Analysis of Channel Selection Methods with Dynamic Spectrum Access Technology

Dynamic spectrum Access （DSA）is used to make use of the spectrum in wireless network. In most situations, control channel is a common approach to negotiation between secondary users. But, based on this feature, the attacker can destroy the communication network only influence the control center. So, in this paper, two methods without control channel are simulated in Qualent platform. The results prove that those methods are available, and the Receiver-directed channel selection is more match to the regular control channel standards in throughput.

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.

Wireless LANs have been widely deployed as edge access networks in home/office/commercial buildings, providing connection to the Internet. Therefore, performance of end-to-end connections to/from such WLANs is of great importance to network applications and end-users. The advent of Dynamic Spectrum Access (DSA) technology is expected to play a major role in improving wireless communication. With DSA enabled, WLANs opportunistically access licensed channels in order to enhance spectrum-usage efficiency, and provide better network performance. In this paper, we explore issues and solutions in realizing this potential of DSA. We first identify the key issues that impact end-to-end TCP performance when a DSA-enabled WLAN is integrated with the wired cloud. Then, we propose a new network management framework, called DSASync, to eliminate or mitigate the performance issues we identified. DSASync requires no modifications to the fixed wired network or existing network stack, while ensuring traditional TCP semantics to be obeyed. DSASync uses a combination of buffering and traffic-shaping algorithms to minimize the adverse side-effects of DSA on the TCP flows. Finally, we evaluate DSASync through a prototype implementation and deployment in a testbed. The results show significant improvements in TCP performance, e.g., a 74 increase in downlink goodput, making it a promising step forward towards applying DSA technology in consumer WLANs.

In this paper we address the control channel assignment problem in a cognitive radio based wireless network, namely the CogMesh. Such a network is featured by the dynamic spectrum sharing of the secondary users coexisting with the primary users. The opportunistic nature of the spectrum utilization among the secondary users makes a global control channel infeasible. The self-coordination of the network, hence, becomes a challenge task. Considering the fact that common channels may temporarily exist among a local group of secondary users, we propose an adaptive approach that selects local common control channels independently by each secondary user according to the qualities of the detected spectrum holes and the choices of its neighbors. To achieve this, a swarm intelligence-based algorithm is used to facilitate the common control channel selection. The idea is to use HELLO messages periodically broadcasted by neighbors as the pheromone to rank the common channels so as to expedite the channel selection process. The algorithm is completely distributed and therefore scalable. Moreover, it is simple, flexible, adaptive, and well balanced on the exploitation and exploration of the radio resources. The behaviors and performance of the proposed algorithm are verified by simulation.

Electromagnetic spectrum is a natural resource and at present its use is regulated by fixed spectrum assignment policy. That is, spectrum is assigned to license holders or services on a long term basis for large geographical regions. This fixed channel allocation served well in the past but the rapid and tremendous growth in wireless communication changed the entire scenario. Introduction of every new communication application, either military or civilian makes the spectrum more and more congested. Meanwhile, the spectrum allocated to specific users does not ensure it is being used effectively at all times. Measurement studies reveal that 15 to 85 percent of the licensed radio spectrum is relatively unutilized or under utilized in most of the geographical locations for a considerable amount of time. The limited available spectrum and its inefficient usage encouraged a new communication paradigm to exploit the radio frequency spectrum opportunistically. This new concept is termed Dynamic Spectrum Access (DSA). The technology that makes DSA possible is Cognitive Radio (CR) which was first suggested by Joseph Mitola. In fact, CR is an all-encompassing term for a wide variety of technologies that enable radios to achieve various levels of self configuration and different functionalities ranging from ubiquitous wireless access to DSA for a device centric interference management. DSA networks define the already existing licensed users as primary users or legacy users and CR as secondary user. CR, sits on top of Software Defined Radio (SDR) is an intelligent wireless system that adapts to its environments to utilize the spectrum by its secondary usage in a 'do no harm' fashion. In simple words, it senses the radio environment, detects vacant spectrum bands, decides the best spectrum and chooses the transmission scheme which insures minimum interference to adjacent legacy users. As DSA networks targets mainly the wideband spectrum, the transmission technology should mitigate multi-path frequency selective fading channel impairments and should have multi-user support. Thus DSA demands for CR transmission scheme of high flexibility, adaptivity, multi-user support and moderate error performance in fading channels.

