Iitk Cognitive Radio research

Koilpillai / Dec 2012 / Cognitive Radio 1

IITB TVWS&CR Workshop

Electrical Engineering

IIT Madras

Control Channel Aspects

for

Cognitive Radio Networks

R. David Koilpillai

Department of Electrical Engineering

Indian Institute of Technology Madras

TV White Space and Cognitive Radio Workshop

IIT Bombay

December 17, 2012




IIT Madras What is a Control Channel ?

When you turn ON your cell phone

How does it find the network ? (synchronization)

How does the network recognise the mobile ?

How do you obtain service if you are Roaming

How does network locate where mobile is currently ? (incoming call)

How does mobile let network know it wants to make a call ? (outgoing)

How does handover occur if mobile changes location during call ?

Answer to all of these questions is the Control Channel(s)

Focus on Control Channel aspects in todays talk




IIT Madras Two Types of Networks

Infrastructure-based Networks

Cellular networks

Infrastructure includes Basestation, Basestation controller, and Core network

All operations controlled by infrastructure

Over air-interface, BTS is Master and MS is Slave

Infrastructure-less Networks

Peer-to-peer (Bluetooth, ZigBee, )

All nodes have equal capability

Nodes may assume different roles based on need

Decisions made by peer entities

Both cases need the functionality of Control Channel(s)

Consider both cases for Cognitive Radio Networks




IIT Madras Family of Networks

Hierarchy of wireless networks

Wide range of data rates, range

Significant developments in

WAN / MAN

Increasing number of users

Need for capacity

need for spectrum ??

Cognitive Radio

- An attractive option

Ref: Cordeiro et al., IEEE 802.22: The First Worldwide

Wireless Standard based on Cognitive Radio, IEEE, 2005




IIT Madras Outline of Presentation

SDR Cognitive Radio a paradigm shift

Spectrum sensing

Cognitive Radio Networks

Control Channel designs

Challenges and Opportunities

Focus on Control Channel aspects




IIT Madras A Interesting Incident

From Spectrum April 2011 article by Prof. K. J. Ray Liu (U Maryland)

June 7 2010 - Apple CEO Steve Jobs unveiling iPhone4

Failed demonstration 571 Wi-Fi basestations

Repeated appeals still not enough capacity to handle demo

So

urc

e: K

.J.

Ray

Liu

, S

pec

trum

Apri

l 2

011




IIT Madras Game Theory

What happened at Apple iPhone demo ?

Room full of bloggers

Each wanting to post iPhone information need to stay connected

Total 571 Wi-Fi Access Points active

Repeated requests (Jobs) to turn off Wi-Fi connections

Most people complied some did not

Assumption: If others have disconnected, then take advantage

Sourc

e: K

.J. R

ay

Liu

, Spec

trum

Apri

l 2011

Do not know other peoples decision

Group behaviour

Greedy / selfish behaviour

Rational participants in any conflict for resources

Will always act selfishly

Result: No one was able to watch demo

Question: Why not cooperate ???




IIT Madras Cooperation

Sourc

e: K

.J. R

ay

Liu

, Spec

trum

Apri

l 2011

Cooperation Sharing information

Control Channel essential for users to share information




IIT Madras SDR Today

Ref: www.vanu.com

A commercial product

Multistandard, multichannel GSM / GPRS / EDGE

CDMA / EV-DO

Flexibility

Scaleability

Cost-effectiveness




IIT Madras

SDR Cognitive Radio




IIT Madras

SDR Cognitive Radio

Cognitive Radio =

SDR + Sense + Learn + Adapt + Use

SDR Frequency + Waveform Agility

Wideband RF Frontend

High speed

DSP




IIT Madras Cognitive Radio Motivation

Increasing demand for radio spectrum

Broadband wireless demand is rapidly growing

Current approach to spectrum allocation Fixed allocation to licensed users

Existing scenario Under-utilization of spectrum

Spatial and temporal spectral holes exist

Innovative approach to improve spectrum utilization Cognitive Radio

Initiated by FCC regarding secondary usage of spectrum

Cognitive Radio techniques much broader than DSA A radio that is aware of its surroundings and adapts intelligently

Reed et al.




