T-Mobile's 4x2 MIMO upgrade proves its worth in recent tests

T-Mobile US (NYSE:TMUS) has been leading the way in the United States to 4x2 MIMO cell site configurations, and a recent Signals Research Group study of the operator's upgraded infrastructure shows impressive gains from the approach.

T-Mobile confirmed in April that it was deploying the new antenna technology into its LTE network in certain markets. As described by Signals, headed by analyst Michael Thelander, 4x2 MIMO entails four transmit antennas at the cell site along with two receive antennas in the mobile devices. There are also four receive antennas at the cell site which can create a diversity gain and lead to higher uplink performance.

Signals, with the assistance of T-Mobile, tested some of the operator's sites in February around Dallas, including those with the standard 2x2 MIMO cell site configuration that most LTE providers started out deploying and others that T-Mobile has upgraded to 4x2 configurations with closed-loop MIMO, rather than the more common open-loop MIMO. The cluster of sites configured with 4x2 MIMO also leveraged 20+20 MHz radio channels.

The 4x2 MIMO antenna technology delivered headline peak data rate of 143.8 Mbps in the downlink (per TTI) and 46.93 Mbps in the uplink, Signals said.

"We found that a 4x2 cell site configuration delivered substantially higher performance in the uplink, including much higher user data rates, far more efficient scheduling of network resources and clear indications that the battery life of the mobile device was greatly enhanced. Generally, the benefits increased the further the mobile device was from the center of the cell, but the improvements in battery life were observed throughout a large portion of the cell," Signals said.

The firm noted it observed meaningful benefits in the downlink performance, again primarily closer to the edge of the cell. Test results also showed that closed-loop MIMO appeared to deliver substantially higher throughput than transmit diversity (TM2).

Signals noted that since all LTE mobile devices inherently support the 4x2 cell site configuration, the benefits of implementing that configuration are immediate and applicable to the entire installed base of mobile devices.

T-Mobile's Dallas market uses infrastructure provided by Nokia (NYSE:NOK), whose Flexi multi-radio base station and remote radio unit (RRU) gear enable a relatively easy upgrade to the 4x2 configuration, Signals said. "Since we did the testing back in February we know that T-Mobile has greatly increased the footprint of the 4x2 cell site configuration and we assume that eventually all of its RAN vendors will deploy the feature in its network," the research firm added.

Ericsson (NASDAQ: ERIC) is T-Mobile's other primary LTE network vendor.

Signals has not quantified the economic benefits associated with the 4x2 cell site configuration and acknowledged there are challenges involved in creating that layout, including those involved in upgrading legacy hardware, making cell site changes and resulting impacts on lease agreements. "Nonetheless, the triple whammy of higher user data rates, increased network efficiency, and a longer battery life shouldn't be dismissed," Signals said.

For the testing, Signals collaborated with Accuver, which supplied its XCAL drive test solution and its XCAP post-processing software. T-Mobile provided Signals with a Datum license and access to a Datum server so the firm could terminate/originate UDP downlink/uplink data sessions on the Samsung Galaxy Note 3 that it bought in a T-Mobile store.

In addition to buying the device, equipped with a Qualcomm (NASDAQ:QCOM) LTE Cat 4 chipset, Signals said it also purchased an unlimited data plan, "which was critical since we burned through 270 GB of data over a period of two days." The data usage cost Signals $0.12 per gigabyte, for a total of $32.75.

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