• 한국통신학회논문지
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• 제33권11B호
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• pp.989-997
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• 2008

The reverse acknowledgment (RA) scheme supports a fast loss recovery for negative acknowledgment (NAK)-based selective repeat automatic repeat request (SR-ARQ) by detecting a retransmission failure quickly before a retransmission timer expires. In this paper, we evaluate the performance of a NAK-based SR-ARQ protocol with the RA scheme and compare it with the conventional NAK-based SR-ARQ protocol. Particularly, we propose a simple analysis model for the transport delay of the NAK-based SR-ARQ protocol considering the traffic condition, the retransmission persistence, the timer-based retransmissions and the RA scheme's behavior. Both NAK-based SR-ARQ protocols with and without the RA scheme are implemented by using the OPNET simulator. We verified the analysis model's accuracy through the simulation results. Also, we evaluate the performance of the NAK-based SR-ARQ protocol with the RA scheme based on analysis and simulation results.

• 전자공학회논문지A
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• 제33A권6호
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• pp.11-22
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• 1996

We address an issue of channel sharing among users by using a random assignment-transmitter-based (RA-T) spread-spectrum transmission scheme which permits the contention mode only in the transmission of a header while avoiding collision during the data packet transmission. Once the header being successfully received, the data packet is ready for reception by switching to one of programmable matched-filters. But the receoption may be blocked due to limited number of matched-filters so that this effect is taken into account in our analysis. For realistic analysis, we integrate detection performance at the physical level with channel activity at the link level through a markov chain model. We also consider an acknowledgement scheme to notify whether the header is correctly detcted and the data packet can be processed continuously, which aims at reducing the interference caused unwanted data transmission. It is shown that receiver complexity can be greatly reduced by choosing a proper number of RA codes at the cost of only a little throughput degradation.

• 인터넷정보학회논문지
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• 제9권2호
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• pp.25-33
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• 2008

본 논문에서는 OFDMA 시스템에서 서로 다른 QoS를 제공하는 다양한 멀티미디어 트래픽 전송을 위해 synchronized RA 기반에서의 상향링크 패킷 전송 프로토콜을 제안한다. 임의 접근 방식에서 발생하는 충돌을 최소화하기 위해 예약 접근 채널을 트래픽 채널에 독립적으로 운영하고, 예약 채널 내에서의 잦은 충돌로 인한 손실을 최소화하기 위하여 예약 채널 접근 확률 함수를 적용하였다. 트래픽별로 제공될 수 있는 예약 채널 접근 확률을 이용하여 우선 순위가 높은 트래픽이 시스템 부하 상태에 관계없이 요구하는 최소 전송률을 보장받을 수 있는 알고리즘을 제시하였고, 성능평가를 통해 확인하였다.

• 한국통신학회논문지
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• 제31권12C호
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• pp.1129-1134
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• 2006

In this paper, we analyze the cycle structure of punctured finite-length RA-type LDPC codes and design interleavers which have good memory efficiency and avoid short cycles. Furthermore, we introduce the check-node merging scheme for punctured finite-length RA-type LDPC codes and design simple interleavers. Simulation results show that punctured finite-length RA-type LDPC codes using the proposed simple interleavers have better performance than those with random and S-random interleavers.

• 한국멀티미디어학회논문지
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• 제6권4호
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• pp.601-609
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• 2003

In wireless mobile networks, the service area is partitioned into several registration areas (RAs). Every RA is associated with a mobility database called Visitor Location Register (VLR). The VLR is used to achieve the location management of the mobile terminals. When a mobile terminal enters a new RA, the VLR stores the current location information of the mobile terminal before serving any mobile services. At that time, if the VLR is full, the registration procedure fails, and the system can not deliver services to the mobile user under the existing cellular technology To resolve this problem, we propose a VLR overflow control scheme considering mobility of mobile users to accomodate incoming users during VLR overflow. The performance of the proposed scheme is evaluated by an analytic model in terms of costs for the location search and the location update, and compared with those of the overflow control scheme proposed by Lin[1].

• 한국통신학회논문지
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• 제32권10C호
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• pp.942-949
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• 2007

In this paper, we propose a new rate-control scheme, called splining, to construct low-rate codes from high-rate codes by splitting rows of the parity-check matrices of LDPC codes, which can construct rate-compatible LDPC codes having good initial transmission performance. Good low-rate codes can be constructed by making the number of distinct check node degrees as small as possible after splitting. The proposed scheme achieves good cycle property, low decoding complexity, and fast convergence speed, especially compared to the puncturing. Especially, rate-compatible repeat accumulate-type LDPC (RA-Type LDPC) code is constructed using splitting, which covers the code rates from 1/3 to 4/5. Through simulation it is shown that this code outperforms other rate-compatible RA-Type LDPC codes for all rates and can be decoded conveniently and efficiently.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.2081-2101
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• 2016

