基于关联规则挖掘的无线电频谱占用预测

无线电频谱占用预测是认知无线电研究中的关键技术之一。实验采用中星世通CS-805 F可搬移监测测向系统对四川省成都市的GSM900上行频段(890~915 MHz)和广播电视业务的部分频段(750~806 MHz)进行了为期24 h的实地监测,针对频谱监测中产生的大量历史数据,选用了部分周期模式的关联规则挖掘方法,挖掘频谱使用中存在的频繁模式,并由信道占用频繁模式生成强关联规则,得到特定业务频段的使用规律,从而实现无线电频谱的占用预测。实验结果表明,该方法在两个业务频段的占用预测均取得了较好的效果,准确率分别可达74.02%和83.98%。另外,实验指出了该算法的敏感参数并进行了简要分析。实验对研究认知无线电设备实施动态频谱接入和提高频谱使用率有一定意义。     

基于认知无线电的GSM频段占用分析与建模

对EGSM、GSM900、DCS1800频段进行了七天频谱监测,统计分析结果表明：不同业务的利用情况不尽相同,上下行信道的占用情况存在较大差异,上行信道的占用度相对较低,并随日常作息呈现出夜间较空闲、工作时段较繁忙的规律.同时,分析了信道的电平概率分布以及占用度概率分布,对信道的占用状态用离散二状态马尔科夫链来建模,并分析了信道空闲持续时长与占用持续时长的概率分布,服从指数分布的修正形式.还仿真分析了不同性能的认知无线电系统对频段利用率的影响.     

射电天文台站准实时电波环境测量方法

随着频率使用率的提高,瞬态信号对射电天文观测影响越来越大,有效的电波环境测量及频谱分析可为现有射电天文台址干扰缓解策略提供依据.基于现有射电望远镜台站电波环境特征,结合信号分析仪原理,深入分析了仪器设备关键参数配置方法及测量时间计算方法;结合实际测量需求,确定了测试时间规划策略,提出一种准实时电波环境测量方法.运用此方法对新疆天文台南山台站电波环境进行测量,分析了频谱、频率占用度随时间变化特点,结果表明,该方法能够有效分析电磁干扰随时间的变化趋势.     

Quantitative spectrum occupancy evaluation in China: based on a large scale concurrent spectrum measurement

Due to the usable frequency becomes more and more crowed,dynamic spectrum access (DSA) is a new hope to solve this problem.However,DSA in China requires a quantitative analysis of the current spectrum ...     

What and how much to gain by spectrum agility?

Static spectrum allocation prohibits radio devices from using spectral bands designated for others. As a result, some bands are under-utilized while other bands are over-populated with radio devices. To remedy this problem, the concept of spectrum agility has been considered so as to enable devices to opportunistically utilize others' spectral bands. In order to help realize this concept, we establish an analytical model to derive performance metrics, including spectrum utilization and spectrum-access blocking time in spectral-agile communication systems. We then propose three basic building blocks for spectral-agile systems, namely spectrum opportunity discovery, spectrum opportunity management, and spectrum usage coordination, and develop protocols for each blocks. These protocols are integrated with the IEEE 802.11 protocol, and simulated using ns-2 to evaluate the protocol overhead. The simulation results show that our proposed protocols can improve the throughput of an IEEE 802.11 wireless LAN by 90% for the simulated scenarios, and the improvements matched well our analytical model. These results demonstrate the great potential of using spectrum agility for improving spectral utilization in an efficient, distributed, and autonomous manner     

A MAC protocol by applying staggered channel model for cognitive radio networks

Cognitive radio (CR) is a novel and promising spectrum management technique, which aims to cope with the spectrum scarcity problem occurring in unlicensed bands and alleviate the inefficient spectrum utilization of licensed bands. To ensure that the operation of licensed users will not be adversely affected and that the licensed bands can be efficiently utilized by unlicensed users, this paper proposes a cognitive radio MAC protocol called SMC-CR-MAC. When any primary user is detected, the proposed SMC-CR-MAC protocol applies Contiguous Channel Switching and Sender-Receiver Channel Swap rules to cope with the rendezvous, packet collision, and channel congestion problems. Simulation results show that the proposed SMC-CR-MAC protocol can significantly improve the network performance in terms of utilization of licensed bands, standard deviation of traffic load on each channel, and probability of successful rendezvous.     

