Spatial Sensing and Cognitive Radio Communication in the Presence of a <inline-formula> <tex-math notation="TeX">$K$</tex-math></inline-formula>-User Interference Primary Network

Abstract

Abstract-We study the feasibility of cognitive radio (CR) communication in the presence of a K-user multi-input multioutput (MIMO) interference channel as the primary network. Assuming that the primary interference network has unused spatial degrees of freedom (DoFs), we first investigate the sufficient condition on the number of antennas at the secondary transmitter under which the secondary system can communicate while causing no interference to the primary receivers. We show that, to maximize the benefit, the secondary transmitter should have at least the same number of antennas as the spatial DoFs of the primary system. We then derive the secondary precoding and decoding matrices to have zero interference leakage into the primary network while the signal-to-interference plus noise ratio (SINR) at the secondary receiver is maximized. As the success of the secondary communication depends on the availability of unused DoFs, we then propose a fast sensing method based on the eigenvalue analysis of the received signal covariance matrix to determine the availability of unused DoFs or equivalently spatial holes. Since the proposed fast sensing method cannot identify the indices of inactive primary streams, we also provide a fine sensing method based on the generalized likelihood ratio test (GLRT) to decide the absence of individual primary streams. Simulation results show that the proposed CR sensing and transmission scheme can, in practice, provide a significant throughput while causing no interference to the primary receivers, and that the sensing detects the spatial holes of the primary network with high detection probability.Index Terms-Cognitive radio, K-user MIMO interference channel, interference alignment, null space sensing, spatial holes, eigenvalue-based sensing, GLRT detector.

An efficient interference mitigating scheme for cognitive radio networks: From the perspective of space pooling

“…For comparison, the performance of the conventional cognitive interference alignment in [11] and the maximum signalinterference-noise-ratio (SINR) scheme in [16] are also simulated in our numerical results in terms of the fraction of MinWIL in [11] Hybrid CIA Scheme in [13] Max−SINR in [16] Poposed Scheme interference signal power in the SUs desired signal subspace and achievable rate, respectively. In the legends, MinWIL denotes the optimization algorithm which only aims to minimize the leakage interference in secondary users' desired signal subspace, Hybrid CIA Scheme represents the scheme that combines subspace interference alignment and MinWIL and Max-SINR is the optimization algorithm which aims to maximize each secondary user's received SINR.…”

“…Thus, we can get the equation (18) with the condition N i=1 p i = p. Following the above theorem, the solution of the problem (16) for power loading at the k-th secondary transmitter can be given by:…”

Precoder Design and Power Allocation for MIMO Cognitive Radio Two-Way Relaying Systems

“…where [·] + = max(0, ·) and µ p is the Lagrange multiplier corresponding to the primary total power constraint expressed in (10). From (11), when the channel gain is poor, i.e., λ j 's have small values, we note that the number of used eigenmodes by PUs can be less than the total number of antennas N p .…”

“…Note that the secondary system is able to determine the free eigenmodes by only knowing the PUs channel H p then determine its SVD and the PUs power allocation locally. However, in the case where determining the free eigenmodes is not possible due to imperfect channel state information, one can rely, e.g., on sensing the free space similarly to [10]. From another side, we mentioned earlier that the SU transmission should be transparent to the PU.…”

Iterative Source and Relay Precoder Design for Non-Regenerative MIMO Cognitive Relay Systems

“…The case of multi-antenna CR systems has gained attention more recently, and the performance of such systems has been partly studied [9]- [11].…”