Performance analysis of an opportunistic multi‐user cognitive network with multiple primary users

A cognitive radio (secondary) network can reuse the under-utilized spectrum licensed to a primary network on a non-interruptive basis. In this paper, we study the uplink capacity of a secondary network where a secondary base station (BS) is located at the center while multiple secondary users are uniformly distributed within a circular cell of radius R. Primary users are assumed to be distributed in the same plane according to a Poisson point process with a density parameter lambdap. To protect primary services, secondary users can only transmit under a peak interference power constraint which guarantees that the instantaneous interference power perceived by any primary user is not larger than a certain threshold. In addition, we assume an opportunistic scheduler at the BS which exploits multi-user diversity among M secondary users and stochastically maximize the cell capacity.We first study the capacity with a simple channel model considering only the path loss and derive the closed-form cumulative distribution function (CDF) of the capacity. We then study the capacity with realistic fading channel models using a semi-analytical approach. The impacts of the parameters R, lambdap, and M on the capacity are quantified and discussed. Moreover, we find that shadowing and fading only have limited impacts on the distribution of the capacity.

Cognitive Radio Network is a form of communication where licensed frequency band of the Primary users (PUs) are made available to the Secondary user (SU) with constraint interference to the PUs. In this work, we have investigated a novel model considering interweave approach for spectrum access, with multiple primary users and single secondary user (SU). Multiple antennas have been considered at both the primary users as well as the secondary users. The activity of primary users are modeled as Poisson process. In addition, we also propose a new approach of sensing for a MIMO cognitive radio network using energy detection. The proposed method provides a closed form expression for probability of detection (P d ) and probability of false alarm (P f ) in a Multiple Input Multiple Output (MIMO) channel. Further, the throughput of secondary user as well as interference on primary users caused due to secondary user transmissions, has been computed for the proposed model.

This paper considers spectrum sharing between a cognitive radio (CR) and a primary radio (PR) where the CR protects the PR transmission by regulating the resultant interference power level at the PR receiver to be below some predefined threshold. The interference-power constraint at the PR receiver is usually one of the following two types: average interference power (AIP) constraint that regulates the average power level over different fading states and peak interference power (PIP) constraint that limits the peak power level at each fading state. From CR's perspective, AIP constraint is more favorable than PIP constraint because of its more flexibility for dynamic power allocations. On the contrary, from the perspective of protecting the PR, the more restrictive PIP constraint appears at a first glance to be a better option. Some surprisingly, this paper shows that in terms of various forms of capacity limits achievable for the PR fading channel, namely, ergodic and outage capacities, AIP constraint is also superior over PIP constraint. This result is based upon an interesting interference diversity phenomenon, i.e., variable interference power levels at the PR receiver in the AIP case are more advantageous over constant ones in the PIP case for minimizing the resulted PR capacity losses. Therefore, AIP constraint leads to larger fading channel capacities over PIP constraint for both CR and PR transmissions.

In this paper, we present an analytical study for the performance of a two-tier primary-secondary network based on IEEE 802.11 DCF mechanism. It is assumed that multiple primary users (PUs) and secondary users (SUs) coexist in the radio environment and share a single band such that the SUs are allowed to contend only if they sense the channel idle for a certain period of time. First, we derive the PUs' medium access delay in the presence of SUs. Then, assuming an exponential packet inter-arrival time for the primary network, and using M/G/1 queue modeling, we determine the collision probability and throughput for the primary and secondary networks, as well as the PUs' average total delay including the queuing delay. Numerical along with simulation results show how the performance in the primary network, with given packet arrival rate, can be affected as functions of the sensing time, packet payload size and population size of the SUs. The findings of this work can be used effectively to study the performance of any IEEE 802.11 based primary-secondary network, such as cognitive radio networks where SUs may exploit a primary channel opportunistically based on a predefined policy, as well as to optimize the performance of distributed cognitive radio MAC protocols.

