WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Cooperative Wireless
Networking: User-centric
networking in the wireless domain
WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Challenges for current systems
 Multimedia applications
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Explosion of wireless data traffic
Error sensitive or delay intolerant
 Wireless channels
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Bandwidth and power limited
Multi-user interference
Unreliable due to signal fading
 Spectrum efficiency is still low at cell edge
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Stations transmit at a much lower data rate compared to peak rate.
Packet transmission for station at the edge takes much longer time
Higher interference levels at the cell edge.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Position Statement
 Wireless channel by nature is a broadcast one.
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The broadcast channel can be fully exploited for broadcast traffic.
But it is considered more as a foe than a friend, when it comes to
unicast.
 Cooperative communications allows the overheard information
be treated as useful signals, instead of interference.
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Relays process this overheard information and forward to
destination.
Network performance improved because edge nodes transmit at
higher rate and spectrum efficiency is improved.
Candidate relays? Mobile user, macro/pico-cell BS, fixed relays,
femto-cell BS, etc.
What are the incentives? Throughput, power, interference.
 A cross-layer design encompassing physical, MAC, network and
application layers is required to address this problem.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Future Research
 Heterogeneous wireless networks – classic macrocell
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architecture reaching its limits
Multilayered networks: Macrocells, picocells,
femtocells, relays, user equipment?
Multi-radio multiband devices: LTE, WiFi, Bluetooth,
WiMAX
Cooperation across these layers and bands
Sophisticated interference management within a
given spectrum and location
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Interference management
 Information theory tells us: Low interference - treat as
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noise, high interference - subtract out, medium
interference: use orthogonal channels
Competing top-down strategy: COMP (Cooperative
Multipoint): Will probably win out over bottom up
approaches in the medium term?
Use backhaul for interference signaling to implement
the above – but at what bandwidth and latency cost?
Or perhaps use an interference sensing approach
with distributed (end system) scheduling (a bit like
multihop ad hoc)
But macrocells still the safety net network (the new
satellite network)
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Research Team @ NYU-Poly
 NYU-Poly’s Wireless Internet Center for Advanced
Technology (WICAT) has focused on cooperative
networking as a signature project, with a history of
close collaboration between all the PIs involved in
this project.
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Elza Erkip is an expert in information theory and the physical
layer.
Shivendra Panwar's research focuses on multimedia
networking and cooperative MAC protocols.
Yao Wang is an expert in video processing and networked
video applications
Sundeep Rangan is a pioneer and expert in cellular
technologies
This team has pursued multiple jointly funded NSF projects
and joint papers.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Research Team @ NYU-Poly
 Our lab facilities provide an ideal setting to facilitate
technology transfer.
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We are equipped with 15 ORBIT nodes, 9 WARP SDR
boards, and an NEC WiMAX base station as part of the
GENI project.
We have prototyped cooperative physical layer, MAC layer
and video transmissions on those platforms.
We are participating by advocating relaying technologies in
standard bodies, and are active members in the IEEE
802.11 and IEEE 802.16 committees.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
For more information, please visit
http://coop.poly.edu
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Our Prior Work
 Physical layer: Cooperative coding
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Seminal paper on cooperative communications.
Sending parity bits over relay improves diversity.
 MAC layer: Cooperative MAC for IEEE 802.11
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Enabled signaling for cooperation in WiFi.
An intermediate station (relay) is allowed to forward a frame from
the source station to the destination station.
 Application layer: Video transmissions with one relay
and multiple relays with sequential transmission
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Synergy between cooperation and layered compression.
 Stronger protection for important layers through cooperation.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Cooperative/Virtual MIMO
 Limitations of previous cooperative methods.
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Single relay: low spatial diversity gain.
Multiple relays: consume more bandwidth resource when
several relays sequentially forward signals.
 Any alternatives?
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Recruit multiple relays to form a virtual MIMO.
Pros: Spatial diversity gains
Constraints:
 Relays need to be indexed, leading to considerable signaling
cost.
 Global channel state information needed.
 Relays not selected cannot forward, sacrificing potential gains.
 Availability of multiple relays?
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Robust Cooperative MIMO
 Randomized cooperation strategies provide powerful PHY layer
coding techniques that
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Alleviate the previous problems and allows robust and realistic
cooperative transmission with multiple relays.
Randomized distributed space-time coding (R-DSTC) for diversity.
Randomized distributed spatial multiplexing (R-DSM) for spatial
multiplexing.
 Highlights for randomized cooperation include:
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The relays are not chosen a-priori to mimic particular antennas.
Multiple relays can be recruited on-the-fly.
Opportunistically use relays according to instantaneous fading
levels.
