Efficient Algorithm for Multi-Constrained Opportunistic Wireless Scheduling

This paper addresses time-efficient broadcast scheduling problem in Cognitive Radio (CR) Networks. Cognitive Radio is a promising technology that enables the use of unused spectrum in an opportunistic manner. Because of the unique characteristics of CR technology, the broadcast scheduling problem in CR networks needs unique solutions. Even for single channel wireless networks, finding a minimum-length broadcast schedule is an NP-hard problem. In addition, the multi-channel nature of the CR networks, especially the non-uniform channel availability, makes it a more complex problem to solve. In this paper, we first present an Integer Linear Programming formulation (ILP) to determine the minimum broadcast schedule length for a CR network. We then present two heuristics to construct minimal length broadcast schedules. Comparison of optimal results (found by solving the ILP formulation) with the result of the heuristics through simulation shows that both heuristics produce schedules of either optimal or very closer to optimal lengths.Keywordscognitive radio networkstime efficient broadcastingbroadcast scheduling

The multichannel rendezvous problem in cognitive radio networks (CRNs) has been a hot research topic lately. One of the most challenging settings of the multichannel rendezvous problem is the oblivious rendezvous problem in heterogeneous CRNs, where: 1) there are no distinguishable roles of users; 2) users’ clocks are not synchronized; 3) users may have different available channel sets; and 4) there is no universal labelling of the channels. Most existing works in the literature focus on achieving deterministic bounds for the maximum conditional time-to-rendezvous (MCTTR) and perform poorly (in comparison with the random algorithm) for the expected time-to-rendezvous (ETTR) due to the “stay” modes in these works. In this paper, we tackle the oblivious rendezvous problem by taking both MCTTR and ETTR into consideration. In order to have guaranteed rendezvous, we only make two assumptions: (A1) there is at least one common available channel and (A2) there is a unique ID for each user. We first propose a new class of strong symmetrization mappings to encode user IDs for speeding up the rendezvous process. Two efficient and yet simple encoding schemes are proposed by utilizing the $\cal C$ -transform and the existing 4B5B encoding. Based on the new class of strong symmetrization mappings, we propose the two-prime modular clock algorithm for the two-user rendezvous problem. The ETTR of our algorithm is almost the same as that of the random algorithm and its MCTTR is also comparable to the best existing bound. We also extend the two-prime modular clock algorithm for multiuser rendezvous by proposing the stick together algorithm and the spread out algorithm. One interesting finding for the multiuser rendezvous problem is that the spread out algorithm is not always better than the stick together algorithm as commonly claimed in the literature.

This paper focuses on the deafness problem in cognitive radio networks and presents a collision-free resident channel selection based distributed solution. Simulation results show that the proposed solution to the problem of deafness has an excellent performance in the overall network throughput and end-to-end delay characteristics, thus improving the network capacity and utilization of spectrum holes to provide quality of service in cognitive radio networks.

In this paper, we investigate an online spectrum auction problem in cognitive radio networks with uncertain activities of primary users (PUs). In our framework, a primary base station (PBS), acted as the spectrum auctioneer, leases its under-utilized channels to secondary users (SUs) who request and access spectrum on the fly. Different from most of existing works in online spectrum allocation, we focus on a more practical situation that the auctioneer (or the PBS) has no prior knowledge of PUs' activities so that its channel states are not static. In order to balance the auction profits from granted SUs' spectrum requests and the potential penalties caused by incomplete services to PUs, we introduce the idea of virtual spectrum sellers and formulate the problem as an online double spectrum auction. We then propose a novel online admission and pricing mechanism which also considers the reusability of wireless spectrum. Theoretical analyses are provided to prove that our auction algorithm satisfies all desired economic properties in terms of budget-balance, individual rationality and truthfulness. Simulation results show that our proposed auction algorithm can increase the utility of the PBS, enhance spectrum utilization and achieve better satisfaction for SUs compared to counterparts.

