NEW YORK-AT&T Labs, Florham Park, N.J., is peering into the future of wireless communications and working on ways to enhance the next generation of services, researchers said at a recent media and analyst briefing.
Closest to fruition is the Location-Aware Information Services research project. The project’s commercial product, a location server, is expected in about six months.
“You can use a variety of technologies to locate someone, depending on what is most appropriate. This works with any location-sensitive technology, regardless of device, extracts the location and provides it to a third party,” said Theodore J. Johnson, principal member of the Labs’ technical staff. “We are trying to develop the architecture to facilitate these location-based applications, which would call our location server. … Things like technical bugs and business agreements need to be worked out.”
Within the next few years, AT&T Labs hopes to have available in stages various editions of space-time coding for GSM/EDGE, said Robert Calderbank, research vice president. “If you have two transmitters spaced far enough apart, instead of just coding across time, you can code across both time and space and (thereby) improve the overall link between transmitter and receiver,” he said. “This will double voice capacity and provide higher data rate modes that are more available farther from cell sites.”
BellSouth Corp. and SBC Communications Inc. have proposed a similar solution for IS-136 technology and for EDGE, he said.
The second phase of space-time coding, “will break the 1 Megabit per second barrier,” Calderbank added.
Ericsson Inc. is working with AT&T Labs on phones to accommodate these advances. There should be “minimal impact on handsets, because this fits inside existing DSPs (digital signal processors),” he said.
When data rates move to 2 Mbps, it will be a lot more complicated for phone manufacturers to handle the demands.
“Someone will get ambitious on the handset side and install two antennas and the necessary hardware. We’re hoping it will be Ericsson,” Calderbank said.
The space-time codes, which AT&T Labs invented, are one means to achieve “transmit diversity,” which will help enable new generations of smart antennas to improve radio link performance, said Nelson Sollenberger, director of fourth-generation research. Transmit diversity also can be based on transmitting delayed copies of a signal on multiple antennas.
AT&T Labs also has developed a prototype of a smart antenna for EDGE that uses a two-antenna receiver with digital signal processing to suppress interference and mitigate against signal fading. The purpose is to improve radio link performance in a network that runs on limited radio-frequency spectrum.
Also in the hopper is a demonstration project for Fourth Generation Wireless Data Access, which is a “pre-standards research initiative,” Sollenberger said. Building on EDGE technology, 4G access focuses on enhancing data rates on the downlink, or receiving end, of wireless data communications.
In a project summary distributed at the briefing, AT&T Labs said the first 4G access prototype “provides a downlink designed to operate at more than 384 kilobits per second at 800 kilohertz bandwidth in a high-mobility, wide-area wireless environment, much like the cellular voice environment today.”
To attain downlink access at 10 Mbps, “orders of magnitude faster than even most wired users enjoy today,” the research laboratory also is investigating the use of Orthogonal Frequency Division Multiplexing. OFDM sends data on a large number of parallel sub-channels, thereby eliminating the “severe degradation normally caused by multipath propagation on a (single) wireless channel,” AT&T Labs said.
OFDM technology already is deployed for use in European High Definition Television, Digital Audio Broadcasting, Digital Subscriber Loop systems and in certain high-speed wireless local area networks.
For mobile wireless networks based on TDMA, OFDM has the advantage of working well in “limited, shared RF spectrum,” AT&T Labs said. OFDM also can use and benefit from advances in general-purpose DSPs.
“By contrast, Code Division Multiple Access, a competing wireless protocol, is based on complex, proprietary algorithms, which do not lend themselves as well to generalized DSPs,” AT&T Labs said. “In addition, OFDM … allows for very flexible RF spectrum allocation. CDMA requires an all-or-nothing approach to spectrum allocation. This has a negative impact on traffic engineering and degrades overall system capacity.”
In a related endeavor, AT&T Labs also is working on a “dynamic packet assignment,” Sollenberger said. “This moves the spectrum, packet by packet, between base stations to give enough resources for high-burst data services. It can improve performance by 50 percent,” he said.
Overall, AT&T Labs’ 4G wireless research is intended to introduce continued improvements during the next five years, Sollenberger said.
