Underlay Spectrum Sharing Research Articles

Adaptive Rate Maximization and Hierarchical Resource Management for Underlay Spectrum Sharing NOMA HetNets with Hybrid Power Supplies

Adaptive Rate Maximization and Hierarchical Resource Management for Underlay Spectrum Sharing NOMA HetNets with Hybrid Power Supplies

Underlay Spectrum Sharing with L-Band Distance Measuring Equipment for Aeronautical Communications

Underlay Spectrum Sharing with L-Band Distance Measuring Equipment for Aeronautical Communications

Two-Stage Adaptive Relay Selection and Power Allocation Strategy for Cooperative CR-NOMA Networks in Underlay Spectrum Sharing

In this paper, we consider a novel cooperative underlay cognitive radio network based on non-orthogonal multiple access (CR-NOMA) with adaptive relay selection and power allocation. In secondary networks, dedicated relay assistance and user assistance are used to achieve communication between the base station and the far (and near) user. Here, a two-stage adaptive relay selection and power allocation strategy is proposed to maximize the achievable data rate of the far user while ensuring the service quality of near user. Furthermore, the closed-form expressions of outage probability of two secondary users are derived, respectively, under interference power constraints, revealing the impact of transmit power, number of relays, interference threshold and target data rate on system outage probability. Numerical results and simulations validate the advantages of the established cooperation and show that the proposed adaptive relay selection and power allocation strategy has better outage performance.

On the Effective Rate of NOMA in Underlay Spectrum Sharing

In this paper, we present the delay-constrained performance analysis of a multi-antenna-assisted multiuser non-orthogonal multiple access (NOMA) based spectrum sharing system over Rayleigh fading channels. We derive analytical expressions for the sum effective rate (ER) for the downlink NOMA system under a peak interference constraint. In particular, we show the effect of the availability of different levels of channel state information (instantaneous and statistical) on the system performance. We also show the effect of different parameters of interest, including the peak tolerable interference power, the delay exponent, the number of antennas and the number of users, on the sum ER of the system under consideration. An excellent agreement between simulation and theoretical results confirms the accuracy of the analysis.

On the Performance of Downlink NOMA in Underlay Spectrum Sharing

Non-orthogonal multiple access (NOMA) and spectrum sharing are two potential technologies for providing massive connectivity in beyond fifth-generation (B5G) networks. In this paper, we present the performance analysis of a multi-antenna-assisted two-user downlink NOMA system in an underlay spectrum sharing system. We derive closed-form expressions for the average achievable sum-rate and outage probability of the secondary network under a peak interference constraint and/or peak power constraint, depending on the availability of channel state information (CSI) of the interference link between secondary transmitter (ST) and primary receiver (PR). For the case where the ST has a fixed power budget, we show that performance can be divided into two specific regimes, where either the interference constraint or the power constraint primarily dictates the performance. Our results confirm that the NOMA-based underlay spectrum sharing system significantly outperforms its orthogonal multiple access (OMA) based counterpart, by achieving higher average sum-rate and lower outage probability. We also show the effect of information loss at the ST in terms of CSI of the link between the ST and PR on the system performance. Moreover, we also present closed-form expressions for the optimal power allocation coefficient that minimizes the outage probability of the NOMA system for the special case where the secondary users are each equipped with a single antenna. A close agreement between the simulation and analytical results confirms the correctness of the presented analysis.

Performance Analysis of Cooperative Underlay Spectrum Sharing System in Co-channel Interference Limited Environment

In this paper, performance analysis of an asynchronous distributed space time block coded system with optimum combining at the cognitive radio receiver (CR-Rx) has been done in a cooperative underlay cognitive Internet of Things network under the influence of multiple co-channel primary users (PUs) interferers. The transmit power strategy being employed at the CR-Tx considers the PIP (peak interference power) at the PU-Rx and peak transmit power constraints at the CR-Tx, respectively. We have derived the probability density function of the signal-to-interference ratio (SIR) at the destination for the proposed system. The system is numerically and mathematically analyzed in terms of average post processed SIR (APPSIR), ergodic capacity ($${\text{C}}_{\text{erg}}$$), average bit error rate (ABER) and outage probability. All the numerical outcomes are in corroboration with its simulation counterpart.