IIT Madras

SDR Cognitive Radio




IIT Madras

Spectrum Sensing




IIT Madras Methods of Spectrum Sensing

Energy Detector

Correlation-based detector

Cyclostationarity-based detector

Hybrid Detector

Filter bank Method Multi-taper Method (MTM)

Sensing Criteria (Regulatory)

Sensing Period

Detection Sensitivity




IIT Madras Aspects of Spectrum Sensing

Time-varying channel

Lack of apriori information

SNR level, interference,

Signal blockage (shadowing, hidden-node)

Primary signal transition ON OFF

Single shot detection vs. sequential detection

Interference due to other CR users

Decentralized vs centralized approach

Cooperative sensing

Control channel for information sharing




IIT Madras

Frequency

T

I

M

E

Spectral Adaptation Waveforms

OFDM in Cognitive Radio

Ref: B. Fette, SDR Technology Implementation for the Cognitive Radio, General Dynamics

OFDM Orthogonal Frequency Division Multiplexing - Multicarrier modulation

Non-Contiguous OFDM (for CR)

Multiple Access OFDM




IIT Madras

Control Channel in Cellular Systems




IIT Madras Radio Interface Protocol

User Plane Radio

Bearers

PDCP

BMC

Logical Channels

Transport Channels

Control Plane User Plane

RRC

Signaling Radio

Bearers

RLC

MAC

PHY

L3 radio network

layer

L2 radio link

layer

L1 radio physical

layer




IIT Madras Radio Interface Protocols

Physical Layer (PHY) Transport data from higher layers via physical channels

Provides transport channels to the MAC layer

Dedicated channels and Common channels

Medium Access Control (MAC) Provides services to RLC via logical channels

Logical channels characterized by type of data carried

Traffic channels and Control channels

Radio Link Control (RLC) Reliable data transmission in control plane and user plane

Radio Resource Control (RRC) Present in both control plane and user plane protocol stacks

Controls all radio-related functionality




IIT Madras GSM Control Channels

Frequency Correction Channel (FCCH)

BTS is Master; MS is Slave (DL only)

Reference tone (unmodulated carrier +67.7 KHz)

Synchronization Channel (SCH)

Information for frame synchronization

Base station ID, TDMA frame number within hyperframe (0,275647),

Broadcast Control Channel (BCCH)

Broadcasts (to all mobiles) general information about cell

Location area identity, Max transmit power on RACH, Min. Rx level for access

Configuration of common control channels

Paging Channel (PCH)

Random Access Channel (RACH)

Slotted Aloha, channel shared by all mobiles

Control channel essential for effective communications




IIT Madras GSM Logical Channels

Logical Channels

Control

Channels

Traffic

Channels

Full rate

Half rate

Physical channel one time-slot on a GSM carrier Many logical channels multiplexed on single physical channel

Dedicated

CC Broadcast

CC

Common

CC

FCCH

SCH

BCCH

RACH

PCH

AGCH

SDCCH

SACCH/FACCH




IIT Madras

Bluetooth & ZigBee




IIT Madras Bluetooth

Universal radio interface

Operates in 2.4 GHz ISM band (license-free, globally)

Short range connectivity

Adhoc networks

Multiple simultaneous links

Low-power, low-cost

1 Mbps, bidirectional

Range: 10-100m

Advantages over Infrared - NLOS

Line-of-sight

Ref: J. Haartsen, Ericsson Review, 1998





Time Division Duplex (TDD) single frequency Tx/Rx

Symmetric and asymmetric transmission

Timeslot duration 625 microsecs

2.4 GHz unlicensed ISM band

Interference: Microwave ovens, cordless,

Frequency hopping to avoid interference

Pseudo-random hop sequence

If collision occurs

Error correction mechanisms will correct errors






Piconets / scatternets for adhoc connectivity

Synchronous and Asynchronous connections

Voice and real-time applications

Packet-data applications

Master unit and slave units

Master controls all timing in piconet

Supports authentication and encryption





IIT Madras Bluetooth Networking Bluetooth units within range adhoc connection Piconets (peer-to-peer)

One unit assumes role of Master (establishes piconet)

BT units in Standby Mode

Subset of 32 carriers (out of 69) as wake-up carriers

Chosen by own identity

Wake-up sequence visit each wake-up carrier once

Listening interval = 18 slots (Correlate incoming signal with own identity)

Establish Connection (via Inquiry)

Transmit inquiry access code (common to all BT units)

