Low-Power Design

Fourth-generation wireless technology has been anticipated for quite some time. This series of articles traces the evolution of 4G and LTE-Advanced, explaining the architectures and their implications for both carriers and consumers.

LTE-Advanced is being specified initially as part of Release 10 of the 3GPP specifications, with a functional freeze targeted for March 2011. The LTE specifications will continue to be developed in subsequent 3GPP releases.

In October 2009, the 3GPP Partners formally submitted LTE-Advanced to the ITU Radiocommunication sector (ITU-R) as a candidate for 4G IMT-Advanced [1]. Publication by the ITU of the specification for IMT-Advanced is expected by March 2011. As more and more wireless operators announce plans to deploy LTE in their next-generation networks, interest in LTE-Advanced is growing.

The application note also introduces Agilent’s LTE-Advanced design and test solutions that are ready for use by early adopters. These solutions will be continuously enhanced as the LTE-Advanced specifications are released.

To get the most from this application note, you should have knowledge of the basic concepts of LTE technology. Detailed information is available in Agilent’s book LTE and the Evolution to 4G Wireless: Design and Measurement Challenges (ISBN 978-988-17935-1-5) www.agilent.com/find/ltebook and in the application note “3GPP Long Term Evolution: System Overview, Product Development, and Test Challenges” (literature number 5989-8139EN), available at www.agilent.com/find/LTE.

Please note that because the final scope and content of the Release 10 specifications are still to be decided, the information covered in this series of articles is subject to change.

Overview of LTE and LTE-Advanced

Fourth generation wireless technology has been anticipated for quite some time. To understand the evolutionary changes in 4G and LTE-Advanced, it may be helpful to summarize what came before.

Evolution of wireless standards

Figure 1. Wireless evolution 1990–2011 and beyond Wireless communications have evolved from the so-called second generation (2G) systems of the early 1990s, which first introduced digital cellular technology, through the deployment of third generation (3G) systems with their higher speed data networks to the much-anticipated fourth generation technology being developed today. This evolution is illustrated in Figure 1, which shows that fewer standards are being proposed for 4G than in previous generations, with only two 4G candidates being actively developed today: 3GPP LTE-Advanced and IEEE 802.16m, which is the evolution of the WiMAX standard known as Mobile WiMAX.

Early 3G systems, of which there were five, did not immediately meet the ITU 2 Mbps peak data rate targets in practical deployment although they did in theory. However, there have been improvements to the standards since then that have brought deployed systems closer to and now well beyond the original 3G targets.

Table 1 shows the evolution of 3GPP’s third generation Universal Mobile Telecommunication System (UMTS), the original wideband CDMA technology, starting from its initial release in 1999/2000. There have been a number of different releases of UMTS, and the addition of High Speed Downlink Packet Access (HSDPA) in Release 5 ushered in the informally named 3.5G. The subsequent addition of the Enhanced Dedicated Channel (E-DCH), better known as High Speed Uplink Packet Access (HSUPA), completed 3.5G. The combination of HSDPA and HSUPA is now referred to as High Speed Packet Access (HSPA). LTE arrived with the publication of the Release 8 specifications in 2008 and LTE-Advanced is being introduced as part of Release 10. The LTE-Advanced radio access network (RAN) functionality is planned to be functionally frozen by December 2010 (excluding the ASN.1 definitions) and the overall Release 10 functional freeze is targeted for March 2011.

Summary of LTE features

The Long Term Evolution project was initiated in 2004 [2]. The motivation for LTE included the desire for a reduction in the cost per bit, the addition of lower cost services with better user experience, the flexible use of new and existing frequency bands, a simplified and lower cost network with open interfaces, and a reduction in terminal complexity with an allowance for reasonable power consumption.

These high level goals led to further expectations for LTE, including reduced latency for packets, and spectral efficiency improvements above Release 6 high speed packet access (HSPA) of three to four times in the downlink and two to three times in the uplink. Flexible channel bandwidths—a key feature of LTE—are specified at 1.4, 3, 5, 10, 15, and 20 MHz in both the uplink and the downlink. This allows LTE to be flexibly deployed where other systems exist today, including narrowband systems such as GSM and some systems in the U.S. based on 1.25 MHz.

