From HSPA to LTE and Beyond: Mobile Broadband Evolution

The promise of 3G mobile broadband has been borne out by more than 630 million UMTS and HSPA subscribers, supported by a vibrant industry ecosystem. Building on these foundations, the first commercial launches of Long Term Evolution (LTE) technology are enhancing the mobile user experience still further. However, even as LTE gains commercial traction, the Third Generation Partnership Project (3GPP) is cementing a new set of standards to shape a new generation of wireless communications.

Mobile Broadband Comes of Age
In September this year, a New York Times article suggested that the video sharing web site YouTube—owned by search giant Google—generates 160 million mobile views a day. That's almost triple the corresponding figure from a year ago. Mobile now accounts for a significant proportion of all YouTube traffic. Indeed, for many viewers it is their only means of interacting with the site.

Around the same time, the social networking site Facebook claimed more than 150 million active mobile users. What is more, the number of people accessing Twitter from their mobile handset has shot up by 250 percent since the beginning of 2010. And with more than 350,000 fresh users signing up to Twitter every day, 16 percent of newcomers initially access the microblogging service from their phone. For these and millions of other users, the PC is increasingly seen as a secondary means of accessing the Internet.

3G mobile broadband—as delivered by over 350 W-CDMA/HSPA networks globally—has changed the way we work and play. For better or worse, it keeps business travelers connected to the office, wherever they are. It has added an irresistible new dimension to YouTube, Facebook and other services that were originally conceived with fixed Internet users in mind. Furthermore, 3G mobile has enabled the rise of a new breed of on-the-move services that have no counterpart in the fixed world. Since its launch in March 2009, location-based social networking site Foursquare has attracted three million users, with new additions running at nearly 20,000 per day.

Non-voice traffic on 3G wireless networks continues to rise organically, fuelled by a compelling user experience delivered by the current generation of feature-rich mobile devices. Smartphones are everywhere, supported by a fertile development ecosystem. Some 250,000 third-party applications are officially available on the App Store, and 100,000 more via the Android Market.

Just as significant in terms of driving data consumption are PC dongles and netbooks with embedded wireless connectivity, plus a new wave of tablet devices. Aside from its primary nomadic application, Internet connectivity via 3G is increasingly seen as a substitute for fixed mobile broadband in many homes and offices. Indeed, PC usage—from big file transfers to HD-quality video streaming—represents a major chunk of all mobile data consumption.

At the end of September 2010, cellular market information provider Wireless Intelligence confirmed over 630 million subscriptions globally to 3G/UMTS networks. Of these, more than half are customers of high-speed HSPA and HSPA+ networks. Enjoying multi-megabit downlink rates that rival fixed broadband connections at home or at work, many of these customers are voracious data users. They rely on mobile to satisfy their thirst for streaming music and HD video, real-time maps, P2P file exchange and non-stop social networking status updates.

This explosion in mobile broadband usage confirms emphatically the success of 3G. It also underlines the pivotal role of the Third Generation Partnership Project (3GPP)—the body that unites six telecommunications standards bodies from around the world—in continually enhancing the performance of wireless networks to meet evolving market needs. Through successive standards releases, 3GPP offers the wireless industry a coherent framework to serve the evolving needs of its customers while optimising the value of operators' current network investments.

3G/UMTS builds directly on the extraordinary success of the original GSM system that now numbers well over 4.5 billion connections globally. The sheer size and reach of the GSM/UMTS footprint infers obvious economies of scale for both network equipment vendors and terminal equipment manufacturers. This, in turn, defrays development costs. Teamed with global competition, it also realises the possibility of lower end-user pricing for hardware and services, as evidenced by the rise of the $20 handset.

The universal success of GSM also impacts positively on 3G operators and their customers. The close family resemblance between second- and third-generation systems lets subscribers enjoy a transparent experience as their terminal switches seamlessly between 2G and 3G networks according to geographic availability. And for the hundreds of GSM operators—and W-CDMA/HSPA greenfield networks—the business case for evolving to higher data speeds via successive technology iterations is compelling.

