Design Considerations for Cognitive Design Considerations for Cognitive White Space Networks

Narayan Mandayam y yDipankar Raychaudhuri

WINLAB Rutgers UniversityWINLAB, Rutgers University

WINLAB1

What is White Space? TV Band Devices: Fixed or Portable

Max. Fixed antenna height = 30m, Portable < 3m Permissible channels (6MHz each) Permissible channels (6MHz each)

XNew Rulingon Sep 23 2010

Transmit Restrictions Protected region around primary TV transmitters Sense and avoid protected devices Sense and avoid protected devices TX power:

Fixed:30 dBm (6dBi antenna gain) = 4W EIRP, Co- and Adjacent-channel not allowed

Portable: 20 dBm (no antenna gain) = 100mW

WINLAB

Portable: 20 dBm (no antenna gain) = 100mW, Co-channel not allowed, Adjacent = 16 dBm

2

What is “Really” White Space?

Economist ≈ $m Markets, Property

Regulator/Politician≈ $≈ $ votes

Social Good Engineer

N T h l C iti R di ≈ ¢

≈ $, votes

New Technology, Cognitive Radios Folks who are “out there”

Free speech Bill of Rights

≈ ¢priceless

Free speech, Bill of Rights Communication/Information Theorist

W

p

WINLAB3

How much White Space is there?

Example of NJ TV Towers around NY City & Philadelphia TV Towers around NY City & Philadelphia

# f h l (fi d) # f 5X5 i id# of channels (fixed) vs. # of 5X5 sq. mi. grids

WINLAB4

Radio Coverage Prime spectrum with a wide range of applications

~50-200 MHz available depending on TV transmitter density Power constraints result in achievable bit-rate profile for fixed-w n n u n p f f f

fixed, fixed-mobile, and mobile-mobile ~5 Mbps @ 2Km range for LOS fixed-mobile ~3-5x WiFi range for non-LOS services, e.g. ~50 Mbps @ 250mg g p

WINLAB5

White Space NetworksR f bl h d Range of possible usage scenarios, with sweet spot in outdoor networks with medium range and speed

Bit-Rate

WINLAB6100 m

Sample Applications: Cellular Data Boost

“Cellular data boost” network can be used to offload fast-growing cellular traffic using dual-mode radio Mesh network of outdoor white space hot spots; backhaul data to existing BTS Mesh network of outdoor white space hot spots; backhaul data to existing BTS Intended for transport of non-real time data such as mail, content, facebook … Potential for ~2-5x capacity boost depending on % coverage & service mix

WINLAB7

Sample Applications: Distribution/Backhaul

DISTRIBUTION AND BACKHAULUSING WHITE SPACE

WINLAB8

Sample Applications: Long range V2V/Emergency Network

Long-range V2V useful for traffic control/warnings, geographic apps, p2p content, etc. Supplements short-range 802.11p/DSRC V2V links (from mandated car radios?) can be used to form a high capacity V2V links (from mandated car radios?) can be used to form a high capacity

emergency backup network using ad hoc mesh between cars and fixed AP’s Application requirements well matched with WS range/bit-rate properties

WINLAB9

Sample Applications: Cognitive Digital Home

GENIE NODE

Central spectrum managerService Provision Device

Provides end-user serviceRelay and Wireless Access Devices

Provides relay/connectivity support

WINLAB10

p g Provides relay/connectivity support

Design Implications for White Space NetworksWhite space radio systems require the following building blocks:

Flexible BW PHY preferably operating in non contiguous spectrum Flexible BW PHY, preferably operating in non-contiguous spectrum

Spectrum sensing for TV primary and other incumbents

Opportunistic link layer access with distributed congestion control procedures for fair sharing among secondary users

Discovery and bootstrap protocols for ad hoc network formation

Common coordination channels and/or spectrum servers for improved Common coordination channels and/or spectrum servers for improved coordination among multiple types of secondary users

