Alireza Attar

Cognitive Radio game for secondary spectrum access problem

In this paper we develop a framework for resource allocation in a secondary spectrum access scenario, where a group of cognitive radios (CR) access the resources of a primary system. We assume the primary system is a cellular OFDM-based network operating in uplink. We develop an optimum resource allocation strategy, using cooperative game theory, which guarantees the primarys required QoS and allocates an achievable rate at a given bit error rate for the secondary, when possible. The proposed cognitive radio game (CRG) is a network-assisted resource management method, where users (both primary and secondary) inform the primary systems BS of their channel state information and power limitation and the base station calculates the optimum sub-channel and power allocation for all users. Using Game theoretic axiom of fairness, i.e., Nash Bargaining Solutions (NBS), we develop an alternative efficient and fair resource allocation and compare its performance with the proposed CRG method. We use Sequential Quadratic Programming (SQP) to solve the proposed non-linearly constrained CRG optimization problem.

Interference-limited resource allocation for cognitive radio in orthogonal frequency-division multiplexing networks

Efficient and fair resource allocation strategies are being extensively studied in current research in order to address the requirements of future wireless applications. A novel resource allocation scheme is developed for orthogonal frequency-division multiplexing (OFDM) networks designed to maximise performance while limiting the received interference at each user. This received interference is in essence used as a fairness metric; moreover, by defining different interference tolerances for different sets of users, the proposed allocation scheme can be exploited in various cognitive radio scenarios. As applied to the scheme, the authors investigate a scenario where two cellular OFDM-based networks operate as primary and secondary systems in the same band, and the secondary system benefits by accessing the unused resources of the primary system if additional capacity is required. The primary system benefits either by charging the secondary system for the use of its resources or by some form of reciprocal arrangement allowing it to use the secondary systems licenced bands in a similar manner, when needed. Numerical results show our interference-limited scheduling approach to achieve excellent levels of efficiency and fairness by allocating resources more intelligently than proportional fair scheduling. A further important contribution is the application of sequential quadratic programming to solve the non-convex optimisation problems which arise in such scenarios.

A Comparison Between the Centralized and Distributed Approaches for Spectrum Management

There is a growing demand for spectrum to accommodate future wireless services and applications. Given the rigidity of current allocations, several spectrum occupancy studies have indicated a low utilization over both space and time. Hence, to satisfy the demands of applications it can be inferred that dynamic spectrum usage is a required necessity. Centralized Dynamic Spectrum Allocation (DSA) and Distributed Dynamic Spectrum Selection (DSS) are two paradigms that aim to address this problem, whereby we use DSS (distributed) as an umbrella term for a range of terminologies for decentralized access, such as Opportunistic Spectrum Access and Dynamic Spectrum Access. This paper presents a survey on these methods, whereby we introduce, discuss, and classify several proposed architectures, techniques and solutions. Corresponding challenges from a technical point of view are also investigated, as are some of the remaining open issues. The final and perhaps most significant contribution of this work is to provide a baseline for systematically comparing the two approaches, revealing the pros and cons of DSA (centralized) and DSS (distributed) as methods of realizing spectrum sharing.

Cognitive Radio Transmission Based on Direct Sequence MC-CDMA

In this paper, we propose a cognitive cellular system based on DS MC-CDMA to coexist with a number of narrow-band legacy systems in the same frequency range. If the bandwidth and the frequency location of each narrow-band system are known to this cognitive MC-CDMA, it is possible to mitigate their interfering effect in the cognitive receivers by adaptive transmission. We will develop an algorithm for calculating the adaptive transmission parameters and show that it combats interference in the channel effectively.

Challenges of real-time secondary usage of spectrum

In this survey paper, we investigate some of the challenges to be addressed before a practical real-time secondary market for spectrum can be developed. We differentiate the methods of dynamic spectrum allocation as coordinated usage of resources, interworking solutions, integration solutions and secondary access of spectrum. Secondary spectrum access approaches are generally classified as real-time and non-real-time secondary access. However, the focus of this work is on real-time secondary spectrum utilization which can follow a negotiated or opportunistic access strategy. While different solutions for increasing spectrum utilization and efficiency are under investigation, many aspects of spectrum sharing technologies are still open questions. After an extensive literature survey, the major challenges and open questions of real-time secondary usage of spectrum are addressed here. We also provide some insights on potentially important design considerations and requirements when developing successful spectrum management schemes to realize real-time secondary spectrum usage.

