Throughput Of Secondary Users Research Articles

Throughput and Outage Probability of Wireless Energy Harvesting Based Cognitive DF Relaying Network

This paper evaluates the throughput performance and outage probability of a secondary user (SU) in a decode-and-forward (DF) relaying network based on wireless energy harvesting under cognitive radio constraint. The energy constrained relay node first harvests energy through radio-frequency (RF) signals from the source node. Next, the relay node uses the harvested energy to forward the decoded source information to the destination node. The power transmitted by source and relay node is constrained by the tolerable interference threshold of the primary unit receiver. The source node transfers energy and information to the relay node through power splitting-based relaying (PSR). In PSR, the relay splits the received power for energy harvesting and information processing. The interference caused by a primary unit transmitter at the SU relay and destination nodes is also considered. Considering wireless energy harvesting constraint at the relay node, we analyse the achievable throughput and outage performance of a cognitive DF relaying network. We study the impact of different system parameters such as power splitting ratio, primary transmitter power and tolerable interference threshold of PU receiver on the throughput and outage performance of SU.

Full-Duplex Communication in Cognitive Radio Networks: A Survey

Wireless networks with their ubiquitous applications have become an indispensable part of our daily lives. Wireless networks demand more and more spectral resources to support the ever increasing numbers of users. According to network engineers, the current spectrum crunch can be addressed with the introduction of cognitive radio networks (CRNs). In half-duplex (HD) CRNs, the secondary users (SUs) can either only sense the spectrum or transmit at a given time. This HD operation limits the SU throughput, because the SUs cannot transmit during the spectrum sensing. However, with the advances in self-interference suppression (SIS), full-duplex (FD) CRNs allow for simultaneous spectrum sensing and transmission on a given channel. This FD operation increases the throughput and reduces collisions as compared with HD-CRNs. In this paper, we present a comprehensive survey of FD-CRN communications. We cover the supporting network architectures and the various transmit and receive antenna designs. We classify the different SIS approaches in FD-CRNs. We survey the spectrum sensing approaches and security requirements for FD-CRNs. We also survey major advances in FD medium access control protocols as well as open issues, challenges, and future research directions to support the FD operation in CRNs.

A novel spectrum handoff-based sensing-throughput tradeoff scheme in cognitive radio

In cognitive radio (CR), there is a tradeoff between spectrum sensing time and throughput of secondary user (SU). In the conventional sensing-throughput tradeoff scheme, when the presence of the primary user (PU) is detected, the SU will stop forwarding data and wait to redetect the PU in the following frame, yielding great throughput loss. In order to improve the SU's throughput, a novel sensing-throughput tradeoff scheme is proposed, which allows the SU to search for a new idle channel through spectrum searching and transfer to this channel to continue communication, when the presence of the PU is detected. An optimization problem is proposed to maximize the SU's throughput in the proposed scheme through jointly optimizing the sensing time, the searching time and the number of available channels, providing that the detection probability to the PU is guaranteed. By fixing the number of channels, based on alternating direction optimization, the joint optimization algorithm of sensing time and searching time is proposed, and then the optimal number of channels is obtained through enumerative searching. The simulation results how that there exist the optimal solutions to the proposed scheme, and the proposed scheme outperforms the conventional scheme notably, with different detection probabilities and sampling frequencies.

Group-Based Multibit Cooperative Spectrum Sensing for Cognitive Radio Networks

In cooperative spectrum sensing (CSS), a multibit combination rule shows better sensing performance than one-bit hard combination rules at the sacrifice of the reporting overhead. To overcome the tradeoff between the sensing performance and the reporting overhead, we propose a novel group-based multibit CSS scheme with a limited reporting overhead. The proposed scheme adopts contention-based reporting to restrain the reporting overhead while achieving multiuser diversity with an increased number of secondary users (SUs). Moreover, SUs report one-bit sensing results to a fusion center instead of sending multibit quantization information, and the rest of the information is embedded in the time slot. The simulation results demonstrate that, as the number of SUs increases, the proposed scheme improves the sensing performance and the average throughput of SUs, whereas the conventional one-bit or multibit combination schemes show a tradeoff between the sensing performance and the throughput of SUs.

