Cognitive Radios (CRs) and Software Defined Radios (SDRs) have ubiquitous applications ranging from handheld to base station devices. In order to meet the computational requirements of such radios, computing heterogeneity, the mixed usage of General Purpose Processors (GPPs), Digital Signal Processors (DSPs), and Field-Programmable Gate Arrays (FPGAs), is attractive. Developing SDR and CR applications already requires a diverse set of skills, and computing heterogeneity further complicates the process. This paper presents a developmental workflow used successfully by the authors for SDR and CR application running on a platform combining DSP and GPP based processors. The paper discusses tools used to set up the platform, create compilation environment, develop code for GPP/DSP communication, integrate the DSP into GNU Radio, and use the environment to develop SDR/CR applications. It presents a case study showing how computing heterogeneity can be used to address diverse application needs.

Emergency communication systems (ECS) are a key element in collaborations among different public safety organizations. The need for interoperability in emergency communication systems has hastened the development of interoperable communication technology that is an enabling technology to automatically identify environmental variables including appropriate radio frequencies and to connect different networks used by different organizations. Even though the technology has been researched from many perspectives and has shown that is possible to connect different organizations, there still remain many issues in terms of socio-cognitive aspects. Thus, this study examines the socio-cognitive dimensions of interoperability, which equal the technical dimensions of the problem in importance. The existential-phenomenological study reported here used semistructured interviews to reconceptualize interoperability in the public safety communication domain. Based on 11 interviews with public safety workers, five important factors were identified that have a major impact on the effectiveness of interoperable groups: information sharedness, operational awareness, communication readiness, adaptiveness, and coupledness. Based on these main concepts, high-level suggestions are provided to guide the design of a new public safety communication system. The results can be directly applied to identify the requirements of communication systems and can be extended to design collaboration systems under stressful environments.

Significant progress has been made in the past few years on Dynamic Spectrum Access (DSA) wireless networks which seek to use RF spectrum more efficiently and dynamically. For example, many measurements of current spectrum utilization are available and theoretical analyses and computational simulations of DSA networks abound. In sharp contrast, few network systems, particularly those with a decentralized structure, have been built even at a small scale to investigate the performance, behavior, and dynamics of DSA networks. Our contribution is designing a decentralized and asynchronous DSA network and building a prototype based on software radio technologies, signal detection and classification methods, distributed cooperative spectrum sensing systems, and mobile ad-hoc network (MANET) protocols. This paper details the network''s design and implementation as well as its enabling technologies. Through systematic experiments, we identify several factors influencing performance for decentralized DSA networks.

This paper introduces the Virginia Tech Center for Wireless Telecommunications' Vehicular Public Safety Cognitive Radio (VPSCR), a vehicle-based extension to our previously fielded cognitive radio prototype for the public safety community. Specifically, the VPSCR can scan the radio spectrum over multiple public safety frequency bands, classify commonly used public safety waveforms and networks, and reconfigure itself for network interoperation. The VPSCR is designed for vehicular assembly, powering itself from the onboard car battery. Such a platform, however, has a significant power requirement, which prevents it from being easily downsized into a handheld mobile device, thereby limiting its mobility. We introduce a new architecture which uses a personal digital assistant (PDA) to remotely control and access services from the VPSCR. Following a modular approach, we designed a remote agent on the VPSCR to advertise services that a PDA can discover and subscribe. This provides a PDA with the capability to remotely control the VPSCR according to a public safety officers own needs. The data link between the PDA and the VPSCR utilizes existing fixed infrastructures such as the 802.11 Wi-Fi or Bluetooth standards, enabling the PDA to extend its operational range.

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.

A universal classifier synchronizer and demodulator (UCSD) is conceived as a self-contained system which forms the heart of a truly cognitive receiver. It can automatically interpret features of the received signal to accomplish physical layer classification, synchronization and demodulation without any priori information about the waveform from the transmitter side. In this paper we propose a cognitive receiver functioning as a finite state machine. The accommodated modulations include AM, FM, FSK, MPSK, and QAM. The designed system has been verified using a stand-alone MATLAB-enabled Anritsu MS2781A Signature Signal Analyzer running Windows, and GNU Radio plus a Universal Software Radio Peripheral (USRP) in Linux.

