Peak Transmit Power Constraint Research Articles

Influence of Channel Information Imperfection on Outage Probability of Cooperative Cognitive Networks with Partial Relay Selection

Influence of channel information imperfection on outage probability of cooperative cognitive networks with partial relay selection over independent and non-identical Rayleigh fading channels and under peak transmit power constraint and interference power constraint is thoroughly analyzed in this paper. To eliminate time-consuming simulations, we propose both exact and asymptotic outage probability expressions in closed-form, which facilitate in quickly evaluating this influence in key operation parameters and acquiring useful insights into performance limits. For comparison, we also derive similar expressions for two benchmark communications schemes in cognitive radio networks, namely direct transmission and dual-hop communications with partial relay selection. Various results show considerable system performance deterioration and performance saturation owing to channel information imperfection, and superiority of cooperative communications to direct transmission and dual-hop communications.

Energy-Efficient Optimal Power Allocation for Fading Cognitive Radio Channels: Ergodic Capacity, Outage Capacity, and Minimum-Rate Capacity

Green communications is an inevitable trend for future communication network design, especially for a cognitive radio network. Power allocation strategies are of crucial importance for green cognitive radio networks. However, energy-efficient power allocation strategies in green cognitive radio networks have not been fully studied. Energy efficiency maximization problems are analyzed in delay-insensitive cognitive radio, delay-sensitive cognitive radio, and simultaneously delay-insensitive and delay-sensitive cognitive radio, where a secondary user coexists with a primary user and the channels are fading. Using fractional programming and convex optimization techniques, energy-efficient optimal power allocation strategies are proposed subject to constraints on the average interference power, along with the peak/average transmit power. It is shown that the secondary user can achieve energy efficiency gains under the average transmit power constraint, in contrast to the peak transmit power constraint. Simulation results show that the fading of the channel between the primary user transmitter and the secondary user receiver and the fading of the channel between the secondary user transmitter and the primary user receiver are favorable to the secondary user with respect to the energy efficiency maximization of the secondary user, whereas the fading of the channel between the secondary user transmitter and the secondary user receiver is unfavorable to the secondary user.

QoS provisioning for multiple Femtocells via game theory

We consider a system with multiple Femtocells (FCs) operating in a Macrocell. The transmissions in one Femtocell interfere with its neighboring Femtocells. Each Femtocell has multiple users, each requiring a minimum transmission rate. There is also peak transmit power constraint in each channel to control interference to the BS and the users in the Macrocell. We formulate the problem of channel allocation and power control in each Femtocell as a noncooperative Game. We develop efficient decentralized algorithms to obtain a Nash equilibrium (NE) that satisfies the Quality of Service (QoS) of each user, in an efficient way. We also obtain efficient decentralized algorithms to obtain fair NE when it may not be feasible to satisfy the QoS of all the users in FCs. Finally, we extend our algorithms to the case where there may be voice and data users in the system.

Optimal Power Allocation for Underlay-Based Cognitive Radio Networks With Primary User's Statistical Delay QoS Provisioning

Due to the highly-stochastic nature of wireless channels, how to provide efficient delay quality-of-service (QoS) provisioning for primary users (PU) while optimizing the performance of secondary users (SU) is a critically important task for cognitive radio networks (CRN). To address the above issue, we investigate the optimal power allocation strategy for underlay-based CRN with PU's statistical delay QoS protection. Instead of utilizing the widely-used interference power constraint to protect PU's transmission, we aim at satisfying PU's statistical delay QoS requirement characterized by the queue-length bound violation probability. By applying the theory of effective capacity, we further convert PU's queue-length bound violation probability constraint to the equivalent maximum sustainable traffic load requirement. Then, we formulate the optimization problem to maximize SU's average throughput while meeting PU's statistical delay QoS requirement as well as SU's average and peak transmit power constraints, which can be proved as a nonconvex problem. By employing the theories of convex hull and probabilistic transmission, we convert the original nonconvex problem to the equivalent strictly convex problem and then obtain the optimal power allocation strategy, which adapts to both PU's delay QoS requirements and channel conditions. Moreover, we also develop for comparison a fixed power allocation scheme that only adjusts with PU's delay QoS requirements. Simulation results are provided which demonstrate that both the optimal and fixed schemes can flexibly allocate the upperbounded transmit power budget according to PU's delay QoS requirements, but the proposed optimal power allocation strategy can also efficiently exploit the time-varying nature of wireless channels and thus significantly outperforms the fixed power allocation scheme.

