4G LTE primer: Long Term Evolution evolves

This 4G LTE primer looks at the development of Long Term Evolution as a fourth-generation high-speed wireless broadband technology, its advantages over 3G wireless, and the challenges facing it, including architecting standardized Voice over LTE.

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Long Term Evolution (LTE) is a 4G wireless broadband technology developed by the Third Generation Partnership Project (3GPP), an industry trade group. LTE got its name because it represents the next step (4G) in a progression from GSM, a second-generation (2G) wireless standard, to UMTS, the 3G  technologies based upon GSM. Unlike its predecessor technologies, however, LTE’s upper layers use TCP/IP, enabling all traffic -- data, voice, video and messaging -- to be carried over an all-IP network.

For many mobile operators, LTE has arisen as the preferred 4G wireless broadband option because it evolves directly from 3G.

4G LTE provides significantly higher peak data rates than the earlier 3GPP technologies, with the potential for 100 Mbps downstream and 30 Mbps upstream, reduced latency, scalable bandwidth capacity, and backwards compatibility with existing GSM and UMTS technology. Future developments could yield peak throughput on the order of 300 Mbps.

LTE uses Orthogonal Frequency Division Multiplexing (OFDM), and in later releases, MIMO (Multiple Input Multiple Output) antenna technology similar to that used in the IEEE 802.11n wireless local area network (WLAN) standard. The higher signal-to-noise ratio (SNR) at the receiver enabled by MIMO, along with OFDM, provides improved coverage and throughput, especially in dense urban areas.

Why you need to know about 4G LTE

For many mobile operators, LTE has arisen as the preferred 4G wireless broadband option because it evolved directly from 3G. In other words, operators can upgrade existing infrastructure to support LTE rather than start from scratch, as many would have to do with WiMAX, the other leading 4G contender. As a 4G technology, LTE becomes increasingly important to mobile operators as the amount of data traffic on their networks grows. Until LTE voice standards are finalized, operators can keep voice calls on the earlier 2G and 3G infrastructures, offloading data services to the LTE network.

Toward that end, some U.S. mobile broadband providers have initiated LTE deployments. By the end of 2010, for example, Verizon Wireless reported LTE operations in 38 U.S. cities (despite operating a CDMA rather than GSM infrastructure). In early 2011, AT&T announced plans to accelerate its LTE deployment, with initial services slated for a mid-year launch. Both carriers have targeted 2013 as the year for LTE network completion. AT&T is evolving its network to LTE from GSM-based HSPA+ technology, which enables 4G speeds when combined with Ethernet or fiber backhaul.

Despite nominal LTE availability in 2010, operators wanted to be able to say they had a 4G service, according to Mike Jude, a telecom program manager at Frost & Sullivan. LTE’s availability is changing quickly. But by the end of 2011, some major markets could have up to three 4G networks available in the U.S.

What you need to know about 4G LTE

Mobile operators are grappling with a number of technical and marketing challenges associated with LTE’s rollout, which could mean the market is in for a period of trial and error, according to industry watchers.

In 2011, mobile operators will reinforce their initial LTE footprints and add more markets here and there, Jude said. “They’ll essentially be trying to establish a market for LTE service and determine what the service will look like. They’re groping their ways toward a value proposition.”

Working out 4G LTE’s kinks. Of course, mobile operators will have some kinks to work out. For example, on the Verizon network, delays of up to two minutes have cropped up in the transition between 4G LTE and 3G Evolution-Data Optimized (EV-DO) connections. Verizon acknowledged the handoff delay, saying it was not unexpected and that it has been working on a fix. It is unclear when an update will be ready.

“If you have a 4G device that starts roaming, and you’re talking a matter of minutes on a handoff to the 3G network, is that reliable enough to call a viable service?” Jude asks. “Well, maybe -- if that’s a definition of service that works for a given market, but that looks more like fixed mobile to me. I certainly wouldn’t expect to pick up my laptop and go running down the street with it.”

Voice over LTE -- standards needed. Beyond technical quirks, voice is the bigger issue that mobile operators have to contend with. While the GSM Association (GSMA), a global mobile industry association, has embraced a standardized way of carrying Voice over LTE (VoLTE), it is working on the interfaces required between the customer’s equipment and the operator’s network, between the home and visited network of a subscriber not on their normal home network, and between the networks of the two parties making a call. Until the LTE voice standards are finished, mobile operators must figure out how they will handle voice (and text) calls that cross from 2G/3G to LTE networks.

“Getting VoLTE to work reliably, especially across different networks for roaming, will be challenging,” Jude said.

Getting this right will be crucial, given that for the bulk of the market, LTE devices would be about being “a telephone first and a data terminal second,” Jude said. “To get any traction, LTE has to address this existing market. Then we can expect that it will be about new types of services that will ride the data stream.”

The good news, Jude added, is that carriers, vendors and standards bodies all have vested interests in working on getting LTE deployments up to snuff.

About the author: Beth Schultz is a freelance technology editor and writer based in Chicago.

This was first published in January 2011

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