across three sectors. Using 120 MHz of 2.5 GHz spectrum together with 64×64 MIMO (16 layers per sector carrier, with each of the 64 transceivers mapped to two antenna elements) and 256QAM could boost sector capacity to 6Gbps.
Ottendorfer said Sprint also plans to use other LTE-Advanced Pro (3GPP Release 14) technologies like carrier aggregation across up to 32 carriers.
Sprint can also use its large store of 2.5 GHz (over 100 MHz in most markets) for 5G since Band 41 has been designated for 5G New Radio in the US. Sprint is the only US operator with over 100 MHz of licensed, contiguous spectrum below 6 GHz and believes that gives it a great advantage in a market which has returned to unlimited data plans. It has said it does not need to move quickly to millimeter wave bands, like Verizon and AT&T, because it has such large assets in this far more familiar band.
Overall, Ottendorfer said that the national move to 5G could create $500bn in US GDP growth and $275bn in investments, including $93bn for building the networks. However, those sums will only materialize, the outgoing COO said, if the operators, regulators, industry groups and others address some critical issues, such as making it easier to deploy small cells and other network elements quickly.
“It takes a technician an hour to deploy a small cell, but it takes a year to obtain the permit” he said. “We would like to see all states pass small cell legislation,” he said (about 12 have already done so). Sprint has embarked on an ambitious densification program to increase capacity in its LTE network, having lost its third place in the US market to T-Mobile USA. It is working with Airspan and other suppliers but its efforts have been slowed by the complexities of accessing sites.