Optimized spectrum sensing algorithms for cognitive LTE femtocells
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RESEARCH
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Optimized spectrum sensing algorithms for cognitive LTE femtocells Mahmoud A Abdelmonem*, Mohammed Nafie, Mahmoud H Ismail and Magdy S El-Soudani
Abstract In this article, we investigate to perform spectrum sensing in two stages for a target long-term evolution (LTE) signal where the main objective is enabling co-existence of LTE femtocells with other LTE femto and macrocells. In the first stage, it is required to perform the sensing as fast as possible and with an acceptable performance under different channel conditions. Toward that end, we first propose sensing the whole LTE signal bandwidth using the fast wavelet transform (FWT) algorithm and compare it to the fast Fourier transform-based algorithm in terms of complexity and performance. Then, we use FWT to go even deeper in the LTE signal band to sense at multiples of a resource block resolution. A new algorithm is proposed that provides an intelligent stopping criterion for the FWT sensing to further reduce its complexity. In the second stage, it is required to perform a finer sensing on the vacant channels to reduce the probability of collision with the primary user. Two algorithms have been proposed for this task; one of them uses the OFDM cyclic prefix for LTE signal detection while the other one uses the primary synchronization signal. The two algorithms were compared in terms of both performance and complexity. 1. Introduction Spectrum scarcity has become one of the serious problems facing the wireless communications regulatory bodies especially when the wireless applications and standards are increasing significantly. At the same time, a recent study by the United States Federal Communications Commission (FCC) shows that most of the allocated spectrum in the US is under-utilized [1]. Cognitive radio (CR) technology enables other secondary users to co-exist with the primary users of a wireless system and to make use of the non-utilized portions of the spectrum, also known as the white spaces, thus making a more efficient utilization of the spectrum [2-4]. One of the most recent wireless standards, where the use of CR is possible, is the long-term evolution (LTE) used for broadband wireless access. LTE could provide data rates up to 100 Mbps in the downlink and 50 Mbps in the uplink in a 20-MHz bandwidth; thanks to its powerful physical layer which uses orthogonal frequency division multiple access (OFDMA), multi-input multi-output technology as well as advanced channel coding techniques [5]. * Correspondence: [email protected] Department of Electronics and Communications Engineering, Faculty of Engineering, Cairo University, Giza 12613, Egypt
Within the context of LTE, CR technology can possibly be used when femtocells are deployed. These are autonomous small cellular base stations designed for use in subscribers’ homes and small business environments. They radiate very low power (< 10 mW) and can typically support two to six simultaneous mobile users [6,7]. Recently, femtocells have attracted strong interest within the
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