LTE: Long Term Evolution

Long Term Evolution (LTE) is a radio platform technology that will allow operators to achieve even higher peak throughputs than HSPA+ in higher spectrum bandwidth. Work on LTE began at 3GPP in 2004, with an official LTE work item started in 2006 and a completed 3GPP Release 8 specification in March 2009. Initial deployments of LTE began in late 2009.

LTE is part of the GSM evolutionary path for mobile broadband, following EDGE, UMTS, HSPA (HSDPA and HSUPA combined) and HSPA Evolution (HSPA+).  Although HSPA and its evolution are strongly positioned to be the dominant mobile data technology for the next decade, the 3GPP family of standards must evolve toward the future. HSPA+ will provide the stepping-stone to LTE for many operators.

 

The overall objective for LTE is to provide an extremely high performance radio-access technology that offers full vehicular speed mobility and that can readily coexist with HSPA and earlier networks. Because of scalable bandwidth, operators will be able to easily migrate their networks and users from HSPA to LTE over time.

LTE assumes a full Internet Protocol (IP) network architecture and is designed to support voice in the packet domain. It incorporates top-of-the-line radio techniques to achieve performance levels beyond what will be practical with CDMA approaches, particularly in larger channel bandwidths. However, in the same way that 3G coexists with second generation (2G) systems in integrated networks, LTE systems will coexist with 3G and 2G systems. Multimode devices will function across LTE/3G or even LTE/3G/2G, depending on market circumstances.

 

 

Standards development for LTE continued with 3GPP Release 9 (Rel-9), which was functionally frozen in December 2009.  3GPP Rel-9 focuses on enhancements to HSPA+ and LTE while Rel-10 focuses on the next generation of LTE for the International Telecommunication Union’s (ITU) IMT-Advanced requirements and both were developed nearly simultaneously by 3GPP standards working groups. Several milestones have been achieved by vendors in recent years for both Rel-9 and Rel-10. Most significant was the final ratification by the ITU of LTE-Advanced (Rel-10) as IMT-Advanced in November 2010.

 

The first commercial LTE networks were launched by TeliaSonera in Norway and Sweden in December 2009; as of November 2012, there were 117 commercial LTE networks in various stages of commercial service. Many trials are underway with up to 130 LTE deployments expected in 2012.

 

For many years now, a true world cellular standard has been one of the industry’s goals. GSM dominated 2G technologies but there was still fragmentation with CDMA and TDMA as well as iDEN. With the move to 3G, nearly all TDMA operators migrated to the 3GPP technology path. Yet the historical divide remained between GSM and CDMA.  It is with the next step of technology evolution that the opportunity has arisen for a global standard technology. Many operators have converged on the technology they believe will offer them and their customers the most benefits. That technology is Long Term Evolution.  Most leading operators, device and infrastructure manufacturers, as well as content providers support LTE as the mobile technology of the future. Operators, including leading GSM-HSPA and CDMA EV-DO operators as well as newly licensed and WiMAX operators, are making strategic, long-term commitments to LTE networks. All roads lead to LTE.

In June of 2008, the Next Generation Mobile Networks Alliance (NGMN) selected LTE as the first technology that matched its requirements successfully. 4G Americas, GSMA, UMTS Forum, and other global organizations have reiterated their support of the 3GPP evolution to LTE.  Additionally, the LSTI Trial Initiative has provided support through early co-development and testing of the entire ecosystem from chipset, device and infrastructure vendors.

LTE products have been tested, trialed and commercially announced in the market by manufacturers that are already part of a well-planned LTE eco-system. The LTE ecosystem will build upon the economies of scope and scale of the entire 3GPP family of technologies.
 

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. WCDMA radio technology is, essentially, as efficient as Orthogonal Frequency Division Multiplexing (OFDM) for delivering peak data rates of about 10 Mbps in 5 MHz of bandwidth. Achieving peak rates in the 100 Mbps range with wider radio channels, however, would result in highly complex terminals and is not practical with current technology. This is where OFDM provides a practical implementation advantage.

The OFDMA approach is also highly flexible in channelization, and LTE will operate in various radio channel sizes ranging from 1.4 to 20 MHz. LTE also boosts spectral efficiency.

On the uplink, however, a pure OFDMA approach results in high Peak to Average Ratio (PAR) of the signal, which compromises power efficiency and, ultimately, battery life. Hence, LTE uses an approach for the uplink called Single Carrier FDMA (SC-FDMA), which is somewhat similar to OFDMA, but has a 2 to 6 dB PAR advantage over the OFDMA method used by other technologies such as WiMAX IEEE 802.16e.

LTE capabilities include:

• Downlink peak data rates up to 326 Mbps with 20 MHz bandwidth
• Uplink peak data rates up to 86.4 Mbps with 20 MHz bandwidth
• Operation in both TDD and FDD modes
• Scalable bandwidth up to 20 MHz, covering 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz in the study phase
• Increased spectral efficiency over Release 6 HSPA by two to four times
• Reduced latency, up to 10 milliseconds (ms) round-trip times between user equipment and the base station, and to less than 100 ms transition times from inactive to active

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