Performance analysis of binary exponential backoff MAC protocol for cognitive radio in the IEEE 802.16e/m network

We propose a distributed MAC protocol for cognitive radio when primary network is IEEE 802.16e/m WiMAX. Our proposed MAC protocol is the Truncated Binary Exponential Backoff Algorithm where the backoff window size of algorithm is doubled at each collision, and the backoff counter is operated by frame basis in IEEE 802.16e/m and is freezed at a frame with no idle slots. We model our proposed MAC protocol as a 3-dimensional discrete-time Markov chain and obtain steady state probability of the Markov chain by using a censored Markov chain method. Based on this steady state probability, we obtain the throughput, packet loss probability and packet delay distribution of secondary users. Our numerical examples show that the initial contention window size can be determined according to the number of secondary users in order to obtain higher throughput for secondary users, and the maximum backoff window has a large impact on the secondary user's packet loss probability. Secondary users' packet delay distribution is much influenced by the initial contention window size and the number of secondary users.

Optimal Cognitive Access and Packet Selection Under a Primary ARQ Process via Chain Decoding

This paper introduces a novel technique that enables access by a cognitive secondary user (SU) to a spectrum occupied by an incumbent primary user (PU) that employs Type-I hybrid automatic retransmission request (ARQ). The technique allows the SU to perform selective retransmissions of SU data packets, whose transmission previously failed. The temporal redundancy introduced by the PU ARQ protocol and by the selective retransmission process of the SU can be exploited by the SU receiver to perform interference cancellation (IC) over multiple transmission slots, thus creating a “clean” channel for the decoding of the concurrent SU or PU packets. The chain decoding (CD) technique is initiated by a successful decoding operation of an SU or a PU packet and proceeds by an iterative application of IC as previously buffered packets become decodable and their interference can be removed, thus making it possible to recover the concurrent data packets, and so on, until no more packets are decodable. Based on this scheme, an optimal policy is designed that maximizes the SU throughput under a constraint on the average long-term PU performance. The optimality of the CD protocol is proved, which determines which packet the SU should send at any given time, based on four basic rules. Moreover, a decoupling principle is proved, which establishes the optimality of decoupling the secondary access strategy from the CD protocol. Specifically, first , the SU access policy, optimized via dynamic programming, specifies whether the SU should access the channel or remain idle, based on a compact state representation of the protocol, and second , the CD protocol embeds four basic rules that are used to select the packet transmitted by the SU. It is shown numerically that CD outperforms by up to 35% other schemes considered in the literature, which do not employ retransmissions at the SU pair and thus do not exploit the full potentiality of IC.

Improving spectrum handoff utilization for prioritized cognitive radio users by exploiting channel bonding with starvation mitigation

In this study, priority based non-preemptive M/G/1 queueing model of spectrum handoff scheme is proposed in Wireless Cognitive Radio Networks. Channel bonding mechanism with starvation mitigation is employed in order to improve spectrum handoff utilization for secondary users. Since spectrum handoff offers an opportunity to secondary users for continuing their communication, it is of critical significance to determine action of primary users. In the queueing model, prioritized data traffic with aging solution to starvation is exploited to meet requirements of the secondary users. In aging mechanism; when the packet of the low priority secondary user waits in the queue more than three frame times, priority of that packet is increased. Packets of secondary users are categorized into three different priority classes, i.e., urgent, real time, and non-real time where non-real time data packets have the lowest priority while urgent data packets have the highest priority. Channel bonding mechanism is described as combining two subsequent time slots if the size of the packet is bigger than one time slot. Idle time slots for channel bonding are determined using both proactive and reactive decision based spectrum handoff schemes. Before starting spectrum handoff process with proactive scheme, first of two subsequent time slot is sensed using reactive scheme. Riverbed Modeler simulation software is utilized to simulate channel bonding and aging mechanisms. Analytical results are shown to be matched with the simulation results obtained under different load and arrival rates. This study has also exposed that the throughput of secondary users could be increased significantly by employing aging solution to starvation, and channel bonding mechanisms.

