Traffic congestions are rapidly increasing in urban areas. In order to reduce these problems, it ... more Traffic congestions are rapidly increasing in urban areas. In order to reduce these problems, it needs real-time data and intelligent techniques to quickly identify traffic activities with useful information. This paper proposes a Fuzzy Domain Ontology(FDO)-based opinion mining system to monitor the transportation network in real-time as well to make a city polarity map for travelers. The proposed system retrieves tweets and reviews related to transportation activities and a city. The feature opinions are extracted from these tweets and reviews and then used FDO to identify transportation and city features polarity. This FDO and intelligent prototype are developed using Protégé OWL (Web Ontology Language) and JAVA, respectively. The experimental result shows satisfactory improvement in tweets and review's analyzing and opinion mining.
2009 9th International Symposium on Communications and Information Technology, 2009
Spectrum sensing is one of the most important functions for cognitive radio. The performance of s... more Spectrum sensing is one of the most important functions for cognitive radio. The performance of some sensing techniques like energy detection is determined by receiving signal to noise ratio (SNR). We applies antenna array using multiple beams to primary user detection. Whole space around cognitive user is divided into several subspaces for multiple beams. The directional beam can improve spectrum sensing performance by increasing receiving SNR. Moreover the approximate direction information of primary user can also be acquired after sensing. The beamformer used here doesn't require channel information and is pre-specified without much computation. The mathematic analysis is given for energy detection using directional beam under different channels. The simulation results prove the performance promotion.
2009 9th International Symposium on Communications and Information Technology, 2009
In this paper, a sequential change detection scheme is proposed to detect the emergence of a prim... more In this paper, a sequential change detection scheme is proposed to detect the emergence of a primary signal with unknown power. It can be shown that the proposed test can do better than the generalized likelihood ratio (GLR) test, under the same worst case average run length (ARL) of detection delay constraint. And performance of our test is evaluated using theoretical analysis and numerical simulations.
Wireless Communications and Mobile Computing, 2010
In order to alleviate the narrowband interference (NBI) to ultra wideband (UWB) systems, we propo... more In order to alleviate the narrowband interference (NBI) to ultra wideband (UWB) systems, we propose two non-linear UWB chirp waveforms based on the arctrigonometric and archyperbolic function in this paper. The proposed UWB pulses can obtain good performance in NBI suppression. Both of the two chirp pulses require only the time domain processing because of the inherent relationship between the frequency domain and the time domain. Theoretical analysis and simulation results show that the direct sequence pulse binary amplitude modulation (DS-BPAM) UWB systems with the proposed chirp waveforms can achieve excellent NBI suppression performance and outperform the linear chirp waveform based UWB system significantly.
2008 3rd International Conference on Cognitive Radio Oriented Wireless Networks and Communications (CrownCom 2008), 2008
In this paper, based on a new pulse waveform design algorithm of ultra wideband pulse [5], we emp... more In this paper, based on a new pulse waveform design algorithm of ultra wideband pulse [5], we employ this algorithm into a cognitive M-ary code selected direct sequence bipolar pulse amplitude modulation ultra wideband communication system. This M-ary DS-UWB system can utilize the cognitive waveform to realize the high performance and high data rate cognitive communication. The bit error rate performance of the M-ary system with the novel pulse waveform is presented in this paper. The proposed scheme can be realized under different situations with lower interference to primary wireless devices and acceptable system complexity. Further more, through the pulse design, we can also generate some good candidate waveform sets which satisfy the FCC regulation.
EURASIP Journal on Wireless Communications and Networking, 2014
We introduce an opportunistic scheduling to enhance the physical layer security with transmit ant... more We introduce an opportunistic scheduling to enhance the physical layer security with transmit antenna selection (TAS) in multiuser environment. We consider a wireless communication system composed of a single transmitter and multiple legitimate users in the presence of several eavesdroppers with each node having multiple antennas under quasi-static Rayleigh fading channel. The transmitter selects the best transmitting antenna and the best user to maximize signal-to-noise ratio (SNR) at the selected user. The user and eavesdropper can employ either selection combining (SC) or maximal ratio combining (MRC) to combine the received signals. New closed-form expressions for probability of positive secrecy and outage are derived. Moreover, asymptotic analysis reveals the outage diversity gain and array gain for the proposed scheme. The impact of number of users, eavesdroppers, and antennas on secrecy performance are clearly demonstrated with mathematical analysis and numerical results.
