An all-IP software radio architecture under RTLinux

This paper presents an overview of software radio architectures for testing quality-of-service (QoS) aware IP data services over a typical third-generation radio interface. The testbed is implemented using a hard real-time micro-kernel known as RTLinux, running beneath the Linux operating system, for providing real-time end-to-end functionality. The testbed runs on a variety of Intel Pentium-based computing platforms including laptops and high-end servers. Layers 1 and 2 are compliant with the 3GPP specifications forTdd operation and layer 3 provides a direct interconnection with an IPv6 core network. The intent is to study the impact of an ip core network and QoS constraints on the physical and link layers as well as the co-design of physical layer configurations and IP layer networking.     

认知无线电技术的研究及发展

认知无线电技术作为软件无线电技术的一个特殊扩展,受到日益广泛的关注.由于该技术能够自动检测无线电环境,调整传输参数,从空间、时间、频率、调制方式等多维度共享无线频谱,可以大幅度提高频谱利用效率.本文首先从认知无线电技术的定义入手,分别讨论了认知无线电的基本概念、功能与实现、标准化的进程.然后介绍了当前应用状况,最后分析了未来的发展及面临的挑战.     

认知无线电:原理、技术与发展趋势

认知无线电是指具有自主寻找和使用空闲频谱资源能力的智能无线电技术。认知无线电技术的提出,为解决不断增长的无线通信应用需求与日益紧张的无线频谱资源之间的矛盾提供了一种有效的解决途径。当前,认知无线电技术从理论到实践都面临很多困难。文章简述了认知无线电的基本原理,对认知无线电涉及的射频、频谱感知和数据传输等物理层核心关键技术进行了总结分析,并结合当前的发展状况对该技术未来的发展趋势进行了预测。     

The European project trust—reconfigurable terminals and supporting networks

To date, research into reconfigurable mobile communications has predominantly focussed on the software radio concept, and specifically on the hardware technologies required to move physical layer processing into a programmable environment [1, 2, 3]. Although an interesting and necessary challenge, this only represents a fraction of the overall support and technology required to realise the potential of the concept. Other necessary developments include network/terminal cooperation for seamless inter-standard handoff, QoS management for software download and reconfiguration, a secure software download mechanism, terminal software and mobile radio network architecture supporting terminal reconfiguration, management for software downloads, configuration management, capability negotiation, radio resource management and spectrum allocation policies etc… This paper describes results from the EuropeanIst Trust (Transparently Reconfigurable UbiquitouS Terminal) [4] project concerning user and operator requirements, the proposed overall system environment, security issues, concerted radio resource management, and expected time frame for the development of reconfigurable terminals.     

Cognitive Radio and Networking Research at Virginia Tech

More than a dozen Wireless @ Virginia Tech faculty are working to address the broad research agenda of cognitive radio and cognitive networks. Our core research team spans the protocol stack from radio and reconfigurable hardware to communications theory to the networking layer. Our work includes new analysis methods and the development of new software architectures and applications, in addition to work on the core concepts and architectures underlying cognitive radios and cognitive networks. This paper describes these contributions and points towards critical future work that remains to fulfill the promise of cognitive radio. We briefly describe the history of work on cognitive radios and networks at Virginia Tech and then discuss our contributions to the core cognitive processing underlying these systems, focusing on our cognitive engine. We also describe developments that support the cognitive engine and advances in radio technology that provide the flexibility desired in a cognitive radio node. We consider securing and verifying cognitive systems and examine the challenges of expanding the cognitive paradigm up the protocol stack to optimize end-to-end network performance. Lastly, we consider the analysis of cognitive systems using game theory and the application of cognitive techniques to problems in dynamic spectrum sharing and control of multiple-input multiple-output radios.     

CRAHNs: Cognitive radio ad hoc networks

Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications. CR networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality-of-service (QoS) requirements. Specifically, in cognitive radio ad hoc networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, intrinsic properties and current research challenges of the CRAHNs are presented. First, novel spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. A particular emphasis is given to distributed coordination between CR users through the establishment of a common control channel. Moreover, the influence of these functions on the performance of the upper layer protocols, such as the network layer, and transport layer protocols are investigated and open research issues in these areas are also outlined. Finally, a new direction called the commons model is explained, where CRAHN users may independently regulate their own operation based on pre-decided spectrum etiquette.     

