(ARCHIVE) Q&A: LTE

Where does LTE lie in the GSM evolutionary path?

What is LTE?

Long Term Evolution, or LTE, is an entirely new radio platform technology with standards currently under development by the 3GPP, and initial deployment planned in 2009. LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) on the downlink, which is well suited to achieve high peak data rates in high spectrum bandwidth. LTE is part of the GSM evolutionary path beyond 3G, following EDGE, UMTS/WCDMA and HSPA (HSDPA and HSUPA combined).

In the same way that 3G coexists with Second Generation (2G) systems in integrated networks, LTE systems will coexist with 3G systems as well as 2G systems. Multimode devices will function across LTE/3G or even LTE/3G/2G, depending on market circumstances.

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What is LTE expected to provide?

Downlink peak data rates up to 100 Mbps with 20 MHz bandwidth
Uplink peak data rates up to 50 Mbps with 20 MHz bandwidth
Operation in both FDD and TDD modes
Scalable bandwidth up to 20 MHz, covering 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. (1.6 MHz channels are under consideration for unpaired frequency bands).
An increase in spectral efficiency of two to four times that of HSPA Release 6
Reduced latency to 10 msec round-trip time between user equipment and the base station and to less than 100 msec transition time from inactive to active.

LTE will address the market needs of at least the next decade, after which time operators might deploy Fourth Generation (4G) networks using LTE technology as a foundation.

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What are the main benefits of LTE?

A simplified, flat architecture from an all IP, packet-based network helps to reduce both latency and cost for LTE. The OFDM technology used by LTE also serves to lower operators' equipment costs.

An important feature of LTE is the amount of flexibility it allows operators in determining the spectrum in which it will be deployed. Not only will LTE have the ability to operate in a number of different frequency bands (so operators will be able to deploy it at lower frequencies with better propagation characteristics) but it also features scalable bandwidth. Whereas UMTS/HSPA uses fixed 5 MHz channels, the amount of bandwidth in an LTE system can be scaled from 1.25 to 20 MHz. This means networks can be launched with a small amount of spectrum, alongside existing services, and adding more spectrum as users switch over. It allows operators to tailor their network deployment strategies to fit their available spectrum resources and not have to make their spectrum fit a particular technology.

LTE will increase spectral efficiency over Rel-6 HSDPA by a factor of two to four, approaching 2 bps/Hz in the downlink and 1 bps/Hz in the uplink in ideal conditions.

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When will LTE be deployed?

LTE should be ready for deployment in the 2009 time frame.

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Where does LTE lie in the GSM evolutionary path?

Although HSPA (HSDPA and HSUPA combined) is strongly positioned to be the dominant mobile data technology for the rest of the decade, it is important to evolve the GSM family of standards toward the future. To this end, 3GPP is examining a series of enhancements to create “HSPA Evolution,” also referred to as “HSPA+.” HSPA Evolution could provide the stepping-stone to LTE.

With relative ease, operators can transition their General Packet Radio Service (GPRS) networks to EDGE. Some operators may choose to deploy UMTS and its enhancement to HSPA directly from GPRS or upgrade from EDGE to HSPA. In the future, they may decide to migrate to HSPA+ and/or LTE.

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