2012 International Symposium on Communications and Information Technologies (ISCIT), 2012
ABSTRACT A joint Tomlinson-Harashima (TH) source and multi-relay beamforming design in decode-and... more ABSTRACT A joint Tomlinson-Harashima (TH) source and multi-relay beamforming design in decode-and-forward (DF) relaying systems with relay selection is proposed, which exploits the relationship between QR decomposition (QRD) and Gram- Schmidt orthogonalization (GSO) to jointly optimize the source precoder and relay beamforming vectors of multiple relays. Then we propose a correlation-based approach which leads to a significant reduction of forward overhead information from the source to the selected relays. Finally a “Best-Last” based relay selection approach is proposed which has a performance close to the optimal global relay selection approach with a significantly reduced computational complexity. Simulation results are provided to support the advantages of the proposed schemes.
2008 International Symposium on Communications and Information Technologies, 2008
This paper investigates energy detection based wideband spectrum sensing for dynamic spectrum acc... more This paper investigates energy detection based wideband spectrum sensing for dynamic spectrum access (DSA) systems. The licensed frequency band of interest is resolved into a series of contiguous frequency bins via the FFT engine of the detector. By employing forward consecutive mean excision (FCME) algorithm and exploiting primary user (PU) signal's contiguity in frequency domain, computationally simple pre-processing of raw
2008 Third International Conference on Convergence and Hybrid Information Technology, 2008
Wideband primary user (PU) signal identification approaches based on enhanced forward consecutive... more Wideband primary user (PU) signal identification approaches based on enhanced forward consecutive mean excision (FCME) algorithms are proposed for cognitive MB-OFDM UWB systems. Each single subband is resolved into a series of contiguous frequency bins via the FFT engine. The identification of PU signals can thus be performed in frequency domain with our proposed methods, namely the localization algorithm based on double thresholding with prior one-dimensional median filtering (MF+LAD) and the FCME algorithm with binary integration (FCME+BI). In both strategies, two thresholds are employed in the detection decision making stage to perform the frequency bin cluster based PU signal identification. It is verified through numerical experiments that the two strategies can significantly improve wideband PU signals' bandwidth and signal-to-noise ratio (SNR) estimation accuracies.
2009 9th International Symposium on Communications and Information Technology, 2009
This paper presents the interference of Ultra Wide-Band (UWB) sensor applied in Korea into Wirele... more This paper presents the interference of Ultra Wide-Band (UWB) sensor applied in Korea into Wireless Broad-band (WiBro) system based on Orthogonal Frequency Division Multiplexing (OFDM) using frequency of 2.3 GHz. The Minimum Coupling Loss (MCL) method and Spectrum Engineering Advanced Monte Carlo Analysis Tool (SEAMCAT) are used to evaluate the interference effects of UWB sensor on WiBro. The required minimum allowable distance is determined by MCL method should be 0.15 m when UWB sensor power spectral density (PSD) is -86.4 dBm/MHz in the case of single interferer in indoor environment. For the case of multiple interferers in outdoor environment, when number of active transmitters is 94, SEAMCAT is used to figure out UWB sensor PSD of -89 dBm/MHz below should be required to avoid the interference probability occurring in WiBro mobile station.
ABSTRACT Cognitive radios may operate in practice under various adverse environments. For typical... more ABSTRACT Cognitive radios may operate in practice under various adverse environments. For typical mobile and short-range scenarios, wireless links may tend to be time and frequency selective, i.e., the multipath propagations with time-varying fading coefficients will be inevitable. To cope with the encountered doubly-selective channels, in this paper we present a new spectrum sensing algorithm for distributed applications. First, a dynamic discrete state-space model is established to characterize sensing process, where the occupancy state of primary band and the time-varying multipath channel are treated as two hidden states, while the summed energy is adopted as the observed output. With this new paradigm, spectrum sensing is realized by acquiring primary states and time-dependent multipath channel jointly. For the formulated problem, unfortunately, Bayesian statistical inference may be impractical due to the absence of likelihoods and involved non-stationary distributions. To remedy this problem, an iterative algorithm is further designed by resorting to sequential importance sampling techniques; thus, the dynamic non-Gaussian multipath channel and primary states are estimated recursively. Another critical challenge, e.g., the noise uncertainty, is also considered, which may be incorporated conveniently into this sensing diagram and, furthermore, addressed effectively by the designed algorithm. Simulations validate the proposed algorithm. While classical schemes fail to deal with doubly selective channels, the new sensing scheme can exploit the underlying channel memory and operate well, which provides a great promise to realistic applications.
