Architecture and Protocol Design
for Cognitive Radio Networks*
Microsoft CR Summit, Jun 2008
Rutgers, The State University of New Jersey
www.winlab.rutgers.edu
Contact: Professor D. Raychaudhuri
ray@winlab.rutgers.edu
*Collaborative project with
Profs. Srini Seshan & Peter Steenkiste, CMU
And Prof. Joe Evans, U Kansas
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Cognitive Radio: Problem Scope
Spectrum
Allocation
Rules
(static)
Spectrum
Coordination
Server
(dynamic)
INTERNET

Auction
Server
(dynamic)

Dynamic frequency
provisioning
Spectrum Coordination
protocols
BTS
AP
Short-range
infrastructure
mode network
(e.g. WLAN)

Etiquette
policy

Spectrum
Coordination
protocols
Collaborative ad-hoc networks
MAC/PHY adaptation
Ad-hoc
sensor cluster
(low-power,
high density)
Dense deployment of
wireless devices, both
wide-area and shortrange
Proliferation of multiple
radio technologies, e.g.
802.11a,b,g, UWB,
802.16, 3G femto, 4G, ..
New cognitive radio
devices with
programmable
PHY/MAC
Available options
include:



Wide-area infrastructure
mode network (e.g. 802.16)
Scope of Cognitive
Radio Protocol Stack

Agile radios (interference
avoidance)
Dynamic centralized
allocation methods
Distributed spectrum
coordination (etiquette)
Collaborative ad-hoc
networks
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Cognitive Radio: Design Space

Broad range of technology & related policy options for spectrum

Need to determine performance (e.g. bps/Hz or bps/sq-m/Hz) of different
technologies taking into account economic factors such as static efficiency, dynamic
efficiency & innovation premium
Unlicensed band +
simple coord protocols
Protocol
Complexity
(degree of
coordination)
Ad-hoc,
Multi-hop
Collaboration
Internet
Server-based
Spectrum
Etiquette
Unlicensed
Band
with DCA
(e.g. 802.11x)
Internet
Spectrum
Leasing
“cognitive radio”
schemes
Radio-level
Spectrum
Etiquette
Protocol
Reactive
Rate/Power
Control
Static
Assignment
Needs protocol support
 unified framework
called “CogNet”
Agile
Wideband
Radios
“Open Access”
+ smart radios
UWB,
Spread
Spectrum
Hardware Complexity
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CogNet Protocol: Architectural Principles

Decentralized spectrum coordination as an integral part
of protocol capabilities


Support for ad hoc network collaboration


Access to cross-layer information necessary for cross-layer adaptation
Logical separation of control & data for flexible design
and low overhead


Control framework that enables on-the-fly selection of data path protocol components
Cross-layer control exchanged across protocol layers


Beacons that enable network bootstrapping and discovery without infrastructure support
Adaptive selection of PHY, MAC, routing methods


“mutual observability” achieved via explicit exchange of spectrum information
Minimize contention between control & data (…>>50% overhead in 802.11 networks!)
Efficient integration with the wired Internet

Aggregation of routing and cross-layer control information at boundary/gateway nodes
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“CogNet” Protocol Stack

Global Control Plane (GCP)


Common framework for spectrum allocation, PHY/MAC bootstrap, topology
discovery and cross-layer routing
Data plane

Dynamically linked spectrum mgmt, PHY, MAC, Network modules and
parameters as specified by control plane protocol
Data Plane
Global Control Plane
Control Plane
Data Plane
Control API
Application
Data
Spectrum
- Bootstrap
Path
Mgmt
Discovery Establish
ment
Naming
&
Addres
sing
Transport
Network
Control MAC
MAC
Control PHY
PHY
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CogNet Protocol: Common Spectrum
Coordination Channel (CSCC)


CSCC enables mutual observation between heterogeneous nodes to
explicitly coordinate spectrum usage
CSCC function is an integral part of the CogNet global control plane (GCP)
• Exchange of CSCC
messages by an extra
narrow-band (low bitrate) radio
• Periodically broadcast
spectrum usage
parameters to neighbors
• Enables distributed
algorithms for spectrum
co-existence
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CogNet Protocol: Packet Format
Generic GCP Packet: Ethernet packet format with control payload (consisting of
variable length information elements)
Message
Type
Flags
Source
Address
1B
1B
6B
0
8
Message type
IE length
2B
IE(1)
IE(n)
variable
variable
16
24
31
Source MAC Address
Flags
Source MAC Address (cont). . .
. . . MAC Address
IE length
. . . Device Name and Description
. .
Type (8b)
Priority (8b)
Price_bid(8b)
. . . Duration (32b)
Channel(8b)
Service Time . . .
Tx Pwr (8b)
Rx Pwr (8b)
Example CSCC message used in WLAN-Bluetooth prototype at WINLAB
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CogNet Protocol: Validating GCP-based
Spectrum Coordination on ORBIT

