3G Shifts

Jul 15, 2001 12:00 PM, By Betsy Harter

It's still a decade away, but 4G already is a big topic of discussion behind closed doors. But what is 4G, exactly, and why is it necessary to think about it today?

Most vendors already have a position on 4G as they prepare to push their visions in front of standards bodies and generate interest among carriers. But each manufacturer has a different definition of 4G. Whether it's spectrum optimization, network capacity or faster data rates, vendors already are dreaming up ways for carriers to spend money and spectrum decades down the road.

Carriers, however, are reluctant to discuss 4G, either because they refuse to take a public position on it when 3G roll-outs still are unfulfilled, or because they are in denial. But carriers soon will find that 4G is not going away.

3G was supposed to be the land of wireless milk and honey for carriers, enabling multimedia, data transfer between wireless phones at lightning speeds and m-commerce. So why is 4G even necessary? Al Javed, Nortel Networks (www.nortel.com) wireless CTO, said that although it is true that 3G will bring transactional services, they will be lower-speed services compared to, say, streaming video.

“That is not to say you won't love these lower-speed transactional services like location-based services, wireless shopping, personal services or e-mail. But when we move to streaming video and audio, we need 4G systems,” he said.

But Hakan Eriksson, Ericsson (www.ericsson.com) vice president of research, said 3G will offer some streaming services. For instance, a consumer subscribing to a service that provides video of her favorite sports team scoring a goal, basket or touchdown would not require high-speed video transmission.

“That will take 15 to 20 seconds at a bit rate of 128kb/s,” he said. “When you talk about 4G, applications will require higher speeds and capacity.”

One such application might be a set of eyeglasses that projects information about a person's location so that only that person can see it. For instance, someone at a museum could see facts about a painting projected onto a wall, or a tourist could see road signs that locals would not see.

An anonymous spokesperson at Siemens (www.usa.siemens.com) — a company that calls future wireless systems “beyond 3G” because it is too difficult to clearly differentiate between 3G, 4G and xG features — said systems beyond 3G are important for several reasons. First, the ever-increasing demand for more powerful and seamless applications drives the need for higher data rates. Next, high-quality streaming video — an essential component of future multimedia-based services — will require higher data rates than 3G will provide.

“Also, providing seamless mobile access to services without regard to the physical network used, from the customer's point of view, is another essential requirement,” the source said. Moreover, standards typically take 10 years to move from conception to commercial products, so now is the time to start thinking about solutions beyond 3G if carriers want a powerful generation of seamless fixed and mobile services in 2010 to 2015.

Reinaldo Valenzuela, Bell Labs (www.bell-labs.com) director for wireless communications research, said that most standards start in Europe with pre-competitive cooperative projects funded by the European Commission under the scientific and technical umbrella of ETSI. European (www.etsi.org) standards bodies already have begun the pre-competitive process for some aspects of 4G.

No two vendors have the same 4G vision but all agree that post-3G systems will be a conglomeration of previous wireless technologies rather than a whole new wireless system.

“This time, the route to 4G will not be a system or a standard,” Eriksson said. “It will be a combination of technologies, building on 3G but capable of much higher speeds.”

4G is synonymous with speeds of 50Mb/s to 100Mb/s. Although wireless LANs are slated to reach these speeds, wireless LANs alone will not comprise 4G because their coverage is limited, he explained.

For Nortel Networks and Siemens, 4G is all about access.

“In terms of networking technologies, we are all moving toward IP, including wireless,” Javed said. “The networks will not change; 4G is a change in access technology.”

The source at Siemens said future wireless networks will be more than just a new radio interface; instead, one goal is to increase capacity to provide new multimedia services with higher data rates for mobile applications or, in some cases, for portability without wire-based plug-ins.

“Another important feature will be seamless mobile access to different networks: access anywhere, anytime,” the source said. A system “beyond 3G” comprises a combination of several optimized-access systems into a common IP-based medium access and core network platform. These different access systems will interwork by horizontal and vertical handover, service negotiation and global roaming to provide globally optimized seamless services to users.

“The borders between 3G and 4G are not that clear,” said the source. “The term 4G seems to skip the need for a constant development of services, applications and the network technology. This is why we think and develop ‘beyond 3G.’”

Carriers are not eager to discuss 4G publicly. Both Cingular Wireless (www.cingular.com) and Sprint PCS (www.sprintpcs.com) said that they are so focused on their 3G plans that they have no time to think about 4G possibilites. Both Verizon Wireless (www.verizonwireless.com) and AT&T Wireless Services are keeping (www.attws.com) mum due to SEC-mandated quiet periods. However, AT&T Labs (www.research.att.com), which is able to discuss 4G because it is not spinning off from the parent company and, therefore, is not affected by the quiet period, has been studying 4G since the 3G standards began gelling, said Bruce McNair, AT&T Labs senior researcher.

“Because we are a research organization, our horizon has to be further out,” he said. “It's not too early to start anticipating 4G.”

McNair said AT&T Labs is pushing for a clean evolution from 3G to 4G so that AT&T Wireless does not have to replace 3G systems. Through research, the organization hopes to understand where 3G is heading, as well as what 4G will present.

