next generation wireless networks: research challenges and opportunities abhay karandikar professor...

Next Generation Wireless Networks: Research Challenges

and Opportunities

Abhay KarandikarProfessorDepartment of Electrical EngineeringIndian Institute of Technology Bombay, Mumbai [email protected]

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mailto:[email protected]

OutlineGlobal Wireless ScenarioIndian ScenarioKey Research Issues and Technology Components of 4GOur Contributions to 4G

Bandwidth Request Procedure in IEEE 802.16mEnergy Efficient Scheduling over Wireless Channels

Going Forward: Towards Bridging the Digital Divide

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Drivers for Broadband

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Peer-to-peer Audio/ Video/ Images Real-Time games

Social CommunitiesOpen-Source

News

VoIPEmail SearchApplications

Plethora of services causing Internet traffic to grow 50% every year

Wireless Broadband

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GSM / EDGE

HSDPA

WCDMA / EVDO

HSPA (3G)

ADSL

ADSL2+

LTE / EVDO-Rev C (UMB)

IMT-A (4G)

VDSLGDON

Ethernet

WiMAX

10x

Kbps

1x

Mbps

100

x

Mbps

Data

Rate

Fixed Mobile

Timelines for IMT-Advanced (4G)

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2008 2009 2010 2011 2012 2013

Proposals

Evaluation

Consensus

Specification Early Deployment

Global Scenario

Nations are becoming increasingly aware of IPR and use their IPR reserves to position trade policyChina – good example

Has pushed its IPR in major 3G/4G standards

Balance of IPR is shifting40% essential patents from Asia




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iPhone Example

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• 700+ Million Cellphone subscribers– Second largest telecom market in the

world

• Fewer products made in India – large part is still imported – Second largest import after Oil

• High outflow of Foreign Currency– Several $$ outflow per handset

• Only country in the top telecom markets with no umbrella body focusing on standards

• Low Geographical Coverage– Only 60% of India– 25% of villages covered

• Very Low Broadband penetration

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Scenario in India

Population Density Map(source: www.reliefweb.int)




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Technology Components for 4G

OFDMA

Multi-Antenna (MIMO)

Spectrum flexibility and Carrier aggregation

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Time

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11

2 233

3Frequency

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Diversity Beamforming

BS BS

Aggregated carriers = 40 MHz

20 MHz 20 MHz

Technology Components for 4GSelf organization and Self optimization

Relaying

Enhanced Quality of Service support

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access link

relay link access link

BSRS




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Wireless Uplink Scheduling

SS1

SS2

SS3

SS4

BS

Requests

Grants

BS computes non-conflicting

schedule

Bandwidth Request (BR) Procedure

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IEEE 802.16mAdvanced Mobile

Station (AMS)IEEE 802.16m

Advanced Base Station (ABS) Gold AMS Silver AMS Bronze AMS

BR Opportunities

ContentionWindow

Contention Window Doubled

•AMS waits for a random number of BR Opportunities •Number of BR opportunities to wait chosen from

Contention Window•Common channel for all AMS

Time

BR collision GrantGrant

CurrentTimeCurrent Time

Drawbacks of BR Procedure

No differentiationNo differentiation in window size based on service class

Lacks fairnessNew users can get channel before old users

Scaling factor of 2 is used independent of System loadNumber of retries

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Current Time

Connection Priority (CP) for each contending Service FlowCP is a function of Service Class & Number of Retries (BR collisions) CP parameters:

Service ClassInitial / Maximum Window SizeWindow Scaling Factor

Our BR Proposal (IEEE C80216m-09_1321r4)

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IEEE 802.16mAdvanced Mobile

Station (AMS)

IEEE 802.16mAdvanced Base

Station (ABS) Gold AMS Silver AMS Bronze AMSContention

WindowContention WindowChanged as per CP

Time

BR collision GrantCurrentTime




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Wireless Channel CharacteristicsWireless Channel is characterized by

Signal strength variation over time, frequency and spaceSmall scale variation (Fading)

InterferenceLimited battery life at hosts

Physical Layer no longer a fixed rate bit pipe

Resource allocation needs to take channel characteristics into account

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Significant performance gains in wireless networks by Cross-Layer Design

SNR Fluctuations in a Multiuser System

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User 2

User 3User 3

User 1

SNR

Time

Multiuser Diversity: A New Form of Diversity

Channel fades independently for each user so …Different users experience different channel gains