Multi-radio node



802.11a/b/g ad-hoc
WiFi infrastructure mode (AP to
clients)
Bluetooth




Zigbee


64kbps voice calls
File synchronization between
PDAs, phones and laptops
Mouse/keyboard
Sensors
Potential WiMax

Aggregated web/email traffic
to base stations
GCP Coordination Range
ORBIT Radio Grid
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CogNet Protocol: Validating GCP-based
Spectrum Coordination on ORBIT (cont.)
BT
Data Radio Service
PHY Type
IEEE 802.11g
(Atheros
AR5212)
Bluetooth
(USB Dongle)
Frequency
2427-2447MHz
2402-2480MHz
Modulation
OFDM (256 FFT)
QAM
FHSS
Transmit
Power
18dBm
4dBm (~10m) (class 2)
20dBm (~100m) (class 1)
PHY Rate
1M-54Mbps
AutoRate
Upto 1Mbps (class 2)
Upto 4Mbps (class 1)
Data session
Pareto ON/OFF
variable rate
CBR: 5 sec
random
session
Constant audio streaming
(64, 128,320,512,
1024kbps)
WiFi
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CogNet Protocol: Validating GCP-based
Spectrum Coordination on ORBIT (cont.)
 UDP throughput results with and without
interference from other BT/WiFi users
Wifi Performance
Percentage Throughput
120.00
802.11g Throughput
100.00
80.00
60.00
40.00
20.00
0.00
No-Interf
With-Interf
Coexistence Effect on Wifi
Throughput Drops by ~3-4x in the case of 802.11g nodes and by ~1.5-2x for bluetooth nodes in dense
topologies with 4 wifi and 4 Bt links. Results Averaged over 5 different topologies & load conditions. 
indicates the need for spectrum coordination
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Characteristics :

Each individiual in the room carries two
radios bluetooth and wifi

Node density High



28 radios in ~3000sqft
14 Bluetooth radio
14 Wifi radio
Throughput Improvement (%)
CogNet Protocol: Validating GCP-based
Spectrum Coordination on ORBIT (cont.)
100
Wifi (BT-Rate)
Wifi (BT-BO)
BT (BT-Rate)
BT (BT-BO)
Total (BT-Rate)
Total (BT-BO)
50
0
1M
5M
10M
15M
-50
WiFi offered load (bps)
BT load 1Mbps
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CogNet Protocol: Beacon Format

Beacon format: (extended form of CSCC)

Short message, low-layer function
1
8
MSG Type
16
24
Flags
32
Sequence Number
Source...
...Identifier
Max Trans mit Power
Num of Reach
MAC Type
8
Flags :

Max PHY Rate
Beacon Trans mit Power
MAC Bus y Indicator
10
NA
CF
12
FD
0
14
0
0
16
0
0
Link weight/metric calculation:

Estimate maximum supported data PHY rate
Rmax ij  min{ Rmax i , Rmax j }  min{ f map ( SNRij ), Rmax j }

SNRij 
Ptmax i  Pr ji( B )
Pt (jiB )  N 0
Direct link weight (proportional to achievable link rate)
Lij  Rmax ij  min{  MACi ,  MACj }
MAC Idle Ratio
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CogNet Protocol: Network Discovery

Obtain global awareness by aggregating local
link states

Discover end-to-end paths with path weight
 Use only one-hop broadcast for periodical update
 Trade-off between network setup time and overhead

Link state aggregation message format

Flags: PR – Poll (0) / Response (1), UB – Unicast (0) / Broadcast (1) response required,
FD – Forwarded or not, FU – Full or updated
1
8
MSG Type
TTL
16
24
Flags
Source...
...Identifier
Valid Time
Number of Vectors
Message Hash ID
Link State Vector 1
32
Flags:
9
10
11
12
13
14
15
16
PR
UB
FD
FU
0
0
0
0
Destination Node...
...Identifier
E2E Path Weight
Next Hop Node...
...Identifier
Hop Count
Link State Vector 2
......
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CogNet Protocol: Data Path
Establishment

