In this paper, we consider a joint design of energy-efficient sensing and transmission durations for a cognitive radio (CR) system in which the primary user (PU) is protected. The design problem is formulated as a function of two variables, which are sensing and transmission durations, subject to the interference to the PU. The optimal solutions are analyzed and a sub-optimal algorithm that maximizes the energy efficiency for the CR system is presented. The performance of the proposed energy-efficient design for the CR system is also evaluated.

From the co-array perspective, sparse spatial sampling can significantly increase the degrees-of-freedom (DOFs), enabling us to perform underdetermined direction-of-arrival (DOA) estimation. By leveraging the increased DOFs from the sparse spatial sampling, we develop a new underdetermined DOA estimation method for wideband signals, named wideband sparse spectrum fitting (W-SpSF) estimator. In W-SpSF, we formulate a sparse reconstruction problem that includes a quadratic (l₂) weighted covariance fitting term added to a sparsity-promoting (l_{2, 1}) regularizer. Meanwhile, the optimal regularization parameter of W-SpSF is studied to ensure robust sparse recovery. Numerical results enabled nested arrays demonstrate that the W-SpSF estimator outperforms the spatial smoothing based MUSIC algorithm and works well in nonuniform noise environment.

Polar codes under successive cancelation list (SCL) decoding are capable of achieving almost the same or better performance than turbo codes or low density parity-check codes with the help of single cyclic redundancy check (CRC). This decoding scheme, however, suffers from very high complexity with long delay and large memory space. Motivated by this research problem, we propose a novel coding scheme called multi-CRC polar code for significant reduction of memory size and decoding delay but with negligible performance loss. Our analysis and simulation have shown that about half reduction of memory size and decoding delay can be achieved in SCL decoding. We also apply this scheme to hybrid automatic repeat request (HARQ) system to aid retransmission and show that the throughput of multi-CRC polar code is higher than that of the single-CRC one.

In this study, the authors focus on energy efficiency of a cognitive radio (CR) system, in which a secondary user (SU) senses periodically and accesses opportunistically a specific band authorised to a primary user (PU). Based on a generalised expression of energy consumption, we jointly optimise sensing, transmission and frame durations to maximise the energy efficiency for a CR system and investigate the performance of the proposed design over Rayleigh fading channels. The problem of energy efficiency is formulated as a function of sensing and transmission durations with the constraints on the interference to the PU. To protect the PU, we limit the detection probability as well as restrict the interference caused by the SU because of the re‐occupancy of the PU. In a generalised model, energy consumptions of sensing, transmission and idling state need to be considered for the SU. The optimal sensing and transmission durations are obtained by a sub‐optimal iterative algorithm. The performance of energy efficiency and duration of the SU over a Rayleigh‐faded channel is investigated. Numerical results show that the proposed reduced‐complexity approach performs comparably with that of the exhaustive search algorithm.

In this letter, the problem of spectrum sensing is addressed for noncircular (NC) signal in cognitive radio networks with uncalibrated multiple antennas. Specifically, by taking both the standard covariance and complementary covariance information of the NC signal into account, a new robust spectrum sensing method called NC covariance (NCC) is proposed, which can fully reap the statistical property of the NC signals. Meanwhile, we derive the asymptotic distribution of the NCC statistic under the signal-absence hypothesis and obtain the theoretical decision threshold of the NCC method. Simulation results demonstrate that the proposed method is capable of outperforming state-of-the-art methods.