Ergodic Sum-Rate Maximization for Fading Cognitive Multiple-Access Channels Without Successive Interference Cancelation

In this paper, the ergodic sum rate of a fading cognitive multiple-access channel (C-MAC) is studied, where a secondary network (SN) with multiple secondary users (SUs) transmitting to a secondary base station shares the spectrum band with a primary user (PU). An interference power constraint (IPC) is imposed on the SN to protect the PU. Under such a constraint and the individual transmit power constraint (TPC) imposed on each SU, we investigate the power allocation strategies to maximize the ergodic sum rate of a fading C-MAC without successive interference cancelation (SIC). In particular, this paper considers two types of constraints: 1) average TPC and average IPC and 2) peak TPC and peak IPC. For the first case, it is proved that the optimal power allocation is dynamic time-division multiple access (D-TDMA), which is exactly the same as the optimal power allocation to maximize the ergodic sum rate of the fading C-MAC with SIC under the same constraints. For the second case, it is proved that the optimal solution must be at the extreme points of the feasible region. It is shown that D-TDMA is optimal with high probability when the number of SUs is large. Moreover, we show that when the SUs can be sorted in a certain order, an algorithm with linear complexity can be used to find the optimal power allocation.

Impact of secondary user communication on security communication of primary user

AbstractCognitive radio network concept has been considered as a promising solution to improve the spectrum utilization. However, it may be vulnerable to security problems as the primary user (PU) and secondary user (SU) access the same resource. In this paper, we consider a system model where an eavesdropper (EAV) illegally listens to the PU communication in the presence of a SU transmitter (SU‐Tx) communicating with a SU receiver (SU‐Rx). The SU‐Tx transmit power is subject to the peak transmit power constraint of the SU and outage probability constraint of the PU. Given this context, the effect of the interference from the SU‐Tx to the EAV on the primary system security is investigated. In particular, analytical expressions of the probability of existence of non‐zero secrecy capacity and secrecy outage probability of the PU are derived. Moreover, the performance analysis of the secondary network is examined where closed‐form expressions of the symbol error probability and achievable rate are presented. Numerical examples are provided to evaluate the impact of the primary system parameters and channel conditions among users on the system performance of secondary and primary networks. Interestingly, our results reveal a fact that the security of the primary network strongly depends on the channel condition of the SU‐Tx to the EAV link and the transmit power policy of the SU‐Tx. Copyright © 2015 John Wiley & Sons, Ltd.

Energy Efficiency and Delay Tradeoff for Time-Varying and Interference-Free Wireless Networks

In this paper, we investigate the fundamental tradeoff between energy efficiency (EE) and delay for time-varying and interference-free wireless networks. We formulate the problem as a stochastic optimization model, which optimizes the system EE subject to network stability and the average and peak transmit power constraints. By adopting the fractional programming theory and Lyapunov optimization technique, a general and effective algorithm, referred to as the EE-based dynamic power allocation algorithm (EE-DPAA), is proposed. The EE-DPAA does not require any prior knowledge of traffic arrival rates and channel statistics, yet yields an EE that can arbitrarily approach the theoretical optimum achieved by a system with complete knowledge of future events. Most importantly, we quantitatively derive the EE-delay tradeoff as [O(1/V),O(V)] with V as a control parameter for the first time. This result provides an important method for controlling the EE-delay performance on demand. Simulation results validate the theoretical analysis on the EE-delay tradeoff, as well as show the adaptiveness of the EE-DPAA.