A generalized order user selection scheme for cognitive networks with imperfect channel estimation and multiple primary users

In this paper, we investigate outage performance of dual-hop cognitive AF relay networks with multiple primary users (PUs) and heterogeneous non-identical parameters, including non-identical Rayleigh fading channels, non-identical interference power constraints of PUs, and non-identical noise powers in signals. To overcome the analysis complexity resulted from the consideration of heterogeneous non-identical parameters completely, we conduct our analysis in two steps. In the first step, we focus on networks with non-identical Rayleigh fading channels but with identical interference power constraints and identical noise powers. As analysis results, both the exact closed-form expression and asymptotic closed-form expression of the cumulative distribution function of equivalent end-to-end signal-to-noise ratio of the network are obtained. Then in the second step, we propose a method for transforming networks with heterogeneous non-identical parameters into new networks with identical interference power constraints and identical noise powers meanwhile guaranteeing that outage performance of the two networks before and after the transformation are identical. Hence, outage performance of networks with heterogeneous non-identical parameters can be obtained by applying the analysis results in the fist step to the corresponding transformed networks. Numerical simulations validate the correctness of our analysis, and the simulations also indicate that taking multiple PUs and the diversity of the parameters into consideration is of key importance in obtaining a more accurate estimation of outage performance of such networks.

In this paper, we present a method of utilizing channel diversity to improve the secrecy outage probability and the intercept probability in a cognitive radio (CR) network. With the presence of channel diversity, an intended receiver can achieve a relatively better secrecy outage probability and intercept probability. We consider a CR network in which a single antenna, which maximizes the secrecy capacity, is selected at the CR transmitter. To demonstrate the advantages of our proposed framework, we derive new exact closed-form expressions for the secrecy outage probability and the intercept probability of the secondary network in Rayleigh fading. The positive impact of the number of receive antennas and the negative impact of the number of primary users on the secondary network are shown. The derived secrecy outage probability is found to be in precise agreement with simulation results. The numerical results strongly support our conclusion that maximal-ratio combining of channel diversity can enhance the physical layer security of a multiantenna based CR network. Furthermore, the numerical results reveal the impact of the primary network on the secondary network in the presence of a multiantenna wiretap channel.

In this study, the problem of robust adaptive power control (PC) in an underlay cognitive radio network with multiple secondary users (SUs) and primary users (PUs) is considered. Due to the effects of uncertainties (i.e. estimation errors, delays), the optimal PC (resource allocation) cannot guarantee the quality of service of SUs and PUs under imperfect channel state information and interference power of PUs. A robust resource allocation problem is formulated to maximise sum throughput of SUs under individual power constraints and signal-to-interference-and-noise ratio constraints of SUs as well as interference temperature constraints of PUs, whereas channel uncertainties and interference uncertainties induced into the secondary system are modelled by multiplicative uncertainties. Under the worst-case approach, the problem is transformed into a geometric programming problem solved by Lagrange dual methods. The performance of the different algorithms and the impact of uncertainties are discussed according to several simulation results.

An uplink cognitive radio system with a single primary user (PU) and multiple secondary users (SUs) is considered. The SUs have an individual average delay constraint and an aggregate average interference constraint to the PU. If the interference channels between the SUs and the PU are statistically different due to the different physical locations of the SUs, the SUs will experience different delay performances. This is because SUs located closer to the PU transmit with lower power levels. A dynamic scheduling-and- power-allocation policy that uses the dynamic programming, is proposed. The proposed policy can provide the required average delay guarantees to all SUs irrespective of their location as well as protect the PU from harmful interference. The policy is shown to be asymptotically delay optimal in the light traffic regime. Motivated, by the high complexity of the dynamic programming algorithm in the optimal policy we exploit the structure of the problem's solution to present an alternative suboptimal policy. Through simulations we show that in both light and heavy traffic regimes, the delay performance of the suboptimal policy is within $0.3\%$ from the optimal policy and both outperforming existing methods.

SummaryIn this, we propose a generalized partial relay selection (PRS) protocol to enhance the secrecy performance for cooperative cognitive radio networks (CRNs) in terms of the secrecy outage probability (SOP) and the probability of non‐zero secrecy capacity (NSC). In the proposed scheme, a secondary source communicates with a secondary destination via the assistance of multiple secondary relays, in the presence of multiple secondary eavesdroppers and multiple primary users (PUs). With a reliance on the source‐relay channel state information (CSI), the source selects a group of the potential relays, and one is then chosen to forward the source data to the secondary destination using the randomize‐and‐forward (RF) technique. We consider the relay selection methods in two practical cases, where the CSIs of the eavesdropping links are available or not available. For the performance evaluation and comparison, we derived exact and asymptotic SOP and NSC closed‐form expressions for the proposed protocols and the corresponding full relay selection (FRS) protocol over Rayleigh‐fading channels. Finally, Monte Carlo simulations are presented to confirm the theoretical‐derivation correction. The results confirmed that the proposed protocols can outperform the conventional PRS protocols by designing the number of the potential relays appropriately.

