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Special Graduate Schools
Graduate School of Information and Communication Technology
Department of Information and Communication
3. Theses(Master)
확산 스펙트럼 시스템을 위한 순회치환 직교상보 코드 설계
- Alternative Title
- Park, Hyung-Won
- Author(s)
- Park, Hyung-Won
- Alternative Author(s)
- Park, Hyung-Won
- Advisor
- 임재성
- Department
- 정보통신전문대학원 정보통신공학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2009-07
- Language
- eng
- Alternative Abstract
- Since the late 1950’s, spread spectrum techniques have been used for military applications in which clandestine operation is a major objective and for cellular applications in which selective addressing capability is a major objective. This dissertation focuses on improving the performance of the spread spectrum system for the cellular and tactical networks, especially the multicarrier code division multiple access (MC-CDMA) system and the Joint Tactical Distribution Systems (JTIDS). For spread spectrum systems, one of the most important design issues is to obtain a set of code sequences that maximizes the system performance. A spread spectrum system relies on signature codes or spreading codes to recruit wanted signals. Therefore, the choice of spreading codes for a spread spectrum will largely determine the fundamental performance of the system. However, performance of the spread spectrum system with existing orthogonal spreading code drops in terms of throughput, low probability intercept or detection, and anti-jamming as the cross-correlation between different spread sequences become larger. To improve the performance of the spread spectrum system, we propose a cyclic shifted orthogonal complementary (COC) code set. Our idea is based on the correlation characteristics of complementary codes. The proposed COC code set has a good periodic cross correlation property and consists of multiple sub-spreading codes. The main drawback of the complementary codes is a lack of available code number. We extend the number of codes by cyclically chip shift the complementary codes. Unlike any of the previously considered approaches, this method constructs the spreading code as a set of multiple sub-spreading codes and provides sufficient number of codes with excellent auto- and cross-correlation properties. It is shown that the proposed COC code yields the significant lower bit error probability over a frequency selective fading channel because it has a lower cross-correlation value than that of conventional orthogonal code. We apply the COC code set for the MC-CDMA and JTIDS systems. We analyze the relationship between average bit error probability and channel diversity in frequency selective fading channel environment, which induces a multiple-access interference. We propose a parallel spreading scheme which transmits mutually exclusive sets of sub-spread sequences over independent channels. The spread sequence of every data symbol is constructed with a set of sub-spread sequences. Since COC codes are constructed as a set of sub-spreading codes, it shows better cross-correlation property among them. Simulation results show that MC-CDMA with COC codes shows better average BER and spectral efficiency. In the tactical data link system, the successful design of spread sequence is a key factor to reduce LPI/LPD performance. For providing LPI/LPD performance to various combat units such as F-15, AWACS in the tactical network, existing spread spectrum system loss considerable throughput. We propose partitioned CCSK scheme based on COC codes. In proposed scheme, we construct spreading code as a set of partitioned sub-spreading codes. They are applied to cyclic shifted code keying (CCSK) modulation and spread data symbols based on the user’s demand. By exploiting cyclic shifted orthogonal complementary codes as a spread code, the system enables to obtain higher spectral efficiency. Furthermore, we maintain almost the same LPI/LPD performance since the COC code maintains the orthogonality in set of sub-spreading codes.
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