decentralized interference management for two-tier … · decentralized interference management ......
TRANSCRIPT
AS Madhukumar
School of Computer Engineering
Nanyang Technological University, Singapore
Outline
February 18, 2013 School of Computer Engineering 1
Introduction
Femtocell Network Issues
Interference Management : A Review
Decentralized Interference Management
Through Femto-Relays
Through Reverse Frequency Allocation
Future Work
Conclusion
Introduction
The wireless capacity has doubled every 30 months since the last 104 years. This
translates into an approximately million-fold capacity increase since 1957.
Breaking down these gains shows the technology contributions as :
– Wider spectrum [25x]
– Spectrum slicing [5x]
– Better modulation and coding [5x]
– Topology and smaller cells [1600x]
M.-S Alouini and A. J. Goldsmith, “Area Spectral Efficiency of Cellular Mobile Radio Systems,” IEEE
Trans.Vehic. Tech., vol. 48, no. 4, July 1999, pp. 1047–66.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
1,000,000=25x5x5x1600
Small cell seem to be the
key factor for improving
future network capacity
Introduction
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This rapid increase in mobile data activity has raised the stakes on developing innovative new
technologies and cellular topologies that can meet these demands in an energy efficient manner
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Introduction
Engineers brought in cellular hierarchy into the legacy cellular network to reduce load on the
macrocell base station and hence increase the coverage.
This resulted in reducing the cell size into still smaller cells creating a cellular pattern within
the existing cellular architecture.
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Small cells provide coverage extension and boost local capacity with
minimal expense and planning.
2G 3G
4G
As throughput demand and usage
increased, cell size decreased
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femtocell Solution
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– Small size cellular base stations for residential
or small business environments
– Use full strength mobile technology but with
simpler deployment
– Connects through internet grade backhaul.
– Operates in licensed spectrum.
– Typically support 2-6 concurrent users
– Available at prices compatible with Wi-Fi
access points.
– Alternative of Fixed Mobile Convergence.
– The concept is applicable to all wireless standards,
including UMTS, GSM, CDMA-2000 and WiMAX solutions.
Vikram Chandrasekhar and Jeffrey G. Andrews, “Femtocell Networks: A Survey,” IEEE Communications
Magazine, September 2008.
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femtocell Network
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femtocell Network Issues
Network Architecture
Mobility Management and Handovers
Self Organization
Security
Timing and Synchronization
Interference Management
L. Perez, D. Valcarce, A.D. Roche, G.J. Zhang, OFDMA femtocells: A roadmap on interference avoidance IEEE Comm.. Mag, vol. 47, no. 9, pp. 41-48, Sept.2009.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femtocell Network Issues
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Irregular deployment will incur inevitable interference
FC
FC
FC FC
FC
FC
FC
MC 1
FC
FC
FC FC
FC
FC
FC
FC
FC
FC
FC
MC 2
FC
FC
FC
FC
FC
FC
MC : Macro Cell
FC : Femto Cell
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Interference Management
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Types of Interference
– Co-tier Interference FBS to FBS Interference (relatively small
due to lower power and wall loss)
– Cross-Tier Interference • MBS to FBS Interference
• FBS to MBS Interference Femtocell
Macrocell
Femtocell
Femtocell
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Interference Management
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UE ASSOCIATION
A : MBS → FUE (DL)
B : MUE → FBS (UL)
C : FBS → MUE (DL)
D : FUE → MBS (UL)
E : FBS → FUE (DL)
F : FUE → FBS (UL)
A
B
C
D
E
F
Interference Scenarios
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Interference Management Techniques
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Zahir, T., Arshad, K., Nakata, A., Moessner.K., “Interference Management in Femtocells ,” IEEE Communications
Surveys & Tutorials, vol. PP, issue 99, pp. 1-19, February 2012.