Best Relay Selection Schemes for NOMA Based Cognitive Relay Networks in Underlay Spectrum Sharing

Cognitive Radio and the emerging Non-Orthogonal Multiple Access (NOMA) techniques hold the potential to fulfill the increasing demands of radio spectrum by 5G-and-B5G wireless systems. It is a usual practice in underlay cognitive radio networks to take assistance from intermediate relays to reach the remote destination. Putting together, NOMA based Cognitive Relay Networks (NCRNs) have recently gained tremendous research attention to improve the spectrum utilization efficiency. This article studies the application of best relay selection (BRS) in downlink scenario of NCRNs in which a base station (BS) being unable to communicate directly with the far user U2 takes assistance from the near user U1 and from the best Decode-and-Forward (DF) relay selected from the potential NCRN operating in underlay environment. Three BRS schemes are proposed selecting a relay which (i) maximizes signal-to-noise ratio (SNR) on relayU2 link, (ii) minimizes interference on relay-primary user (PU) link, (iii) maximizes the quotient of relay-U2 link's SNR and relay-PU link's interference power. Scheme 3 considers the existence of U1 -U2 link as well whereas the other two schemes do not. To characterize the performance of the proposed schemes assuming Rayleigh channel model, closed-form expressions of probability distribution function (PDF) of received SNR at U2, average number of reliable relays, outage probability and bit error rate are obtained. For insight analysis, analytical results are validated through simulations which reveal that relay selection in NCRNs is different from non-cognitive networks and is feasible in low-to-medium SNR regions. The signal from near user further improved the outage performance.

Intelligent Interference Exploitation for Heterogeneous Cellular Networks Against Eavesdropping

This paper explores the co-existence of a macro cell and a small cell for heterogeneous cellular networks, where a macro base station (MBS) and small base station (SBS) transmit to respective macro user (MU) and small user (SU) through their shared spectrum in the face of a common eavesdropper. We consider two spectrum sharing mechanisms, namely the overlay spectrum sharing (OSS) and underlay spectrum sharing (USS). In the OSS, the MBS and the SBS take turns to access their shared spectrum. By contrast, the USS allows the MBS and SBS to simultaneously transmit over the shared spectrum with the aid of power control for limiting their mutual interference, thus called interference-limited USS (IL-USS). In order to take advantage of mutual interference in confusing the eavesdropper without causing adverse effect on the MU, we propose an interference-canceled USS (IC-USS) scheme, where a sophisticatedly designed signal is emitted at the MBS to cancel out the interference received at the MU, which is also beneficial in terms of defending the common eavesdropper. Closed-form expressions of overall outage probability and intercept probability are derived for OSS, IL-USS, and IC-USS schemes by taking into account both MBS-MU and SBS-SU transmissions. The secrecy diversity analysis is also carried out by characterizing an asymptotic behavior of the overall outage probability with a given intercept probability in the high signal-to-noise ratio region. It is shown that the secrecy diversity gains of conventional OSS and IL-USS are zero, whereas the proposed IC-USS achieves a higher secrecy diversity gain of one. This implies that with an arbitrarily low overall intercept probability, the conventional OSS and IL-USS methods converge to their respective outage probability floors; however, the proposed IC-USS scheme can make the overall outage probability asymptotically decrease to zero by simply increasing the transmit power. In addition, numerical results demonstrate an obvious advantage of the proposed IC-USS over OSS and IL-USS against eavesdropping.

