Spectrum-sharing Networks Research Articles

Application of Non-Orthogonal Multiple Access in Cooperative Spectrum-Sharing Networks Over Nakagami- $m$ Fading Channels

This paper proposes a novel non-orthogonal multiple access (NOMA)-based cooperative transmission scheme for a spectrum-sharing cognitive radio network (CRN), whereby a secondary transmitter (ST) serves as a relay and helps transmit the primary and secondary messages simultaneously by employing NOMA signaling. This cooperation is particularly useful when the ST has good channel conditions to a primary receiver but lacks the radio spectrum. To evaluate the performance of the proposed scheme, the outage probability and system throughput for the primary and secondary networks are derived in closed forms. Simulation results demonstrate the superior performance gains for both networks thanks to the use of the proposed NOMA-based cooperative transmission scheme. It is also revealed that NOMA outperforms conventional orthogonal multiple access (OMA) and achieves better spectrum utilization.

Massive MIMO in Spectrum Sharing Networks: Achievable Rate and Power Efficiency

Massive multiple input multiple output (MIMO) is one of the key technologies for fifth generation and can substantially improve energy and spectrum efficiencies. This paper explores the potential benefits of massive MIMO in spectrum sharing networks. We consider a multiuser MIMO primary network, with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -antenna primary base station (PBS) and K single-antenna primary users (PUs), and a multiple-input-single-output secondary network, with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> -antenna secondary base station and a single-antenna secondary user. Using the proposed model, we derive a tight closed-form expression for the lower bound on the average achievable rate, which is applicable to arbitrary system parameters. By performing large-system analysis, we examine the impact of large number of PBS antennas and large number of PUs on the secondary network. It is shown that, when N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> and K grow large, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> must be proportional to ln K or larger, to enable successful secondary transmission. In addition, we examine the impact of imperfect channel state information on the secondary network. It is shown that the detrimental effect of channel estimation errors is significantly mitigated as N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> grows large.

Effective Capacity of a Novel Spectrum-Band Selection Scheme in Spectrum-Sharing Networks

In this paper, a spectrum-band selection scheme is developed for secondary users (SUs) in underlay spectrum-sharing networks to balance the performance between SUs and primary users (PUs) while guaranteeing PUs' priority. With the developed scheme, among multiple candidate spectrum bands, a given secondary transmitter (ST) is scheduled to access the spectrum band with minimum ratio of the ST–PU channel power gain to the SU link channel power gain. To evaluate this scheme, the SU's performance is investigated concerning its service delay. Under the constraint on average interference from the ST to PUs, the ST's optimal power allocation is obtained in a closed form to achieve the maximum effective capacity (EC) over SU links. Illustrative numerical results and asymptotic discussions substantiate the validity of our derivations and, moreover, demonstrate that, for the case of stringent delay requirements but loose average interference constraint, the band-selection scheme developed in this paper achieves better performance than both the selection of the band with maximum SU link channel power gain and that with minimum ST–PU channel power gain.

Cognitive full-duplex relay networks under the peak interference power constraint of multiple primary users

This paper investigates the outage performance of cognitive spectrum-sharing multi-relay networks in which the relays operate in a full-duplex (FD) mode and employ the decode-and-forward (DF) protocol. Two relay selection schemes, i.e., partial relay selection (PRS) and optimal relay selection (ORS), are considered to enhance the system performance. New exact expressions for the outage probability (OP) in both schemes are derived based on which an asymptotic analysis is carried out. The results show that the ORS strategy outperforms PRS in terms of OP, and increasing the number of FD relays can significantly improve the system performance. Moreover, novel analytical results provide additional insights for system design. In particular, from the viewpoint of FD concept, the primary network parameters (i.e., peak interference at the primary receivers, number of primary receivers, and their locations) should be carefully considered since they significantly affect the secondary network performance.

On Proportional Fairness in Power Allocation for Two-Tone Spectrum-Sharing Networks

To efficiently trade off system sum rate and link fairness, power allocation in wireless spectrum-sharing networks often concentrates upon proportional fairness. The corresponding problem has been proved to be convex for a single tone but NP-hard for more than two tones. However, in the two-tone case, the complexity of the problem for achieving proportional fairness has not been addressed yet. In this paper, we prove that the issue of proportional-fairness optimization for the two-tone situation is NP-hard by reducing the problem of finding the maximum independent set in an undirected graph to it. Moreover, a computationally efficient algorithm is proposed to provide an efficient suboptimal solution. Simulation results are presented to illustrate the effectiveness of our proposal.