Cognitive radio is regarded as a promising technology to provide high bandwidth to mobile users via heterogeneous wireless network architectures and dynamic spectrum access techniques. However, cognitive radio networks may also impose some challenges due to various factors such as the ever increasing complexity of network architecture, the high cost of configuring and managing large-scale networks, the fluctuating nature of the available spectrum, diverse QoS requirements of various applications, and the intensifying difficulties of centralized control. A plethora of work has been carried out to address the challenges aforementioned by employing cognitive radio functionalities with self-organization features. In this article, variant aspects of self-organization paradigms in cognitive radio networks, including critical functionalities of MAC- and network-layer operations, are surveyed. The main contributions of this survey include introducing the fundamentals of existing cognitive radio and self-organization techniques as well as their current progress, surveying critical cognitive radio issues (including common control channel management, cooperative spectrum sensing, bioinspired spectrum sharing, network scalability and adaptive routing) as well as their self-organization features, and identifying new directions and open problems in cognitive radio networks.

Wireless networks communicate with each other using radio spectrum bands which are assigned to license owners. Due to the fixed spectrum assignment policy, a large portion of the spectrum stays unused. The aim of cognitive radio is enabling users which do not hold a license to be able to access the spectrum assigned to license owners. In the channel assignment problem, the objective is to assign channels to unlicensed users in order to maximize channel utilization without causing any interference to licensed users. In this study, we propose a hyper-heuristic approach to solve the channel assignment problem in cognitive radio networks. Results show that our approach gives high channel utilization rates by allowing unlicensed users to access the channels owned by licensed users. The results are promising and promote further study.

In this study, the power control problem in cognitive radio networks with the spectrum underlay model is considered. The secondary users (SUs) can access the spectrum belonging to primary users (PUs) only if the interference imposed on the PUs is below a certain threshold. All network nodes are assumed to be equipped with multiple antennas. Using game theory approach and the primal decomposition method, a low complexity distributed algorithm based on Nash bargaining solution (NBS) is proposed for spectrum sharing and power allocation for multiple-input multiple output cognitive radio networks. The proposed algorithm is configured in two iterative algorithms, Jacobi and Gauss-Seidel algorithms, and their performance is investigated through simulations. The convergence of the proposed algorithm is further proved analytically. Simulation results show that proposed algorithm achieves an effective tradeoff between fairness and efficiency.

Turning foes to allies in cognitive radio networks

Channel Hopping (CH) is a representative technique to solve the rendezvous problem for Cognitive Radio Networks (CRNs). Multiple radios technique were utilized in several latest researches on CH owing to the fact that it can significantly reduce the Time-To-Rendezvous (TTR) while the cost of the device is low. However, the radios of one unlicensed Secondary User (SU) may access same channel at the same time for most of the existing multi-radio CH protocols, which is a waste of energy. Moreover, the number of radios for the SUs is implicitly assumed same or must be more than one, which is unrealistic for heterogeneous CRNs. In this paper, an energy-efficient CH protocol, Hybrid Radio Rendezvous (HRR) protocol is proposed to address the above issues. Furthermore, theoretical analysis is presented to derive the upper bound on the Maximum TTR (MTTR) for the HRR protocol. In addition, the theoretical analysis is corroborated by extensive simulations while the simulation results show that the HRR protocol outperforms the state- of-the-art CH protocols in terms of the TTR and the energy efficiency.

Cognitive radio is an innovative technique for spectrum management which uses Dynamic Spectrum Access (DSA). DSA has the potential to mitigate the spectrum scarcity by letting the Secondary User (SU) access the idle spectrum unused by the Primary User (PU). DSA improves the spectrum efficiency via spectrum sensing and optimal spectrum access. Spectrum sensing should be perfect so that the SU does not cause interference to the PU. Moreover, the channel selected should be the best for maximising throughput of the SU. In this paper we consider a best channel selection problem in Cognitive Radio Networks (CRNs). The problem is modelled as optimal stopping problem where the controller at each state can stop or continue sensing based on the channel gains achieved. There is a Markovian relation given between the channel occupancies of PU. The stopping rule comes out to be simple threshold rule. The controller stops sensing when the channel gain exceeds the given threshold.

