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Co-channel interference among Keywords: D2D; Interference alignment; D2D discovery; Channel state informationCopyright © 2016 Universitas Ahmad Dahlan. All rights reserved. IntroductionAs device-to-device (D2D) communications have the advantages of supporting a higher data rate, lowering communication delay, and reducing energy consumption, it has been considered as a key technology for future 5G mobile communication systems [1][2]. Hence, cochannel interference (CCI) among D2D users are major issues that must be resolved for successful transmission when they are utilizing the same frequency bands. To reduce the cochannel interference among D2D users, several techniques have been proposed in the existing literature. In [3], a novel location-based resource allocation scheme is proposed. In this paper, the D2D users which utilize the same frequency bands usually have long distance, therefore, the interferences from others' transmitter are reduced because of the pathloss of interference signal. In [4], an effecitve time-domain interference coordination (ICIC) approach was proposed by using almost blank subframes (ABS). Even though the above proposed schemes can reduce the interferences among D2D users, the spectrum effeicieny becomes low.Recently, a new interference management scheme called interference alignment (IA) was presented in [5] to align the interference from the different transmitters in a spectific signal demension. Then, the remainder of the dimension becomes interference-free space. Therefore, IA can achieve high multiplexing gain and degrees freedom of the channel. However, the majority of the papers [6-11] which consider the IA technolog for conventional cellular network or D2D communications, they all assumed that the channel state information (CCI) between transmitter and receiver of a D2D pair and cross-channel state information (C-CCI) among D2D pairs are known to each other. Therefore, an effective method which can measure the CCI and C-CCI is inevitable for the applcation of IA from theory to practial.Fortunately, D2D discovery in D2D communications provides possibility for the measurement of CSI and C-CSI among D2D pairs. Because an accurate description of signaling message exchange between the entities of the network with recpect to the necessaary information for identifying a new D2D pairs. The exchange of discovery messages will provide the network with information about the CSI and C-CSI. Therefore, based on the description provided by above, in this paper, we propose an effective D2D discovery for the channel measurement of IA, which not only can measure the CSI, but also can measure the C-CSI.

WSDM, as a new way of wireless channel multiplexing, could be widely used in communication anti-jamming. WSDM separates the mixed signal and extracts the signal which is needed. As we all know, most communication signals are cyclostationarity. This property could be used as the prior information to extract the useful signal more correctly. In this paper, we propose a new algorithm which could extracts concerned signal by making use of the cyclostationarity. Theory analysis and computational simulation show that the proposed algorithm can recover signal correctly and dispose the interferences which are often in use to jam the communication system

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