Wireless Mesh Networks

1. Wireless Mesh Networks Spezialvorlesung Anatolij Zubow (zubow@informatik.hu-berlin.de) Cognitive Radio

2. Spectrum Efficiency and Cognitive Radio • Technological advances are forcing the wireless industry to feel the feared “spectrum crunch”. • To solve the problem, there are several questions that must be addressed… What exactly is the “spectrum”? How is it used? What is the history of its evolution? Why is there a problem today? What is the solution?

3. What is the RF Spectrum? Is it a physical block… …or an open space?

4. The Current Wireless Paradigm • The RF Spectrum is really only a range of oscillations suitable for radio communications, and therefore, is not a true physical medium. Modeled by the Swimmer Analogy • This begs the question: Why is something inherently non-physical partitioned like a tangible object?

5. RF Spectrum – 1.39 to 5.923 GHz

6. The RF Spectrum Dilemma • As more and more devices are added to the wireless community, they must jockey for the right to transmit at frequencies in the same bands. • However, there exist a large number of frequency bands that have considerable, and sometimes periodic, dormant time intervals.

7. What Solutions Exist? • The way we manage spectrum must change. • Whereas before radios were assigned “lanes” in which to operate, cognitive frequency-agile radios could now be allowed to intelligently “switch lanes” and adjust parameters. • Ultra-Wideband “underlay” transmission techniques could be employed to “talk under” primary users in a given frequency band. • Cooperative networking, specifically a mesh architecture, would allow a true web of ad hoc radio nodes, allowing each radio to act as both a transmitter and receiver in the network.

8. Frequency-Agile Radios • Software-Defined Radios (SDR) introduce the ability for instantaneous frequency reconfiguration. • Evolution of the SDR concept leads to Cognitive Radio, defined as “an SDR that additionally senses its environment, tracks changes, and reacts upon its findings.” [Jondral-06] • User-centric vs. Technology-centric CR Operation • A preliminary step in achieving true “open spectrum” is the implementation of a cooperative Primary User-Secondary User system.

9. Software-Defined Radio • Ziel eines SDR ist es die gesamte Signalverarbeitung eines Hochfrequenz-Senders oder -Empfängers mit Hilfe anpassbarer Hardware in Software abzubilden. • Es handelt es sich um ein Funktelekommunikationssystem, das eine software-konfigurierbare Plattform zur Modulation/Demodulation und Aufwärts-/Abwärtsmischung eines Datensignals benutzt. • Ein SDR-System führt einen Großteil der Signalverarbeitung mit einem Universalrechner (z.B. Intel X86) oder programmierbarer Digitalhardware aus (DSPs oder FPGAs)  Flexibilität • Unterschiedliche Funkverfahren können durch alleinige Änderung der Software implementiert werden. • Die Kernkomponente eines SDR ist programmierbare Digitalhardware wie FPGAs. • Ein FPGA ist ein programmierbarer Integrierter Schaltkreis (IC) der Digitaltechnik. In FPGAs können durch spezifische Konfiguration interner Strukturen die verschiedenartigsten Schaltungen gebildet werden.

10. WIRELESS OPEN-ACCESS RESEARCH PLATFORM (WARP) • WARP ist eine programmierbare Plattform für drahtlose Kommunikation. • Ziel ist die prototypische Umsetzung von physikalischen sowie Mediumzugriff- Schichten zukünftiger drahtloser Systeme. • Open-Software/Hardware Plattform, d.h. der Community wird der Zugriff auf Software + Spezifikation der Hardware gegeben. • Für die Programmierung der PHY sowie MAC-Schicht kommt ein Xilinx FPGA zum Einsatz.

11. WIRELESS OPEN-ACCESS RESEARCH PLATFORM WARP FPGA Board WARP Radio Board

12. WIRELESS OPEN-ACCESS RESEARCH PLATFORM (WARP) • Besonderheiten: • Unterstützt Multiple Input Multiple Output (MIMO) • Multi-Gigabit Ethernet zum Verbinden mehrerer WARP Boards • Realisierte Prototypen für kooperative Kommunikation, Beamforming for MIMO • Testumgebungen: WiTestLab (http://witestlab.poly.edu/) • Kosten: • MIMO Kit (2 Radios) – 12 T€ • SISO Kit (1 Radio) – 10 T€ • Dokumente: • http://warp.rice.edu/

13. Universal Software Radio Peripheral (USRP) • USRP (http://www.ettus.com/) • USRP wird mit einem Host-PC über USB2/Ethernet verbunden • Vollständige Design von USRP ist Open Source • Software: GNU Radio (http://gnuradio.org/trac) • Besonderheiten: • Verarbeitung von Wideband-Signalen, Gigabit Ethernet • Mehrere USRP-Boards können zusammengeschlossen werden  MIMO • GNURadio – sehr aktive Community (viele Projekte; GPS-Empfänger auf Basis von GNURadio/USRP) • Kosten: • Sehr günstig – ca. 1000 € für USRP • Dokumente: • USRP - http://www.ettus.com/ • GNURadio - http://www.gnuradio.org

