Cognitive radio based 5G wireless network

1. Cognitive Radio Based 5G
Wireless Networks
1

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

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 Motivations
6
Crowded radio spectrum

7. Background and Motivations
7
Low spectrum utilization

8. Examples of the Spectrum Opportunities
54 MHz to 88 MHz (TV broadcasting), 24 hour period starting during Sep. 01 to Sep. 09 2009
Most of the
spectrum is
unused
Evidence of
overcrowding

9. Examples of the Spectrum Opportunities
2390 MHz to 2500 MHz (mobile satellite), 24 hour period starting during Sep. 01 to Sep. 09 2009
Most of the
spectrum is
unused
Evidence of
overcrowding

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
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 Idea
15
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
16
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.”
Why So Many
Definitions?

17. 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. 18
Cognitive Radio Applications

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

20. Cognitive Radio Wireless Networks
 Two types of cognitive users
1) Primary users (PUs) or licensed users
2) Secondary users (SUs) or unlicensed users
 Two types of cognitive radio networks
1) Synchronous
2) Asynchronous
 Three types of spectrum sharing modes
1) Overlay
2) Underlay
3) 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
PU
S
SU
R1
PU
D
SU
R2

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