Outage Probability Analysis of MIMO Cognitive Radios with Single Transmit and Receive Antenna Selection

For multiple-input multiple-output cognitive radio systems, we propose an optimal single transmit and receive antenna selection scheme which maximizes the signal-to-interference-and-noise ratio. Considering peak interference power constraint, peak transmit power constraint, and interference from primary transmitter to cognitive receiver, we theoretically derive the exact system outage probability. It is shown that the theoretical results match simulation results.

Adaptive rate and power transmission in spectrum‐sharing systems with statistical interference constraint

The present study attempted to investigate the capacity gains in a spectrum-sharing system where the transmit power and rate of the secondary user (SU) are adapted based on the spectrum sensing information about activity of primary user (PU) and statistical channel fading gain between the SU transmitter (SUT) and PU receiver (PUR). It was assumed that the SU can use the spectrum band originally allocated to PU, based on the definition that when the PU is present in the spectrum band, the SU must consider the peak transmit power and statistical interference constraints. In addition, when the PU is absent at the spectrum band, the SU can only consider the peak transmit power constraint. The main advantage of using statistical interference constraint is that it does not require the instantaneous feedback channel between SUT and PUR. Furthermore, to maximise the achievable capacity of the SU, the average transmit power was first calculated. Then the adaptive rate and power policy were inspected for maximising the achievable capacity under said constraints and bit error rate requirements in multilevel quadrature amplitude modulation. Numerical and comparison results representing the efficiency of the proposed system are also provided.

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

AbstractConsider a multi‐user underlay cognitive network where multiple cognitive users concurrently share the spectrum with a primary network with multiple users. The channel between the secondary network is assumed to have independent but not identical Nakagami‐m fading. The interference channel between the secondary users (SUs) and the primary users is assumed to have Rayleigh fading. A power allocation based on the instantaneous channel state information is derived when a peak interference power constraint is imposed on the secondary network in addition to the limited peak transmit power of each SU. The uplink scenario is considered where a single SU is selected for transmission. This opportunistic selection depends on the transmission channel power gain and the interference channel power gain as well as the power allocation policy adopted at the users. Exact closed form expressions for the moment‐generating function, outage performance, symbol error rate performance, and the ergodic capacity are derived. Numerical results corroborate the derived analytical results. The performance is also studied in the asymptotic regimes, and the generalized diversity gain of this scheduling scheme is derived. It is shown that when the interference channel is deeply faded and the peak transmit power constraint is relaxed, the scheduling scheme achieves full diversity and that increasing the number of primary users does not impact the diversity order. Copyright © 2014 John Wiley & Sons, Ltd.

Capacity maximisation of the secondary link in cognitive radio networks with hybrid spectrum access strategy

A hybrid spectrum access strategy which is different from traditional underlay or overlay strategy is proposed. In this strategy, the secondary users cooperatively sense the states of the primary users in the sharing spectrum band. Based on the sensing results and an additional requirement on the bit error rate, the secondary transmitter adapts its transmit power and modulation level. Specifically, if the primary user is detected to be inactive, the secondary transmitter allocates its power subject to a peak transmit power constraint. Else if the primary user is active, the average interference power constraint would also be imposed to protect the primary transmission. To demonstrate the superiority of the hybrid strategy, capacity of the secondary link with this strategy over Rayleigh fading channel is studied. It has been assumed that diversity combing technique is available at the secondary receiver. Perfect and imperfect estimations of the channel power gain from secondary transmitter to primary receiver are also considered. Then the expression of capacity of the secondary link is derived by using Lagrange dual decomposition method. Simulation results demonstrate that the capacity of the secondary link with hybrid strategy is significantly improved when compared with the traditional ones.