Many of the performance enhancements delivered by successive 3GPP releases can be realised by relatively simple, cost-effective software upgrades to operators' existing networks. Even in the case of more fundamental upgrades, this transformation can be achieved while retaining key portions of their network assets, from cell site infrastructure and backhaul to billing and customer care functions.

Faced with the inexorable rise in network traffic, mobile operators must continue to evaluate their options for carrying these massive data volumes more efficiently while catering for further increases in future demand. The needs of today's data-hungry customers are already being met as operators roll out HSPA+ and now LTE, the latest commercial iteration of the 3GPP family that is already live in the US and Europe.

Even as LTE steadily gains commercial traction, 3GPP is currently fine-tuning a new set of standards that will shape a new generation of wireless communications over the next decade and beyond. Here, we briefly review the status of wireless standardisation in 3GPP and corresponding commercial activity. In particular, we examine the objectives and timescales for the ITU's IMT-Advanced project, examining how 3GPP has responded to the ITU's challenge with its own candidate for the 'true' fourth generation of mobile systems.

Towards a New Generation: LTE-Advanced and 'True' 4G
Standardised in 3GPP Release 8, LTE can be seen as the culmination of a globally co-ordinated development project over the past quarter of a century to create the first truly international broadband multimedia mobile telecommunication system.

Today, the first family of standards derived from the ITU's original IMT concept—IMT-2000, or '3G' as it is commonly known to operators and end-users alike—has delivered voice and broadband data capabilities to almost 800 million subscribers. Of this total, the great majority (over 630 million) are connected to the UMTS/W-CDMA/HSPA family of 3G systems as specified by 3GPP. They are complemented by an estimated 150+ million subscriptions to 1xEV-DO networks, based on the CDMA-based IMT-2000 family member as standardised by 3GPP2.

However, with IMT-2000 requirements now over 10 years old, it is time to set a fresh direction for the next major epoch in mobile communications. User expectations have changed dramatically since the first set of radio interfaces were approved for IMT-2000 in 1999. A decade ago, affordable, ubiquitous, high-speed Internet access—even in the fixed world—was still a dream. Outside the office and academia, access to the web was slow via dial-up connection. On the move, 'mobile data' effectively meant SMS.

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"The requirements for IMT-Advanced are a significant milestone in capability when compared to those of IMT-2000. IMT-Advanced is a leap beyond. It offers new capabilities for the physical layer of the radio interface and brings into play a greater level of radio resource management and control, advanced capabilities from spectrum channel and bandwidth aggregation, and improved performance at all levels, including quality of service aspects. IMT-Advanced represents a wireless telecommunication platform that has the flexibility to accommodate sercies that are yet to be imagined."
(See Figure 1)
Stephen M. Blust, Chairman of ITU-R
Working Party 5D

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In this context, the ITU's original goals for IMT-2000—data speeds of 384 kbps at pedestrian speeds rising to 2 Mbps indoors—are impressive in themselves. More than a decade on, the ITU's fresh vision for a completely new generation of mobile systems is equally ambitious. A decade from now, the wireless landscape will look very different. Users will access a new breed of ultra-high speed mobile broadband services and applications via a heterogeneous blend of radio access methods, network topologies and radical approaches to spectrum usage: a 'network of networks'.

Users will connect and interact with these services via radically new types of terminal devices. Wireless connectivity will not be restricted to phones, PCs and tablets. It will be embedded as a matter of course in domestic appliances, vehicles and consumer electronics devices. Machine-to-machine communications will be ubiquitous, with the 'Internet of things' numbering not millions but billions of end-points.

Building on the extraordinary global success of 3G, including W-CDMA, HSPA and now LTE, the ITU has articulated a new vision for this next era of global wireless communications. Termed 'IMT-Advanced', it is a name that echoes the ambitions of the previous century's original IMT project. This time, however, the goals are still higher.

