1. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Cavalcanti, D. and Ghosh, M. Cognitive Radio Oriented Wireless Networks and Communications, (CrownComm 2008)
Lecturer: Chang Han-Tien
2018/11/14
Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

2. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Outline
Introduction
Regulatory Scenario
Overview of The Standard
Spectrum Management Model
Conclusions
Comments
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

3. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Introduction
Last-mile broadband access
different solutions may be more efficient for different applications and deployment regions
A successful deployment of wireless broadband in rural communities should consider
Coverage, Capacity, Installation and operational costs, Business models
WiFi network (IEEE )
design for short/medium range connectivity
solution for long-distance access [2]
Cellular system
the deployment cost is an issue for rural communities.
WiFi, WiMax, Cellular system 3G …
different advantages and drawbacks
In rural communities and emerging markets
Technical aspects : Coverage and capacity
[2] Experiences in using WiFi for Rural Internet in India
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

4. Introduction (cont’d)
Cognitive Radio [4]
an intelligent wireless communication system that is aware of its environment (sensing spectrum)
uses the methodology of understanding-by-building to learn from the environment
adapt to statistical variations in the input stimuli
Two objectives
highly reliable communication whenever and wherever needed
efficient utilization of the radio spectrum
Cognitive Radio
aware of its environment and uses the methodology of understanding-
by-building to learn from the environment and adapt
to statistical variations in the input stimuli
Tech Objective
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

5. Introduction (cont’d)
IEEE (WRANs)
operate in the TV spectrum band (54 MHz~862 MHz) as secondary users
under regulatory rules to avoid interference with the primary users (incumbent, TV broadcasting)
Key issues
Incumbent protection
Self-coexistence
Spectrum management
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

6. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Regulatory Scenario
Cognitive radio networks
enable flexible, efficient and reliable spectrum
by adapting the radio’s operation characteristics to the real-time conditions of the environment
limited applicability under legacy spectrum usage
Command and control
Exclusive-use
New dynamic spectrum access models
In order to exploit the full capabilities of CRNs
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

7. Regulatory Scenario (cont’d) Dynamic spectrum access models
Shared-use of primary licensed spectrum
where secondary users share the spectrum with primary users on a non-interfering basis
Spectrum underlay
Limit the secondary users’ transmit power to very low level in order not to interfere with primary users
Spectrum overlay
Enable devices to operate in the spectrum white spaces
Implement reliable incumbent detection and frequency agility mechanisms
Ultra Wide Band tech for short-range
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

8. Regulatory Scenario (cont’d) Dynamic spectrum access models
Spectrum commons
the spectrum is shared under equal rights by all devices on an unlicensed basis in the model
Open-access model in ISM (2.4GHz) and I-NII (5 GHz)
Reduce the overcrowding condition in these unlicensed bands
IEEE standard
shared-use spectrum model
protection of primary users while providing Quality of Service (QoS) for the secondary users.
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

9. Regulatory Scenario (cont’d) Protection of Incumbents
Spectrum sensing is a key technology to detect incumbents in the TV bands.
Incumbent Detection Thresholds (IDT)
If an incumbent signal above the IDT is detected, the secondary system must react appropriately to avoid harmful interference.
The incumbent signal shall be detected with probability exceeding the Probability of Detection (PD) parameter
Probability of false alarm shall be equal or lower the the PFA parameter
Channel Detection Time (CDT)
CDT
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

10. Regulatory Scenario (cont’d) Protection of Incumbents
If an incumbent signal above the IDT
In the adjacent channels
apply transmit power control to avoid leakage in other channels
In the operating channel
vacate the channel within the Channel Move Time (CMT)
an aggregate transmission time equal to the Channel Closing Transmission Time when switch to backup channel
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

11. Regulatory Scenario (cont’d) Protection of Incumbents
PFA is important for the secondary systems’ QoS and efficient spectrum utilization [13]
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

12. Overview of the 802.22 standard
WRAN is a point-to-multipoint system
Base station (BS)
Consumer Premise Equipments (CPEs)
equipped with a spectrum sensing module
meet the regulatory requirement of sensing
Expected coverage area is around 30 Km
Address markets in sparse populated areas
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

13. Overview of the 802.22 standard (cont’d) The 802.22 PHY
OFDMA multiple access
Data rate
1.5 Mbit/s in the downstream (DS)
384 Kbit/s in the upstream (US)
Support 255 CPEs per BS per TV channel (6MHz)
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

14. Overview of the 802.22 standard (cont’d) The 802.22 MAC
BS controls the access to wireless medium
take on-demand basis in the US direction
use TDM (Time Division Multiplexing) in the DS
New range of cognitive radio feature supports
Reliable incumbent detection
Frequency agility
Self-coexistence
the coexistence amongst WRANs
Borrow some of the basic concepts from the IEEE standard[14]
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

15. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Superframe and frame structures
Superframe consists of 16 frames
facilitate incumbent protection, synchronization, and self-coexistence
start with the superframe preamble, frame preamble, Superframe Control Header (SCH), and Frame Control Header (FCH)
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

16. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Superframe and frame structures
Frame is divided into DS and US sub-frames
DS/US MAPs and channel descriptor broadcast messages (DCD and UCD)
Option in the US sub-frame
be used for ranging, bandwidth request and Urgent Coexistence Situation (UCS) notification
Self-Coexistence Window (SCW)
For coexistence beacon transmissions at the end of US sub-frame
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

17. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

18. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Incumbent Detection Support
Scheduling of network quiet periods (QPs)
avoid overlapping of data transmissions
BS schedules network QPs for sensing
suspend all the traffic in the cell, let CPEs sample the channel for detecting the incumbent
intra-frame and inter-frame quiet periods
minimize the impact of QPs on users’ QoS
Two important capabilities
Overlapping of data transmissions and sensing on the same channel (or even adjacent channels) may negatively impact the sensing performance, resulting in a high rate of false alarms, especially given the very low IDTs to be met by the CPE’s spectrums sensing module (see TABLE I. ).
The number of QPs scheduled should also be limited to a minimum necessary to achieve the required sensing reliability in terms of PD and PFA parameters
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

19. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Incumbent Detection Support
Channel measurement management
In-band (i.e. in the operating channel and first adjacent channels)
scheduled by the BS during the QPs
Out-of-band (other channels that may be used as backup
may be done during the CPEs idle time
Occupied by other WRANs, should use the QPs schedule
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

20. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Incumbent Detection Support
Notification phase
advertising the QP scheduling in the SCH
channel quiet request message (CHQ-REQ) to stop traffic within its cell
bulk measurement request message (BLM-REQ) to request CPEs to perform measurements
the result are reported back in bulk measurement reply message (BLM-REP)
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

21. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Incumbent Detection Support
a CPE detected the presence of incumbent
use the UCS notification slots to inform BS
the notification transmitted using a contention-based or CDMA-based
BS combines the information from various CPEs
React more efficiently in timely manner
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

22. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Frequency Agility
An incumbent is detected on the operating channel (N) or adjacent channels (N-1,N+1)
BS triggers a switch to a backup channel
Maintain a list of back channels
Challenge: a seamless channel transition
Two channel management mode
Implicit mode (DCD Broadcast message)
Don’t require extra management messages
Explicit mode (CHS-REQ, Channel switch request)
Provides greater flexibility in different granularities
To single CPE or to a group of CPEs (multicast message)
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

23. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Self-coexistence
Synchronize the QPs among neighboring cells, in order to reduce the overall QPs
Synchronize the superframes using positioning satellite capabilities at the BSs
Exchange their QP schedule through the SCH as well as the Coexistence Beacon Protocol
use SCW to allow CPEs (BSs) to exchange coexistence beacons (QP schedule’s information)
Each BS should select CPEs to transmit CBP packets according a periodic schedule, and it should also select CPEs to listen for CBP packets
Base on location information
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

24. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Self-coexistence
When a CPE receives a CBP packet from a neighboring cell
Forward to the information to its BS
Exchange information amongst neighboring cells
Efficient spectrum sharing
Using the intelligent scheduling mechanism
Dynamic resource renting/offering
On-demand spectrum contention
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

25. Spectrum Management Model
Spectrum Manager
a central entity collocated with the WRAN BS
taking the key decisions and triggering the proper events/actions (central intelligence)
a part of the MAC layer management entity
Spectrum Automaton
act as a slave to the SM
control the local CPE’s spectrum sensing function as requested by the BS’s SM
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

26. Spectrum Management Model (cont’d)
Spectrum Manager’s main functions
1. Maintain spectrum availability information;
2. Channel classification and selection;
3. Association control;
4. Trigger frequency agility related actions;
5. Manage mechanisms for self-coexistence.
Geo-location module
acquire precise positioning and time synchronization information
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

27. Spectrum Management Model (cont’d)
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

28. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Overview of the standard - The MAC (cont’d) Superframe and frame structures
Collaborative spectrum sensing and incumbent database
Aggregating information from other sources
Make decisions based on spectrum sensing information only when the incumbent database isn’t available
Frequency agility actions
Switch the entire cell to a new operating channel;
Direct a single CPE or a group of CPEs to a different operating channel;
Terminate operation in a given channel for a single CPE, a group of CPEs or the entire cell;
Inform CPEs of channels status updates
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

29. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Conclusions
The shared usage model with primary users can be realized with existing cognitive radio technologies
Enable new opportunities for wireless broadband access
Protection of incumbents and achieve efficient spectrum utilization
Future work
Optimized scheduling algorithms
Channel selection and intelligent scheduling algorithm
Collaborative sensing techniques
System level evaluation to assess the robustness of
system level evaluation to assess the robustness of with respect to both data transmission and sensing against
interference from other cells.
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Cognitive Radio Network: Enabling New Wireless Broadband Opportunities

30. Cognitive Radio Network: Enabling New Wireless Broadband Opportunities
Comments
It’ important to find the balance point between the incumbent protection and the secondary user’s QoS
The importance of spectral resources
Need more improvements for the draft
2018/11/14
Cognitive Radio Network: Enabling New Wireless Broadband Opportunities