Smart Antennas Facilitate 4G

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.