According to the ITU's definition: "IMT-Advanced is a leap beyond new radio interface physical layer capabilities and brings into play a greater level of radio resource management and control, advanced capabilities for spectrum aggregation, and improved performance at all levels including QoS [Quality of Service] aspects."

"International Mobile Telecommunications-Advanced (IMT-Advanced) systems are mobile systems that include the new capabilities of IMT that go beyond those of IMT-2000," states a contribution from ITU's Radiocommunication Sector (ITU-R) Working Party 5D in March 2008. "Such systems provide access to a wide range of telecommunication services, including advanced mobile services, supported by mobile and fixed networks, which are increasingly packet-based."

The description hints strongly at a heterogeneous future, where mobility is characterised by a total user experience across a mesh of fixed and mobile networks: "IMT-Advanced systems support low to high mobility applications and a wide range of data rates in accordance with user and service demands in multiple user environments. IMT-Advanced also has capabilities for high quality multimedia applications within a wide range of services and platforms, providing a significant improvement in performance and quality of service."

In its earliest discussions about IMT that date back to the early years of this millennium, the ITU was circumspect in describing this new generation of advanced systems as '4G'. By October 2009, however, ITU explicitly used the term when it announced that six candidate technology submissions for 4G had been received in response to an open invitation in March 2008 (see Figure 2).

Currently, several operators and vendors have branded their LTE (and WiMAX) offerings as '4G'. However, this nomenclature is potentially confusing when seen in the light of the ITU's official terminology. LTE and WiMAX certainly offer a significant step forward in terms of data rates compared with previous approaches. Their capabilities, however, fall some way short of the ITU's formal requirements for IMT-Advanced.

As such, LTE and other systems are better described as '3.9G'—the last evolutionary step before LTE-Advanced. From the customer's perspective, discussions about what properly constitutes 3G or 4G are of little interest. The immense, globally coordinated standardisation effort by 3GPP is easily obscured by the seamless simplicity of today's mobile user experience. Whether I am updating my Facebook status or uploading some slides before a meeting, all that I am aware of is an experience that is slicker and quicker than it was a year agoÖ and the year before that.

A Break with the Past
The 'LTE-Advanced' name reflects its roots in LTE and the systems that preceded it—from HSPA+ and HSPA though W-CDMA right back to GSM.

Specified in 3GPP Release 10, LTE-Advanced has been explicitly dimensioned to meet—or even exceed—the requirements of IMT-Advanced. Building on the pyramid of previous releases, LTE-Advanced is also backward compatible with Release 8 (LTE), helping operators to effectively leverage their current wireless investments.

The advanced performance requirements of 4G mandate a break with the past. While interworking with 2G and 3G legacy systems will be supported, 4G demands radically new transmission technologies, plus fresh approaches to spectrum usage. Building on the agenda now being set by LTE, 4G will represent a total break from a circuit-switched world. (By comparison, while a number of approaches are currently being considered, it is likely that at least some operators will initially support voice in LTE via circuit-switched fall-back to 2G/3G.)

So what exactly will 3GPP Release 10 offer? As you would expect, the key dimensions where LTE-Advanced scores over previous technologies include speed, spectral efficiency and flexibility, capacity, coverage and interworking.

Captured in Report ITU-R M.2134, the basic requirements of IMT-Advanced are as follows:

• A high degree of commonality of functionality worldwide while retaining the flexibility to support a wide range of services and applications in a cost efficient manner;
• Compatbility of services within IMT and with fixed networks;
• Capability of interworking with other radio access systems;
• High-quality mobile services;
• User equipment suitable for worldwide use;
• User-friendly applications, services and equipment;
• Worldwide roaming capability;

One of the standout attractions of LTE-Advanced is its ability to exploit variable, ultra wide carrier bandwidths of 40 MHz, right up to 100 MHz. This, in turn, supports extremely high data rates in the mobile environment. A new transmission scheme—based on OFDMA/SC-FDMA plus sophisticated MIMO techniques and other measures—will together achieve theoretical peak data rates of 100 Mbps in high mobility situations.

