Differences, Common Ground Seen in Definition of 4G

The ITU determines what is a generation change, such as between 3G and 4G, said Adrian Scrace, head of the Mobile Competence Centre at standard group 3GPP. There are two schools of thought on what’s 4G, he said. Some claim International Mobile Telecommunications (IMT) 2000 is synonymous with 3G and IMT-Advanced is synonymous with 4G, he said. Based on that doctrine, Universal Mobile Telecommunications System, HSPA, HSPA+ and LTE are all 3G technologies because they have been submitted to the ITU as IMT2000 technologies, he said. LTE-Advanced has been submitted to the ITU as an IMT-Advanced technology so it may be considered as 4G, he said. From a 3GPP viewpoint, Release 8 (LTE) and Release 9 (LTE) are 3G technologies but Release 10 (LTE-Advanced) will be a 4G technology, Scrace said. 3GPP expects to freeze Release 10 in March 2011, he said.

The alternative view is that time division multiple access is a 2G technology, Wideband Code Division Multiple Access is a 3G Technology and Orthogonal Frequency-Division Multiple Access (OFDMA) is a 4G technology, Scrace said. Under this doctrine, everything from Release 8 (LTE) onward is considered 4G, he said.

For IMT-Advanced (LTE-Advanced), the peak theoretical data rate (downlink) is 100 Mbps with full mobility and 1 Gbps with limited mobility, Scrace said. But these are “theoretical” and “peak” rates and so they're of limited utility, he said. “Of more interest are the typical average rates which a user may experience, but there are no targets specified for this.” As carriers move to LTE and LTE-Advanced, other parameters like latency and spectrum efficiency are much more important than rates, he said. Meanwhile, both WiMAX and LTE-Advanced have been submitted for ITU approval. It’s highly likely that both will be deemed to meet performance requirements and thus both will be accepted as IMT-Advanced technologies, Scrace said.

This isn’t a 4G vs. 3G issue for public safety, said Dereck Orr, program manager for public safety communications with the Office of Law Enforcement Standards at the National Institute of Standards and Technology. NIST is setting up an LTE public safety demonstration network, looking at how LTE will deal with public safety requirements. The agency hopes to have the network operational by the end of the year, he said. It’s about having an improved technology over the current broadband technology, he said. Even though LTE might not be fully 4G-compliant yet, the current standard is an improvement from the last generation, he said. One of the hopes of moving to a commercially driven technology is being able to have the benefit of quicker refresh rates, he said.

NIST is looking at interoperability of the LTE network, among other things, to ensure devices will work in a very diverse multi-vendor environment and ensure inter- and intra-network roaming, Orr said. The technology is so new that there are many questions about what are the critical elements of interoperability, he acknowledged. There’s no ecosystem now, he said. The agency hopes to have Band Class 14 devices -- those for LTE public safety -- for testing soon, he said. There’s still a lot of R&D going on for Band Class 14 subscriber units, he noted. There are multiple working groups to work on aspects of the network’s planning and deployment, he said.

LTE has a defined migration path to meet the ITU IMT-Advanced 4G requirements, said Jeff Bratcher, division chief with NTIA’s Institute for Telecom Sciences. “I believe that’s a primary reason” public safety has chosen a commercial-based broadband cellular standard so as to continue to leverage the same upgrade paths for this technology from Release 8 on up for LTE, he said.

Spectrum efficiency is probably the most important part of 4G, said Chris Neisinger, Verizon Wireless executive director of network planning. Regarding speeds, he said “the testing that we have done has been better than we expected.” A key element of 4G is low latency, he said. Many high bandwidth applications work well on 3G networks but 3G has a higher latency, he said. The latency on 4G networks is very minimal, which enables a new set of applications, he said. 4G is about enabling advanced applications and opening up wireless in new areas, he said. ITU doesn’t care what bands carriers use, said Chris Pearson, president of 3G Americas. How carriers use the limited amount of spectrum is what matters, he said. Regarding different definitions of 4G, he said it’s really “technical versus marketing."

AT&T’s approach on 4G is different from its competitors, an company spokesman said. The competitors “seem to be in a hurry,” he said. It will take several years to establish a mature 4G ecosystem, he said. When it’s ready, AT&T will move full-speed toward it, he said. Before that, the carrier will continue to invest and improve its 3G network “for the simple fact that 3G is going to be around for a long long time,” he said. Meanwhile, “speed claims don’t mean a whole lot if you don’t have a robust backhaul capability,” he said.

"4G is a disruptive change in the user experience,” said Dan Locklear, a senior director at Alcatel-Lucent. Market definition of 4G focuses on end-user experience, he said. Sprint 4G offers mobile broadband speeds of more than 10 Mbps download, a spokeswoman said. The carrier advertises average download speeds of 3-6 Mbps with peak download speeds of up to 10 times faster than today’s 3G from any carrier, she said. WiMAX is an OFDM-based technology, as is LTE, and “is clearly a next-generation technology” being introduced by many carriers around the world, she said. WiMAX has been certified as a 4G technology by the WiMAX Forum and is at a performance level that can’t be achieved by present 3G technologies, she said.

Standards bodies may ultimately set higher speed goals for what they would like to define as “official” 4G services, but those goals won’t be met for another few years at the earliest, and there is no single agreed-upon definition of 4G today, the Sprint spokeswoman said. The wireless industry has generally adopted the term 4G as a shorthand way to describe advanced wireless technologies that, among other things, are based on or employ wide channel OFDM technology and an all-IP based architecture, she said. Sprint’s 4G technology meets these parameters, she said.

T-Mobile claims that its HSPA+ network provides speeds similar to 4G speeds as it feels the urgency not to get left behind, the Sprint spokeswoman said. 4G is more than just speed, she said, saying “true 4G is the way a network is built from the ground up for data only.” Spectrum is fundamental to any discussion about 4G is spectrum, she said. Cost savings is a key part -- moving data is cheaper for a carrier with a 4G network build from the ground up: Data transfer on Sprint 4G costs about five times less per bit due to the spectrum efficiencies of an OFDM data network, she said. HSPA+ isn’t an OFDM network, she said.

T-Mobile’s HSPA+ network operates at today’s 4G speeds, offering theoretical peak throughput of 21 Mbps, a company spokeswoman said. That’s based on comparison with 4G network speeds currently available to mobile device users in the U.S., she said. The carrier will deliver 4G speeds across the vast majority of its 3G footprint in 2010 with HSPA+, and plans to offer 42 Mbps theoretical speeds in 2011, she said. “Our competitors have defined 4G speeds (WiMAX) as 3 to 6 Mbps in their marketing and are asking consumers to pay more for WiMAX service with limited coverage and very few capable devices.” HSPA+ continues to evolve so speeds are expected to get faster and get close to LTE, said Pearson.

Despite their differences, carriers agree that consumers don’t care what technology powers the network. Consumers want quality, affordable services that are an advancement over 3G and work where and when they want, the AT&T spokesman said. Clearwire agreed. “Customers don’t care about the underlying technical standards of today’s wireless networks,” a company spokeswoman said. For Clearwire, “4G is an evolution from the slower 3G service to the true mobile broadband speeds and experience,” she said.

It might be too early to tell what’s beyond the current technology plans, carriers said. “While LTE is a logical path for us, we are not in a hurry to get there,” the T-Mobile spokeswoman said. As the carrier maximizes current network investments, it will strongly leverage the LTE capabilities of its parent company, Deutsche Telekom -- rolling out LTE in eastern Germany, she said. Verizon is focusing on getting LTE up and running, Neisinger said.