Blind Source Separation-based Full-Duplex Cognitive Radio A. Nasser *‡ , A. Mansour † , K.-C. Yao * , H. Assaf ‡ and H. Abdallah ‡ * LABSTICC, ENSTA Bretagne, 2 Rue Franc ¸ois Verny, 29806 Brest, France † LABSTICC, UBO, 6 Avenue le Gorgeu, 29238 Brest, France ‡ Faculty of Science, American University of Culture and Education (AUCE), Beirut, Lebanon Email: abbass.nasser@ensta-bretagne.fr, mansour@ieee.org, koffi-clement.yao@univ-brest.fr haniabdallah@auce.edu.lb, hassanassaf@auce.edu.lb Web Page: www.lab-sticc.fr; www.auce.edu.lb; ali.mansour.free.fr Abstract—Full-Duplex has been emerged in Cognitive Radio Network in order to avoid the silence period of the Secondary User (SU) during the Spectrum Sensing. SU should monitor the Primary User (PU) activities in order to avoid any harmful interference. The conventional Full-Duplex Cognitive Radio (FD- CR) systems are based on the Self-Interference Cancellation, where a problem of Residual Self-Interference and Hardware Imperfections leads to an important loss in the detection perfor- mance. In this paper, we develop spectrum sensing techniques for FD-CR based on the Blind Source Separation (BSS). In BSS, multi receiving antennas are required to detect the presence of the Primary User (PU) signal without the need for a silence period during the spectrum sensing. This fact enhances the data rate of the SU. In addition, this algorithms do not require any priori knowledge about the SU or the PU signal. Experimental results show that in addition to eliminating the silence period, the performance of our developed algorithms based on BSS outperforms the classical spectrum sensing Energy Detector (ED). Keywords—Cognitive Radio, Spectrum Sensing, Blind Source Separation, Full-Duplex, Half-Duplex I. I NTRODUCTION In classical Cognitive Radio (CR) system, Primary User (PU) and Secondary User (SU) can share the same frequency band but not simultaneously. SU can operate on this frequency band only when PU is absent in order to avoid any interference. For this reason, SU should monitor the PU activity continu- ously by performing the Spectrum Sensing. Spectrum Sensing provides CR with the PU status: active or idle. During the Spectrum Sensing, SU stops the transmission in order to do not affect the sensing decision by the Self-Interference (SI). For this reason, classical CR is called Half-Duplex CR (HD- CR) in which the activity period of SU can be divided into two slots, the first one is allocated to the Spectrum Sensing and the second one for the transmission. In the first slot when SU detects a PU transmission, then SU should immediately vacate the channel, else, SU continues to the second slot and operates on the channel. The silent period of SU during the Spectrum Sensing period affects the SU data rate [1], [2]. Full-Duplex Cognitive Radio (FD-CR) has been recently pro- posed as a promising solution to cancel the silent period of the Secondary User (SU) [1], [3], [4], [5], [6], [2]. Based on the recent advances in the Self-Interference Cancellation (SIC) [7], FD-CR has gained a lot of attention during the last years. FD-CR concerns mainly the Spectrum Sensing, where this approach is based on the elimination of the SU received signal on the SU receiving antenna (R X ). In fact, SU has a perfect knowledge on its signal transmitted from its transmitting antenna (T X ). After estimating the channel between T X and R X , SI is cancelled by regenerating an estimation of the SU received signal using the channel estimation, and subtract it from the overall received signal. In fact, in addition to the non- perfect estimation of the channel, the hardware components do not work perfectly. Many imperfections are presented in both the transmitting and the receiving circuits. Even the residual of SI and the hardware imperfections related to the SI signal are of negligible power compared to SI signal, they are of important power compared to the PU signal. This is due to the short distance between T X and R X which implies a very high received SI power. In Full-Duplex communication, the residual of SI and the hardware imperfections are assumed to be acceptable if their power level becomes equal to that of the noise. This condition is not sufficient in Spectrum Sensing, since such level of power may deteriorate the Spectrum Sensing performance. In fact, in [8], we treated the performance of the energy detector in both HD and FD modes. In addition, we rely the performance of ED in FD mode to that in HD mode. As results, we obtain that for a loss of only 10 % (i.e. detection rate in FD mode = 90 % of the detection rate in HD mode for the same false alarm rate), the RSI should be 7 dB bellow the noise level. Accordingly, the lower the loss the lower the RSI power. Such level of RSI power is very difficult to be achieved, keeping the Spectrum Sensing performance efficient in FD-CR is very important to CR in order to remain reliable. In addition, FD-CR using SIC means that the asymptotic performance of Spectrum Sensing in FD mode is the performance under HD mode. The BSS techniques have been introduced in CR in order to avoid the silence period during the spectrum sensing [9], [10]. BSS consists in the separation of N independent sources based on M observations (Generally M ≥N) [11]. Since the PU and SU signals are independent, the BSS can be used in this context. Once the separation is achieved, a test of kurtosis can be carried out on the separated signal in order to make a decision on the presence of PU [10], [12]. Unlike [10], [12], where the kurtosis test is only considered, the separated signals are tested using different spectrum sens- ing algorithms a Goodness of Fit (GoF) [13] and autocorrela- tion (AC) tests [14] will be applied on the separated signals. ISBN: 978-1-5090-0717-2 ©2017 IEEE 86