This greatly reduces signaling overheads and channel feedback.
Enjoys performance comparable to centralized MIMO.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Video Streaming with R-DSTC
 Scenario: BS unicast video to
one MS.
 Both hops can operate at
much higher data rate
compared to direct
transmissions.
 For IEEE 802.11g, video
streaming rate can be
improved up to 4.5 times
(assuming both hop rates are
the peak data rate).
 Each hop rate and spacetime code dimension can be
adjusted to provide unequal
error protection for layered
video.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Video Upload Using R-DSM
 Scenario: A mobile device
with M antennas to the BS
with N antennas (N>M).
 If source can recruit enough
relays, spatial multiplexing
gain of N is achievable.
 Video streaming rate can be
improved up to 7 times (IEEE
802.11g, four antennas AP,
one antenna MS).
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Two-Way Real-Time Video
 Scenario: Video conferencing
/Internet video chatting.
 R-DSTC and network coding
are employed for higher
efficiency.
 Video rate can be improved
up to 6 times (factor 4.5 for
R-DSTC and factor 4/3 for
network coding).
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Video Multicast Using R-DSTC
 Scenario: BS/AP
multicast/broadcast video to
MS’s.
 Cooperation is a natural fit for
video multicast.
 Multicast must handle
receiver heterogeneity in
channel conditions. Only
base rate can guarantee full
coverage.
 With cooperation, it is
possible to transmit at peak
rate in both hops. Video rate
can be improved up to 4.5
times (IEEE 802.11g).
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Cooperative MIMO for Heterogeneous
Networks
 It enables fully opportunistic use of all available radios and
reduces number of handovers for smaller cell sizes.
 Signaling can be over macro-cell and data over femto, wireless
relay or pico-cells.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
The second-last mile problem
 Explosively increasing traffic demand
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More than 3 billion cell phones by 2009
Increasing number of data intensive applications
3G/4G standards are pushing up the macrocell data rates
(~100 Mbps)
 Poor Cellular infrastructure
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Most of the BS backhauls use 4 T1/E1 lines (up to 8 Mbps)
Adding BSs or updating data lines is expensive (more than
$10,000 per line and $50,000 per site annually)
 Macrocell backhaul
has become the
bottleneck!
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Femtocell Concept
 A femtocell is a low-power and low-cost base station
overlaid on the existing cellular network
 Spatial Reuse: Enables femtocells to provide significant gain in capacity while
saving the user’s battery use.
 Home Broadband Connection: carries the
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traffic originally transported on the macrocell
backhaul, reducing the load on the macrocell
backhaul.
But macrocell backhaul is still the bottleneck
for users outside femtocell.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Solution: FemtoHaul
 System Architecture for FemtoHaul
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FemtoHaul is a novel solution to the macrocell backhaul problem.
In FemtoHaul, the femto
backhaul is used to carry nonfemto user traffic by forwarding
through a relay.
 Detailed Design
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Channel allocation
mechanism based on
OFDMA WiMAX;
Policy for base stations to
schedule user transmissions.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
FemtoHaul Performance Evaluation
 Backhaul Supply
 Average Download Rate
Rate Comparison
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in Stationary Scenario
Simulations demonstrate that our solution can significantly reduce the
macrocell backhaul traffic while still guaranteeing a high rate to the
subscribers
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Where our work fits in
 Our work on cooperative networking, can extend the life of this
infrastructure by providing the 4-7X gains.
 Ad hoc networking will play a part in vehicular networks and
provide coverage in areas with poor cellular service (“few hop
not multi-hop networking”).
 Cooperative networking, employing cooperative PHY and MAC
layer forwarding, can be used either instead of, or combined
with, traditional store and forward (network layer) ad hoc
networking.
 Application layer methods (other than video coding) are also
essential to address the bandwidth needs of video, such as
content caching and P2P techniques.
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WIRELESS INTERNET CENTER FOR ADVANCED TECHNOLOGY
NSF INDUSTRY/UNIVERSITY COOPERATIVE RESEARCH CENTER
Relationship to emerging trends
 The future network architecture is heterogeneous, with macro-,
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pico- and femto-cells, along with WiFi and (some) ad hoc
networking.
In our view, a large part of the 66X increase predicted by Cisco
will be drained by increased deployment of WiFi, femto/picocells
for stationary or slow moving users.
Femtocells, in particular, are the carrier’s Trojan Horse!
Macrocell bandwidth, which is really the main bottleneck, should
be used only when there is no alternative (like satellite networks
are today).
Cooperative networking can be used in this emerging
environment by using user end devices, femtocells, WiFi access
points, picocells, and macrocell infrastructure as the devices
that constitute the cooperating nodes.
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