Abstract — This paper presents a novel mechanism which

increases mobile terminal battery performance. It supports a

cell reselection algorithm which decides on which cell, user

equipment (UE) is camped on when in idle mode (there is no

active radio connection with a mobile network). Study is based

on real 3G UTRA network measurements. Authors propose a

technique to reduce UE current consumption in idle mode

based on dynamic Sintrasearch neighbour cell measurements

threshold optimization. System analysis covers both UTRA and

E-UTRA - Long Term Evolution (LTE) technology.

Index Terms — Energy-Efficient Protocols, Cell Reselection,

Land Mobile Radio Cellular Systems, SON, LTE, UE power

consumption, idle mode measurements

I. INTRODUCTION

he design of cellular mobile communication systems has

traditionally been based on conventional radio network

planning. One of the main problems, which can be found in

any cellular wireless system, is achieving a good radio

network configuration and optimization. In currently

deployed 3G networks (based on 3GPP UTRAN

technology), a mobile operator needs to put significant

amount of effort to optimize parameters controlling its radio

access network performance. This process can be very

expensive and time consuming as it may require human

input rather than dynamic automated procedures (high

OPEX). Increasing complexity of network configuration

resulted in new trends introduced by network operators to

simplify and automate those procedures. This could be

achieved by new automated self-optimization mechanisms

and algorithms available in the mobile network. As a part of

ongoing cellular mobile network evolution, 3GPP

organization specified some features for future 3.9G Long

Term Evolution (LTE) networks to support Self Organizing /

Optimizing Network (SON) concept in Evolved UMTS

Terrestrial Radio Access Network (E-UTRAN) specification

[1, 2]. In addition to that, another industry organization -

Next Generation Mobile Networks Alliance (NGMN)

further developed proposed 3GPP SON use cases providing

technical view of the mobile operator community on the

problem of network planning, deployment, optimization and

maintenance [6, 7]. Another example of the continuous self-

organization vision in wireless networks was developed and

described as a result of research project SOCRATES [9, 10].

Current state of the art in SON research refers mainly to

improvements in network algorithms (e.g. main driver for

energy savings use case is OPEX decrease achieved by

reduced energy consumption in the network e.g. cell switch

on/off [1]). In addition it would be desirable to study

application of SON algorithms to UE performance

improvements. Currently less research focus has been given

to self-optimization mechanisms dedicated to increase UE

energy efficiency. From commercial point of view, main

driver for mobile terminal development is increased data

throughput. A serious disadvantage of higher quality of

service provided by new multimedia services is significantly

increased current consumption in a mobile terminal. To

overcome this problem, in parallel to increasing data transfer

speeds, consideration should be given to new system level

methods to optimize UE battery efficiency. Current research

activities in SON mainly relate to UE active mode (there is a

dedicated radio connection established with RAN and cell

mobility is controlled by handovers triggered by the

network). There has been less work focused on idle mode

(no dedicated RAN connection) and on minimising UE

battery consumption. In this paper, we present an idea to

support lower UE battery consumption without

compromising general idle mode performance.

II. IDLE MODE UE BATTERY PERFORMANCE FACTORS IN THE

3GPP 3G UTRAN TECHNOLOGY

In idle mode of operation, UE periodically (using

discontinuous reception - DRX) monitors performance of

current serving cell and neighbour cells to maintain service

continuity for the user. Based on relative cell quality or

power, UE triggers cell reselection procedure when there is

better cell available from a radio point of view.

Interfrequency and inter-RAT reselections may also be

prioritized depending on eg the level of service offered on

each carrier. These procedures allow the UE to camp on the

most appropriate cell. To facilitate reselections, the UE shall

attempt to detect, synchronise, and monitor intra-frequency,

inter-frequency and inter-RAT cells indicated in the

measurement control system information of the serving cell.