Outage-Constrained Power Allocation in Spectrum Sharing Systems with Partial CSI

Due to limited cooperation between the primary users and the secondary users (SUs) in practical spectrum sharing systems, the secondary transmitters and receivers are assumed to have partial channel state information related to the primary receiver. Under such an assumption, this work investigates power allocation strategies for the SUs subject to an outage probability constraint on the primary transmission and a peak transmit power constraint on the secondary transmission. The challenge lies in the non-convexity of the outage probability constraint. Firstly, we prove that strong duality holds and that the Karush-Kuhn-Tucker (KKT) conditions are necessary for optimality. The optimal solution is then derived by addressing the optimality issues of the KKT solutions. Secondly, in order to further reduce the algorithmic complexity, two suboptimal strategies are proposed. The first one is designed based on several simplifications of the optimal strategy. The second one is derived from the convex relaxation of the non-convex primal problem, which corresponds to the problem with the conventional interference temperature constraint. The performance for both suboptimal strategies is derived in closed form. All proposed strategies are shown to outperform non-adaptive power transmission. The near-optimality of the two suboptimal strategies is also validated, in particular for the first one.

Performance Analysis of a Power Limited Spectrum Sharing System With TAS/MRC

Capacity of the cognitive radio network degrades due to the interference constraint from the primary network. The secondary network capacity can be enhanced in a cost effective way by means of spatial diversity, that can be achieved by adding multiple antennas on the secondary network terminals and performing antenna selection. In this paper, the performance of a multiple-input multiple-output (MIMO) secondary link with transmit antenna selection (TAS) at the transmitter and maximum ratio combining (MRC) at the receiver is analyzed. A peak transmit power constraint at the secondary transmitter is considered in addition to the interference power constraint and two scenarios are considered; 1) the MIMO cognitive system with TAS/MRC (MCS-TM) does not experience interference from the primary network (denote by MCS-TM-NI), and 2) MCS-TM does experience interference from the primary network (denote by MCS-TM-WI). The performance of both MCS-TM-NI and MCS-TM-WI is analyzed and, for a Rayleigh faded channel, closed-form expression for the outage probability is derived. In addition, closed-form expressions of the moment generating function, the symbol error rate and the ergodic capacity are obtained for the MCS-TM-NI. Asymptotic performance analysis of the MCS-TM-NI reveals that TAS/MRC in a MIMO cognitive system achieves a generalized diversity gain equal to the product of the number of transmit and receive antennas. Numerical results are also presented to corroborate the derived analytical results.

SEP-Optimal Transmit Power Policy for Peak Power and Interference Outage Probability Constrained Underlay Cognitive Radios

In underlay cognitive radio (CR), a secondary user (SU) can transmit concurrently with a primary user (PU) provided that it does not cause excessive interference at the primary receiver (PRx). The interference constraint fundamentally changes how the SU transmits, and makes link adaptation in underlay CR systems different from that in conventional wireless systems. In this paper, we develop a novel, symbol error probability (SEP)-optimal transmit power adaptation policy for an underlay CR system that is subject to two practically motivated constraints, namely, a peak transmit power constraint and an interference outage probability constraint. For the optimal policy, we derive its SEP and a tight upper bound for MPSK and MQAM constellations when the links from the secondary transmitter (STx) to its receiver and to the PRx follow the versatile Nakagami-m fading model. We also characterize the impact of imperfectly estimating the STx-PRx link on the SEP and the interference. Extensive simulation results are presented to validate the analysis and evaluate the impact of the constraints, fading parameters, and imperfect estimates.

Achievable Transmission Rate of the Secondary User in Cognitive Radio Networks with Hybrid Spectrum Access Strategy

A hybrid spectrum access strategy which is different from traditional underlay or overlay strategy is proposed for cognitive radio networks. In proposed strategy, the secondary users (SU) cooperatively sense the state of the primary user (PU) in a given spectrum band. Based on the sensing results and an additional requirement on the bit error rate, the SU adapts its transmit power and modulation level. Specifically, if the PU is inactive, the SU allocates its power subject to a peak transmit power constraint. Else if the PU is active, the average interference power constraint would be further imposed to protect the primary link. We assume that the maximal ratio combing (MRC) technique is available at the secondary receiver. Imperfect spectrum sensing and imperfect estimations of the channel power gain from the secondary transmitter to primary receiver are also considered. Achievable transmission rate of the SU over Rayleigh fading channel is formulated as an optimization problem and solved by using Lagrange dual decomposition method. Simulation results demonstrate that the transmission rate of the SU with hybrid strategy is significantly improved when compared with the traditional ones.

