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Cognitive Radio from a Mobile Operator's Perspective: System Performance and Business Case Evaluations (PhD defense Pål Grønsund 18.oct 2013)
1. Cognitive Radio from a Mobile Operator’s Perspective:
System Performance and Business Case Evaluations
PhD Dissertation, 18.october 2013
Pål Grønsund
Supervisors: Paal E. Engelstad, Przemyslaw Pawelczak, Audun F. Hansen, (Ole Grøndalen)
2. Mobile operators need to solve the key challenges for
future wireless access
Massive growth in
Massive growth in
Wide range of
Traffic Volume
Connected Devices
Requirements
•
•
•
•
•
•
Data rate
Latency
Coverage
Energy
Device cost
….
Spectrum
Available
Network
Traffic capacity = Spectrum X Density X Efficiency
(MHz)
(sites/km2) (Mbps/MHz/site)
2
4. Cognitive radio is an “intelligent” and flexible radio
system that can observe and learn from the environment
and adapt accordingly
4
5. Cognitive Radio can be used to dynamically access
spectrum that is underutilized
Spectrum Holes
(White Spaces)
Frequency
Power
Cognitive
Radio
Time
t1
t2
t3
Spectrum occupied
by licensed users
5
6. The problem statement
Increased performance
Lower costs, increased revenue
New business models, services
How can a mobile operator benefit from using cognitive radio
to opportunistically access white spaces, with the potential
to enable sustaining and disruptive innovation?
6
7. Cognitive Radio brings threats and opportunities for the
mobile operator
Threats
• Reduced value of spectrum licenses
• Increased interference if other cognitive radios uses
•
the mobile operator’s own spectrum
Increased (unfair) competition
Opportunities
• Access to more spectrum in existing networks
• Opportunity to access spectrum in new markets
7
8. The methodology focused on both technical and
economical evaluation of Cognitive Radio systems
8
9. We studied three important areas for Cognitive Radio with
focus on the mobile operator's perspective
Dynamic spectrum access in primary
OFDMA systems
(Paper A)
Sensor Network Aided Cognitive
Radio Systems
(Papers B - E)
Performance of the first Cognitive
Radio Standard IEEE 802.22
(Papers F - I)
9
10. Outline
Dynamic spectrum access in primary
OFDMA systems
(Paper A)
Sensor Network Aided Cognitive
Radio Systems
(Papers B - E)
Performance of the first Cognitive
Radio Standard IEEE 802.22
(Papers F - I)
10
11. Dynamic spectrum access in the time dimension in primary
OFDMA networks can be possible
…but, our results show that cooperation with the primary operator
is important to reduce interference and increase capacity
11
12. Outline
Dynamic spectrum access in primary
OFDMA systems
(Paper A)
Sensor Network Aided Cognitive
Radio Systems
(Papers B - E)
Performance of the first Cognitive
Radio Standard IEEE 802.22
(Papers F - I)
12
14. Three business case scenarios were studied for the
SENDORA concept
Spectrum
owner 1
Spectrum
owner 2
Spectrum
owner N
Business case II
Spectrum
broker
Business case I
Joint venture
“Spectrum Sharing”
New entrant
New entrant
Business case III
14
New entrant
15. The “spectrum sharing” business case is probably one
of the best cases for a SENDORA system
It has free access to spectrum from the mother companies, and good
possibilities for re-using existing infrastructure.
The most critical aspects for profitability are:
• Fixed sensor density
• Fixed sensor OPEX
• Subscription fee (service offered)
• Share of new sites
A “new entrant” cognitive radio operator might get a positive business
case if it gets the spectrum for free, otherwise it will be difficult.
15
16. A SENDORA system was implemented in a simulator to
evaluate the capacity for different cell sizes
Primary System
Inter-BS-dist: 2km
Radius rp =1.15km
Secondary System
Radius rs = ?
Wireless Sensor
Network*:
65 sensors/km2
Sensor radius
rws=87.7m
(*values from business
case analysis)
Primary
Base Station
Sensor
Primary
terminal
Secondary
Base Station
Secondary
terminal
16
Fusion
Centre
17. Cognitive radio is best suited for smaller cells such as
WiFi access points and femtocells
… but relaxed interference requirements
to the primary user can increase cell size
25% co-location
PN=90%
100% co-location
rs=1.15 km
Access rule: the interference generated to the primary system should correspond to an
increase of the noise floor of less than 0.5 dB with a certain probability PN%.