UE measurement activity is controlled by measurement

rules, allowing the UE to limit its measurement activity and

thus save power if certain conditions are fulfilled [8]. The

reselection procedure is controlled by UE and is using

configuration parameters broadcasted by RAN on a per cell

basis in system information messages (SIB messages). From

mobility point of view, idle mode cell reselection is similar

Battery Life Idle Parameter Optimization of UE

in Self Organizing Network

Tomasz Mach, Rahim Tafazolli

Centre for Communication Systems Research, University of Surrey, U.K. t.mach@surrey.ac.uk, r.tafazolli@surrey.ac.uk

T

2010 IEEE 21st International Symposium on Personal Indoor and Mobile Radio Communications

978-1-4244-8016-6/10/$26.00 ©2010 IEEE 1332

to active mode hard handover except that the evaluation of

the need for reselections is performed autonomously by the

UE, rather than under network control.

As a result of detailed 3GPP UTRAN system analysis,

authors identified an interesting problem related to the

optimisation of neighbour cell measurement threshold

(Sintrasearch) in idle mode. Sintrasearch is an optional parameter

provided by network in SIB data and specifies the threshold

(in dB) below which intrafrequency measurements should be

performed.

According to the 3GPP Release 8 specification TS 25.304

[3] section 5.2.6.1.1, neighbour cell measurements rules are

defined as follows:

• If Squal > Sintrasearch, UE may choose to not perform

intra-frequency measurements

• If Squal <= Sintrasearch, perform intra-frequency

measurements

• If Sintrasearch, is not sent for serving cell, perform intra-

frequency measurements

Where:

• Squal [dB] = Qqualmeas – Qqualmin

• Qqualmeas – Measured cell quality value. The quality of

the received signal expressed in CPICH (Common

Pilot Channel) Ec/No [dB], see [5] for detailed

definition

• Qqualmin – Minimum required quality level in the cell

[dB]

Detailed requirements for intra-frequency measurements and

filtering in UE are defined in [8]. Fig. 1 graphically presents

idle mode neighbour cell measurements parameters

described above used during cell reselection process in UE.

As it can be seen on the Fig. 1, Sintrasearch setting in SIB could

make UE battery life worse in idle mode if set too high. This

would happen due to additional UE effort required for

measuring adjacent cells performance before cell reselection

happens. The higher the Sintrasearch threshold value, the sooner

UE starts neighbour cell measurements before expected cell

reselection to better quality cell. Current commercial 3G

networks appear to typically define Sintrasearch as a static

parameter on a per cell basis. Such a solution includes the

following disadvantages:

• When cell conditions change (Ec/No) due to traffic

load change, static Sintrasearch could be suboptimal

• Finding the optimal parameter value taking into

account scattered and varying cell coverage could be

difficult and costly for mobile operator

• When Sintrasearch is set too high there could be many

UEs in the cell which measure neighbour cells

unnecessarily

Considering those factors it was identified that current

solution based on static network setting could be suboptimal

with possible space for some UE battery performance

improvement with development and support of new

dedicated Sintrasearch optimisation algorithm. An identical

argument would be applicable to E-UTRAN (LTE)

technology.

To support further analysis, ‘How serious is the UE battery

performance problem?’ study was done based on real Ec/No

measurements taken from UE in four different commercial

3G mobile networks. This will be further described in next

section.

Fig. 1. Neighbour cell measurements parameters in idle mode

III. HOW SERIOUS IS THE UE BATTERY PERFORMANCE

PROBLEM IN REAL 3G NETWORKS ?

Based on real-time logs gathered by UMTS user terminal

in four commercial wireless networks, a study was done on

how much intrafrequency Sintrasearch threshold setting could

be optimised. All measurements are based on outdoor

mobility scenario between many macro cells (user in a car).

Based on the logs provided, analysis of the time spent above

and below the threshold shows how much UE idle mode

battery consumption could be decreased by optimising

Sintrasearch value in the network (without failing to perform

any of the reselections that were seen in the mobility

scenario captured in the logs). Table 1 presents logs

characteristics for the four networks analysed: A, B, C, D.

Figures 2, 3, 4 and 5 present UE measured Ec/No values

with related Sintrasearch parameter set by the network operator.