페이딩 채널에서 직접 대역확산 부호분할 다중접속 통신을 위한 일반화된 혼합 전력/전송률 적응화 기법

We investigate a generalized combined power and rate adaptation scheme in direct-sequence (DS) code-division multiple-access (CDMA) communications over Nakagami fading channels. The transmission power allocated to user i is proportional to , where is the channel gain of user i and p is a real number, and the data rate (i.e., spreading gain) is jointly adapted so that a desired QoS is maintained. We analyze the average data rate of the proposed adaptation scheme subject to fixed average and peak transmission power constraints. Our results show that the proposed joint adaptation scheme provides a significant performance improvement over power-only and rate-only adaptation.

Cognitive Proactive and Reactive DF Relaying Schemes under Joint Outage and Peak Transmit Power Constraints

In this letter, outage performance of cognitive cooperative radio networks using two decode-and-forward (DF) schemes is investigated. Subject to the joint outage constraint of the primary user and the peak transmit power constraint of the secondary user, adaptive power allocation policies for the secondary transmitter and secondary relays are studied. Based on these strategies, expressions for the outage probability of proactive and reactive DF schemes are obtained. Interestingly, our results show that an increase in the transmit power of the primary transmitter (PU-Tx) does not always degrade the performance of the secondary network. In fact, the PU-Tx transmit power is a substantial parameter that the secondary users can adapt to in order to improve the system performance. The numerical results additionally show that the performance of the reactive DF scheme outperforms the proactive DF scheme if the outage threshold in the first hop of the reactive DF scheme is less than that of the proactive scheme.

Joint Beamforming and Power Allocation for Multiple Primary Users and Secondary Users in Cognitive MIMO Systems via Game Theory

We consider a system where a licensed radio spectrum is shared by multiple primary users(PUs) and secondary users(SUs). As the spectrum of interest is licensed to primary network, power and channel allocation must be carried out within the cognitive radio network so that no excessive interference is caused to PUs. For this system, we study the joint beamforming and power allocation problem via game theory in this paper. The problem is formulated as a non-cooperative beamforming and power allocation game, subject to the interference constraints of PUs as well as the peak transmission power constraints of SUs. We design a joint beamforming and power allocation algorithm for maximizing the total throughput of SUs, which is implemented by alternating iteration of minimum mean square error based decision feedback beamforming and a best response based iterative power allocation algorithm. Simulation results show that the algorithm has better performance than an existing algorithm and can converge to a locally optimal sum utility.

Joint single transmit and receive antenna selection for MIMO cognitive radios without channel state information

For multiple-input multiple-output cognitive radios, a single transmit and receive antenna selection scheme is proposed for when the channel state information from a cognitive transmitter to a cognitive receiver is unknown to the transmitter. In the proposed scheme, the transmit antenna at the cognitive transmitter that maximises the transmit power and the receive antenna at the cognitive receiver that maximises the signal-to-interference-and-noise ratio are selected. Also derived is the exact closed-form outage probability considering the peak interference power constraint, the peak transmit power constraint, and interference from the primary transmitter to the cognitive receiver.

Joint Beamforming and Antenna Subarray Formation for MIMO Cognitive Radios

The antenna subarray formation (ASF) is a promising technique for multiple-input multiple-output (MIMO) receiver. For MIMO cognitive radio systems, we propose a joint beamforming and ASF scheme in this letter which maximizes the cognitive achievable capacity subject to the peak transmit power constraint at the secondary transmitter, peak interference power constraint at the primary receiver, and the limited number of nonzero elements in the ASF matrix. To solve the joint optimization problem, we propose a relax-and-recover scheme. Simulation results have shown that the proposed scheme outperforms the conventional antenna selection scheme.