• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.5 no.6
• /
• pp.1113-1132
• /
• 2011

In wireless sensor networks (WSNs), most energy saving asynchronous MAC protocols are custom tailored for unicast communications only. However, broadcast protocols are very commonly used in WSNs for a variety of functionalities, such as gathering network topology information, event monitoring and query processing. In this paper, we propose a novel low-power asynchronous broadcast MAC protocol called Alarm Broadcast (A-CAST). A-CAST employs the strobe preamble that specifies the residual waiting time for the following data transmission. Each receiver goes back to sleep upon hearing the strobe preamble for the residual time duration, to conserve energy and to wake up just before data transmission starts. We compute the energy consumption of A-CAST via rigorous mathematical analysis. The analytic results show that A-CAST outperforms B-CAST, a simple broadcast extension of the well-known B-MAC. We also implement A-CAST on sensor motes and evaluated its performance through real experiments. Our experimental results show that A-CAST reduces the energy consumption by up to 222% compared to the previously proposed protocols.

• Journal of Computing Science and Engineering
• /
• v.7 no.4
• /
• pp.231-241
• /
• 2013

Improvements in wireless sensor network (WSN) technology have resulted in a large number of applications. WSNs have been mainly used for monitoring applications, but they are also applicable to target tracking, health care, and monitoring with multimedia data. Nodes are generally deployed in environments where the exhausted batteries of sensor nodes are difficult to charge or replace. The primary goal of communication protocols in WSNs is to maximize energy efficiency in order to prolong network lifetime. In this paper, various medium access control (MAC) protocols for synchronous/asynchronous and single/multi-channel WSNs are investigated. Single-channel MAC protocols are categorized into synchronous and asynchronous approaches, and the advantages and disadvantages of each protocol are presented. The different features required in multi-channel WSNs compared to single-channel WSNs are also investigated, and surveys on multi-channel MAC protocols proposed for WSNs are provided. Then, existing broadcast schemes in such MAC protocols and efficient multi-hop broadcast protocols proposed for WSNs are provided. The limitations and challenges in many communication protocols according to this survey are pointed out, which will help future researches on the design of communication protocols for WSNs.

• The KIPS Transactions:PartD
• /
• v.12D no.1 s.97
• /
• pp.21-30
• /
• 2005

In mobile computing environments, a mobile host caches the data to use the narrow bandwidth efficiently and improve the response time. A server periodically broadcasts the update data for maintaining the cache consistency of a mobile host. However, a method for maintaining cache consistency using periodic invalidation report has a problem that defers the commit decision of a mobile transaction to guarantee its serializable execution. In this paper, we propose CCM-AD method that guarantees the serializable execution of a mobile transaction even in the case that it is executed using cached data. As CCM-AD method guarantees the serializable execution of mobile transactions by using the intersection between the data broadcast to mobile host and the data updated at server. Then the CCM-AD method can reduce the delay of commitment decision of a mobile transaction. Also our method can reduce the size of invalidation report.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2001.11b
• /
• pp.21-25
• /
• 2001

지상파 디지털방송에서는 기존 아날로그 방송에 비해 뛰어난 품질의 영상/음성 서비스가 제공될 뿐만 아니라 신문이나 잡지에서 볼 수 있었던 프로그램 정보를 TV 화면상에서 바로 받아 볼 수 있는 EPG(Electronic Program Guide) 서비스와 각종 데이터 서비스도 함께 제공된다. 이러한 EPG 정보와 함께 수신기에 필요한 각종 시스템 정보를 수신측에 전달하려면 ATSC(Advanced Television Systems Committee)의 PSIP(Program and System Information Protocol)에 따라 정보를 가공하는 장비가 필요하며 데이터 서비스를 위해서는 ATSC A/90의 송출 규격에 따라 데이터를 가공하는 장비가 필요하게 된다. 데이터서버 시스템은 PSIP의 생성과 데이터의 스케줄링을 담당하는 Data/PSIP 제어기와 데이터를 ATSC 송출 규격에 맞추어 가공하는 데이터 인젝터로 구성된다. 데이터서버 시스템은 방송 편성 정보를 담고 있는 KBS 편성 DB, 각종 콘텐츠를 관리하는 콘텐츠 DB, 그리고 실시간 독립정보 서비스를 제공하기 위한 실시간 어플리케이션 에이전트와의 인터페이스를 갖추고 있다. Data/PSIP 제어기와 데이터 인젝터에서는 편성된 PSIP 정보와 콘텐츠 데이터를 ASI(Asynchronous Serial Interface) 인터페이스를 통해서 다중화기로 전송한다. 다중화기는 PSIP 정보와 인코딩된 데이터 정보를 A/V TS(Transport Stream)와 함께 다중화하여 최종적으로 디지털 데이터 방송용 TS를 출력시킨다.

• Smart Media Journal
• /
• v.9 no.1
• /
• pp.9-15
• /
• 2020

Recently there have been increasing attempts to apply blockchains to businesses and public institutions. Blockchain is a distributed shared ledger with excellent transparency and security of data and through consensus algorithm, the same data can be shared to all nodes in order. In this paper, Modified PBFT which does not modify the PBFT consensus algorithm is proposed. MPBFT is able to tolerate Byzantine faults on a private blockchain on an asynchronous network. Even with the increase of participating nodes, the network communication cost can be effectively maintained. Modified PBFT takes into account the characteristics of an asynchronous network environment where node-to-node trust is guaranteed. In response to the client's request, PBFT performed the entire participation broadcast several times, but Modified PBFT enabled consensus and authentication through the 2 / N leader. By applying the Modified PBFT consensus algorithm, the broadcast process can be simplified to maintain the minimum number of nodes for consensus and to efficiently manage network communication costs.

• The KIPS Transactions:PartD
• /
• v.10D no.4
• /
• pp.655-660
• /
• 2003

The cache used by mobile host is an important device that recovers the weak points of limited power and bandwidth, in mobile computing environments. However, it has to stand and maintain the consistency with the server data. In this paper, we propose a 'Selective Cache Consistency Scheme'. The server allows an effective broadcasting by selecting data of high usability using 'Cache State Table' and 'Data Access Table'. Moreover, this scheme prevents the loss of data that nay occur by a long period of disconnection, by asynchronous broadcasting and transmitting those broadcast data preserved in the server. This also allows user to possess the latest data. Through experiments, we have found that the enlargement of autonomy is possible by reducing the dependence of server.