Current Issue : April - June Volume : 2012 Issue Number : 2 Articles : 5 Articles
Cognitive radio (CR) engines often contain multiple system parameters that require careful tuning to obtain\r\nfavorable overall performance. This aspect is a crucial element in the design cycle yet is often addressed with ad\r\nhoc methods. Efficient methodologies are required in order to make the best use of limited manpower, resources,\r\nand time. Statistical methods for approaching parameter tuning exist that provide formalized processes to avoid\r\ninefficient ad hoc methods. These methods also apply toward overall system performance testing. This article\r\nexplores the use of the Taguchi method and orthogonal testing arrays as a tool for identifying favorable genetic\r\nalgorithm (GA) parameter settings utilized within a hybrid case base reasoning/genetic algorithm CR engine\r\nrealized in simulation. This method utilizes a small number of test cases compared to traditional design of\r\nexperiments that rely on full factorial combinations of system parameters. Background on the Taguchi method, its\r\ndrawbacks and limitations, past efforts in GA parameter tuning, and the use of GA within CR are overviewed.\r\nMultiple CR metrics are aggregated into a single figure-of-merit for quantification of performance. Desirability\r\nfunctions are utilized as a tool for identifying ideal settings from multiple responses. Kiviat graphs visualize overall\r\nCR performance. The Taguchi method analysis yields a predicted best combination of GA parameters from nine\r\ntest cases. A confirmation experiment utilizing the predicted best settings is compared against the predicted mean,\r\nand desirability. Results show that the predicted performance falls within 1.5% of the confirmation experiment\r\nbased on 9 test cases as opposed to the 81 test cases required for a full factorial design of experiments analysis....
In this article, we analyze the packet transmission time in spectrum sharing systems where a secondary user (SU)\r\nsimultaneously accesses the spectrum licensed to primary users (PUs). In particular, under the assumption of an\r\nindependent identical distributed Rayleigh block fading channel, we investigate the effect of the peak interference\r\npower constraint imposed by multiple PUs on the packet transmission time of the SU. Utilizing the concept of\r\ntimeout, exact closed-form expressions of outage probability and average packet transmission time of the SU are\r\nderived. In addition, employing the characteristics of the M/G/1 queuing model, the impact of the number of PUs\r\nand their peak interference power constraint on the stable transmission condition and the average waiting time of\r\npackets at the SU are examined. Moreover, we then extend the analysis for point-to-point to point-to-multipoint\r\ncommunications allowing for multiple SUs and derive the related closed-form expressions for outage probability\r\nand successful transmission probability for the best channel condition. Numerical results are provided to\r\ncorroborate our theoretical results and to illustrate applications of the derived closed-form expressions for\r\nperformance evaluation of cognitive radio networks....
In this paper, we propose two time of arrival estimators for ultra wideband signals based on the phase difference\r\nbetween the discrete Fourier transforms (DFT) of the transmitted and received signals. The first estimator is based\r\non the slope of the unwrapped phase and the second one on the absolute unwrapped phase. We derive the\r\nstatistics of the unwrapped phase. We show that slope-based estimation almost achieves asymptotically the\r\nbaseband Cramer-Rao lower bound (CRLB), while the absolute-phase-based estimator achieves asymptotically the\r\npassband CRLB. We compare the proposed estimators to the time-domain maximum likelihood estimator (MLE).\r\nWe show that the MLE achieves the CRLB faster than the DFT-based estimator, while the DFT-based estimator\r\noutperforms the MLE for low signal to noise ratios. We describe also how to use the proposed estimators in\r\nmultipath UWB channels....
In this article, we investigate to perform spectrum sensing in two stages for a target long-term evolution (LTE)\r\nsignal where the main objective is enabling co-existence of LTE femtocells with other LTE femto and macrocells. In\r\nthe first stage, it is required to perform the sensing as fast as possible and with an acceptable performance under\r\ndifferent channel conditions. Toward that end, we first propose sensing the whole LTE signal bandwidth using the\r\nfast wavelet transform (FWT) algorithm and compare it to the fast Fourier transform-based algorithm in terms of\r\ncomplexity and performance. Then, we use FWT to go even deeper in the LTE signal band to sense at multiples of\r\na resource block resolution. A new algorithm is proposed that provides an intelligent stopping criterion for the\r\nFWT sensing to further reduce its complexity. In the second stage, it is required to perform a finer sensing on the\r\nvacant channels to reduce the probability of collision with the primary user. Two algorithms have been proposed\r\nfor this task; one of them uses the OFDM cyclic prefix for LTE signal detection while the other one uses the\r\nprimary synchronization signal. The two algorithms were compared in terms of both performance and complexity....
This article presents a spectrum sensing algorithm for wideband cognitive radio exploiting sensed spectrum\r\ndiscontinuity properties. Some work has already been investigated by wavelet approach by Giannakis et al., but in\r\nthis article we investigate an algebraic framework in order to model spectrum discontinuities. The information\r\nderived at the level of these irregularities will be exploited in order to derive a spectrum sensing algorithm. The\r\nnumerical simulation show satisfying results in terms of detection performance and receiver operating\r\ncharacteristics curves as the detector takes into account noise annihilation in its inner structure....
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