• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.6A
• /
• pp.558-564
• /
• 2007

3G Long Term Evolution, which aims for various mobile multimedia service provision by enhanced wireless interface, proposes VoIP-based voice service through a Packet Switching (PS) domain. As delay and loss-sensitive VoIP traffic flows through the PS domain, more challenging technical difficulties are expected than in Circuit Switching (CS) domain based VoIP services. Moreover, since 3G LTE, which adopts the OFDM as its physical layer, introduces Physical Resource Block (PRB) as a unit for transmission resources, new types of resource management schemes are needed. This paper proposes a PRB scheduling algorithm of MAC layer for VoIP service in 3G LTE and shows the simulation results. The proposed algorithm has two key parts; dynamic activation of VoIP priority mode to satisfy VoIP QoS requirements and adaptive adjustment of the priority mode duration in order to minimize the degradation of resource utilization.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.6A
• /
• pp.617-623
• /
• 2007

A novel c-DSDV routing protocol is proposed in clustered mobile ad hoc networks. Clusterheads that manage members in their own cluster construct a higher layer backbone to which the DSDV concept is applied. Each clusterhead maintains its own global routing table by exchanging Update Request (UREQ) messages with its neighboring clusterheads. A number of entries in the table is as small as a number of clusterheads unlike a number of nodes in DSDV Since a UREQ message travels from one clusterhead to all its neighboring clusterheads that are at most 3 hops away, the topology convergence range by each UREQ message is at least 9 times as wide as that of DSDV and CGSR, greatly improving accuracy of routing information. However, overhead in c-DSDV is similar to that of DSDV because only clusterheads initiate UREQ messages. Delivery ratio increases by about 32$\sim$50%.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.6A
• /
• pp.537-543
• /
• 2007

In this paper, we propose a new stopping criterion for the turbo processing (Turbo-BLAST) of MIMO-OFDM system. To reduce the high computational complexity of turbo-BLAST, it is desirable to lessen the outer-loop iteration number. In a system such as IEEE 802.16e Mobile WiMax, no CRC bits are available except the last encoding packet of a transmitted burst, so early stopping criteria without the help of CRC bits are needed. The proposed criterion counts the sign differences between received parity bits and the re-encoded parity bits from received information bits. With the tail-biting code which is accepted for IEEE 802.16e, a method that the re-encoder operates at half complexity is also proposed. Computer simulations show that the proposed stopping criterion approaches the performance of GENIE aided criterion with less average number of iterations than the other early stopping criteria.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.9A
• /
• pp.905-915
• /
• 2007

This paper proposes a filter-based algorithm to adaptively adjust the contention window in IEEE 802.11 DCF. The proposed mechanism is focused on the general and realistic environments that have various conditions regarding to noise, media types and network load. For this flexible adaptation, Filter-based DCF(FDCF) takes a more realistic policy such as median filter concept in the image processing technologies. We can handle these various environments by adjusting the contention window size according to the result of filtering based on history-buffer. We can ignore temporarily and randomly occurred transmission failures due to noise errors and collisions in noisy environments. In addition, by changing the reference number and history-buffer size, FDCF can be extended as a general solution including previous proposed mechanism. We have confirmed that the proposed mechanism can achieve the better performance than those of previous researches in aspects of the throughput and the delay in the realistic environments.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.5A
• /
• pp.479-486
• /
• 2008

In this paper, an efficient training symbol design with m-sequence is proposed for the MIMO-OFDM based next generation wireless transmission system which supports gigabits per second data rate. In the traditional blute force method, the preamble design is based on the case by case comparison with the system requirements. This paper discusses a training symbol design methodology for the MIMO-OFDM system based on the m-sequence which has been widely used in the spread spectrum communication areas due to its good correlation characteristics. Also the step-by-step design and performance verification method within the limited search space is discussed. The proposed method targets the design of the training symbol which satisfies system requirements for the packet based MIMO-OFDM wireless communication system including automatic gain control(AGC), timing synchronization, frequency and sampling offset estimation, and MIMO channel estimation.