QoS-Aware Admission Control and Resource Allocation in Underlay Device-to-Device Spectrum-Sharing Networks

Device-to-device (D2D) communications underlaying a cellular infrastructure have been recognized as an important network-organization architecture in 5G networks. In these scenarios, existing works have explored the impacts of one or several factors among mode selection, admission control, partner assignment, and power allocation on the network performance. In this paper, we put forward an optimization framework that considers all of these coupled factors to investigate the spectrum sharing problem in D2D networks. In particular, we introduce an objective that combines the access rate and the network sum rate and then maximize it subject to users’ quality-of-service requirements and resource allocation constraints. Due to its mixed combination, we focus on designing cost-efficient and easy-to-implement algorithms instead of finding globally optimal but exponentially complex solutions. By decomposition, we first devise two novel mode selection criteria and an admission-prioritized partner assignment scheme and obtain closed-form solutions for both admission control and power allocation. Moreover, we present a simple but interesting geometric interpretation on the physical implication of admission conditions. To further reduce the computational cost, we also exploit the structure of the formulation to devise a much faster heuristic algorithm, which usually runs at an order of millisecond. Simulation results show the low computational complexity of the proposed algorithms and exhibit their superiority against other schemes in terms of the access rate and the sum rate.

Channel Selection for Spectrum Sharing in Wireless Networks

In this paper, we study a spectrum sharing network (SSN) where a spectrum sharing device (SSD) coexists with multiple wireless communication systems (WCSs) in the same channel. The SSD can operate with either a duty cycle (DC) channel access mechanism or a listen-before-talk (LBT) channel access mechanism, whereas WCSs operate with an LBT mechanism. An opportunistic channel selection scheme for the SSD in the SSN is first proposed to minimize the outage probability. The optimal data transmission time for the DC-based SSD is derived to further improve the outage probability. We also derive the exact and closed-form outage probability of the proposed channel selection in the SSN by assuming that the number of WCSs operating in each channel is uniformly distributed. The simulation results show that the proposed channel selection scheme outperforms other channel selection schemes. It was also observed that a DC-based SSD with an optimal data transmission time provides a better outage performance than an LBT-based SSD. As the number of available channels increases, the channel selection scheme plays an important role in minimizing the outage probability of the SSNs.

Performance analysis of cognitive decode-and-forward dual-hop relay networks over [formula omitted] shadowed channels

In this paper, a decode-and-forward relay based dual-hop spectrum-sharing network is considered in cognitive radio perspective. The channels at all links are assumed to be κ–μ shadowed distributed with arbitrary fading and shadowing parameters. The κ–μ shadowed fading is a composite channel model of multipath fading and shadowing, unifying many classical fading models. The outage probability and the ergodic capacity of the considered network are derived under peak interference power constraint of the primary (licensed) network. It is shown that when channels at all links are identically distributed, the secondary user’s communication is favored by the severe channel conditions for a low peak interference power constraint of the primary network. For high values of peak interference power, the secondary network shows improved performance under less severe channel conditions. Two simple forms of the outage probability and the ergodic capacity are also evaluated when the channels between secondary nodes are Nakagami-m and Rician/Rician-shadowed distributed. In all scenarios, the analytical results are validated by Monte-Carlo simulations.

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To efficiently trade off system sum-rate and link fairness, this paper is dedicated to maximizing the sum of $\alpha$ -fair utility in spectrum-sharing networks, where multiple interfering links share one channel. In the literature, three special cases, including $\alpha=\mbox{0}$ (sum-rate maximization), $\alpha=\mbox{1}$ (proportional fairness), and $\alpha=\infty$ (max-min fairness), have been investigated; the complexity for cases $\mbox{1} and $\mbox{0} is still unknown. In this paper, we prove that the problem is convex when $\mbox{1} and is NP-hard when $\mbox{0} . To deal with the latter case, we transform the objective function and represent it by the difference of two concave functions (D.C.). Then, a power allocation algorithm is proposed with fast convergence to a local optimal point. Simulation results show that the proposed algorithm can obtain global optimality in two-link cases when $\mbox{0} . In addition, we can get a flexible tradeoff between sum-rate and fairness in terms of Jain's index by adjusting $\alpha$ .

Artificial-Noise Aided Secure Transmission in Large Scale Spectrum Sharing Networks

We investigate beamforming and artificial noise generation at the secondary transmitters to establish secure transmission in large scale spectrum sharing networks, where multiple noncolluding eavesdroppers attempt to intercept the secondary transmission. We develop a comprehensive analytical framework to accurately assess the secrecy performance under the primary users’ quality of service constraint. Our aim is to characterize the impact of beamforming and artificial noise generation (BF&AN) on this complex large scale network. We first derive exact expressions for the average secrecy rate and the secrecy outage probability. We then derive an easy-to-evaluate asymptotic average secrecy rate and asymptotic secrecy outage probability when the number of antennas at the secondary transmitter goes to infinity. Our results show that the equal power allocation between the useful signal and artificial noise is not always the best strategy to achieve maximum average secrecy rate in large scale spectrum sharing networks. Another interesting observation is that the advantage of BF&AN over BF on the average secrecy rate is lost when the aggregate interference from the primary and secondary transmitters is strong, such that it overtakes the effect of the generated AN.

