Analytical evaluation of adaptive-modulation-based opportunistic cognitive radio in Nakagami-m fading channels

The performance of adaptive modulation for cognitive radio with opportunistic access is analyzed by considering the effects of spectrum sensing, primary user (PU) traffic, and time delay for Nakagami- m fading channels. Both the adaptive continuous rate scheme and the adaptive discrete rate scheme are considered. Numerical examples are presented to quantify the effects of spectrum sensing, PU traffic, and time delay for different system parameters

Adaptive Modulation in Multi-user Cognitive Radio Networks over Fading Channels

In this paper, the performance of adaptive modulation in multi-user cognitive radio networks over fading channels is analyzed. Multi-user diversity is considered for opportunistic user selection among multiple secondary users. The analysis is obtained for Nakagami-$m$ fading channels. Both adaptive continuous rate and adaptive discrete rate schemes are analysed in opportunistic spectrum access and spectrum sharing. Numerical results are obtained and depicted to quantify the effects of multi-user fading environments on adaptive modulation operating in cognitive radio networks

Power Allocation and Cooperative Diversity in Two-Way Non-Regenerative Cognitive Radio Networks

In this paper, we investigate the performance of a dual-hop block fading cognitive radio network with underlay spectrum sharing over independent but not necessarily identically distributed (i.n.i.d.) Nakagami-$m$ fading channels. The primary network consists of a source and a destination. Depending on whether the secondary network which consists of two source nodes have a single relay for cooperation or multiple relays thereby employs opportunistic relay selection for cooperation and whether the two source nodes suffer from the primary users' (PU) interference, two cases are considered in this paper, which are referred to as Scenario (a) and Scenario (b), respectively. For the considered underlay spectrum sharing, the transmit power constraint of the proposed system is adjusted by interference limit on the primary network and the interference imposed by primary user (PU). The developed new analysis obtains new analytical results for the outage capacity (OC) and average symbol error probability (ASEP). In particular, for Scenario (a), tight lower bounds on the OC and ASEP of the secondary network are derived in closed-form. In addition, a closed from expression for the end-to-end OC of Scenario (a) is achieved. With regards to Scenario (b), a tight lower bound on the OC of the secondary network is derived in closed-form. All analytical results are corroborated using Monte Carlo simulation method

Performance study of an underlay cognitive radio network in the presence of co-channel interference

PhD ThesisMassive innovation in all aspects of the wireless communication network has been witnessed over the last few decades. The demand for data throughput is continuously growing, as such, the current regulations for allocating frequency spectrum are not able to respond to this exponential growth. Cognitive radio (CR), has been proposed as a solution to this problem. One of the possible scenarios of the implementation of CR is underlay cognitive radio. In this thesis the performance of an underlay cognitive radio network (UCRN) in the presence of the co-channel interference (CCI) is assessed. Firstly, the impact of CCI on the dual-hop cooperative UCRN is investigated over Rayleigh fading channels. In order to do this, the exact outage probability (OP), average error probability (AEP) and the ergodic capacity (EC) are studied. In addition, simple and asymptotic expressions for the OP and AEP are derived. Furthermore, the optimal power allocation is investigated to enhance the network performance. Moreover, the performance of a multi-user scenario is studied by considering the opportunistic SNR-based selection technique. Secondly, the effect of both primary network interference and CCI on the dual-hop UCRN over Rayleigh fading channels are studied. The equivalent signal-to-interference-plus-noise ratio (SINR) for this network scenario is obtained by considering multi-antenna schemes at all receiver nodes. The different signal combinations at the receiver nodes are investigated and compared, such as selection combining (SC) and maximum ratio combining (MRC) techniques. Then, the equivalent probability density function (PDF) and cumulative distribution function (CDF) of the network’s equivalent SINR are derived and discussed. Furthermore, expressions for the exact OP, AEP, and EC are derived and reviewed. In addition, asymptotic OP expressions are obtained for different case scenarios to gain an insight into the network parameters. Thirdly, multiple-input multiple-output (MIMO) UCRN is investigated under the influence of primary transmitter interference and CCI over Rayleigh fading channels. The transmit antenna selection and maximum ratio combining (TAS/MRC) techniques are considered for examining the performance of the secondary network. At first the equivalent SINR for the system is derived, then the exact and approximate expressions for the OP are derived and discussed. Fourthly, considering Nakagami-m fading channels, the performance of the UCRN is thoroughly studied with the consideration of the impact of primary network interference and CCI. The equivalent SINR for the secondary system is derived. Then, the system equivalent PDF and CDF are derived and discussed. Furthermore, the OP and AEP performances are investigated. Finally, for the cases mentioned above, numerical examples in conjunction with MatLab Monte Carlo simulations are provided to validate the derived results. The results show that CCI is one of the factors that severely reduces the UCRN performance. This can be more observable when the CCI power increases linearly with the transmission power of the secondary transmitter nodes. Furthermore, it was found that in a multi-user scenario the opportunistic SNR-based selection technique consideration can improve the performance of the network. Moreover, adaptive power allocation is found to give better results than equal power allocation. In addition, cooperative communication can be considered to be an effective way to combat the impact of transmission power limitation of the secondary network and interference power constraint. The multi-antenna schemes are another important consideration for enhancing the overall performance. In fact, despite the interference from the CCI and primary user sources, the multi-antennas scheme does not lose its advantage in the UCRN performance improvementHigher Committee for Education Development in Iraq (HCED). I am also grateful to the Ministry of Transportation and Communication, Kurdistan Regional Government-Iraq

