Energy and Performance of Smartphone Radio Bundling in

Outdoor Environments

Ana Nika*, Yibo Zhu*, Ning Ding+, Abhilash Jindal+, Y. Charlie Hu+

Xia Zhou^, Ben Y. Zhao* and Haitao Zheng*

*UC Santa Barbara, ^Dartmouth College, +Purdue Universityanika@cs.ucsb.edu

2

Wireless Bandwidth Crisis

• Many data-hungry applications for smartphones

How do we support these new applications?

3

Single Radio Not Enough

• Optimal: 75Mbps• In practice:

outdoors 2%-20%o movemento congestion

Cellular (LTE)

4

Single Radio Not Enough

Indoors

WiFi60GHz WiFi: ~150Mbps

60GHz: ~6Gbps

What about outdoors?WiFi suffers from interference, poor quality

60GHz small range, easily blocked

5

Radio Bundling

WiFi

LTE

1Mbps2Mbps

RadioBundling:3Mbps

6

Our Goals

1. What is the maximum benefit that can be provided by bundling on today’s devices?

2. What is the energy cost of bundling?

Via real measurements using a smartphone app

in 5 US cities and 63 outdoor locations.

7

Existing Work

• MPTCP: transport-layer bundling implementation– non-optimal (fair to non-MPTCP users)– not designed for wireless radios– does not consider energy

• Our goal is to study optimal radio bundling– understand fundamental limitations of bundling– how different radio usage options compare– how we can improve current implementations

Energy

Throughput

WiFi-only

LTE-onlyMPTCP ?

Bundling ?

Bundling ?

8

Methodology

• Android-based app– turn on WiFi & LTE radios simultaneously

• Power model for bundling and non-bundling– take into account CPU & WiFi, LTE radios

• Measurements at 5 cities & 63 outdoor locations– file download/upload (0.5MB-5MB in size)– derive throughput and energy of different radio usage

options– capture different RF conditions

o in terms of

Not available by

default

9

Radio Usage Options

• Bundling – Optimal traffic partitioning

o trace playback analysis– MPTCP

• Non-bundling– Single Radio: LTE-only, WiFi-only– Best Radio: max (LTE-only, WiFi-only)– Radio Switching: instantaneous switching

between two radios

10

Energy Profiling

• Accurate signal-strength aware power model– componentized: WiFi, LTE radios & CPU– takes into account energy tail– < 8% error rate

• Power draw projection over time

Details

Energy tail

11

Outline

• Motivation

• Methodology

• Throughput Performance

• Energy Consumption

• Conclusion

12

Radio Frequency Conditions

LTE 100x better than WiFi

WiFi 100x better than LTEq

13

Bundling’s Throughput Improvement

Gain:2x – 5x

MPTCP:40%-85% of

optimal bundling

14

Sources of Bundling Gain

• Radio independence– LTE and WiFi radios do not interfere with each other– dual-core CPU supports both radios

• Traffic partitioning matters!!! – accurately projects radio throughput to fully utilize both radios

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

20

40

60

80

100

Ratio over Ideal Bundling

CD

F (

%)

Even

Noisy-2%

MPTCPNoisy-50%

MPTCP performs poorly.

An approach with high noise performs better than MPTCP.

15

Energy Analysis

• LTE is the heaviest energy drainer– consumes at least 50% of the total power draw

• CPU consumes a significant amount of energy– 60% for WiFi-only– 20%-23% for Bundling, MPTCP, LTE-only

16

Bundling Energy Cost

• Energy cost of a file transfer

LTE-only

WiFi-only

• Bundling energy cost ≤ LTE-only cost

• Bundling energy cost > WiFi-only cost, because of LTE radio

• MPTCP sometimes saves energyo Bundling

consumes more CPU energy

17

Energy Cost vs. Throughput Gain

• Bundling improves transfer throughput & transfer ends earlier

• Energy saving due to reduced transmission time – compensates the extra power draw of the additional radio

Potential bundling implementation

18

Conclusion• Bundling is highly beneficial, achieve 2x-5x improvement over

single radio

• MPTCP achieves only a portion of the total performance possible

• Bundling has higher instantaneous power draw, but can lead to lower energy cost due to faster transmission

• Our accurate componentized power model identifies the significant role CPUs play in energy usage

• There is ample room for a new bundling protocol that provides a better tradeoff between performance and energy usage

19

Thank You!Questions?

20

Impact of File Size on Throughput

• Consistent across all transfer sizes

• Slightly higher for 512KB and 1MB transfers o TCP slow start

21

Impact of File Size on Energy

• Consistent across all transfer sizes

• Higher for 512KB and 1MB transfers o LTE energy tail