Performance Analysis of MIMO Spectrum-Sharing Networks With Pre-Whitened Interfering Signals Under Outdated Channel Information

In this letter, the performance of multiple-input multiple-output based spectrum-sharing networks is analyzed when pre-whitening of spatially correlated interfering signals is performed at the secondary user transmitter (ST) using outdated channel state information (CSI). The channel capacities and outage probabilities are derived for both primary and secondary systems under maximum transmission power and peak interference constraints of the ST and primary system, respectively. It is shown that the reliability of interfering CSI at ST renders a performance gain of the secondary system, while the minimum performance limit of the primary system is maintained under peak interference constraint for sufficiently high maximum transmission power of ST. Finally, the analytical results are validated by the simulation results.

On Convexity of Fairness-Aware Energy-Efficient Power Allocation in Spectrum-Sharing Networks

The optimization of energy efficiency (EE) in spectrum-sharing networks has received increasing attention. While much effort has been devoted to the network-side overall EE, the fairness of EE among users has not been adequately concerned. Due to the complicated interference between different users, the global optimality of power allocation problems for achieving proportional, harmonic, and max–min fair EE with guarantees on users’ quality of service has not been fully addressed. By introducing auxiliary variables, changing variables, and transforming the objective and constraint functions, we convert the proportional, harmonic as well as max–min fairness-aware problems to convex ones. As a result, mature algorithms, such as interior-point methods, can be applied to achieve the global optimality with considerable efficiency.

Energy Harvesting Aided Multiuser Transmission in Spectrum Sharing Networks

Multiuser transmission with shared spectrum is investigated in the presence of energy harvesting. For each user, the data generation, the harvested energy arrival, and the channel state variation are, respectively, considered as stochastic processes. Each user aims to maximize its own average throughput. Accordingly, a stochastic game is formulated at first. Next, we analyze the stochastic game in infinite-stage and finite-stage scenarios, respectively. On the basis of theoretical studies, an iterated distributive algorithm with solving a linear problem in each iteration is designed for the infinite case. For the finite case, two distributed algorithms named CVPBI and GoPGA are proposed. Finally, the effectiveness of the proposed algorithms is demonstrated by simulations.

Enhanced Physical Layer Security in D2D Spectrum Sharing Networks

In this letter, the issue of security for device-to-device (D2D) underlaying cellular networks is considered. The cellular communication is overheard by randomly distributed eavesdroppers. By sharing the spectrum between D2D users and cellular users, the interference generated by D2D users is used as a source of jamming to confuse the eavesdroppers. We first derive the connection probability of the D2D links and the secrecy outage probability of the cellular link based on stochastic geometry tools. We then propose a joint guard zone and threshold-based access control scheme for the D2D users to maximize the achievable secrecy throughput. Moreover, when only the selection threshold is considered, a closed-form expression of the optimal selection threshold is derived. Simulation results show that improved secrecy throughput can be achieved by allowing the transmission of the D2D users.

Network Layer Scheduling and Relaying in Cooperative Spectrum Sharing Networks

We consider network layer cooperation in spectrum sharing networks whereby some secondary users relay primary users' packets, in return for more favorable spectrum access rules. Under this cooperative scheme, we investigate how primary and secondary networks can be stabilized without explicit knowledge of the packet arrival rates. We consider a primary packet generation process wherein a packet is formed by aggregating constant amount of bits that arrive in every time slot from upper-layers of the primary transmitter. For this primary packet generation model we develop a relaying and scheduling algorithm using Lyapunov drift techniques that does not require knowledge of packet arrival rates. We also construct a guaranteed stability region representing packet generation rates for which the algorithm can stabilize the network. The set of secondary packet generation rate vectors for which the network can be stabilized do not decrease under cooperation when the primary packet generation rate is lower than what can be maximally supported without cooperation. For higher primary packet generation rates the algorithm stabilizes the network for a non-empty set of secondary packet generation rate vectors.

Multihop Cognitive Relaying Over Composite Multipath/Shadowing Channels

The composite multipath/shadowing model is key to accurate modeling of real-world wireless channels, due to the combination of the effects of both fading and shadowing. However, the fundamental limits of spectrum-sharing cognitive radio have not been studied for such propagation conditions, leaving a gap in the analysis of these systems and, hence, the communication strategies that can be built upon toward improving performance. In this paper, we consider a primary/secondary spectrum-sharing network and study the performance of the secondary's multihop link by taking the composite multipath/shadowing model, which is described by the generalized- $K$ distribution, for the radio channels. In the multihop system, communication between secondary users (SUs) is assisted by intermediate relay terminals, under coexistence constraints with the primary users (PUs) . We assess the performance of the multihop system, first by deriving the moment generating function (mgf) and the probability density function (pdf) of the upper bounded end-to-end signal-to-noise ratio in closed form. The result is then used to obtain closed-form expressions of bounds on the ergodic capacity and the average bit error rate (ABER) , under the resource sharing constraints. The theoretical results are assessed with numerical analysis for different operating conditions.