2008 IEEE International Conference on Ultra-Wideband, 2008
In this paper, we present the space time block codes (STBC) based M-ary code-selected modulation ... more In this paper, we present the space time block codes (STBC) based M-ary code-selected modulation scheme of direct sequence bipolar pulse amplitude modulation (DSBPAM) ultra wideband (UWB) system with selective Rake (SRake) receiver and maximum ratio combining (MRC) over multipath channels in order to improve the system performance and transmission rate of the conventional DS UWB system. The system bit
2010 10th International Symposium on Communications and Information Technologies, 2010
Cooperative multi-cell transmit strategies typically require full channel state information (CSI)... more Cooperative multi-cell transmit strategies typically require full channel state information (CSI) at the base station. Most previous works in this area have assumed that base stations have common knowledge of both data dedicated to all terminals and full or partial CSI of all links. In this paper, a more practical limited-feedback scenario is studied for multi-cell joint beamforming. The proposed algorithm provides higher sum rates over the virtual SINR one.
2008 4th International Conference on Wireless Communications, Networking and Mobile Computing, 2008
Wireless Relaying is one of the promising solutions to overcome the channel impairments and provi... more Wireless Relaying is one of the promising solutions to overcome the channel impairments and provide high data rate coverage that appears for beyond 3G mobile communications. In this paper we present an end to end BER performance analysis of dual hop wireless communication systems equipped with multiple Decode and Forward relays over the Rayleigh fading channel with relay selection. We select the best relay based on end to end channel conditions. We apply Orthogonal Space Time Block coding (OSTBC) at source, and also present how the multiple antennas at the source terminal affects the end to end BER performance. This intermediate relay technique will cover long distance where destination is out of reach from source.
Traffic congestions are rapidly increasing in urban areas. In order to reduce these problems, it ... more Traffic congestions are rapidly increasing in urban areas. In order to reduce these problems, it needs real-time data and intelligent techniques to quickly identify traffic activities with useful information. This paper proposes a Fuzzy Domain Ontology(FDO)-based opinion mining system to monitor the transportation network in real-time as well to make a city polarity map for travelers. The proposed system retrieves tweets and reviews related to transportation activities and a city. The feature opinions are extracted from these tweets and reviews and then used FDO to identify transportation and city features polarity. This FDO and intelligent prototype are developed using Protégé OWL (Web Ontology Language) and JAVA, respectively. The experimental result shows satisfactory improvement in tweets and review's analyzing and opinion mining.
2009 9th International Symposium on Communications and Information Technology, 2009
Spectrum sensing is one of the most important functions for cognitive radio. The performance of s... more Spectrum sensing is one of the most important functions for cognitive radio. The performance of some sensing techniques like energy detection is determined by receiving signal to noise ratio (SNR). We applies antenna array using multiple beams to primary user detection. Whole space around cognitive user is divided into several subspaces for multiple beams. The directional beam can improve spectrum sensing performance by increasing receiving SNR. Moreover the approximate direction information of primary user can also be acquired after sensing. The beamformer used here doesn't require channel information and is pre-specified without much computation. The mathematic analysis is given for energy detection using directional beam under different channels. The simulation results prove the performance promotion.
2009 9th International Symposium on Communications and Information Technology, 2009
In this paper, a sequential change detection scheme is proposed to detect the emergence of a prim... more In this paper, a sequential change detection scheme is proposed to detect the emergence of a primary signal with unknown power. It can be shown that the proposed test can do better than the generalized likelihood ratio (GLR) test, under the same worst case average run length (ARL) of detection delay constraint. And performance of our test is evaluated using theoretical analysis and numerical simulations.