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
• Interference Cancellation
– Successive Interference
Cancellation
– Parallel Interference
Cancellation
– Multi-Stage Interference
Cancellation
– Multi-User Detection
• Interference Avoidance
– Spectrum Splitting
– Power Control
– Time Hopping
– Spectrum Arrangement
• Fractional frequency
Reuse
• Soft frequency Reuse
– Resource Allocation
– Spectrum Sensing
• Cognitive Femtocells
– Inter-cell coordination
• Distributed Interference
Management
– Distributed power control
algorithm
– Distributed dynamic inter-
cell interference avoidance
scheme
– Geo-static power control
scheme
– Adaptive power control
scheme
– Pilot power minimization
scheme
Decentralized Interference Management
– Minimal involvement of a centralized controller
– No disturbance to the legacy macrocell network
– Base stations will self-configure, self-optimize and self-
heal.
– Rely more on existing architecture, framework and
resources to improve the system performance.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays Challenges
– Ever increasing demand for data intensive applications.
– Excessive load on the macrocell network.
– Increase in call drops due to limited macrocell backhaul.
– Dead-zones created in the macrocell coverage area.
– Extensive high density deployment of femtocells which seem to be
under-utilized.
– Limited coverage area of femtocells.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays Solutions – How to offload the heavy traffic from the macrocell network
• Increasing base station density through small cells or femtocells.
• Cisco expects that by 2015, over 800 million terabytes of mobile data traffic will be offloaded to the fixed network by means of femtocells.
• Telecoms & Media expects the small cell market to experience significant growth over the next few years, reaching just under 60 million femtocell access points in the market by 2015.
– Is the capacity of these femtocells fully exploited? • Obviously NO.
– How to make use of the large number of under utilized femtocells? • Extending the coverage of femtocells beyond the home environment to serve
macrocell users as well.
– How to extend femtocell coverage beyond the home environment? • Through relay nodes a.k.a FEMTO-RELAYS
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays A novel air interface solution which integrates multihop
transmission into femtocell networks.
– Extends the coverage further, even beyond the home
environment.
– Accommodate more users.
– Higher capacity gains in both Uplink and Downlink direction.
– Improved data rate offered by the femtocells.
– Power efficiency offered by multi-hop transmission.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays : System Model
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays : System Architecture
Assumptions
– Each user is capable of sensing the pilot signal channels from the Macro Cell
Base Station [ MBS] as well as from the nearby femtocell which helps it in
updating its Neighboring Cell List [NCL].
– MBS always maintains information about the femtocells and the UEs
associated with the femtocells, within its coverage area.
– The voice calls being highly delay sensitive will be served by the MBS itself
except for that of the registered femtocell users
– When the UE needs to make a high data rate request, it notifies the same to the
MBSby sending the NCL (Neighboring Cell List) along with its request.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays : System Architecture
– On reception of request from the UE, MBS makes a decision on whether to
serve it by itself or through the femtocell based on:
• Available Macrocell Backhaul.
• Average Backhaul Utilization greater than the Backhaul Utilization Threshold.
– If the MBS does not have sufficient resources, it initiates the handover of the
request to a femtocell chosen from the NCL based on two factors:
• Number of idle users attached to the femtocell.
• Largest value for available uplink data rate to average uplink data rate usage ratio.
– The femtocell now connects with the UE through multiple hops, the first hop
being to its associated user and the next hop from the associated user to the
destination UE.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays : Performance Analysis
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Assuming multi-hop routes support the worst hop SIR and that; an optimal SIR and hence
capacity is achieved when relay node is located half way between the FBS and MUE:
Femto-Relays : Performance Analysis
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Simulation Parameters
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays: Results Uplink Capacity Gain
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• Uplink capacity gain
increases with decrease in
femtocell transmit power
• Largest multihop capacity
gains are experienced at the
lower SNRs, where the
SNR improvements due to
relaying have the greatest
effect.
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
50 100 150 200 250 300
5
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
Number of femtocells
Uplin
k C
apacity g
ain
of
Fem
to w
ith R
ela
yin
g
Capacity analysis with respect to number of femtocells
-25 dB
-20 dB
-15 dB
-10 dB
-5 dB
Femto-Relays: Results
Downlink Capacity Gain
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50 100 150 200 250 300
5
5.2
5.4
5.6
5.8
6
Number of femtocells
Dow
nlin
k C
apacity G
ain
of
Fem
to w
ith R
ela
yin
g
Capacity analysis with respect to number of femtocells
-20 db
-10 db
0 db
10 db Capacity gain increases with
decrease in femtocell transmit
power and reaches almost a stable
state at about -20 dB.
