• 한국군사과학기술학회지
• /
• 제9권4호
• /
• pp.24-31
• /
• 2006

To reduce the interferences between the radio equipments which are operated in frequency hopping mode, the frequency resource should be assigned to each equipment without overlapping when several groups of radio equipments operate in the same area. If the radio equipments are in a different area, the partial frequency overlaying can be permitted. From the isotropic multi-dimensional array, several frequency assignment tables can be extracted for a same area. Also several tables can be extracted for different areas. Since there can be no overlapped frequencies between the tables for the same area, no interference between the radio equipments in an area is guaranteed. The frequencies overlapped between 2 tables for 2 different areas are pre-planed as required. The interference performance in frequency hopping radio can be controlled as desired using the proposed Frequency Resource Assignment Algorithm using Isotropic multi-dimensional Array.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제10권3호
• /
• pp.1052-1070
• /
• 2016

Wireless Body Area Networks (WBANs) have received a lot of attention as a promising technology for medical and healthcare applications. A WBAN should guarantee energy efficiency, data reliability, and low data latency because it uses tiny sensors that have limited energy and deals with medical data that needs to be timely and correctly transferred. To satisfy this requirement, many multi-radio multi-channel MAC protocols have been proposed, but these cannot be implemented on current off-the-shelf sensor nodes because they do not support multi-radio transceivers. Thus, recently single-radio multi-channel MAC protocols have been proposed; however, these methods are energy inefficient due to data duplication. This paper proposes a TDMA-based single-radio, multi-channel MAC protocol that uses the Unbalanced Star+Mesh topology to satisfy the requirements of WBANs. Our analytical analysis together experiments using real sensor nodes show that the proposed protocol outperforms existing methods in terms of energy efficiency, reliability, and low data latency.

• 대한전자공학회논문지TC
• /
• 제44권5호
• /
• pp.33-39
• /
• 2007

본 논문은 cognitive radio (CR) 기능을 갖는 무선 멀티홉 릴레이 네트워크의 throughput 용량에 대한 연구 결과이다. 본 논문에서는 TDMA/FDMA에 기반한 프레임 구조를 갖는 릴레이가 기지국과 통신할 때 CR 기술을 이용하여 현재 사용되고 있지 않는 주파수 자원을 측정하여 동적으로 이용하는 시스템을 제안하고 이의 throughput 용량 모델을 제안 하였다. 특히, 본 논문에서는 Utilization factor를 이용하여 제안된 시스템을 위한 throughput 용량 모델을 제안하였다. 해석 모델링 결과 본 논문에서 제안한 CR 기반 멀티홉 릴레이 시스템은 throughput 용량을 매우 향상하는 결과를 보였다.

• Journal of Communications and Networks
• /
• 제8권4호
• /
• pp.401-409
• /
• 2006

Orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) technologies provide additional dimensions of freedom with spectral and spatial resources for radio resource management. Multi-dimensional radio resource management has recently been identified to exploit the full dimensions of freedom for more flexible and efficient utilization of scarce radio spectrum while provide diverse quality of service (QoS) guarantees. In this work, a multi-dimensional radio resource scheduling scheme is proposed to achieve above goals in hybrid orthogonal frequency division multiple access (OFDMA) and space division multiple access (SDMA) systems. Cochannel interference (CCI) introduced by frequency reuse under SDMA is eliminated by frequency division and time division between highly interfered users. This scheme maximizes system throughput subjected to the minimum data rate guarantee. for heterogeneous users and transmit power constraint. By numerical examples, system throughput and fairness superiority of the our scheduling scheme are verified.

• Journal of Communications and Networks
• /
• 제4권4호
• /
• pp.344-350
• /
• 2002

This work summarizes the current state of the art in software radio for 4G systems. Specifically, this work demonstrates that classic radio structures, e.g., heterodyne reception, homodyne reception, and their improved implementations, are inadequate selections for multi-mode reception. This opens the door to software defined radio, a novel reception architecture which promises ease in multi-band, multi-protocol design. The work presents the many advantages of such an architecture, including flexibility, reduced cost via component reduction, and improved reliability via, e.g., the elimination of environmental instability. The work also explains the limitations that currently curtail the widespread use of SDR, including issues surrounding A/D converters, management of software and power, and clock generation. This provides direction for future research to enable the broad applicability of SDR in 4G cellular and beyond.

