Spectrum Agile Radio
Team 4
Jim Kile
Don Little
Samir Shah
Structure of Presentation
Definition, why?, and evolution
Background concepts

White space, measurements
Regulatory environment
Wireless standards
Implementations
Spectrum Agile Radio (SAR)
Use of a licensed radio band by other than
the license holders on a non-interfering
basis.
WHY?
Wireless LAN’s & MAN’s
Palm
PocketPC
Blackberry
Cell phone
Wearable computing
Other consumer electronics
Evolution of Devices
Necessary radio spectrum will not be available in the future
HOW?
Almost all radio bands suitable for wireless
communications have been allocated
Preliminary studies indicate that much of
the radio spectrum is not in use


For a significant amount of time
At large numbers of locations
Definition
Radio resources
Radio frequency bands
Can be used/occupied
For certain duration
In a certain area
Called “footprint”
Definition
Primary Users
Conventional legacy users

Rightful owners
Hardware and protocols have strict priority
on spectrum access
Should not be required to retrofit to meet
secondary user access needs
Definition
Secondary users
Spectrum-agile devices
Sense environment
Adapt to appropriate



Frequency
Power
Transmission schemes
Opportunistically access unused spectrum
vacated by idle primaries
Definition
Rules for Coexistence
When a primary user is using the band

Secondary users are not allowed to co-exist
Channel availability of secondary users
determined by the activities and properties
of primary users
Definition
Opportunistic Spectrum Utilization
Usage by Secondary Users
On a non-interfering basis


Band not used
Used in deterministic pattern
CURRENTLY ILLEGAL
Definition
Spectrum Agile Radio
Communicates using available radio
resources
Licensed to OTHER radio services
Without interfering with the operation of
licensed radio devices
Spectrum Agile Radio
Definition: White Space
Almost all of the radio spectrum has been
allocated
But, there are areas of the radio spectrum
not currently in use by primary user
A band is counted as white space when:
Wider than 1 MHz and
Remains unoccupied for 10 minutes or longer
Significance?
Resource is scarce
Provides an opportunity for dynamic spectrum usage
White Space Example
White Space Example – Even in
the unlicensed spectrum
Return
Measuring Spectrum White Space
Why?

Understand the amount of under-utilized spectrum
Conditions


30 MHz to 3,000 MHz (3 GHz)
Use a “worse case” location
Downtown Washington, DC
Both government and commercial spectrum use

Several hour duration during high use periods
Spectrum Measurement
Requirements
Elevated location


Higher detection probability
Eliminates line of site
obstacles
Use of high quality RF
equipment

Detection sensitivity
Whitespace Estimate
Study conducted in June 2003 by the
Shared Spectrum Company
What constitutes white space for this
estimate?


Bands  1MHz wide
Unoccupied for 10 minutes or longer
62% white space in the licensed spectrum
Regulatory Environment
Bandwidth is a natural resource


Heavily regulated
Expensive
A 3 GHz mobile communications band costs $17
Billion!

In the U. S., almost all bandwidth is allocated
(licensed)
Regulatory Environment
- U. S. FCC Models
Licensed primary user model

Set aside for exclusive use
Examples: TV and radio
Unlicensed non-exclusive use model

Set aside for non-exclusive use
Examples: ISM band applications such as
Wireless LAN (802.11) or Bluetooth

Represents a small fraction of the total
bandwidth available
Regulatory Environment circa 1940
“Dumb device” assumption
Tightly regulated to prevent interference

Example: Television VHF/UHF band channel
allocation
No way to share inefficiently used
spectrum
Regulatory Environment Today
Fast processing power and intelligent
radios
New technology which is more tolerant to
interference


Spread spectrum
Spectrum agile radio
Regulatory Environment Today
Introducing underlays/noise
floor rights
Developing a noise
temperature measure

Devices measure the level
of interference and transmit
according
Development of co-existence
modes
Allow multiple uses of a
spectrum (spectrum agile
radio – SAR)
Regulatory Environment
Spectrum policy task force
Setup by Chairman Michael Powell in June 2002
Headed by Paul Kolozdy
Purpose



Conduct a comprehensive review of spectrum policy
Modernize spectrum management and utilization
rules
“Command and control”  consumer-oriented
Submitted findings and recommendations in
December 2002
Regulatory Environment
Spectrum Policy Task Force
“[T]he time is ripe for spectrum policy reform.
Increasing demand for spectrum-based
services and devices are straining
longstanding, and outmoded, spectrum
policies. While the Commission has recently
made some major strides in how spectrum is
allocated and assigned in some bands . . .
spectrum policy is not keeping pace with the
relentless spectrum demands of the market.”
Regulatory Environment
Spectrum policy task force
Findings




