• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.1
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• pp.241-269
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• 2012

Wireless networks composed of multimedia-enabled resource-constrained sensor nodes have enriched a large set of monitoring sensing applications. In such communication scenario, however, new challenges in data transmission and energy-efficiency have arisen due to the stringent requirements of those sensor networks. Generally, congested nodes may deplete the energy of the active congested paths toward the sink and incur in undesired communication delay and packet dropping, while bit errors during transmission may negatively impact the end-to-end quality of the received data. Many approaches have been proposed to face congestion and provide reliable communications in wireless sensor networks, usually employing some transport protocol that address one or both of these issues. Nevertheless, due to the unique characteristics of multimedia-based wireless sensor networks, notably minimum bandwidth demand, bounded delay and reduced energy consumption requirement, communication protocols from traditional scalar wireless sensor networks are not suitable for multimedia sensor networks. In the last decade, such requirements have fostered research in adapting existing protocols or proposing new protocols from scratch. We survey the state of the art of transport protocols for wireless multimedia sensor networks, addressing the recent developments and proposed strategies for congestion control and loss recovery. Future research directions are also discussed, outlining the remaining challenges and promising investigation areas.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12B
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• pp.1259-1266
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• 2010

M2M communication is considered as a key enabling technology to monitor the status of objects, vehicles, humans through auto-configuring wireless networks. In M2M network, there are active research activities to enhance the reliability on data while being collected from wireless sensor network. The reliability issue becomes more important as wireless sensor networks carry multimedia data, which is delay sensitive. The interference caused by the adjacent neighbor sensor nodes is a major factor in network performance degradation, which becomes more severe in multi-hop routing environment. In this paper, we propose inerfernce-free multipath routing protocol for M2M wireless network for enhancement of packet delay performance. The simulation results show that the proposed routing algorithm outperforms the existing routing protocols in terms of packet delay and throughput.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.1454-1460
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• 2006

This paper assesses communication performance using a roaming simulator when roaming occurs between onboard and ground wireless communication devices for communication based train control system (CBTC). Generally, CBTC is defined as the system regularly collecting location and speed data from each train, transmitting distance information to a train, and optimizing train speed according to train performance. When a train is moving, roaming is also performed to continuously transmit and receive train control information between the ground controller and the train. To operate CBTC, packet loss rate should be less than 1%, roaming time less than 100ms during roaming. We developed a roaming simulator to check communication performance before installing ground and onboard equipments on actual wireless sections. The roaming simulator to be introduced in this paper is for roaming simulation before conducting CBTC field test, which is the project to develop Urban Rail Signaling System Standards, being conducted in KRRI. The simulation consists of one onboard wireless communication device and three ground wireless communication devices, and the roaming simulator estimate packet loss rate occurring during roaming process of the two devices. Therefore, if you use the roaming simulator before the field test, you can predict various problems to occur in actual environment and reduce time, cost and people necessary to resolve these problems.

• Journal of information and communication convergence engineering
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• v.5 no.2
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• pp.93-97
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• 2007

In this paper, centralized access control and slot allocation algorithm is proposed for wireless networks. The proposed algorithm is characterized by the contention-based reservation. In order to reduce the collision probability of reservation request, the base station calculates and broadcasts the transmission probability of reservation requests, and the wireless terminal transmits its reservation request with the received transmission probability. The scheduler allocates the uplink data slots based on the successful reservation requests. Simulation results show that the proposed algorithms can provide high channel utilization, and furthermore, maintains constant delay performance in the heavy traffic environment.

