• Title, Summary, Keyword: CDMA

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Performance Improvement of MFSK-MDPSK/DS-CDMA System Employing MRC Diversity Techniques and Convolution Coding Techniques in Nakagami Fading Environment (나카가미 페이딩 환경하에서 MRC 다이버시티기법과 컨벌루션 부호화 기법을 채용한 MFSK-MDPSK/DS-CDMA 시스템의 성능 개선)

  • 박형호;김영철;강희조;이권현;조성준
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.8 no.2
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    • pp.173-184
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    • 1997
  • In most DS-CDMA systems, the modulation scheme used is a simple one. In this paper, the error performance of DS-CDMA system employing a MFSK-MDPSK combined moulation techniques in adopting MRC diversity reception and convolution coding technique are evaluated. The obtained result show that the error performance of MFSK-MDPSK/DS-CDMA system in Nakagami fading environments is improved by increasing the number of diversity branch and coding gain. Also the power efficiency and bandwidth efficiency combined system in MFSK/ DS-CDMA, MDPSK/DS-CDMA are better than conventional MFSK-MDPSK/DS-CDMA systems.

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An Enhanced Mechanism of Security Weakness in CDMA Service (CDMA 서비스의 보안취약성과 개선방안)

  • Ryu, Dae-Hyun;Jang, Seung-Ju
    • Journal of KIISE:Information Networking
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    • v.30 no.6
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    • pp.729-742
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    • 2003
  • Mobile Communication has a possibility of eavesdropping by nature of wireless channel. It is known that eavesdropping of CDMA system is impossible because the voice data spreads with the PN. First of all, we show that it is possible to eavesdrop the CDMA channel by analysis of the forward channel in case that we know the ESN and the MIN. We can monitor the forward traffic channel with easy since ESN and MIN are exposed during the call processing in CDMA service in Korea. In this paper, we will show security weakness and propose an enhanced mechanism for CDMA service. We consider the problem of security in the CDMA service. CDMA system has wireless channels to transmit voice or data. By this reason, CDMA communication has a possibility of being eavesdropped by someone. It is known that eavesdropping in CDMA system is impossible because the voice data spreads with the PN. However, we can eavesdrop the CDMA data in FCM protocol in case that we know the ESN and the MIN. In CDMA system, ESN and MIN are exposed to the wireless channel. In this paper, we analyze the flow of the voice and signal in the CDMA system and monitor the forward traffic channel by the FCM protocol. The FCM protocol is proposed to monitor the forward channel in CDMA system. We can show the possibility of monitoring in one-way channel of CDMA system by the FCM protocol. The test instrument based on the FCM protocol is proposed to monitor the CDMA forward channel. We will show the system architecture of the test instrument to monitor the forward channel in CDMA.

Design of Binary Constant Envelope System using the Pre-Coding Scheme in the Multi-User CDMA Communication System (다중 사용자 CDMA 통신 시스템에서 프리코딩 기법을 사용한 2진 정진폭 시스템 설계)

  • 김상우;유흥균;정순기;이상태
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.15 no.5
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    • pp.486-492
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    • 2004
  • In this paper, we newly propose the binary CA-CDMA(constant amplitude CDMA) system using pre-coding method to solve the high PAPR problem caused by multi-user signal transmission in the CDMA system. 4-user CA-CDMA, the basis of proposed binary CA-CDMA system, makes binary output signal for 4 input users. It produces the output of binary(${\pm}$2) amplitude by using a parity signal resulting from the XOR operation of 4 users data. Another sub-channel or more bandwidth is not necessary because it is transmitted together with user data and can be easily recovered in the receiver. The extension of the number of users can be possible by the simple repetition of the basic binary 4-user CA-CDMA. For example, binary 16-user CA-CDMA is made easily by allocating the four 4-user CA-CDMA systems in parallel and leading the four outputs to the fifth 4-user CA-CDMA system as input, because the output signal of each 4-user CA-CDMA is also binary. By the same extension procedure, binary 64 and 256-user CA-CDMA systems can be made with the constant amplitude. As a result, the code rate of this proposed CA-CDMA system is just 1 and binary CA-CDMA does not change the transmission rate with the constant output signal(PAPR = 0 ㏈). Therefore, the power efficiency of the HPA can be maximized without the nonlinear distortion. From the simulation results, it is verified that the conventional CDMA system has multi-level output signal, but the proposed binary CA-CDMA system always produces binary output. And it is also found that the BER of conventional CDMA system is increased by nonlinear HPA, but the BER of proposed binary CA-CDMA system is not changed.

A CDMA Education Content Utilizing Regional GIS Information (지역지리정보를 활용한 CDMA 교육 콘텐츠)

  • 이영대;연상호
    • Proceedings of the Korea Contents Association Conference
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    • pp.245-250
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    • 2003
  • Of all wireless technologies for personal communications, CDMA(Code Devision Multiple Access) offers the best combination of good signal quality, high security and system reliability. CDMA2000 provides Internet and internet services for variable multimedia aplications. However, good educational CDMA web contents, which focus on the easy understability and good readability, are rare dute to the difficulties and the broad range of CDMA technologies. This content is developed based upon the following two aspects. First, a basic CDMA communication theoy, which contains much color figures and animation, is introduced combing the experimental results and corresponding explanations utilizing the information obtained by the TIMS CDMA equitments. It can improve the understabiliy virtual experience of the site visitors interested in the CDMA. Secondly, the recent CDMA coverage prediction and engineering technology is introduced using the RF plan tool C24 combined for the CDMA engineers

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Application of Rate Compatible Punctured Turbo Coded Hybrid ARQ to MC-CDMA Mobile Radio

