Post on 13-Apr-2017
Graph-based Framework for Flexible Baseband Function Splitting
Jingchu LIU*, Sheng ZHOU*, Jie GONG*, Zhisheng NIU*, and Shugong XU+
Network Integration for Ubiquitous Linkage and Broadband (NiuLab)
Tsinghua University, Beijing, China *and
Intel Labs, Beijing, China +
Graph-based framework for flexible baseband function splitting
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Contents
• Fronthaul Bottleneck of C-RAN• Baseband Compression via Function Splitting• Graph-based Framework for BB function splitting• Customized Genetic Algorithm• Simulation Results• Future Work
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Contents
• Fronthaul Bottleneck of C-RAN• Baseband Compression via Function Splitting• Graph-based Framework for BB function splitting• Customized Genetic Algorithm• Simulation Results• Future Work
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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FH Bottleneck of C-RAN
• C-RAN and Fronthaul (FH)[1]
• C-RAN centralizes BB processing from radio site• FH carries BB samples (I/Q data) btw. RRH and BBU• Reduce cost, ease implementation of cooperative technology, flexibility
• FH Bottleneck[2]
• Bandwidth: 10Gbps/ant. for typical LTE UL/DL (100Mbps backhaul)• Delay: 3ms maximum processing latency for LTE HARQ -> maximum
500us fronthaul transmission dealy• Synchronization: ~1ppb frequency accuracy, ~1us phase difference
• C-RAN is sound, but FH is (too) expensive
FH = Fronthaul BB = BasebandRRH = Remote Radio Head BBU = Baseband Unit
[1] CMRI. C-RAN: The road towards green RAN[2] CPRI Specification, “interface specification,” 2013.
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Contents
• Fronthaul Bottleneck of C-RAN• Baseband Compression via Function Splitting• Graph-based Framework for BB function splitting• Customized Genetic Algorithm• Simulation Results• Future Work
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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BB Compression via Function Splitting
• Transparent BB compression[3]
• Time-domain or frequency domain• Compress at RRH(BBU), reconstruct at BBU(RRH)• Transparent: no changes needed for BBU/RRH
[3] Samardzija, “Compressed Transport of Baseband Signals in Radio Access Networks.,“ TWC 2012Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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BB Compression via Function Splitting
• Transparent BB compression• Around 3x compression at the cost of distortion (EVM<1.5%)• Enough?
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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BB Compression via Function Splitting
• Transparent BB compression• Compression via function splitting[4][5]
• Preprocessing at remote site to reduce FH bandwidth• … “move” some BB processing from data center back to radio site
[4] Lorca and Cucala. “Lossless compression technique for the fronthaul of LTE/LTE-advanced cloud-RAN architectures,” in WoWMoM 2013[5] Dotsch, "Quantitative Analysis of Split Base Station Processing and Determination of Advantageous Architectures," Bell Labs Journal, 2013Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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BB Compression via Function Splitting
• Transparent BB compression• Compression via function splitting
• Why it works?
200+ times
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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BB Compression via Function Splitting
• Transparent BB compression• Compression via function splitting• Why FLEXIBLE function splitting[6][7][8]
• Various implementation constraint (BW, delay)• Continuous evolvement of PHY technology (massive MIMO)• Unpredictable service requirements (sub-ms latency in 5G)
• Decide splitting option “on-the-fly”!• Need a framework for deciding the “best split”
Research Question:How to decide the best BB function splitting scheme?
[6] P. Rost , et al., “Cloud technologies for flexible 5G Radio Access Networks”, Comm. Mag. May 2014[7] D.Wubben , et al., Benefits and Impact of Cloud Computing on 5G Signal Processing, SPM, Nov 2014[8] J. Liu, et al., “CONCERT: A Cloud-Based Architecture for Next-generation Cellular Systems”, IEEE WCM, Dec 2014
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Contents
• Fronthaul Bottleneck of C-RAN• Baseband Compression via Function Splitting• Graph-based Framework for BB function splitting• Customized Genetic Algorithm• Simulation Results• Future Work
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Graph-Based Framework for BB Function Splitting
• BB processing structure and graph• Basic processing structures are chains• Cooperative processing structures like CoMP may form loops
Typical baseband processing structure of LTE BSJingchu Liu Tsinghua University
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Graph-Based Framework for BB Function Splitting
• BB processing structure and graph• Basic processing structures are chains• Cooperative processing structures like CoMP may form loops• General BB processing structures are graphs :
• Each node : BB processing function• Each (directed) link : logical link btw. BB processing fcn.• Node weight : computational complexity of a node• Link weight : fronthaul BW requirement• Sources and sinks terminate BB processing chain (path)
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Graph-Based Framework for BB Function Splitting
• BB processing structure and graph• Function splitting and graph clustering
• Graph-clustering: group nodes by “similarity”• Here, places to place BB functions define cluster• Therefore, where to place a function = which cluster to assign a node
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Graph-Based Framework for BB Function Splitting
• BB processing structure and graph• Function splitting and graph clustering
• Computational cost of cluster i w.r.t scheme• Fronthauling cost between clusters i, j w.r.t scheme• Path delay constraint
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
Graph-based framework for flexible baseband function splitting
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Graph-Based Framework for BB Function Splitting
• BB processing structure and graph• Function splitting and graph clustering• Graph clustering is multi-obj. combinatorial opt.
• Clustering schemes can be represented with integer valued vectors• Overall formulation is 2-obj. opt. with delay constraint
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Contents
• Fronthaul Bottleneck of C-RAN• Baseband Compression via Function Splitting• Graph-based Framework for BB function splitting• Customized Genetic Algorithm• Simulation Results• Future Work
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Customized Genetic Algorithm (GA)
• Natural encoding• Use to represent the chromosome
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Customized Genetic Algorithm (GA)
• Natural encoding• Linearly combined and delay punished fitness fcn.
• Computational cost + fronthauling cost + delay penalty
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Customized Genetic Algorithm (GA)
• Natural encoding• Linearly combined and delay punished fitness fcn.• Dispersive crossover
• 2 Parents generate 1 offspring• Genes are randomly passed down from parents
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Customized Genetic Algorithm (GA)
• Natural encoding• Linearly combined and delay punished fitness fcn.• Dispersive crossover• Graph-based mutation
• ONLY mutate to connected clusters• Graph seeding
• Some modules can not be placed arbitrarily in reality, e.g. antennas• Seed nodes are assigned with fixed cluster indices• DO NOT take part in crossover or mutation
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Contents
• Fronthaul Bottleneck of C-RAN• Baseband Compression via Function Splitting• Graph-based Framework for BB function splitting• Customized Genetic Algorithm• Simulation Results• Future Work
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Simulation Setup• BB processing structure, NOTE for CoMP• Link weight (fronthauling cost)
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Simulation Setup• Node weights (computational cost)
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Simulation Setup• Exponential cost and productive delay fcn.
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Simulation Setup• GA parameters
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Tradeoff between computational and fronthauling cost
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Tradeoff between computational and fronthauling cost
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Cooperative processing (like CoMP)
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Simulation Results
• Delay constraint
Delay tolerance decrease
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Contents
• Fronthaul Bottleneck of C-RAN• Baseband Compression via Function Splitting• Graph-based Framework for BB function splitting• Customized Genetic Algorithm• Simulation Results• Future Work
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Future Work
• Realistic simulation parameters• Analytic derivation of optimal split schemes• Information-theoretic interpretation of BB split
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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Thanks
• Any problems / suggestions?
Jingchu Liu Tsinghua University
Graph-based framework for flexible baseband function splitting
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