Inquiry wake-up carriers

Recipient responds with ID and clock

Paging to establish connection





IIT Madras ZigBee

For Control and Sensor Networks

Based on the IEEE 802.15.4 Standard

Ref: Diamond et al., ZigBee Presentation, EE 418/518

PHY 868MHz / 915MHz / 2.4GHz

MAC

Network

Star / Mesh / Cluster-Tree

Security 32- / 64- / 128-bit encryption

Application

API

ZigBee

Alliance

IEEE

802.15.4

Customer

Silicon Stack App

ZigBee Alliance

Network, Security & Application layers

IEEE 802.15.4

PHY and MAC specifications

Focus on low data rate, long battery life

and secure networking

Supports wireless mesh networking




IIT Madras ZigBee Specifications

Dual PHY (2.4GHz and 868/915 MHz)

Data rates 250 kbps (2.4 GHz), 40 kbps (915 MHz), and 20 kbps (868 MHz)

Direct Sequence Spread Spectrum (CDMA)

Optimized for low duty-cycle applications (




IIT Madras ZigBee Beacon Method

ZigBee routers transmit periodic beacons

to confirm their presence to other network nodes

Nodes sleep between beacons, lowering their duty cycle and extending battery life

Beacon intervals depend on data rate

Range from 15.36 msec - 251.66 sec at 250kbps

24 msec - 393.216 sec at 40 kbps

48 msec - 786.432 seconds at 20 kbps

Low duty cycle operation with long beacon intervals requires precise timing

ZigBee protocols minimize radio ON time reduce power use

Beaconing networks

Nodes active only during beacon transmission




IIT Madras Observations

Bluetooth

Frequency hopping

Peer-to-peer

Scatternets

ZigBee

Direct Sequence Spread Spectrum

Mesh network

FFD and RFD

Coordinator, Router, End Device

Beacon and Non-beacon mode

Well-defined MAC protocols are key




IIT Madras

Control Channel in CR Networks




IIT Madras Cognitive MAC

MAC protocols + Spectrum Sensing Spectrum Opportunity map

MAC enables

Dynamic Spectrum Access

Dynamic Spectrum Sharing

Dynamic Spectrum Mobility

CR MAC classification

Functionality, role

Design aspects

Secondary users parameters RF power, information rate, codebook, used channel

Coordinate access to available channels, avoid collisions

Multichannel MAC for adhoc wireless networks Hidden terminal problem




IIT Madras Control Channel

Requirements

Information sharing in cooperative spectrum sensing

Broadcasting spectrum-aware routeing information

Coordinating spectrum access

Needed for peer-to-peer and for infrastructure-based

Common Control Channel (CCC)

Always ON

Reliable

Robust to unpredictability of PU activity

Scenario

PU may force CCC to change frequency

CRs unable to negotiate new CCC freq

To Study

Design challenges

CCC design schemes

Issues

Robustness

Coverage

Security

Efficiency

Signaling




IIT Madras CR-MAC Categories

Direct Access Based (DAB)

No global optimization

Each sender-receiver pair maximizes its optimization goal

Resource negotiation via sender-receiver handshake protocol

A simple protocol architecture

Minimizes computational cost and latency

Dynamic Spectrum Access (DSA)

Exploits complex optimization

Achieve a global purpose

Adaptive approaches

Ref: Domenico et al, IEEE Surveys & Tutorials, 2012




IIT Madras CR-MAC Categories

Distributed architectures

Distributed robustness

Centralized architecture

Single node coordinates

Information exchange

Radio access

May exploit access to complementary information

Cognitive Pilot Scheme (CPC)

Common Spectrum Cordination Channel (CSCC)

Operators, RATs and frequencies allocated in a given area

Cognitive terminals reduced scanning requirements

Improve co-existence with Primary Users




IIT Madras Out-of-Band CC

Channel 0 CC

Channels 1,2,3 data

Option 2

Channel 0

Control + Data

Channels 1,2,3 data

Split Phase

In-band CC

Channel 0, 1, 2, 3

Control + Data




IIT Madras Out-of-Band CC

Common Control Channel

Dedicated channel

Users share information

Singalling information, sensing outcome, channel selection

Does not require time synchronization

Requires dedicated receiver

Split Phase

Works with single receiver

Cost of synchronization overhead

Divide time frames into two parts

Control phase

All terminals hear the network status

Data phase

Transmissions are performed

Resources wasted during Control Phase




IIT Madras Common Control Channel

CCC Medium for control message exchange between CR users

CCC facilitates the following

Transmitter (Tx) Receiver (Rx) handshake

Neighbour discovery

Channel access negotiation

Sharing of information regarding PU activity

Topology change

Routeing information update

Cooperation between CR users

CRs show their presence by broadcasting on CCC

Non CR networks CCC is well-defined and fixed Dedicated CCC

Example: Cellular

CCC design impacts CR performance

Tradeoff between

CCC establishment overhead and CR performance




IIT Madras Classification

Underlay

Using same spectrum as PU

Spread spectrum (UWB)

Unaffected by PU activity

Dedicated

Overlay

Non-overlapping with PU

In-band versus Out-of-band

Control and data on shared resources (In-band)

Number of radios required

Is separate radio needed for CCC ?

