Haleh Hosseini

Proactive integrated handoff management in cognitive radio mobile ad hoc networks

In cognitive radio networks, the secondary users (SUs) switch the data transmission to another empty spectrum band to give priority to primary users (PUs). In this paper, channel switching in cognitive radio mobile ad hoc networks (CR-MANETs) through an established route is modeled. The probability of channel availability in this route is calculated based on the PUs activity, SUs mobility, and channel heterogeneity. Based on the proposed model, the channel and link availability time are predicted. These predictions are used for channel assignment in the proposed channel allocation scheme. A handoff threshold as well as a life time threshold is used in order to reduce the handoff delay and the number of channel handoffs originating from the short channel usage time. When the channel handoff cannot be done due to the SUs mobility, the local flow handoff is performed to find an appropriate node in the vicinity of a potential link breakage and transfer the current data flow to it. The local flow handoff is performed to avoid possible flow disruption and also to reduce the delay caused by the link breakage. The study reveals that the channel heterogeneity and SUs mobility must be considered as important factors, which affect the performance of the handoff management in the CR-MANETs. The results emphasize on the improvement of the route maintenance probability after using the local flow handoff. It is also stated that the amounts of handoff requirement and handoff delay are decreased after using the predicted channel usage life time and handoff threshold time.

Efficient In-Band Spectrum Sensing Using Swarm Intelligence for Cognitive Radio Network

Spectrum sensing mechanisms enable cognitive radio networks to detect primary users (Upsi) and utilize spectrum holes for secondary user (SU) transmission. However, precise PU detection leads to longer sensing time and lower achievable throughput. In this paper, we propose a particle swarm optimization (PSO)-based scheme for an in-band local spectrum sensing to address the tradeoff between sensing time and throughput. Using methodological analysis, a fast convergence PSO (FC-PSO) scheme is derived by implementing a distribution-based stopping criterion subject to detection performance, optimization time, and SU gain. At the target probability of detection of at least 90%, the results show significant improvements of ~45% for sensing time, 70% for the probability of false alarm, and 12% for achievable throughput compared with nonoptimal sensing scheme at signal-to-noise ratio of 0 dB. FC-PSO also outperforms other optimization schemes in terms of convergence speed. The proposed scheme is proved to be an energy-efficient solution for practical implementation as it outperforms the other algorithms in terms of lower computational complexity as well as providing the best tradeoff values in meeting the objective function of sufficient opportunistic access for an SU under optimized sensing time for maximized throughput, while providing high protection to the PU.

Performance analysis of Doppler shift effects on OFDM-based and MC-CDMA-based cognitive radios

The present development of high data rate wireless applications has led to extra bandwidth demands. However, finding a new spectrum bandwidth to accommodate these applications and services is a challenging task because of the scarcity of spectrum resources. In fact, the spectrum is utilized inefficiently for conventional spectrum allocation, so Federal Communications Commission has proposed dynamic spectrum access mechanism in cognitive radio, where unlicensed users can opportunistically borrow unused licensed spectrum, which is a challenge to obtain contiguous frequency spectrum block. This also has a significant impact on multicarrier transmission systems such as orthogonal frequency division multiplexing OFDM and multicarrier code division multiple access MC-CDMA. As a solution, this paper develops non-contiguous OFDM NC-OFDM and non-contiguous MC-CDMA NC-MC-CDMA cognitive system. The implementation of NC-OFDM and NC-MC-CDMA systems provides high data rate via a large number of non-contiguous subcarriers without interfering with the existing transmissions. The system performance evaluates NC-OFDM and NC-MC-CDMA for mobile scenario where each propagation path will experience Doppler frequency shift because of the relative motion between the transmitter and receiver. The simulation results of this paper proved that NC-OFDM system is a superior candidate than NC-MC-CDMA system considering the mobility for cognitive users. Copyright

Compressed Wavelet Packet-Based Spectrum Sensing With Adaptive Thresholding for Cognitive Radio

Cognitive radio is a system to utilize spectrum holes efficiently as a solution of spectrum scarcity. The availability of channels for secondary users is determined in the spectrum sensing phase by energy detection. Energy levels of sampled primary users (PUs) signal can be measured by wavelet transform with more accuracy compared with Fourier-based methods. Wavelet packet-based spectrum sensing measures the energy level at each subcarrier and sets the decision threshold. However, at the first step of energy detection for wideband spectrum sensing, high-rate analog-to-digital converter (ADC) sampling requires a large dynamic range and high-speed signal processors. In this paper, compressed sampling for PUs signal acquisition is proposed to reduce the rate of sampling and solve the implementation complexity of ADC. The simulation results verify that this mechanism is promising to estimate the power spectrum density (PSD) of PUs signals. The graphs prove low side-lobes of the detected PSD and acceptable probability of detection and false alarm due to the target values and certain compression ratio.

