• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제7권8호
• /
• pp.1955-1971
• /
• 2013

This paper studies relay selection and power allocation for amplify-and-forward (AF) based two-way relay networks (TWRN) with asymmetric traffic requirements (ATR). A joint relay selection and power allocation algorithm is proposed to decrease the outage probability of TWRN with ATR. In this algorithm, two sources exchange information with the help of the relay during two time slots. We first calculate the optimal power allocation parameters based on instantaneous channel state information (CSI), and then derive a tight lower bound of outage probability. Furthermore, we propose a simplified relay selection criterion, which can be easily calculated as harmonic mean of instantaneous channel gains, according to the outage probability expressions. Simulation results verified the theoretical analyses we presented. It is shown that the outage probability of our algorithm improves 3-4dB comparing with that of other existing algorithms, and the lower bound is tight comparing with actual value for the entire signal-to-noise ratio (SNR) region.

• 한국경영과학회:학술대회논문집
• /
• 대한산업공학회/한국경영과학회 2002년도 춘계공동학술대회
• /
• pp.418-425
• /
• 2002

Bluetooth is an emerging technology expected to provide users with short range, low cost, pico-cellular wireless connectivity. The access to the medium for Bluetooth is based on a Master driven Time Division Duplexing (TDD) scheme. A slave transmits packets in the reverse slot only after the master polls the slave (or transmits a packet to the slave) in a forward slot. The master transmits packets to a slave in even slots while the slave transmits packets to the master in an odd slot. The way in which the master schedules packets transmission to slaves or polls them determines system performance. In this paper. we propose a traffic adaptive MAC scheduling scheme for Bluetooth. The proposed scheme adopts the ISAR (Intelligent Segmentation and Reassembly) policy, which adjusts the packet size to the traffic patterns, to adapt the polling frequency to the traffic conditions. Also for achieving fairness among master-slave connections our scheme includes a priority policy assinging prioritised service tlimes to each connection. By considering a scenario where a Bluetooth master is used as wireless access point to the Internet, we show that our scheme improve the system throughput and average queue delay with regard to a naive Round Robin (RR) scheme.

• ETRI Journal
• /
• 제37권6호
• /
• pp.1242-1250
• /
• 2015

It is very important to provide a parameterized quality of service (QoS) using traffic specification (TSPEC), such as mean data rate, maximum burst size, and peak data rate, when packets from the application layer need to be transmitted with guaranteed services in a high-rate wireless personal area network (HR-WPAN). As medium resources are limited, the optimal medium time required for each device needs to be estimated to share the resources efficiently among devices. This paper proposes a variable-service interval-based resource allocation algorithm to efficiently make a reservation of medium resources based on a parameterized QoS. In other words, the proposed algorithm calculates the number of medium access slots (MASs) based on TSPEC, local resources, and local conditions and determines suitable locations for the MASs within a superframe to accommodate more devices. The simulation results show that the proposed algorithm can accommodate more devices and has greater than 10% resource allocation efficiency in an HR-WPAN compared to existing schemes.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2001년도 추계종합학술대회
• /
• pp.117-120
• /
• 2001

본 논문에서는 무선 ATM망에서 비실시간성의 버스트 트래픽을 서비스하기 위한 경쟁기반 예약형 MAC 프로토콜을 제안하였다. 제안한 기법에서는 예약요청 패킷의 충돌을 줄이기 위하여 예약요청 패킷 전송을 위한 RAS 미니슬롯의 수와 예약요청 부하를 기반으로 기지국 스케줄러가 전송 확률을 계산하고, 이를 하향 제어채널을 통하여 단말기들에게 방송한다. 전송할 트래픽 버스트가 있는 단말기들은 임의의 RAS 미니슬롯을 선택하여 기지국으로부터 수신한 전송 확률로 단말기 버퍼에 있는 패킷 수를 포함하는 예약요청 패킷을 전송한다. 한편, 기지국에서는 성공적으로 수신한 단말기의 버퍼 상태정보를 기반으로 슬롯을 할당한다.

• Journal of Communications and Networks
• /
• 제11권4호
• /
• pp.375-383
• /
• 2009

The WiMedia alliance has specified a distributed medium access control (WiMedia MAC) protocol based on ultra wideband (UWB) for high data rate WPANs (HR-WPANs). The merits of WiMedia MAC such as distributed nature and high data rate make it a favorite candidate in HR-WPAN. Although QoS parameters such as the range of service rates are provided to a traffic stream, the WiMedia MAC is not able to use the QoS parameters and to determine or adjust a service rate using the QoS parameters for the traffic stream. In this paper, we propose a fair and adaptive resource allocation method that allocates time slots to isochronous streams according to QoS parameters and the current traffic load condition in a fully distributed manner. Although the traffic load condition changes, each device independently recognizes the changes and calculates fair and maximum allowable service rates for traffic streams. From the numerical and simulation results, it is proved that the proposed method achieves high capacity of traffic streams and fair QoS provisioning under various traffic load condition.

