Abstract
In this letter we study the potential benefits of improper signaling for a secondary user (SU) in underlay cognitive radio networks. We consider a basic yet illustrative scenario in which the primary user (PU) always transmit proper Gaussian signals and has a minimum rate constraint. After parameterizing the SU transmit signal in terms of its power and circularity coefficient (which measures the degree of impropriety), we prove that the SU improves its rate by transmitting improper signals only when the ratio of the squared modulus between the SU-PU interference link and the SU direct link exceeds a given threshold. As a by-product of this analysis, we obtain the optimal circularity coefficient that must be used by the SU depending on its power budget. Some simulation results show that the SU benefits from the transmission of improper signals especially when the PU is not highly loaded.
Highlights
Interference management techniques, the main limiting factor in current wireless networks, have received a lot of attention in recent years
We consider a cognitive radio (CR) scenario, modeled as a two-user singleinput single-output interference channel (SISO-IC), where a secondary user (SU) wishes to access the channel in presence of a primary user (PU)
In this letter we have analyzed the benefits of improper Gaussian signaling for underlay CR
Summary
Interference management techniques, the main limiting factor in current wireless networks, have received a lot of attention in recent years. One of the most interesting results is regarding the statistical nature of the transmitted signals in an interference-limited network In such scenarios, the use of proper complex Gaussian signals has typically been assumed due to the fact that these are capacity achieving in the point-to-point, broadcast and multiple access channels [1]. Improper signals have real and imaginary parts that have unequal power and/or are correlated They have been successfully applied to enlarge the achievable rate region of the K-user multiple-input multiple-output interference channel (MIMO-IC) [3], as well as to provide additional degrees of freedom in some specific scenarios [4], [5].
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