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A Performance Study of Power Minimization for Interleaved and Localized FDMA
Lei You, Lei Lei (speaker), and Di Yuan
Linköping University Sweden
IEEE CAMAD, Athens, Dec. 01, 2014
Outline
l Introduc)on
-‐-‐ localized channel alloca)on in SC-‐FDMA
-‐-‐ Interleaved channel alloca)on in SC-‐FDMA
l Power minimiza)on problem
l Performance evalua)on
l Conclusions
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Downlink and Uplink in LTE
• Standard mul)ple user access schemes in LTE
OFDMA -‐-‐ Orthogonal Frequency Division Mul)ple Access
SC-‐FDMA -‐-‐ Single Carrier -‐ Frequency Division Mul)ple Access
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Downlink – OFDMA
Uplink – SC-‐FDMA
SC-FDMA for LTE Uplink
• Main drawback of OFDMA: high peak-‐to-‐average power ra)o (PAPR)
-‐-‐ more complicated circuit design in power amplifier
-‐-‐ higher power consump)on at the transmiMer
• Concerns for mobile terminals in uplink: power consump)on
• Benefit from SC-‐FDMA in uplink:
-‐-‐ similar structure and performance to OFDMA
-‐-‐ lower PAPR, power saving
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Source: http://allthingsd.com
Channel Allocation in Uplink SC-FDMA Two types of subcarrier mapping schemes in SC-‐FDMA:
• Interleaved FDMA:
-‐ subcarriers occupied by a UE are distributed equidistantly over the
en)re frequency band
• Localized FDMA (consecu)ve channel alloca)on)
-‐ each UE uses a set of consecu)ve subcarriers to transmit its symbols
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Frequency
UE2 UE1 UE3
Frequency
UE1 UE2 UE3
Task: Optimal Channel-User Allocation
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• Interleaved FDMA:
Form all the possible channel block, to be assigned to users
• Localized FDMA:
Form all the possible consecu)ve channel block
-‐-‐ e.g., N = 3, with N={1, 2, 3}. The possible combina)ons are {1}, {1, 2},
{1,2,3}, {2}, {2,3} and {3}, N(N+1)/2 possible consecu)ve blocks in total
-‐-‐ Peak power limit for each user (uplink) -‐-‐ uniform power alloca@on over subcarriers in a block
UE1
Channel Allocation for Power Minimization
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• Develop a unified Min-‐Power op)miza)on framework:
find the op?mal channel-‐user alloca?on
• Same framework for localized and interleaved FDMA
-‐-‐ different forms of subcarrier blocks in IFDMA and LFDMA
one user -‐-‐ one block at most
no subcarrier reuse
Sa@sfy users’ demand
-‐-‐ Peak power limit for each user (uplink) -‐-‐ uniform power alloca@on over subcarriers in a block
Channel Allocation for Power Minimization
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NP Hardness results:
• Power Minimiza)on in Localized FDMA
-‐-‐ NP hard problem, (Max-‐U)lity, Min-‐Power)
-‐-‐ the complexity jus)fies the development of sub-‐op)mal algorithms
• Power Minimiza)on in Interleaved FDMA
-‐-‐ hard problem or not ?
-‐-‐ we give the answer: polynomial )me solvable
-‐-‐ perfect matching problem in a bipar)te graph
L. Lei, D. Yuan, C. K. Ho, and S. Sun, “A unified graph labeling algorithm for consecutive-block channel allocation in SC-FDMA,” IEEE Trans. on Wireless Commun., vol. 12, no. 11, pp. 5767–5779, Nov. 2013.
Graph Presentation for Min-Power in Interleaved FDMA
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• Power Minimiza)on in Interleaved FDMA
-‐-‐ perfect matching problem in a bipar)te graph
-‐-‐ develop an algorithm to systemically search the op)mal solu)on for
min-‐power in IFDMA
-‐-‐ achieve global op)mality in
Subcarrier block: 1, 4, 7, 10, 13, 16
Subcarrier block: 2, 5, 8, 11, 14, 17
Subcarrier block: 3, 6, 9, 12, 15, 18
One illustration for min-power in a bipartite graph
Performance Evaluation: Sum Power
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LPN: 50 mW
• Simula)on setup: LTE uplink scenario, single cell with random and uniform user distribu)on, 10 users, 64 subcarriers
Obtain op?mal power value -‐-‐ Min-‐power in LFDMA: use solver, )me consuming -‐-‐ Min-‐power in IFDMA: proposed algorithm, polynomial-‐)me solvable
Performance Evaluation: Maximum User Demand
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LPN: 50 mW
• For Min-‐Power problem in LFDMA and IFDMA Increase user demand ⇒ more and more user-‐block pairs become infeasible (due to UE’s peak power) ⇒ Difficult to finding a feasible channel alloca)on, even becomes infeasible
Conclusions
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l Characteriza)ons for two types of channel alloca)on op)miza)on problems in uplink SC-‐FDMA:
localized and Interleaved FDMA
l Develop a unified op?miza?on framework for Min-‐Power problem in both localized and Interleaved FDMA
l NP Hardness results:
l localized FDMA: NP-‐hard
l interleaved FDMA: polynomial-‐?me solvable
● Performance evalua)on: LFDMA outperforms IFDMA in terms of power consump)on and maximum supported user demand
www.liu.se