17
18. Offloading the LTE network using Cognitive Femtocells
aided by a sensor network
1) deploy
cognitive
femtocells
2) deploy
sensors
3) increase
power
18
19. We compare with the case of using conventional
femtocells and additional base stations
1) deploy
conventional
femtocells
2) deploy
macro
base
stations
19
20. Offloading LTE with cognitive femtocells can be more cost
effective than using conventional femtocells and additional
base stations
The most business critical parameters for the cognitive femotcell:
• cost for backhaul
• number of users supported
• coverage radius
21. Outline
Dynamic spectrum access in primary
OFDMA systems
(Paper A)
Sensor Network Aided Cognitive
Radio Systems
(Papers B - E)
Performance of the first Cognitive
Radio Standard IEEE 802.22
(Papers F - I)
21
22. We implemented a detailed simulator to evaluate performance
of the first standard for Cognitive Radio, IEEE 802.22
System Model
It provides fixed wireless
broadband in rural areas
It uses two-stage
spectrum sensing
NO detection
NO detection
YES
Coarse sensing stage detection Fine sensing stage
(tc=1ms, at end of frame)
(ts=30ms)
22
YES
detection
Switch
channel
23. Performance for different sensing strategies should be
considered dependent on required Quality of Service (QoS)
Scenario
3 users receiving Video with Best Effort QoS profile
1 user receiving Voice over IP (VoIP) with Guaranteed Bit Rate QoS profile
23
24. Spectrum selection (SSE) functions that utilize sensing results
to provide long term statistics can increase performance
SSE-OnOff: selects the channel with
highest probability of being available.
SSE-Distance: selects the channel
with shortest distance to WMs.
SSE-Hybrid: uses the optimal of
SSE-Distance and SSE-OnOff
depending on distance to WMs.
24
25. In conclusion, a mobile operator can use Cognitive Radio to achieve
well performing technical and economic viable solutions
There is a potential to utilize white spaces in primary OFDMA
networks, but cooperation with the primary is important.
Operators can get access to more spectrum, increase
capacity and reduce costs significantly by using sensor
network aided cognitive radio systems.
Spectrum selection functions that utilize sensing result
statistics to predict primary user behavior can increase
performance in IEEE 802.22.
25
Pål Grønsund
(Pal.Gronsund@telenor.com)
Hinweis der Redaktion
JointVenture:Easy to implement from a regulatory point of view since only the joint venture owners’ own spectrum are usedThe scenario is an example of spectrum sharing, which can be seen as a natural extension of infrastructure sharing: The joint venture is a good way to share the expenses and incomes between the companiesThe joint venture can be composed in a way that makes it very probable that:at least some unused spectrum is available at all timeslittle new cognitive radio access infrastructure is requiredSpectrum Broker:New Entrant:
PS: Point ontheusabilityoftheresults:Sensor network planning (density of sensors and coordination between fixed and integrated sensors)Sensor design to minimize CAPEX and OPEXSolutions that allow re-use of existing infrastructure and require few new sites
- Secondary cell size = 1/2 primary cell size (rs=0.575km)Secondary system performed well with high throughput.However, 75% of secondary BSs will not be co-located with primary BSs, leading to high costs for the establishment of new sites.This points in the direction of smaller and less expensive BSs such as WiFi access points and femtocells.Secondary cell size = primary cell size (rs=1.15)100% BS co-location will not be achievedPotential solutions which could be studied for future work:Cell sectorizationRelaxed requirement to allow secondary operation, and dynamic requirements when primary nodes have good connectivityDynamic transmit powers- comesto the costs of a decrease in primary system performance with a slight reduction in throughput and increased packet loss with avg. 2%.-This can be considered as tolerable for business models where the primary operator has an economical benefit in improved secondary system performance.
Two-stage: coarse sensing of 1 msec every 2nd frame, (pd =0.9, pf =0.1), fine sensingof 30 msec (pd =0.99, pf =0.01).Two-stage consecutive: same as two-stage, but 3 consecutivecoarsedetectionsareneeded to trigger fine sensing.Single-stage-30: fine sensingof 30 msecevery 0.5 sec (pd =0.99, pf =0.01).Single-stage-100: fine sensingof 100 msecevery 0.5 sec (pd =1, pf =0).
By characterizing spectrum usage and analyzing potential capacity in primary OFDMA networks, we showed that there is a potential for CR systems to utilize white spaces.We found that one of the most promising business cases for an operator using a sensor network aided CR system is that of a joint venture that gets the rights to use the ``unused'' spectrum resources of spectrum owners. The most business critical parameters were found to be the fixed sensor density, the fixed sensor OPEX and the number of new base station sites required.By using technical simulations we found that high reuse of existing base station sites is difficult to achieve, which points in the direction of shorter range and less expensive access points such as femtocells.However, we found that full reuse of base station sites can be achieved by relaxing interference requirements for the CR to the primary network.We showed that a promising business case is to use cognitive femtocells aided by a sensor network to offload the LTE network. The most business critical parameters were found to be the price for backhauling the cognitive femtocell and the number of supported users by the cognitive femtocell.We evaluated performance of a CR system based on the IEEE 802.22 standard with spectrum sensing and found that the activity of wireless microphones as the primary users should be quite high to reduce throughput and delay.Interference from IEEE 802.22 devices to the wireless microphone was found to be low in general and to occur only for short periods when using novel sensing strategies.We showed that the guaranteed bit rate QoS service for VoIP can be prioritized in IEEE 802.22, though the sensing strategy is important to satisfy strict QoS requirements for throughput and delay.We showed that spectrum selection functions that utilize sensing results to provide long-term spectrum usage statistics as basis for channel selection can enhance performance in IEEE 802.22.
