Jae Moung Kim

Spectral correlation based signal detection method for spectrum sensing in IEEE 802.22 WRAN systems

In this paper, signal detection methods for spectrum sensing in IEEE 802.22 wireless RAN systems are discussed. As most of the manmade signals can be treated as a cyclostationary random process, the spectral correlation function is effective for the detection of these signals. In WRAN systems, due to the specific detection environment, the computational complexity of the spectral correlation based method is significantly reduced. Peak detection in the high SNR environment together with contour figure based unique patterns search method in the low SNR environment are proposed for the primary user signal detection

An Alternative Energy Detection Using Sliding Window for Cognitive Radio System

Cognitive radio is one of the most effective techniques to improve the spectrum utilization efficiency. To implement the cognitive radio, spectrum sensing is considered as the key functionality because secondary users should identify the spectrum holes and utilize them efficiently without causing interference to primary users. In generally, there are three major spectrum sensing methods, including matched filter, energy detection and feature detection. The most common and simplest method is energy detection. However, the conventional energy detection suffers from large degradation in performance under low SNR environment. In this paper, we proposed alternative energy detection which can estimate the exact power of primary user without the noise effect and lead to the better performance. In order to reduce the effect of noise fluctuation, the sliding window function is utilized to assist the proposed detector. The simulation result shows that our proposed method outperform conventional one.

HMM-based Adaptive Frequency-Hopping Cognitive Radio System to Reduce Interference Time and to Improve Throughput

Cognitive Radio is an advanced enabling technology for the efficient utilization of vacant spectrum due to its ability to sense the spectrum environment. It is important to determine accurate spectrum utilization of the primary system in a cognitive radio environment. In order to define the spectrum utilization state, many CR systems use what is known as the quiet period (QP) method. However, even when using a QP, interference can occur. This causes reduced system throughput and contrary to the basic condition of cognitive radio. In order to reduce the interference time, a frequency-hopping algorithm is proposed here. Additionally, to complement the loss of throughput in the FH, a HMM-based channel prediction algorithm and a channel allocation algorithm is proposed. Simulations were conducted while varying several parameters. The findings show that the proposed algorithm outperforms conventional channel allocation algorithms.

Improved Resource Allocation Scheme in LTE Femtocell Systems based on Fractional Frequency Reuse

Femtocells provide high quality indoor communications with low transmit power. However, when femtocells are applied in cellular systems, a co-channel interference problem between macrocells and femtocells occurs because femtocells use the same spectrum as do the macrocells. To solve the co-channel interference problem, a previous study suggested a resource allocation scheme in LTE cellular systems using FFR. However, this conventional resource allocation scheme still has interference problems between macrocells and femtocells near the boundary of the sub-areas. In this paper, we define an optimization problem for resource allocation to femtocells and propose a femtocell resource allocation scheme to solve the optimization problem and the interference problems of the conventional scheme. The evaluation of the proposed scheme is conducted by System Level Simulation while varying the simulation environments. The simulation results show that the proposed scheme is superior to the conventional scheme and that it improves the overall performance of cellular systems.

Spectrum sensing method for increasing the spectrum efficiency in wireless sensor network

As the spectral recourses are limited, the spectrum efficiency is more important for the design of wireless sensor network. In this paper, a spectral correlation based detection method for spectrum sensing is proposed to increase the spectrum efficiency in wireless sensor network. The signal of interests is modeled as a cyclostationary random process, therefore, the spectral correlation function could be used, and a squared coherence function is used as the decision criterion. Simulations are made based on the 4-FSK signal. The results verify that the proposed method outperforms the conventional energy detection.

Dynamic frequency selection in OFDMA

In an OFDM system, dynamic frequency selection is an approach to efficiently improve the spectrum usage. According to the channel magnitude response, each user selects the subcarriers with the highest channel gain. The existing algorithm divides the whole subcarriers into partitions, and each user selects one for simplicity. To get better performance, a larger number of partitions with less subcarriers is needed. The existing algorithm is modified by increasing the successful allocation probability to allocate more partitions to each user. And to guarantee cooperation among users, the higher priority to allocate is given to the user which has the largest amount of deep fading partitions

A Cognitive UWB Testbed Employing Adaptive Pulse Generation

Ultra wideband (UWB) is an promising underlying method for coexistence among different systems. However, the performance may not be as good as expected due to the changing spectrum environment. Thus, cognitive UWB radio is proposed by taking the advantage of cognition, which enables the radio to learn the spectrum environment by itself. In this paper, we explore a cognitive UWB testbed in physical layer, including cognitive pulse generator, stream view and performance evaluation. In order to protect the potential narrowband systems, the specific mask and channel information are utilized to adapt the system parameters with the help of pulse mask code and pulse generation block. Simulation results show that the proposed testbed is capable to generate the adaptive pulse that suitable for different spectrum environment.

The spectrum sensing algorithm using the soft decision algorithm in cognitive UWB system

In this paper, sensing algorithms to select the available sub-bands in the cognitive UWB system are proposed; grouped time division sensing technique and decision methods for sub-channel selection. We employ energy detection method for spectrum sensing, which has low complexity in the wide spectrum sensing. Grouped time division sensing technique is proposed to transmit training symbols and to measure the interference level of sub-bands efficiently. It simplifies the procedure of spectrum sensing, because this scheme requires less number of sensing blocks in receiver. Finally, the decision methods, hard and soft decision, are proposed and compared. Proposed sensing algorithms in this paper can provide wider application of cognitive UWB system and smarter service in coexisting with other wireless system.

Cognitive Radio in Multiple-Antenna Systems

This chapter presents an overview of the techniques used in a multiple-antenna 1 system and discusses the key issues in introducing cognitive radio (CR) technology. This discussion is followed by an explanation of the applications of the new system, which combines CR and multiple-antenna (MA) techniques. This chapter discusses the issues that combine the MA system with CR technology to increase the utilization of spectrum by sharing the spectrum among different systems as well as to improve the transmission efficiency by selecting the optimum transmission schemes under certain operational environments. It introduces the new functionalities, namely, radio environment observation and cognitive engine, in the MA system by adding cognitive capability. In such a system, besides signal detection and identification, the DOA and antenna correlation information should be obtained with the help of multiple antennas. By combining the environmental information, CE is able to select an optimum operation mode for the radio, depending on the related position between the primary units (PUs) and secondary units (SUs).

UWB Interference Mitigation by Detecting the Passive Receiver

[Abstract] UWB is one of the promising solutions for next generation wireless communication. With the help of Cognitive Radio, UWB system can effectively avoid the possible interference to primary equipment s. However, th is method can not be applied if satellite system operating in the same area , due to the characteristics of passiv e receivers. In this paper, we propose a method to recognize the existence of the active primary user terminals in the operation area by detecting the LO signal which is re -transmitted by satellite receiver with a proposed structure in passive receivers, w here the LO signal containing carrier information is amplified and couples back through another antenna. The simulation results show that the proposed method can identify the existence of satellite system with very high probability .