In this paper, we study the performance of point-to-point communication in spectrum sharing systems under the peak interference power constraint of multiple primary users. In particular, we assume that the channels undergo independent but not necessarily identically distributed Nakagami-m fading with integer values of fading severity parameter m. The cumulative distribution function and probability density function for the signal-to-noise ratio are derived. Based on these formulas, we obtain analytical expressions for the outage probability, the ergodic capacity, and the symbol error probability. Numerical results are also provided to investigate the impact of the peak interference power-to-noise ratio, the number of primary users, and fading parameters on the performance of the secondary network.

In this paper, we investigate users’ performance under the hybrid spectrum access model in the massive cognitive radio network (CRN), where multiple primary users (PUs) and secondary users (SUs) transmit on the same channel simultaneously. SUs first detect the state of the channel via channel sensing and select an appropriate channel access scheme (either underlay or overlay) for their transmissions based on the outcome of the channel sensing. When at least one PU is active, SUs transmit under the underlay channel access scheme by employing the power control technique to ensure that the interference generated in the primary network is below the pre-defined interference threshold. In the absence of PU, SUs transmit with full transmit power under the overlay channel access scheme, thereby maximizing their throughput. Using the tool of stochastic geometry, we obtained tractable analyses for important metrics such as success probability, throughput, and the average age of information (AoI) in both primary and secondary networks, while capturing the interference between the two networks. The obtained analyses offer an efficient way to understand the metrics of AoI, throughput and success probability in the hybrid spectrum access-based CRN. We further compared users’ performance under the hybrid spectrum access scheme with performances under overlay and underlay spectrum access schemes. The outcome of the numerical simulations shows that the hybrid spectrum access scheme can significantly improve the performance of users in the network, while also capturing more key features of real-life systems.

This paper investigates the performance of power limited Cognitive Radio system with optimum combining at the cognitive user receiver under the influence of interference from multiple primary users’ transmitters (Lt) in flat Rayleigh fading channels. An approximate analytical result of the probability density function of maximum signal-to-interference ratio at the output of CR-OC receiver is derived. Using this derived PDF, the closed form expressions for the performance metrics viz. Average post processed SIR, Ergodic capacity, Average bit error rate and outage probability of CR-OC system are derived by taking into account peak interference power constraint denoted by ‘Q’ at PU-Rx. Based on the achieved result, it is concluded that the performance of the proposed system degrades when number of primary interferers exceeds from Lt=3. Analytical results for CR-OC system are validated through Monte Carlo simulations also.DOI: http://dx.doi.org/10.5755/j01.eie.24.1.20159

In this report, we point out on a system in which secondary user (SU) transmitter communicates with a SU receiver via a secondary relay (SR) under the interference from multiple primary users (PUs). Power allocated to SU transmitter on the basis of two constraints of PU, viz., outage threshold and outage transmission rate. In this case, performance of PU does not degrade due to these tolerable constraints. Direct link does not occur between the SU transmitter and receiver because of shadowing. A SR used to link the SU transmitter to SU receiver that is based on decode-and-forward (DF) scheme. Outage probability (OP) calculated by considering the interferences from all PUs at SR and secondary receiver. We see that the performance of SU network does not always degrade after the consideration of interferences from all PUs and thus, SU transmitter reliably communicates with its receiver under the specific range of primary transmit power of PUs in this system model. Results of this model are verified by the MATLAB simulation.

The effect of multiple primary users on spectrum-sensing performance is investigated. Different models for primary user traffic are considered. The effects of different system parameters on sensing accuracy are examined. Numerical results show that the spectrum-sensing performance is significantly degraded by the primary user traffic and that the degradation decreases when the number of primary users increases.