An Efficient Transmit Power Control Strategy for Underlay Spectrum Sharing Networks With Spatially Random Primary Users

With the ever-increasing spectrum requirements for transmitting explosively growing mobile data, spectrum-efficient solutions need to be integrated into future mobile networks. Spectrum sharing enables the primary system to share licensed spectrum with the secondary system. Thus, it is conceived as an appealing solution for improving spectrum usage to eliminate the spectrum supply-demand gap. In this paper, we develop an efficient transmit power control strategy for underlay spectrum sharing networks with spatially Poisson-distributed primary users. A distinguishing feature of the proposed strategy is that it only requires channel state information and location information of a few primary users close to the secondary transmitter, rather than those for all primary users. Furthermore, we evaluate the outage performance of the secondary system and the interference situation of the primary system under this kind of transmit power control strategy. Numerical results demonstrate that the proposed transmit power control strategy can achieve near-optimal outage performance compared to the perfect power control strategy, while reducing the control complexity and the feedback burden significantly at the same time.

Secrecy Outage Analysis for Distributed Antenna Systems in Heterogeneous Cellular Networks

In this paper, we study physical-layer security for a spectrum-sharing heterogeneous cellular network consisting of a macro cell and an underlaying small cell, where a small base station (SBS) and a macro base station (MBS) transmit to their respective small user (SU) and macro user (MU) over their shared spectrum. A common eavesdropper is assumed to tap both the small-cell and macro-cell transmissions. In the macro cell, multiple distributed antennas of MBS are deployed around the far-off MU and only a single antenna is selected to transmit to MU. Meanwhile, SBS directly transmits to SU in the small cell. To improve the spectrum efficiency, we consider underlay spectrum sharing (USS), which allows SBS and MBS to simultaneously access the shared spectrum. We present two USS schemes, namely, the interference-cancelled opportunistic antenna selection (IC-OAS) and interference-limited opportunistic antenna selection (IL-OAS), where a sophisticatedly-designed signal is exploited in the IC-OAS to perfectly cancel out the interference received at MU from SBS. Closed-form expressions of the secrecy outage probability are derived for both the IC-OAS and IL-OAS schemes over Rayleigh fading channels. Numerical results show that the IC-OAS scheme significantly performs better than the IL-OAS scheme for the macro-cell transmission in terms of the secrecy outage probability. Moreover, with an increasing number of distributed antennas, the secrecy outage probabilities of both IC-OAS and IL-OAS decrease substantially.

Heuristic Algorithms for Underlay Spectrum Sharing in Cognitive Radio Networks

Cognitive radio is the enabling technology that allows the design of dynamic spectrum sharing algorithms that makes unlicensed users able to use frequency bands owned by license holders. Hence, this technology can be considered as the perfect candidate to enhance the spectrum allocation for the next generation of wireless networks. In this paper, we propose two low complexity heuristic algorithms for dynamic spectrum sharing in cognitive radio networks assuming the spectrum underlay paradigm. We mean by spectrum underlay a wireless system where primary and secondary users can transmit simultaneously on the same frequency bands at the condition that the interference perceived by the primary receivers is kept below a determined threshold. The formulated spectrum sharing is shown to be equivalent to a variant of knapsack problems which is \({\mathcal {NP}}\)-hard. Therefore, resolving the tradeoff between computational complexity and system performance is the main concern in the design of the proposed algorithms. The first algorithm is based on a graph-theory. First, the cognitive radio network is modeled as an undirected weighted graph. The spectrum sharing problem is then reduced to the one of finding a sensitive vertex coloring of a subgraph on the constructed graph. The second algorithm involves the use of genetic algorithms and uses a mixed integer coding. We show that the proposed algorithms reduce considerably the computational complexity of finding a near optimal solution.