• 한국멀티미디어학회논문지
• /
• 제11권12호
• /
• pp.1716-1721
• /
• 2008

Currently, Wireless Networks have some nice characteristics such as multi-hop, multi-channel, multi-radio, etc but these kinds of resources are not fully used. The most difficulty to solve this issue is to solve mixed integer optimization. This paper proposes a method to solve a class of mixed integer optimization for wireless networks by using AMPL modeling language with CPLEX solver. The result of method is scheduling and congestion control in multi-channel multi-radio wireless networks.

• Journal of Communications and Networks
• /
• 제16권2호
• /
• pp.155-161
• /
• 2014

Mobility can lead to continual loss of data and service interruptions during communications in multi-hop cognitive radio networks. Mobility of primary users (PUs) or cognitive users (CUs) requires adjustment of multi-hop communications among CUs to avoid any interference to PUs. To provide durable and reliable data routing that ensures continuous network service, we propose mobility-aware cognitive routing (MCR) for multi-hop cognitive radio networks. MCR examines the risk level of each node against interference regions and selects the most reliable path for data delivery using a Markov predictor. Through simulation, we verify that the proposed scheme can avoid route destruction preemptively and achieve reliable data delivery.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제5권11호
• /
• pp.1976-1996
• /
• 2011

Cognitive radio (CR) MAC protocol provides access control of unused spectrum resources without causing interference to primary users. To achieve this goal, in this paper a TDMA based cooperative multi-channel cognitive radio MAC (MCR-MAC) protocol is proposed for wireless ad hoc networks to provide reliable protection for primary users by achieving cooperative detection of incumbent system signals around the communication pair. Each CR node maintains transmission opportunity schedules and a list of available channels that is employed in the neighbor discovery period. To avoid possible signal collision between incumbent systems and cognitive radio ad hoc users, we propose a simple but efficient emergency notification message exchanging mechanism between neighbor CR nodes with little overhead. Our simulation results show that the proposed MCR-MAC can greatly reduce interference with primary users and remarkably improve the network throughput.

• Journal of the Optical Society of Korea
• /
• 제14권4호
• /
• pp.351-356
• /
• 2010

We investigated the combined effect of fiber chromatic dispersion and self-phase modulation (SPM) in multi-channel subcarrier multiplexed (SCM) optical transmission systems. We theoretically analyzed the transmission characteristics of the SCM signals with the effect of SPM and chromatic dispersion in a single-mode optical fiber by numerical simulations based on the nonlinear Schrodinger equation. The numerical simulation results revealed that the effect of fiber dispersion and SPM could occur independently between subcarrier channels in two-channel SCM systems for small optical modulation index (OMI) and large channel spacing. However, for large OMI, small channel spacing, and large fiber launching power, we found a performance degradation of the two-channel system compared to that of a single-channel system. These parameters are therefore important for the optimization of multi-channel SCM systems applicable to radio over fiber networks.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제52권11호
• /
• pp.496-500
• /
• 2003

A low-cost, large area, random, maskless texturing scheme independent of crystal orientation is expected to significantly impact terrestrial photovoltaic technology. We investigated silicon surface microstructures formed by reactive ion etching (RIE) in Multi-Hollow cathode system. Desirable texturing effect has been achieved when radio-frequency (rf) power of about 20 Watt per one hollow cathode glow is applied for our RF Multi-Hollow cathode system. The black silicon etched surface shows almost zero reflectance in the visible region as well as in near IR region. The etched silicon surface is covered by columnar microstructures with diameters from 50 to 100 nm and depth of about 500 nm. We have successfully achieved 11.7% efficiency of mono-crystalline silicon solar cell and 10.2% multi-crystalline silicon solar cell.