1. Cognitive Radio Based 5G Wireless Networks1
Cognitive Radio Based 5G Wireless Networks

2. 2
I. Introduction
Different spectrum bands for different services

3. Exponential Growth in Number of Wireless Applications Over 5G Networks

4. Increasing Demand For Spectrum Use
More and more people subscribe to one or many of the wireless services
Rapid growth of wireless devices
Increasing demand for additional bandwidth

5. Cell Phone Statistics (2006)
Global Cell Phone Users > 2 Billion
New Cell Phone Sales > 1 Billion (2006)
#1 Cell Phone Country –China > 400M
European Union > 450M
U.S. > 200M
Recorded usage in 221 Countries
SMS Messages -235M (36/user/month)

6. Background and Motivations6
Background and Motivations
Crowded radio spectrum

7. Background and Motivations7
Background and Motivations
Low spectrum utilization

8. Examples of the Spectrum Opportunities
Most of the spectrum is unused
Evidence of overcrowding
54 MHz to 88 MHz (TV broadcasting), 24 hour period starting during Sep. 01 to Sep

9. Examples of the Spectrum Opportunities
Most of the spectrum is unused
Evidence of overcrowding
2390 MHz to 2500 MHz (mobile satellite), 24 hour period starting during Sep. 01 to Sep

10. Example of the Spectrum Opportunities
Spectrum hole analysis for 54 – 88 MHz frequency band.

11. Example of the Spectrum Opportunities
Spectrum hole analysis for 2390 – 2500 MHz frequency band.

12. Spectrum Occupancy Measurements in Seven Different Places
Most of the spectrum in most of the places at most of the time is completed unused!

13. Current Spectrum Allocation Policies
Today, frequency bands are statically assigned to specific wireless operators/services.
Frequency allocation policies lead to a low utilization of the licensed frequency spectrum. For example, in most of the time only 6% of the frequency spectrum is active.
Current spectrum policy needs to be reconsidered !
Solutions?

14. II. Cognitive Radio (CR)14
II. Cognitive Radio (CR)
Large amount of white space in time and frequency
Unused portions of licensed spectrum is called spectrum holes or White Spaces.
Dynamic spectrum sensing helps with identifying and assessing quality of unused channels

15. Cognitive Radio: Basic Idea15
Cognitive Radio: Basic Idea
Cognitive Radio (CR) technique has been proposed by the Federal Communication Committee (FCC) as a solution to such spectrum scarcity problem.
Cognitive radios enhance the control process by adding:
Intelligent control of radio;
Ability to sense the environment;
Processes for learning about environmental parameters;
Awareness of its environment: signals & channels;
Awareness of capabilities of the radio;
Ability to negotiate waveforms with other radios.

16. Definitions FCC: ITU (Wp8A): IEEE USA16
Definitions
Why So Many Definitions?
FCC:
“A radio that can change its transmitter parameters based on interaction with the environment in which it operates.”
ITU (Wp8A):
“A radio or system that senses and is aware of its operational environment and can dynamically and autonomously adjust its radio operating parameters accordingly.”
IEEE USA
“A radio frequency transmitter/receiver that is designed to intelligently detect whether a particular segment of the radio spectrum is currently in use, and to jump into (and out of, as necessary) the temporarily-unused spectrum very rapidly, without interfering with the transmissions of other authorized users.”

17. Our cognitive radio definition
Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment and uses methodology of understand-by-building to learn from environment and adapt  its internal states to statistical variations by making corresponding changes in its operating parameters.
Intelligence is defined as “The capacity to acquire and apply knowledge, especially toward a purposeful goal.”

18. Cognitive Radio Applications

19. Three Solutions
Overlays (e.g. Cognitive Radio –Frequency Agile / Smart Radios / Software Defined Radio)
Creation of Unlicensed Bands (esp. ISM / UNII –0.9, 2.4, 5 GHz)
Underlays (e.g. Ultrawideband –UWB –min. 500 MHz bandwidth)

20. Cognitive Radio Wireless Networks
Two types of cognitive users
Primary users (PUs) or licensed users
Secondary users (SUs) or unlicensed users
Two types of cognitive radio networks
Synchronous
Asynchronous
Three types of spectrum sharing modes
Overlay
Underlay
Interweave

21. PUs & SUs
Primary User: A user who has higher priority or legacy rights on the usage of a specific part of the spectrum.
Secondary User: A user who has a lower priority and therefore exploits the spectrum in such a way that it does not cause interference to primary users.
Spectrum Sensing: The task of obtaining awareness about the spectrum usage and existence of primary users in a geographical area.

22. PUs & SUs
SUs can sense occupancy of licensed channels and use licensed channels when they are not occupied by PUs based on spectrum sensing results.
PUs and SUs form primary wireless network and secondary wireless network (cognitive radio network), respectively.

23. 1) Synchronous Cognitive Radio Networks
Time axis is divided into slots
SUs are synchronized with PUs
Same knowledge on the time-slot boundary
PUs spectrum activity is consistent during a given time slot
An example of Synchronous CRN with interweave spectrum sharing mode

24. 2) Asynchronous Cognitive Radio Networks
SUs are NOT synchronized with the PUs
Different licensed channels for different types of PUs can also be asynchronous

25. Cognitive Radio Spectrum Sharing Modes
Overlay
Cognitive radios overhear and enhance PU’s` transmissions
Underlay
Cognitive radios constrained to cause minimal interference to PUs
Interweave
Cognitive radios find and exploit spectral holes to avoid interfering with PUs
Knowledge
and
Complexity

26. Spectrum Sharing Modes (1)
Type 1: Overlay
SUs may use a part of their energy to assist communications of PUs through cooperative communication techniques and the rest of energy to transmit their own signals.
Interference from SUs' signals can be compensated with gain for PUs' signal quality through cooperation of SUs.
It requires SUs to know PUs' packets before PUs begin their transmissions
SU R2
SU R1
PU S
PU D

27. Spectrum Sharing Modes (2)
Type 2: Underlay
SUs transmit signals in such a low-power level that interference caused by SUs is below noise floor of the spectrum.
In the view point of PUs, transmissions by SUs are nothing but noise with low-level power.
SUs and PUs can co-exist in same spectrum
If PUs’ topology and transmission power do not change
No need to sense the channel
Do not cause packet collision for PUs for both synchronous and asynchronous cognitive networks

28. Spectrum Sharing Modes (3)
Type 3: Interweave
Listen first and talk later
Exclusive utilization
SUs frequently sense channel
SUs do not need to worry about interference temperature constraint of PUs
Relax power constraints imposed onto SUs as compared with underlay spectrum sharing mode.
No interference to PUs in synchronous CRNs
Inevitable interference to PUs in asynchronous CRNs due to half- duplex nature of wireless radios