Cloud-Aided Wireless Networks with Edge Caching: Fundamental Latency Trade-Offs in Fog Radio Access Networks. ISIT 2016, Barcelona

Transcription

1 Cloud-Aided Wireless Networks with Edge Caching: Fundamental Latency Trade-Offs in Fog Radio Access Networks Ravi Tandon Osvaldo Simeone ISIT 2016, Barcelona 1

2 Introduction Content delivery, e.g., video, is driving growth in wireless traffic 2

3 Introduction Content delivery, e.g., video, is driving growth in wireless traffic Edge- vs cloud-based solutions 3

4 Introduction Cache-aided wireless network (or edge caching): storage of popular content at wireless edge nodes [Golrezaei et al 12] EN EN EN EN EN EN: Edge Node Cache Reduces latency due to backhaul usage

5 Introduction Information-theoretic analysis of cache-aided interference channels - Achievable 1/DoF for 3 3 system [Maddah-Ali and Niesen 15] - Bounds on 1/DoF for more general models with caching also at the receiver [Naderializadeh et al 16] [Hachem et al 16] [Xu et al 16]

6 Introduction Cloud-aided wireless network (or C-RAN): Centralization of baseband processing at the cloud cloud fronthaul EN EN EN EN EN EN: Edge Node

7 Introduction cloud fronthaul EN EN EN EN EN (Digital) fronthauling approaches: - Hard fronthaul transfer [Patil and Yu 14] - Soft fronthaul transfer: Fronthaul compression [Simeone et al 14] Centralized interference management

8 Fog-RAN (F-RAN) Fog Radio Access Network (F-RAN): Cloud and cacheaided wireless network for content delivery cloud fronthaul EN EN EN EN EN EN: Edge Node Cache

9 Fog-RAN (F-RAN) Optimal operation of an F-RAN: complex design problem over fronthaul, cache and spectral resources Fundamental trade-off between delivery latency and system resources

10 System Model 10

11 System Model 11

12 System Model 12

13 System Model Quasi-static channel model with continuous distribution Power constraint P 13

14 System Model 14

15 System Model 15

16 System Model 16

17 Cache-Fronthaul-Edge Policy Tx interval Time

18 Cache-Fronthaul-Edge Policy Tx interval Caching interval Time Cache storage policy: What to cache - No knowledge of instantaneous users requests and CSI - No inter-file coding (intra-file coding allowed) file cached content at EN k,

19 Cache-Fronthaul-Edge Policy Tx interval Time Cache storage policy: What to cache Fronthaul policy: What to transmit on the fronthaul links - Based on instantaneous users requests and CSI

20 Cache-Fronthaul-Edge Policy Tx interval Time Cache storage policy: What to cache Fronthaul policy: What to transmit on the fronthaul links Edge transmission policy: What to transmit on the wireless channel - Based on instantaneous users requests and CSI

21 Normalized Delivery Latency Serial fronthaul-edge transmission Tx interval Fronthaul TF Wireless Delivery time per bit (e.g., [Liu and Erkip 11]) TE (, C, P) max lim F user's requests L T F T L E Time

22 Normalized Delivery Latency Serial fronthaul-edge transmission Tx interval Fronthaul TF Wireless Delivery time per bit (e.g., [Liu and Erkip 11]) TE (, C, P) max lim F user's requests L T F T L E Time Normalized Delivery Time (NDT): (, r) lim P (, rlog P, P) 1/logP Ideal system: interference-free and unlimited caching

23 Normalized Delivery Latency Pipelined fronthaul-edge transmission Tx interval Wireless Fronthaul T Delivery time per bit and NDT (, C, P) max lim F user's requests L T L and (, r) lim P Time (, rlog P, P) 1/logP Practical implications in, e.g., [Leconte et al 16]

24 Main Result: NDT for 2 2 of F-RANs Theorem: The minimum NDT for the 2 2 F-RAN with is given as 1 2 max 1, 2 for 0 r 1 * r (,r) 1 1 for r 1 r 24

25 Main Result: NDT for 2 2 of F-RANs 25

26 Main Result: NDT for 2 2 of F-RANs 26

27 Main Result: NDT for 2 2 of F-RANs 27

28 Main Result: Achievability Full caching: Cooperative zero-forcing beamforming at the ENs 28

29 Main Result: Achievability No caching: Zero-forcing beamforming at the cloud + softtransfer fronthauling (compression with bits/ sample) 29

30 Main Result: Achievability Caching of half file: Interference alignment on an X-channel [Motahari et al 14] [Cadambe and Jafar 09] 30

31 Main Result: Converse 31

32 Main Result: Converse 32

33 Main Result: Converse 33

34 Main Result: Converse 34

35 Main Result: Converse Information cut 1: Information cut 2: Information cut 3: Linear combinations of the inequalities above yield the desired result 35

36 Conclusions and Outlook F-RAN leverages the synergy and complementarity of cloud processing and edge caching Definition of NDT as high-snr worst-case latency relative to an ideal system Characterized the NDT for a 2 2 system Extensions (see arxiv w/ Avik Sengupta): - General lower and upper bounds - Characterization of NDT for a general F-RAN within a multiplicative gap of 2 - Extension to pipelined model Open problems: partial connectivity, imperfect CSI,