Mixed-integer programming based techniques for resource allocation in underlay cognitive radio networks: A survey

For about the past decade and a half research efforts into cognitive radio networks (CRNs) have increased dramatically. This is because CRN is recognized as a technology that has the potential to squeeze the most out of the existing spectrum and hence virtually increase the effective capacity of a wireless communication system. The resulting increased capacity is still a limited resource and its optimal allocation is a critical requirement in order to realize its full benefits. Allocating these additional resources to the secondary users (SUs) in a CRN is an extremely challenging task and integer programming based optimization tools have to be employed to achieve the goals which include, among several aspects, increasing SUs throughput without interfering with the activities of primary users. The theory of the optimization tools that can be used for resource allocations (RA) in CRN have been well established in the literature; convex programming is one of them, in fact the major one. However when it comes to application and implementation, it is noticed that the practical problems do not fit exactly into the format of well established tools and researchers have to apply approximations of different forms to assist in the process. In this survey paper, the optimization tools that have been applied to RA in CRNs are reviewed. In some instances the limitations of techniques used are pointed out and creative tools developed by researchers to solve the problems are identified. Some ideas of tools to be considered by researchers are suggested, and direction for future research in this area in order to improve on the existing tools are presented.

Spatial-Temporal Spectrum Access Analysis for Multi-Channel Mobile Cognitive Radio Networks

Cognitive radios have demonstrated its ability in improving spectrum efficiency by accessing licensed spectrum bands opportunistically. Along with the popularity of mobile broadband devices in future mobile communications, research for cognitive radios with mobility will be paid more and more attentions. In this paper, a multi-channel cognitive radio network with mobile secondary users is investigated. Based on the reality that the primary licensed channels have different available states on spatial and temporal dimensions for secondary users, we analyze the spatial-temporal spectrum utilization rate and derive the network throughput of secondary users combined with successful probability of wireless transmission. Finally, through maximizing the throughput we obtain the optimal spectrum access strategy. Numerical results show the effect of the system parameters on the proposed strategy and verify our proposed strategy outperforms other strategies such as equiprobable, inverse proportional and random access strategies.

On Stable Throughput of Cognitive Radio Networks With Cooperating Secondary Users

In this paper, we study cooperative cognitive radio networks consisting of a primary user and multiple secondary users. Secondary users transmit only when primary user is sensed as silent and may interfere with primary transmission due to imperfect sensing. When primary activity is sensed correctly, secondary users cooperate with primary user by assisting retransmission of failed packets of primary user. We analyze packet throughput of primary and secondary users for three variations of proposed cooperation method. Signal flow graph (SFG) based approach is employed to obtain closed form expressions of packet throughput. The analysis is done for two cases; individual sensing and cooperative sensing. Further, we characterize optimal transmission probability of secondary users that maximizes individual secondary packet throughput keeping all queues in the system stable. Results present a comparison of throughput performance of proposed cooperation methods under different scenarios and show their benefits for both primary as well as secondary user throughput.

Energy-Aware Cooperative Wireless Networks With Multiple Cognitive Users

In this paper, we study and analyze cooperative cognitive radio networks with arbitrary number of secondary users (SUs). Each SU is considered a prospective relay for the primary user (PU) besides having its own data transmission demand. We consider a multi-packet transmission framework that allows multiple SUs to transmit simultaneously because of dirty-paper coding. We propose power allocation and scheduling policies that optimize the throughput for both PU and SU with minimum energy expenditure. The performance of the system is evaluated in terms of throughput and delay under different opportunistic relay selection policies. Toward this objective, we present a mathematical framework for deriving stability conditions for all queues in the system. Consequently, the throughput of both primary and secondary links is quantified. Furthermore, a moment generating function approach is employed to derive a closed-form expression for the average delay encountered by the PU packets. Results reveal that we achieve better performance in terms of throughput and delay at lower energy cost as compared with equal power allocation schemes proposed earlier in the literature. Extensive simulations are conducted to validate our theoretical findings.

Resource Allocation and Fairness in Wireless Powered Cooperative Cognitive Radio Networks

We integrate a wireless powered communication network with a cooperative cognitive radio network, where multiple secondary users (SUs) powered wirelessly by a hybrid access point (HAP) help a primary user relay the data. As a reward for the cooperation, the secondary network gains the spectrum access where SUs transmit to HAP using time division multiple access. To maximize the sum throughput of SUs, we present a secondary sum-throughput optimal resource allocation (STORA) scheme. Under the constraint of meeting target primary rate, the STORA scheme chooses the optimal set of relaying SUs and jointly performs the time and energy allocation for SUs. In particular, by exploiting the structure of the optimal solution, we find the order in which SUs are prioritized to relay primary data. Since the STORA scheme focuses on the sum throughput, it becomes inconsiderate toward individual SU throughput, resulting in low fairness. To enhance fairness, we investigate three resource allocation schemes, which are: 1) equal time allocation; 2) minimum throughput maximization; and 3) proportional time allocation. Simulation results reveal the tradeoff between sum throughput and fairness. The minimum throughput maximization scheme is the fairest one as each SU gets the same throughput, but yields the least SU sum throughput.