• Journal of KIISE:Information Networking
• /
• v.29 no.1
• /
• pp.15-23
• /
• 2002

We present a new MDA-based Mobile-IPv6 multicast routing algorithm for wirelese service operators to offer Mobile-IP over IMT-2000 service under IMT-2000 network by taking advantage of the existing infrastructure for IMT-2000 multimedia application services. The extended IMT-2000 system architectures use an PDSNs (i.e. IWFs), and the home network (i.e. Internet) backbone and intermediate network are composed of ATM entities. A key feature of the new protocol is the use of MDA(Multicast Delivery Agent) to reduce delivery path length of the multicast datagram. We show that proposed protocol is efficient in terms of various performance measures such as multicast traffic load, multicast related handoff, and average routing length when we implement it using the Mobile-IPv6. Particularly, the number of tunneling and average routing length of datagram are reduced relatively, the multicast traffic load is also decreased.

• Journal of KIISE:Information Networking
• /
• v.30 no.6
• /
• pp.755-763
• /
• 2003

To improve performance over noisy wireless channels, mobile wireless networks employ forward error correction(FEC) techniques. The performance of static FEC algorithms, however, degrades by poorly matching the overhead of their correction code to the degree of the fluctuating underlying channel error. This paper proposes an adaptive FEC technique called FECA(FEC-level Adaptation), which dynamically tunes FEC strength to the currently estimated channel error rate at the data link layer. FECA is suitable for wireless networks whose error rate is high and slowly changing compared to the round-trip time between two communicating nodes. One such example network would be a sensor network in which the average bit error rate is higher than $10^{-6}$ and the detected error rate at one time lasts a few hundred milliseconds on average. Our experiments show that FECA performs 15% in simulations with theoretically modeled wireless channels and in trace-driven simulations based on the data collected from real sensor networks better than any other static FEC algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.3B
• /
• pp.224-236
• /
• 2003

MANET(Mobile Ad hoc networks) is a mobile, multi-hop, and wireless network which is bandwidth constrained, energy constrained, resource constrained, autonomous, and self operating systems with dynamic topology. These constraints make the routing between communicating nodes in ad hoc networks difficult. In this paper we survey several routing protocol for mobile ad hoc networks. Especially, we focus on Zone Routing Protocol, hybrid routing framework suitable for a wide of mobile ad hoc networks and analyze performance of ZRP. In the case of ZRP protocol, it is essential that the use of optimal zone radius for efficient use. Otherwise it was proved through an simulation that performance of whole network is rapidly decrease with greatly increasing overhead of ZRP traffic that need for transmission of packet by IARP or IERP traffic. Also we suggest the process of finding QoS path that use in-band signal for QoS routing in ad hoc network. This method guarantees route that make real time multimedia service for QoS enabled path.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.1C
• /
• pp.67-77
• /
• 2007

Virus throttling technique, one of many early worm detection techniques, detects Internet worm propagation by limiting connect requests within a certain ratio. The typical virus throttling controls the period of rate limiter autonomically by utilizing weighted average delay queue length to reduce connection delay time without hanving a large effect on worm detection time. In the existing virus throttling research, a minimum period of variable rate limiter is fired and a turning point which is a point that the period of rate limiter has been being decreased and starts to be increased is also fixed. However, these two performance factors have different effects on worm detection time and connection delay. In this paper, we analyze the effect of minimum period and turning point of variable rate limiter, and then propose an algorithm which determines values of performance factors by referencing current traffic pattern. Through deep experiments, it is verified that the proposed technique is more efficient in respect of reducing worm detection time and connection delay than the existing virus throttling which fixed the performance factors.

• The KIPS Transactions:PartC
• /
• v.16C no.2
• /
• pp.209-216
• /
• 2009

In the wireless sensor network, flooding is required for the dissemination of queries and event announcements. The simple flooding causes the implosion and the overlap problems, so the simple flooding may result in the reduced network lifetime. Therefore, in this paper, we propose the flooding overlay structure (FOS) so that the overhead caused by flooding can be reduced. We propose two variants of FOS mechanisms, the centralized FOS (CFOS) and the distributed FOS (DFOS). In CFOS, the sink collects the network topology information and selects forwarding nodes based on that information. On the other hand, DFOS allows each sensor node to decide whether to act as a forwarding node or not based on its local information. For the performance evaluation of our proposed mechanisms, we carry out NS-2 based simulations and compare ours with the simple flooding and the gossiping. The simulation results indicate that the proposed FOS mechanisms outperform the simple flooding in terms of the network lifetime and the gossiping in terms of the data delivery ratio.