Changhyun Park

Development of a case-based reasoning cognitive engine for IEEE 802.22 WRAN applications

On Nov. 4 2008, the Federal Communications Commission adopted rules for unlicensed use of television white spaces. The IEEE 802.22 Wireless Regional Area Networks (WRAN) standard is the first IEEE standard utilizing cognitive radio (CR) technology to exploit the television white space. A decision engine that is able to respond to the changes in the radio environment is necessary to efficiently exploit underutilized spectrum resources and avoid interfering with the licensed systems (e.g., TV services). This paper discusses the development of a case-based reasoning cognitive engine (CBR-CE) for the IEEE 802.22 WRAN applications. The performance of the CBR-CE is evaluated under various radio scenarios and compared to that of several multi objective search based algorithms, including the hill climbing search (HCS) and the genetic algorithm (GA). The simulation results show that the developed CBR-CE can achieve comparable utility with faster adaptation than the search based cognitive engines after appropriate training / learning. The learning process of the CBR is also simulated and discussed.

HMM Based Channel Status Predictor for Cognitive Radio

Nowadays, many researchers are interested in cognitive radio (CR) technology. We can say that the CR is the extended technology of software defined radio. Both technologies seem to be similar but there is an important difference. That is a sensing and channel management function. CR always senses incumbent users (IU) (or primary users) appearing on the channel the CR has been used and the CR must evacuate from that channel for preventing IU from interferences. For this purpose, CR should include a functionality of being able to find new relevant channel to move. So, CR must evaluate the quality of empty channels. From the point of view, we propose the HMM based channel status predictor, which helps the CR evaluate the quality. We will implement a HMM channel predictor and it will predict next channel status based on past channel states.

The detection and classification of the Wireless Microphone signal in the IEEE 802.22 WRAN system

For the use of the IEEE 802.22 WRAN, the spectrum sensing of the TV band is essential. In this paper, the Testbed for the signal detection and sorting algorithm and verification was proposed among the spectrum sensing algorithm about the part 74 wireless microphone (WM) signal. In case a plurality of WM signals exists within 6 MHz bandwidth, this algorithm uses the polyphase filterbank and grasps the signal absence. And by using the cyclostationary property, it has the advantage of moreover accurately knowing with the number of WM signals and frequency location.

A Design of the Predistorter Using Same Structure of the IMD Generators

In this paper, we propose the new linearization scheme for nonlinear RF power amplifier, generating the third and fifth intermodulation distortion signals it uses the identical structure of intermodulation signal generator. The proposed predistorter generates and controls predistorted third and high order IM signals independently. Using predistorted signals, intermodulation distortion signals of power amplifier are suppressed effectively. The predistortion linearizer has been implemented to operate in Korean PCS base-station transmitting band(1840~1870 MHz). The test results show that IM3 and IM5 (C/I) of power amplifier are improved more than 45 dB and 30 dB for CW two tone signals, respectively. The predistorter improves the adjacent channel power ratio (ACPR) more than lOdB at 885 kHz offset point for CDMA (IS-95) signals.