1 Cognitive Radio Networks Zhu Jieming Group Presentaion Aug. 29, 2011

2 Outline 1. Wireless mobile communication 2. Introduction to cognitive radio networks 3. Dynamic spectrum management 4. Interference mitigation 5. Summary

1G2G 2.5G 2.75G 3G4G 3 1. Wireless mobile communication The development of wireless mobile communications Directions for development High data rate BroadbandHeterogeneityUbiquity

1G2G 2.5G 2.75G 3G4G 4 1. Wireless mobile communication 1G: Analog mobile phone FDMA ( Frequency Division Multiple Access ) Low system capacity and security problems

1G2G 2.5G 2.75G 3G4G 5 1. Wireless mobile communication 2G: GSM ( Global System for Mobile Communications ) TDMA ( Time Division Multiple Access ) SMS ( Short Message Service ) Data Rate: 9.6kbps

1G2G 2.5G 2.75G 3G4G 6 1. Wireless mobile communication 2.5G/2.75G: Circuit switch  Packet switch 2.5G: GPRS ( General Packet Radio Service ) 2.75G: EDGE ( Enhanced Data Rate for GSM Evolution ) Data Rate: 384kbps

1G2G 2.5G 2.75G 3G4G 7 1. Wireless mobile communication 3G: CDMA ( Code Division Multiple Access ) Data Rate: 2.4Mbps 3G Standards WCDMA (Europe) CDMA2000 (America) TD-SCDMA (Datang, China)

1G2G 2.5G 2.75G 3G4G 8 1. Wireless mobile communication 4G (Standardization is on-going): OFDMA (Orthogonal Frequency Division Multiple Access) WiMax (Worldwide Interoperability for Microwave Access)/ LTE (Long Term Evolution for 3G )  Based on an all-IP packet switched network  VoIP(Voice over Internet Protocol )  Peak data rates up to 100 Mbps for high mobility and 1Gbps for low mobility. LTE networks in Universiade Shenzhen: 50Mbps

9 1. Wireless mobile communication Challenges in future wireless communications Scarcity of radio frequency Scarcity of radio frequency Low spectrum utilization Heterogeneous networks Increasing demand for spectrum Problems in future wireless networks

10 1. Wireless mobile communication We should have a technology that  can solve the scarcity of available spectrum  can satisfy the increasing spectrum requirement for wireless service  and can communicate seamlessly over the heterogeneous networks CR( Cognitive Radio ) and CRN( Cognitive Radio Networks ) are proposed…

11 2. Introduction to CRNs CR is defined as a radio that can change its transmitter parameters according to the interactions with the environment in which it operates. SDRCognitive RadioCognitive Radio Networks CR is based on the platform of software definition radio(SDR) which can easily reconfigure itself without changing any hardware.

12 2. Introduction to CRNs Features of CR  Cognitive capability Detect the spectrum holes and occupy the spectrum to enhance the data rate and spectrum utilization Support seamless handoff to optimize the performance among the heterogeneous networks of GSM, WiMax, LTE…  Reconfigurability Dynamically change the transmitter frequency, power and modulation parameters to adapt to the environment CR is a hot research issue and faced with a lot of challenges.

13 2. Introduction to CRNs Challenges of CR  Cognition Information Detection Spectrum Sensing  Cognition Information Processing and Decision Dynamic spectrum management Radio Resource Management  Reconfigurable Protocols  System architecture of CRNs

14 3. Dynamic spectrum management Scarcity of spectrum vs. low spectrum utilization DSM( Dynamic Spectrum Management ) is proposed to enhance the spectrum utilization

15 3. Dynamic spectrum management DSM vs. FSM ( Fixed spectrum management ) DSM vs. FSM Dynamic spectrum allocation and sharing Optimize the spectrum utilization Maximize the system capacity

16 3. Dynamic spectrum management Steps for DSM  Spectrum sensing: detect the spectrum holes  Spectrum decision: model for choose the best available spectrum channel  Spectrum sharing: share the spectrum with primary users  Spectrum mobility: leave the channel occupied and find another suitable channel for communication Primary user; Cognitive user; Spectrum holes

17 3. Dynamic spectrum management Challenges in research of DSM: spectrum decision, wideband spectrum sensing, QoS awareness, seamless handoff, hardware support... Interference mitigation is one of the most important challenges for research.

18 4. Interference Mitigation Interference Scenarios  Interference between primary users and cognitive users It’s difficult to detect the status of PUs, So it may interfering PUs when they occupy the spectrum again.  Interference among cognitive users When several CUs access the spectrum holes of one PU, there exists interference among CUs.

19 4. Interference Mitigation Coloring graph model PU: Ⅰ~Ⅳ CU: 1~5 Channels: A,B,C Interference range of PUs Interference of CUs

20 4. Interference Mitigation Interference mitigation between PUs and CUs If the CU is in the interference range of a PU, the CU can’t use the channel which the PU is occupied.

21 4. Interference Mitigation Interference mitigation among CUs If there exists interference between CUs, there exists an edge between them and they can’t use a channel simultaneously.

22 4. Interference Mitigation Interference graph and coloring model Coloring: Taking the each channel as one color, then color the vertexes with available colors, and the neighbor vertex can’t be colored with one color. A C B C C

23 4. Interference Mitigation Spectrum allocation algorithms  Greedy algorithm: maximize the spectrum utilization  Fair algorithm: maximize the fairness among cognitive users  Random algorithm: lower complexity and time delay

24 5. Summary The development of wireless mobile communications The advances of cognitive radio networks Challenges in dynamic spectrum management Coloring graph based interference mitigation

25 Thank you!