Utility Based Scheduling in Cognitive Radio Networks

Term ProjectCmpE-300 Analysis of Algorithms

Spring 2009Computer Engineering, Boğaziçi University, Istanbul

1

Outline

• Wireless networks– FDMA, TDMA, CDMA

• Dynamic Spectrum Access

• Cognitive Radio Networks

• Problem Formulation

2

Cellular Networks

3

Cellular Networks

4

Cellular Networks

• 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:

http://www.tk.gov.tr/Duzenlemeler/teknik/marfl/_marfl1.asp

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 802.22 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’sReliable communication with the CBS is achievedNo 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

• Uif= Maximum number of packets that can be transmitted by user i to the CBS using frequency f

(in a time slot)•

• ti = Throughput (data rate) of SU i

• g(ti)=The level of satisfaction of SU i from throughput ti

• timin= Minimum throughput required by SU i

18

";0

""""";1

otherwise

ttimeslotinffrequencywithtransmitsiuserifXift

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. 2127-2159, 2006.

[2] Mitola, J., “Cognitive Radio: An Integrated Agent Architecture for Software Defined Radio”, Doctor of Technology, Royal Institute of Technology (KTH), Stockholm, Sweden, 2000.

22

Questions?

23