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays: Results
Coverage Extension Outage Probability
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-100 -80 -60 -40 -20 0 200
50
100
150
200
250
Femtocell maximum transmit power (dBm)
Covera
ge r
adiu
s (
m)
Coverage of femtocells
With dual hop
Direct transmission
-150 -140 -130 -120 -110 -100 -90 -80 -70 -60
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Tsnr (dB)
Outa
ge P
robability
Outage Probability Analysis
Direct mode
Femto-relay mode
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays: Results
Dead Zone Control
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-90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -40
5
10
15
20
25
30
35
40
45
Macrocell RSSI
Deadzone R
adiu
s
Deadzone radius analysis with respect to femtocell transmit power
-20 db
-10 db
0 db
10 db
20db
• Dead zone radius is dependent on FBS
transmit power for constant MCBS RSSI
• Dead zone radius can be decreased by
reducing the femtocell transmit power.
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Femto-Relays: Benefits Power efficient
Extends the coverage of femtocells to accommodate more users.
Reduction in interference to macrocell network.
Offloads the load on macrocell network.
Provides better capacity gains in uplink and downlink.
Improvised dead zone control.
Reduced outage probability.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Challenges
– Decrease in cell size and increase in BS density followed by the need for more
frequency carriers.
– The available radio spectrum is a finite, scarce and expensive resource.
– Femtocells operating on same licensed spectrum as that of macrocells resulting
in interference.
– Demand for high data rate multimedia applications requiring larger bandwidth
increasing day by day.
– Higher bandwidth requirement in the downlink than in the uplink.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Reverse Frequency Allocation (RFA)
Reverse Frequency Allocation (RFA)
Solutions
• Shared spectrum usage
• Results in higher cross-tier interference
• Dedicated spectrum usage
• Results in spectral inefficiency
• A hybrid spectrum allocation scheme incorporating
advantages of both is the need of the hour.
• Hence the Reverse Frequency Allocation scheme was
proposed.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Frequencyf1 f2
Femtocell
Macrocell
Frequencyf1 f2
Femtocell
Macrocell
Reverse Frequency Allocation (RFA)
• A novel spectrum utilization method that assures increased spectral efficiency and reduced interference in FDD operation.
• It does not need any dedicated spectrum allocation for femtocells.
• The entire macrocell spectrum is made available to the femtocell in the reversed fashion.
• “Reverse Frequency” means that the UL frequency of the MUE is allocated as the DL frequency for the FBS and the DL frequency of the MBS is allocated as the UL frequency for the FUE.
• To bring about better interference avoidance, we partition the cell into cell-center region (inner region) and cell-edge region (outer region) and allocate complementary frequency spectrum in both these regions.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
February 18, 2013 School of Computer Engineering 31
UPLINK
FCFC
FC
FC
FC
FC
DOWNLINK
FCFC
FC
FC
FC
FC
System Model
MC FC
FCFC
FC
FCFC
FC
FCFC
FC
FCFC
MC
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Comparison
Region Interferers In
Conventional
Method
Interferers In Soft
Frequency Reuse
Method
Interferers In RFA
Method
Inner Region
Femtocells
MBS and FBS in
the inner and outer
region
MBS and FBS in the
inner region
FBS in the inner region
and MUEs in the outer
region
Outer Region
Femtocells
MBS and FBS in
the inner and outer
region
MBS and FBS in the
outer region
FBS in the outer region
and MUEs in the inner
region
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Reverse Frequency Allocation (RFA)
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
RFA: Performance Analysis
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𝑆𝐼𝑁𝑅𝐷𝐿_Fi= 𝑃𝑖𝑙
𝐼j𝑙𝐹𝑖
𝑗=1,𝑗≠𝑖 + 𝐼k 𝑙 + 𝜎2𝑀𝑜
𝑘=1
𝑆𝐼𝑁𝑅𝐷𝐿_Fo= 𝑃𝑖𝑙
𝐼j𝑙𝐹𝑜
𝑗=1,𝑗≠𝑖 + 𝐼k 𝑙 + 𝜎2𝑀𝑖
𝑘=1
𝑆𝐼𝑁𝑅𝑈𝐿_Fi = 𝑃𝑙𝑖
𝐼j𝑖𝐹𝑖
𝑗=1,𝑗≠𝑙 + 𝐼k𝑖 + 𝜎2𝑀𝑜
𝑘=1
𝑆𝐼𝑁𝑅𝑈𝐿_Fo = 𝑃𝑙𝑖
𝐼j𝑖𝐹𝑜
𝑗=1,𝑗≠𝑙 + 𝐼k𝑖𝑀𝑖
𝑘=1 + 𝜎2
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