Improved cooperative spectrum sensing based on the reputation in cognitive radio networks

Cognitive radio (CR) is a promising technology to improve the utilisation of wireless spectrum resources. Spectrum sensing is the core functionality in CR networks (CRN). When there exist malicious users (MUs) in CRN and MUs start to attack the network after accumulating reputation to some extent, the performance is deteriorated. In this paper, a scheme is proposed by employing Orthogonalized Gnanadesikan–Kettenring (OGK) to mitigate the effect of MUs without the assistance of trusted nodes, and it can improve the robustness of CRN. Simulations verify the effectiveness of the proposed scheme.     

Filter Bank Spectrum Sensing for Cognitive Radios

The primary task in any cognitive radio (CR) network is to dynamically explore the radio spectrum and reliably determine portion(s) of the frequency band that may be used for the communication link(s). Accordingly, each CR node in the network has to be equipped with a spectrum analyzer. In this paper, we propose filter banks as a tool for spectrum sensing in CR systems. Various choices of filter banks are suggested and their performance are evaluated theoretically and through numerical examples. Moreover, the proposed spectrum analyzer is contrasted with the Thomson's multitaper (MT) method - a method that in the recent literature has been recognized as the best choice for spectrum sensing in CR systems. A novel derivation of the MT method that facilitates our comparisons as well as reveals an important aspect of the MT method that has been less emphasized in the recent literature is also presented.     

A survey on spectrum management in cognitive radio networks [cognitive radio communications and networks]

Cognitive radio networks will provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques. However, CR networks impose challenges due to the fluctuating nature of the available spectrum, as well as the diverse QoS requirements of various applications. Spectrum management functions can address these challenges for the realization of this new network paradigm. To provide a better understanding of CR networks, this article presents recent developments and open research issues in spectrum management in CR networks. More specifically, the discussion is focused on the development of CR networks that require no modification of existing networks. First, a brief overview of cognitive radio and the CR network architecture is provided. Then four main challenges of spectrum management are discussed: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility.     

OFDM for cognitive radio: merits and challenges [accepted from open call]

Cognitive radio is a novel concept that enables wireless systems to sense the environment, adapt, and learn from previous experience to improve the quality of the communication. However, CR requires a flexible and adaptive physical layer in order to perform the required tasks efficiently. In this article, CR systems and their requirement of a physical layer are discussed, and the orthogonal frequency division multiplexing technique is investigated as a candidate transmission technology for CR. The challenges that arise from employing OFDM in CR systems are identified. The cognitive properties of some OFDM-based wireless standards also are discussed to indicate the trend toward a more cognitive radio.     

Effects of Location Awareness on Concurrent Transmissions for Cognitive Ad Hoc Networks Overlaying Infrastructure-Based Systems

Through wide-band spectrum sensing, cognitive radio (CR) can identify the opportunity of reusing the frequency spectrum of other wireless systems. However, wide-band spectrum sensing requires energy consumption processes. In this paper, we aim to relieve the burden of spectrum scanning in a CR system by means of location awareness. We investigate to what extent a CR system with location awareness capability can establish a scanning-free region where a peer-to-peer connection of the secondary CR users can coexist with an infrastructure-based connection of the primary user. We compute the concurrent transmission probability of a peer-to-peer connection and an infrastructure-based connection in a system based on the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol. It has been shown that the frequency band of the legacy system can be reused up to 45% by the overlaying cognitive ad hoc network if certain location techniques help CR users locate primary and other secondary users. In summary, a CR system equipped with location awareness techniques can dramatically reduce the need of spectrum sensing thanks to the capability of identifying the concurrent transmission region in a hybrid infrastructure-based and ad hoc overlaying systems. Hence, from another aspect, the issue of wide-band spectrum sensing in CR systems is resolved fundamentally.     

