2006 Fiscal Year Final Research Report Summary
Asynchronous DS/CDMA systems employing spreading codes generated by chaos maps with Markovity
| Project/Area Number |
15360206
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Communication/Network engineering
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| Research Institution | KYUSHU UNIVERCITY |
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Principal Investigator |
KOHDA Tohru Kyushu University, Graduate School of Information Science and Electrical Engineering, Professor, 大学院システム情報科学研究院, 教授 (20038102)
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| Co-Investigator(Kenkyū-buntansha) |
OOHAMA Yasutada The University of Tokushima, Faculty and School of Engineering, Professor, 工学部, 教授 (20243892)
JITSUMATSU Yutaka Kyushu University, Graduate School of Information Science and Electrical Engineering, Associate Professor, 大学院システム情報科学研究院, 助教授 (60336063)
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| Project Period (FY) |
2003 – 2006
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| Keywords | CDMA communication / spread spectrum codes / pseudorandom number generator / chip waveforms / Markov chain / pulse shaping filter / FIR filter / Welch bound |
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| Research Abstract |
In DS-CDMA communications, linear feedback shift register (LFSR) sequences, such as Gold and Kasami codes, are employed as spread spectrum (SS) codes. In mobile cellar systems, propagation delay is randomly spread for uplink channels and synchronization timing error cannot be eliminated. Hence, we have evaluated the chip-asynchronous systems. Our results are summarized as follows 1) Chip-asynchronous version of total square correlation (CA-TSC) was defined as the total value of all users' interference and its lower bound, named chip-asynchronous version of Welch bound, was presented. Mutual interference depends on spreading codes and chip waveforms. They are normally designed independently but joint optimization of them should give better performance. We relaxed the Nyquist condition, which guarantees zero inter symbol interference and is often assumed to be satisfied, to minimize total interference. We showed that the pair of Gaussian pulse and Markov codes give better performance than the conventional pair of raised cosine pulse and LFSR sequences, where both pulses are adjusted to have the same excess-band energies. 2) Based on a posteriori probability calculations, we proposed a new code acquisition algorithm. The proposed method, called "counting method", is very simple and effective; it counts only the number of events that receiver outputs exceed the pre-determined threshold and it realizes faster code acquisition than the serial search. More importantly, this method guarantees the maximum acquisition error rate. 3) Close relation between the associate memory model of neural networks and CDMA system is investigated. Associative memory corresponding to chip-asynchronous CDMA system was proposed, which was shown to memorize Markov patterns better than i.i.d. patterns
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Research Products
(12 results)
