1
Age of Information
Status Updating Systems and Networks
Roy Yates
ECE/WINLAB, Rutgers
NSF Workshop on Ultra Low Latency Wireless Networks
March 26, 2015
WINLAB
2
Motivation
• 50 years of rate maximization
– at the expense of delay
•
•
•
•
long (coded) packets on wireless channels,
ARQ
video streaming with large delays to absorb packet jitter
Caching to compensate for network latency
• high throughput “best-effort” networks
WINLAB
3
Applications
(The Samsung 5G List)
• V2X
~1 ms
– timely delivery of critical messages for traffic safety
• Mission-Critical IoT (M2M)
– mission-critical systems – process monitoring/detection and
disaster response
• Virtual/Augmented Reality
1-10 ms
– seamless virtual/real-world interaction
• Real-time remote access (tactile feedback)
– long range, real-time control for remote surgery, driving, etc.
• Everything-on-Cloud
10-100ms
– instantaneous cloud-based services/multimedia content
WINLAB
4
57 mph
Applications=
(The Samsung 5G List)
1 inch/ms
• V2X
~1 ms
– timely delivery of critical messages for traffic safety
• Mission-Critical IoT (M2M)
– mission-critical systems – process monitoring/detection and
disaster response
• Virtual/Augmented Reality
1-10 ms
– seamless virtual/real-world interaction
• Real-time remote access (tactile feedback)
– long range, real-time control for remote surgery, driving, etc.
• Everything-on-Cloud
10-100ms
– instantaneous cloud-based services/multimedia content
WINLAB
5
Applications
(The Samsung 5G List)
• V2X
~1 ms
– timely delivery of critical messages for traffic safety
• Mission-Critical IoT (M2M)
– mission-critical systems – process monitoring/detection and
disaster response
• Virtual/Augmented Reality
1-10 ms
– seamless virtual/real-world interaction
• Real-time remote access (tactile feedback)
– long range, real-time control for remote surgery, driving, etc.
• Everything-on-Cloud
10-100ms
– instantaneous cloud-based services/multimedia content
• Wireless Network on Chip
– Cloud on Chip?
?? ms
WINLAB
6
Network Delay
(H. Viswanathan, Bell Labs)
WINLAB
7
Remote Surgery
WINLAB
8
Remote Surgery
WINLAB
9
PHY
• Wider Channels (but not UWB )
– 30+ GHz mmWave
• M2M: reliability is essential
• Practice: Emerging low latency 5G
– Channel Estimation, Modulation, Coding, Framing
• (check out Fettweis CTW 2013 talk)
• Theory:
– Delay-Limited Capacity, Short blocklength
source/channel coding
WINLAB
10
Latency-Sensitive MAC
• Practice:
– 2G/3G packet voice MAC
– LTE Scheduling
– Sleep protocols!
WINLAB
11
Latency-Sensitive MAC
• Practice:
– 2G/3G packet voice MAC
– LTE Scheduling
– Sleep protocols!
• What Randy said:
“CSMA style random access seems ill-matched to low
latency unless the network is very underutilized.”
• Theory: Are rate/delay tradeoffs fundamental?
WINLAB
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V2V Safety Messaging
Source
Large Networks (Hundreds of cars)
Frequent Updates
Reliability and Timeliness are required
WINLAB
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V2V Safety Messaging
Source
•
•
DSRC standard MAC protocol
• Message Scheduling, Forwarding/Piggybacking
• Power/rate adaptation, coverage …
Performance Metrics?
WINLAB
14
Network
• Car u sends updates to car v
• Updates pass through network/service system
• Car v wants latest state information.
• Metric: Age of the latest status update
WINLAB
15
Update Age
D(t)
Update
Sent
Received
t1
t 1’
t
t 2 t 2'
WINLAB
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Update Age
D(t)
Update
Arrival
Departure
t1
t 1’
t
t 2 t 2'
• Low Update Rate
 Age gets large between updates
WINLAB
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Update Age
D(t)
t1 t 2 t 3 t 1’
t 2'
t 3'
• High Update Rate  Queueing Delay
WINLAB
18
Average Update Age
D(t)
•
Average Age
Update Rate:
• High  Queueing delays
• Low  Infrequent updates
High Average Age
WINLAB
19
FCFS Average Update Age
D(t)
• X= Interarrival Time
• T= System Time
𝑋
•
•
𝑇
Weak ergodicity requirements
E[XT ] is tricky, negative correlation
WINLAB
20
Average Age
WINLAB
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Average Age
No
throughput/delay
tradeoff
WINLAB
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Other Age Metrics
D(t)
D1
D(t)
D*
Average Peak Age
D2
D3
P[D(t)>D* ]
WINLAB
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Competing Updates
• How often is too often?
WINLAB
24
Multiple Sources
WINLAB
25
Multiple Sources
Models for Source 2:
• Competing status updater
• Other traffic
WINLAB
26
Multiple Sources
FCFS Status Age Region
Optimal
Sharing
Nash
Equilibrium
WINLAB
27
Source
1
𝜇
Monitor
Source
2
•
Queueing delays increases status age
•
Reduce/Eliminate the queues?
•
“Packet Management”
[Costa, Codreanu, Ephremides ISIT’14]
WINLAB
28
LCFS
Pre-emption & Discarding
(No Queueing)
Source
1
l1
𝜇
Source
2
Monitor
l2
WINLAB
29
V2V Safety Messaging
Network
•
•
•
Multiple Sources
Fast local server interface
Slow Server
WINLAB
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Multiple Sources
FCFS/LCFS Age
WINLAB
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Timely Compression
A Status Updating Problem
Encoder
a1 a2 a3 …
FIFO
buffer
01 110
Rate R
bit pipe
Decoder
11…
a1 a2 a3 …
• Encoder input symbol = status update
• Age = Decoder symbol lag
• Block coding  Bursty bit arrivals at FIFO buffer
Bit pipe queueing delay
Decoding delay
• [Sahai&Cheng ISIT’07]
WINLAB
32
Timely Compression
A Status Updating Problem
FIFO
buffer
Encoder
Rate R
bit pipe
Decoder
a 1 a2 a 3 a 4 a 5 a 6 a 7 …
01 110
a1
a2
11…
a3 a4 …
t
WINLAB
33
Timely Compression
Status Age
Huffman Block Coding Example
Low rate pipe:
Use large
blocks
Channel Rate R
High rate pipe:
use small
blocks
WINLAB
34
Summary
• Information Age Minimization
– Match the load to the network/system
• “Rate” is an input for controlling delay
– Redesign the system
• Give priority to timely updates
• Packet Management
• Ultra Low Latency Networks
– Sub 1ms latency applications?
• Better Theory for Network Latency
WINLAB