• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2006년도 하계종합학술대회
• /
• pp.265-266
• /
• 2006

In this paper, we propose an efficient rate control scheme based on the received power level to overcome a quality degradation of video under time varying channel condition caused by the movement of mobile devices. First, we statistically obtain the relation between the PLR and the received power level. With this information and the sequences of received power level, we calculate the transition probability for the Markov Channel Model. Then, with using Markov chain rule, we obtain the probability where the channel condition remains in a good state and finally find the efficient target bit rate by multiplying it by the offered bandwidth when the network access has begun. We use TMN8 to adjust the bit rate to our proposed outcome. Experimental results show that the proposed method can efficiently enhance the video quality and provide better PSNR performance than with only using TMN8 rate control method.

• 한국통신학회논문지
• /
• 제31권4B호
• /
• pp.270-277
• /
• 2006

AMC(Adaptive Modulation and Coding)를 사용하는 무선 네트워크에서는 사용자의 이동 및 페이딩 환경에 따라 변화하는 채널특성으로 인하여 연결중인 서비스의 modulation 방식 또한 동적으로 변화 할 수 있다. 이러한 변화는 시스템 용량에 영향을 미치며 연결중인 서비스가 단절될 수 도 있다. 본 논문에서는 보장성 서비스에 초점을 맞추어 장기 AMC에 근거한 수락제어(CAC: Call Admission Control) 문제를 접근하고자 한다. CAC 과정에 있어 신규 호, 핸드오프 호, modulation 방식 변경 호와 같은 3가지 종류에 대하여 고려하였다. 또한 가드채널 기법을 고려하였으며 핸드오프 호와 마찬가지로 modulation 방식 변경 호에 대하여 가드 채널을 사용할 수 있게 하였다. CAC 방식에 대하여 Markov 모델을 제시하고 분석과 실험 결과로 호 단절 확률을 얻을 수 있었다. 결론적으로 이와 같은 분석 모델을 이용하여 무선 AMC 네트워크에서 호 단절을 감소시키기 위한 적절한 가드채널 임계치를 결정하는데 도움이 될 것이다.

• 전자공학회논문지
• /
• 제51권6호
• /
• pp.43-49
• /
• 2014

본 논문에서는 4개의 전송 안테나 시스템에서 좌표축 인터리빙된 직교 신호로 디자인(Coordinate interleaved orthogonal design: CIOD)된 시 공간 블록 부호(Space time block code: STBC)가 시간 선택적 페이딩 채널인 1차 Markov 채널을 통과하였을 때에 성능 분석을 다룬다. 채널이 준 정지 페이딩 채널(Quasi-static fading channel)일 경우 STBC-CIOD는 최대 전송률과 최대 다이버시티(Full rate full diversity: FRFD)를 만족하고, 단일 심볼 복호가 가능한(single symbol decodable: SSD) 코드이나, 시간 선택적 페이딩 환경에서는 신호간의 간섭이 생기므로 FRFD을 만족시키더라도 단일 심볼 복호를 수행하였을 때 간섭에 의한 성능 열화가 생길 것이다. 심볼 오류율(Symbol error rate: SER)의 Union bound를 신호 쌍 오류 확률(pairwise error probability)을 유도하여 구한다. 그리고 4-ary PSK 신호에 대한 모의실험을 통하여 유도된 심볼 오류율을 구하고 이를 수식으로 구한 심볼 오류율의 union bound 와 비교한다.

• Journal of Communications and Networks
• /
• 제15권2호
• /
• pp.222-227
• /
• 2013

This paper presents an analytical framework for dynamic spectrum allocation in cognitive radio networks. We propose a distributed queuing based Markovian model each for single channel and multiple channels access for a contending user. Knowledge about spectrum mobility is one of the most challenging problems in both these setups. To solve this, we consider probabilistic channel availability in case of licensed channel detection for single channel allocation, while variable data rates are considered using channel aggregation technique in the multiple channel access model. These models are designed for a centralized architecture to enable dynamic spectrum allocation and are compared on the basis of access latency and service duration.

• 한국전자파학회논문지
• /
• 제25권2호
• /
• pp.223-234
• /
• 2014

본 논문은 위성통신 시스템에서 OTM(On-The-Move: 이동형) 위성단말이 운용되는 지역의 채널 특성을 분석한 결과를 다룬다. 무궁화 5호 위성의 20 GHz 대역 수신 신호를 이용하여 대전~대천까지 실 주행시험을 수행하였고, 측정 결과를 고속도로 환경과 국도 환경 두 부분으로 구분하여 통계적 분석을 수행하였다. 통계적 분석에는 확률밀도 함수와 Markov 모델을 이용하여 위성 채널의 특성을 분석하였고, 더불어 국도 환경과 고속도로 환경에서 수신 전력의 임계값 설정에 따른 ACD(Average Connection Duration), AFD(Average Fade Duration), LCR(Level Crossing Rate)을 각각 제시하고, 서로 비교하였다.