High probability that some user will have a strong channelBS schedules the user with the strongest (best) channelHence … “Opportunistic Scheduling”Transmitting in favorable channel condition also minimizes power but at the expense of delayScheduling- Power is minimized subject to delay constraint

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Energy EfficiencyRate-Power relationship is convex

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Rate (R)

Pow

er

(P)

R1

P1

P2

R2

R2 = 2R1

P2 > 2P1

Energy Efficient SchedulingSingle Receiver (Base Station) and multiple transmittersBase station is the centralized scheduler

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Energy Efficient SchedulingQueue transition, average queue length, average power for user i

Problem: Minimize the power consumption of each user subject to delay constraint of each user

Multi-objective constrained optimization problem

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in

in

in

in

in

in

in QRARIQQ ,11

M

n

inM

M

i QQ1

1suplim

M

n

in

in

inM

M

i RIXPP1

1 ),(suplim

NiQP iii ,,1, subject to Minimize

Uplink SolutionVisualize a link between user and base station as a Point-to-Point scenarioEach user

Determines its transmission rate as if it was the only userInforms this rate to the base station

The base station schedules the user with the highest rateQueue transitions for a user who is scheduled and not for othersPower and queue cost are appropriately updated

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Base Station Scheduler

(User selection policy)

UpdatePhase

RateDeterminition

Phase

User i

InformScheduling

Decision

Inform rate to Base Station

Uplink Solution : Auction InterpretationThe base station auctions each time slotThe user quoting the highest rate wins the bidUser quote rates that are just sufficient to satisfy their delay constraintsQuoting unnecessarily high rates not favorable since power minimization is the objectiveIt can be proved that the queue lengths converge to cooperative equilibrium and delay constraints are satisfied

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Nitin Salodkar, Abhay Karandikar, Vivek Borkar, “A Stable On-line algorithm for Energy Efficient Scheduling” IEEE Transactions on Mobile Computing October 2010




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Driving Research Agenda

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Challenges

Backhaul connectivityLow cost wireless backhaul

Low ARPULow cost infrastructure Tight integration with IP

Infrastructure sharing

DSL like experienceArchitecture for high speedHigh speed spectral efficiency at cell edge

Power SupplyVery high energy efficiency

Present ScenarioBackhaul

PSTN

TDM/ ATM/IP / MPLS

EdgeRouter

Internet

Voice VideoAudio

Packet switching

Node

Gateway

Access & Devices Core Services Backhaul

TDM / ATM/ETHERNET

MSC

GSM /EDGE

UMTS/ HSPA

WiFi

BSC/RNC

Data centre

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DSLAM

•Optimized MAC for outdoor point to point link•Interference management for multi-hop link•E1 circuit emulation for Legacy access GSM/CDMA)

•Inexpensive radio (<$50)•Low power (<10 W)•License free band•But designed for Indoor

WiFi long distance link Benefits

Technical Innovation

IP over Distributed Cellular Architecture

Present Scenario - Hierarchical Wireless access connect to packet core

Heavy Link LayerHandover and QoS at accessNetwork Discovery and topology between access and coreIP attachment at core

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IP over Distributed Cellular Architecture

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TDM/ ATM/IP / MPLS

Wireless access network as IP network of base stations

Base station cooperate to manage topology discovery

TDM/ ATM/IP / MPLS

Mobility, QoS and network discovery managed at IP layer

Self Configuring Distributed Architecture

IP

IP

Concluding RemarksIndia – one of the largest telecom marketIndian requirements and IPR must get reflected into international standards

Significant opportunity to push our research into next generation wireless networksThis will catalyze manufacturing scenario in India

We have outlined representative effortsBandwidth Request procedures for QoS in 4GEnergy Efficient Scheduling

More efforts needed- academia and research labs need to address relevant research problems

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Acknowledgements

Joint work with

Prateek Kapadia, Gauri Joshi, B Srinadh, Dr Nitin Salodkar. Prof Bhaskaran Raman (IITB), Prof Vivek Borkar (TIFR)

Funding support from TTSL-IIT Bombay Center for Excellence in Telecom (TICET)

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next generation wireless networks: research challenges and opportunities abhay karandikar professor...

Documents

wireless channels

wireless broadband

asia slide

year slide

technology components

g bandwidth request

global scenario nations

g self organization