RFA: Performance Analysis
February 18, 2013 School of Computer Engineering 35
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Outage probability
RFA: Results DL Capacity Comparison
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150 200 250 300 350 400 450 500 550
5.2
5.3
5.4
5.5
5.6
5.7
5.8
5.9
6
6.1
x 107
Distance from the Macro cell
Thro
ughput
Downlink Capacity analysis of femtocells
Reverse UL-DL Allocation
Soft frequency
Conventional Method
Inner region Outer region
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
150 200 250 300 350 400 450 500 5500.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
x 108
Distance from the Macro cell
Thro
ughput
Downlink Capacity analysis of Femto-Macro System
Reverse Frequency Allocation
Soft Frequency Allocation
Conventional Method
Inner region Outer region
RFA: Results Outage Probability
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
150 200 250 300 350 400 450 500 550
0.17
0.175
0.18
0.185
0.19
0.195
Distance from the Macro cell
Outa
ge P
robabili
ty
Outage Probability Analysis of femtocells
Reverse Frequency Allocation
Soft Frequency Allocation
Conventional Method
RFA Benefits
Femtocells and macrocells making use of independent frequency resource in a
given direction (say UL /DL), assures minimal interference.
Increase in Downlink throughput helps to meet the ever increasing consumer
demands.
Doubles the spectral efficiency.
Requires neither any complex power control scheme nor any signal exchange
between the FBS and the MBS.
FBS coverage area is not restricted due to power control even if the femtocell is
located closer to the MBS.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Future Work Advanced Decision Algorithm for Coverage Management and Intelligent Handovers
– Enable the femtocells to dynamically adapt their coverage radius through cell breathing
– Carry out intelligent handoff management to load balance users across the tiers. • Minimize frequent handoffs through proper maintenance of coverage
radius and thereby conserve FAP power
• Reduce traffic in the backbone network
• Introduce cluster algorithm that groups femtocell into different frequency reuse clusters.
• Handoffs will be initiated among clusters.
• Figure out the algorithm for cluster head selection and optimal resource allocation for each cluster.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Future Work
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Femtocell Clusters that can initiate intelligent handovers
Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Future Work Self Organizing Femtocells with Adaptive Access and
Adaptive Power Control – Smart planning algorithms to enable femtocells in making their own decision
based on the channel conditions and information from its neighbors.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Future Work Distributed Interference Management for dense
deployment of closed subscriber femtocell groups
– Involves the development of a hybrid scheme that ensures
• Minimize additional load on the legacy operator infrastructure
• Scalability to millions of femtocell units in the same network
• Suitable admission control mechanisms
• Introducing orthogonally polarized transmissions in two-tier networks
for interference mitigation.
• Open-standard management interface, with reduced interactions with
the femtocell management systems.
• Complexity as minimal as possible
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion
Conclusion
Technical challenges confronting tiered cellular wireless systems were addressed which include :
– Coverage extension
– Interference reduction
– Power control
– Accommodating more users with the existing cellular architecture
– Intelligent allocation of spectrum in both the tiers
– Improving system capacity
Femto-Relays helps in coverage extension and power savings along with interference management
Reverse Frequency Allocation maximizes the spatial reuse in two-tier networks employing OFDMA, while guaranteeing a minimum desirable quality-of-service to users in either tier.
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Introduction Femtocell Network Issues Interference Management Femto-Relays Reverse Frequency Allocation Future Work Conclusion