Graph-based Framework for Function Splitting in CRAN
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Presentation@ICC15: To discover the function splitting plan with best computation-fronthauling tradeoff, we formulate the problem as a graph clustering problem and develop a genetic algorithm to solve it. Paper: Graph-based Framework for Flexible Baseband Function Splitting and Placement in C-RAN
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Graph-based Framework for Function Splitting in CRAN
- 1. 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 +
- 2. 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 2 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 3. 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 3 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 4. 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 4 FH = Fronthaul BB = Baseband RRH = 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
- 5. 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 5 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 6. 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 6 [3] Samardzija, “Compressed Transport of Baseband Signals in Radio Access Networks.,“ TWC 2012 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 7. BB Compression via Function Splitting • Transparent BB compression • Around 3x compression at the cost of distortion (EVM<1.5%) • Enough? 7 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 8. 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 8 [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, 2013 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 9. BB Compression via Function Splitting • Transparent BB compression • Compression via function splitting • Why it works? 9 200+ times Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 10. 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” 10 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
- 11. 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 11 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 12. 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 12 Typical baseband processing structure of LTE BS Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 13. 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) 13 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 14. 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 14 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 15. 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 15 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 16. 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 16 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 17. 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 17 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 18. Customized Genetic Algorithm (GA) • Natural encoding • Use to represent the chromosome 18 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 19. Customized Genetic Algorithm (GA) • Natural encoding • Linearly combined and delay punished fitness fcn. • Computational cost + fronthauling cost + delay penalty 19 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 20. 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 20 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 21. 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 21 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 22. 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 22 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 23. Simulation Results • Simulation Setup • BB processing structure, NOTE for CoMP • Link weight (fronthauling cost) 23 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 24. Simulation Results • Simulation Setup • Node weights (computational cost) 24 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 25. Simulation Results • Simulation Setup • Exponential cost and productive delay fcn. 25 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 26. Simulation Results • Simulation Setup • GA parameters 26 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 27. Simulation Results • Tradeoff between computational and fronthauling cost 27 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 28. Simulation Results • Tradeoff between computational and fronthauling cost 28 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 29. Simulation Results • Cooperative processing (like CoMP) 29 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 30. Simulation Results • Delay constraint 30 Delay tolerance decrease Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 31. 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 31 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 32. Future Work • Realistic simulation parameters • Analytic derivation of optimal split schemes • Information-theoretic interpretation of BB split 32 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 33. Thanks • Any problems / suggestions? 33 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
- 34. 34 Jingchu Liu Tsinghua University Graph-based framework for flexible baseband function splitting
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