• Journal of Internet Computing and Services
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• v.7 no.3
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• pp.41-51
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• 2006

In the case of CDMA-based packet data systems such as 1xEV-DO which are designed to support high rate services, BSs transmit data packets with a maximum power based on time multiplexing mode such that only one user can be serviced at a time. In this paper, we propose a joint power allocation and scheduling algorithm for 1xEV-DO-like systems in which we adopt a code division multiplexing (CDM) transmission method in the downlink common channel in order to utilize channel orthogonality such that we can serve more than one user at a time slot especially when there exist remaining resources after serving the firstly selected user by the scheduler. Simulation results demonstrate that the proposed scheme can improve the performances of conventional schemes such as the maximum rate and the proportional fair algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9A
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• pp.837-843
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• 2006

IEEE802.15.3 and IEEE802.15.4 have defined the hybrid MAC protocols based on TDMA and CSMA where a multi-frame TDMA structure is employed so that multiple data frames can be transmitted within one timeslot to guarantee minimum delay bounds of isochroous traffic. However, TDMA has an intrinsic problem that cannot dynamically allocate optimal length of timeslot to each station. Therefore the idle timeslot can be produced by stations when each transmission queue is instantaneously empty during its timeslot, which would waste lots of timeslots especially in the multi-frame TDMA systems. In this paper, we propose a more flexible multiple-access scheme for the multi-frame TDMA system based on the concept of virtual slot which is accessible by every station with the highest priority for slot owner and lower priority for other stations. Finally, our simulation results from various environments show that proposed scheme can achieve magnitude improvement of total system throughput and average message delay by maximizing channel utilization.

• The Journal of the Korea Contents Association
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• v.12 no.4
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• pp.60-68
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• 2012

In recent years, the requirements on the high quality environment monitoring by using the sensor nodes which can handle the multimedia data in WSN have been increased. However, because the volume of multimedia data is tremendous, the limited bandwidth of a wireless channel may incur the bottleneck of a system. To solve such a problem, most of the existing distributed multi-path routing protocols based on multimedia data just focused on overcoming the limited bandwidth in order to enhance the energy efficiency and the transmission rate. However, because the existing methods can not apply a key-based technique to encrypt the multimedia data, they are very weak for the security. In this paper, we propose a secure disjointed multipath routing scheme for multimedia data transmission. Since our proposed scheme divides multimedia data(eg. image) into pixels and sends them through disjointed multipath routing, it can provide security to the whole network without using the key-based method. Our experimental results show that our proposed scheme reduces about 10% the amount of the energy consumption and about 65% the amount of the missed data packets caused by malicious nodes over the existing methods on average.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.43-51
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• 2015

Upcoming cellular networks such as LTE-advanced and IEEE 802.16m are enhanced by relay stations to support high data rate multimedia services and minimize the shadow zone with low cost. Enhancing the relay stations, however, divides the multihop cellular network into smaller microcells and the distance between microcells is closer, which intends large intra-cell and inter-cell interference. Especially the access link on downlink in the OFDMA cellular network is the throughput bottleneck due to the severe interference caused by base stations and relay stations transmitting large data to mobile stations simultaneously. In this paper, we present interference aware channel allocation algorithm to avoid severe interference on multihop cellular networks with random topology. Proposed algorithm increases SINR(signal to interference plus noise ratio) and decreases number of required control messages for channel allocation, so that increases overall throughput on the networks.

• Information and Communications Magazine
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• v.25 no.5
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• pp.47-56
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• 2008

향후 유비쿼터스 시대는 센서 네트워크와 같은 저전송률을 요구하는 분산형 소규모 무선 네트워크에서부터 고정 및 이동 통신 서비스를 위한 중규모 네트워크, 고품질 고전송률이 요구되는 방송용 대규모 네트워크들이 혼재된 이종통신 환경이 도래하게 될 것으로 예상된다. 이와 더불어 고속데이터 전송 및 넓은 지역에 걸친 끊김 없는 서비스, 이동성 제공이라는 통신 서비스 사용자들의 급격한 요구 증대로 스펙트럼 자원에 대한 수요가 확산되는 추세에 있으며, 이로 인해 전 세계적으로 스펙트럼 자원 확보 경쟁이 더욱 심화되고 있는 상태이다. 본고에서는 빠르게 변화하고 있는 무선통신 환경 및 미래 주파수 자원의 고갈에 대처하기 위한 방편으로 선진국을 중심으로 활발히 연구가 진행되고 있는 상황인지 기술에 대한 국내외 기술 동향 및 연구 진행상황, 본 기술을 수행함에 있어 극복되어야 할 해결 과제에 대해 소개하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7B
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• pp.536-549
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• 2012