Due to the traditional wireless networks, fixed allocation of spectrum is one of the main reasons causing low utilization of spectrum. To solve the problem, a new wireless communication model has been proposed, which called Cognitive Radio Networks (CRN). CRN adopts Dynamic Spectrum Access (DSA) technology, thus it can flexibly use the spectrum which primary user temporarily unused. In cognitive radio networks, due to each secondary user (SU) has different location and surrounding spectrum environment, it may have variety of available channels. How to assign these available channels is the crucial point of system performance. However, existing methods doesn't consider the problem of multipath fading, therefore, this study proposed an improved channel allocation mechanism. We consider the received signal strength to define the channel access priority of secondary users applied by fuzzy theory. Finally, the simulation results show the superior of our approach and verify the effectiveness of the proposed mechanism.

The spectrum scarcity problem can be tackled by promoting a more efficient use of the radio spectrum. Spectrum sharing techniques like TV White Spaces (TVWS), Licensed Shared Access (LSA), and Spectrum Access System (SAS), are adequate solutions for this problem and there exist already regulation and standardization efforts worldwide. To evaluate the coexistence between primary and secondary spectrum users, a Long Term Evolution (LTE) multi-cell simulator has been designed, which employs a generic spectrum sharing technique, Dynamic Spectrum Access (DSA), in order to obtain additional network capacity. As a way to bring attention and confidence of the telecommunications sector regarding the benefits that this technology may bring, the analysis is done in terms of interference suffered by incumbents (primary users) and capacity by secondary users. Results have confirmed the unfeasibility of co-channel coexistence for moderate distances between the cordless camera service (incumbent) and LTE network (secondary user) due to high interference. However, for adjacent bands, a gain of 40% in the secondary users’ capacity is possible following more restrictive interference protection requirements and 30% gain with the smaller frequency separation between primary and secondary operating frequencies.

In order to fully utilize the scarce spectrum resources and improve the efficiency of wireless spectrum resource utilization, dynamic spectrum access is proposed as a solution. There are two kinds of dynamic spectrum access system, one is overlay dynamic spectrum, and the other is dynamic spectrum access under interference temperature constraints. In this paper, we use a three-dimensional Markov chain to model the dynamic spectrum access under interference temperature constraints, and analyze the performance of secondary users in the system. Two important parameters, i.e., secondary user interrupting probability and blocking probability are derived using the proposed model. The performance of secondary users in different dynamic spectrum access systems are analyzed and compared. The numerical results show that the performance of secondary users can be improved significantly in dynamic spectrum access under interference temperature constraints comparing to overlay dynamic spectrum access. Specially, the advantage of interference temperature constraints based dynamic spectrum access is more notable on the condition that there are not enough resources to provide to secondary users for access.

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.

Recently, a dynamic spectrum access technology has been in the spotlight for maximizing the utilization of the limited radio spectrum resource while accommodating the increasing amount of services and applications in the wireless networks. A cognitive radio is one of the key technologies based on dynamic spectrum manner. Although there have been many advances in cognitive radio with respect to the technology development, an additional research for the reformation of regulation, policy and market structure is still required to make CR-based dynamic spectrum access feasible and successful in the wireless market. Therefore, this paper classifies cognitive radio based network and application scenarios, and investigates feasibility of them. According to the analyses, this paper examines strategic approaches in the service providers', manufacturers', and policy makers' standpoints for the successful commercialization of cognitive radio with the dynamic spectrum management policy.

Cognitive radio (CR) and dynamic spectrum access (DSA) are the effective ways to solve the spectrum congestion problem. Three kinds of basic DSA approaches are respectively dynamic exclusive use, open sharing and hierarchical access. The hierarchical access model is perhaps the most compatible with solving the current spectrum congestion problem. So, in this paper, we will set up an overlay DSA system which is an effective approach of the hierarchical access model. Firstly, we make use of the spectrally modulated spectrally encoded (SMSE) framework to generate OFDM waveforms for the secondary user (SU) which can be considered as the overlay waveform. Then we use the signal which is generated by the walkie-talkie to access the overlay DSA system as a primary user (PU) or an interference signal. The universal software radio peripheral (USRP) and spectrum analyzer are used to generate and analyze the power spectrum density (PSD) of the coexistence of a SU and a PU or an interference signal. The experimental result demonstrates that the overlay DSA system can achieve the function of turning off the sub-carriers corresponding to the frequency of the PU. It also shows that the system can greatly improve the efficiency of the spectrum utilization due to dynamically allocate the spectrum.

