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R2D2: Embracing Device-to-Device Communication in Next Generation Cellular Networks. Tarun Bansal*, Karthik Sundaresan + , Sampath Rangarajan + and Prasun Sinha* Speaker: Zhixue Lu* * Ohio State University and + NEC Labs America. Device-to-Device (D2D) Communication. - PowerPoint PPT Presentation
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R2D2: Embracing Device-to-Device Communication in Next Generation Cellular Networks
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Tarun Bansal*, Karthik Sundaresan+, Sampath Rangarajan+ and Prasun Sinha*
Speaker: Zhixue Lu*
*Ohio State University and +NEC Labs America
Device-to-Device (D2D) Communication Normally smartphones communicate with each other through
cellular base station
2
Without D2D With D2D
D2D Traffic Applications
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(a) Base Station Assisted: Localized communication and Machine-to-
Machine (M2M) communication
Benefit: Service provider helps with security, neighbor discovery and ensuring Quality-of-
Service
(b) Peer-to-Peer: Public Safety when traditional infrastructure is not available
Benefit: No interference
Our focus is on integration of Base Station Assisted D2D Traffic withexisting cellular communication
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D2D Benefits Spatial Reuse of Resources
– Multiple D2D transmissions per cell [Janis 2009, Doppler 2009, Lee 2013]
D1 D2
D4
D4
D1
D2Cell divided into 3 sectors with each sector covering
120o
Not possible to schedule multiple
D2D transmissions in the same sector.
D3
D3
Our analysis for sectored deployments: Very little benefit from additional spatial reuse
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D2D Benefits (contd.)
Offloading– Fewer time slots taken [Janis 2009, Doppler 2009, Lee 2013]
Time slot 1 Time slot 2
Time slot 1
Without D2D With D2D
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Benefit of D2D in sectored deployments(Static Channel Allocation)
Offload benefit is significant (1 time slot instead of 2)
Additional Spatial Reuse benefit (due to D2D) is not significant in sectored deployments due to small sector size
0 10 20 30 4010
15
20
25
30
35
40
No D2D Baseline
D2D Baseline
D2D Genie
D2D Traffic (in %)
Thro
ughp
ut (i
n M
bps) Spatial Reuse
BenefitOffload Benefit
D2Dclassifiedas cellular
Tries to schedule
multiple D2D transmissions
per sector
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Identifying third D2D Benefit: Flexible Load
Use as flexible load– Resources need to be fixed in both Uplink and Downlink directions– In practice, UL-DL traffic distribution varies both in space and time e.g. residential
vs. commercial, morning vs. evening – D2D can go on either on the Uplink or Downlink resources– Use resources that would have been otherwise wasted
time
frequency
D2D flows
time
frequency
Uplink Flows Downlink Flows
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D2D Benefits
Offloading (1 time slot instead of 2)
Use as flexible traffic (Place on either DL or UL resource)
How do we maximize these two benefits?
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Static vs. Dynamic Channel Allocation
Static Channel Allocation
Dynamic Channel Allocation leverages spatial
traffic variations
Two co-located sectors
can have the same channel
Too much traffic: Borrow channels from neighboring sectors
Interior Channels Exterior Channels
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Challenges in Incorporating D2D with Dynamic Channel Allocation
UL or DL communications (directional) can still go simultaneously
D2D (omnidirectional) may cause interference to coexisting transmissions in sectored deployments (not considered before)
Determining interference from D2D transmission requires knowledge of path loss between all users (costly).
D1
D3D2
Similarly, D2D transmission cannot coexistwith UL or D2D
D2D presents a new challenge: Transmissions may cause interference if co-located sectors are using the same resource.
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D2D Interference (Dynamic Channel Allocation)
0 10 20 30 4050
60
70
80
90
D2D Baseline
No D2D Baseline
D2D Traffic (in %)
Thro
ughp
ut (i
n M
bps)
Lower throughput with D2D due to collisions among neighboring sectors
D2Dclassifiedas cellular
Omnidirectional nature of D2D makes it non-trivial to schedule transmissions
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Objective• How to do dynamic resource allocation in multi-cell deployments
with D2D traffic?