Parameter Network A Network B Network C Network D

Log length [s] 940 640 640 710

Number of

intrafrequency

cell reselections

11 7 14 14

Sintrasearch[dB] -6 -4 -7 -2

Table 1. Detailed log data (length, number of idle mode cell reselections,

and Sintrasearch value) for analysed networks A, B, C and D

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-25

-20

-15

-10

-5

0

Ec/No[dB]

Sintrasearch

940[s]

Fig. 2. UE measured Ec/No values in network A with Sintrasearch threshold

-25

-20

-15

-10

-5

0

Ec/No [dB]

Sintrasearch

640[s]

Fig. 3. UE measured Ec/No values in network B with Sintrasearch threshold

-25

-20

-15

-10

-5

0

Ec/No[dB]

Sintrasearch

640[s]

Fig. 4. UE measured Ec/No values in network C with Sintrasearch threshold

-25

-20

-15

-10

-5

0

Ec/No[dB]

Sintrasearch

710[s]

Fig. 5. UE measured Ec/No values in network D with Sintrasearch threshold

IV. ANALYSIS DETAILS AND THRESHOLD OPTIMISATION

METHOD IN SON

Based on the logs from real networks, it can be seen that

in all cases UE spent significant amount of time below

Sintrasearch threshold. As a result of high value of this

threshold set in networks B and D, measured Ec/No value

stays below configured Sintrasearch almost all the time. From

UE implementation point of view, this requires continuous

attempts (based on DRX cycle) to search and measure new

neighbour cells on this frequency despite high serving cell

signal quality. As a result, some idle mode battery life

improvement could be achieved by Sintrasearch threshold

optimisation but the process should not compromise idle UE

mobility. It could be achieved by introducing new automated

dynamic measurement threshold adjustment mechanism (per

cell) supported by SON algorithms. The following algorithm

could implement this mechanism in every cell:

1. Set initial Sintrasearch threshold value in the cell

(Current Sintrasearch on Fig.6)

2. During every cell reselection, UE(s) measures

‘Sintrasearch delta’ parameter ( defined as a difference

between Current Sintrasearch and Ec/No during cell

reselection event - see Fig. 6 for details) and report it

to the network.

3. Based on statistical analysis of reported parameters

from many UEs, network could adapt Sintrasearch value

accordingly (Optimised Sintrasearch on Fig.6) .

More detailed analysis of gathered logs shows how much

UE idle mode battery consumption could be decreased by

optimising Sintrasearch value in the network. To quantify

expected savings a method was proposed to find optimal

value of intrafrequency Sintrasearch measurement threshold in

UE based on ‘Sintrasearch delta’ parameter calculation in idle

mode. The method with definition of the ‘Sintrasearch delta’

parameter is illustrated on Figure 6.

Fig. 6. Method of finding optimal value of intrafrequency Sintrasearch

measurement threshold in UE based on ‘Sintrasearch delta’ calculation during

idle mode cell reselection (Treselection shown is a SIB parameter (timer)

after which reselection to the neighbour cell is triggered in UE). Parameter

‘Sintrasearch delta’ is defined as a difference between ‘Current Sintrasearch‘ and

Ec/No during cell reselection event. ‘Optimised Sintrasearch’ parameter is

‘Current Sintrasearch ‘ reduced by ‘Sintrasearch delta ‘

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The following assumptions were used in the evaluation of

the proposed method:

• Based on a Ec/No values in the logs, Sintrasearch delta

was calculated during every cell reselection.

• Gathered Sintrasearch delta values were averaged on a

per log basis to find Optimised Sintrasearch threshold

value based on a formula:

Optimised Sintrasearch = Current Sintrasearch +

Sintrasearch delta averaged

• Based on calculated Optimised Sintrasearch value,

potential UE battery saving in the log was estimated

assuming 10% and 20% higher battery consumption

when measured Ec/No was below optimised

measurement threshold (due to additional UE

processing effort required for searching and

measuring neighbour intrafrequency cells).

Table 2 shows as an example Ec/No values with related

Sintrasearch delta values measured during cell reselections in

network D.

