Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> This paper provides details of a distributed genetic algorithm (GA) based cognitive radio engine model for disaster communications and its implementation in a cognitive radio test bed using programmable radios. Future applications include tactical and covert communications. The cognitive system monitor (CSM) module presented here permits cross layer cognition and adaptation of a programmable radio by classifying the observed channel, matching channel behavior with operational goals, and passing these goals to a wireless system genetic algorithm (WSGA) adaptive controller module to evolve and optimize radio operation. The CSM module algorithm provides for parallel distributed operation and includes a learning classifier and meta-GA functions that work from a knowledge base (which may be distributed) in long term memory to synthesize matched channels and operational goals that are retained in short term memory. Experimental results show that the cognitive engine finds the best tradeoff between a host radio's operational parameters in changing wireless conditions, while the baseline adaptive controller only increases or decreases its data rate based on a threshold, often wasting usable bandwidth or excess power when it is not needed due its inability to learn. <s> BIB001 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> We can think of a cognitive radio as having three b asic parts that make it cognitive: the ability to sense, inclu ding at a minimum sensing the RF spectrum, geographical surroundings, and the user’s needs; the capacity to learn, ideally in both supervised and unsupervised modes; and finally, the capability to adapt within any layer o f the radio communication system. At the Virginia Tech (VT) Center for Wireless Telecommunications (CWT), we have developed a cognitive radio engine to perform all o f these tasks. This paper presents the adaptive component, which uses genetic algorithms (GAs) to evolve a radio def ined by a chromosome. The chromosome’s genes represent the adjustable parameters in a given radio, and by gene tically manipulating the chromosomes, the GA can find a set of parameters that optimize the radio for the user’s c urrent needs. At the end of this paper, we present experim ental results on both a hardware platform and software si mulation. <s> BIB002 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> Cognitive radios have been advanced as a technology for the opportunistic use of under-utilized spectrum. Cognitive radio is able to sense the spectrum and detect the presence of primary users. However, primary users of the spectrum are skeptical about the robustness of this sensing process and have raised concerns with regards to interference from cognitive radios. Furthermore, while a number of techniques have been advanced to aid the sensing process, none of these techniques have been verified in a practical system. To alleviate these concerns, a real time testbed is required, which can aid the comparison of these techniques and enable the measurement and evaluation of key interference and performance metrics. In this paper, we present such a testbed, which is based on the BEE2, a multi-FPGA emulation engine. The BEE2 can connect to 18 radio front-ends, which can be configured as primary or secondary users. Inherent parallelism of the FPGAs allows the simultaneous operation of multiple radios, which can communicate and exchange information via high speed low latency links <s> BIB003 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> This paper presents an overview of the ORBIT (open access research testbed for next-generation wireless networks) radio grid testbed, that is currently being developed for scalable and reproducible evaluation of next-generation wireless network protocols. The ORBIT testbed consists of an indoor radio grid emulator for controlled experimentation and an outdoor field trial network for end-user evaluations in real-world settings. The radio grid system architecture is described in further detail, including an identification of key hardware and software components. Software design considerations are discussed for the open-access radio node, and for the system-level controller that handles management and control. The process of specifying and running experiments on the ORBIT testbed is explained using simple examples. Experimental scripts and sample results are also provided. <s> BIB004 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> Sharing spectrum with systems that employ frequency reuse over large geographical areas (e.g., TV stations) provides an opportunity to improve spectrum utilization. The Federal Communications Commission (FCC) is considering such sharing in the TV hands (2004). This technical and regulatory opportunity prompted the IEEE to create a new committee, 802.22, that will develop a wireless regional area network (WRAN) standard for operating on vacant TV channels. This paper quantifies the idle bandwidth in the current TV band assignments; although the TV station information incorporated here is specific to the United States, the methodology and findings should be relevant to a global audience. The methodology for this analysis is distinct from prior literature on spectrum use measurements and offers a complementary perspective. Furthermore, the statistics from the analysis point to the value of systems that can operate on discontiguous portions of the radio spectrum. One approach, a modified form of OFDM here termed Discontiguous OFDM (DOFDM), could be well-suited to this dynamic spectrum access application. This paper provides a preliminary description of a DOFDM prototype and describes special considerations for its implementation <s> BIB005 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> To address the recent FCC initiatives that encourage the use of locally unused or under-used television broadcast spectrum for unlicensed broadband wireless access, a cognitive-enabled experimental system was developed to explore secondary spectrum utilization and user coordination through autonomous operation on a non-interference basis. This paper describes the enabling technologies and concepts, such as secondary spectrum usage, spectrum opportunity identification, user coordination, and interference mitigation that were incorporated into the experimental system <s> BIB006 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> Spectrum sensing has been identified as a key enabling functionality to ensure that cognitive radios would not interfere with primary users, by reliably