Does CCC design require synchronization of all CR users ?

Does CCC include mechanism for Neighbour discovery

Other aspects

CCC Saturation, Robustness to PU activity, Coverage, Jamming

Ref: B.F.Lo, Elsevier, Physical Comm, 2011




IIT Madras CCC Aspects

Control Channel Saturation

Throughput degradation

Collision of control packets

Function of network load

Likely to occur on Dedicated CCC

Well-known techniques to alleviate overload

Limit the Control traffic

Challenge for cooperative sensing

Quantization of sensing data

Frequency of reporting of sensing data

Variable CCC bandwidth Dynamic channelization

Robustness to PU Activity

Primary challenge in CR Networks

Not an issue for Out-of-band CCC

Can use licensed or unlicensed bands (ISM)

Sequence based (Frequency Hopped) CCC is more robust to PU





Robustness to PU Activity

How soon can CCC be re-established

Channel evacuation protocol

If PU is detected

CR broadcasts warning

A pre-defined warning message

All CR users stop transmission to avoid interference to PU

Proposal: Warning message via CDMA signal with predefined code

CDMA signals are robust to PU and minimize interferece

Reactive way of protecting PU

Does not address re-establishment of new CCC

Sequence based (Frequency Hopped) CCC is more robust to PU

Diversity of CCC allocation

At the cost of stringent synchronization





CCC Coverage

Spectrum heterogeneity

not all CRs listening to same CCC

Larger coverage efficient signaling

Desireable to increase CCC coverage

Coverage Set of CR users tuned to CCC

In geographic proximity

For Sequence-based CCC Coverage is usually limited to node pair

Focus on rendezvous of transmitting and receiving nodes

Group-based CCC CCC Coverage varies with group size

CCC Security

Jamming CCC Denial of Service Protect single point of failure




IIT Madras CCC Security

CCC facilitates cooperation

CR Users

Network operations

CCC exposed to security attacks

Jamming CCC Denial of Service

Strong interfering signal to the CCC

Protect single point of failure

Reliability of CCC affects reliability of entire network

Use of Spread Spectrum Techniques

Pseudo-random channel access Unknown to attackers

Ineffective if compromised by one of the CR users

Anti-Jamming via Dynamic CCC allocation

Cross channel Communication

Frequency Hopping

Anti-Jamming via CCC Key distribution




IIT Madras Classification

Overlay

Non-overlapping with PU

In-band versus Out-of-band

Control and data on shared resources (In-band)

In-band schemes local

Susceptible to PU activity re-establishment of CCC

Variation based on location

Link-based and Group-based designs

Out-of-band schemes dedicated, global (not affected by PU activity)

Wider coverage, usage of unlicensed bands

Option of licensed band of CR operator




IIT Madras Sequence-Based CCC

Random or pre-determined Hopping Sequence

Spread Spectrum technique

Interference immunity

Diversify CCC allocation over time and frequency

Pairs of CRs use different frequencies

In same neighbourhood

Also referred as Multiple Rendezvous Control Channel (MRCC)

Hopping sequence is key to performance

Pseudo-random

Permutation-based

Adaptive MRCC

Key issues

Synchronization of all CR users

Vulnerability to jamming

Time-to-Rendezvous (TTR) may be long if there are large number of channels




IIT Madras Sequence-Based CCC

Permutation-based Hopping Sequences

CRs construct non-orthogonal hopping sequences

Permutations of the available channels

Hopping sequence can be adapted

Adaptive MRCC

A channel ranking table (increasing order of PU activity)

Based on periodic sensing

Biased Random Sequence Generator

Longer dwell times can be provided to high-ranking channels

Challenges Creation of Broadcast capability in neighbourhood coverage

Method suitable for pairwise connections

Responding to PU activity




IIT Madras Dedicated CCC

Pre-defined Common Control Channel

Reserved for all the secondary users

Channel general not used by the Primary User

Advantages:

Network-wide CCC has lower coordination overhead between groups of CRs

Allows for scalability

Avoids need for maintaining specialized network topologies for the CCC operation

Initial setup times and overheads are minimized

Disadvantages:

Difficult to have a dedicated channel (in licensed band)