Stochastic spectrum handoff protocols for partially observable cognitive radio networks

Recent studies have been conducted to indicate the ineffective usage of licensed bands due to static spectrum allocation. In order to improve spectrum utilization, cognitive radio (CR) is therefore suggested to dynamically exploit the opportunistic primary frequency spectrums. How to provide efficient spectrum handoff has been considered a crucial issue in the CR networks. Existing spectrum handoff algorithms assume that all the channels can be correctly sensed by the CR users in order to perform appropriate spectrum handoff process. However, this assumption is impractical since excessive time will be required for the CR user to sense the entire spectrum space. In this paper, the partially observable Markov decision process (POMDP) is applied to estimate the network information by partially sensing the frequency spectrums. A POMDP-based spectrum handoff (POSH) scheme is proposed to determine the optimal target channel for spectrum handoff according to the partially observable channel state information. Moreover, a POMDP-based multi-user spectrum handoff (M-POSH) protocol is proposed to exploit the POMDP policy into multi-user CR networks by distributing CR users to frequency spectrum bins opportunistically. By adopting the policies resulted from the POSH and M-POSH algorithms for target channel selection, minimal waiting time at each occurrence of spectrum handoff can be achieved which will be feasible for multimedia applications. Numerical results illustrate that the proposed spectrum handoff protocols can effectively minimize the required waiting time for spectrum handoff in the CR networks.     

Optimal channel access for TCP performance improvement in cognitive radio networks

Cognitive radio (CR) is a promising technology to improve spectrum utilization. Most of previous work on CR networks concentrates on maximizing transmission rate in the physical layer. However, the end-to-end transmission control protocol (TCP) performance perceived by secondary users is also a very important factor in CR networks. In this paper, we propose a novel multi-channel access scheme in CR networks, where the channel access is based on the TCP throughput in the transport layer. Specifically, we formulate the channel access process in CR network as a restless bandit system. With this stochastic optimization formulation, the optimal channel access policy is indexable, meaning that the channels with highest indices should be selected to transmit TCP traffic. In addition, we exploit cross-layer design methodology to improve TCP throughput, where modulation and coding at the physical layer and frame size at the data-link layer are considered together with TCP throughput in the transport layer to improve TCP performance. Simulation results show the effectiveness of the proposed scheme.     

Open Architecture Standard for NASA's Software-Defined Space Telecommunications Radio Systems

NASA is developing an architecture standard for software-defined radios used in space- and ground-based platforms to enable commonality among radio developments to enhance capability and services while reducing mission and programmatic risk. Transceivers (or transponders) with functionality primarily defined in software (e.g., firmware) have the ability to change their functional behavior through software alone. This radio architecture standard offers value by employing common waveform software interfaces, method of instantiation, operation, and testing among different compliant hardware and software products. These common interfaces within the architecture abstract application software from the underlying hardware to enable technology insertion independently at either the software or hardware layer. This paper presents the initial Space Telecommunications Radio System architecture for NASA missions to provide the desired software abstraction and flexibility while minimizing the resources necessary to support the architecture.     

Dynamically optimized spatiotemporal prioritization for spectrum sensing in cooperative cognitive radio

In this paper, an enhanced cooperative, statistics-driven spectrum sensing algorithm, called Dynamically Optimized Spatiotemporal Prioritization (DOSP), is developed for improving spectrum sensing efficiency in the media access control (MAC) layer of cognitive radio (CR) systems. The target of the DOSP algorithm is to improve spectrum sensing efficiency and achieve better spectrum access opportunities by prioritizing channels for fine sensing. The sensing priority is determined dynamically and intelligently based on an optimal statistical fusion that jointly considers both the local statistics obtained by the individual cognitive radios as well as the long-term spatiotemporal statistics obtained by other cognitive radios in the network. As such, the individual cognitive radio peers work together to get the most out of available spectrum opportunities. Numerical results demonstrate that the proposed DOSP algorithm is capable of achieving better performance compared with recently reported cooperative spectrum sensing methods in terms of overhead and percentage of missed spectrum opportunities. Furthermore, results show that the DOSP algorithm is more robust to the environment of low cognitive radio densities than that by using other state-of-the-art cooperative spectrum sensing methods.     

