• 대한전자공학회논문지TC
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• 제48권11호
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• pp.60-66
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• 2011

LTE는 다양한 서비스 클래스를 가지고 QoS를 지원한다. 각각의 트래픽 클래스에 대해 BER 요구사항이 크게 다르다. 이는 다양한 클래스의 트래픽에 대해 전송 전력이 상이함을 의미한다. 본 논문에서는 우선순위와 목표 BER을 고려하여 서비스 클래스를 지원하는 새로운 LTE를 위한 스케줄러를 제안한다. CQI와 QCI에 의해 각 사용자당 크래픽 클래스에 대한 목표 BER로 부터 최소 전송 전력이 할당된다. 따라서 사용자의 과거 사용 전송율과 트래픽의 우선순위와 같은 다른 정보를 이용하여 점유 채널의 확률이 결정된다. 서비스 클래스 스케줄링의 시뮬레이션 결과는 최대전송율 및 비례균일과 비교될 것이다. 실험결과는 서비스 클래스 기반의 스케줄링이 전체 시스템 수율을 개선할 수 있음을 보여주고 있다.

• Journal of Communications and Networks
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• 제16권4호
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• pp.397-406
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• 2014

Radio frequency (RF) jamming is a denial of service attack targeted at wireless networks. In resource-hungry scenarios with constant traffic demand, jamming can create connectivity problems and seriously affect communication. Therefore, the vulnerabilities of wireless networks must be studied. In this study, we investigate a particular type of RF jamming that exploits the semantics of physical (PHY) and medium access control (MAC) layer protocols. This can be extended to any wireless communication network whose protocol characteristics and operating frequencies are known to the attacker. We propose two efficient jamming techniques: A low-data-rate random jamming and a shot-noise based protocol-aware RF jamming. Both techniques use shot-noise pulses to disrupt ongoing transmission ensuring they are energy efficient, and they significantly reduce the detection probability of the jammer. Further, we derived the tight upper bound on the duration and the number of shot-noise pulses for Wi-Fi, GSM, and WiMax networks. The proposed model takes consider the channel access mechanism employed at the MAC layer, data transmission rate, PHY/MAC layer modulation and channel coding schemes. Moreover, we analyze the effect of different packet sizes on the proposed jamming methodologies. The proposed jamming attack models have been experimentally evaluated for 802.11b networks on an actual testbed environment by transmitting data packets of varying sizes. The achieved results clearly demonstrate a considerable increase in the overall jamming efficiency of the proposed protocol-aware jammer in terms of packet delivery ratio, energy expenditure and detection probabilities over contemporary jamming methods provided in the literature.

• 한국통신학회논문지
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• 제25권8A호
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• pp.1177-1185
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• 2000

본 논문에서는 긴 전파 지연과 높은 에러율을 지닌 위성링크에 TCP를 사용하는 경우 나타나는 문제점을 도출하고 그에 대한 성능향상방안으로 ENA(Error Notification Ack) 알고리즘을 제안했다. TCP는 에러에 의한 세그먼트 손실과 Network Congestion에 의한 손실을 구분하지 못하고 두 경우 모두 Network Congestion 으로 판단한 후 Slow Start나 Congestion Aboidance 알고리즘을 적용시킨다 위성링크에서는 에러에 의한 세그먼트 손실이 자주 발생하는데 이손실을 Network Congestion에 의한 손실로 받아들여 매번 Congestion Control 알고리즘을 적용시킨다 그로인해 전송률을 줄어들고 성능은 급격히 떨어진다. 본 논문에서는 에러에 의한 손실과 Congestion 의한 손실을 구분해 주는 ENA 알고리즘을 제안하고 구현 방법 또한 제시하였다 그리고 ENA 알고리즘을 Tahoe, Reno. Sack TCP에 적용하여 성능의 변화를 비교 분석했다 그 결과 에러율이 높을수록 성능이 더 향상됨을 알수 있었다.

• 한국항행학회논문지
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• 제11권4호
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• pp.408-414
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• 2007

마이크로 센서 소자와 무선 네트워크 기술의 발전으로 인하여 에너지 효율적이고 저가격의 무선 센서 노드의 개발이 가능하게 되었다. 본 논문에서는 낮은 전력 소모와 우수한 BER(Bit Error Rate) 성능을 위해 FEC 기술을 적용한 FSK 모뎀 기반의 멀티 홉 무선 센서 네트워크를 제안한다. FEC 기술은 부호화 및 복호화를 위한 추가의 전력을 필요로 하며 센서 노드안에 구현하기 위한 복잡한 기능을 필요로 한다. 성능 평가를 위하여 본 논문에서는 채널 파라미터, 홉의 수, 전송 비트의 수, 노드사이의 거리를 함수로 하여 수신된 비트 및 부호어의 확률을 계산하였다.