• ETRI Journal
• /
• 제40권2호
• /
• pp.237-245
• /
• 2018

The Distributed Modulated Wideband Converter (DMWC) is a networking system developed from the Modulated Wideband Converter, which converts all sampling channels into sensing nodes with number variables to implement signal undersampling. When the number of sparse subbands changes, the number of nodes can be adjusted flexibly to improve the reconstruction rate. Owing to the different attenuations of distributed nodes in different locations, it is worthwhile to find out how to select the optimal sensing node as the sampling channel. This paper proposes the spectrum sensing of DMWC based on a Markov random field (MRF) to select the ideal node, which is compared to the image edge segmentation. The attenuation of the candidate nodes is estimated based on the attenuation of the neighboring nodes that have participated in the DMWC system. Theoretical analysis and numerical simulations show that neighboring attenuation plays an important role in determining the node selection, and selecting the node using MRF can avoid serious transmission attenuation. Furthermore, DMWC can greatly improve recovery performance by using a Markov random field compared with random selection.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제11권9호
• /
• pp.4180-4196
• /
• 2017

In this paper, we analyze average capacity of an amplify-and-forward (AF) cooperative communication system model in multi-relay multiuser networks. In contrast to conventional cooperative networks, relays in the considered network have no embedded energy supply. They need to rely on the energy harvested from the signals broadcasted by the source for their cooperative information transmission. Based on this structure, a two-step selection scheme is proposed considering both channel state information (CSI) and battery status of relays. Assuming each relay has infinite or finite energy storage for accumulating the energy, we use the infinite or finite Markov chain to capture the evolution of relay batteries and certain simplified assumptions to reduce computational complexity of the Markov chain analysis. The approximate closed-form expressions for the average capacity of the proposed scheme are derived. All theoretical results are validated by numerical simulations. The impacts of the system parameters, such as relay or user number, energy harvesting threshold and battery size, on the capacity performance are extensively investigated. Results show that although the performance of our scheme is inferior to the optimal joint selection scheme, it is still a practical scheme because its complexity is much lower than that of the optimal scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권4호
• /
• pp.989-1005
• /
• 2012

In this paper, throughput of IEEE 802.11 carrier-sense multiple access (CSMA) with collision-avoidance (CA) protocols in non-saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the utilization of IEEE 802.11 analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the choice of the best probability detection while maintaining probability of false alarm is less than 0.5 is a key factor for maximizing utilization of IEEE 802.11.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2004년도 심포지엄 논문집 정보 및 제어부문
• /
• pp.65-67
• /
• 2004

Change of state of Channel between two wireless terminals which is caused by noise and multiple environmental conditions for happens frequently from the Wireles Network. So, When it is like that planning a wireless network protocol or performance analysis, it follows to change of state of time-varying channel and packet the analysis against a transmission efficiency is necessary. In this paper, analyzes transmission time of a packet and a packet in a time-varying and packet based Wireless Network. To reflecte the feature of the time-varying channel, we use a Signal Flow Graph model. From the model the mean of transmission time and the mean of queue length of the packet are analyzed in terms of the packet distribution function, the packet transmission service time, and the PER of the time-varying channel.

• 한국통신학회논문지
• /
• 제34권5A호
• /
• pp.355-362
• /
• 2009

In real-time communication services, delay constraints are among the most important QoS (Quality of Service) factors. In particular, it is difficult to guarantee the delay requirement over wireless channels, since they exhibit dynamic time-varying behavior and even severe burst-errors during periods of deep fading. Channel throughput may be increased, but at the cost of the additional delays when ARQ (Automatic Repeat Request) schemes are used. For real-time communication services, it is very essential to predict data deliverability. This paper derives the delay distribution and the successful delivery probability within a given delay budget using a priori channel model and a posteriori information from the perspective of queueing theory. The Gilbert-Elliot burst-noise channel is employed as an a Priori channel model, where a two-state Markov-modulated Bernoulli process $(MMBP_2)$ is used. for a posteriori information, the channel parameters, the queue-length and the initial channel state are assumed to be given. The numerical derivation is verified and analyzed via Monte Carlo simulations. This numerical derivation is then applied to a rate control scheme for real-time video transmission, where an optimal encoding rate is determined based on the future channel capacity and the distortion of the reconstructed pictures.