Spectrum sensing is a critical function for enabling dynamic spectrum access (DSA) in wireless networks that utilize cognitive radio (CR). In DSA networks, unlicensed secondary users can gain access to a licensed spectrum band as long as they do not interfere with primary users. Spectrum sensing is subject to errors in the form of false alarms and missed detections. False alarms cause spectrum under-use by secondary users, and missed detections cause interference to primary users. Although existing research has demonstrated the utility of a Markov chain for modeling the spectrum access pattern of primary users over time, little effort has been directed toward spectrum sensing based upon such models. In this paper, we develop soft-input sequence detection algorithms of Markov sources in noise for spectrum sensing in DSA networks. We assign different Bayesian cost factors for missed detections and false alarms, and we show that a suitably modified Forward-Backward sequence detection algorithm is optimal in minimizing the detection risk. Along the way, we observe new fundamental limitations that we call "Risk Floor" and "Limiting ROC" for energy detection and coherent detection due to the PU's spectrum access pattern.

In order to mitigate the problem of crowded radio spectrum, dynamic spectrum access (DSA) has become the solution and a research focal point. The number of works in wideband spectrum sensing is dramatically increasing recently due to its importance in cognitive radio (CR) networks. Most works assume that secondary users (SUs) are synchronous with the primary users' (PUs) network. However, in many practical systems the SUs will have no information about the PUs' communication protocols. Furthermore, it is also possible that communications among PUs are not based on synchronous operation. In order to address such problems, a contention-based wideband DSA algorithm with asynchronous cooperative spectrum sensing (CSS), called the DySac, is proposed. In this scheme, the SUs need not maintain synchronism with the PUs, and the SUs who intend to access the primary network compete among each other for available channels. Performance analysis and simulations are conducted to evaluate the proposed DySac.

A prototype Dynamic Spectrum Access (DSA) system is implemented, for ease of implementation, using the audio spectrum. In this setup, laptop PCs behave as two software defined radios (SDR), one a primary user (PU) and the other a secondary user (SU). The radios communicate digital information over the air, using the audio capabilities of standard soundcards. The PU, which is emulating the licensed user of an audio channel centered at 4 kHz, communicates using binary phase shift keying (BPSK) modulated data in periodic bursts. A cognitive radio (CR) based SU wishes to opportunistically occupy the PU channel during the inter-burst times, i.e. during the temporal ‘spectrum holes,’ while not interfering with the PU traffic. The PU link is implemented in MATLAB, while the SU is defined in GNU Radio with a separate Python control module defining its algorithm for spectrum sensing and hopping. The implementation of both communication links is described, as well as the initial performance evaluation of the preliminary system in terms of bit error rate performance of the PU with and without the presence of an active SU. The measured BER achieved for the best of the PU bursts with DSA was on the order of a few percent, just slightly higher than without DSA.

The most noted effect of rapid growth in wireless networks in recent years has been the issues of spectrum usage and management because of its importance in wireless communication as the medium of data transmission. Efficient utilization of spectrum has been the major concerns in spectrum management over recent years because of the notion that radio spectrum is scarce, finite, and non-replicable. New technologies find it difficult to be allocated frequencies for their operations because most usable frequencies have already been allocated to licenced users while the unlicenced spectrum bands are becoming overcrowded. Researches have however shown that some of the allocated spectrum bands are not been used at some particular time in a particular location. The development of technologies like 4 th generation (4G) technology, Ultra Wide Band (UWB) techniques, Software-defined Radios (SDRs), and Cognitive Radios (CRs) help to improve the overall utilization of the limited spectrum. This paper surveyed these technologies and their impact in improving spectrum efficiency in terms of spectrum management and utilization. The paper concluded that dynamic spectrum access (DSA) technologies have greater impact when compare with other technologies. Cognitive Radios in particular have the potentials to substantially improve spectrum efficiency by opportunistically using spectrum. Spectrum efficiency in this context means that a large number of users are able to use available spectrum.