1 11 frequency reuse techniques for attaining both coverage and high spectral efficiency in ofdma...
DESCRIPTION
3 Frequency Reuse Factor Effective reuse of resources can highly enhance the system capacity Frequency reuse factor (FRF) K defines frequency reuse pattern With a smaller frequency reuse factor (FRF), more available bandwidth can be obtained by each cellTRANSCRIPT
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Frequency Reuse Techniques for Attaining both Coverage and
High Spectral Efficiency in OFDMA Cellular Systems
Zheng Xie and Bernhard Walke
RWTH Aachen UniversityAachen, Germany
WCNC 2010
222
Outline Introduction Previous Schemes
Soft Frequency Reuse (SFR) Incremental Frequency Reuse (IFR)
Enhanced Fractional Frequency Reuse (EFFR) Evaluation Conclusion
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Frequency Reuse Factor Effective reuse of resources can highly enhance
the system capacity Frequency reuse factor (FRF) K defines frequency
reuse pattern
With a smaller frequency reuse factor (FRF), more available bandwidth can be obtained by each cell
4
Previous Frequency Reuse Schemes With the usage of FRF-1, the most user terminals (UTs) are
afflicted with heavy Inter-cell interference (ICI) Especially near the cell edge
The conventional method to figure out this problem is by increasing the FRF mitigate the ICI efficiently but decrease on available bandwidth
The most representative approaches improving cell-edge performance while retaining spectrum efficiency Soft Frequency Reuse (SFR) scheme Incremental Frequency Reuse (IFR) scheme
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Soft Frequency Reuse (SFR) Scheme
CCU: cell-centre usersCEU: cell-edge users
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Limitations of SFR How to define the borderline to divide cell area for CCUs
and CEUs is a key issue Generally, there are more CEUs than CCUs in a cell
since the outer surface area is much larger than the inner part CEUs have maximum one third of the entire bandwidth to utilize,
which results in lower spectrum efficiency
More ICI could happen even in a low traffic-load situation, while there are still subchannels in idle and underutilized in the system The resource allocation via the SFR scheme starts always from
the first subchannel up
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Incremental Frequency Reuse (IFR) Scheme (1) The only difference between the IFR design and
the classical reuse-1 Classical reuse-1: allocate resources always from the
first subchannel IFR: start dispensing resources from different points
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Incremental Frequency Reuse (IFR) Scheme (2) IFR scheme can overcome the low spectrum reuse
efficiency problem and the more ICI at low loading traffic problem
IFR scheme only performs better when just fewer traffic exists in a system When the loading factor is greater than 0.3, it is
inferior to the SFR scheme
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Enhanced Fractional Frequency Reuse (EFFR) (1) Enhanced Fractional Frequency Reuse (EFFR) scheme
intends to retain the advantages of the both approaches Concept
Define 3 cell types for directly contiguous cells in a cellular system Reserves for each cell-type a part of the whole frequency band named
Primary Segment The Primary Segments among different type cells should be
orthogonal The Primary Segment of each cell will be further divided into
reuse-3 part: cannot be reused by directly neighboring cells reuse-1 part: is at the same time a part of the Secondary Segments
belonging to the other two cell-types
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Enhanced Fractional Frequency Reuse (EFFR) (2)
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Power Allocation and SINR Estimation Transmission Power Allocation
Any cell-type is not allowed to use the reuse-3 subchannels dedicated to the other two cell types The power allotted to the reuse-3 subchannels can be tripled
Signal-to-Interference-Ratio (SINR) Estimation A cell acts on the Secondary Segment as a guest, and occupying
secondary subchannels is actually reuse the primary subchannels belonging to the directly adjacent cells
Reuse on the Secondary Segment should conform to two rules: monitor before use resource reuse based on SINR estimation
Each cell listens on every secondary subchannel all the time Before occupation, a cell makes SINR evaluation and chooses resources
with best estimation values for reuse If all available secondary resources are either occupied or not good
enough to a link, this cell will give up scheduling resources
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Resource Allocation The reuse-3 subchannels will be assigned to CEUs
If there are still resources remained after all CEUs are served, they will be continuing allotted to such CCUs with relatively poor SINR values
When the reuse-3 subchannels are exhausted, the remaining reuse-1 subchannels in the Primary Segment are allocated to residual unsatisfied users
If still resources are requested, available reuse-1 subchannels in the Secondary Segment will be scheduled to adequate users by applying interference-aware-operation
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Distinctions between the EFFR Scheme and the Two Aforementioned Schemes
CEUs are very susceptible against ICI, the reuse-3 subchannels in the Primary Segment are exclusively available for the users
To reduce excessive ICI to the neighboring cells, packets will be sent on a reuse-1 subchannel in lower strength
Allocation of reuse-1 subchannels in the Secondary Segment is not blindly carried out, but in an interference-aware way according to SINR estimation
In the Primary Segment unsatisfied users, whether they are CCUs or CEUs, have the same chance to get resources in the Secondary Segment
IFR SFREFFR
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Relevant Factors The following relevant factors play paramount
roles and could influence the system performance The ratio of the number of reuse-3 subchannels M to
reuse-1 subchannels N in the Primary Segment The power ratio of high power level to low power level Range definition for partition of CCUs and CEUs
This is the first work to present simulation results of the SFR scheme with varying range definitions
SINR threshold for reuse
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Simulation Environment (1) Simulation Tool
The Open Wireless Network Simulator (OpenWNS)
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Simulation Environment (2) For all simulations
We consider an OFDMA uplink cellular system in an omni-cell case
UTs are uniformly distributed within each hexagonal cell Each UT has a maximal transmission power of 200mW
Different cell specific power
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Scenario with 15 UTs in each cellMean Overall Uplink Cell Capacity
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Scenario with 15 UTs in each cellMean Weakest User Uplink Throughput
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Scenario with 25 UTs in each cellMean Overall Uplink Cell Capacity
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Scenario with 25 UTs in each cellMean Weakest User Uplink Throughput
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Conclusion A novel frequency reuse technique named the EFFR
scheme for ICI mitigation in OFDMA networks is proposed
The EFFR scheme uses dedicated FRF-3 and higher transmission power for CEU allows CCU to occupy resources with FRF-1 and interference
awareness
With respect to the range definition for division CCU-zone and CEU-zone, the EFFR scheme can provide more flexibility and robustness than the SFR scheme