Successive interference cancellation (SIC) is considered to be a promising technique to mitigate multi-user interference and achieve concurrent uplink transmissions, but the optimal power allocation (PA) issue for SIC users is not well addressed. In this article, we focus on the optimization of the PA ratio of users on an SIC channel and analytically obtain the optimal PA ratio with regard to the signal-to-interference-plus-noise ratio (SINR) threshold for successful demodulation and the sustainable demodulation error rate. Then, we design an efficient resource allocation (RA) scheme using the obtained optimal PA ratio. Finally, we compare the proposal with the near-optimum RA obtained by a simulated annealing search and the RA scheme with random PA. Simulation results show that our proposal achieves a performance close to the near-optimum and much higher performance than the random scheme in terms of total utility and Jain's fairness index. To demonstrate the applicability of our proposal, we also simulate the proposal in various network paradigms, including wireless local area network, body area network, and vehicular ad hoc network.

• ETRI Journal
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• 제44권4호
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• pp.543-559
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• 2022

To determine a suitable waveform for Internet of Things (IoT) transmission over low-Earth orbit (LEO) satellites, this paper reports the results of a performance comparison between chirp spread spectrum (CSS)-based LoRa and direct sequence spread spectrum (DSSS)-based Ingenu. The performance of both waveforms was measured in terms of the packet error rate, throughput, and packet loss rate, considering the Doppler effect caused by the high speed of LEO satellites and the interference among multiple terminals. Simulation results indicate that the DSSS scheme is more suitable than the CSS scheme for high-traffic IoT services because of its robustness against interference among multiple terminals. However, the CSS scheme is more suitable than the DSSS scheme for high-mobility IoT services because of its robustness against the Doppler effect. We discuss various solutions, such as the preprocessing of Doppler effect and avoidance of packet collision, to enhance the performance of the DSSS and CSS schemes. The simulation results of the proposed solution show that the enhanced DSSS scheme can be a proper waveform in IoT transmission over LEO satellites for both the high-traffic and high-mobility services.

• International Journal of Advanced Culture Technology
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• 제4권4호
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• pp.1-5
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• 2016

In this paper, we present the study on the proposed design of a real-time transmission of a video from the drone to broadcasting station (OBVan) by using F8L10D-N LoRa Module. Nowadays, LoRa technology is proved to be the mass of low cost, long range machine-to-machine connectivity. Particularly in the field of broadcasting and communication system, F8L10D-N LoRa RF Module spread spectrum technology with long transmission distance and strong penetrative ability that is double stronger than traditional FSK as well as PSK modulation scheme.

• 대한전자공학회논문지TC
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• 제43권12호
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• pp.53-60
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• 2006

WiBro의 핸드오버는 IEEE 802.16e 기반인 하드 핸드오버 방법이고 핸드오버시 주위 neighbor advertisement 메시지에서 주위 cell의 상태와 RAS(Radio Access Station) ID를 확인하여 핸드오버를 한다. 이때 주변 RAS로 HO-notification 메시지를 보낸다. 예상되는 RAS로 HO-notification 메시지를 보냄으로써 불필요한 signal이 많이 발생하게 되고 핸드오버 수행 시 packet 손실이 발생한다. 이로 인하여 서비스의 품질저하가 발생한다. 이러한 문제점을 해결하기 위하여 LPM(Last Packet Marker) 핸드오버 방법이 제안되었다. LPM 핸드오버는 핸드오버 동안 미리 data packet을 저장하기 때문에, seamless 핸드오버를 지원한다. 또한, GPS를 이용하여 PSS(Portable Subscriber Station)의 위치를 파악함으로써, 이동이 예상되는 RAS를 예측하는 방법과 선인증 과정을 이용하여 이동하고자 하는 RAS를 미리 예약하는 방법들이 제안되고 있다. LPM 핸드오버 방법과 선인증 과정을 이용한 방법은 PSS와 RAS에 부담을 주고, 많은 traffic이 발생한다. 본 논문에서는 이러한 문제점을 해결하기 위해 PSS 이동 예측 알고리즘을 제안한다. PSS가 history cache를 가지고 있고 history cache가 가지고 있는 과거의 핸드오버 data와 비교하여 target RAS를 정하고 HO-notification-RSP 메시지를 target RAS로부터 받을 때 crossover node에 target RAS를 알림으로써 serving RAS와 target RAS로 data 패킷을 bicast하고 target RAS는 buffer에 저장하였다가 핸드오버 완료시 전송함으로써 패킷 손실을 막고 불필요한 시그널링 트래픽을 막는 알고리즘을 제안하였다. 시그널링 트래픽은 history cache가 성공시 약 48%의 traffic이 감소되었고 history cache 실패시 약 기존 핸드오버 보다 약 6%의 traffic이 증가되었다.