Hybrid Overlay/Underlay Transmission Scheme with Optimal Resource Allocation for Primary User Throughput Maximization in Cooperative Cognitive Radio Networks

Recent studies to improve the spectrum utilization and efficiency show that Dynamic Spectrum Access and Cognitive Radio are the two techniques to satisfy these requirements. The use of such techniques will overcome the inefficient spectrum utilization due to fixed frequency allocation techniques. To enable the Secondary Users to coexist with the Primary Users, Overlay and Underlay are the two transmission techniques that are widely used. In this paper, we present a hybrid overlay/underlay spectrum access strategy that has the features of both the traditional overlay and underlay strategies. This strategy presents a novel approach in which the primary users can use the secondary users to maximize their throughput. In addition to the hybrid overlay/underlay transmission strategy, this paper also provides a resource allocation protocol that decides the best secondary user to be selected as relay, power levels of these secondary users and best channel to be selected. Unlike the previous works done on hybrid transmission protocols, where the main aim is to maximize the secondary user throughput, this paper aims to maximization of primary user capacity and avoiding harmful interference to other active primary users and avoids the need to switch between the overlay and underlay protocols. Performance analysis is done with simulations of hybrid overlay/underlay, underlay and overlay techniques and discussions on results are presented. Discussions are also provided on the criterion for relay power selection between interference only constraint and power only constraint.

Throughput of a cooperative energy harvesting secondary user in cognitive radio networks

AbstractThis paper investigates the maximum throughput of a rechargeable secondary user (SU) sharing the spectrum with a primary user (PU). The SU is assumed to be an energy harvesting node, which harvests energy packets from the environmental energy sources (e.g. solar, wind and acoustics) with a certain harvesting rate. The PU is equipped with a data buffer to store the randomly arrived data packets at its receiver. In addition to its own data buffer, the SU is equipped with another data buffer for storing the unsuccessfully decoded packets at the primary destination in a given time slot due to channel fading. Moreover, it has an energy buffer for storing the energy packets harvested from the environment. We propose a new cooperative cognitive relaying protocol that allows the SU to gain channel access when it relays a fraction of the undelivered primary packets. We consider an interference channel model [or a multipacket reception (MPR) channel model], where simultaneous transmissions can be decoded correctly at the corresponding destinations with certain decoding probabilities characterised by the complement of channel outages under interference. Our proposed protocol exploits the PU's data burstiness because of the random and sporadic packet arrival at its queue. Moreover, the proposed protocol takes advantage of the receivers' MPR capabilities. In addition, it efficiently expends the secondary energy packets under the objective of secondary throughput maximisation. Our numerical results show the benefits of cooperation, receivers' MPR capabilities and secondary energy queue arrival rate on the system's performance from a network layer standpoint. Copyright © 2016 John Wiley & Sons, Ltd.

Improving CSMA/CA network performance under hidden collision

AbstractDynamic spectrum access policy allows a secondary user (SU) to access a primary user (PU) channel when it is idle. However, the idle state may result from the PU's silent activities, which can be wrongly perceived as an opportunity for the SU to access the channel and lead to “hidden collision” when it effectively tries to access the channel under this condition. At best of our knowledge, this issue has yet to be addressed in the literature. In this paper, we will first define a three‐state model that describes hidden collision conditions, then propose a probabilistic model in which a transient state is added to force the SU to wait a certain period of time before accessing the channel, thereby translating into better protection for the PU. Based on this model and using Carrier Sense Multiple Access/Collision Avoidance protocol, we will evaluate the PU's and SU's throughput and delay with and without transient state as well as the gain in using our approach. Our computation results show a substantial improvement of the PU's throughput from 19.6 to 61.1%.