Unlicensed bands are unreliable

Opportunistic CCC

Exploit a spectrum hole in licensed bands

Implementing in-band signaling on the available channels

Send beacon messages on the available channels




IIT Madras Ultra Wideband (UWB)

Cognitive network an interconnection set of CR devices

Devices sharing of information to facilitate CR functions

Suitable control channel needed collaboration between CR nodes

Ultra Wideband (UWB)

Bandwidth (BW) > 500 MHz or

Fractional BW

FCC permits unlicensed use of UWB (2002)

Methods for UWB

OFDM-based UWB

(OFDM-UWB)

Impulse radio based UWB

(IR-UWB)

2.0

2

LH

LH

ff

ff

Source: Arslan et al., Cognitive

Wireless Communication Networks,

Springer




IIT Madras UWB-based CCC

Each CR node is equipped with UWB interface

For CCC

Other radio interfaces for data communication

UWB cause negligible interference to NB systems

Using a common spreading code, nodes discover each other

UWB radio interfaces with low complexity and power consumption

May be able to achieve radio range of 100 m

UWB spreading code common to all nodes

After two nodes connect, fix spreading code message exchange

Accessing CCC via Aloha scheme

Commonly used in UWB systems




IIT Madras Research / Design Challenges

CCC Design

Security of CC seldom addressed in licensed systems

Anti-Jamming techniques widely known

New challenges in CR networks

Impact of jamming on PU Activity

Will affect CC of CR Network

Needs to be investigated

CRAHN Cognitive Radio Ad Hoc Networks

CCC jamming in CRAHN

Does not have single node with authority for coordinated action

Cluster-based CCC

Challenge if Cluster Head is compromised

Key Issue - Jamming-resilient CCC Scheme




IIT Madras 802.22 Spectrum Sensing

IEEE 802.22 CR-based WRAN PHY and MAC layer protocols

Contention based DAB protocol with centralised architecture

Each cell Base station (BS) + Associated Secondary users (CPEs)

BS and CPEs perform in-band and out-of-band sensing

BS indicates the channels to sense, sensing period and false alarm

Two stage sensing

Fast Sensing rapid measurements 1 msec (per channel)

Fine Sensing 25 msec (per channel) Search for particular signatures of licensed transmissions

Avoid intra-network interferencce




IIT Madras 802.22 Dynamic Frequency Hopping

Increase 802.22 performance

Communicating on Channel i (in-band channel)

Observe availability of next working Channel j (Out of band)

To avoid interference to PU, CR network hops to Channel j

Begin sensing on Channel i

Each user has two receivers

Sensing and transmission done in parallel

Simultaneous Sensing and Data Transmission (SSDT)

Guard bands mitigate interference

Dynamic Frequency Hopping Community (DFHC) of coordinated WRANs




IIT Madras 802.22 Double Frequency Hopping

Double Hopping for three neighbouring cells

Tdata = Transmit time, Tsens = Sensing time

No transmission during Quiet period (QP)

After Tdata, hop to Sensing Frequency and after Tsens return to working frequency

Max number of

Neighbour cells

= Tdata / Tsens




IIT Madras Summary

The context of Cognitive Radio

A paradigm shift in wireless communications

Role of Common control channels (CCC)

Cellular, Bluetooth, Zigbee

Aspects of CCC for CRs

Design of CCC

CCC a key enabler for CR Networking

Exploit the full potential of CR technology

Significant effort needed to design CCC

Overall, CR is an exciting field




IIT Madras

Best wishes to all participants

of TVWS & CR Workshop

Thank You !

Q&A

[email protected]




IIT Madras David Koilpillai Profile

Education

B.Tech, IIT Madras, MS, PhD Caltech, USA

Work Experience IIT Madras (2002 present)

Professor, Electrical Engineering Department

Dean (Planning) (October 2011 present)

CEWiT Chief Scientist (Jan 2007 July 2007)

Co-Chair, IIT Hyderabad Task Force (June 2008 Dec 2009) Ericsson Inc, USA (1990-2002)

Director, Advanced Technologies, Research and Patents

(R&D team of 75 engineers)

Professional Areas of expertise: Cellular, wireless systems, DSP

32 Issued US patents, 3 Indian patent applications

Publications: 11 Journal, 45 Conference

Research Interests: Broadband wireless communications, 4G cellular, Cognitive Radio

Ericsson Inventor of Year Award 1999

Fellow, Indian National Academy of Engineering

Iitk Cognitive Radio research

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