22 nd September 2008 | Tariciso F. Maciel Suboptimal Resource Allocation for Multi-User MIMO-OFDMA...
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Transcript of 22 nd September 2008 | Tariciso F. Maciel Suboptimal Resource Allocation for Multi-User MIMO-OFDMA...
22nd September 2008 | Tariciso F. Maciel
Suboptimal Resource Allocation forMulti-User MIMO-OFDMA Systems
Tarcisio F. Maciel
Darmstadt, 22nd September 2008
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 2
Outline
1. Resource Allocation Problem Overview
2. Suboptimal Resource Allocation Strategies: Single Resource
3. Suboptimal Resource Allocation Strategies: Multiple Resources
4. Conclusions and Outlook
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 3
Outline
1. Resource Allocation Problem Overview
2. Suboptimal Resource Allocation Strategies: Single Resource
3. Suboptimal Resource Allocation Strategies: Multiple Resources
4. Conclusions and Outlook
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 4
Resource Allocation Problem OverviewScenario and Optimization Objective
Frequency Division Multiple Access (FDMA)
Fre
quen
cyTime
…
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 5
Resource Allocation Problem OverviewScenario and Optimization Objective
Time Division Multiple Access (TDMA)
Fre
quen
cyTime
…
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 6
Resource Allocation Problem OverviewScenario and Optimization Objective
Current systems FDMA/TDMA (e.g., GSM)
Fre
quen
cyTime
…
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 7
Resource Allocation Problem OverviewScenario and Optimization Objective
Fre
quen
cy
Time
Space
Future mobile radio systems High flexibility and high capacity
Orthogonal Frequency Division Multiple Access (OFDMA)
Multiple Input Multiple Output (MIMO) Space Division Multiple Access (SDMA)
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 8
Resource Allocation Problem OverviewScenario and Optimization Objective
Fre
quen
cy
Time
Space
Future systems High flexibility and high capacity
Orthogonal Frequency Division Multiple Access (OFDMA)
Multiple Input Multiple Output (MIMO) Space Division Multiple Access (SDMA)
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 9
Resource Allocation Problem OverviewDescription of Subproblems
Users must be separable in space Many possible groups of users Finding the group with highest
capacity requires an Exhaustive Search
SDMA groupingproblem
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 10
Resource Allocation Problem OverviewDescription of Subproblems
Users must be separable in space Many possible groups of users Finding the group with highest
capacity requires an Exhaustive Search
SDMA groupingproblem
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 11
Resource Allocation Problem OverviewDescription of Subproblems
Beamforming done at the base station Linear precoding used to compute
precoding vectors and form beams
SDMA groupingproblem
Precoding problem
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 12
Resource Allocation Problem OverviewDescription of Subproblems
How should power be allocated to the different users served by the system
SDMA groupingproblem
Precoding problem
Power allocation problem
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 13
Resource Allocation Problem OverviewDescription of Subproblems
How should power be allocated to the different users served by the system
SDMA groupingproblem
Precoding problem
Power allocation problem
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 14
Resource Allocation Problem OverviewDescription of Subproblems
Fre
quen
cy
Time
Space
Resource 1
Resource 2
SDMA groupingproblem
Resource assignmentproblem
Precoding problem
Power allocation problem
Objective Maximize the capacityof the system
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 15
Resource Allocation Problem OverviewDescription of Subproblems
Resource assignment problem
Precoding problem
SDMA grouping problem
Power allocation problem
Joint solution of the subproblems
Separated solutionsto the subproblems
RA strategy Optimal Suboptimal Complexity Too high Low
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 16
Resource Allocation Problem OverviewDescription of Subproblems
Resource assignment problem
Resource assignment algorithm
Precoding problem Precoding algorithm
SDMA grouping problem
SDMA algorithm
Power allocation problem Power allocation algorithm
Joint solution of the subproblems
Separated solutionsto the subproblems
RA strategy Optimal Suboptimal Complexity Too high Low
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 17
Resource Allocation Strategies
Resource assignment algorithm
Precoding algorithm
SDMA algorithm
Power allocation algorithm
Single-resource case Multiple-resource case
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 18
Outline
1. Resource Allocation Problem Overview
2. Suboptimal Resource Allocation Strategies: Single Resource
3. Suboptimal Resource Allocation Strategies: Multiple Resources
4. Conclusions and Outlook
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 19
Resource Allocation Strategies: Single Resource
Resource assignment algorithm
Precoding algorithm
SDMA algorithm
Power allocation algorithm
Single-resource case Multiple-resource case
•Grouping metric
•Grouping
algorithm
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 20
SDMA algorithmGrouping metric
Group capacity Suitable to maximize sum rate, but quite complex
Convex combination of spatial correlation and channel gains Less complex than group capacity
Spatially uncorrelated
h2
h2 h1
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 21
SDMA algorithmGrouping metric
Group capacity Suitable to maximize sum rate, but quite complex
Convex combination of spatial correlation and channel gains Less complex than group capacity
Spatially uncorrelated
h2
h2
h1
h1
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 22
SDMA algorithmGrouping metric
Group capacity Suitable to maximize sum rate, but quite complex
Convex combination of spatial correlation and channel gains Less complex than group capacity
Spatially uncorrelated Spatially correlated
h2
h2
h1
h2
h2
h1