Adaptive Power Allocation Schemes for Spectrum Sharing in Interference-Alignment-Based Cognitive Radio Networks

Interference alignment (IA) is a promising technique for interference management and can be applied to spectrum sharing in cognitive radio (CR) networks. However, the sum rate may fall short of the theoretical maximum, particularly at low signal-to-noise ratio (SNR), and the quality of service (QoS) of the primary user (PU) may not be guaranteed. In addition, power allocation (PA) in IA-based CR networks is largely ignored, which can further improve its performance. Thus, in this paper, PA in IA-based CR networks is studied. To guarantee the QoS requirement of the PU, its minimal transmitted power is derived. Then, we propose three PA algorithms to maximize the throughput of secondary users (SUs), the energy efficiency (EE) of the network, and the requirements of SUs, respectively, while guaranteeing the QoS of the PU. To reduce the complexity, the closed-form solutions of these algorithms are further studied in detail. The outage probability of the PU according to its rate threshold is also derived to analyze the performance of these algorithms. Moreover, we propose a transmission-mode adaptation scheme to further improve the PU's performance when its QoS requirement cannot be guaranteed at low SNR, and it can be easily combined with the proposed PA algorithms. Simulation results are presented to show the effectiveness of the proposed adaptive PA algorithms for IA-based CR networks.

Relay-Based Spectrum Sharing With Secondary Users Powered by Wireless Energy Harvesting

Spectrum sharing and energy harvesting are promising techniques to improve the bandwidth and energy efficiencies to meet the ever-growing demand of wireless data transmissions. In this paper, we propose an efficient relay-based spectrum sharing protocol in the cognitive radio network, where the secondary user (SU) can implicitly harvest the radio frequency (RF) energy from the primary user (PU) transmissions. Using the harvested energy, the SU can assist the PU transmission to exchange for the opportunity of spectrum access. Both the Alamouti coding and the superposition coding techniques are adopted by the transmitters to facilitate the primary data relaying and the secondary data transmission simultaneously. The joint decoding and the interference cancelation techniques are adopted by the receivers to retrieve the desired signals. The more power allocated for the primary data relaying, the higher throughput can be achieved for the PU, while the less throughput is available for the SU with less energy remained. The optimal power allocation is numerically determined by maximizing the SU throughput while guaranteeing the PU throughput. Numerical results show that our protocol can greatly improve the system throughput and the impacts of various system settings are revealed for the network deployment.

Leasing-Based Performance Analysis in Energy Harvesting Cognitive Radio Networks.

In this paper, we consider an energy harvesting cognitive radio network (CRN), where both of primary user (PU) and secondary user (SU) are operating in time slotted mode, and the SU powered exclusively by the energy harvested from the radio signal of the PU. The SU can only perform either energy harvesting or data transmission due to the hardware limitation. In this case, the entire time-slot is segmented into two non-overlapping fractions. During the first sub-timeslot, the SU can harvest energy from the ambient radio signal when the PU is transmitting. In order to obtain more revenue, the PU leases a portion of its time to SU, while the SU can transmit its own data by using the harvested energy. According to convex optimization, we get the optimal leasing time to maximize the SU’s throughput while guaranteeing the quality of service (QoS) of PU. To evaluate the performance of our proposed spectrum leasing scheme, we compare the utility of PU and the energy efficiency ratio of the entire networks in our framework with the conventional strategies respectively. The numerical simulation results prove the superiority of our proposed spectrum leasing scheme.

Robust adaptive power control for cognitive radio networks

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.

Secondary User Aggressiveness Optimization in Sensing-Transmission Scheduling for Cognitive Radio Networks

The constraint of limited frequency spectrum for wireless communication is very daunting. The radio spectrum licensed to permanent users is wasted at times when not used continuously. Cognitive radio technology involves a change in regulation of radio spectrum. In cognitive radio networks a secondary user network is designed for efficiently using gaps in spectrum and not causing at the same time harmful interference to license holding primary users. There is a continuous tradeoff between the opposing goals of Primary User transmission protection and Secondary User throughput maximization. For a Secondary User, both sensing and transmitting is important so as to avoid collisions, packet loss and improve throughput. This paper presents optimization of Secondary User packet length in sensing-transmission scheduling for dynamically accessing the spectrum in cognitive radios. The need to maximize the Secondary User access is achieved by optimizing its packet length with respect to collision cost in a threshold based sensing-transmission structure using Matlab simulations. The results are presented in the form of traces of thresholds for different packet lengths and collision costs. This scheme optimizes Secondary User aggressiveness and throughput while safeguarding Primary User interests