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Dynamic Spectrum Access: Challenges and Applications

TCD ussher lecturer talk
by

Daniel Willkomm

on 17 July 2011

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Transcript of Dynamic Spectrum Access: Challenges and Applications

conclusions
spectrally efficient
spectrum usage
Main challenges
primary user
protection
ensure
achieve
1
3
In this talk I have
Generic
Link capacity
Amount and continuity of spectrum used for secondary communication
: average link capacity
: alpha quantiles of the link capacity (Minimum capacity achieved in alpha per-cent of the time)
Non-contiguous
secondary user links (SULs)
secondary
QoS support
provide
2
Performance metrics
Robustness against link reconfigurations
Scatter SUL over multiple PU bands
Reduce impact of PU appearance on secondary QoS
Sub-channels on which a PU was detected have to be immediately excluded from the SUL
Link capacity is temporarily reduced
Link reconfiguration (adding new sub-channels) usually takes some time
Daniel Willkomm
Trinity College Dublin
July 18th, 2011
introduction
Constraints
Easy deployment


Low cost and low complexity
Can be easily enhanced as technology improves
No infrastructure needed
Operational with only a few SUs
Detect unused spectrum
(find spectrum opportunities)
Detect reappearing PU
Use for SU communication
Reconfigure SU
communication
Basic operation
Secondary spectrum usage
Overcome discrepancy between spectrum assignment and usage by
Allowing Secondary Users (SUs) to use temporarily available spectrum
Most spectrum is licensed to Primary Users (PUs), but
PUs do not always use all their spectrum everywhere
PUs keep strict priority for using the spectrum:
SUs have to vacate spectrum as soon as PU returns
for secondary spectrum usage based on dynamic spectrum access:
Link reconfiguration
Reliable PU protection
Secondary QoS support
Spectral efficiency
1
2
3
No differentiation between true positive and false positive possible
Thank
You

PU present
PU not present
PU detected
no PU detected
false positive
type I error
true positive
true negative
false negative
type II error
correct outcome
correct outcome
Sensing-based PU detection
Receiver Operating Characteristic (ROC)
low false negatives
=
increased false positives
high false positives
=
"jumpy" system
(many reconfigurations)
CR system
design
spectrally efficient
spectrum usage
Main challenges
primary user
protection
ensure
achieve
1
3
secondary
QoS support
provide
2
Metric for
reliable PU protection
Impact of false positives on link capacity
Average link capacity
Does it pay of to use many small sub-channels?
Investigate the impact of false positives on the link capacity for different PU activity patterns
Alpha=0.9999 quantile
Relation to CTVR research
Investigations so far have been mostly analytically or simulative
How do the proposed approaches perform in real life?
IRIS
is ideal platform to experimentally evaluate and validate proposed concepts
Implement and evaluate non-contiguous secondary user links
Implement and evaluate periodic sensing approaches (not presented in todays talk)
Current and Future Research:
Its Relationship to CTVR and the
TCD Electronic Engineering Curriculum
Dynamic Spectrum Access:
Challenges and Applications