14. Universal Software Radio Peripheral (USRP) USRP 2 Board

15. CalRadio • CalRadio ist ein hybrides Software-Defined Radio • Die physikalische Schicht kann nicht verändert werden • Z.Z. nur IEEE 802.11b (Intersil (Conexant) Prism chip) • Der Mediumzugriff (MAC) kann hingegen vollständig programmiert werden. • Es wird ein C5471 Texas Instruments Digital Signal Processor verwendet.

16. CalRadio • Besonderheiten: • Programmierung des Digital Signal Processing (DSP) in C (keine spezielle Entwicklungsumgebung) • Linux als Betriebssystem (ARM Prozessor) • Zur Zeit lediglich ein RF Frontend (802.11b) • Kosten: • Hardware - 2 T€ • Dokumente: • http://calradio.calit2.net/ CalRadio Architektur

17. A Software-Defined GPS and Galileo Receiver • Ziel ist die Entwicklung eines kombinierten GPS/Galileo Empfängers auf der Basis von SDR. • Dokumente: • http://ccar.colorado.edu/gnss/ • http://www.amazon.com/Software-Defined-GPS-Galileo-Receiver-Single-Frequency/dp/0817643907 • http://www.sparkfun.com/commerce/product_info.php?products_id=8238 SDR captures raw GPS data

18. Spectrum Leasing Spectrum Pooling is the concept that a non-licensed radio may use a given frequency when the original licensee is not. There are two approaches to the leasing of spectrum pools with which the license owner may operate: • The license owner is aware of other radios using its allocated frequency band. It may avoid other radios, but has the right to reclaim any frequency. • The license owner is completely unaware of the presence of other radios, forcing them to change.

19. Application - CORVUS System A new spectrum management system (CORVUS*) has been designed, based upon: • Abundance of spectra available for sharing • Secondary Users utilizing Cognitive Radio technology This system is comprised of cognitive-unaware Primary Users (PUs) and cognitive-capable Secondary Users (SUs). * “A Cognitive Radio Approach for Usage of Virtual Unlicensed Spectrum”, Čabrić, Mishra, Willkomm, Brodersen, Wolisz

20. Two Kinds of Users • Primary User • Cognitive Radio unaware • Does not need to provide special signaling to access its frequency band (F-Band) • PUxcan tolerate maximal interference for Δtx seconds • Each PU has its own unique Primary User Footprint (PUF) with which it can be identified • Secondary User • All SUs possess cognitive radio capablity • Monitors the presence of PUs at least every Δtx seconds • “Listen before talk” to not disrupt PU activity • Form Secondary User Groups (SUGs) to facilitate SU communication and coordination • SUs use logical sub-channels to inter-communicate

21. CORVUS Spectrum Pooling • Defined as a frequency range used by a SUG, which may overlap with other SUG spectrum pools • Divided into n Sub-Channels, being a small fraction of the spectrum pool • Secondary User Links (SULs) are formed with Sub-channel patterns over multiple F-Bands

22. CR Efficiency and Interference The system must evaluate how well the CR-capable SUs avoid interfering with PU transmissions. • Interference Metric • Spectrum Efficiency

23. System Functions • Cognitive capabilities will be achieved in the Physical and Link layers of radio design • The following six system functions can be distributed between these two layers: • Spectrum Sensing • Channel Estimation • Data Transmission • Group Management • Link Management • Medium Access Control (MAC)

24. Requirements for CR • Dynamic Spectrum Developments • Spectrum Etiquette (“Listen before talk”) • Bandwidth Snapshot (frequency monitoring) • Provide Operating Information to Owner • Global Positioning Knowledge • Group Cooperation and Planning

25. Future Work Facing CR • Using elements of game theory, CR interactions can be modeled and predicted to optimize behavior. • Radio metrics must be redefined to better analyze frequency availability (spectrum sensing) and radio sensitivity (transmission power). • Much like the Traffic Analogy, SUs must intelligently recognize PUs and yield to their transmission. • Federal Regulations and Incumbent Frequency Band Licensees pose a valid threat to CR advancement.

26. Other Spectrum Efficiency Solutions • Ultra Wideband (UWB) - RF Interference is non-destructive, allowing radios to “talk” through each other due to the receiver’s ability to intelligently identify the speaker. • Many conversations can occur within the same space when volume is limited, highlighting the need for power constraints. • Cooperative mesh networking is equivalent to note passing amongst each “person” in the room. As the crowd increases, coverage and throughput also increase.

27. Resources • http://web.syr.edu/~ejhumphr/