Paul D. Sutton

Cyclostationary Signatures in Practical Cognitive Radio Applications

We define a cyclostationary signature as a feature which may be intentionally embedded in a digital communications signal, detected through cyclostationary analysis and used as a unique identifier. The purpose of this paper is to demonstrate how cyclostationary signatures can be exploited to overcome a number of the challenges associated with network coordination in emerging cognitive radio applications and spectrum sharing regimes. In particular we show their uses for signal detection, network identification and rendezvous and discuss these in the context of dynamic spectrum access. We present a theoretical discussion followed by application-oriented examples of the cyclostationary signatures used in practical cognitive radio and dynamic spectrum usage scenarios. We focus on orthogonal frequency division multiplexing (OFDM) based systems and present an analysis of a transceiver implementation employing these techniques developed on a cognitive radio test platform.

Iris: an architecture for cognitive radio networking testbeds

Iris is a software architecture for building highly reconfigurable radio networks. It has formed the basis for a wide range of dynamic spectrum access and cognitive radio demonstration systems presented at a number of international conferences between 2007 and 2010. These systems have been developed using heterogeneous processing platforms including general-purpose processors, field-programmable gate arrays and the Cell Broadband Engine. Focusing on runtime reconfiguration, Iris offers support for all layers of the network stack and provides a platform for the development of not only reconfigurable point-to-point radio links but complete networks of cognitive radios. This article provides an overview of Iris, presenting the unique features of the architecture and illustrating how it can be used to develop a cognitive radio testbed.

A Reconfigurable Platform for Cognitive Networks

By introducing self-awareness and computational intelligence to reconfigurable radio networks, cognitive networks are viewed as the key to a new generation of self-configuring, self-optimizing and self-healing communications systems. However, in order to make such systems realizable, a paradigm shift in the design of network node architectures is required. This paper presents a reconfigurable platform based on an architecture specifically designed for nodes within a cognitive network

Cyclostationary Signatures for Rendezvous in OFDM-Based Dynamic Spectrum Access Networks

Distributed coordination of operating frequencies and bandwidths is one of the key challenges in the development of dynamic spectrum access (DSA) technology. The spectrum efficiency of DSA networks is achieved through the use of spectrum white spaces, frequency bands which are unoccupied at a given time and place. The issue of frequency rendezvous arises as the availability of these white spaces may change dynamically in frequency, time and space. We propose a novel solution to the problem of distributed rendezvous in dynamic spectrum access networks using cyclostationary signatures. By embedding a cyclostationary signature or watermark in a transmitted signal, the received signal can be uniquely detected, classified, and used for frequency acquisition by distributed dynamic spectrum access-enabled nodes in a network. This paper therefore makes three key contributions. First, a solution to the problem of distributed rendezvous in DSA networks using the novel concept of cyclostationary signatures is presented. Second, a low-complexity technique for generating these cyclostationary signatures in OFDM (orthogonal frequency division multiplexing) waveforms is described. Finally, an initial performance analysis of an implemented test platform is discussed.

Cyclostationary Signature Detection in Multipath Rayleigh Fading Environments

Cognitive radio-based Open Spectrum systems offer a solution to the issue of spectrum scarcity by allowing wireless networks to dynamically access spectrum while coordinating to co-exist and avoid the creation of harmful interference. However, before a practical open spectrum system may be implemented, a number of significant technical and policy challenges must be overcome. One such technical challenge is the distributed coordination of operating frequencies and bandwidths between co-existing systems. Cyclostationary signatures have been shown to be a powerful tool in overcoming this challenge. A cyclostationary signature is a unique identifier or watermark which may be embedded in the physical properties of a communications signal. Such signatures may be used to aid peer devices in performing a number of critical tasks, including signal detection, classification and frequency acquisition. A key limitation of cyclostationary signatures when implemented in orthogonal frequency division multiplex (OFDM)-based systems is the sensitivity exhibited in time-variant multipath Rayleigh fading environments. Although OFDM-based systems offer robust performance under multipath conditions, detection of cyclostationary signatures can be severely degraded. As signature detection is adversely affected, the ability of Open Spectrum Systems to coordinate and coexist is seriously undermined. This paper therefore presents techniques for effectively over-coming the issue of multipath Rayleigh fading in the detection of cyclostationary signatures for Open Spectrum systems. Approaches for the generation and detection of signatures in OFDM-based waveforms are outlined and improvements in detection performance are illustrated using simulation results.