McNair said the big difference between 3G and 4G will be traffic flow. Right now, Internet traffic flows from server to user, but most wireless systems assume a symmetrical link.

“When we get to high data rates, the laws of physics make it difficult to imagine how we can transfer from a portable terminal to a network, so in terms of 4G, we envision a high-speed downlink added to the existing 2.5G or 3G system that provides the uplink,” he said. Here, short requests or mouse clicks would travel over a lower-speed 2.5G system, but downloaded images would come over a 10Mb/s or 20Mb/s return path.

“Some people argue that you limit yourself when you start thinking of asymmetry, but, in fact, a challenge is making the terminal device run, which requires a reasonable battery lifetime, size, power and cost, so 3G networks need higher-speed downlinks,” McNair said.

For AT&T Labs, smart antennas — in particular multiple input multiple output (MIMO) antennas — will be important to 4G networks.

“To get the kinds of range and throughput we are looking for, we will be using smart-antenna technology,” McNair said, adding that the company will use OFDM in its 4G networks. “There is a natural fit between OFDM and smart antennas, so people see it as sort of the technology that enables this to happen.”

McNair said AT&T Labs is looking for ways to improve network performance, extend the range of antennas and improve frequency reuse in its 2.5G and 3G systems. Smart-antenna technology will enable carriers to use their spectrum more efficiently.

“(Smart antennas) open up spectrum and pack users in,” he said. “If you follow Moore's Law, which predicts that the adoption of technologies doubles every 18 months, that makes 4G smart antennas practical.”

Vendors already are dabbling in 4G smart antennas. Bell Labs' technology — called Bell Labs Layered Space-Time (BLAST) — is being studied as part of one EU-sponsored pre-competitive advanced antenna-technology project. A BLAST prototype uses an array of eight transmit and 12 receive antennas. During its first weeks of operation, it achieved at least 10 times the wireless capacities of today's fixed-wireless-loop systems.

“The idea here is if you try to increase capacity of a wireless system, you run up against a brick wall because capacity is limited by the interference of other users, so increasing bit rate by increasing power does not work at all,” Valenzuela said.

Although the classic approach is to throw more bandwidth at the problem, high prices and low spectrum availability have made this option unattractive. However, several years ago, the idea was introduced that adding transmit and receive antennas can create parallel channels that don't interfere with one other. This process does not require increased power or additional frequency.

“MIMO antennas are a very practical system, and if you combine it with adaptive coding and modulation, interference cancellation and beam-forming technologies, you can realize gains that are 30 times better, in terms of bit rates and capacity, than 3G,” Nortel's Javed agreed.

Nortel has operational MIMO systems in its lab. Tests show a 10X capacity increase at speeds of 20Mb/s. Next year, the company expects to hit 40Mb/s, as well as conduct field trials of its technologies.

Betsy Harter (betsyharter@aol.com) is a freelance writer based in Athens, GA.

Unlike vendors that promise to reduce interference through smart antennas, LinkAir (www.linkair.com) claims it can completely eliminate interference with its large-area synchronized CDMA (LAS-CDMA) technology. LAS-CDMA, which merges CDMA and TDD technologies, uses a smart CDMA code that is different from Qualcomm's CDMA code. This means the company is not subject to Qualcomm's IPRs.

LinkAir's smart code transmits voice, data and video images in the same channel. Although the company will not give hard numbers, it promises speeds six times faster than current 3G technology.

According to William Lee, LinkAir Communications chairman, LAS-CDMA uses LAS, a spreading and encoding scheme that reduces system-generated interference by combining two levels of coding called LA and LS codes. By isolating certain smart codes during transmission, the LAS-CDMA system optimizes spectrum and increases efficiency. These smart codes separate voice from data during transmission.

As for deployment, Lee hopes to make it easy on wireless carriers. The company is negotiating with handset vendors to create dual-mode handsets that work on LAS-CDMA and 3G networks — whatever 3G technology a carrier has chosen. Carriers will overlay their 3G systems with Link-Air's LAS-CDMA system, and customers would use dual-mode phones to access the 4G network.

In December 2000, the Wireless Strategic Initiative (www.ist-wsi.org) organized a workshop to start an open international discussion on “Visions of the Wireless World.” From its think tank, the group formed the Wireless World Research Forum (www.wireless-world-research.org) in March 2001, to research future wireless technologies. Founded jointly by Alcatel (www.alcatel.com), Ericsson (www.ericsson.com), Nokia (www.nokia.com) and Siemens (www.usa.siemens.com), the Wireless World Research Forum brings together industry and academia to generate, identify and promote research areas and technical trends for mobile and wireless system technologies. Open to all interested parties, the forum will organize three working sessions and a workshop in 2001.

Equipment vendors also are coming together to speed the adoption of OFDM, which could be part of the 4G set of standards. The OFDM Forum (www.ofdm-forum.com) recently formed to promote the transmission standard. Members include Ericsson, Nokia, Philips (www.philips.com), Sony (www.sony.com), Wi-LAN (www.wilan.com) and Alcatel.