• 디지털산업정보학회논문지
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• 제5권2호
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• pp.141-156
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• 2009

As the TCP is the protocol designed for the wired network that packet loss probability is very low, because TCP transmitter takes it for granted that the packet loss by the wireless network characteristics is occurred by the network congestion and lowers the transmitter's transmission rate, the performance is degraded. The Snoop Protocol was designed for the wired network by putting the Snoop agent module on the BS(Base Station) that connect the wire network to the wireless network to complement the TCP problem. The Snoop agent cash the packets being transferred to the wireless terminal and recover the loss by resending locally for the error occurred in the wireless link. The Snoop agent blocks the unnecessary congestion control by preventing the dupack (duplicate acknowledgement)for the retransmitted packet from sending to the sender and hiding the loss in the wireless link from the sender. We evaluated the performance in the wired/wireless network and in various TCP versions using the TCP designed for the wired network and the Snoop designed for the wireless network and evaluated the performance of the wired/wireless hybrid network in the wireless link environment that the continuous packet loss occur.

• Journal of information and communication convergence engineering
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• 제9권5호
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• pp.530-538
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• 2011

Performance of TCP can be severely degraded in Mobile IP-based wireless networks where packet losses not related to network congestion occur frequently during inter-subnetwork handoffs by user mobility. To solve such a problem in the networks using Mobile IP, the packet buffering method at a base station(BS) recovers those packets dropped during handoff by forwarding the buffered packets at the old BS to the mobile users. But, when the mobile user moves to a congested BS in a new foreign subnetwork, those buffered packets forwarded by the old BS are dropped and TCP transmission performance of a mobile user degrades severely. In this paper, we propose a Modified BLUE(MBLUE) buffer required at a BS to increase TCP throughput in Mobile IP-based networks. When a queue length exceed a threshold and congestion grows, MBLUE increases its packet drop probability. But, when a TCP connection is added at new BS by a handoff, the old BS marks the buffered packets. And new BS receives the marked packets without dropping. Simulation results show that MBLUE buffer reduces congestion during handoffs and increases TCP throughputs.

• 한국멀티미디어학회논문지
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• 제7권3호
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• pp.340-348
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• 2004

본 논문에서는 단일의 전송매체를 여러 스테이션이 사용하기 위한 효율적인 매체접속제어 방식을 제안하였다. 매체접속제어 방식은 크게 예약방식과 충돌 허용방식으로 구분되며 네트워크 환경에 따라 각각의 방식이 효율성에서 장점을 지닌다. 제안된 매체접속제어 방식은 충돌 허용방식인 CSMA/CD를 기본으로 하며 충돌현상을 지연하여 채널을 예약하는 기능을 부가하였다. 따라서 충돌이 발생하면 예약과정을 거쳐 채널에는 예약에 성공한 스테이션만 경쟁에 참여하게 되어 매체접속 확률을 높이게 된다. 제안된 프로토콜은 충돌의 횟수가 감소하여 전체적으로 채널의 활용도가 향상되는 것을 시뮬레이션으로 확인하였다.

• Journal of Communications and Networks
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• 제12권2호
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• pp.174-180
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• 2010

Automatic Repeat reQuest (ARQ) is a very effective technique against transmission error at the medium access control (MAC) layer. An erroneous MAC protocol data unit can be typically retransmitted within a given limit. In order to improve the IP-level performance, which directly affects the user-perceived quality-of-service (QoS), we propose a new truncated ARQ strategy, called MAC service data unit-based ARQ (S-ARQ), where the finite number of opportunities for retransmissions are shared by multiple fragments out of an IP datagram. We describe how SARQ can be implemented in a practical system, and then propose another variant of S-ARQ employing a functionality called early detection of failure. Basically, we evaluate the performance of SARQ in two different manners. First, assuming i.i.d. error process, we analyze both the probability of the delivery failure and the average delay of IP datagram. Then, we assess the performance of S-ARQ via simulation over a 2-state Markov channel.

• Journal of information and communication convergence engineering
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• 제2권1호
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• pp.9-14
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• 2004

In this paper the modeling of the RLP layer in CDMA2000 is presented, which uses the NAK based ARQ scheme for Random Error Channels. The RLP performs a partial link recovery through limited number of RLP frame transmission in case of frame error. In case when the RLP fails due to excessive frame error, the control is passed on to the higher (TCP) layer. The TCP layer provides the complete end-to-end recovery. Thus the reliable performance at the TCP/RLP is essential to maintain the required Quality of Service in the DS-CDMA wireless links. The modeling is done for the performance analysis of the system in terms of the throughput and the mean extra delays, which are calculated analytically and are compared with the results generated by the simulations. This paper studies the effect of the random errors over different types of RLP frame formats and also the performance of the NAK based ARQ mechanism used under these conditions. The simulation provides with the over all characteristics of the throughput and the mean extra delay in terms of realistic environment parameters like Eb/No and probability of packet error (PE), based on the channel conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4957-4976
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• 2016

This paper investigates the error performance of the amplify-and-forward (AF) relaying systems in the context of full-duplex (FD) communication. In addition to the inherent self-interference (SI) due to simultaneous transmission and reception, coexistent FD terminals may cause crosstalk. In this paper, we utilize the information exchange via the crosstalk channel to construct a particular distributed space-time code (DSTC). The residual SI is also considered. Closed-form pairwise error probability (PEP) is first derived. Then we obtain the upper bound of PEP in high transmit power region to provide more insights of diversity and coding gain. The proposed DSTC scheme can attain full cooperative diversity if the variance of SI is not a function of the transmit power. The coding gain can be improved by lengthening the frame and proper power control. Feasibility and efficiency of the proposed DSTC are verified in numerical simulations.