Finite Block-Length Analysis of Spectrum Sharing Networks Using Rate Adaptation

This paper studies the throughput of spectrum sharing networks utilizing rate adaptation. We use some recent results on the achievable rates of finite block-length codes to analyze the secondary user (SU) throughput with a constraint on the primary user (PU) codeword drop probability. With codewords of finite length, we derive closed-form expressions for the SU activation probability and throughput. The results are obtained in different scenarios with perfect or no channel state information at the SU transmitter. As demonstrated numerically and analytically, using finite-length codewords and rate adaptation, there is considerable potential for the data transmission of unlicensed secondary users under different quality-of-service requirements of the licensed primary users.

Spectrum-Sharing AF Relay Networks with Switch-and-Examine Relaying and Multiple Primary Users Using Orthogonal Spectrums

In this paper, we propose and evaluate the behavior of a new cognitive amplify-and-forward relaying scenario where the multiple primary users utilize orthogonal spectrum bands. Using orthogonal bands aims to reduce the interference between users as in the downlink transmission in cellular networks where a base station transmits the data of different users using orthogonal frequency bands. In the proposed scenario, the spectrum of the primary user whose channel enhances the secondary system performance is shared with the secondary users. In this paper, the low-complexity switch-and-examine diversity combining relaying scheme is used to select among the secondary relays. In this scheme, the relay whose end-to-end signal-to-noise ratio (SNR) satisfies a predetermined switching threshold is selected instead of the best relay to forward the source message to destination. Approximate expressions are derived for the outage probability and average symbol error probability of the studied system assuming Rayleigh fading channels. Also, the ergodic channel capacity is numerically calculated in this paper. Furthermore, to simplify the achieved expressions and to get more insights about the system behavior, the system is studied at the high SNR values where approximate expression is derived for the outage probability in addition to the derivation of the diversity order and coding gain of the system. The achieved results are validated by Monte Carlo simulations. Main findings illustrate that the diversity order of the studied system is the same as its non-cognitive counterpart and it is independent of the primary network. In contrast to the existing systems where the same spectrum band is utilized by different primary users, increasing the number of primary users in the proposed scenario enhances the overall behavior via improving the coding gain.

Radio Resource Allocation for OFDM-Based Dynamic Spectrum Sharing: Duality Gap and Time Averaging

This paper considers radio resource allocation (RRA) in the downlink of an orthogonal frequency division multiple access (OFDM)-based spectrum-sharing network. The objective of RRA is to maximize the average achievable throughput subject to the primary service interference threshold and the secondary service transmit power constraint. RRA is usually implemented based on a time window T over which system parameters are averaged and checked against resource constraints. We use short-term ( T=1 time slot) and long-term ( T ≫ 1 slots) averaging as approximations to instantaneous and average constraints, respectively. RRA is also investigated for this system with long-term interference threshold and short-term interference threshold constraints. RRA optimization is a nonconvex optimization problem in which the duality principle is adopted to obtain approximate solutions. The duality gap indicates the degree of approximation in the thus-obtained solution. We prove that the duality gap corresponding to each resource allocation asymptotically decays at least with an exponential rate of T. We further show that OFDMA is, asymptotically, the optimal subcarrier assignment. We also propose a practically implementable online power and subcarrier allocation with on-the-fly channel state information measurement. An extensive simulation study has been conducted to verify the theoretically predicted duality gap behavior and to investigate the impact of different system parameters on the secondary service performance. The developed algorithms are also validated to be robust in practical settings and converge fast to theoretical bounds, and thus practically implementable.

A Power Allocation Strategy for Multiple Poisson Spectrum-Sharing Networks

This paper develops a power allocation strategy for multiple networks of Poisson-distributed single-antenna nodes that share the available spectrum in a spectrum underlay scenario. This strategy aims to maximize the overall throughput obtained by sharing the spectrum while limiting the degradation of the successful transmission probability of each network. In its original form, this joint power allocation problem is difficult to solve. However, we demonstrate that the problem can be transformed into a convex optimization formulation, which can be efficiently solved. Furthermore, we obtain a quasi-closed-form solution that has a water-filling interpretation by analyzing the optimality conditions. Numerical results indicate that, when a spectrum-sharing scheme employs the proposed optimal strategy of power allocation, the throughput substantially improves over that obtained by exclusively allocating the spectrum to the primary network. Moreover, when the number of spectrum-sharing networks increases, the enhancement is significant, being up to the limit imposed by the maximum allowable degradation in the performance of each network.