Energy Detection Approach for Spectrum Sensing in Cognitive Radio Systems with the Use of Random Sampling

In radiomobile contexte, radio frequency spectrum is a ressource that needs to be used with appropriate efficiency. This can be achieved by the mean of spectrum sensing operation. This function consists to analyze the occupancy of the radio frequency spectrum in order to detect which bands are unused. This concept is largely appreciated in cognitive radio where more flexibility is required to adapt to the communication environment. Different techniques are presented in the literature. In this paper, we are interested by the application of the energy detector method for spectrum sensing. This application is performed in cognitive radio systems with the use of random sampling. The performance of this approach is evaluated in term of its receiver operating characteristic curve and compared to the uniform sampling case.     

Review of Robust Cooperative Spectrum Sensing Techniques for Cognitive Radio Networks

Cognitive radio networks sense spectrum occupancy and manage themselves to operate in unused bands without disturbing licensed users. The detection capability of a radio system can be enhanced if the sensing process is performed jointly by a group of nodes so that the effects of wireless fading and shadowing can be minimized. However, taking a collaborative approach poses new security threats to the system as nodes can report false sensing data to reach a wrong decision. This paper makes a review of secure cooperative spectrum sensing in cognitive radio networks. The main objective of these protocols is to provide an accurate resolution about the availability of some spectrum channels, ensuring the contribution from incapable users as well as malicious ones is discarded. Issues, advantages and disadvantages of such protocols are investigated and summarized.     

Access to RF White Spaces in Romania: Present and Future

As the demand for frequency resources increases because of the great number of new wireless technologies, the frequency spectrum becomes overcrowded and solutions have to be found in order to solve this problem. One possible solution would be to take advantage of the so called white spaces (WS), frequency bands that are actually not used by the primary (licensed) radio communication systems, by using a dynamic spectrum access (DSA) approach. In order to take advantage of these spaces, secondary (unlicensed) users have to perform a spectrum sensing process in order to accurately detect the presence of a primary system and avoid unwanted interference with it. This paper provides an overview of the status of WS in Romania by analysing the current regulations and the analogue switch-off that is planned to take place in the near future (2015). The current state of the art regarding several standards that incorporate DSA elements is being made, emphasizing the high interest in using this WS in upcoming communication systems. In order to prove the low degree in which the RF spectrum is currently used, the results of a measurement campaign performed in both urban and rural locations of Romania are discussed. A comparison with the results of other similar measurement campaigns conducted in several locations worldwide is performed as well. Several frequency bands are identified as possible WS for future opportunistic use.     

S-transformation based integrated approach for spectrum estimation,storage, and sensing in cognitive radio

Cognitive Radio (CR) uses the principle of dynamic spectrum allocation to improve the utilization of spectrum bands. The estimation of missing data is essential for maintaining an uninterrupted quality of service in the CR. However, the existing methods are not suitable for interpolating missing data in high frequency signals. The storage of spectrum occupancy information is crucial for learning the spectrum usage and prediction. The existing techniques for wideband spectrum sensing suffer from poor edge detection capabilities. This paper proposes an S-Transformation (ST) based approach to solve these problems. For missing samples, the proposed method improves the accuracy of estimation. The ST can also be used to store the spectrum occupancy information. The simulation results show that the proposed scheme outperforms others by improving the accuracy of edge detection. Further, the simple implementation of the ST in the frequency domain is an advantage for the real time application.     

Spectrum Occupancy Statistics and Time Series Models for Cognitive Radio

While dedicated spectrum occupancy monitoring provides vital information for frequency planning and management, it usually cannot tell the common properties in spectrum occupancy. As a complement, the models approach can be used to describe and compare the occupancy situations under similar conditions. Time series analysis has been applied to modeling the radio spectrum occupancy. This paper categorizes different time series models to different occupancy patterns. Occupancy analysis of the Global System for Mobile communications (GSM) band is given as an example.     