Wideband spectrum sensing is a fundamental problem in cognitive radio networks. In this paper, a wideband spectrum sensing procedure which consists of four steps, i.e., coarse support recovery, fine binary detection, band edges detection and clustering, for modulated wideband converter (MWC) based cognitive radio system at sub-Nyquist rate is proposed. Simulations show that with a sub-Nyquist sampling rate, the proposed spectrum sensing procedure can locate spectrum holes correctly.

A repeated Bayesian auction game for cognitive radio spectrum sharing scheme

MEMS reconfigurable circular-rectangular shaped slotted microstrip patch antenna is designed for the cognitive radio application. Main problem in cognitive radio networks is to utilize the available bandwidth effectively so that reconfigurable microstrip patch antenna is preferred. By utilizing the unused spectrum bandwidth can be utilized in efficient manner which in turn will increases the overall performances of the system. Reconfiguration can be done with tree different types of techniques which are frequency, pattern, and polarization. Here frequency reconfiguration technique is used with the help of MEMS switches. PSO and Nature inspired optimization algorithms are used for sensing and optimization of patch antenna. Microstrip line feed and FR4 substrate is used. Slots are introduced in this system to reduce the return loss and to improve the gain. Two different shapes of antennas are incorporated into that same substrate which helps to operate the antenna in various frequencies. Patch antenna is designed to operate within (2 to 5) GHz frequency range.

ABSTRACTThe invention of cognitive radio (CR) concept aims to overcome the spectral scarcity issues of emerging radio systems by exploiting under‐utilization of licensed spectrum. Determining how to allocate unused frequency bands among CR is one of the most important problems in CR networks. Because different CRs may have different quality‐of‐service requirements, they may have different objectives. Invoice communication, high‐speed transmission is the most important factor; hence,voice radiosalways try to maximize their transmission rate. However, indata communication, the most important factor is the bit error rate. Thedata radiosalways try to maximize their signal‐to‐interference‐plus‐noise ratio (SINR). In this paper, two non‐cooperative games named interference minimization game and capacity maximization game, which reflect the target ofdata radiosandvoice radios, respectively, are proposed. From the simulations, after these games are applied, the average SINRs of all players at each channel are improved. The average SINR of players in each channel after applying the capacity maximization game is smaller than that after applying the interference minimization game. However, in comparison with that after applying the interference minimization game, the average capacity of players after applying capacity maximization approach is larger. Copyright © 2012 John Wiley & Sons, Ltd.

As a promising approach to the rendezvous problem in cognitive radio networks (CRNs), a blind rendezvous paradigm has recently spawned various asynchronous channel-hopping (CH) rendezvous schemes that enable any two neighboring secondary users to meet among multiple channels within a finite time, even with no synchronization. However, the rendezvous delay that was derived in existing work is unable to reflect the actual channel access delay performance in multiuser CRNs, as it only relies on hopping patterns of the elaborately designed CH sequences (CHSs) and ignores the impact of network factors (e.g., channel availability and multiuser contention). In this paper, channel access delay is investigated by jointly considering asynchronous CH rendezvous schemes, channel availability, and a medium-access control (MAC) protocol in a single-hop multiuser CRN. To coordinate multiuser contention, a carrier sense multiple access with collision avoidance (CSMA/CA) MAC is adopted by tailoring the IEEE 802.11 distributed coordination function (DCF) properly to the operation features of existing asynchronous CH rendezvous schemes. The channel access delay is analyzed based on a modified Bianchi model and an absorbing Markov chain model, which captures the aggregate effect of hopping patterns of CHSs, the dynamic nature of channel availability, and the behavior of the MAC protocol. The analytical results are verified through extensive simulations. Both simulation and analytical results reveal that the rendezvous delay in existing asynchronous CH rendezvous schemes is insufficient to ensure satisfactory channel access delay in multiuser CRNs.