… and of course, cognitive SDR platforms (wideband, flexible, low-cost)

WINLAB11

… and of course, cognitive SDR platforms (wideband, flexible, low cost)

WS Building Blocks: Spectrum Sensing

Sensing module required to reliably detect TV and incumbents Simple methods such as energy detection higher order statistics Simple methods such as energy detection higher order statistics

(HOS) Further improvements with receiver feedback, cooperation, data base …

Probability of Detection vs Sensing Time for Pfa =0.1TV White Space Sensing Scenario

Wireless Microphones

WINLAB

WS Building Blocks: NC OFDMA PHY

NC OFDMA approach used to opportunistically fill spectrum p

Center freq White Space

Primary

freq

Min tones needed for

Al d ll f fl ibl h i f

Min. tones needed for freq. synchronization

Also need to allow for flexible spectrum sharing for secondary coexistence

Link rendezvous protocol needed for mutual

WINLAB

pagreement on carriers used at TX and RX

WS Building Blocks: NC OFDMA MAC

NC OFDMA offers the possibility of a simple FDMA MAC instead of CSMA or TDMA (..CSMA may still be used for end-user access)

Simplifies ad hoc network operation and avoid classical mesh self interference and exposed node problems

Requires a cooperative access policy (i.e. not greedy, and with some form of congestion backpressure)g p

f1

f2

f3

rate r1 rate r2 rate r3

f1

LINK 1

freq

LINK 2 LINK 3

WINLAB

Rates r1, r2, r3 periodically adjusted via cooperative procedures

Secondary Coexistence: Reactive Schemes

Reactive (autonomous) methods used to avoid interference via: Frequency agility: dynamic channel allocation by scanning Power control: power control by interference detection and scanning Power control: power control by interference detection and scanning Time scheduling: MAC packet re-scheduling based on observed activity Waveform agility: dynamism in signal space

Reactive schemes (without explicit coordination protocols) have limitations: Interference is a receiver property!

B

C

D’s agile radio waveformwithout coordination protocol

B

C

D’s agile radio waveformwithout coordination protocol

Coverage area of D

Y

A

D

A cannot hear DA’s agile radio waveform

with coordination

Coverage area of D

Y

A

D

A cannot hear DA’s agile radio waveform

with coordination

WINLAB15

Hidden Terminal Problem

Coverage area of A

Hidden Terminal Problem

Cognitive Approaches: Outlook Cognitive radio networks require a large of amount of network (and

channel) state information to enable efficient Discovery, Self-organization Resource Management Cooperation Techniques

S l bilit ?

CBootstrapped PHY &control link

End-to-end routed pathFrom A to F

Scalability?

BB

DD

E

PHY A

PHY BPHY C

AA

F

Control(e.g. CSCC)

Multi-mode radio PHYAd-Hoc Discovery& Routing Capability

F ti lit b it

WINLAB16

Functionality can be quitechallenging!

Cognitive Radios need help too!

Architectures that can facilitate secondary coexistence

Examples of coordination mechanisms:

Information aids Information aids “Spectrum Coordination Channel” to enable

spectrum sharingp g “Global Control Plane” for coordination

Network architectures “Spectrum Servers” to advise/mediate sharing

WINLAB17

Architectures for Secondary Coexistence

Secondary co-existence an important requirement for WS Various schemes possible depending on system model Various schemes possible depending on system model

Completely autonomous, using performance feedback only Common coordination channel Common Internet based spectrum server

Spectrum Server (optional)

WS APw/ backhaul

freq

Secondary A Spectrum

Secondary BSpectrumInternet

WS MobileAccess Protocol

Controlinformation

WINLAB

Secondary System A Secondary System BCommon Coordination Channel (optional)

WSN Prototyping: Cognitive Radio Platforms

USRP

RICE WARP PlatformU. Of Colorado

WINLABWINLAB WINC2R System

WINLAB/RST GENI SDR SystemUSRP2