Transcript Slides - INLAB

LOW LATENCY WIRELESS: A CELLULAR NETWORK PERSPECTIVE
Harish Viswanathan
Bell Labs & CTO, Alcatel-Lucent
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
CELLULAR NETWORKS: THE MARCH TOWARDS LOW LATENCY
Two Decades and 10X
• UE processing delay
• Base station
processing delay
• Frame duration
• Resource allocation
delay
• Retransmissions
• Number of elements
(2010)
2
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
UK – MOBILE - OFCOM - 2014
Source: Ofcom – Measuring mobile broadband performance in the UK – November 2014
3
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
LATENCY BREAK UP IN LTE
PGW
SGW
eNode B
Metro
Access and Aggregation
~20 ms
~30 ms
~30 ms (Location
Dependent)
AIR-INTERFACE
DL
(eNB  UE)
UL
(UE  eNB)
ACK
NACK
Grant
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
1 ms
8 ms
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 90 1 2 3
Sched
Req
Core
Data Tx
Re Tx
4
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
5G
1 Gb/s
10 yrs
500 km/h
200 k
per km²
3 ms
E2E 10 ms
99.9%
• Few 100 MHz to GHz of bandwidth at spectrum
above 6 GHz
• Low latency and reliable communication in both
high and low band
5
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
REDUCING NETWORK LATENCY
Core Network and
Application resides in
local DC
SDN CONTROL
Point to point optical
connectivity
TOR
Edge computing
enabled by
network function
virtualization
vL2/3_RAN
TOR
L1 BBU
vL2/3_RAN
L1 BBU
SGW
L1 BBU
vPGW
L1 BBU
Video
Web App
• Reduced transport
costs
Distribured DC
Wireless Access
Aggregation
IP/Optical Core
Web App
Video
content
Wireline network latency essentially reduced to data center switching latency
6
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
REDUCING AIR-INTERFACE LATENCY
0
• Efficient asynchronous (open loop
synchronized) communication
UF-OFDM
- Introduce filtering in OFDM to avoid closedloop timing advance (UF-OFDM)
• Smaller sub-frame durations through
Reduced symbol periods for low latency
flows
Rel. power [dB]
-10
-20
CP-OFDM
-30
-40
-50
-60
0
20
40
60
80
100
Frequency spacing in subcarrier steps
120
Layer
Type III and Type IV
- Mixture of smaller and longer symbol periods
made possible through filtering
Time
• Pre-emptive scheduling
- “Always on” devices monitoring control
channel for new packets
- New packet sent in the place of an ongoing
packet during the rest of the TTI
140
Type II
Type I
Frequency
7
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.
FUNDAMENTAL TRADEOFFS
• Spectral Efficiency versus Latency in Multiple Access
- Grant free slotted Aloha type transmissions with light loading for low latency uplink
- Removal of HARQ implies loss of efficiency
• Energy versus Latency
- Devices need to sleep to save battery resources
- Lower latency calls for frequently waking up to check for messages which drains battery
- Wide area wake up circuit that consumes less energy
• What is the loss incurred when there is mix of low latency and delay tolerant
traffic?
- Pre-emption versus reservation
8
COPYRIGHT © 2014 ALCATEL-LUCENT. ALL RIGHTS RESERVED.