Chang-Joo Kim

Channel management in IEEE 802.22 WRAN systems

Channel management policy is one of the key functions of any cognitive radio system. The channel management decision in a cognitive radio system depends on various factors such as government regulations, limitations of transmission power between communicating devices, availability of geo-location information, and the quality of various available channels. The main purpose of channel management in a cognitive radio system is to protect the incumbent users (licensed users). The first international standard based on cognitive radio technology is IEEE 802.22, Wireless Regional Area Networks, which aims at providing broadband access in rural areas by effectively utilizing the unused TV channels. This standard aims at describing both PHY and MAC layer functionalities in an infrastructure- based broadband wireless access network for communication between consumer premises equipment using a base station. This article presents the cognitive radio functionality of this standard in detail. The cognitive functionality is provided by the dynamic channel management using channel sensing, channel classification, and maintenance of channel information. Using these techniques, this standard effectively protects the incumbent users and dynamically manages the channel allocation in IEEE 802.22 WRAN systems.

Adaptive acquisition of PN sequences for DSSS communications

Since the received signal levels in mobile communications are unknown and the location is varying, acquisition schemes for pseudonoise (PN) sequences with fixed thresholds cannot provide satisfactory performance. This fixed-threshold scheme may cause too many false alarms or result in a low detection probability for a selected threshold value. We present an adaptive acquisition scheme for PN sequences which estimate the background power level, multiply it with a threshold coefficient to keep the false alarms constant, and use it as a threshold.

GA-Based Design of Multi-Ring Arrays With Omnidirectional Conical Beam Pattern

The optimal design is presented of single- and multi-ring arrays with an omnidirectional conical beam by using a genetic algorithm (GA). The design parameters to be optimized are ring radii, excitation phases and amplitudes, requiring that the excitations of all elements in the same ring have the same amplitude and periodic phase for minimal azimuth-dependence in beam pattern. Parametric studies of the beam pattern were conducted and the theoretical radiation pattern was also validated from the experimental result with a single ring array antenna. As examples of GA-based design, two types of conical beam pattern were considered, illuminating a significant circular zone for satellite communications on moving vehicles. All results gave an omnidirectional conical beam pattern, in good agreement with the desired mask pattern.

Policy and Technology of Dynamic Spectrum Access in Korea

In this paper, we introduce spectrum policies and dynamic spectrum access technologies in Korea. In the past, Korea spectrum management was the command and control with exclusive usage rights and small portions of spectrum commons bands. With the development of the radio technologies, recently, Korea government, MIC (Ministry of Information and Communication), has been adopting new spectrum policies based on dynamic spectrum access technology such as LBT (listen before talk) for RFID, UWB, and FACS (flexible access common spectrum) etc. MIC is also considering spectrum reallocation of digital dividend bands after DTV transition. New radio techniques such as cognitive radio and SDR will be applied to new services in this UHF band. MIC is trying to open the radio spectrum in an efficient way and adopt new technology into spectrum policy. Thus MIC is extending the open spectrum such as spectrum commons and spectrum liberalization bands.

Novel Ka-band microstrip antenna fed circular polarized horn array antenna

This paper introduces a novel microstrip antenna fed circular polarized array antenna composed of 8-element horn antennas. This horn can be divided into two parts, microstrip antenna and square horn. The microstrip antenna has the role of feeder and polarizer of the horn antenna, and it is designed for stacked type having a metal spacer for high gain, high isolation and wideband characteristic. And, the horn improves gain of microstrip antenna by about 2dB. By this structural characteristic, the horn antenna needs no additional structure such as feeder and polarizer, and the size can be considerably reduced. The element horn antenna has typical gain of 8 dBi and 3 dB axial-ratio bandwidth around 4.9 %. The horn array antenna was designed to have array spacing of 0.9 /spl lambda//sub 0/ with parallel feeding network. We obtained about 14 dBi array gain and 8.2 % axial-ratio bandwidth.

Detection analysis of a generalized order statistics CFAR detector for a correlated Rayleigh target

Abstract We analyze the performance of the generalized order statistics constant false alarm rate detector for a correlated Rayleigh target model. Detection probability is computed by contour integration. It is shown that the resulting detection performance depends on the degree of correlation. The more the correlation, the poorer the detection probability becomes.

Analysis of Spectrum Sharing Policy and Spectrum Usage Rights

In this paper, we analyze the paradigm shift of radio policy with the development of radio technology. In particular, we propose the definition of spectrum sharing, which is now omitted in the Korean radio law, and analyze the category of spectrum sharing depending on the licensing regime. Also we propose to extend the spectrum usage right, which defines only exclusive usage rights by spectrum auction in the Korean radio law, to all the stations which use radio spectrum and to restructure the Korean radio law.

Cognitive Radio test-bed based on ECMA-392 International Standard

Cognitive Radio (CR) technology is one of the promising technology to efficiently utilize the unused radio spectrum. Recently, the Federal Communications Commission (FCC) allowed TV white space (TVWS) to be used for data communications provided the licensed user operations should be protected. The FCC made the rules and regulation for using the TVWS. Till now there is no real deployment of any communication system that operates on TVWS. As the first step towards the deployment of a communication system that operates on TVWS, we developed a UHF band CR test-bed based on ECMA-392 international standard. ECMA-392 standard defines the MAC and PHY for operation in TVWS for communication between portable devices. In this paper, we present the design and implementation of our test-bed system in detail. We also verified that the test-bed system operates in lines with the FCC rules.

Multi-Server Queueing Model with Broadcasting Service

We consider a multi-server queueing model with novel customers admission discipline. The customer who sees several free servers upon arrival is served by all these servers. Such a situation occurs, e.g. in modeling wireless communication network with broadcasting. The main performance measures of the system are calculated.

Novel hybrid antenna design having a shaped reflector for mobile satellite communication applications

This paper presents novel hybrid antenna (HA) design based on shaped reflector for mobile satellite communications. HA is composed of a shaped reflector and the feeder having a 1×8 linear phased array, and reflector shaping method is applied for the performance optimization with minimum aperture size. And, in the feeder design, HA has another merit to minimize the manufacturing cost by optimizing the number of element. Proposed HA is designed at Ka-band and can electrically control a beam pattern within ±3° in the basic angle of +45° in elevation. This antenna is designed to meet the international regulations for very small aperture terminals (VSAT) including ITU-R S.465-5 for beam pattern including side-lobe level.