Speed is probably the feature most associated with LTE. Examples of downlink and uplink peak data rates for a 20 MHz channel bandwidth are shown in Table 2. Downlink figures are shown for single input single output (SISO) and multiple input multiple output (MIMO) antenna configurations at a fixed 64QAM modulation depth, whereas the uplink figures are for SISO but at different modulation depths. These figures represent the physical limitation of the LTE frequency division duplex (FDD) radio access mode in ideal radio conditions with allowance for signaling overheads. Lower rates are specified for specific UE categories, and performance requirements under non-ideal radio conditions have also been developed. Figures for LTE’s time division duplex (TDD) radio access mode are comparable, scaled by the variable uplink and downlink ratios.

Table 2. Peak data rates for LTEUnlike previous systems, LTE is designed from the beginning to use MIMO technology, which results in a more integrated approach to this advanced antenna technology than does the addition of MIMO to legacy system such as HSPA.

Finally, in terms of mobility, LTE is aimed primarily at low mobility applications in the 0 to 15 km/h range, where the highest performance will be seen. The system is capable of working at higher speeds and will be supported with high performance from 15 to 120 km/h and functional support from 120 to 350 km/h. Support for speeds of 350 to 500 km/h is under consideration.

What’s new in LTE-Advanced

In the feasibility study for LTE-Advanced, 3GPP determined that LTE-Advanced would meet the ITU-R requirements for 4G. The results of the study are published in 3GPP Technical Report (TR) 36.912. Further, it was determined that 3GPP Release 8 LTE could meet most of the 4G requirements apart from uplink spectral efficiency and the peak data rates. These higher requirements are addressed with the addition of the following LTE-Advanced features:

Other performance enhancements are under consideration for Release 10 and beyond, even though they are not critical to meeting 4G requirements:

These features and their implications for the design and test of LTE-Advanced systems will be discussed in detail later in this application note.

3GPP documents for LTE-Advanced

3GPP publishes all the documents relating to the development of LTE-Advanced. These documents are free to the public and can be downloaded from the 3GPP web site (www.3GPP.org) or at the addresses given below. The versions and dates shown here are current at the time of this writing.

Study phase Technical Report on E-UTRA UE Radio Transmission and Reception
TR 36.807
Summarizes study of CA, enhanced multiple antenna transmission and CPE
ftp://ftp.3gpp.org/Specs/html-info/36807.htm

Stage 3 technical specifications begin to appear in the Release 10 36-series
documents dated 2010-09.

LTE-Advanced timeline

Work on Release 8 LTE, including test development, is expected to be finished in 2010. The Global Certification Forum (GCF) released its scheme for test validation in early 2010 and will release a scheme for User Equipment (UE) certification by late 2010, when it expects to see the first major wave of LTE commercial network rollouts [3]. Deployment is expected to continue over the next few years. The deployment timeline for LTE-Advanced will be influenced by the success of LTE in the market.

Figure 2. Timelines for IMT-Advanced (4G) and
LTE-Advanced developmentFigure 2 shows the timeline for the development of IMT-Advanced and LTE-Advanced. At the top of the figure is the timeline of the ITU-R, which is developing the fourth generation requirements, which are described in more detail in the next section. In March 2008, the ITU-R issued an invitation for proposals for a new radio interface technology (RIT), with a cutoff date of October 2009 for submission of candidate RIT proposals. The cutoff date for submitting the technology evaluation report to the ITU was June 2010. In October 2010 the ITU Working Party 5D (WP 5D) decided that the first two RITs to meet the IMT-Advanced requirements were 3GPP’s LTE-Advanced and IEEE’s WirelessMAN-Advanced, which is also known as 802.16m [4]. WP 5D is scheduled to complete development of radio interface specification recommendations by February 2011.

The bottom of Figure 2 shows the work by 3GPP on LTE-Advanced, which is occurring in parallel with the development of the ITU requirements. With the completion of the documents listed at the bottom of the figure, 3GPP formally submitted LTE-Advanced to the ITU as an IMT-Advanced candidate technology.

References

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