Cognitive radio for disaster response networks: survey, potential, and challenges

In the wake of a natural or man-made disaster, restoration of telecommunications is essential. First responders must coordinate their responses, immediate casualties require assistance, and all affected citizens may need to access information and contact friends and relatives. Existing access and core infrastructure may be damaged or destroyed, so to support the required services, new infrastructure must be rapidly deployed and integrated with undamaged resources still in place. This new equipment should be flexible enough to interoperate with legacy systems and heterogeneous technologies. The ability to selforganize is essential in order to minimize any delays associated with manual configuration. Finally, it must be robust and reliable enough to support mission-critical applications. Wireless systems can be more easily reconfigured than wired solutions to adapt to the various changes in the operating environment that can occur in a disaster scenario. A cognitive radio is one that can observe its operating environment, make decisions and reconfigure in response to these observations, and learn from experience. This article examines the use of cognitive radio technologies for disaster response networks and shows that they are ideally suited to fulfill the unique requirements of these networks. Key enabling technologies for realizing real-world cognitive radio networks for disaster response are discussed and core challenges are examined.

Dynamic Spectrum Access and Coexistence Experiences Involving Two Independently Developed Cognitive Radio Testbeds

The Centre for Telecommunications Value-Chain Research (CTVR) and the Center for Wireless Telecommunications (CWT) are carrying out joint research work investigating the potential of different software-defined radio (SDR) and cognitive radio (CR) systems that can coexist in common frequency bands. This paper describes the independently developed dynamic spectrum access test beds used in a practical coexistence experiment. An initial analysis of actual coexistence experiences involving a primary user and a secondary opportunistic spectrum user in a common frequency band is also presented. The results in this paper include an analysis of a worst case scenario where the primary user and secondary opportunistic user are coexisting with no guard bands separating each other. The experimental results showed that the primary user experienced zero packet loss when guard bands separated the primary and secondary services. Additionally, when no guard bands were used and the spectrum segment was maximally used over the geographical area involved in the experiments, the signal to noise and interference ratio (SNIR) needed to be adjusted to 20 dB by modifying the secondary user transmissions in order to minimise the interference experienced by the primary user.

An Encapsulation for Reasoning, Learning, Knowledge Representation, and Reconfiguration Cognitive Radio Elements

State and contextual awareness, reasoning and conclusions formation, and a means of directing application, structural and parameter-level radio reconfiguration are key elements of a cognitive radio. This paper describes a cognitive radio design capable of scaling between the two extremes of minimal cognitive capabilities and complex highly-evolved cognitive radio abilities, which is being adopted for real tests using licensed cognitive radio test spectrum. A memory element stores state, sensor, objectives, actions and conclusions information and the relevance of this information can be varied in order to identify or ignore common traits or occurrences. The decision-making and conclusions formation abilities of this cognitive radio design can use (or choose to ignore using the variable weighting facility) external information relating to the network, and etiquettes in conjunction with the memory element. A set of actions formulated by the reasoning and conclusions formation stages direct the radio reconfiguration. This design is implemented using a general-purpose processor (GPP) platform as it currently offers the very high level of reconfigurability required for very malleable cognitive radio design

OFDM Pulse-Shaped Waveforms for Dynamic Spectrum Access Networks

In dynamic spectrum access networks (DySPANs), users share access to available spectrum while minimizing the likelihood of harmful interference. In this demonstration we present a dynamic spectrum access network which employs a reconfigurable orthogonal frequency-division multiplexing (OFDM) based waveform. In order to avoid the creation of harmful interference, the out-of-band (OOB) emissions of the waveform are dynamically tailored to the properties of spectrum neighbours through the use of OFDM pulse shaping. The demonstration network is built upon the highly reconfigurable Iris 2.0 software radio platform and illustrates the capabilities of this platform as well as the utility of OFDM pulse shaping in the context of dynamic spectrum access networks.

Bandwidth-Adaptive Waveforms for Dynamic Spectrum Access Networks

This paper presents a novel solution to the challenge of waveform bandwidth estimation in DySPAN systems using intentionally embedded cyclostationary signatures. Dynamic spectrum access networks (DySPANs) achieve high levels of spectrum use efficiency by exploiting spectrum white spaces, radio frequencies which are unused at given times and places. These white spaces have bandwidths which may not be known in advance and so, in order to fully exploit them, a DySPAN system must employ bandwidth-adaptive waveforms. It has been shown that multi-carrier transmission schemes can be leveraged to generate waveforms of flexible bandwidth. However, robust bandwidth estimation techniques are required for receiving nodes to successfully detect these signals and establish communication links. This paper makes three key contributions. Firstly, a novel technique for the generation of bandwidth-adaptive multi- carrier waveforms is proposed. Secondly, two approaches for parametrization of these bandwidth-adaptive waveforms in receiving DySPAN nodes are presented. The advantages and disadvantages of both bandwidth estimation techniques are examined and comparisons are drawn with approaches adopted for the IEEE 802.16 and draft IEEE 802.22 standards. Finally, the performance of both techniques under multipath fading conditions are examined using simulation results.