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| Low-Complexity Localized Walsh Decoding For CDMA Systems | |||
| Chan,Albert | Vanu, Inc. | ||
| Madyastha,Raghu | Vanu, Inc. | ||
| Karger,David | MIT CSAIL | ||
| Indyk,Piotr | MIT CSAIL | ||
| Feldman,Jon | Vanu, Inc. | ||
| The design of code division multiple access (CDMA) receiver algorithms that run in software on a general-purpose processor is challenging because signals must be processed at rates higher than other cellular phone standards. In traditional hardware implementations of the CDMA IS-95 standard, signals received at the base station are despread prior to Walsh decoding. In this paper, we take advantage of the flexibility afforded by software implementations and develop three classes of Walsh decoding algorithms that do not require full despreading of incoming signals at the base station. Two proposed classes of algorithms exploit the fact that Walsh codes are locally decodable codes, which have the surprising property that any bit of the message can be recovered (with some probability) by examining only a small number of symbols of the codeword. We also describe a third class of algorithms based on code puncturing. All these algorithms enable trading off computation for performance, and we use them to dynamically minimize the computational requirements of the despreader and subsequent Walsh decoder such that a target bit-error rate is maintained with changing channel conditions. | |||
| Albert M. Chan received the B.A.Sc. degree from the University of Toronto, Canada, in 1997 and the S.M. and Ph.D. degrees from the Massachusetts Institute of Technology (MIT) in 1999 and 2004 respectively, all in electrical engineering. During his studies, he spent leaves at Motorola, Mansfield, MA (1998), Ericsson Inc., Research Triangle Park, NC (2000), and at Agere Systems, Murray Hill, NJ,(2001). In 2004, he was a Postdoctoral Fellow in the Signal, Information, and Algorithms Group at MIT. Since 2004, he has been a Member of Technical Staff at Vanu, Inc. His research interests include signal processing and communication systems. He is author of a number of papers in these areas and has several patents pending. Among the awards he has received are the MIT Frederick C. Hennie III Award for Teaching Excellence, a Natural Sciences and Engineering Research Council of Canada (NSERC) Postgraduate Scholarship, the General Electric Canada Special Award in Recognition of Engineering Leadership, and a Canada Scholarship. | |||