• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.6
• /
• pp.2992-2998
• /
• 2013

The future mobile communication system can support not only voice but also multimedia applications such as data, image and video. It requires greater resources than the voice-oriented mobile system. We propose user and sub-channel priority based resource allocation for mobile multimedia services in the OFDMA systems. Our method is able to guarantee QoS continuity of realtime services and carry the maximum number of non-realtime subscriber. Simulation is focused on total throughput and blocking rate. The simulation results show that our proposed method provides a better performance than the conventional method.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.18 no.8
• /
• pp.1827-1832
• /
• 2014

In this thesis, we use one by one each of the analog switch and a high-speed DAC instead of the DAC that two or more are used in transmitting and receiving antennas multiple systems, maintaining the advantages of the existing method, reducing design costs, physical to provide a method that can reduce the data converters from MIMO system can improve the economic efficiency and the size reduction of a basis.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.8B
• /
• pp.1012-1020
• /
• 2011

In this paper a design of $\pi$/4-DQPSK baseband receiver for the exchange of digital data and e-mail between shore and ship stations and/or among ship stations in the maritime mobile service VHF channels is described. Due to the permitted relatively big frequency instability of local oscillators at the transmitter and the receiver of maritime communication system, the designed baseband receiver should have the capabilities of correct estimation and compensation of the synchronization parameters, such as symbol timing and frequency offset, from the received signal which might include relatively big frequency error. Simulated BER results show that the designed baseband receiver works less than 0.5dB loss under AWGN channel when the normalized frequency offset of the received signal is more then 20%.

• Journal of KIISE:Information Networking
• /
• v.27 no.3
• /
• pp.323-330
• /
• 2000

이동통신망의 발전으로 인해 한정적인 주파수 자원을 효율적으로 사용하여 폭증하는 가입자를 수용하기 위해 셀의 반경은 점점 작아지고 있다. 가입자에게 신규호의 실패보다 더 민감한 핸드오프호가 자주 발생함에 따라 핸드오프호 처리의 중요성이 증대되었다. 따라서, 셀마다 핸드오프호를 위한 예약 채널을 두어 어느 정도 신규호의 블록킹율의 증가를 감수하더라도, 핸드오프호의 강제종료율을 낮추는 방법이 제안되었다. 이러한 예약 채널 할당 기법에서는 예약 채널을 몇 개로 할 것인가가 중요한 문제가 된다. 왜냐하면 예약 채널 수를 과다하게 설정하면 핸드오프가 빈번하지 않은 셀에서는 채널의 낭비를 초래하고, 적게 설정하면 핸드오프가 빈번한 셀은 핸드오프 강제종료율이 높아지게 되기 때문이다. 이러한 문제를 해결하기 위해 본 논문은 신경망 모델 중 다층 퍼셉트론을 이용하여 셀에서 요구되는 최적의 예약율을 구하여 셀의 환경이 변할 때마다 적용할 수 있는 방법을 제안한다. 본 논문에서는 모의 실험을 통해 이동통신 시스템에서의 핸드오프 예약율을 주기적으로 최적화 시킴으로써 핸드오프가 자주 발생하는 셀에서는 핸드오프 강제종료율을 낮추고, 핸드오프가 빈번하지 않은 셀은 채널의 손실을 막아 시스템의 전체적인 효율이 향상됨을 보인다.

• Journal of the Institute of Convergence Signal Processing
• /
• v.6 no.2
• /
• pp.100-106
• /
• 2005

OFDM is one of the promising modulation candidates for a fourth generation broadband mobile communication system because of its robustness against inter-symbol inteference(ISI). The OFDM transmission technique has the inherent flexibility to adapt the modulation scheme on each subcarrier according to the signal-to-noise ratio(SNR). In this paper, the adaptive modulation scheme of OFDM system is proposed in broadband mobile channel. The proposed algorithm allocates initially the number of bits in each subcarrier using the threshold SNR according to the target BER and controls the total number of target bits using the well-known algorithm of Chow et al. In addition, the subcarriers of the proposed algorithm are clustered in blocks, that the signalling overhead can be reduced for the bit allocation of subcarriers. For the simulated experiments, this paper presents an evaluation for the effects of target BER, the various numbers of subcarriers in the subband block, and Doppler frequency on the performance of adaptive OFDM in broadband mobile channel.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.12A
• /
• pp.1034-1043
• /
• 2011

