1 © Nokia Siemens Networks

More battery life with LTE connected state DRX

2 © Nokia Siemens Networks

LTE connected state DRX (Discontinuous Reception)

What is DRX?

We know that 2G and 3G terminal uses discontinuous reception in idle state to increase battery life

time. HSPA and LTE have introduced DRX also for connected state. By idle state, we understand

that the smartphone is not utilizing radio resources. Whereas in connected state, smartphone

utilizes radio resources and battery consumption is very high due to 'over the air' communication

between mobile terminal and network antenna (base station).

What is connected state DRX (cDRX) in LTE smartphones?

In LTE, any data transmission requires that the smartphone is in ’high power’ RRC connected

state. With all data applications there are often short moments when no data is sent or received

and during those moments connected state DRX can save energy. Connected state DRX cyclically

wakes up and shuts down the receiver circuits in order to save energy.

cDRX - ON cDRX - OFF

Discontinous Reception (DRX) In LTE, DRX mode can be enabled in both

RRC_IDLE and RC_CONNECTED states.

In the RRC_IDLE state, the UE is

registered with the evolved packet system

(EPS) mobility management (EMM) but

does not have an active session. In this

state the UE can be paged for DL traffic.

UE can also initiate UL traffic by requesting

RRC connection with the serving eNB. In

LTE DRX mode can also be enabled in

RRC_CONNECTED state. In the

RRC_CONNECTED state DRX mode is

enabled during the idle periods during the

packet arrival process. When there are no

outstanding/new packets to be

transmitted/received, eNB/UE may initiate

the DRX mode.

Source: IEEE communication

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More battery life with LTE connected state DRX Insignificant delay impact

Summary:

• Up to 95% lower current consumption during the inactivity periods in RRC connected state

(UE radio unit in RRC connected state when no data is transmitted)

• 20 - 40% lower UE current consumption for background apps

(UE savings with background activities such as keep-alive and push notifications)

• 14% lower average UE current consumption measured with active use of multiple favorite apps

(Average current measured over user activity with browser, Facebook, weather app, email and Skype)

• Lower signaling load with cDRX energy efficiency

Allows operators to use longer RRC inactivity timers

4 © Nokia Siemens Networks

Examples of cDRX support in early LTE smart devices

No cDRX support

• UE capability information indicates

that UE does not support cDRX

“Virtual cDRX support” in RRC

• UE capability information indicates that

UE supports cDRX

• However UE does not implement power

saving DRX

Partial cDRX support

• UE capability information indicates

that UE supports cDRX

• UE implements power saving DRX

for some long cDRX parameters

• cDRX capability depends on modem chipset and its firmware version. Even devices with same chipset model can

have different support.

• cDRX capability expected to improve in devices coming to market 2H2012.

LG Optimus LTE

November 2011

The new iPad

(AT&T variant)

March 2012

HTC Velocity 4G

April 2012

5 © Nokia Siemens Networks

UE current consumption in cDRX

• Test UE connected to power measurement tool with display off.

• Average current measured in RRC connected state during the DRX long cycles.

Reference

measurements:

• Idle 9,6 mA

(1280 ms paging)

• No cDRX 352,4 mA

UE current (mA)

DRX long cycle [ms]

160 320 640 1280 2560

DR

X d

ura

tio

n tim

er

[ms]

10 113,5 66,7 37,4 24,3 17,6

20 140,8 73,9 44,1 27,2 19,2

40 201,5 92,1 52 33,1 22,1

80 286,5 145 75,5 44,1 28

100 339,6 in practice

looks like a

noDRX

157,8 104,2 49,7 30,3

200 n/a n/a 145,8 77,8 45,5

640 ms cDRX cycle together with 640 ms paging cycle provides energy savings with good latency

experience for best effort Internet apps

6 © Nokia Siemens Networks

cDRX comparison with active use of multiple apps

Make a 1 min

Skype call

Browse Check

weather

Send &

receive

emails

Take a picture

and upload to

Facebook.

UE current

without DRX

342,70 mA

(time 8:20,88)

UE current

with DRX

300,86 mA

(time 8:22,70)

DRX inactivity 750 ms

DRX cycle 640 ms

DRX on duration 10 ms

1 min user

inactivity,

screen off

1 min user

inactivity,

screen off

1 min user

inactivity,

screen off

1 min user

inactivity,

screen off

1 min user

inactivity,

screen off

7 © Nokia Siemens Networks

Receiving WhatsApp text message

Whatsapp

service

Smart

phone

Data

Ack

Ack

Ack

Data

Data

Radio access

delay

Total service delay

in radio access

Delay measured between messages in S1 interface

(Idle case includes paging and e-RAB setup delay).

00,000

00,432

00,864

01,296

01,728

02,160

Connected, no DRX

Idle DRX 160 ms cycle

DRX640 ms cycle

DRX2560 ms cycle

Average total service delay in S1 (s), paging cycle 640 ms, 20 ms DRX on duration

00,000

00,173

00,346

00,518

00,691

00,864

01,037

01,210

01,382

Connected, no DRX

Idle DRX 160 ms cycle

DRX640 ms cycle

DRX2560 ms cycle

Average delay of the first ACK in S1 (s), paging cycle 640 ms, 20 ms DRX on durationcDRX impact on data application latencies is not

significant based on the fact that any transaction can

anyway start either from idle or connected state.

8 © Nokia Siemens Networks

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