Spectrum access
versus scarcity
New methods as a
solution to access
Interference tolerance
Need to define rights
and responsibility
Recommendations




Modernizing the regulator
model
Increase access to
spectrum through the time
dimension
New inferences
management standards
Legislative
recommendations
Regulatory Environment
FCC 2005 Rule Changes
March 2005, FCC adopts rule changes for
smart radios


Allows sharing spectrum with primary users
without causing harmful interference
Regulate emission characteristics rather than
the type of service
Allows rapid development of new
applications

Unencumbered by regulatory delays
Regulatory Environment
FCC 2005 Rule Change Principles
Provide reasonable security measures to
prevent unauthorized software modifications
affect the RF operating parameters
Manufacturer to supply a high level operational
description of the software that controls the
radio’s RF characteristics
A description of the software security measures
employed to prevent unauthorized modifications
Regulatory Environment
FCC 2005 Rule Change Principles cont’d
Manufacturers to market radios that have
the hardware-based capability to transmit
outside authorized United States
frequency bands
Required software controls to limit
operation to authorized frequency bands
when used in the United States.
Regulatory Environment
FCC 2005
Commission concluded that


Technical measures that cognitive radios can
employ will allow a reliable secondary use of
licensed spectrum
Maintains
Availability of the spectrum
Rapid reversion to the licensee when needed

Saw no need to adopt any particular technical
model for interruptible spectrum leasing
Defense Advanced Research
Projects Agency (DARPA)
Working on developing new technologies

Allow multiple radio systems to share the
spectrum through adaptive mechanisms
NeXt Generation communications (XG)
program

Identify behaviors versus detailed descriptions
Dynamically align rules with technologies for future
radio systems
DARPA
NeXt Generation communications (XG)
program concepts (continued)


Abstract behaviors, protocols, and a policy
language
Flexibility, long-term impact, and the need for
regulatory approval
US Army
“Adaptive Spectrum Exploitation” (ASE)
Real-time spectrum management in the
battlefield




“Tactical battlefield spectrum management”
Importance of spectrum planning
Dynamic apportionment
Dynamic interference resolution
Spectrum Agile Radio
Salient Features
Rules for radios as opposed to rules for
services/applications

Radio regulators will continue to decide policy that
specify behaviors of these radios
Spectrum sharing, interference management,
and coordination between users, based on radio
environment awareness
Real-time measurements, dissemination and
opportunity identification
Spectrum Agile Radio
Salient Features
Awareness of primary and secondary
usage

Radio behaviors influenced by evolving
policies
Policies set by regulators
Policies for wireless network management

Examples:
For U-NII bands, using etiquette as discussed in
Wi-Fi
For hospitals
IEEE
LAN/MAN Standards Series
Local Area Network standards
Metropolitan Area Network standards
Task Groups (TGs) to develop extensions

IEEE 1900 Next Generation Radio Standards

IEEE 802.22 Wireless Regional Area Networks

IEEE 802.11 Wireless Local Area Networks
802.11h Spectrum Managed 802.11a
802.11k Physical measurement of wireless energy
IEEE 1900
Next Generation Radio Standards
Established in the first quarter 2005


IEEE Communications Society (ComSoc)
IEEE Electromagnetic Compatibility (EMC)
Society
Develop supporting standards

Next generation radio

Advanced spectrum management
IEEE 802.22
Wireless Regional Area Networks
Working Group on Wireless Regional Area
Networks
Develop standard for spectrum agile radiobased air interface


License-exempt devices on a non-interfering
basis
Spectrum allocated to TV Broadcast Service
IEEE 802.11
Wireless Local Area Networks
Current wireless LAN standard
802.11h Spectrum Managed 802.11a
802.11k Physical measurement
wireless energy
IEEE 802.11h
Spectrum Managed 802.11a
Resolve interference issues 802.11a in 5
GHz band
 Military radar systems
 Medical devices
 Satellite communications
Transmit Power Control (TPC)
Dynamic Frequency Selection (DFS)
IEEE 802.11h
Dynamic Frequency Selection (DFS)
Detects the presence/type of other devices
on a channel
Requires quiet periods
Responds based upon type of device
identified

