Frequency Reuse Techniques for Attaining both … Reuse Techniques for Attaining both Coverage and...
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Zheng Xie, ComNets, RWTH Aachen University Frequency Reuse Techniques for Attaining both Coverage and High System Capacity in OFDMA Cellular Systems Dipl.-Inform. Zheng Xie March 12th, 2010, Aachen, Germany 17. FFV-Workshop 2010
Transcript of Frequency Reuse Techniques for Attaining both … Reuse Techniques for Attaining both Coverage and...
Zheng Xie, ComNets, RWTH Aachen University
Frequency Reuse Techniques for Attaining both Coverage and High
System Capacity in OFDMA Cellular Systems
Dipl.-Inform. Zheng Xie
March 12th, 2010, Aachen, Germany
17. FFV-Workshop 2010
2Zheng Xie, ComNets, RWTH Aachen University
Contents
• Introduction
• Soft Frequency Reuse (SFR)
• Incremental Frequency Reuse (IFR)
• Enhanced Fractional Frequency Reuse (EFFR)
• Performance Evaluation
• Conclusion
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
3Zheng Xie, ComNets, RWTH Aachen University
Motivation
• Classical frequency reuse factor 1Heavy inter-cell interference (ICI), especially near cell edgeinferior area coveragelower cell capacity
High spectrum usage
• Conventional frequency reuse factor 3 or 7 Reduced inter-cell interference (ICI) Better cell coverage
Lower system spectrum efficiencyLow cell capacity
• Highly desirable of interference limited system while retaining system spectrum efficiency of reuse 1
Resource Reuse to enhance system capacity
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
4Zheng Xie, ComNets, RWTH Aachen University
Frequency Reuse Techniques
• Soft Frequency Reuse (SFR) Scheme
– Adopted in the 3GPP-LTE system
– Overcome severe ICI for cell edge users by increasing• Frequency reuse factor
• Transmission power
• Incremental Frequency Reuse (IFR) Scheme
– Ki Tae Kim, 2008
– ICI avoidance for low loading traffic
• Enhanced Fractional Frequency Reuse (EFFR) scheme
– ComNets
– Enhancement design based on IFR & SFR
NEW
Most promising approaches
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
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Soft Frequency Reuse (1/2)
f5
f2
f11
f7
f4
f5
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Cell
C
Cell
B
Cell
B
Cell
B
Cell
A
Cell
C
Cell
C
Reuse factor 1 cell-center users (CCU)
Reuse factor 3 cell-edge users (CEU)
• CCU
– Whole bandwidth
– Lower power
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
• CEU
– 1/3 bandwidth: Major Segment
– Higher power
P(f)
P(f)
P(f)
f
f
f
Cell A
Cell B
Cell C
major subchannel
normal subchannel
Benefits
• ICI mitigation at cell edge
• Improved bit rate at cell edge
• Improvement of cell coverage & capacity
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Soft Frequency Reuse (2/2)
f4
Limitations
1. Key issue: zone definition for CCUs and CEUs
2. Low spectrum reuse efficiency
– More CEUs, less CCUs
– Less available resource for CEUs, whereas more for CCUs
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
P(f)
P(f)
P(f)
f
f
f
Cell A
Cell B
Cell C
occupied idle
3. More co-channel interferences even at low loading traffic situation
4. CEUs still grievously interfered by co-users in the neighboring cells
– Inclusive reuse for CEUs
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Incremental Frequency Reuse
Cell B
Cell C
Cell C
Cell A
Cell B
Cell C
Cell B
Frequency reuse factor 1
Different start point of subchannel assignment in neighboring cells static
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
1
f
Cell A
Cell B
Cell C
Start point of subchannel allocation
2 3 4 5 6 7 8 9
7
f
8 9 1 2 3 4 5 6
4
f
5 6 7 8 9 1 2 3
Benefits
• Part of the limitations by applying SFR eliminated
• Effective ICI avoidance with low offered traffic
Limitations
• Not better than the classical reuse-1 system in full-load situation
8Zheng Xie, ComNets, RWTH Aachen University
Enhanced Fractional Frequency Reuse (1/2)
f5
f2
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f4
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Cell A
Cell C
Cell B Cell B
Cell B
Cell CCell C
FSUM - F1 - F4 - F7
F1 F4 F7
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
