Next Generation Wireless Networks: Research Challenges and Opportunities Abhay Karandikar Professor...
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Transcript of 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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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
2
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
3
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
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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• 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)
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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Technology Components for 4G
OFDMA
Multi-Antenna (MIMO)
Spectrum flexibility and Carrier aggregation
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Time
23
11
2 233
3Frequency
23
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
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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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
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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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
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
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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
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
28
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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