The Symbiosis of Cognitive Radio and WMNs from “Guide to WMNs” by Sudip Misra and et al, 2009 Myungchul Kim

–CR provides WMNs with additional bandwidth and improved efficiency Atstract

Unlicensed spectrum: cordless phones, remote controls, and even microwave ovens Obtaining additional spectrum is very difficult More efficient use of available bandwidth? Introduction

Radio communication –The wave attenuates, reflects, and refracts. –Signal-to-noise ration (SNR), signal-to-interference-plus- noise (SINR) –The radio spectrum can be shared along three dimensions – frequency, time, and space Spectrum allocation –Frequency division FCC, CRTC, KCC ITU, ITR-R –Spectrum auction Background

Spectrum usage –new spectrum increasingly scarce –Spectrum is vastly under-used: 5.2% usage Change –“command and control” approach to spectrum regulation Background

What is Cognitive Radio? –By J. Mitola, 1999 –Describe a device that used its awareness of its environment to intelligently choose the best parameters to use for its own communications –Key factors An incredible boom in wireless networks and devices Increased interest in wireless research Software Defined Radio (SDR) allows the behavior of the radio to be controlled by software rather than in fixed hardware and allows a device to switch between different network technologies using a single physical radio. SDR focuses on specifying architectures and the wired interface, an important component for building CR devices. Cognitive radio

Key characteristics of a Cognitive Radio –Advanced interoperability Antenna technologies: antenna arrays, MIMO, and adaptive beam-forming UWB using the medium without adding significantly to overall interference levels At least the first generation of CR devices will have to coexist with existing noncognitive wireless technologies –Frequency agility Being able to dynamically adjust the frequencies and bandwidth of their transmissions A CR will require a much better ability to detect different types of transmissions, including those spread over a range of frequencies. Cognitive radio

Key characteristics of a Cognitive Radio? –Awareness The ability to detect transmissions The ability to sense and measure channel conditions throughout the spectrum Awareness of its hardware, applications, user characteristics and its goals –Cognition The CR must decide what transmission must occur – to whom, on what network – and when and how the transmission will occur. –Collaboration The CR must consider the interactions between not only different nodes in ins network, but in all networks. Cognitive radio

How CR changes spectrum management –Open Spectrum Policy –Researchers have proposed different methods for CR devices to use the same licensed frequencies –IEEE Share the frequencies occupied by broadcast television –A CR uses Guard bands of TV bands –CR can communicate at transmission powers and ranges that are low enough to avoid interfering with TVs. –If a CR can determine when and where there are no users of the primary technology, it may be able to make full use of spectrum Cognitive radio

How CR changes spectrum management –Shorter-term licenses (and more frequent auction), licenses allowing for secondary cognitive use while maintaining primary user rights and priority, and a fully dynamic spectrum market. –Ability to buy, sell, trade, or lease spectrum rights Cognitive radio

WMN characteristics –The access and transit links to operate over separate wireless interface and on different channels –Transit network Openly shared wireless medium Multihop forwarding To or from the gateway Directional antennas and multiple channels -> multiple links Applying CR to a WMN

Benefits of CR to WMNs –Providing additional bandwidth Transient frequency holes could be used by the WMN –Rebalancing the access and transit network bandwidth If both the access and transit links use the same technology? Multichannel MAC Multiple interfaces –Changing the nature of gateways WiMAX as a gateway Multiple gateways –Multiple user technologies Legacy devices Applying CR to a WMN

–Find ways to allow intermediate technological advances to enter mainstream use before the completion of a fully capable CR Transmission –How much usable information can be encoded on a channel using different techniques –UWB, MIMO, directional antennas, frequency agility Awareness –A huge volume of environmental data collected and shared –Spectrum sensing is difficult when wide spectrum is considered –Dynamic nature of the wireless medium CR research

Awareness –Radio Knowledge Representation Language (RKRL) –Interference Temperature: a metric for estimating the cumulative interference energy at a receiver -> “not a workable concept” by FCC –Virtual cubes with time, frequency and power –Active and passive (receiver only): user locations and characteristics –Network loads and application conditions CR research

Sharing information –Different nodes will have a different set of collected knowledge in location, configuration, and history. –The system must be able to control or limit the exchanged information –Cf. sensor networks: filtering information Decision making –Conventional wireless interface: linear, modeled on protocol stack –CR interface: nonlinear, all parts of the communication must be decided through cross-layer protocols CR research

Decision making –CR utilizes all available information in all communication-related decisions –What to send Communicate now or wait later Adjust the traffic according to the network condition –Where to send it Vertical handoff Different networks for different traffic types Routing in multihop networks CR research

Decision making –How to send After where to send, choose the appropriate parameters based on the current environment –When to send The MAC determines when to access the medium Choose to transmit now or delay CR research

Regulatory agencies –On what time-scale should spectrum be allocated –Should a centralized or a distributed approach to be used For very short leases, the fully centralized system of a single regulatory body Real-time spectrum auction Spectrum could be allocated for single flows or even single packets –Should access be scheduled or contention-based –Secondary spectrum market Cellular provider –Dynamic spectrum necessitates an integrated enforcement solution Thoughts for practitioners

Static core topology –For CR, the fixed network changes the problem of collecting awareness of the network’s surroundings Spectrum information collection –The WMN presents a distributed infrastructure to collect spectrum data at a large number of locations –CR devices act as sensors to gauge interference levels Traffic awareness –Fairly easy to obtain from the gateway Directions for future research

Data distribution and decision making –Within the mesh itself Spectrum monitoring and policing –Primary spectrum rights should be protected –The WMN may be able to collaborate to detect users and determine the location of illegal transmissions Directions for future research