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Spectrum Efficiency and
Cognitive Radio
Thinking Differently
=
;
About the World of
Wireless
Eric
Humphrey
7.19.2006
![](3D"master36_image004.gif")
![](3D"master36_image005.gif")
The Ra=
dio
Frequency (RF) Spectrum
Technological
advances are forcing the wireless industry to feel the feared “spectrum crunch.” But to solve=
the
problem, there are sever=
al
questions that must be addressed…
=
l
What exactly is the
“spectrum”?
How is it used?
What is the history of its
evolution?
Why is there a problem
today?
What is the solution?
What is the RF Spectrum?
lIs it a physical block…
=
<=
span
style=3D'visibility:hidden'>l
<=
span
style=3D'visibility:hidden'>l
l …or an open
space?
![](3D"slide0003_image007.jpg")
![](3D"slide0003_image009.jpg")
The Current Wireless Paradigm
<=
span
style=3D'font-size:80%'>lThe RF Spectru=
m is
really only a range of oscillations suitable
for radio communications, and therefore, is not a true physical medium.
Modeled by the Swimmer Analogy
<=
span
style=3D'font-size:80%;display:none'>
l
<=
span
style=3D'font-size:80%;display:none'>
<=
span
style=3D'font-size:80%;display:none'>
l
l
l
![](3D"slide0004_image010.jpg")
RF Spe=
ctrum
– 1.39 to 5.923 GHz
=
l
=
l
=
l
=
l
=
l
=
lMid-Band
=
l
=
l
=
l
=
l
=
l
=
l
=
lHigh-Band
![](3D"slide0026_image012.jpg")
![](3D"slide0026_image014.jpg")
RF Allocation History
lIn 1927, the Federal Communications Commission =
(FCC) passed the Federal Radio Act, allowing predetermined users the right to transmit at a giv=
en frequency, after pressure from the “Titanic&=
#8221;
fiasco.
lNon-licensed users became “harmful
interference,” and in
most cases side bands were implemented to ensure interference was not an issue.
<=
/div>
=
lAs technology advanced, higher frequency bands wer=
e sold at auction bringing considerable revenue to t=
he government (since the 1994 PCS auction, over $30 <=
/span>billion has been generated).
The RF Spectrum Dilemma
lAs more and more devices are added to the wireless
community, they must jockey=
for
the right to transmit at frequencies in the same bands.
![](3D"slide0006_image016.jpg")
What Solutions Exist?
lWith policy still hinging on the capabilities of
1920’s techn=
ology,
a the way we manage spectrum must change. Whereas before radios were assigned “lanes&#=
8221;
in which to opera=
te,
cognitive frequency-agile radios could now be allowed to intelligently “switch lanes”=
; and
adjust parameters.
lUltra-Wideband “underlay” transmission
techniques could be emplo=
yed to
“talk under” primary users in a given frequency =
band.
lCooperative networking, specifically a mesh
architecture, would=
allow
a true web of ad hoc radio nodes, allowing each radio to act as both a transmitter and receiver in=
the
network.
![](3D"slide0007_image018.jpg")
Frequency-Agile Radios
lSoftware-Defined Radios introduce the ability for =
instantaneous frequency reconfiguration.
lEvolution of the SDR concept leads to Cognitive Ra=
dio, =
defined as “an SDR that additionally senses =
its environment, tracks changes, and reacts upon its <=
/span>findings.” [Jondral-06]
lUser-centric vs. Technology-centric CR Operation&#=
13;
lA preliminary step in achieving true “open
spectrum” is the
implementation of a cooperative Primary User-Secondary User system.
<=
span
style=3D'visibility:hidden'>l
Spectrum Leasing
Spectrum
Pooling, first defined by Joseph Mitola III, is the concept that a non-licensed radio may use a given =
frequency when the original licensee is not.
<=
/span>
There are two approaches to the leasing of spectrum
pools with which the li=
cense
owner may operate:
1.The
license owner is aware of other radios using its allocated frequency band. It may avoid other radio=
s, but has the right to reclaim any frequency.
2.The
license owner is completely unaware of the =
presence of other radios, forcing them to change. =
CORVUS System Overview
lA new spectrum manage=
ment
system (CORVUS) has b=
een
designed, based upon:
lAbundance of spectra available for sharing
l<=
/span>Secondary Users utilizing Cognitive Radio
technology
lThis system is compri=
sed of
cognitive-unaware Prima=
ry
Users (PUs) and cognitive-capable Secondary
Users (SUs).
The Primary User
lCognitive Radio unaware
lDoes not need to provide special signaling to access its frequency band (F-Band)
<=
span
style=3D'font-size:93%'>lPUx <=
/i>can tolerate maximal interference for Δtx seconds
lEach PU has its own unique Primary User Footprint (PUF) with which it can be identified
<=
span
style=3D'font-size:93%;visibility:hidden'>l
The Secondary User
<=
span
style=3D'font-size:80%'>lAll SUs possess
cognitive radio capablity
<=
span
style=3D'font-size:80%'>lMonitors the prese=
nce of
PUs at least every Δtx<=
/span> seco=
nds
<=
span
style=3D'font-size:80%'>l“Listen befo=
re
talk” to not disrupt PU activity
<=
span
style=3D'font-size:77%'>lUniversal Control
Channels
<=
span
style=3D'font-size:77%'>lGroup Control Chan=
nels
CORVUS Spectrum Pooling
lDefined as a frequency range used =
by a
SUG, which may overlap with other SUG spectrum
pools
lDivided into n Sub-Channels,
being a small fraction of the spectrum pool
<=
span
class=3DBB style=3D'position:absolute;left:-4.08%;top:.39em'>lSecon=
dary
User Links (SULs) are formed with Sub-channel patterns over mult=
iple
F-Bands
CR-Specific System Metrics
With the advent of a new technology, new methods
of evaluating the system must be developed. There are thr=
ee
fields that must be quantified:
<=
span
class=3DB1B style=3D'position:absolute;left:-4.65%;top:.39em'>lPerf=
ormance
<=
span
class=3DB1B style=3D'position:absolute;left:-4.65%;top:.39em'>lCR
Efficiency
<=
span
class=3DB1B style=3D'position:absolute;left:-4.65%;top:.39em'>lHard=
ware
Costs
Performance Metrics
lSaturation Throughput and Fairness
lPacket Length Distribution
lChannel Model
lStation Distribution
lDelay vs. System Load
The
Delay is calculated as a function of S, the relative load, where the nominal station rate, B <=
/span>(bits/sec), can be defined as:
<=
/div>
1.Peak
value for adaptive radios
2.Set=
value
for non-adaptive radios
3.
