Cognitive Radio Networks

1. Cognitive Radio Networks Azin Dastpak August 2010 Simon Fraser University

2. Presentation Outline • Introduction • Definition • Cognitive radio network architecture • Cognitive radio systems • Spectrum sharing in cognitive radio networks • Game theoretical overview of spectrum sharing • References

3. Introduction 1

4. Why cognitive radio? • Current wireless networks are regulated by fixed spectrum assignment policy. • According to Federal Communication Commission, temporal and geographical variations in the utilization of the assigned spectrum ranges from 15% to 85%.

5. Why cognitive radio Fixed Spectrum Assignment policy spectrum white spaces Inefficient spectrum utilization • Cognitive radio network is : • A new paradigm that provides the capability to share or use the spectrum in an opportunistic manner.

6. Definition 2

7. Cognitive radio • Cognitive radio is a wireless communication system which is aware of the environment and its changes and can adapt its transmission parameters accordingly. • Cognitive Capability: The ability to sense the unused spectrum at a specific time and location (spectrum hole) • Reconfigurability: The ability to receive and transmit at different frequency band enables the cognitive radio to reconfigure its parameters and select the best band.

8. Spectrum hole

9. Cognitive radio network architecture 3

10. Components of CRN • Primary network • Primary users: • Primary users have the license to operate in certain spectrum bands • Primary base station: • Controls the access of primary users to spectrum • Secondary network • Secondary users: • Secondary users have no licensed bands assigned to them. • Secondary base-station: • A fixed infrastructure component with cognitive radio capabilities and provides single hop connection to secondary users. • Spectrum broker : • Scheduling server shares the spectrum resources between different cognitive radio networks.

11. Cognitive radio architecture

12. Network access types • CR Network Access: CRs can access their own base station on both licensed and unlicensed spectrum bands • CR Ad Hoc Access: CRs can communicate with other CRs through an ad hoc connection on both licensed and unlicensed spectrum bands. • Primary Network Access : CRs can access primary base station through the licensed bands.

13. Cognitive radio systems 3

14. Functionalities of a CRN • Spectrum sensing: Cognitive radio user has the ability to sense the unused spectrum at any time and location. • Spectrum management: Based on the availability of the spectrum and other policies, CR user allocates the best available spectrum band. • Spectrum mobility: CR user shall vacate the spectrum in the presence of any primary user and move to next best available spectrum band • Spectrum sharing: CR network has to provide a fair and optimal spectrum allocation method among multiple CR users.

15. Challenges • Interference avoidance • QOS awareness • Seamless communication Requires a cross layer design

16. Cognitive radio functionalities

17. Functions of network layers • Physical layer: • spectrum sensing • data reconfigurable transmission based on Software Defined Radio (SDR). • Link Layer : • spectrum analysis • spectrum selection(spectrum adjustment) • spectrum coordination.

18. Functions of network layers • MAC layer: • Obtaining information on channel occupancy. • Performing negotiation among primary users and secondary users for spectrum allocation and also among secondary users for channel sensing and access. • Synchronizing transmission parameters (e.g. channel, time slot) between transmitter and receiver. • Facilitating spectrum trading functions (e.g. spectrum bidding and pricing).

19. Cognitive radio systems • Static cognitive radio system: Secondary user observes the activity of the primary users in a fixed spectrum band and access the entire spectrum band if it senses the opportunity. Can be built on the following standards: • 802.11 • 802.15 • 802.3 • Dynamic cognitive radio system: Secondary users can transmit using different bandwidths by changing the transmission parameters in the physical layer (based on OFDM or MC-CDMA).

20. IEEE 802.22 Wireless Regional Area Networks (WRAN) • The first IEEE standard utilizing cognitive radio (CR) technology to exploit the television white space. • The focus was on building fixed point-to-multipoint WRAN that utilizes UHF/VHF TV bands between 54 and 862 MHz.

21. Applications of CRNs • Leased network • Cognitive mesh network • Emergency network • Military network

22. Spectrum Sharing in Cognitive radio networks 4

23. Spectrum sharing • Spectrum sensing: The secondary user can only allocate a spectrum if it’s not used by an unlicensed user. • Spectrum allocation: Allocation of a channel not only depends on spectrum availability but also depends on internal and external policies. • Spectrum access: Since there are multiple secondary users trying to access the spectrum, their access should be coordinated to avoid colliding in overlapping portions of the spectrum

24. Spectrum sharing • Transmitter-receiver handshake: After deciding a portion of the spectrum, the receiver of this communication should also be indicated. • Spectrum mobility: If the specific portion of the spectrum is needed by a licensed user, the communication needs be continued in another vacant portion.

25. Classifications of spectrum sharing • Architecture: • Centralized : The spectrum allocation and process are controlled by a central entity. • Distributed : Spectrum allocation and access are based on local or global policies that are performed by each node distributively. distributed solutions closely follow the centralized solutions but they have the extra cost of message passing between nodes.

