AT&T’s LTE network in the real world

Results of AT&T's LTE demo on

That spectrum shortage isn’t stopping AT&T’s newly launched LTE network from delivering some smoking speeds, according to test results from Signals Research this weekend. AT&T(s T), which launched LTE in Chicago, Atlanta, Houston, Dallas and San Antonio, Texas on Sunday, delivered LTE speeds averaging 23.6 Mbps on the download and 15.2 Mbps on the upload side over a three-day period.

LTE can feed your need for speed …

From the Mobile Business Briefing, which cites the research report:

Signals Research tested the network in the greater Houston area, transferring almost 90GB of data over a three-day period using a Sierra Wireless USBConnect Momentum 4G dongle and achieved average downlink data rates of 23.6Mb/s, with peak data rates of 61.1 Mb/s. “Both results meaningfully exceeded our expectations,” noted the firm. The data rate also exceeded 40Mb/s for 8.6 percent of the time and 21Mb/s – the theoretical peak data rate of the operator’s HSPA+ network – for 38.2 percent of the time. “Most importantly, the data rate was greater than 5Mb/s for 95 percent of the time,” said Signals Research.

On the uplink, the average throughput was 15.2Mb/s with a peak data rate of 23.6Mb/s.  “The uplink results were also much higher than we anticipated,” said Signals.  “Sixty percent of the time the uplink Physical Layer data rate exceeded 15Mb/s and 98.2 percent of the time it exceeded 5Mb/s.”

The report noted that latency was a bit of an issue, ranging from between 40 and 49 milliseconds, but only compared to wireline networks, since Verizon’s (s vz) competing LTE network also had a bit of a lag time. It also said that moving between an LTE and AT&T’s HPSA network was fairly seamless, and it took about 2.4 seconds to make the transition when inside an application. As a bonus, given the speeds of the HSPA network, folks transitioning from that to an LTE network are less likely to notice a huge change in speed, unlike what may happen moving between LTE and Verizon’s slower CDMA network.

But before you get excited, a few caveats …

The performance Signals saw was on a relatively empty network, with few consumers transferring data, which means real-world speeds are likely to slow over time as more people pick up devices and hop on the network. AT&T is already selling devices, so that will bring customers online, but it’s probably the introduction of a mass market handset such as an LTE-enabled iPhone (s aapl) that will really dial back the speeds.

The final issue worth noting is cost. Transferring 90 gigabytes of data over three days — as Signals did — is a pricey proposition. AT&T charges $50 a month for 5GB of data and $10 for every gigabyte over that limit,which would bring a bill for a similar experiment to a whopping $900 for three days of data. That’s something I don’t recommend trying at home.