TV
white space
usage
sub-GHz spectrum range
very attractive signal propagation characteristics
Open up TV bands for secondary spectrum usage
Goal: broadband wireless Internet access in rural areas
PU detection based on geolocation database and spectrum sensing
Very strict requirements on sensing process
As of Sept. 2011
No sensing required anymore (database only)
2 TV channels excluded from secondary usage and reserved for part 74 devices
Launched SE43 in 2009
Goal: investigate requirements for secondary usage of TV white spaces
EEC report 159: Reliable PU protection based on sensing alone impossible
Sensing approach
very strict requirements (detect TV signals at -114 dBm)
hard to achieve
nevertheless not trusted by PUs
wireless microphones (low power) very hard to be detected reliably
Coordinator
logical entity (can be PU or regulation - "broadcasters" are attractive candidates)
maintains spectrum usage database
makes final decisions on spectrum usage
Spectrum usage database
contains information from frequency usage plan (occupancy of TV channels)
information can be LOCALLY augmented / enhanced through sensing data
contains information about microphone and secondary usage
spectrally efficient
spectrum usage
Main challenges
primary user
protection
ensure
achieve
1
3
secondary
QoS support
provide
2
TV
white
space
basics
Sensing
augmented
database
TV frequency bands
not all TV channels are used everywhere all the time
Primary usage
1. TV broadcasting
very static usage characteristic
2. Wireless microphones (part 74 devices)
manual selection of free channels
sometimes supported by manual sensing
Good news
white
spaces
(temporarily unused frequency bands) available for
secondary spectrum usage
Regulation
FCC (US)
CEPT (Europe)
Database vs. sensing
Database approach
very static
only suited for large white spaces (in time and space)
wireless microphones not considered
General idea
combine advantages of database and sensing approaches
Microphone
Coordinator
Request channel
Optionally
Provide sensing data
Send channel preference list (based on sensing results)
Assign channel
Enter new usage in database
Update database with sensing results
Coordinator
Coordinator
Secondary
user
Request channel
Assign channel
Enter new usage in database
Coordinator
Secondary
user
Request channel
Request sensing results
Validate sensing results
Update database with sensing results
Add secondary usage to database
Perform sensing on requested channels
Send sensing results
Assign channel
Coordinator can validate sensing by requesting to sense channels known to be occupied
Coordinator can initiate "active" measurements (e.g. request wireless microphone to transmit at full power during measurments)
Coordinator can optimize spectrum usage among multiple SUs
Initiate active measurements
Negotiate spectrum usage between SUs
Coordinate spectrum usage between SUs
Secondary
user
Secondary
user
Request channel
Assign channel
Request channel
Initiate active measurement
Initiate active measurement
Wireless microphone
Database modus
Sensing & database modus
Coordination of secondary usage
Both TV broadcasting and wireless microphones can be reliably protected
Final decision on secondary spectrum usage stays with coordinator
Coordinator can validate spectrum sensing results
Coordinator supports allocation of channel with least PU activity
Coordinator supports coordination between differents SUs
Better exploitation of white spaces through sensing augmented database
Efficient, coordinated usage of spectrum between wireless microphones and SUs
Relation to CTVR research
TV white spaces one of focus areas of CTVR
Test and Trail ideal for experimental investigations
Some aspects fit into COGEU project
Approach can be used as baseline for FP7, call 8, objective 1.1. Future networks project proposals
We have submitted a proposal on national level in Germany, so there is already a big network of high class interested researchers
Contact
willkomm@tkn.tu-berlin.de
Publications
http://www.tkn.tu-berlin.de/~willkomm
PhD thesis
http://opus.kobv.de/tuberlin/volltexte/2011/3082/
Enabling technology
Cognitive radio (CR)
Environmental awareness
Frequency agility
introduced 3 fundamental challenges for dynamic spectrum access / secondary spectrum usage
presented approaches for enabling secondary QoS support
presented an initial sketch of an innovative approach for TV white space usage
put my current and future research in relation to current CTVR research
so far not addressed the relation of my research with the TCD Electronic Engineering Curriculum, but
I strongly believe in Humboldt's approach of the
Unity of teaching and research
i.e. any research should be reflected in the curriculum
I usually do so through
student project / final year projects
seminars for graduate students
"Hot topic" units in undergraduate lectures
who
am
I

Dipl.-Ing. (MSc) in October 2005
Dr.-Ing. (PhD) in May 2011
Active in cognitive radio / dynamic spectrum access research since 2004
Technische
Universität Berlin
Proud dad of my 1 month old daughter Lina Saphira
Research assistant at the
m: number of sensors
: number of sub-channels
: number of sub-channels
Remember:
PU detected = true positive + false positive
Full transcript