Bidirectional AF Relaying With Underlay Spectrum Sharing in Cognitive Radio Networks

This paper investigates the impact of primary transmissions on the performance of a dual-hop bidirectional cognitive radio system. The secondary users (SUs) communicate with each other in an underlay mode with the assistance of amplify-and-forward (AF) relays in the presence of primary users (PUs). Depending on whether there exists interference at the secondary transceivers, originating from the primary transmissions, or there is a possibility of employing the best relay selection technique at the secondary side, two operating cases are considered for the secondary network (SN). For both cases, tight lower bounds on the outage probability (OP) and the average symbol error probability (SEP) are derived in closed form. Moreover, a novel and general closed-form expression for the bit error rate (BER) of $M$ -ary square quadrature amplitude modulation (QAM) for both single- and multiple-relay systems, under additive white Gaussian noise (AWGN) when Gray coded bit mapping is employed, is presented. In addition, we provide an upper bound and closed-form approximate expression for the ergodic capacity (EC). Numerical results provide important insights into the impact of system parameters on performance; for instance, it is demonstrated that, in both cases, under consideration of power constraints on the secondary nodes as dictated by the underlay mode of operation, the SN always achieves the full diversity order similar to the noncognitive counterpart.

Wireless Energy Harvesting in Cognitive Massive MIMO Systems with Underlay Spectrum Sharing

The achievable sum rate of a wireless-powered multi-cell/multi-user cognitive radio massive multiple-input multiple-output system with underlay spectrum sharing is investigated. The secondary user nodes can harvest energy from the primary user transmissions, and then access and utilize the primary network spectrum for information transmission. The signal-to-interference-plus-noise ratio and achievable sum rate are derived for two specific antenna configurations: 1) unlimited base-station antenna arrays and 2) limited base-station antenna arrays. Furthermore, the optimal time-switching factor and the energy-rate trade-off are quantified in closed-form. The asymptotic analysis reveals that the secondary system can be operated by using its maximum harvested energy when the number of primary base-station antennas grows without bound without hindering the primary transmission.

Energy-aware Dynamic Selection of Overlay and Underlay Spectrum Sharing for Cognitive Small cells

Small cell (SC) base stations with cognitive capabilities are seen as an efficient way to cope with interference between the SC base stations and macrocell base stations (MBSs). Cognitive SCs may access the spectrum by means of overlay or underlay mode. An efficiency of the overlay mode fully depends on the activity of macrocell users (MUEs), since insufficient resources remain for small cell users (SUEs). Contrarily, the main weakness of the underlay mode is that it can result in low transmission efficiency due to restricted transmission power. Apart from the transmission efficiency of both modes, an energy consumption of the SCs should not be disregarded. Thus, we propose a centralized scheme selecting the spectrum sharing mode in the downlink, according to both the SUEs’ throughput and the energy consumption of the SCs. The objective is to maximize the overall performance of the SCs, while their energy consumption is taken into account. Then, we also propose a distributed algorithm in order to decrease complexity and signaling overhead of the centralized scheme. The results show that the proposed dynamic selection significantly outperforms all competitive schemes in terms of the SUEs’ throughput, while the throughput of MUEs is intact, and only negligible signaling overhead is generated in the case of the proposed distributed algorithm. Moreover, the proposed algorithm is able to notably decrease the energy consumption of the SCs.

Transmit Power Minimization using Fuzzy Rule based System in Relay Assisted Cognitive Radio Networks

power minimization is one of the major research challenges in Relay-Assisted Cognitive Radio Networks. In this process, the transmit power of each individual relay is adjusted in such a way that the overall transmit power consumption at the relay network is minimized while satisfying the minimum Quality-of-Service (QoS) requirements of primary and secondary networks. In this paper, a similar constrained optimization problem is focused in which a secondary source-destination pair is assisted by a potential relay network having Cognitive Radio capabilities. A Fuzzy Rule Based System (FRBS) is proposed for intelligent relay selection such that total transmit power at the relay network is minimized while achieving the desired signal-to-noise ratio (SNR) at the destination and keeping the primary communication undisturbed. The effectiveness of the proposed scheme is highlighted through simulation results. KeywordsRadio Network, Underlay Spectrum Sharing, Cooperative Communication, Amplify-and-Forward, Fuzzy Rule Based System

