cloud-aided wireless networks with edge caching ...simeone/isit16_simeone_pres.pdf · isit...
TRANSCRIPT
Ravi Tandon Osvaldo Simeone
ISIT 2016, Barcelona
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Cloud-Aided Wireless Networks withEdge Caching: Fundamental Latency Trade-Offs
in Fog Radio Access Networks
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• Content delivery, e.g., video, is driving growth in wireless traffic
Introduction
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• Content delivery, e.g., video, is driving growth in wireless traffic
Introduction
• Edge- vs cloud-based solutions
Introduction
EN ENEN EN
ENCache
EN: Edge Node
• Cache-aided wireless network (or edge caching): storage of popular content at wireless edge nodes [Golrezaei et al ‘12]
• Reduces latency due to backhaul usage
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]
• Cloud-aided wireless network (or C-RAN): Centralization of baseband processing at the cloud
cloud
EN ENEN EN
EN EN: Edge Node
fronthaul
Introduction
Introduction
• (Digital) fronthauling approaches:
- Hard fronthaul transfer [Patil and Yu ‘14]- Soft fronthaul transfer: Fronthaul compression [Simeone et al ‘14]
• Centralized interference management
cloud
EN EN EN EN
EN
fronthaul
Fog-RAN (F-RAN)
cloud
fronthaul
EN ENEN EN
EN
CacheEN: Edge Node
• Fog Radio Access Network (F-RAN): Cloud and cache-aided wireless network for content delivery
• Optimal operation of an F-RAN: complex design problem over fronthaul, cache and spectral resources
• Fundamental trade-off between delivery latency and system resources
Fog-RAN (F-RAN)
System Model
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System Model
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System Model
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System Model
• Quasi-static channel model with continuous distribution• Power constraint P 13
System Model
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System Model
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System Model
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Cache-Fronthaul-Edge Policy
Time
Tx interval
• 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 ,
TimeCaching interval
Tx interval
Cache-Fronthaul-Edge Policy
Time
Tx interval
Cache-Fronthaul-Edge Policy
• Cache storage policy: What to cache
• Fronthaul policy: What to transmit on the fronthaul links
- Based on instantaneous users’ requests and CSI
Time
Tx interval
Cache-Fronthaul-Edge Policy
• 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
• Delivery time per bit (e.g., [Liu and Erkip ’11])
Fronthaul Wireless Time
Tx interval
FT ET
Normalized Delivery Latency• Serial fronthaul-edge transmission
user's requests( , , ) limmax F E
F L
T TC PL
• Delivery time per bit (e.g., [Liu and Erkip ’11])
Fronthaul Wireless Time
Tx interval
FT ET
Normalized Delivery Latency• Serial fronthaul-edge transmission
user's requests( , , ) limmax F E
F L
T TC PL
( , log , )( , ) lim1/ logP
r P PrP
• Normalized Delivery Time (NDT):
Ideal system: interference-free and unlimited caching
Normalized Delivery Latency• Pipelined fronthaul-edge transmission
FronthaulWireless
Time
Tx interval
T• Delivery time per bit and NDT
and
• Practical implications in, e.g., [Leconte et al ‘16]
user's requests( , , ) limmaxF L
TC PL
( , log , )( , ) lim1/ logP
r P PrP
Main Result: NDT for 2 2 of F-RANs
Theorem: The minimum NDT for the 2 2 F-RAN with is given as
*
1 2max 1 ,2 for 0 1( , r)
11 for 1
rr
rr
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Main Result: NDT for 2 2 of F-RANs
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Main Result: NDT for 2 2 of F-RANs
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Main Result: NDT for 2 2 of F-RANs
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Full caching:Cooperative zero-forcing beamforming
at the ENs
Main Result: Achievability
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No caching:Zero-forcing
beamforming at the cloud + soft-
transfer fronthauling
(compression with bits/
sample)
Main Result: Achievability
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Caching of half file:Interference
alignment on an “X-channel”
[Motahari et al ‘14] [Cadambe and
Jafar ‘09]
Main Result: Achievability
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Main Result: Converse
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Main Result: Converse
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Main Result: Converse
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Main Result: Converse
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Main Result: Converse
• Information cut 1:
• Information cut 2:
• Information cut 3:
• Linear combinations of the inequalities above yield the desired result
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Conclusions and Outlook• F-RAN leverages the synergy and complementarity of
cloud processing and edge caching
• Definition of NDT as high-SNR worst-case latencyrelative 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, …