Ec/No during reselection [dB]

Sintrasearch delta[dB]

-10 -8

-9 -7

-11 -9

-7.2 -5.2

-10.4 -8.4

-11.6 -9.6

-14 -12

-14 -12

-15.5 -13.5

-12 -10

-7.5 -5.5

-12 -10

-11.5 -9.5

-11.3 -9.3

Table 2. Measured Ec/No values with related Sintrasearch delta values during

cell reselections in network D

V. SUMMARY OF RESULTS

Table 3 below shows estimated UE battery saving figures

for all analysed networks based on Optimised Sintrasearch

threshold. It could be observed from the table that estimated

UE battery saving values are between 2 - 8% (assuming 10%

increase in battery consumption below Sintrasearch) or 4 - 16%

(assuming 20% increase in battery consumption below

Sintrasearch). Those numbers are directly related to the terminal

standby time in idle mode.

Parameter Network

A

Network

B

Network

C

Network

D

Log length [s] 940 640 640 710

Number of intrafrequency cell

reselections in log

11

7

14

14

Sintrasearch[dB] -6 -4 -7 -2

Optimised Sintrasearch [dB] -8.3 -10.17 -9.28 -11.21

Estimated UE battery saving

based on Optimised Sintrasearch

(assuming 10% higher battery

consumption below Sintrasearch)

2.88%

8.11%

1.83%

8.22%

Estimated UE battery saving

based on Optimised Sintrasearch

(assuming 20% higher battery

consumption below Sintrasearch)

6.07%

16.36%

3.94%

16.43%

Table 3. Calculated Optimised Sintrasearch values derived from Sintrasearch

delta averaged with estimated UE battery saving figures for networks A,

B, C and D

The following conclusions were drawn from the analysis

performed in previous sections:

• Current UTRAN Sintrasearch scheme seems to be

typically based on static setting provided by a

network which is ineffective in terms of UE battery

consumption

• Sintrasearch setting is a balance between UE battery

efficiency and camping cell quality which could be

optimised with minimal compromise of idle

mobility performance

• Studied commercial networks were observed to use

the same constant Sintrasearch value across many cells

in their network, as a result there is still space for

Sintrasearch threshold optimisation on a per cell basis

• Problem of suboptimal static Sintrasearch threshold

exists both for UTRAN and E-UTRAN (LTE)

• Existing mechanism is proposed to be improved by

novel automated dynamic Sintrasearch threshold

adaptation mechanism supported by new SON

algorithms

• Estimated idle mode battery savings are different

between analysed networks but based on the logs

provided and assuming 20% higher UE battery

consumption below Sintrasearch threshold, possible

averaged savings could be between 4 - 16%.

Assuming 10 days average mobile terminal idle

standby time, possible increase in standby time

would be between 0.5 – 1.5 days

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• Battery saving results would be higher if Sintrasearch

separately adjusted on a per cell basis instead of a

fixed value for the area evaluated in the log

• Similar solutions could be applied to interfrequency

(Sintersearch parameter) and interRAT (SinterRAT

parameter) neighbour cell measurement thresholds

to support further battery savings.

REFERENCES

[1] 3GPP TS 36.902 Evolved Universal Terrestrial Radio Access

Network (E-UTRAN); Self-configuring and self-optimizing network

(SON) use cases and solutions, 2009

[2] 3GPP TS 32.521 Telecommunication management; Self-Organizing

Networks (SON); Self-optimization; Concepts and requirements,

2009

[3] 3GPP TS 25.304 User Equipment (UE) procedures in idle mode and

procedures for cell reselection in connected mode, 2009

[4] 3GPP TR 36.805 Evolved Universal Terrestrial Radio Access (E-

UTRA); Study on minimization of drive-tests in next generation

networks, 2009

[5] 3GPP TS 25.215 Physical layer – Measurements (FDD), 2009

[6] NGMN Alliance “Next Generation Mobile Networks Use Cases

related to Self Organising Network, Overall Description”, 2008

[7] NGMN Alliance “Next Generation Mobile Networks Informative List

of SON Use Cases”, 2007

[8] 3GPP TS 25.133 Requirements for support of radio resource

management (FDD), 2009

[9] SOCRATES (Self-Optimisation and self-ConfiguRATion in wirelEss

networkS) research project, www.fp7-socrates.eu, 2009

[10] INFSO-ICT-216284 SOCRATES D2.2 Requirements for Self-

Organising Networks, www.fp7-

socrates.eu/files/Deliverables/SOCRATES_D2.2%20Requirements%

20for%20self-organising%20networks.pdf, 2009

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