Outage Performance of Spectrally Efficient Schemes for Multiuser Cognitive Relaying Networks with Underlay Spectrum Sharing

We analyze the outage performance of two spectrally efficient schemes for exploiting multiuser diversity in cognitive relaying networks. We consider a secondary network composed by one source node communicating with the best one out of $L$ available destinations, selected according to the channel quality of the direct links. If the transmission through the selected direct link drops below a given threshold, then a half-duplex decode-and-forward relaying transmission is invoked. At this stage, two schemes are considered. In the first scheme, the previously selected secondary destination employs maximal-ratio combining to handle the signals received from the secondary source and relay. In the second scheme, maximal-ratio combining is employed as well, but at a possibly different secondary destination, selected so as to maximize the signal-to-noise ratio at the combiner output. In both schemes, we consider an underlay spectrum-sharing mechanism. We derive exact analytical expressions for the outage probability of the proposed schemes and validate them by Monte Carlo simulations. An asymptotic analysis reveals that the proposed schemes can achieve full diversity order, equal to $L+1$. Importantly, we show that, at high signal-to-noise ratio, the mean spectral efficiency of the proposed schemes approximates that one attained by direct transmission.

Passive Primary Receiver Detection for Underlay Spectrum Sharing in Cognitive Radio

In this letter, we propose a passive detection method to enable cognitive user to detect active primary receiver. With our method, cognitive user may conduct underlay spectrum sharing without the need of channel state information between primary and cognitive users. Simulation results show that our detector can provide about 100% to 300% more access probabilities in average than conventional energy detector.

Optimal Precoder Design for Non-Regenerative MIMO Cognitive Two-Way Relay Systems with Underlay Spectrum Sharing

We study the optimal precoder design for a MIMO cognitive two-way relay system with underlay spectrum sharing. The system consists of two secondary users (SUs) and one relay station (RS). We jointly optimize the precoders for SUs and RS with perfect and imperfect channel state information (CSI) between SUs/RS and the primary user, where our design approach is based on the alternate optimization method. For the perfect CSI case, we derive the optimal structure of the RS precoding matrix, which generalizes the result for single-antenna SUs and helps to reduce the search complexity. We develop gradient projection (GP) algorithm to calculate the optimal RS precoder numerically. When the RS precoder is given, we propose a fast algorithm based on generalized water-filling theorem to compute the optimal SU precoders. For the imperfect CSI case, we derive equivalent conditions for the interference power constraints and convert the robust SU precoder optimization into the form of semi-definite programming. As for the robust RS precoder optimization, we relax the interference power constraint related with the RS precoder to be convex and then the GP algorithm can be applied. Finally, simulation results demonstrate the effectiveness of the proposed schemes.

Distributed Resource Allocation for Multi-Cell Cognitive Radio Networks Based on Intra-Cell Overlay and Inter-Cell Underlay Spectrum Sharing

Distributed Resource Allocation for Multi-Cell Cognitive Radio Networks Based on Intra-Cell Overlay and Inter-Cell Underlay Spectrum Sharing

Ergodic Sum Rate Maximization for Underlay Spectrum Sharing with Heterogeneous Traffic

A radio resource allocation framework is proposed for underlay spectrum sharing. The ergodic capacity maximization problem in orthogonal frequency division multiple access-based network on point to multi point transmission is formulated and solved. Heterogeneous traffic is also considered in which two types of traffic is assumed: streaming traffic which has strict delay requirements, and elastic traffic with flexible delay requirements. Considering the effect of channel state information (CSI) imperfection in the evaluation of the secondary users' expected rate, we further assume that the estimated CSI between the secondary users and secondary base station (secondary channel) is not perfect. Moreover three different cases are considered depending on the availability of the CSI between the secondary base station and the primary receivers (interference channel). Using simulations, we evaluate the impact of streaming traffic and imperfect CSI on the sum capacity of the secondary elastic users for different values of parameter systems.