Joint resource reconfiguration and robust routing for cognitive radio networks: a robust optimization approach

Cognitive radio (CR) networks comprise a number of spectrum agile nodes with the capability of spectrum detection. Applying techniques of spectrum sharing in CR networks can achieve the efficient utilization of network resources. Usually, data rates of user sessions are time varied because of the dynamic behaviors of CR networks. It is expected that the occurrence of link outage should be avoided and incorporated into the routing design under conditions of increasingly crowded spectrum. This paper proposes an integral framework, which considers these two correlated schemes (resource reconfiguration and robust routing) simultaneously. For that, the resource reconfiguration scheme is developed for the efficient usage of network resources and aims at reducing the occupancy of licensed bands. The link outage, resulting from random session rate, is confined within an acceptable range by using strategy of virtual ‘network portfolio’. A robust optimization approach is proposed to guarantee reliable data transmission among possible interfering links. Both these two items (resource reconfiguration and robust routing) are formulated in a framework of cross‐layer optimization. The evolutionary process of CR network states is provided in simulations, where the results show that the joint design proposal can achieve the least interferences among different licensed users while realizing robust routing. Copyright © 2013 John Wiley & Sons, Ltd.     

Prediction based channel allocation performance for cognitive radio

The interdependency, in a cognitive radio (CR) network, of spectrum sensing, occupancy modelling, channel switching and secondary user (SU) performance, is investigated. Achievable SU data throughput and primary user (PU) disruption rate have been examined for both theoretical test data as well as data obtained from real-world spectrum measurements done in Pretoria, South Africa. A channel switching simulator was developed to investigate SU performance, where a hidden Markov model (HMM) was employed to model and predict PU behaviour, from which proactive channel allocations could be made. Results show that CR performance may be improved if PU behaviour is accurately modelled, since accurate prediction allows the SU to make proactive channel switching decisions. It is further shown that a trade-off may exist between achievable SU throughput and average PU disruption rate. When using the prediction model, significant performance improvements, particularly under heavy traffic density conditions, of up to double the SU throughput and half the PU disruption rate were observed. Results obtained from a measurement campaign were comparable with those obtained from theoretical occupancy data, with an average similarity score of 95% for prediction accuracy, 90% for SU throughput and 70% for PU disruption rate.     

A Multiagent Based Scheme for Unlicensed Spectrum Access in CR Networks

In recent wireless network domains static spectrum access is a major concern. Generally, this access leads to spectrum scarcity problem by creating empty holes or white spaces. However, the scarcity is temporary and can be alleviated if spectrum access is performed dynamically and efficiently. One important step towards dynamic spectrum access is the development of cognitive radio (CR) technology, which senses nearby spectrum portions (or bands) and tries to use them either opportunistically or by negotiating with the neighboring users. Nonetheless, dynamic spectrum access raises several challenges which need to be addressed in detail. These challenges include efficient allocation of spectrum for users in order to maximize spectrum utilization and to avoid user level conflicts both under licensed and unlicensed bands. In this paper, considering the relative rarity of solutions for unlicensed spectrum access and their inadequacy, we propose a scheme, where the CR devices (equipped with agents) interact with their neighbors to form several coalitions over the unlicensed bands. These types of coalitions can provide a less-conflicted access as the agents mutually agree for spectrum sharing and they allow other CR users to enter in their vicinity of acquired spectrum via bilateral message exchanges. Further, we present continuous time Markov chains to model the spectrum access process in continuous time and derive important performance metric as the blocking probability for without and with queuing systems. Amongst others, the important comparisons we made between analytical and simulation results in terms of blocking probability verify that our proposed model is correct. In essence, our proposed solution aims to increase dynamic spectrum usage by enabling cooperation between the users.     