Wireless Communications and Mobile Computing, 2010
In order to alleviate the narrowband interference (NBI) to ultra wideband (UWB) systems, we propo... more In order to alleviate the narrowband interference (NBI) to ultra wideband (UWB) systems, we propose two non-linear UWB chirp waveforms based on the arctrigonometric and archyperbolic function in this paper. The proposed UWB pulses can obtain good performance in NBI suppression. Both of the two chirp pulses require only the time domain processing because of the inherent relationship between the frequency domain and the time domain. Theoretical analysis and simulation results show that the direct sequence pulse binary amplitude modulation (DS-BPAM) UWB systems with the proposed chirp waveforms can achieve excellent NBI suppression performance and outperform the linear chirp waveform based UWB system significantly.
2008 3rd International Conference on Cognitive Radio Oriented Wireless Networks and Communications (CrownCom 2008), 2008
In this paper, based on a new pulse waveform design algorithm of ultra wideband pulse [5], we emp... more In this paper, based on a new pulse waveform design algorithm of ultra wideband pulse [5], we employ this algorithm into a cognitive M-ary code selected direct sequence bipolar pulse amplitude modulation ultra wideband communication system. This M-ary DS-UWB system can utilize the cognitive waveform to realize the high performance and high data rate cognitive communication. The bit error rate performance of the M-ary system with the novel pulse waveform is presented in this paper. The proposed scheme can be realized under different situations with lower interference to primary wireless devices and acceptable system complexity. Further more, through the pulse design, we can also generate some good candidate waveform sets which satisfy the FCC regulation.
EURASIP Journal on Wireless Communications and Networking, 2014
We introduce an opportunistic scheduling to enhance the physical layer security with transmit ant... more We introduce an opportunistic scheduling to enhance the physical layer security with transmit antenna selection (TAS) in multiuser environment. We consider a wireless communication system composed of a single transmitter and multiple legitimate users in the presence of several eavesdroppers with each node having multiple antennas under quasi-static Rayleigh fading channel. The transmitter selects the best transmitting antenna and the best user to maximize signal-to-noise ratio (SNR) at the selected user. The user and eavesdropper can employ either selection combining (SC) or maximal ratio combining (MRC) to combine the received signals. New closed-form expressions for probability of positive secrecy and outage are derived. Moreover, asymptotic analysis reveals the outage diversity gain and array gain for the proposed scheme. The impact of number of users, eavesdroppers, and antennas on secrecy performance are clearly demonstrated with mathematical analysis and numerical results.
2012 International Symposium on Communications and Information Technologies (ISCIT), 2012
ABSTRACT A joint Tomlinson-Harashima (TH) source and multi-relay beamforming design in decode-and... more ABSTRACT A joint Tomlinson-Harashima (TH) source and multi-relay beamforming design in decode-and-forward (DF) relaying systems with relay selection is proposed, which exploits the relationship between QR decomposition (QRD) and Gram- Schmidt orthogonalization (GSO) to jointly optimize the source precoder and relay beamforming vectors of multiple relays. Then we propose a correlation-based approach which leads to a significant reduction of forward overhead information from the source to the selected relays. Finally a “Best-Last” based relay selection approach is proposed which has a performance close to the optimal global relay selection approach with a significantly reduced computational complexity. Simulation results are provided to support the advantages of the proposed schemes.
2008 International Symposium on Communications and Information Technologies, 2008
This paper investigates energy detection based wideband spectrum sensing for dynamic spectrum acc... more This paper investigates energy detection based wideband spectrum sensing for dynamic spectrum access (DSA) systems. The licensed frequency band of interest is resolved into a series of contiguous frequency bins via the FFT engine of the detector. By employing forward consecutive mean excision (FCME) algorithm and exploiting primary user (PU) signal's contiguity in frequency domain, computationally simple pre-processing of raw
2008 Third International Conference on Convergence and Hybrid Information Technology, 2008
Wideband primary user (PU) signal identification approaches based on enhanced forward consecutive... more Wideband primary user (PU) signal identification approaches based on enhanced forward consecutive mean excision (FCME) algorithms are proposed for cognitive MB-OFDM UWB systems. Each single subband is resolved into a series of contiguous frequency bins via the FFT engine. The identification of PU signals can thus be performed in frequency domain with our proposed methods, namely the localization algorithm based on double thresholding with prior one-dimensional median filtering (MF+LAD) and the FCME algorithm with binary integration (FCME+BI). In both strategies, two thresholds are employed in the detection decision making stage to perform the frequency bin cluster based PU signal identification. It is verified through numerical experiments that the two strategies can significantly improve wideband PU signals' bandwidth and signal-to-noise ratio (SNR) estimation accuracies.