The Centre for Telecommunications Value-Chain Research (CTVR) and the Center for Wireless Telecommunications (CWT) are undertaking a joint collaborative research project investigating the potential of different software-defined radio (SDR) and cognitive radio (CR) systems that can interoperate and co-exist in common frequency bands.This paper presents some key results from this experience so far, including an over-the-air interoperability analysis of two different SDR architectures in the same frequency band.An initial analysis of actual co-existence experiences involving primary users and secondary opportunistic spectrum users in a common frequency band is also presented.

Abstract A cognitive radio (CR) is a transceiver that is aware, adaptive, and capable of learning. It may be visualized and realized as an intelligent software package (cognitive engine) controlling a software defined radio platform. The cognitive engine executes a set of nested loops constituting a cognition cycle, drawing on experience and stored knowledge to optimize a set of user‐chosen quality of service measures. The process relies on the effectiveness of a set of tools that are individually well known but rarely found together: multi‐objective genetic algorithms, case‐based decision theory, and neural networks. Practical implementation problems include passing environmental information from the radio to the cognitive engine, acting on that information, and performing real‐time control of the radio platform by the cognitive engine. In this paper, we discuss our approach to developing and implementing a CR. Copyright © 2007 John Wiley & Sons, Ltd.

The IEEE 802.11 wireless local area network (WLAN) standard supports multiple transmission modes. However, the higher mandatory data rate mode does not necessarily yield higher throughput. We show the relationship between the link throughput and the channel's carrier-to-noise (C/N) ratio. We propose a throughput optimization and transmitter power saving (TOTPS) algorithm based on the knowledge of the C/N ratio at the receiver. In particular, we take the approach of adjusting link parameters, like transmitter power and transmission mode, to achieve the maximum throughput at different C/N values. Since this algorithm tends to reduce the transmitter power without degrading the link throughput, transmitter power can be saved. This not only prolongs battery life, which is critical in ad hoc wireless networks, but also reduces the potential interference to neighboring wireless network systems. This algorithm can also be applied to IEEE 802.11a and IEEE 802.11g links.

Broadband wireless access (BWA) is a promising emerging technology. The IEEE 802.16 task group recently standardized the physical (PHY) and medium access control (MAC) layers for BWA systems. To operate in a wide range of physical channel conditions, the standard defines a robust and flexible PHY. A wide range of modulation and coding schemes are defined. While the standard provides a framework for implementing link adaptation, it does not define how exactly adaptation algorithms should be developed. The paper evaluates the performance of IEEE 802.16 using a few typical PHY burst profiles defined in the standard. Based on these performance results, TCP delay is identified as a suitable metric to serve as the link quality indicator. A simple link adaptation algorithm is developed to minimize the end-to-end (ETE) TCP delay based on the measured signal-to-noise ratio (SNR). The effects of TCP performance enhancements, namely dynamic window scaling and selective acknowledgements, on the adaptation algorithm are also studied.

This paper presents the results of a recent 28 GHz continuous-wave (CW) building corner diffraction measurement campaign in the Washington, DC area. Observed diffraction losses showed little dependence on polarization and building material. For diffraction angles greater than 5/spl deg/, a simple linear equation accurately describes the diffraction loss in dB vs. angle in degrees. A logarithmic equation describes the dependence at small angles. The model showed very good agreement with theory. In addition to the measurement results, the paper discusses the experiment layout and procedure.

The authors present the results of average and impulsive noise measurements inside several office buildings and retail stores. The noise measurement system operated at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3-dB RF bandwidth. Omnidirectional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels. Statistical analyses of the measurements are presented in the form of peak amplitude probability distributions, pulse duration distributions, and interarrival time distributions. Simple first-order mathematical models for these statistical characterizations are also presented. These analyses indicate that photocopiers, printers (both line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulse noise in office and retail environments.>

Earth-space communications links operating above 10 GHz may be adversely affected by the earth's atmosphere and hydrometeors, particularly rain. These propagation phenomena are usually evaluated only for fading and depolarization effects. However, dispersion is an important factor in wide-band digitally modulated satellite links. In this paper we examine the mechanisms responsible for dispersion over bandwidths as great as 500 MHz in the 10-30 GHz range. The amplitude and phase effects of dispersion are quantified for a wide range of propagation conditions. The resulting propagation model is then used to generate estimates of performance degradation in wide-band QPSK systems through the use of computer simulation.