Utility Based Scheduling in Cognitive Radio Networks Term Project CmpE-300 Analysis of Algorithms Spring 2009 Computer Engineering, Boğaziçi University, Istanbul 1

Outline Wireless networks –FDMA, TDMA, CDMA Dynamic Spectrum Access Cognitive Radio Networks Problem Formulation 2

Cellular Networks 3

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MSC: Mobile Switching Center How do different mobile stations communicate simultaneously with the BS? 5

Frequency Division Multiple Access (FDMA) Each mobile device tunes to a frequency band Analogous to people talking in different rooms 6

Frequency Division Multiple Access (FDMA) 7

Time Division Multiple Access (TDMA) Each mobile device transmits data in a different time slot Analogous to people talking one by one GSM: Combination of FDMA and TDMA –25 MHz bandwidth divided into 124 carrier frequencies of 200 KHz bandwidth –Each carrier frequency divided into 8 time slots using TDMA 3G licenses: –Type-A: 40 MHz, Turkcell –Type-B: 35 MHz, Vodafone –Type-C: 30 MHz, Avea 8

Time Division Multiple Access (TDMA) 9

Code Division Multiple Access (CDMA) Analogous to people talking in different languages 10

Dynamic Spectrum Access (DSA) PROBLEM : Underutilized spectrum resources due to fixed assignment strategy IDEA : Utilizing “white spaces” in the spectrum without disturbing licensed users [1] CHALLENGE : –Sensing the environment, detecting “white spaces” –“white spaces” frequently change by time and space –Changing radio parameters on the fly 11

Frequency Allocation Charts In Turkey: 12

White Space Concept 13

Cognitive Radio (CR) Concept Initially proposed by Mitola [2] Next step evolution of Software Defined Radio (SDR) Cognitive Radio (CR): Intelligent devices that can [2]: – Sense and autonomously reason about their environment –Adapt their communication parameters accordingly –Realize DSA concept 14

Terminology Primary User (PU): –Licensed user –Has exclusive rights for the spectrum Secondary User (SU): –Unlicensed user –Opportunistically utilizes the white spaces –Has to vacate the spectrum band as soon as a PU appears –Also called cognitive user 15

IEEE Network Architecture 16

Research Problem totalNetworkUtility: Total number of SU’s that are satisfied in terms of throughput Maximize (totalNetworkUtility) subject to No interference is imposed on the PU’s Reliable communication with the CBS is achieved No collisions occur among the SU’s 17

Research Problem Terminology N: Total number of SU’s F: Total number of frequencies T: Total number of time slots U if = Maximum number of packets that can be transmitted by user i to the CBS using frequency f (in a time slot) t i = Throughput (data rate) of SU i g(t i )=The level of satisfaction of SU i from throughput t i t i min = Minimum throughput required by SU i 18

Problem Formulation 19 totalNetworkUtility Each SU is assigned at least 1 time slot At most 1 user is assigned a certain time slot and frequency pair Throughput of SU i

Problem Formulation 20

Problem Formulation 21

References [1] Akyildiz, I., 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 , [2] Mitola, J., “Cognitive Radio: An Integrated Agent Architecture for Software Defined Radio”, Doctor of Technology, Royal Institute of Technology (KTH), Stockholm, Sweden,

Questions? 23