Wavelet Packet-Based Transceiver for Cognitive UWBÉmetteur-récepteurà base de paquet d'ondelette pour les applications cognitives UWB

Wideband spectrum in cognitive ultrawideband (UWB) is subjected to interference from licensed users although it consumes lower power. Wavelet packet transform is an alternative to Fourier transform with higher flexibility and spectrum utilization. In this paper, a wavelet packet-based transceiver is designed for cognitive UWB to improve robustness against interference from primary users. The proposed transceiver consists of two main components: 1) wavelet packet multicarrier modulation (WPMCM) for data transmission and 2) wavelet packet-based spectrum sensing (WPSS). In the transceiver, the presence of the primary user is sensed via WPSS with adaptive thresholding. Then, the WPMCM signal is transmitted over the detected unoccupied channels. The simulation results show interference reduction due to lower sidelobes level of power spectrum density compared with the Fourier-based system. Significant performance enhancement has been achieved in terms of probability of detection, probability of false alarm, and bit-error rate over UWB channels.

Study on multiband UWB system via WPMCM in the context of cognitive radio

Cognitive radio (CR) introduces the opportunistic usage of frequency bands and Orthogonal frequency division multiplexing (OFDM) is a strong candidate for CR design. Ultra wideband (UWB) radio fulfills some of the key cognitive radio requirements. Regarding the power limitations for UWB systems the main challenging issue is the impact of narrowband interference (NBI). Wavelet packet transform (WPT) is a possible choice for designing OFDM systems and has been shown as a solution to reduce interference. In this research, we explain the benefits of WPT from the literature, compare wavelet packet based MCM (WPMCM) for multiband UWB with its conventional version, and provide analytic schemes and block diagrams to implement proposed system.

CSI Feedback Model in the Context of Adaptive Cognitive Radio Systems

Cognitive radio has the ability to sense the environment and adapt its behavior to optimize communication features, such as quality of service in the presence of interference and noise. In physical layer to achieve this goal, different phases of sensing, channel estimation, and configuration selection are necessary. The sensing part measures the interference level, recognize the spectrum holes, and send this information to Channel estimator. In the next step, channel state information (CSI) is used for data detection and also sent to the transmitter through a limited feedback. CSI feedback consists of achievable rate, SNR value, modulation or coding schemes (MCS). Feedback link improves the system performance in the cost of complexity and delay. In this paper, we present and compare different feedback schemes for cognitive radio and study the channel capacity when an imperfect feedback link is corrupted by noise and delay.

Dynamic Spectrum Access (DSA) for multimedia application

With the rapid growth of wireless multimedia applications over the wireless Internet in recent years, the demand for radio spectral resources has increased significantly. In order to meet the quality of service, delay, and large bandwidth requirements, various techniques such as source and channel coding, distributed streaming, multicast have been considered. In this paper, we propose a technique for multimedia transmission over the secondary user network, which uses Dynamic Spectrum Access (DSA). Sensing the radio frequency environment and avoiding busy channel by hopping to vacant channel are the major part in DSA. We address the impact of this technique to multimedia data such as audio signal and image since random hopping and different rate of hopping from one channel to another channel may influence the signal quality. With the help of Software Defined Radio (SDR), we have adopted a flexible and reconfigurable platform for this project. Simulation results are presented based on the received data transmitted through this mechanism.

Compensation of link distortion for cognitive WPMCM UWB system

Cognitive radio performs efficient utilization of available communication resources. Cognitive ultra wideband (UWB) system is a tempting candidate for short range and high data rate communication with low cost, and low power consumption. Wavelet packet based multicarrier modulation (WPMCM) UWB has inherent potential to fulfill cognitive radio requirements. In this research, we survey the literature on cognitive radio sensing mechanism in the presence of distortion and propose a novel link effect compensation accompanied by power loading, to mitigate the effects of interference from primary signal. Wavelet transform is used for spectrum sensing, and Lagrange multiplier applied for power allocation to minimize the bit error rate at the receiver. System performance is investigated by MATLAB to compare the system under different UWB channel models