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More than an adaptive system, the cognitive radio system should be a kind of intelligent system. In the paper, a Q-learning algorithm of the intelligent control theory is adopted to solve the sensing task selection problem among cognitive radio users in the distributed cognitive radio networks. In the proposed scheme, each cognitive radio user selects its sensing task through times of interaction...
In this paper, we develop a distributed cooperative spectrum sensing algorithm based on network code to decrease the need for bandwidth in cognitive radios. The model of the distributed cooperative spectrum sensing is analyzed, and the algorithm of distributed scheme based on network code is described. The simulation results show that compared with the distributed scheme without network code and the...
From the mathematic expression, we can see that sidelobe power of multi-band orthogonal frequency-division multiplexing (MB-OFDM) signal is a function of the data symbols loaded on the sub-carriers. Through the derivation of the minimum of the function, relationships among data symbols, which help to suppress sidelobes, are obtained. Two types of methods, referred as sub-carrier adding (SA) method...
Spectrum sensing is the key enabling technology for cognitive radio networks. The main objective of the spectrum sensing is to provide more spectrum access opportunities to cognitive radio (CR) users without interfering with the licensed users. In this paper, we propose a half-voting based twice-cooperative spectrum sensing scheme. Simulation results show that the proposed sensing method can achieve...
Cognitive radio technology has arisen as a hot topic in wireless communication in recent years. Special spectrum allocation algorithms are essential to adapt to the time-space varying characteristics of wireless spectrum in cognitive networks. In this paper, we study and simulate the guard channel policy proposed by Huang Zhen, etc. We find that the blocking probability of secondary users is relatively...
Spectrum sensing is a key technology in cognitive radio (CR) and cooperative spectrum sensing is derived due to the effects of channel fading. In this paper, we focus on the optimal number of secondary users in cooperative spectrum sensing to maximize the utility in CR network. By considering both the detection error probability and the resource used by the secondary users in cooperation, we derive...
Cognitive radio network technology brings a novel approach to share the open spectrum flexibly and efficiently. However, how to further improve the network construction for reducing the redundant information has become the hot topic. Minimum independent dominating set (MIDS) in graphs is a classic problem in operations research with important application in network construction design. The single...
Cooperative spectrum sensing enables a Cognitive Radio (CR) networks to reliably detect primary users and avoid causing interference to primary user's communications, and data fusion technique is a key component of it. However, when the number of CR users tends to be large, the bandwidth for reporting their sensing results to the fusion center will be very enormous. In this paper, censoring schemes...
The use of ldquocognitive radiordquo (CR) technology is viewed as the key technology to fully utilize the bandwidth. In this paper, a CR-based dynamic spectrum access (DSA) device named fuzzy active period adaptor (FAPA) is proposed in a downlink transmission of IEEE 802.16h systems. FAPA decides the active period of IEEE 802.16h system to efficiently coexist with a WLAN system in unlicensed spectrum...
Spectrum sensing is a critical phase in building a cognitive radio network. However, when the number of cognitive user is very large, the bandwidth for reporting cognitive users' sensing results will be insufficient. In this paper, we propose a new cooperative spectrum sensing algorithm to alleviate the bandwidth problem of reporting channel. Compared with conventional method, only the cognitive users...
In this paper, designing channel sensing policies for cognitive radio networks is discussed. A discrete-time semi- Markov channel model is first introduced, which facilitates the analysis on more general channel occupancy behaviors and possible asynchronism among primary and secondary users. Based on the characteristics of the channels at the stationary state, multiple channel sensing policies have...
This paper presents queueing analysis of opportunistic access in cognitive radios. The primary (licensed user) has priority over the secondary user and it does not need to care about the secondary user transmissions. A time slotted system is assumed, so that the secondary user can perform spectrum sensing at the beginning of the slot to know if it is occupied by primary or not. If the slot is free,...
Slotted Aloha is an effective random access protocol and can also be an important element of more advanced media access protocols. This paper investigates slotted Aloha in a cognitive radio environment where one access point provides services for both primary users and secondary users. Considering packet capture effects in a Rayleigh fading channel, we present the mathematic derivations of system...
In cognitive radio systems, as the sensing ability of single cognitive user is limited, the opportunistic spectrum access has to allow different cognitive users to cooperatively search for and exploit instantaneous spectrum availability. In this paper, we address the design of opportunistic spectrum access for cognitive radio system employing cooperative spectrum sensing. The opportunistic spectrum...
Spectrum sensing is an essential mechanism in a cognitive radio network. However, the detection performance will be greatly degraded when few untrusted secondary users exist which can be identified as 'Always Yes' users and 'Always No' users. In this paper, we propose an energy detector with double thresholds combined with revised data fusion rules to find these untrusted users and counteract their...
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