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ABSTRACT: Cognitive radio devices will be able to seek and dynamically use frequency bands for network access. This will be done by autonomous detection of vacant sub-bands in the radio spectrum. In this paper, we propose a new method for blind detection of vacant sub-bands over the spectrum band. The proposed method exploits model selection tools like Akaike information criterion (AIC) and Akaike weights to sense holes in the spectrum band. Specifically, we assume that the noise of the radio spectrum band can still be adequately modeled using Gaussian distribution. We then compute and analyze Akaike weights in order to decide if the distribution of the received signal fits the noise distribution or not. Our theoretical result are validated using experimental measurements captured by Eurecom RF Agile Platform. Simulations show promising performance results of the proposed technique in terms of sensing vacant sub-bands in the spectrum.
Cognitive Radio Oriented Wireless Networks and Communications, 2008. CrownCom 2008. 3rd International Conference on; 06/2008
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ABSTRACT: Motivated by the desire for efficient spectral utilization, we present a novel algorithm for power allocation for sum rate maximization in cognitive radio context while preserving a guaranteed QoS for the primary network. To this effect, we propose a distributed cognitive radio coordination that maximizes the cognitive radio network (CRN) sum rate while minimizing the interference to the primary users (PU). Our goal is to realize spectrum sharing by optimally allocating secondary users (SU) transmit powers in order to maximize the total SU throughput under interference and noise impairments. Both theoretical and simulation results under realistic wireless network settings are shown to exhibit interesting features in term of CRN deployment while maintaining QoS for the primary system.
Cognitive Radio Oriented Wireless Networks and Communications, 2008. CrownCom 2008. 3rd International Conference on; 06/2008
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ABSTRACT: In this contribution , we investigate the idea of using cognitive radio to reuse locally unused spectrum to increase the total system capacity. We consider a multiband/wideband system in which the primary and cognitive users wish to communicate to different receivers, subject to mutual interference and assume that each user knows only his channel and the unused spectrum through perfect sensing. Under this scheme, a cognitive radio will listen to the channel and, if sensed idle, will transmit during the voids. We impose the constraint that users successively transmit over available bands through proper water filling. Within this setting, we derive the total spectral efficiency of the cognitive radio system as well as the spectral efficiency gains and prove that we can improve the overall system spectral efficiency by considering cognitive communications in the system.
Global Telecommunications Conference, 2007. GLOBECOM '07. IEEE; 12/2007
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ABSTRACT: In this work, we study fundamental limitation to the performance of time-delay estimation schemes of IR-UWB signals. We are specially interested in deriving lower bound on the mean square error (MSE). As UWB systems are expected to operate at low signal-to-noise ratio (SNR) (80211.15.4 low-power low rate standard), the improved Ziv-Zakai lower bound (IZZLB) [1] is then more suited to characterize the lower bound on the MSE, than the Cramer-Rao lower bound (CRLB). We express then the lower bound on MSE of maximum likelihood estimator based on perfect knowledge of the 2nd order statistics of the received signal by mean of the IZZLB.
Signals, Systems and Computers, 2007. ACSSC 2007. Conference Record of the Forty-First Asilomar Conference on; 12/2007
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ABSTRACT: Future mobile terminals will be able to communicate with various heterogeneous systems which are different by means of the algorithms used to implement baseband processing and channel coding. This represents many challenges in designing flexible and energy efficient architectures. Using the sensing phase, the mobile can sense its environment and detect the spectrum holes and use them to communicate. Current research are investigating different techniques of using cognitive radio to reuse locally unused spectrum to increase the total system capacity. They aim also to develop efficient algorithm able to maximize the quality of service (QoS) for the secondary (unlicensed) users while minimizing the interference to the primary (licensed) users. However, there are many challenges across all layers of a cognitive radio system design, from its application to its implementation.
Signals, Systems and Computers, 2007. ACSSC 2007. Conference Record of the Forty-First Asilomar Conference on; 12/2007
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ABSTRACT: This work presents a simple and realistic UWB channel model based on physical propagation effects and UWB channel measurements conducted at Eurecom. A mathematical description of the model is discussed and the corresponding parameters extraction is presented. This model is described entirely by a set of four parameters, namely the number of MPCs, the MPC amplitude, the MPC delay and the MPC decay constant. These parameters are extracted using SAGE algorithm. It presents a good fit to measurement data and is easy to implement.
Communications and Networking in China, 2007. CHINACOM '07. Second International Conference on; 09/2007
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ABSTRACT: In this paper, we investigate the idea of using cognitive radio to reuse locally unused spectrum for communications. We consider a multiband/wideband system with two users in which the primary (licensed) user and the secondary (cognitive) user wish to communicate to the base station, subject to mutual interference. We introduce the notion of the virtual noise-threshold which represents a proxy for the primary user to allow cognitive communications. We determine, under the assumption that each user knows only his own channel, the acceptable interference level within a given quality of service. Moreover, we obtain a characterization of the distributed power allocation for each user, as well as the resulting virtual noise threshold. We prove that a cognitive user can vary its transmit power in order to maximize the sum capacity while maintaining a guarantee of service to the primary user.
Signal Processing and Its Applications, 2007. ISSPA 2007. 9th International Symposium on; 03/2007
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ABSTRACT: Ultra-wideband (UWB) has been recently presented as a promising radio technology due to the large bandwidth available. This feature enables point to point high data rates at short range as well as high temporal resolution with long channel impulse responses (CIR). Due to the their large bandwidth, UWB systems enables high temporal resolution with long CIR. In this paper, we evaluate an original multiple access scheme called channel division multiple access (ChDMA), where we use the CIR as a user signature. The signature code is given by the channel and the users are separated by their position: this signature is uniquely determined by the user's position, which changes from one position to another. This signature location- dependent property provides decentralized flexible multiple access as the codes are naturally generated by the radio channel. The framework is analyzed and validated by capacity assessments using UWB measurements performed at Eurecom and compared with classical CDMA schemes with random spreading codes. The analysis is focused on the impact of the user's asynchronism and the period of symbol on system performance. Two structures are considered at the receiver: single-user matched filter and MMSE receiver with Gaussian and BPSK signaling schemes.
Vehicular Technology Conference, 2006. VTC-2006 Fall. 2006 IEEE 64th; 10/2006
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ABSTRACT: UWB systems were presented as a promising radio technology. Because of their large bandwidth, these networks are supposed able to deliver high data rates at short ranges. This motivates the work presented in this paper where we analyze UWB channel behavior based on path model derived from physical approach. We will show then the impact of large bandwidth on path impulse response time dispersion due to physical phenomena like reflection and diffraction. Afterwards, we will propose a new UWB channel model based on previous physical analysis.
Telecommunications, 2006. AICT-ICIW '06. International Conference on Internet and Web Applications and Services/Advanced International Conference on; 03/2006
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ABSTRACT: In this paper, we apply Akaike information criterion (AIC) and minimum description length (MDL) to estimate the number of degrees of freedom (DoF) of an ultra-wide band channel (UWB) in an indoor environment. We evaluate our solution under both scenarios, line-of-sight (LOS) and non-line-of-sight (NLOS). Based on AIC and the MDL criterion, we find that this number is large; this has important consequences on the receiver design. We show also, that in opposition to the accepted idea in the literature, the number of DoF does not increase linearly with the channel bandwidth.
Vehicular Technology Conference, 2005. VTC 2005-Spring. 2005 IEEE 61st;