Cognitive Radio Game: A Framework for Efficiency, Fairness and QoS Guarantee

In this paper we develop a framework for resource allocation in a secondary spectrum access scenario where a group of cognitive radios (CR) access the resources of a primary system. We assume the primary system is a cellular OFDM-based network. We develop the optimum resource allocation strategies which guarantee a level of QoS, defined by minimum rate and the target bit error rate (BER), for the primary system. Using the game theoretic axiom of fairness, i.e., Nash bargaining solutions (NBS), we show that by allocating a priority factor to all players an efficient and fair resource allocation can be achieved. We show how the priority factors are assigned in this scheme and outline a method to select the users who are allowed to share a specific sub-channel.

A Universal Resource Awareness Channel for Cognitive Radio

Cognitive radio is certain to transform our traditional radio resource allocation regimes. Through cognitive radio, better spectrum efficiency can be leveraged by radios intelligently altering their radio resource usages dependent on locally available information about radio conditions. A significant challenge for cognitive radio, however, is awareness of these local radio conditions. One crude solution is for the radio to periodically scan the complete spectrum band over which cognition in radio resource usages can apply. Such an operation would be time-consuming and wasteful of power, and ultimately would be entirely impractical. In this paper, we therefore propose the concept of a resource awareness channel (RAC)-a single universally available channel on a fixed frequency, on which information about resource usage is conveyed by all radios using the cognitive radio spectrum band. This allows cognitive radios that want to alter their transmission resources to make an informed decision about the practicality or these prospective changes in terms or interference for the system as a whole, simply by listening to the RAC. We analyse the performance or this proposed RAC concept, and show it to be practical even in areas that are highly populated by radios

Development of a Radio Enabler for Reconfiguration Management within the IEEE P1900.4 Working Group

An important emerging capability is for mobile terminals to be dynamically reconfigured. Through ongoing advances in technology such as software defined radio, reconfiguration of mobile terminals will in the near future be achievable across all layers of the protocol stack. However, along with the capability for such wide-ranging reconfiguration comes the need to manage reconfiguration procedures. This is necessary to coordinate reconfigurations, to ensure that there are no negative effects (e.g. interference to other RATs) as a result of reconfigurations, and to leverage maximal potential benefits of reconfiguration and ensuing technologies such as those involving dynamic spectrum access. The IEEE P1900.4 working group is therefore defining three building blocks for reconfiguration management: network reconfiguration management (NRM), terminal reconfiguration management (TRM), and a radio enabler to provide connectivity between the NRM and TRMs. In this paper we concentrate on aspects of the radio enabler, highlighting its relevance in heterogeneous radio access scenarios, its advantages, and some aspects of its technical realization.

Interference Management in Shared Spectrum for WiMAX Systems

Spectrum sharing methods, such as secondary spectrum access, are powerful candidates to improve spectrum utilization and efficiency. In this paper, we develop a novel resource allocation scheme for WiMAX networks, which is designed to maximize performance while limiting the received interference at each user. By defining different interference tolerances for different sets of users, the proposed allocation scheme can be exploited in a secondary spectrum access scenario where two WiMAX operators, one as the primary operator and the other one as the secondary operator, are using a shared band. The primary system benefits either by charging the secondary system for the use of its resources, or by some form of reciprocal arrangement allowing it to use the secondary systems licensed bands when needed. Numerical results show our resource allocation approach to achieve an excellent fairness, while incurring only a slight reduction in system throughput compared with the theoretical upper limit of opportunistic scheduling.

Architectures and Protocols for Dynamic Spectrum Sharing in HeterogeneousWireless Access Networks

1 Centre for Telecommunications Research, King’s College London, UK {Oliver.Holland, Ali.Attar, Hamid.Aghvami}@kcl.ac.uk 2 Toshiba Research Europe Ltd., Bristol, UK {Mahesh.Sooriyabandara, Tim.Farnham}@toshiba-trel.com 3 Motorola Labs, Gif-sur-Yvette, France (Markus Muck has since moved to Infineon Technologies, Munich, Germany) markus.muck@gmail.com 4 Intel Corporation, Communications Technology Lab, St. Petersburg, Russia vladimir.ivanov@intel.com 5 Alcatel-Lucent Deutschland AG, Bell Labs, Germany klaus.nolte@alcatel-lucent.de