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KSU Researchers Improve Spread Spectrum Technology

Kansas State University (K-State) associate professor of electrical and computer engineering Bala Natarajan and former K-State graduate student Justin Dyer have received a patent for an algorithm that enables the use of multiple access code sets of varying length in spread spectrum communications and radar systems.

"Many of the traditionally used code sets are binary code sets that have stringent restrictions on the length of the code," said Natarajan. "And once I fix the length, that means I also have restrictions on how many codes I can generate of that length, and so it limits how many users you can support on a network. Our algorithm can provide customized code sets that give you to the best possible trade-off. Many families of code already exist, but our algorithm can design a customized code set of any length for the performance you want on a specific technology."

US Patent 7587660, Multiple-access code generation states that this technology "may be advantageous to systems employing CDMA (e.g. cmdaOne, cdma2000, 1xRTT, cdma 1xEV-DO, cdma 1xEV-DV, and cdma2000 3x), W-CDMA, Broadband CDMA, Universal Mobile Telephone System (UMTS) and/or GPS signals" but is not limited to those systems. The patent includes block diagrams showing how the patented technology can be used.

A Kansas State University news release described the algorithm.

"Dyer and Natarajan developed an algorithm that can be used to generate complex-valued code sets of any length and can be optimized for various performance measures like interference. Their approach involves the use of a specific type of algorithm, an asymptotically optimal decoding algorithm like a Viterbi algorithm. This algorithm allows a systematic search over the phase space to determine the best set of complex-valued code elements that satisfy a desired performance measure."

In addition to its use in CDMA voice and data communications systems, the algorithm will have applications in radar and smart radios. The news release noted that when radar systems emitted multiple beams simultaneously, the specialized pulse compression coding schemes based on the Kansas State University algorithm could ensure that the beams didn't interfere with each other.

Unfortunately, while it could help wireless broadband networks—including wireless LAN systems—it does not appear the technology would have use in broadcast systems, where the transmitter has no knowledge of the path to the receiver and all receivers use the same coding.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.