• How to schedule UL, DL and D2D transmissions while avoiding interference?
• Previous work only looks at resource allocation without D2D traffic, OR
Scheduling with D2D in single cell deployments with no sectorization.
R2D2 Contributions A light-weight scalable solution (R2D2) that works at two
different time-scales
– Phase 1: Allocate resources to each base station at coarser time scale (cross-sectors)
– Phase 2: Allocate resources to each flow independently at each base station at finer time scale (co-located sectors) while avoiding interference
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R2D2 Contributions Practical: Works in sectored deployments with multiple cells
Proposed multiple scheduling algorithms with provable guarantees
Showed using simulation results that proposed algorithms perform close to optimal in practice
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Phase 1: Cross-Base Station Resource Allocation
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Cell\ Historical Demand
DL UL D2D
Cell J X X X
Cell L X X X
Cell M X X X
Resources Available
X X
Input
Cell\ Resources Allocated
DL UL
Cell J X X
Cell L X X
Cell M X X
OutputR2D2Phase 1
Algorithm
J ML
Phase 1: Cross-Sectors Resource Allocation
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Objective: Allocate UL and DL resources across 3 sectors in each of the directions
Proposed algorithm satisfies following properties:‒ Flexibly places the D2D traffic on UL and DL resources
‒ Localized and Scalable
‒ Ensure no interference across sectors belonging to different base stations
See Paper for more constraints and detailed solution
Phase 2: Per-frame Scheduling
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D1
D2
D3
Each sector was a part of different interfering
set in Phase 1:
Same resourcemay get assigned toco-located sectors
Phase 2: Per-frame Scheduling (contd.)
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Schedule UL, DL and D2D transmissions such that total throughput is maximized while avoiding interference
‒ Assign a time-frequency resource block to each flow in the three sectors
‒ Challenge: Path loss information between devices is unknown
D1
D2
D3
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Phase 2 Contributions
Scheduling algorithms at each Base Station:– A greedy polynomial algorithm with approximation ratio
of ½
– A faster greedy polynomial algorithm with approximation ratio of ¼
– More challenging since D2D can go on either DL resources or UL, but not both
• A greedy polynomial algorithm with approximation ratio of 1/3
Time-Divisioned System
Frequency-Divisioned
System
See Paper for detailed solutions
Simulation Setup Simulation with 19 base stations and 57 sectors
– Modeled practical parameters including path loss, shadowing
Other algorithms simulated– R2D2 Low Complexity
– D2D Dynamic Genie (Optimal, knows path loss information between all users)
– No D2D Dynamic (Uses dynamic resource allocation and classifies all D2D traffic as Cellular)
– Existing Algorithm Static (Uses static resource allocation and does not use D2D as flexible traffic, Janis et al., IJCNS 2009) 20
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Results with variation in D2 traffic R2D2 Low Complexity
performs within 5% of optimal
R2D2 Low Complexity gives a throughput of 2.5x and 4.9x compared to existing solution and No D2D, respectively
Benefits coming from‒ Intelligent resource
allocation during Phase 1 while placing D2D traffic flexibly
‒ Interference-free scheduling during Phase 2
2.5x4.9xwithin
5%
0 10 20 30 400
30
60
90
120
150
180
R2D2 Low Complexity D2D Dynamic Genie
No D2D Dynamic Janis et al. Static
D2D Traffic (in %)
Tota
l Thr
ough
put (
in M
bps)
22
Conclusions Investigated the problem of incorporating D2D
communication in next generation cellular deployments with sectorization
Identified a new benefit of D2D communications: Flexibility‒ Towards that, proposed a solution that works at two different time
granularities that ensures scalability‒ Synergy between the two phases makes R2D2 light weight while
avoiding all interference
Proposed multiple algorithms with provable approximation ratios for resource allocation and scheduling
Thank You