Entire frequency spectrum divided into 2 segments
- Primary Segment: orthogonal among neighboring cells
- Secondary Segment
f
Primary Segment
f
f
reuse-3 subchannel for each type of cell
reuse-1 subchannel in the Primary Segment
Quality good for
me, try to occupy
idle subchannel
reusing secondary subchannel after CQI estimation
P(f)
P(f)
P(f)
F2
F2
F2
F1 F3
F3
F3
F9F5
F4 F5
F5
F6
F6
F6 F7
F8
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F8
F9
F9
Cell A
Cell B
Cell C
Exclusive reuse-3 subchannels in Primary Segment
- PriorityCEU > PriorityCCU
- Higher transmission power
Reuse-1 subchannels
- Lower transmission power
9Zheng Xie, ComNets, RWTH Aachen University
Enhanced Fractional Frequency Reuse (2/2)
f5
f2
f11
f7
f4
f5
f12
Cell A
Cell C
Cell B Cell B
Cell B
Cell CCell C
FSUM - F1 - F4 - F7
F1 F4 F7
Resource allocation
1. Primary Segment occupation
- CEUs reuse-3 subchannels
- CCUs reuse-1 subchannels
2. Secondary Segment occupation
- Monitor before use
- Interference-aware reuse: SINR estimation
f
Primary Segment
f
f
reuse-3 subchannel for each type of cell
reuse-1 subchannel in the Primary Segment
Quality good for
me, try to occupy
idle subchannel
reusing secondary subchannel after CQI estimation
P(f)
P(f)
P(f)
F2
F2
F2
F1 F3
F3
F3
F9F5
F4 F5
F5
F6
F6
F6 F7
F8
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F8
F9
F9
Cell A
Cell B
Cell C
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
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ScenarioContents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
• Implementation of SFR, IFR & EFFR in OpenWNS simulation environment
• EFFR with three M to N combinations
– M: number of reuse-3 subchannels in Primary Segment
– N: number of reuse-1 subchannels in Primary Segment
• Scenarios with surrounding cells up to 2nd-tier
• Constant total system transmission power assumption
– Max. transmission power of UT: 23dBm
– SFR & EFFR: α
• UL considered
• UTs uniformly distributed in each cell
3High LowP P
11Zheng Xie, ComNets, RWTH Aachen University
Mean cell capacity with 25 users in each cell
• Increasing offered traffic per use
– r/R = 0.5
Simulation parameter
System bandwidth: 20 MHz
Center frequency: 5470 MHz
Subcarriers (FFT size): 2048
Subchannls: 30
OFDMA symbol duration:
102.858 µs
Frame length: 10 ms
DL : UL-ratio: 1:1
Cell radius: 1100m
Path loss exponent: 2.9
Interfering cells: 18
(up to 2 tiers)
Traffic model: symmetric,
neg. exp IAT
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
_
CCURadius
Cell Radius
12Zheng Xie, ComNets, RWTH Aachen University
Mean throughput with 15 users in each cell
• Mean weakest user throughput Coverage
• Mean overall cell capacity
- 333 kbps offered traffic per user- Zone for weakest users: 900m – 1100
Contents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
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ConclusionContents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
• For wide area coverage & high system capacity
– SFR & IFR overview
– Design of an EFFR scheme for ICI mitigation & implementation in OpenWNS
• Exclusive reuse partitioning
• Power allocation
• Interference-aware reuse mechanism
• Theses: EFFR achieves
– Effective ICI limitation at cell edge
– Effective ICI avoidance with low offered traffic
– Substantial improvements in terms of both overall cell capacity & the cell coverage
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Thank you for your attention !
Zheng Xie
Any questions?
15Zheng Xie, ComNets, RWTH Aachen University
ScenarioContents – Introduction – SFR – IFR – EFFR – Performance Evaluation – Conclusion
• Implementation of SFR, IFR & EFFR in OpenWNS simulation environment
• EFFR with three M to N combinations
– M: number of reuse-3 subchannels in Primary Segment
– N: number of reuse-1 subchannels in Primary Segment
• Constant total system transmission power assumption
– Max. transmission power of UT: 200mW
• Scenario with surrounding cells up to 2nd-tier
• UL considered
P(f)
f
Cell A
P(f)
f
Cell B
P(f)
f
Cell C
P(f)
fP(f)
fP(f)
f
P(f)
f
P(f)
f
P(f)
fP(f)
fP(f)
f
P(f)
f
(a) Classical reuse-1 & IFR (b) SFR (c) EFFR (d) Classical reuse-3