detecting primary user signals. Recent research studied spectrum sensing using energy detection and network cooperation via modeling and simulations. However, there is a lack of experimental study that shows the feasibility and practical performance limits of this approach under real noise and interference sources in wireless channels. In this work, we implemented energy detector on a wireless testbed and measured the required sensing time needed to achieve the desired probability of detection and false alarm for modulated and sinewave-pilot signals in low SNR regime. We measured the minimum detectable signal levels set by the receiver noise uncertainties. Our experimental study also measured the sensing improvements achieved via network cooperation, identified the robust threshold rule for hard decision combining and quantified the effects of spatial separation between radios in indoor environments. <s> BIB007 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> The idea of cognitive radios has created a great interest in academic and industrial research. As a result, there are a large number of proposals for their physical and network layer functionalities. However, most of these research results rely on a theoretical analysis or computer simulations. In order to enable this technology and fully understand system design issues in its implementation, these theoretical results should be verified and demonstrated in realistic scenarios through physical implementation and experimental studies. In this paper, we present an experimental platform based on the Berkeley Emulation Engine 2 (BEE2) that can facilitate the development of physical and network layer functionalities for cognitive radios. We take spectrum sensing as an example that incorporates both signal processing and networking techniques to show how this platform could be used to conduct comprehensive research in cognitive radios. In particular, we focus on energy and cyclostationary detectors and indoor network cooperation. <s> BIB008 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> This paper describes a framework for research on architectural tradeoffs and protocol designs for cognitive radio networks at both the local network and the global internetwork levels. Several key architectural issues for cognitive radio networks are discussed, including control and management protocols, support for collaborative PHY, dynamic spectrum coordination, flexible MAC layer protocols, ad hoc group formation and cross-layer adaptation. The overall goal of this work is the design and validation of the control/management and data interfaces between cognitive radio nodes in a local network, and also between cognitive radio networks and the global Internet. Protocol design and implementation based on this framework will result in the CogNet architecture, a prototype open-source cognitive radio protocol stack. Experimental evaluations on emerging cognitive radio platforms are planned for future work, first in a wireless local-area radio network scenario using wireless testbeds such as ORBIT, and later as part of several end-to-end experiments using a wide-area network testbed such as PlanetLab (and GENI in the future). <s> BIB009 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> Research in the physical (PHY) and medium access control (MAC) layers for dynamic spectrum access (DSA) and dynamic spectrum sharing (DSS) is still at its infancy. Aspects such as spectrum sensing, coexistence, measurement and spectrum management, network reliability and QoS support in face of the need to avoid causing harmful interference into incumbents, to name a few, are key to the success of future cognitive radio (CR) systems and have received little attention so far. In addition, it is critical to understand the interplay of these various cognitive radio concepts and how they impact the overall network performance. In this paper we address these questions by presenting the design and performance evaluation of a CR-based PHY and MAC for DSA and DSS of vacant television (TV) channels. This air interface described here forms the baseline of the current IEEE 802.22 draft standard, and features a number of key PHY and MAC CR-based components for use by license-exempt devices in the spectrum that is currently allocated primarily to TV services. Through simulations and prototyping, we analyze the performance of this first CR-based wireless network with respect to spectrum sensing, system capacity, QoS support, coexistence, and network reliability. <s> BIB010 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> One of the key challenges of the emerging cognitive radio-based IEEE 802.22 wireless regional area networks (WRANs) is to address two apparently conflicting requirements: ensuring QoS satisfaction for WRAN services while providing reliable spectrum sensing for guaranteeing licensed user protection. To perform reliable sensing, in the basic operation mode on a single frequency band (non-hopping mode), one must allocate quiet times, that is, periodically interrupt data transmission that could impair the QoS of WRAN. This critical issue can be addressed by an alternative operation mode proposed in 802.22 called dynamic frequency hopping (DFH), where WRAN data transmission is performed in parallel with spectrum sensing without interruptions. DFH community, as described in this article, is a mechanism that coordinates multiple WRAN cells operating in the DFH mode, such that efficient frequency usage and reliable channel sensing are achieved. The key idea of DFH community is that neighboring WRAN cells form cooperating communities that coordinate their DFH operations <s> BIB011 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> This contribution presents and discusses the system concept approach which has been proposed by the European Integrated Project IST-E2R II in the IEEE P1900.B Standardization Study Group (SG); it currently is under further elaboration in the framework of the follow-up IEEE P1900.4 Working Group (WG) whose Project Authorization Request (PAR) was accepted in December 2006. This effort targets reconfigurable (typically software defined radio (SDR) based) networks and terminals in a heterogeneous wireless environment, with multi-homing capable terminals enabling the users to operate multiple wireless links simultaneously. In order to ensure backwards compatibility to legacy standards, the approach is to introduce three new building blocks into the (existing and/or evolving) heterogeneous landscape: i) A network reconfiguration management module, ii) a radio