Last week, T-Mobile (NASDAQ:TMUS) announced that it had added an additional 430 markets to its LTE Advanced network. The new LTE Advanced signals allow phones equipped with Qualcomm's Snapdragon Gigabit LTE modems to receive blazing fast wireless speed -- a live demonstration showed download speeds of 611 Mbps. For context, the average mobile download speed in the U.S. is just under 23 Mbps.

The news expands T-Mobile's LTE Advanced footprint to more than 920 markets, more than any other U.S. wireless carrier. But the announcement especially stings for Sprint (NYSE:S), which was recently in talks to merge with T-Mobile before the deal fell through.

Broken smartphone on a table.

Image source: Getty Images.

The lack of a deal between the two carriers has left Sprint responsible to once again focus on improving its network and try to become a stronger rival to T-Mobile, AT&T, and Verizon.

T-Mobile surpassed Sprint two years ago to become the nation's third-largest wireless carrier by customers and has since built out one of the strongest and fastest wireless networks available.

The problem for Sprint is that even before T-Mobile's latest network upgrade, it was already an uphill battle for Sprint to take on T-Mobile -- and now it's nearly an impossible feat.

A tale of two networks

T-Mobile said in its press release that its LTE Advanced network can double the carrier's previous download speeds in some markets, which is not just an impressive move but a huge blow to Sprint's recent announcement. 

At the beginning of October, the nation's fourth-largest carrier said it was the "most improved" network this year, according to Ookla Speedtest data, and that its download speeds have improved by 33% since last year.

Here are just a few examples of Sprint's network improvements:

  • Washington, D.C.: up 45% to 20 Mbps
  • Atlanta: up 86% to 32 Mbps
  • LA Metro: up 55% to 23 Mbps
  • Colorado: up 44% to 25 Mbps

Those are big percentage improvements, but they pale in comparison to T-Mobile's demonstration of 600-plus Mbps downloads.

Of course, T-Mobile isn't getting those speeds in all of its markets, but the point is, Sprint is far behind T-Mobile's LTE speeds, and just as it's starting to make progress, T-Mobile made another move that once again leaves Sprint in the dust.

Why this matters

Sprint has made progress, sure, but it's not nearly enough. Morningstar analyst llan Nichols recently wrote, "Sprint's network quality gap is narrowing, but it still ranks last on an absolute basis." And he added that the company currently doesn't have any kind of economic moat.

In the past, Sprint has hemorrhaged customers because of its poor network quality and subpar speeds. Those losses have subsided recently, and the company just had its ninth consecutive quarter of net additions.

But those customer additions have come a little too late. Sprint's stock is down nearly 13% over the past year, and the possibility that the company can become a serious contender in the wireless space again is still unknown. 

Until Sprint can prove that it can keep up with T-Mobile's innovations, I think it's best for investors to stay away from the carrier's stock. Sprint's fate is still very volatile, and with much uncertainty surrounding the company, it's probably best to just leave Sprint alone for now.

Chris Neiger has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Verizon Communications. The Motley Fool recommends T-Mobile US. The Motley Fool has a disclosure policy.