Hop-by-hop cross-layer parameter setup

Configure data plane and reserve radio resources by joint
frequency/power/rate/bandwidth allocation
 Unified message format for “up/down” hop setup
1
8
16
24
32
MSG Type
Control Plane
Coverage
Multi-channel Data Path
Link State Aggregation
Source
Destination
Hop-by-hop
Resource
Allocation Link State
Table
Flags
Mes s age Sender ...
... Identifier
Flow Des tination ...
... Identifier
Ses s ion Duration
Current Time Stamp
Hop Receiver ...
... Identifier
MAC Type as Sender
Channel Availability Map
Min PWR
Max PWR
Min Rate
Max Rate
Hop Sender ...
... Identifier
MAC Type as Receiver
Frequency
Bandwidth
Modulation
Coding
TX Power
PHY Rate
9
Flags: UC
10
11
12
13
14
15
16
RV
SD
OT
0
0
0
0
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CogNet Protocol: ns2 Simulation

Evaluation by ns-2 simulations

Bootstrap/Discovery: network setup time, overhead, theoretical end-to-end rate
 DPE: joint F/P/R allocation success ratio, overhead
 Naming/addressing: uniqueness of IP/Name

Ad hoc network – nodes randomly boot up
Control Interface
(802.11b)
Data Interface
(generic OFDM
radio parameters)
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CogNet Protocol: Discovery & Path Setup
Simulation Results
Maximum and average network setup time
(BSB interval 2sec, LSA interval 5sec, nodes randomly start [0, 4]sec)
Control overhead
Theoretical max end-to-end rate
averaged over the network
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CogNet Protocol: Dynamic MAC
Switching Using GCP Control



GCP offers control support necessary for MAC switching, for example from
CSMA to TDMA
GCP messages carry state information needed by decentralized MAC
switching algorithm at each node
GCP control used to set up TDMA schedule involving multiple nodes
Control link
Data path
CH1_CSMA
Sender
CH4_CSMA
CH3_CSMA
CH5_CSMA
CH2_CSMA
A
CH10_TDMA
Slot = 3
B
CH10_TDMA
Slot = 5
Delay increase > 20%
Request TDMA Switch
CH1_CSMA
CH10_TDMA
Slot = 1
Receiver
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CogNet Protocol: Dynamic MAC
Switching Using GCP Control (cont.)


GNU radio implementation currently in progress
Sample protocol exchange between nodes shown below
Sender
Node B
Node A
Receiver
Preferred Channel List
Match channel
CH3_CSMA
Preferred Channel List
Match channel
CH5_CSMA
Preferred Channel List
Match channel
CH1_CSMA
Delay > 20%
Request TDMA switch
TDMA Join (Slot #1)
TDMA Join (Slot #3)
TDMA Join (Slot #5)
CH10_TDMA (Slot #3)
CH10_TDMA (Slot #1)
CH10_TDMA (Slot #5)
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CogNet Protocol: Future Work

Complete validation of key components


Complete baseline v1.0 protocol spec


CR supernode and aggregation gateway details
Protocol implementation on GNU radio platform


Support for dynamic spectrum, bootstrap/discovery, MAC switching and crosslayer routing
End-to-end wired Internet integration issues


MAC switching, cross-layer routing protocols, adaptation algorithms, …
GNU/ORBIT release planned for AY08-09  ORBIT upgrade to URSP2
Experiments with adaptive wireless networks

Apply to dynamic networking scenarios (tactical, vehicular) and demonstrate value of
coordination, cooperation and adaptation
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Future work: ORBIT Node Upgrade to CR


ORBIT radio grid testbed currently supports ~10 GNU radios and for
~100 low cost programmable radio boards
Plan to upgrade ~64 radio nodes with combination of GNU/USRP2
boards and WINLAB hardware platforms for higher performance
evaluations; will include baseline CogNet stack
Suburban
ORBIT Radio Grid
Current ORBIT sandbox with GNU radio
20 meters
500 meters
Office
30 meters
Urban
300 meters
400-node Radio Grid Facility at WINLAB Tech Center
Planned upgrade
(2007-08)
Radio Mapping Concept for ORBIT Emulator
Programmable
ORBIT radio node
URSP2
CR board
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