When radar is identified
Devices MUST change channels

Will coexist with other 802.11 traffic
IEEE 802.11k
“Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY)
Specifications: Radio Resource
Management of Wireless LANs”
Final approval of this amendment is
targeted for January 2007
Defines measurement framework
IEEE 802.11k
Where?
IEEE 802.11 wireless local area networks
operate in the unlicensed



2.4 GHz Industrial, Scientific and Medical
(ISM )
4.9 GHz (Japan)
5 GHz Unlicensed National Information
Infrastructure (UNII) bands
IEEE 802.11k
Why?
Enable more accurate and efficient
operation of Wireless LANs
Optimize radio environments


More devices can coexist
Reduce wireless network traffic
congestion
IEEE 802.11k
How?
Enhanced measurements and
diagnostics
Medium sensing measurement
requests and reports
Collects spectrum usage patterns
IEEE 802.11k
What?
Provides information about other
radio systems on a channel



Could be 802.11 devices
Could be non-802.11 radiators such as a
microwave
Can derive operational parameters for
802.11 stations
IEEE 802.11k
Standards
Radio resource measurements not
standardized
Standardized frame formats

Request for a specific measurement
One radio device to another

Report of such a measurement
Response to the request
IEEE 802.11k
What do you want to know?
Is channel suitable for use?
Percent busy
Non-802.11 signals
Patterns of these Non-802.11
signals
IEEE 802.11k
Clear Channel Assessment (CCA)
Logical function found within physical
layers
Determines the current state of use of
wireless medium
Aids in contention avoidance

Process that determines if the device
can transmit on the channel
IEEE 802.11k
Clear Channel Assessment
Reports
Channel Load Report
Noise Histogram Report
Medium Sensing Time Histogram
Report
IEEE 802.11k
Channel Load Report
Percentage of time the medium
is busy during the measurement
period
IEEE 802.11k
Noise Histogram Report
Samples non-802.11 energy
Samples medium only when CCA
indicates that no 802.11 signal is
present
Reports noise and other non-802.11
signals
IEEE 802.11k
Medium Sensing Time Histogram
Histogram of busy and idle time
observed
Assesses spectrum usage pattern of
other radio devices
Shows pattern of medium usage so
that medium can be shared
Summary
Spectrum Agile Goals
Identify spectrum not used by primary users
(‘spectrum white spaces’).


Transmit in white spaces with appropriate power
levels
Do not cause interference to primary users
Detect the transmission of other secondary
devices


Share some or all of the channels occupied by other
secondaries
Reduce own blocking probability
Identify Spectrum
Hidden Node Problem
Receivers are passive and their
presence cannot be detected directly
Interference is caused at the
receivers
Agile radios have to detect primary
signal at thresholds that are under
signal levels of primary devices
For example, directional antenna
Identify Spectrum
Power
Higher the transmit power employed
by the spectrum agile radio
Further away that it must be able to
detect a television transmitter
Identify Spectrum
Timeframe
Sensing approaches must assess
signal presence quickly
Wideband of spectrum must be
sensed possibly one channel at a
time

Different primary users

Different transmission characteristics
Identify Spectrum
How?
Energy Detection Approach
Feature Detection Approach
Identify Spectrum
Energy Detection Approach
Wireless device measures RF energy
in the channel
Sense the presence of a primary if
energy is above threshold
Cannot arbitrarily lower the threshold

Result in non-detection because of
Signal/Noise Ratio
Energy Detection Approach
Disadvantages
Not be able to distinguish

Other secondary users
Share the medium

Primary users
Require movement to another
channel
Identify Spectrum
Feature Detection Approach
Used in the military to detect the presence
of weak signals
Uses cyclostationary signal processing to
detect the presence of primaries

Process exhibits cyclostationarity if its
statistics vary periodically with time
Can be detected at very low signal-tonoise ratios (SNR)
Identify Spectrum
Implementation
Collocated Sensing Architecture
Single Radio Sensing Architecture
 Dual Radio Sensing Architecture

Sensor Network Architecture
Agile Radio Policy
Identify Spectrum
Collocated Sensing Architectures
Sensing function and the data
transmission collocated in a single
device
Agile radio itself responsible for
sensing spectrum usage


Single radio sensing architecture
Dual radio sensing architecture
Single Radio Sensing Architecture
Advantages
Single radio