Improved list coloring algorithm in cognitive radio based on time cost and demand satisfaction

For the cognitive users to access the licensed frequency bands opportunistically, cognitive radio is the best solution to mitigate the spectrum resource scarcity at the moment. Dynamic spectrum allocation is a key technology to implement cognitive radio efficiently on the condition that the licensed users must not be interfered. Up to now, the spectrum allocation algorithms based on the graph model seldom focus on enhancing spectrum utilization, speedy accomplishing and requirement satisfaction simultaneously. In this paper, an improved algorithm is proposed to decrease time cost and increase demand satisfaction simultaneously based on a List-Coloring algorithm provided by Wei Wang research group. This improved algorithm was studied by handling connected component in parallel and depressing user’s priority which demand has been met, respectively. And the spectrum utilization is effectively guaranteed at the same time. Our experimental results show that the proposed algorithm is an efficient method. Compared with the original List-Coloring algorithm, the time cost is reduced obviously and the demand satisfaction is greatly improved while only a few bandwidth rewards are lost by using the algorithm proposed in our study.     

Optimal distributed power allocation for a new spectrum sharing paradigm in cognitive radio networks

The problem of power allocation in cognitive radio networks plays an important role to improve the efficiency of spectrum utilization. However, most of previous works focus on the power allocation for secondary users in spectrum sharing overlay or spectrum sharing underlay, which needs to frequently handoff between the idle spectrum bands or considers the interference constraints in all spectrum bands respectively. In order to reduce the handoff and fully utilize the spectrum resource, we propose a new spectrum sharing paradigm which not only can just need to adjust the transmit power in spectrum bands instead of frequently handoff between idle spectrum bands, but can fully utilize the spectrum resource as we only consider the interference power constraints in active spectrum bands rather than in all spectrum bands. Then based on this new spectrum sharing paradigm and the constraint conditions, we study the distributed power allocation for secondary users and formulate the optimization problem as a non-cooperative game problem, after that the variational inequality approach is used to solve this game problem and a Nash equilibria solution is got, finally simulation results are illustrated to demonstrate the performance of the proposed scheme.     

Shortwave broadcasting band spectrum occupancy and signal levels inthe continental United States and Western Europe

The initial results are described for monitoring using a mobile spectrum monitoring unit (MSMU) that has the capability of fast sampling of radio signals in the frequency spectrum between 2 MHz and 1 GHz. In the summer and autumn of 1987, the MSMU was used to measure signal level and spectrum occupancy in the shortwave band (2-30 MHz) at four locations in the continental United States (CONUS) (i.e. Stanford, California; Ft. Huachuca, Arizona; Ft. Sill, Oklahoma; and Annapolis, Maryland) and at two locations in Europe (Seckenheim and Geinsheim, Federal Republic of Germany). After the measurement period, the recorded data was used to compute occupancy statistics at 111 signal amplitude thresholds. Comparison of spectrum-occupancy and signal-level data between CONUS and Europe is reported     

A framework for statistical wireless spectrum occupancy modeling

In this paper, we propose a novel spectrum occupancy model designed to generate accurate temporal and frequency behavior of various wireless transmissions. Our proposed work builds upon existing concepts in open literature in order to develop a more accurate time-varying spectrum occupancy model. This model can be employed by wireless researchers for evaluating new wireless communication and networking algorithms and techniques designed to perform dynamic spectrum access (DSA). Using statistical characteristics extracted from actual radio frequency measurements, first- and second-order parameters are employed in a statistical spectrum occupancy model based on a combination of several different probability density functions (PDFs) defining various features of a specific spectrum band with several concurrent transmissions. To assess the accuracy of the model, the output characteristics of the proposed spectrum occupancy model are compared with realtime radio frequency measurements in the television and paging bands.     

实高斯信号下的能量检测技术

认知无线电被认为是目前提高频谱资源利用率的最有效手段。次用户要使用主用户的空闲频段,必须能够准确的检测到主用户是否出现。能量检测技术由于无需信号的任何先念知识,应用最为广泛。在实高斯信号下,对基于能量的独立检测和协作检测方式进行了仿真研究。仿真结果表明：信号样本数和参与协作的用户数的增加可以有效地改善系统检测性能,但当用户数达到一定数目后,错误率基本无变化,反而还会增加系统开销。