Sunmin Lim

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.

Cooperative Spectrum Sensing for IEEE 802.22 WRAN System

In this paper, we propose two novel data fusion schemes for cooperative spectrum sensing in the IEEE 802.22 WRAN system. The data fusion structure is proper for the WRAN system due to its centralized structure, and it can provide reliable sensing performance. The proposed data fusion schemes improve the sensing reliability by utilizing confidence vector of the sensing result. Moreover, application with statistic weight on the confidence vector provides additional performance gain. The computer simulation results show that the proposed data fusion methods guarantee better sensing performance than the conventional data fusion algorithms.

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.

Efficient multi-channel signal detection algorithms for cognitive radio systems in TV white space

In this paper, we propose novel spectrum sensing algorithms to detect multi-channel CR signal in TV white space. Most of CR systems in TV white space are considering multi-channel operation to support enhanced system throughput. Therefore, spectrum sensing algorithm to detect multi-channel CR system is essentially required for coexistence in TV white space. The proposed algorithms can detect various types of multi-channel CR signal with reasonable detection performance. By employing the proposed algorithms, we can contribute to efficient implementation of spectrum sensing process as well as intelligent coexistence mechanisms in TV white space.

Novel CR signal detection algorithms for coexistence in TV white space

In this paper, we propose novel signal detection algorithms for coexistence of CR systems in TV white space. As various CR standards appear in TV white space, technologies for detecting CR signals are required to enabling coexistence between CR systems. The proposed signal detection algorithms detect and classify CR networks utilizing cyclo-stationary features of each CR system. They consider multiple periodic properties of OFDM signal which is varied by parameters of each CR standard. The simulation results show that the proposed schemes can improve signal detection performance up to 50% compare with the conventional schemes.

Novel incremental spectrum sensing method based on sequential tone detection

In this paper, we propose a novel incremental spectrum sensing method based on sequential tone detection. The conventional spectrum sensing algorithm using FFT computes all frequency components in a process, thus it requires unnecessary complexity. To overcome this drawback, sequential spectrum sensing algorithm utilizing DFT was proposed, and it shows almost same detection performance with reduced complexity. The proposed method of this paper utilizes Goertzel algorithm, and it provides improved signal detection performance with further reduced computational complexity compare with the conventional schemes. The simulation results verify that it provides 10% enhancement on detection probability with significantly reduced system complexity.

Efficient spectrum sensing algorithm utilizing sequential partial band search

In this paper, we propose an efficient spectrum sensing algorithm utilizing sequential partial band search. The conventional sensing algorithm using FFT contains redundant computation due to the characteristic of FFT which computes all frequency components at one time. The proposed sensing algorithm utilizing DFT computes a frequency component once at a time according to the priority and decides presence of signal. The proposed sensing algorithm can provide similar detection performance to the conventional scheme while computations of the sensing process could be reduced significantly depends on an early detection of signal.

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.

Implementation of sensing module for spectrum sharing in TV white space

Spectrum sensing module is implemented for cognitive radio system in TV white space. The sensing module provides real-time signal detection for incumbent users as well as other cognitive radio systems with reliable detection performance for spectrum sharing.