Both sensing and data transmission
Completely distributed
Simple to implement with less
equipment
Longer battery life
Single Radio Sensing Architecture
Disadvantages
“Lost transmit opportunity costs”


Radio has to reserve time for sensing
Decreasing time to transmit/receive data
Significant processing overhead



Obtain measurement results
Compare with past results
Estimate how channel is going to
behave in the future
Single Radio Sensing Architecture
Disadvantages cont’d
Imposes limitation on MAC layer design
 Collision - MAC has no means to
determine cause
Transmission by another agile radio device
Channel error
Primary user
Does not overcome hidden node problem
Dual Radio Sensing Architecture
Advantages
Two radios
One is exclusively dedicated for
sensing
 Other is dedicated for data
transmission

Removes “Lost transmit
opportunity costs”
Dual Radio Sensing Architecture
Disadvantages
Additional complexity
Additional power constraints
Cost per device likely higher
Does not overcome hidden node
problem
Identify Spectrum
Sensor Network Architecture
Two complementary networks
 Sensing network
 One or more operational
networks
Identify Spectrum
Sensor Network Architecture
Sensor Network Architecture
Operational Networks
Responsible for traditional data
transmission
Opportunistic use of the spectrum
Accept the information about sensor
network



Channel to use
When to use
How long to use
Sensor Network Architecture
Sensor Network
Separate network fully dedicated to
spectrum sensing
Deployed in the desired target area
Communicate the results to sink node
Sink node makes the information available
to operational networks
Sensor Network Architecture
Advantages
Numerous measurements made

Provide needed location diversity to
identify multipath fading
No “Lost transmit opportunity costs”
Reduces power requirements for the
Operational Network
Sensor Network Architecture
Advantages
Sensors
Inexpensive
 Small form factor
 Very energy efficient

Sensor Network Architecture
Additional Benefits
Can be designed to serve a wide and
evolving range of purposes

Offer new measurement capabilities for
older, regulated bands
Localizing illegal emitters

Spatial diversity allows this feature
Identify Spectrum
Agile Radio Policy
FCC identifies licensed band with
white space
FCC assigns policies for use of
band
Policies published in machineunderstandable form
Agile Radio Policy
Advantages
Autonomous spectrum management
Authority for radio regulation and spectrum
management remains with Federal
Communications Commission (FCC)
No need to sense the medium with
additional equipment
No “Lost transmit opportunity costs”
Agile Radio Policy
Distribution
Policies are published in a machinereadable form
Policies are available for download from
FCC servers
Agile radio devices obtain updates of
policies from servers
Policies could be made available through
memory devices such as flash cards
Agile Radio Policy
Distribution cont’d
After update local information base
Disseminate updates to other agile
radio devices
Devices that belong to different
networks may coordinate sharing of
radio resources with the help of
spectrum etiquette
Identify Spectrum
One Proposed Architecture
Opportunity Identifier
Determines opportunity bands
Senses available white space
Estimates white spaces duration
Passes results to Opportunity Manager
Policy Interaction
Understands policies set by
regulatory body
Interpretation passed to Opportunity
Manager
Opportunity Manager
Core of this architecture
Requests measurements in target bands
Determines if particular band is an opportunity
Passes parameters to the flexible PHY
Responsible to map traffic to the MAC queue to
these opportunities
Flexible PHY Layer
Takes inputs from Opportunity
Manager
Shapes waveforms so that they
comply with transmission policies set
by regulation
Overall Summary
More radio spectrum will be available
to support new devices
New technologies will be required to
make use of the spectrum
Lots of research opportunities
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References
"RADIO RESOURCE MANAGEMENT SPEC FOR IEEE 802(R) WIRELESS LANs
PASSES MILESTONE", http://standards.ieee.org/announcements/pr_p820.html.
Testimony of Dr. Paul Kolodzy Former Director of the Spectrum Policy Task Force
Federal Communications Commission.
J. A. Hoffmeyer, "Regulatory and standardization aspects of DSA technologies - global
requirements and perspective", p. 700, 2005.
S. Mangold, Z. Zhun, K. Challapali and C. Chun-Ting, "Spectrum agile radio: radio
resource measurements for opportunistic spectrum usage", vol. 6, p. 3467, 2004.
N. Sai Shankar, C. Cordeiro and K. Challapali, "Spectrum agile radios: utilization and
sensing architectures", p. 160, 2005.
L. Xin and W. Wei, "On the characteristics of spectrum-agile communication networks",
p. 214, 2005.