enabler and iii) a terminal reconfiguration management module. Within this paper, the key functionalities of these building blocks are detailed and discussed; it is furthermore outlined how the introduction of distributed decision-making concepts improves the efficiency of the heterogeneous system in terms of i) signaling overhead, ii) reactivity of user mobile terminals (MTs) and iii) numerical resource selection optimization complexity on the network side. <s> BIB012 </s> Advances in cognitive radio networks: A survey <s> V. COGNITIVE RADIO PLATFORMS AND STANDARDS <s> This paper presents an integrated view of cognitive radio technologies for efficient wireless services in dense spectrum environments. The rationale for cognitive radio based systems is discussed, leading to an identification of the available design space that ranges from reactive interference avoidance to spectrum etiquette and eventually network collaboration. After reviewing prior work in the dynamic spectrum area, a specific distributed spectrum etiquette protocol called ''common spectrum coordination channel (CSCC)'' is introduced. Performance gains achieved with CSCC relative to simpler reactive time/frequency/power control algorithms are evaluated for example in WiFi/Bluetooth and WiFi/WiMax co-existence scenarios. The next level of system performance can be achieved through opportunistic collaboration between radios to form ad hoc multi-hop networks in which neighboring nodes associate with each other at high bit-rate and low power. Adaptive wireless networks of this type will require new protocol architectures which integrate flexible PHY/MAC and cross-layer capabilities with ad hoc network discovery and multi-hop routing. A specific ''CogNet'' protocol architecture based on the concept of a ''global control plane (GCP)'' is described. Major CogNet protocol modules for bootstrapping, discovery, data path setup and naming/addressing are outlined, and representative ns-2 simulation results are provided for validation. In conclusion, the paper gives a preview of the network-centric WiNC2R prototype under development at WINLAB as an experimental cognitive radio platform. <s> BIB013
Although many works have been proposed to improve the performance of spectrum sensing and dynamic spectrum access and sharing, most of them only focus on the theoretical modeling and analysis and few of them have been verified in a practical system. Therefore, CR platforms need to be developed as a real-world testbed that can verify the theoretical analysis. In this section, we will first review some existing testbed/platforms and their features, followed by a brief discussion about standardization of CR techniques. Researchers at the University of California at Berkeley have proposed an experimental setup based on the Berkeley Emulation Engine 2 (BEE2) platform BIB003 to compare different sensing techniques and develop metrics and test cases so as to measure the sensing performance. In specific, a good CR system should provide sufficient protection to the PU, which casts certain requirements on a CR testbed, including the capability to support multiple radios, connect various different front-ends to support different frequency ranges, the capability for physical/link layer adaptation and fast information exchange for sensing and cooperation, and the capability to perform rapid prototyping. The BEE2 can meet these requirements, and support the features for a CR testbed. Using the BEE2 platform, research on spectrum sensing using energy detection and sensing with cooperation is tested by experiments BIB007 , which shows the feasibility and practical performance limits of energy detection under real noise and interference in wireless environments. In BIB008 , the feasibility of cyclostationary feature detection is further investigated. A distributed genetic algorithm based CR engine is proposed in the center for wireless telecommunications at Virginia Tech BIB001 , BIB002 . The cognitive engine focuses on how to provide CR capability to the physical and MAC data link layers. The cognitive system monitor enables cross layer cognition and adaptation by classifying the observed channel, matching channel behavior with operational goals, and passing the goals to a wireless system genetic algorithm adaptive controller module to gradually optimize radio operation. Researchers at Rutgers University have constructed an Open Access Research Testbed for Next-Generation Wireless Networks (ORBIT) BIB004 to perform experimentation on CR research. Based on the architectural foundation BIB009 , high performance CR platform with integrated physical and network layer capabilities BIB013 is under development using the ORBIT testbed. IEEE 802.22  is proposed to reuse the fallow TV spectrum without harmful interference to TV incumbents. A CR based PHY and MAC for dynamic spectrum sharing of vacant TV channels is evaluated in BIB010 , which studies spectrum sensing, coexistence of primary and secondary users, spectrum management, reliability and QoS, and their impact on the overall network performance. Dynamic frequency hopping (DFH) is recently proposed in IEEE 802.22  , where sensing is performed on the intended next working channels in parallel to data transmission in current working channel and no interruption is required for sensing. Efficient and mutual interference-free spectrum usage can only be achieved if multiple users operating in DFH can coordinate their hopping behavior. In BIB011 , DFH communities are proposed so that neighboring secondary users form cooperating communities and coordinate their hopping patterns in DFH. The analysis in BIB005 , quantifies the idle bandwidth in the current TV band assignments, and the statistical analysis shows that secondary users can operate on the discontiguous idle spectrum using OFDM. A feature detector design for TV bands is studied in BIB006 . The IEEE P1900 BIB012 is a new standard series focusing on next generation radio and spectrum management. One important focus of the standard is to provide reconfigurable networks and terminals in a heterogeneous wireless environment, where the multi-homing capable terminals enable users to operate multiple links simultaneously. The architectural building blocks include a network reconfiguration management (NRM) module that provides information about the environment, a terminal reconfiguration management (TRM) module that takes information from the NRM and determines the optimal radio resource usage strategies, a radio enabler of reconfiguration management that acts as a link between the NRM and the TRM.