L: load P: data packet,=
in
bytes N: stations X: seconds=
CR Efficiency and Interference
lThe system must evaluate how well the CR-capable
SUs avoid interfering with PU transmissions.
lInterference Metric
lSpectrum Efficiency
![](3D"slide0029_image024.jpg")
Hardware Costs
The expense of the
system’s implementation is directly impacted by its
size, power, and per-unit cost.
<=
span
class=3DB1B style=3D'position:absolute;left:-4.25%;top:.39em'>lPower
measured in Millions of Operations per Second (MOPS) per Watt=
3;
<=
span
class=3DB1B style=3D'position:absolute;left:-4.25%;top:.39em'>lOccu=
pied
Chip Area measured in MOPS/mm2
System Functions
lCognitive capabilities will be
achieved in the Physical and Link layers of radio design
lThe following six system functions=
can
be distributed between these two layers:
Spectrum Sensing
Channel Estimation
Data Transmission
Group Management
Link Management
Medium Access Control (MAC)
Physical Layer Functions
lSpectrum Sensing must be conducted before and duri=
ng transmission, and SUs will communicate sensing information to better monitor activity.
lChannel Quality Estimation is achieved through transmission parameter adjustments based upon channel sounding.
lData Transmission will most likely be attained wit=
h a modulation scheme similar to Orthogonal Frequency =
Division Multiplexing (OFDM).
Link Layer Functions
lGroup Management is attained through use of the UC=
C, so that SUs may join or form groups as they appear=
.
lMAC must provide a means to handle access to SULs =
by a large number of different SUs on different Su=
b-Channels.
Requirements for CR
lDynamic Spectrum Developments
=
lSpectrum Etiquette (“Listen
before talk”)
lBandwidth Snapshot (frequency
monitoring)
<=
span
class=3DBB style=3D'position:absolute;left:-4.23%;top:.39em'>lProvi=
de
Operating Information to Owner
lGlobal Positioni=
ng
Knowledge
lGroup Cooperatio=
n and
Planning
Future Work Facing CR
lUsing elements of game theory, CR interactions can=
be modeled and predicted to optimize behavior.
lRadio metrics must be redefined to better analyze =
frequency availability (spectrum sensing) and radi=
o sensitivity (transmission power).
lFederal Regulations and Incumbent Frequency Band <=
/span>Licensees pose a valid threat to CR advancement.
Other
Spectrum Efficiency Solutions
=
lUltra Wideband (UWB) - RF Interference is non-=
destructive, allowing radios to “talk”
through each other due to t=
he
receiver’s ability to intelligently identify the speaker.
lMany conversations can occur within the
same space when volume is li=
mited,
highlighting the need for po=
wer
constraints.
lCooperative mesh networking is equivalent to note =
passing amongst each “person” in the r=
oom.
As the crowd increases,
coverage and throughput also increase.
![](3D"slide0012_image025.jpg")
Unlicensed SDR Successes
lWi-Fi - IEEE
802.11b/a
<=
span
class=3DB2B style=3D'position:absolute;left:-4.11%;top:.39em'>l5 Bi=
llion
Dollar industry in 2005
<=
span
class=3DB2B style=3D'position:absolute;left:-4.11%;top:.39em'>l4000=
US
Hotspots in 2002
<=
span
class=3DB2B style=3D'position:absolute;left:-4.11%;top:.39em'>lExte=
nsive
implementation in
private, collegiate, and commercial sectors
lBluetooth
<=
span
class=3DB2B style=3D'position:absolute;left:-4.11%;top:.39em'>lVery
short-range ad hoc networking
<=
span
class=3DB2B style=3D'position:absolute;left:-4.11%;top:.39em'>l2005
Shipping statistics have reached
5 million a week
![](3D"slide0011_image027.jpg")
![](3D"slide0011_image029.jpg")
Benefi=
ts of
Redefining the Spectrum
lOperational Efficiency
=
lService Reliability
lCapacity Increase
lEmergency Relief
lMilitary Applications
Steps Toward Radio Efficiency
1=
.Foster
Cooperation
<=
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Spectrum Efficiency and Cognitive Radio
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2=
.Expand
Unlicensed Spectrum
<=
/div>
3=
.Relax
Underlay Restrictions
<=
/div>
4=
.Promote
Further Research
Conclu=
sion
– A Look to the Future
lTrue Open Spectrum
lFully Unlicensed Users, with Prior=
ity
Given to Emergency Services
lEasily Deployable Radio Networks&#=
13;
lUniversal Wirele=
ss
Internet Coverage
lPersonally Tailo=
red
Digital Assistants
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