h1
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 23
SDMA algorithmGrouping metric
Group capacity Suitable to maximize sum rate, but quite complex
Convex combination of spatial correlation and channel gains Less complex than group capacity
h2
h2
h1
h1
h2
h2
h1
h1
Spatially uncorrelated Spatially correlated
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 24
SDMA algorithmGrouping algorithm
1. Exhaustive Search + Group capacity metric Upper bound2. Random Grouping Lower bound
3. Best Fit + Group capacity metric Benchmark
4. Convex Grouping + Convex comb. spatial correlation & channel gains
5. Best Fit + Convex comb. spatial correlation & channel gains
Channel gains
Spatial correlation
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 25
Resource Allocation Strategies: Single Resource
Resource assignment algorithm
Precoding algorithm
SDMA algorithm
Power allocation algorithm
Single-resource case Multiple-resource case
•Grouping metric
•Grouping algorithm
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 26
Precoding and power allocation algorithms
Precoding algorithm Linear Zero-Forcing
Power allocation algorithm Water-filling
Other proposed/investigated algorithms can be found in the written work
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 27
Simulation Parameters
Parameter Value
System frequency 5 GHz
# of used subcarriers 48 subcarriers organized in 8 resources
Subcarrier spacing 9.77 kHz
Channel modelWINNER channel model, macro-cell urban scenario C2, Non-Line of Sight
# of antennas at the BS 4 omnidirectional antennas in a uniform linear array
# of users 16 single-antenna users
Average user’s speed 10 km/h
Target SDMA group size Initially set to 4 users
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 28
Performance of the RA Strategies: Single Resource
1. Upper bound: Cap.-basedExhaustive Search
2. Lower bound: Random GroupingSingle User
3. Benchmark:Cap.-based Best Fit
4. Proposed ConvexComb.-basedConvex Grouping5. Proposed Convex
Comb.-based Best Fit
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 29
Sequential Removal Algorithm
Removes users from the SDMA group increase the group capacity
User are removed, e.g., according to their effective channel gain Users with the lowest channel gain
removed first
Computes group capacity of the resulting groups
Keeps the group with the highest capacity
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 30
Performance of the RA Strategies: Single ResourceImprovement due to the Sequential Removal Algorithm
1. Upper bound: Cap.-basedExhaustive Search
2. Lower bound: Random GroupingSingle User
4. Proposed ConvexComb.-basedConvex Grouping
5. Proposed Convex Comb.-based Best Fit
3. Benchmark:Cap.-based Best Fit
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 31
Performance of the RA Strategies: Single ResourceComputational complexity
Benchmark and proposed strategies Sum rates close to those achieved through the Exhaustive Search But considerably different complexity
1. Upper bound:Cap.-basedExhaustive Search
3. Benchmark:Cap.-based Best Fit
2. Lower bound:Random Grouping
4. Proposed Convex Comb.-basedConvex Grouping
5. Proposed Convex Comb.-based Best Fit
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 32
Outline
1. Resource Allocation Problem Overview
2. Suboptimal Resource Allocation Strategies: Single Resource
3. Suboptimal Resource Allocation Strategies: Multiple Resources
4. Conclusions and Outlook
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 33
Resource Allocation Strategies: Single Resource
Resource assignment algorithm
Precoding algorithm
SDMA algorithm
Power allocation algorithm
Single-resource case Multiple-resource case
•Grouping metric
•Grouping algorithm
•Priority
•Assignment algorithm
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 34
Resource Allocation Strategies: Multiple ResourcesAssignment Algorithms
1. Assign resourcesone-by-one
2. Assign resourcesto initial users
3. Assign resourcesto SDMA groups
For capacity maximization almost same sum rate of the Exhaustive SearchFor proportional fairness better degree of throughput fairness
small reduction of the sum rate
Assign a resourceto an initial user based
on user priorities
Build an SDMA group
Apply precodingand power allocation
Assign resourcesto initial users based
on user priorities
Build an SDMA groupon each resource
Apply precodingand power allocation
Build severalcandidate SDMA groups
Apply precodingand power allocation
Assign resources toSDMA groups basedon the user priorities
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 35
Resource Allocation Strategies: Multiple ResourcesProportional Fair Priorities
Benchmark: Cap.-based Best Fit
Proposed Convex Comb.-based Best Fit
Proportional Fair
Capacity Maximization
3. Assign resourcesto SDMA groups
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 36
Resource Allocation Strategies: Multiple ResourcesThroughput Fairness
ProportionalFair
CapacityMaximization
1. Assign resourcesone-by-one
3. Assign resourcesto SDMA groups
Proposed Strategy 2: Convex Comb.-based Best Fit
SNR = 10 dB
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 37
Outline
1. Resource Allocation Problem Overview
2. Suboptimal Resource Allocation Strategies: Single Resource
3. Suboptimal Resource Allocation Strategies: Multiple Resources
4. Conclusions and Outlook
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 38
Conclusions and Outlook
Performance and complexity Proposed some new RA strategies Sum rate close to that achieved by the Exhaustive Search Lower complexity compared to the benchmark strategy and Exhaustive Search Provide a good trade-off between performance and complexity
Throughput fairness Higher throughput fairness at the expense of small reduction of the sum rates Provide a good trade-off between performance and fairness
Outlook Extension to multi-antenna users Extension to ensure minimum QoS levels Extension to multiple cells, including relay networks and cooperation among
base stations
22nd September 2008 | Tariciso F. Maciel | Suboptimal Resource Allocation for Multi-User MIMO-OFDMA Systems 39
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