• 항공우주기술
• /
• 제10권2호
• /
• pp.65-73
• /
• 2011

위성의 발사 후 정지궤도위성을 운용궤도에 진입시키기 위해서는 전이궤도 원지점 (Apogee)에서 위성에 장착된 액체원지점엔진을 발사하여 근지점(Perigee) 고도를 정지궤도 고도에 이르도록 높여준다. 이 과정에서 궤도결정 결과를 피드백하여 정밀하게 궤도조정을 수행하고 종료 후 원하는 경도에 안착시키기 위해 상황에 따라 엔진발사를 3회에서 4회로 나누어 수행하게 된다. 본 논문에서는 먼저 임펄스 형태의 기동을 가정하여 각 액체원지점 엔진 발사시점과 ${\Delta}V$ 벡터를 결정하기 위한 알고리즘을 수립하였고, 추가적으로 연속점화에 따른 오차를 보정하기 위한 기법을 제안하였다. 또한 시뮬레이션을 통하여 제안된 기법의 타당성을 분석하였다.

• 한국통신학회논문지
• /
• 제31권2B호
• /
• pp.129-136
• /
• 2006

이 논문에서는 DMB에서의 주문형 데이터 방송을 위한 새로운 데이터 캐러셀 스케줄링 알고리듬을 제안한다. 클라이언트로부터 리궤스트를 받으면 서버는 그 리궤스트에 대한 통계치를 이용하여 아이템을 두 집합으로 나눈다. hot 아이템을 한 캐러셀 내에서 여러 번 반복하여 방송하도록 하여 그 아이템에 대한 클라이언트의 대기시간을 줄이도록 하였으며, hot 아이템의 방송회수에 상한선을 두어 cold 아이템의 방송 기회를 늘이도록 하여 클라이언트의 리퀘스트에 대한 응답 성공률을 높이도록 하였다. 모의실험을 통해 캐러셀 기반의 다른 알고리듬과 비교하였을 때 원하는 결과를 얻어낼 수 있었다.

• 한국정보통신학회논문지
• /
• 제3권1호
• /
• pp.155-162
• /
• 1999

본 논문에서는 혼합형 TDMA/CDMA 시스템을 이용한 광대역 무선망에서 음성과 데이타 트래픽을 통합 서비스하기 위한 R_ALOHA_CDMA 프로토콜을 제안하고, 이에 대한 성능을 분석했다. 역방향 논리 채널은 타임 슬롯과 각 슬롯별 확산 코드 채널에 의해서 제공된다. 본 논문에서 제안한 프로토콜은 R_ALOHA 기법을 적용하여, 음성 트래픽은 슬롯과 확산 코드 채널 예약 방식을 사용하는 반면, 데이타 트래픽은 매 패킷이 발생할 때마다 임의의 빈 채널을 선택해서 전송하는 S_CDMA_ALOHA 방식을 사용한다. 성능 분석의 결과, 협대역 TDMA 시스템의 R_ALOHA 기법과는 달리 확산 코드에 의하여 다중 채널이 제공되므로 동시에 서비스할 수 있는 음성 단말기가 상당히 증가함을 알 수 있었다. 또한 충돌한 음성 패킷의 빈번한 재전송에도 불구하고 비교적 안정적인 성능을 나타냈다.

• 한국통신학회논문지
• /
• 제33권8A호
• /
• pp.805-814
• /
• 2008

Both EPCglobal Generation-2 (Gen2) for passive RFID systems and Intelleflex for semi-passive RFID systems use probabilistic slotted ALOHA with Q algorithm, which is a kind of dynamic framed slotted ALOHA (DFSA), as the tag anti-collision algorithm. A better tag anti-collision algorithm can reduce collisions so as to increase the efficiency of tag identification. In this paper, we introduce and analyze the estimation methods of the number of slots and tags for DFSA. To increase the efficiency of tag identification, we propose two new tag anti-collision algorithms, which are Chebyshev's inequality (CHI) algorithm and hybrid Q algorithm, and compare them with the conventional Q algorithm and adaptive adjustable framed Q (AAFQ) algorithm, which is mentioned in Part I. The simulation results show that AAFQ performs the best in Gen2 scenario. However, in Intelleflex scenario the proposed hybrid Q algorithm is the best. That is, hybrid Q provides the minimum identification time, shows the more consistent collision ratio, and maximizes throughput and system efficiency in Intelleflex scenario.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제18권8호
• /
• pp.2281-2297
• /
• 2024

Employing multiple drones as a swarm to complete missions can sharply improve the working efficiency and expand the scope of investigation. Remote UAV swarms utilize satellites as relays to forward investigation information. The increasing amount of data demands higher transmission rate and complex field network coding (CFNC) is deemed as an effective solution for data return. CFNC applied to UAV swarms enhances transmission efficiency by occupying only two time slots, which is less than other network coding schemes. However, conventional CFNC applied to UAVs is combined with constant coding and modulation scheme and results in a waste of spectrum resource when the channel conditions are better. In order to avoid the waste of power resources of the relay satellite and further improve spectral efficiency, a CFNC transmission scheme with MPSK modulation is proposed in this paper. For the proposed scheme, the satellite relay no longer directly forwards information, but transmits information after processing according to the current channel state. The proposed transmission scheme not only maintains throughput advantage of CFNC, but also enhances spectral efficiency, which obtains higher throughput performance. The symbol error probability (SEP) and throughput results corroborated by Monte Carlo simulation show that the proposed transmission scheme improves spectral efficiency in multiples compared to the conventional CFNC schemes. In addition, the proposed transmission scheme enhances the throughput performance for different topology structures while keeping SEP below a certain value.