Verizon Wireless Monday continued to maintain that it has the "largest and most reliable 4G LTE network" in the U.S. despite the recent admission by some company executives of some dents in the armor.

Verizon Communications CEO Lowell McAdam told analysts a week ago that "there are certain hot spots that, frankly, the network hasn't performed at the level that we would like it to." In October, Chief Financial Officer Fran Shammo acknowledged that Verizon's 4G LTE network had "a little bit of a speed issue" in New York, San Francisco an Chicago, forcing the company to revert some customers to 3G speeds that can be 10 times slower than 4G.

Root Metrics, which compares network performance of various carriers, detected a 20% cut in Verizon data upload speeds in Chicago and San Francisco from the first half of 2013 to the second half, said CEO Bill Moore.

All other measures, including downloads, email, Web searches and texting, Verizon's performance was the same in the first and second halves of this year.

Moore said in an interview that the latest Root Metrics findings should not lead any smartphone user to "lose sleep or to consider switching providers." He said there's an "ebb and flow" of network speeds as carriers, like Verizon, add new technology.

Verizon spokesman Tom Pica Monday described to Computerworld how the carrier is beefing up speeds over the carriers LTE network, which began rolling out about three years ago. The network is now deployed in more than 500 cities in 50 states, accessible to some 303 million people, according to a recent Verizon blog post. Fully two-thirds of all Verizon Wireless data traffic now rides on its 4G LTE.

Verizon's goal is to make the LTE speeds for all its customers range from 5 Mbps to 12 Mbps on downloads and 2 Mbps to 5 Mbps on uploads.

Verizon has launched a major upgrade program -- adding the AWS (Advanced Wireless Services) spectrum which Verizon first acquired from cable companies in 2012 -- to help with data demands in major cities.

The AWS spectrum uses 1700 MHz for uplinks and 2100 MHz for downlinks tied into Verizon's earlier use of 700 MHz spectrum for LTE.

AWS requires an AWS-ready smartphone, including the Verizon-sold Samsung Galaxy S4, Apple's iPhone 5C and iPhone 5S, along with the Droid Maxx, Ultra and Mini. Pica said a coming software upgrade will increase the list of AWS-ready smartphones and that 20% of Verizon LTE devices with be able to use AWS by year's end.

Moore said Root Metrics has done LTE testing on a non-AWS phone over Verizon networks in New York City and found that speeds there have improved slightly in specific cell areas where AWS was added. He theorized that the addition of AWS is taking capacity pressure off of the older LTE network.

Any problems reported by customers with Verizon LTE could stem from the fact that the carrier started rolling out the technology a year earlier than other U.S. carriers and "has a higher installed base that would be pushing down some of those speeds," Moore said.

AWS has helped Verizon triple LTE capacity in New York, Chicago, Atlanta, Boston, Seattle and Washington, while boosting capacity by 150% in San Francisco and Los Angeles, Verizon Wireless Chief Network Officer Nicola Palmer said in a recent interview with Gigaom. Download speeds in those cities could reach 80 Mbps, with theoretical speeds of up to 150 Mbps.

Pica also noted that Verizon is adding more macro and small cells to make its coverage more dense, and adding more in-building wireless systems. LTE-Advanced is also in the works, he said.

Pica said McAdam's comment last week stems partly from his being a "very upfront guy." He indicated also that Verizon deals with more data demands than ever on its LTE network.

Video was largely a novelty in wireless before LTE came to Verizon and "when customers discovered it, they ate it up," Pica said. User concerns about network speeds have occurred in "pockets that we are quickly addressing with our AWS spectrum deployment, our plan all along," Pica said.

Jack Gold, an analyst at J. Gold Associates, said that capacity and speed concerns over wireless "usually are in selected areas, just like on highways with commuters. Sometimes you move forward, and then hit a curve and it all slows down."

All the carriers struggle in certain markets, said Phillip Redman, vice president of mobile solutions and strategy at Citrix. Redman, a former Gartner analyst who closely followed carrier networks for years, said Verizon was known to have speed problems in San Francisco and San Diego in particular.

"Bigger markets are especially difficult due to the network demands," Redman said, adding that "networks are built with an estimated amount of capacity. It is expensive to overbuild. In some cases demand exceeds capacity, which leads to poor network performance."

The fact that Verizon and other carriers are constantly expanding networks and will acknowledge the need to do so is a plus for consumers, said Moore. "The bottom line of the ebb and flow of network performance is that the consumer is still winning," he said. "It's an arms race."

Matt Hamblen covers mobile and wireless, smartphones and other handhelds, and wireless networking for Computerworld. Follow Matt on Twitter at @matthamblen, or subscribe to Matt's RSS feed . His email address is mhamblen@computerworld.com.

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