• Journal of information and communication convergence engineering
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• v.8 no.6
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• pp.660-664
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• 2010

This paper proposes a backoff control scheme for guaranteeing fair packet transmissions in TDMA wireless networks. In order to maximize the system performance, the number of packets transmitted in a frame should be kept at a proper level. In the proposed scheme, the base station calculates the packet transmission probability according to the offered loads and then broadcasts to all the mobile stations. Mobile stations attempt to transmit a packet with the received probability. Simulation results show that the proposed scheme can offer better system throughput and delay performance than the conventional one regardless of the offered loads.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.274-277
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• 2008

Rekeying is the process of changing the encryption key of an ongoing communication. The main objective is to limit the amount of data encrypted with the same key. The IEEE 802.11 standard defines the Wired Equivalent Privacy, or WEP, encapsulation of 802.11 data frames. MAC at sender encrypts the payload (frame body and CRC) of each 802.11 frame before transmission using RC4 stream cipher. MAC at receiver decrypts and passes data to higher level protocol. WEP uses symmetric key stream cipher (RC4) where same key will be used for data encryption and decryption at the sender and the receiver. WEP is not promising with the advancement of the wireless technology existing today. We propose to use the existing information to define the security attributes. This will eliminate the steps that regenerated keys have to be sent to each other over certain period. The rekeying scheme is according to the number of bytes transmitted. Therefore, even the attacker has recorded the packets, it will be insufficient information and time for the attacker to launch the attacks as the key is not deterministic. We develop a packet simulation software for packet transmission and simulate our propose scheme. From the simulation, our propose scheme will overcome the weak WEP key attack and provide an alternative solution to wireless packet transmission. Besides that, our solution appears to be a software approach where only driver updates are needed for the wireless client and server.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.2 no.1 s.2
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• pp.93-100
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• 2003

In this farer, An ADSRC(Advanced Dedicated Short Range Communication) packet communication system developed by ETRI is introduced. The ADSRC system has been developed to provide high-speed, short-range wireless racket communication in roadside environment for mobile office services. The requirements of the ADSRC system for mobile office services and the system design specification to meet them with regard to mobile of nce environment are discussed. The ADSRC packet communication systems consist of the MAC(Medium Access Control) Processor block the OFDM() modem block and the RF block. The MAC processor block handles medium access control. The OFDM modem transmits data packets at up to 24Mbps adaptively and recovers the data from RF block. The ADSRC packet communication system architecture is described.

• Journal of Internet Computing and Services
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• v.4 no.5
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• pp.61-68
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• 2003

In this paper, we propose a wireless MAC protocol named APRMA, which is capable of supporting the ABR type data service and Maximizing channel utilization. Data terminals with random data packets are not provided slot reservation with PRMA protocol. That is, slot reservation is applicable to the time constraint voice packet exclusively. But the reservation scheme have to be performed for loss sensitive data packet, and contended their quality of service, Therefore, in wireless MAC, reservation technique has to be used for both voice and data services. So the terminal which wants to request for ABR type service, is allocated a minimum bandwidth from system for the first time, If the system have some extra available bandwidth, ABR terminals would acquire additional bandwidth slot by slot, As a result, APRMA protocol can support the data service with loss sensitivity and maintain their channel utilization high.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.65-72
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• 2004

A basic access method using for IEEE 802.11a wireless LANs is the DCF method that is based on the CSMA/CA. But, Since IEEE 802.11 MAC layer uses original backoff algorithm (Exponential backoff method), when collision occurs, the size of contention windows increases the double size. Hence, packet transmission delay time increases and efficiency is decreased by original backoff scheme. In this paper, we have analyzed TCP packet transmission time of IEEE 802.11 MAC DCF protocol for wireless LANs using a proposed enhanced backoff algorithm. From the results, in OFDM/quadrature phase shift keying channel (QPSK), we can achieve that the transmission time in wireless channel decreases as the TCP packet size increases and based on the data collected, we can infer the correlation between TCP packet size and total message transmission time, allowing for an inference of the optimal packet size in the TCP layer.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.5
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• pp.1139-1145
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• 2010

Wireless mesh network is similar to ad-hoc network, so when transferred to the data packet in the wireless environment, interfered factor arise. When TCP(Transport Control Protocol) was created, however as it was design based on wired link, wireless link made more transmission error than wired link. It is existent problem that TCP unfairness and congestion collapse over wireless mesh network. But packet losses due to transmission errors are more frequent. The cause of transmission error in wireless ad-hoc network may be inexactly regarded as indications of network congestion. And then, Congestion Control Algorithm was running by this situation causes the TCP performance degradation. In this paper, proposed TCP can adaptively regulate the congestion window through moving node in the Wireless Mesh Network. And it enhanced the performance.