Wideband distributed spectrum sharing with multichannel immediate multiple access

This paper describes a radio architecture for distributed spectrum sharing of multiple channels among secondary users (SUs) in a wide band of frequencies and a localized area. A novel multichannel immediate multiple access (MIMA) physical layer is developed such that each SU can monitor all the channels simultaneously for incoming signals and achieve fast rendezvous within the multiple channels. The spectrum utilized by an SU pair can be changed dynamically based upon spectrum sensing at the transmitter and tracking synchronization and control messages at the receiver. Although information about the number of active SUs can be used to improve the spectrum sharing efficiency, the improvement is small relative to the cost of obtaining such information. Therefore, the architecture adopts multichannel carrier sense multiple access for medium access control regardless of the number of active SUs. A prototype implementation of the architecture has been developed using an advanced software defined radio platform. System tests demonstrate that the spectrum sharing efficiency of the prototype is close to an upper bound if the signal-to-noise ratio is sufficiently high. Among other practical issues, imaged interference caused by hardware IQ imbalance limits system performance. In the prototype, the MIMA is based on an LTE waveform. Therefore, the spectrum sharing radio can be potentially applied to the 3.5 GHz radar band for citizens broadband radio service (CBRS).     

Jointly optimal power and admission control for delay sensitive traffic in CDMA networks with LMMSE receivers

Quality-of-service (QoS) guarantees for multiclass code division multiple access networks are provided by means of cross-layer optimization across the physical and network layers. At the physical layer, the QoS requirements are specified in terms of a target signal-to-interference ratio (SIR) requirement, and optimal target powers are dynamically adjusted according to the current number of users in the system. At the network layer, the QoS requirements are the blocking probabilities and the call connection delays. The network layer guarantees that both physical layer and network layer QoS are met by employing admission control. An optimal admission control policy is proposed based on a semi-Markov decision process formulation. The tradeoff between blocking and delay is discussed for various buffer configurations. The advantage of advanced signal processing receivers is established using a comparative capacity analysis and simulation with the classical scenario in which the system uses matched filter receivers.     

Channel status prediction for cognitive radio networks

The cognitive radio (CR) technology appears as an attractive solution to effectively allocate the radio spectrum among the licensed and unlicensed users. With the CR technology the unlicensed users take the responsibility of dynamically sensing and accessing any unused channels (frequency bands) in the spectrum allocated to the licensed users. As spectrum sensing consumes considerable energy, predictive methods for inferring the availability of spectrum holes can reduce energy consumption of the unlicensed users to only sense those channels which are predicted to be idle. Prediction‐based channel sensing also helps to improve the spectrum utilization (SU) for the unlicensed users. In this paper, we demonstrate the advantages of channel status prediction to the spectrum sensing operation in terms of improving the SU and saving the sensing energy. We design the channel status predictor using two different adaptive schemes, i.e., a neural network based on multilayer perceptron (MLP) and the hidden Markov model (HMM). The advantage of the proposed channel status prediction schemes is that these schemes do not require a priori knowledge of the statistics of channel usage. Performance analysis of the two channel status prediction schemes is performed and the accuracy of the two prediction schemes is investigated. Copyright © 2010 John Wiley & Sons, Ltd.     

Evolution and future trends of research in cognitive radio: a contemporary survey

The cognitive radio (CR) paradigm for designing next‐generation wireless communications systems is becoming increasingly popular, and different aspects of it are being implemented in currently available wireless systems. In the last decade, a significant amount of research efforts has been made to solve CR challenges, and several standards related to CR and dynamic spectrum access have been developed. Also, there have been advances in software‐defined radio platforms to implement the CR systems. In this article, we provide a comprehensive survey on the evolution of CR research covering aspects such as spectrum sensing, measurements and statistical modeling of spectrum usage, physical layer aspects such as waveform and modulation design, multiple access, resource allocation and power control, cognitive learning, adaptation and self‐configuration, multihop transmission and routing, and robustness and security in CR networks. Also, state‐of‐the‐art research on the economics of CR networks, CR simulation tools, testbeds and hardware prototypes, CR applications, and CR standardization efforts is summarized. Emerging trends on CR research and open research challenges related to the cost‐effective and large‐scale deployment of CR systems are outlined. Copyright © 2013 John Wiley & Sons, Ltd.     

协作频谱感知在认知网络中的应用

认知无线电能够灵敏感知周围环境的变化,通过频谱感知功能发现频谱空洞,使得认知无线电能够与周围通信环境相适应。在认知无线电网络中,认知用户（次用户）必须连续地监控频谱,检测主用户是否存在。如果主用户存在,次用户必须尽快地退出该频段,从而不影响主用户。在文中采用一种协作机制,即两用户进行协作频谱感知,从而提高主用户的检测率,减少了检测时间,并且得到捷变增益。我们用Matlab给出仿真结果。