In stationary environments, this theoretical performance rises as high as 1 Gbps—an order of magnitude faster than LTE. Uplink transmission is similarly enhanced, targeting data rates up to 500 Mbps. To realise these performance targets, Release 10 boosts peak spectral efficiency in both uplink and downlink by an order of magnitude compared with HSPA. Other measures, like relay functionality, will boost cell edge coverage, improving the end-user experience in rural and non-optimal coverage areas.

Physics dictates that data rates of the order of 1 Gbps in 4G systems require bandwidths approaching 100 MHz. This infers that spectrum sharing—either through regulatory measures or technology developments involving spectrally agile systems—will inevitably be part of future considerations about maintaining a competitive environment in mobile broadband.

Of equal appeal to real-world users, LTE-Advanced cuts round-trip latency times to 10 ms or less, a fraction of even the 30 ms (approx.) attained with HSPA+. For comparison, HSPA (corresponding to Releases 5 and 6) manages a latency performance no better than 70 ms, while the original W-CDMA standard (Release 99) lags still further behind at around 250 ms. Latency is a useful measure of the all-important round-trip speed that is vital to the user appeal of real-time, interactive applications. Think of multi-player gaming and media-rich social networking for an idea of just some of the applications that will be enhanced by LTE-Advanced. Table 1 shows the performance characteristics for each technology.

Also taking centre stage is the ability of LTE-Advanced to leverage advanced topology networks. Reflecting the ITU’s vision for IMT-Advanced, Release 10 caters for seamless interworking with a jigsaw of radio access systems. Macro-, micro-, pico- and femto-cells all figure in a heterogeneous network environment, covering cell sizes from tens of kilometres to just a few meters.

As long ago as 2003, ITU-R articulated its long-term strategic vision for IMT-Advanced: a global platform to build the next generation of interactive mobile services, encompassing fast data access, unified messaging and broadband multimedia.

The ITU’s formal process of identifying technology candidates for this, a new wireless generation moved forward with an invitation (issued in March 2008) for the submission of proposals for candidate radio interface technologies for the terrestrial components of IMT-Advanced.

In October 2009, the 3GPP Partners made their formal submission to the ITU, proposing LTE Release 10 and beyond—‘LTE-Advanced’—as a candidate for IMT-Advanced. Of the five other technology candidates that were submitted in parallel, some were technically identical, leaving just two main candidates. Self-evaluation results in 3GPP have shown that LTE-Advanced meets—or in some cases exceeds—all requirements of ITU-R.

After the expected approval of LTE-Advanced specifications in December 2010, it is anticipated that work on Release 10 will be effectively completed by mid-2011. Following final approval of LTE-Advanced by the end of 2011, this will give vendors and operators a clear target to start building 4G networks. While estimates vary, this timeframe points to initial LTE-Advanced deployments around 2015.

As proposed by the 3GPP Partners, LTE-Advanced is the next technological iteration in a continuum of wireless standardisation at a global level that spans almost three decades.

As with GSM and W-CDMA/HSPA/LTE currently, there will be a long period of co-existence between 3G and 4G systems—maybe for two decades or more. As 2010 draws to a close, there are a growing handful of commercially deployed LTE networks based on 3GPP Release 8, with a flood of further launches expected during 2011 and 2012. These ‘3.9G’ networks are already giving customers an early taste of the possibilities of ultra-high speed mobile broadband, and—tantalisingly—a glimpse of our true 4G future.

Jean-Pierre Bienaimé was elected Chairman of the UMTS Forum in 2003. Since joining France Telecom (FT) in 1979, he has served as Advisor to the General Director of Moroccan Telecommunications in Rabat, Director of Marketing and Product Development for international business networks and services at FT, Director of Business Development and Subsidiaries at France Cables and Radios, Chief Executive Officer of Nexus International and VP International Development at France Telecom Mobile. After the purchase of Orange by FT, he was appointed VP Group Technical Support. He is currently Senior VP, Strategy and Communications at Orange Wholesale.