2009 9th International Symposium on Communications and Information Technology, 2009
This paper presents the interference of Ultra Wide-Band (UWB) sensor applied in Korea into Wirele... more This paper presents the interference of Ultra Wide-Band (UWB) sensor applied in Korea into Wireless Broad-band (WiBro) system based on Orthogonal Frequency Division Multiplexing (OFDM) using frequency of 2.3 GHz. The Minimum Coupling Loss (MCL) method and Spectrum Engineering Advanced Monte Carlo Analysis Tool (SEAMCAT) are used to evaluate the interference effects of UWB sensor on WiBro. The required minimum allowable distance is determined by MCL method should be 0.15 m when UWB sensor power spectral density (PSD) is -86.4 dBm/MHz in the case of single interferer in indoor environment. For the case of multiple interferers in outdoor environment, when number of active transmitters is 94, SEAMCAT is used to figure out UWB sensor PSD of -89 dBm/MHz below should be required to avoid the interference probability occurring in WiBro mobile station.
ABSTRACT Cognitive radios may operate in practice under various adverse environments. For typical... more ABSTRACT Cognitive radios may operate in practice under various adverse environments. For typical mobile and short-range scenarios, wireless links may tend to be time and frequency selective, i.e., the multipath propagations with time-varying fading coefficients will be inevitable. To cope with the encountered doubly-selective channels, in this paper we present a new spectrum sensing algorithm for distributed applications. First, a dynamic discrete state-space model is established to characterize sensing process, where the occupancy state of primary band and the time-varying multipath channel are treated as two hidden states, while the summed energy is adopted as the observed output. With this new paradigm, spectrum sensing is realized by acquiring primary states and time-dependent multipath channel jointly. For the formulated problem, unfortunately, Bayesian statistical inference may be impractical due to the absence of likelihoods and involved non-stationary distributions. To remedy this problem, an iterative algorithm is further designed by resorting to sequential importance sampling techniques; thus, the dynamic non-Gaussian multipath channel and primary states are estimated recursively. Another critical challenge, e.g., the noise uncertainty, is also considered, which may be incorporated conveniently into this sensing diagram and, furthermore, addressed effectively by the designed algorithm. Simulations validate the proposed algorithm. While classical schemes fail to deal with doubly selective channels, the new sensing scheme can exploit the underlying channel memory and operate well, which provides a great promise to realistic applications.
2008 IEEE International Conference on Ultra-Wideband, 2008
In this paper, we present the space time block codes (STBC) based M-ary code-selected modulation ... more In this paper, we present the space time block codes (STBC) based M-ary code-selected modulation scheme of direct sequence bipolar pulse amplitude modulation (DSBPAM) ultra wideband (UWB) system with selective Rake (SRake) receiver and maximum ratio combining (MRC) over multipath channels in order to improve the system performance and transmission rate of the conventional DS UWB system. The system bit
2010 10th International Symposium on Communications and Information Technologies, 2010
Cooperative multi-cell transmit strategies typically require full channel state information (CSI)... more Cooperative multi-cell transmit strategies typically require full channel state information (CSI) at the base station. Most previous works in this area have assumed that base stations have common knowledge of both data dedicated to all terminals and full or partial CSI of all links. In this paper, a more practical limited-feedback scenario is studied for multi-cell joint beamforming. The proposed algorithm provides higher sum rates over the virtual SINR one.
2008 4th International Conference on Wireless Communications, Networking and Mobile Computing, 2008
Wireless Relaying is one of the promising solutions to overcome the channel impairments and provi... more Wireless Relaying is one of the promising solutions to overcome the channel impairments and provide high data rate coverage that appears for beyond 3G mobile communications. In this paper we present an end to end BER performance analysis of dual hop wireless communication systems equipped with multiple Decode and Forward relays over the Rayleigh fading channel with relay selection. We select the best relay based on end to end channel conditions. We apply Orthogonal Space Time Block coding (OSTBC) at source, and also present how the multiple antennas at the source terminal affects the end to end BER performance. This intermediate relay technique will cover long distance where destination is out of reach from source.
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Papers by Kyung Sup Kwak