26. Classifications of spectrum sharing • Spectrum Allocation behavior: • Cooperative Spectrum sharing : The effect of the communication of one node on other nodes in considered. • Closely reach global optimum. • Result in fairness and improved throughput. • Non-cooperative Spectrum Sharing : Only a single node is considered. • As the interference in other CRs are not considered this solution may result in reduced spectrum utilization. • They don’t need frequent message passing as in cooperative solutions • Energy consumption

27. Classifications of spectrum sharing • Spectrum access technique: • Overlay spectrum sharing: Portion of the spectrum can be accessed that has not been used by licensed users. • Underlay spectrum sharing: Transmission of a CR node is regarded as noise by licensed users.

28. Classifications of spectrum sharing • Scope: • Intra-network Spectrum Sharing: Spectrum allocation between the entities of a CR network. The users of a CR network try to access the available spectrum without causing interference to the primary users. • Inter-network Spectrum Sharing: This setting enables multiple systems to be deployed in overlapping locations and spectrum.

29. Inter and Intra-network spectrum sharing

30. Game theoretical overview of dynamic spectrum sharing 5

31. Game Models • The behavior of the cognitive radios in dynamic spectrum access networks can be modeled as a dynamic spectrum sharing game (DSSG).

32. Game Models • Non-cooperative DSSG without centralized control • The focus is on distributed design and cooperation simulation. • Cooperative DSSG • users do enforceable spectrum sharing through centralized authorities. Nash bargaining Solution plays an important role in cooperative games. • Negotiated or leasing-based dynamic spectrum sharing • This scenario can be modeled as multiplayer non-cooperative game with incomplete information. Auction theory is applied to formulate and analyze the interactions.

33. Dynamic spectrum sharing approaches • Local Bargaining • The product of user throughput is considered the optimization goal of local bargaining • Repeated Spectrum Sharing Game Model • A similar static game is played many times. It gives the observers the opportunity to make decision based on past moves. One of the most important results in repeated game theory is Folk Theorem.

34. Dynamic spectrum sharing models • Auction-Based Spectrum Sharing Game • VCG is usually used to achieve socially optimal solution • It may not be suitable for spectrum sharing because of the temperature-constraint, information overhead and computational burden. Two other auctions are generally used: • SINR Auction: charging secondary users according to their received signal-to-interference-plus-noise ratio. • Power Auction: charging secondary users based on their received power

35. Dynamic spectrum sharing models • Belief-Assisted Pricing • To achieve efficient pricing distributively in DSSGs with incomplete information, the belief metrics are proposed to predict other user’s future possible strategies according to the game histories and assist each user’s decision making.

36. Optimality analysis The spectrum sharing needs to be efficient and fair • Price of Anarchy • In non-cooperative DSSG without centralized authorities, the interactions between selfish users may lead to an inefficient Nash Equilibrium • The price of anarchy is an important measure. • Nash Bargaining Solution in Spectrum Sharing Games • To achieve fair and efficient dynamic spectrum sharing, NBS is an important optimality analysis. • Dynamic Programming for DSSGs: • In one case the Bellman equation can be applied to represent each secondary user’s payoff in the form of summation of two terms • 1. it’s current pay off based on current spectrum sharing states. • 2. it’s expected future payoff based on the updated spectrum sharing state.

37. References 6

38. References • [1] I. Akyildiz, W. Lee, M. Vuran, and S. Mohanty, “NeXt generation/dynamic spectrum access/cognitive radio wireless networks: a survey,” Computer Networks, vol. 50, no. 13, pp. 2127–2159, 2006. • [2] L. Hu, V. Iversen, and L. Dittmann, “Survey of PHY and LINK Layer Functions of Cognitive Radio Networks for Opportunistic Spectrum Sharing,” Communications and Networking in China, pp. 10–24, 2009. • [3] Y. Xiao and F. Hu, Cognitive radio networks. Auerbach Publications, 2008. • [4] I. Akyildiz, W. Lee, M. Vuran, and S. Mohanty, “A survey on spectrum management in cognitive radio networks,” IEEECommunications Magazine, vol. 46, no. 4, pp. 40–48, 2008. • [5] Y. Yi, J. Zhang, Q. Zhang, T. Jiang, and J. Zhang, “Cooperative Communication-Aware Spectrum Leasing in Cognitive Radio Networks,” in 2010 IEEE Symposium on New Frontiers in Dynamic Spectrum, 2010, pp. 1–11. • [6] Z. Ji and K. Liu, “Cognitive radios for dynamic spectrum access-dynamic spectrum sharing: A game theoretical overview,” IEEE Communications Magazine, vol. 45, no. 5, pp. 88–94, 2007. • [7] L. Chen, S. Iellamo, M. Coupechoux, P. Godlewski, P. da Vinci, and I. Milan, “An Auction Framework for Spectrum Allocation with Interference Constraint in Cognitive Radio Networks.”