As an introduction of an open spectrum allocation approach with technology and service neutrality is expected as a way to solve problems of frequency shortage due to the expansion of demand for wireless multimedia communications, recently, the new management model of interferences and its standard setting are required. In this paper, as a model for this new interference management considering several candidates, Block Edge Mask(BEM) approach is chosen as the most appropriate model. And to investigate the effects of interference resulting from the standard setting of BEM, assuming the use of LTE systems in the Digital Dividend, BEM out-of-band baseline in the boundaries between digital terrestrial television (DTV) service and LTE mobile communications services which are heterogeneous systems for analysis is derived and the effect of setting guard band is analyzed.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.18 no.5
• /
• pp.69-75
• /
• 2018

Recently, Non-orthogonal multiple access (NOMA) has been focused for the next generation multiple access, which has more spectral efficiency under the limited spectrum bandwidth. Moreover, the spectrum efficiency can be improved by cognitive radio in which the unlicensed secondary users can access the spectrum that is used by the licensed primary user under the limited interference. Hence, we consider the combination of NOMA and cognitive radio, and derive the performance of the cognitive cooperative NOMA system. For the cooperation, a relay is selected among near users, and the selection combining is assumed at a far user. The outage probability of the selected relay and the far user is derived in closed-form, respectively. The provided numerical results are matched well with the Monte Carlo simulation. Numerical results showed that the performance of the relay is affected from the power allocation coefficient, the minimum outage probability is observed at 0.86 of the power allocation coefficient for far user under the given conditions. More than 15 dB of signal-to-noise ratio is required to meet the outage probability of $1{\times}10^{-13}$ for the far user with the frequency acquisition probability of 0.5 compared to that of 1. It shows that the performance of the far user is very sensitive to the acquisition probability of the cognitive relay.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.23 no.2
• /
• pp.179-192
• /
• 2019

Additional frequencies are allocated in maritime digital data exchange to alleviate overload of the VHF data link. The shipborne ad-hoc network (SANET) for this frequencies was subsequently proposed, which provides various IP-based services to ships on behalf of satellite communications. In SANET, a ship should determine its own IP address to achieve IP connectivity to the shore. Accordingly, this paper proposes a SANET configuration (SANETconf) protocol as an IP configuration protocol. SANETconf propagates non-overlapping IP addresses across the network from the shore to ships. A ship obtains its IP address by exchanging Request and Response messages with its neighbors. Therefore, SANETconf eliminates the process of DAD and managing the movement of ships. Extensive simulations were performed to verify the applicability of SANETconf. Based on results, 85% of the ships can determine their own IP address within one frame. Also, SANETconf has a high resource efficiency by using 0.024 percent of resources for IP configuration.

• The Journal of the Acoustical Society of Korea
• /
• v.41 no.2
• /
• pp.218-226
• /
• 2022

The main characteristics of the underwater acoustic channel have varying multipath and fast fading. Especially, Frequency Shift Keying (FSK) signals with multiple frequency bands caused loss of information bits allocated on the specific frequencies due to selective fading phenomenon. Therefore, this paper proposes frequency gain control algorithm based on preamble error rates. The proposed algorithm estimates optimal gain value in the range of preamble error rate with less than 10 % for specific faded frequency. By employing turbo equalized FSK signals with rate of 1/3, the experiment was conducted on a lake in Munkyeong city with distance of 300 m to 500 m. The result confirms that packets are decoded successfully by applying proposed algorithm as increasing number of iterations.

• Proceedings of the KIEE Conference
• /
• 2008.07a
• /
• pp.1401-1402
• /
• 2008

UHF 대역의 RFID는 기존의 13.56MHz의 RFID에 비해 인식 범위가 넓어 다양한 응용 서비스를 가능하게 하는 장점을 제공하는 반면, 900MHz대 이동(Cellular) 통신과 같은 이종 무선통신과의 간섭과 멀티 리더 환경에서의 리더간 간섭의 충돌이 발생하기 때문에 시스템 성능에 제약을 받는다. 더욱이 국내의 경우 모바일 RFID의 이용이 활성화되면 현재의 협소한 주파수 대역내에서 기존의 서비스인 고정형 및 이동형 RFID가 동시 운용할 경우 리더간 간섭으로 인하여 안정적인 서비스 제공이 곤란하게 된다. 따라서 본 논문에서는 국내 UHF대역 RFID 서비스 환경에서의 전파 간섭 분석 및 효율적인 채널 운용 방안을 제시 하였다. 시뮬레이션 환경의 정확도를 높이기 위하여 MATLAB과 ADS를 연동하여 본 논문의 제안된 방안을 입증하였고, 후리의 공식을 이용해 경로손실을 모델링 하였다.