  • Garg, Deepshikha;Adachi, Fumiyuki
    • ETRI Journal
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    • v.26 no.5
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    • pp.405-412
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    • 2004
  • MC-CDMA, a multicarrier (MC) modulation scheme based on code division multiple access (CDMA), is the most likely candidate for the next generation of mobile radio communications. The rate compatible punctured turbo (RCPT) coded hybrid automatic repeat request (HARQ) has been found to give improved throughput performance in a direct sequence (DS) CDMA system. However, the extent to which the RCPT HARQ improves the throughput performance of an MC-CDMA system has not been fully understood. In this paper, we apply the RCPT HARQ to MC-CDMA and evaluate by computer simulations its performance in a frequency selective Rayleigh fading channel. We found that the performance of RCPT HARQ MC-CDMA is almost insensitive to channel characteristics. The performance can be drastically improved with receive diversity combined with space-time transmit diversity. In addition, the comparison of RCPT HARQ MC-CDMA, orthogonal frequency division multiplexing, and DS-CDMA shows that under similar conditions the throughput of MC-CDMA is the best in a frequency selective fading channel.

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Performance Analysis of Mini Slotted CDMA ALOHA System For Wireless Data and Personal Communication (무선 데이타 통신 및 개인 통신을 위한 Mini Slotted CDMA ALOHA 기법의 성능 해석)

  • Heo, Jeong-Seok;Yang, Seong-Ryong;Lee, Jeong-Tae
    • The Transactions of the Korea Information Processing Society
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    • v.1 no.4
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    • pp.502-510
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    • 1994
  • CDMA technique has been largely focused for Wireless Data Communication and Personal Communication Network. ALOHA protocol also has been proven to be effective for Packet Radio Radio Network regardless of low throughput due to channel collisions. In this paper, we evaluate the performance of MS-CDMA-ALOHA (Mini-Slotted-CDMA-ALOHA) system, by analytic and simulation method. The superiority of the MS-CDMA-ALOHA system over conventional Slotted ALOHA and Slotted-CDMA-ALOHA systems are clearly demonstrated for throughput, delay and stability performances.

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Performance Analysis of RRA_CDMA MAC Protocol In the Cellular Parket CDMA Systems (셀룰러 패킷 CDMA 시스템에서 RRA_CDMA MAC 프로토콜의 성능 분석)

  • 임인택
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.24 no.8A
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    • pp.1141-1148
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    • 1999
  • In this paper, an RRA_CDMA protocol is proposed for the integrated voice and data services in the cellular packet CDMA systems. The proposed protocol employs the RRA scheme. In the cellular CDMA systems, the backward logical channels are composed of time slots with multiple spreading codes per slot based on WB-TD-CDMA concept. When a voice terminal begins a talkspurt, it reserves one of the available spreading codes in the next slot and uses the reserved channel exclusively untill it ends the talkspurt. On th other hand, whenever a data terminal generates a packet, it selects an avaliable spreading code and transmits its packet. Throughout the results, it is shown that the system capacity increases in proportion to the number of spreading codes.

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Performance Improvement Techniques for an OFDM-CDMA System without Guard Interval (보호구간이 없는 OFDM-CDMA 시스템의 성능 향상 기법)

  • Lee Hyun-Woo;Park Joong-Hoo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.31 no.5A
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    • pp.501-508
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    • 2006
  • Orthogonal frequency division multiplexing-code division multiplexing access(OFDM-CDMA) systems without guard interval can enhance the bandwidth performance more efficiently than the systems with guard interval. In this paper, a new technique for an OFDM-CDMA system without guard interval, which can eliminate inter-symbol interference(ISI) and inter-channel interference(ICI), is presented. The proposed algorithm is a new demodulation technique, based on the Pseudo-Decorrelator, and it is named PD algorithm. Simulation results show that the PD algorithm can combat ISI and ICI efficiently for an OFDM-CDMA system without guard interval. The BER performance of the PD algorithm is much better than that of a conventional OFDM-CDMA system without guard interval.

Performance Analysis of Dualrate MC-CDMA Systems Based on Code Grouping (코드그룹화에 의한 이중전송률 MC-CDMA 시스템의 성능분석)

  • Kim, Nam-Sun
    • Journal of the Korea Industrial Information Systems Research
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    • v.11 no.4
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    • pp.112-120
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    • 2006
  • Multicarrier code division multiple access(MC-CDMA) system that combines multicarrier modulation with CDMA offers robustness to frequency selective fading and can support higher rate data transmission with higher spectral efficiency. A new asynchronous MC-CDMA system to implement multiple data rate communications is proposed in this paper. In a W-CDMA downlink the orthogonal variable spreading factor(OVSF) code is used for variable spreading factor for various multimedia traffic. Proposed system utilizes the OVSF code that generated by generation property for spreading. The proposed MC-CDMA system use different lengths of OVSF code as a spreading code according to their data rate. The groupwise processing is accomplished by code grouping in OVSF code generation tree. For the analysis of average BER performance, numerical method and computer simulation were used. We also compare the system performance with that of a single rate MC-CDMA system used orthogonal code as a spreading code.

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Analysis of CI/DS-CDMA Communication Systems using Interference of Multiple Carriers (다중반송파간섭을 이용한 CI/DS-CDMA 통신시스템 특성분석)

  • 이강봉;이정재
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • pp.129-132
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    • 2001
  • In this paper a new multiple access scheme, CI/DS-CDMA rising the interference of multiple carriers, is introduced. In this system the chip is made up of N orthogonal carriers equally spaced in frequency, where N corresponds to the number of chips in DS-CDMA. The characteristics of CI/DS-CDMA systems in a typical frequency selective fading channel environment, are analyzed. And it is shown that the frequency diversity benefits of this system result in significant performance enhancements relative to traditional DS-CDMA with RAKE receivers.

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