Long Term Evolution-Advanced (LTE-Advanced)

Long Term Evolution-Advanced (LTE-Advanced) is a mobile wireless broadband standard (for some background and context, read my overview of wireless broadband) designed to meet the ITU’s requirements for 4G wireless broadband. 4G describes wireless networks that comply with IMT-Advanced requirements as detailed in ITU-R report M.2134.

4G is defined as a high bandwidth (>100 Mbps), spectrally efficient wireless broadband technology handling only IP packets for voice and data services. 4G networks are interoperable with other wireless networks, and they provide the Quality of Service required to deliver the whole range of broadband Internet technologies, including real-time services like interactive audio and video.

The IEEE is developing standards for WiMAX-m, which is an alternative 4G wireless broadband technology quite similar to LTE-Advanced. One difference is that LTE-Advanced terminals are expected to be substantially more energy efficient for uplink transmissions (because LTE-Advanced’s SC-FDMA uplink transmitters use much less transmit power than SOFDMA transmitters, which are used for WiMAX-m uplinks) allowing smaller batteries and/or longer battery life in LTE-Advanced mobile terminals.

3GPP’s take on 4G, LTE-Advanced is part of its Release 10, which is planned for release in early 2011. Work on Release 10 and LTE-Advanced did not begin until early 2008.  3GPP’s progression of wireless broadband standards, mapped to the ITU 2G, 3G, and 4G requirements, is given in the diagram below (from 3GPP).

LTE-Advanced will use spectrum in 20 Mhz chunks allocated in what is called carrier aggregation up to a total of 100 Mhz (5 component carriers) used for transmission in each direction. 100 Mhz is a lot of spectrum, especially in a Frequency Division Multiplexed (FDD) system which has separate spectrum for the uplink and the downlink (requires a total of 200 Mhz). In reality, the uplink spectrum allocation is likely to be much lower than the downlink allocation.  If 100 Mhz is assigned to the downlink, the uplink may have perhaps only 20 Mhz. These asymmetric FDD assignments will conserve spectrum and are a good fit for the typically asymmetric bandwidth utilization by broadband subscribers.

LTE-Advanced can achieve a max downlink rate of 1 Gbps with as little as 40 Mhz (two 20 Mhz allocations) of assigned spectrum. Peak uplink rate for LTE-Advanced is expected to be 500 Mbps. LTE-Advanced will provide somewhat higher rates to fixed subscribers than to mobile subscribers. Like LTE, LTE-Advanced uses OFDMA for the downlink, SC-FDMA for the uplink, and MIMO to achieve its high rates. Beyond just the higher peak rate, LTE-Advanced will provide broadband data rates over a larger area than is possible with LTE.

As the successor to LTE, LTE-Advanced will be backward and forward compatible with LTE, which means LTE terminals will work in LTE-Advanced networks (this is why LTE-Advanced uses spectrum in 20 Mhz chunks), and LTE-Advanced terminals will work in LTE networks. Each component carrier of the LTE-Advanced spectrum will appear as an LTE carrier to LTE terminals. Initial LTE deployments are expected in late 2009 and early 2010. Initial LTE-Advanced deployments are expected perhaps three years later.

If you want even more detail on LTE-Advanced, including some simulation data, read this article from Ericsson Research (only 5 pages, moderately technical, just one equation). And, if you really want the whole story on mobile data, then this brand new 118-page article (not very technical) from Rysavy Research entitled HSPA to LTE-Advanced is for you.

And finally, here is a video about how folks might use LTE.

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© 2009, The Product Group LLC. All rights reserved.

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