Performance analyses and design for cognitive radios

Cognitive radio has been proposed as a promising solution to the conflict between the spectrum scarcity and spectrum under-utilization. As the demand increases for wireless communication services, cognitive radio technology attracts huge attention from both commercial industries and academic researches. The purpose of this thesis is to provide an analytical evaluation of the cognitive radio system performance while taking into consideration of some realistic conditions. Several problems are investigated in this thesis. First, by adopting a dynamic primary user traffic model with one primary user occupancy status change and exponentially distributed channel holding times, its effect on the cognitive radio system performance is evaluated. In the evaluation, the sensing-throughput tradeoff of the cognitive radio is used as the examination criteria, while energy detection is applied during the spectrum sensing. The thesis then takes the investigation further by establishing a primary user multiple changes traffic model which considers multiple primary user occupancy status changes and any reasonable channel holding time distributions. The effect of the primary user multiple changes traffic on the spectrum sensing performance is investigated while the channel holding times are assumed to be exponential, Gamma, Erlang and log-normal distributed. The analytical evaluation of cognitive radio is also carried out from the secondary user transmission perspective, where the performance of the adaptive modulation in cognitive radio system is investigated. The effect of the cognitive radio distinctive features on the performance of both the adaptive continuous rate scheme and the adaptive discrete rate scheme of the adaptive modulation are examined. The BER performance and the link spectral efficiency performance are derived for both schemes. A novel frame structure where the spectrum sensing is performed by using the recovered received secondary frames is also evaluated in this thesis. A realistic scenario which considers the secondary user signal decoding errors is examined for the novel structure, while an ideal upper bound performance is given when the decoding process is assumed perfect. By extending the system to include multiple consecutive secondary frames, the performance of the novel structure is compared to the performance of the traditional frame structure proposed by the IEEE 802.22 WRAN standard. The effect of the primary user multiple changes traffic is also examined for the novel structure. Several major findings are made from the analytical evaluations presented in this thesis. Through numerical examinations, it was shown that, first, the dynamic primary user traffic degrades the performance of cognitive radio systems. Second, the degree of the performance degradation of the cognitive radio systems is related to the number of primary user status changes and the primary user traffic intensity. Different primary user channel holding times distributions also lead to different sensitivities of the system performance to the primary user traffic. Third, cognitive radio distinctive features degrades the performance of the adaptive modulation. When the novel structure is applied for cognitive radio, a higher secondary achievable throughput can be obtained with a limited saturation threshold

Average Rate of Downlink Heterogeneous Cellular Networks over Generalized Fading Channels - A Stochastic Geometry Approach

In this paper, we introduce an analytical framework to compute the average rate of downlink heterogeneous cellular networks. The framework leverages recent application of stochastic geometry to other-cell interference modeling and analysis. The heterogeneous cellular network is modeled as the superposition of many tiers of Base Stations (BSs) having different transmit power, density, path-loss exponent, fading parameters and distribution, and unequal biasing for flexible tier association. A long-term averaged maximum biased-received-power tier association is considered. The positions of the BSs in each tier are modeled as points of an independent Poisson Point Process (PPP). Under these assumptions, we introduce a new analytical methodology to evaluate the average rate, which avoids the computation of the Coverage Probability (Pcov) and needs only the Moment Generating Function (MGF) of the aggregate interference at the probe mobile terminal. The distinguishable characteristic of our analytical methodology consists in providing a tractable and numerically efficient framework that is applicable to general fading distributions, including composite fading channels with small- and mid-scale fluctuations. In addition, our method can efficiently handle correlated Log-Normal shadowing with little increase of the computational complexity. The proposed MGF-based approach needs the computation of either a single or a two-fold numerical integral, thus reducing the complexity of Pcov-based frameworks, which require, for general fading distributions, the computation of a four-fold integral.Comment: Accepted for publication in IEEE Transactions on Communications, to appea