• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.5A
• /
• pp.593-601
• /
• 2000

In a multi-bandwidth CDMA system, the performance of multiple order selection combining rake receivers are analyzed according to the spreading bandwidth of the system and the delay spread of the Rayleigh fading channel. The results for various channel environments indicate a tradeoff between total received signal energy and multipath fading immunity. Increasing the occupied bandwidth of the system(wide-bandwidth spreading) gives better performance for small delay spread environments, while gathering more energy(narrow-bandwidth spreading)gives better performance for large delay spread environments. It is shown that the performance difference between low and high order selection combining grows larger as the spreading bandwidth increases. It is also noted that performance degrades by increasing the bandwidth above a certain point and the optimum spreading bandwidth for each channel environment decreases as the delay spread of the channel increases.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.11
• /
• pp.1124-1131
• /
• 2014

The chirp spread spectrum (CSS) technique that transmits data signal by using a chirp signal is often used for maritime wireless communication systems such as sound detection radar systems for submarines. However, maritime multipath environment could reduce the data rate of the CSS system. To tackle the problem, an overlap-based CSS transmission scheme is proposed and analyzed in this paper: Based on the approximated Gaussian Q function, we derive a closed form expression of the bit error rate (BER) of the proposed overlap-based CSS system and investigate the mathematical relationship between the number of overlaps and the intersymbol interference (ISI).

• Journal of Satellite, Information and Communications
• /
• v.2 no.2
• /
• pp.22-28
• /
• 2007

Spectrum spreading, in its general form, can be conceived as an artificial expansion of the signal bandwidth with respect to the minimum Nyquist band required to transmit the desired information. Spreading can be functional to several objectives, including resilience to interference and jammers and reduction of power spectral density levels. In the paper, signal spreading is manly used for increasing the received energy, thus satisfying link budget constraints, for terminals with low aperture antennas, without increasing the transmitted EIRP. As a matter of fact, in many mobile scenarios, even when MODCOD configurations with very low spectral efficiency (i.e. QPSK-1/4) in DVB-S2 standard, are used, the link budget cannot be closed. Spectrum spreading has been recently proposed as a technique to improve system performance without introducing additional MODCOD configurations under the constraint of fixed power spectrum density level at the transmitter side. To this aim, the design of spectrum spreading techniques shall keep into consideration requirements such as spectrum mask, physical layer performance, link budget, hardware reuse, robustness, complexity, and backward compliance with existing commercial equipments. The proposed implementation allows to fully reuse the standard DVB-S2 circuitry and is inserted as an 'inner layer' in the standard DVB-S2 chain.

• Information and Communications Magazine
• /
• v.30 no.12
• /
• pp.17-24
• /
• 2013

본고에서는 세계전파통신회의(WRC: World Radio Conference)에서 IMT로 지정된 주파수 현황과 국내 이동통신 주파수 현황 및 계획을 알아본다. 또한 현재 시점에서 데이터 트래픽 증가 추세에 비추어 2020년 Beyond4G(5G)시대를 대비한 ITU(국제전기통신연합) 해당 표준화그룹의 소요량 예측 및 통신방식별 분담 율을 분석하였다. 주파수 수요예측에 따라 WRC-15에서 IMT 추가 주파수 지정 목적으로 진행하고 있는 위성, 방송, 과학 및 고정 등 기존업무와의 공유 연구 진행현황을 주파수 대역별로 살펴본다. 또한 도시 밀집 지역에서 대용량 데이터 전송을 위한 서비스 기술이 중요해진 시점에서 Beyond4G(5G) 시대를 위해 우리나라가 주도하고 있는 6GHz 이상 대역을 IMT로 활용하기 위한 활동을 소개한다. 마지막으로 WRC가 주파수를 분배 할당하는 방식인 '주파수 대역에 서비스 방식 지정'과 달리 '서비스 방식에 의한 주파수 대역 점유(예: LTE 기술표준(PS-LTE)을 PPDR대역에서 활용) 가능성'등 LTE 기술표준의 확산 추세에 대응하기 위해 5G시대에 준비할 사항에 대한 시사점을 언급하였다.

• Aerospace Engineering and Technology
• /
• v.8 no.1
• /
• pp.179-186
• /
• 2009

This paper describes the design and implementation for spread spectrum FTS encoder and decoder. The FTS command format is defined by 64 bit encrypted packet that contains all required information relayed between the ground and the vehicle. Encryption is accomplished using the Tripple-DES encryption algorithm in block encryption form. The proposed FTS encoder and decoder is using the Convolution Encoding and Viterbi Decoding for forward error correction. The Spread Spectrum Modulation is done using a PN code, which is 256 bit gold code. The simulation result shows that the designed FTS decoder is compatible with the designed FTS encoder.

• The Magazine of the IEIE
• /
• v.15 no.1
• /
• pp.7-14
• /
• 1988

• The Magazine of the IEIE
• /
• v.18 no.2
• /
• pp.18-25
• /
• 1991

• Journal of Satellite, Information and Communications
• /
• v.4 no.2
• /
• pp.39-45
• /
• 2009

This paper proposes the specific code synchronization technique for DS-SS(Direct Sequence-Spread Spectrum transmission in the DVB-RCS +M standard. DS-SS is better than multi-carrier transmission method under nonlinear channel but imposes a long acquisition time. To improve the synchronization aspect, the robust correlation structure is introduced for acquisition and the nonlinear delay lock loop is done for tracking. MAT(Mean Acquisition Time) performances is shown to validate its superiority. In addition, code tracking and jitter performances are done when code tracking algorithm based on 2 oversamples which is not influenced by sampling clock timing offset and carrier freq. offset is used.

• The Journal of the Acoustical Society of Korea
• /
• v.31 no.7
• /
• pp.441-448
• /
• 2012

Spread spectrum provides the minimized inter-symbol interference, the low probability of intercept and the multiple access capability. This paper presents a direct sequence spread spectrum with carrier/timing recovery and equalizer which compensates the delay spread caused by multipath transmission. When the sea trials were performed in Korean East Sea, the bit error rates of QPSK and direct sequence spread spectrum are $1.46{\times}10^{-2}$ and $5.17{\times}10^{-4}$ at 3 km source-receiver range, respectively.

• Proceedings of the Korean Institute of Communication Sciences Conference
• /
• 1995.10a
• /
• pp.50-54
• /
• 1995