An ad hoc network consists of nodes with limited energy. Therefore, the data transmission can fail abruptly due to lack of energy of transmitting node. A previous work PAMP proposed to build multiple low-energy paths to support stable packet delivery exploiting the nodes with low energy. It has energy-reservation scheme and multi-path selection scheme for stationary wireless ad hoc networks. In this paper, we propose an extended version of PAMP by incorporating network coding opportunity in path selection process. The simulation results show that our proposed scheme shows better packet delivery ratio and lower energy consumption compared with PAMP and a legacy energy-aware multipath routing protocol REAR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12B
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• pp.1371-1379
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• 2009

In this paper, we propose a new multi-path routing protocol to provide reliable and stable data transmission in MANET that is composed of high-mobility nodes. The new multi-path routing establishes the main route by the mechanism based on AODV, and then finds the backup route that node-disjoint from the main route by making add nodes in the main route not participate in it. The data transmission starts immediately after finding the main route. And the backup route search process is taking place while data is transmitted to reduce the transmission delay. When either of the main route or the backup route is broken, data is transmitted continuously through the other route and the broken route is recovered to node-disjoint route by the route maintenance process. The result of the simulation based on the Qualnet simulator shows that the backup route exists 62.5% of the time when the main route is broken. And proposed routing protocol improved the packet transmission rate by 2~3% and reduced the end-to-end delay by 10% compared with AODV and AODV-Local Repair.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8A
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• pp.827-835
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• 2007

In this paper, the extension method of data transmission range as adapting AAS(Adaptive Antenna Systems) in ECMA(European Computer Manufacturers Association) standard MB-OFDM(MultiBand-Orthogonal Frequency Division Multiplexing) UWB systems is proposed, and the complementary beamforming method which can solve hidden beam problem when we adapt AAS in CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) systems is proposed. To design the complementary beamforming, Gram-Schmidt orthogonalization is utilized, whose beam pattern exhibits perfect nulling at the main beam angles and provides uniform power for detection of channel utilization out of main beam. The proposed method can be utilized with any arbitrary beamforming when we make main beamforming. Through computer simulation, it can be shown that proposed AAS and complementary beamforming increase data transmission range from 2m to 3.95m in 480Mbps data transmission system and increase throughput about 20% as compared with general UWB AAS systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.4
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• pp.378-386
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• 2013

In this paper, we propose a multi-way relaying system, in which N communicating nodes interchange their information one another by the help of a multiple-antenna non-regenerative relay station (RS). While the conventional multi-way relaying requires 2N transmission phases to complete the data exchange, the proposed system completes the mission with N phases composed of one multiple access phase and N-1 broadcast phases. For effective broadcast transmission, the proposed system pairs users for signal transmission with a new RS beamforming matrix not to interfere with the nodes of different pairs and a self-interference canceler at each node. The performance evaluation in terms of the average sum rate shows that the proposed system outperforms the conventional one with more significant gain when the number of RS antennas is comparable to the number of communicating nodes. The proposed schemes can be applicable to marine communications where the ships need to share their information with extended coverage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.603-610
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• 2006

This paper considers the problem of mitigating CCI(Co-channel Interference) in cellular OFDMA downlink systems. The users in the cell-edge area suffer from large CCIs, and their SINR requirements are hard to be maintained. To guarantee their QoS, we propose a new exclusive sub-carrier allocation and power control algorithm. The performance of the proposed two-step algorithm is simulated in SUI-A path-loss model, and it is compared with that of the conventional algorithm. The simulation results show that the data transmission rate in the cell-edge area was increased by 600Kbps within the same power constraint. The results indicate that with proposed algorithm, the data rate stability can be achieved independently of the user location in the cell.