Asoka_Korale_Event_based_CYM_IET_2013_submitted linkedin

Annual Conference 2013 - IET- Sri Lanka

A SCHEME FOR EVENT TRIGGERED CELLULAR

YIELD ENHANCEMENT IN THIRD GENERATION

MOBILE NETWORKS

Asoka J.M. Korale, Ph.D, C.Eng. MIET.

Abstract: Competition between mobile network

operators has made it imperative that their

telecommunications network infrastructure is

used efficiently. Peak and off peak tariffs were

an attempt to put underutilised network

resources to use while ensuring that the network

was also able to meet the demands of the busy

hour traffic. This scheme however does not allow

for the close optimisation of network and cellular

resources as the local traffic conditions in groups

of cells across the network will have widely

different utilisation levels across time of day and

day of week. This requires that the cellular

utilization is enhanced in a dynamic way

considering groups of cells in particular localities

and at particular times as opposed to on a global

or network wide basis.

This paper presents a method by which cellular

utilisation levels can be enhanced in selected cells

by making offers to subscribers encouraging

them to utilize network services. The offers will

be made in a dynamic fashion choosing different

cells at different times of the day depending on

the cellular load level and be communicated to

the subscribers using the cell broadcast service.

With this technique it will be possible to offer

reduced tariffs during times of low utilisation in

certain cells, while at the same time ensuring

that the tariffs in cells with high load are not

impacted. This will result in maximising the

revenues that can be obtained by maximizing the

cellular yield. The paper also presents key

performance indicators and measures that can

be used for assessing the load in a cell and a

framework for selecting candidate cells in which

the utilisation enhancement is to be carried out.

1. INTRODUCTION

The competitive challenges faced by mobile

network operators have made it imperative that their

telecommunications network infrastructure is used

efficiently. There is little room to leave idle

resources in the network. The pressure on capital

expenditure outlays, determine the level to which

the network is overbuilt to handle busy hour traffic.

Choosing the right mix of network coverage and

capacity has a great impact on the quality of service

experienced by the subscribers which in turn

determines their loyalty and churn propensity.

It is therefore incumbent upon the operators to

ensure a more even utilisation of the network

elements by trying to avoid peaks and troughs in the

utilisation level across time of day and day of week.

The special tariffs for peak and off peak times of the

day, is an attempt to put underutilised network

resources to use while ensuring that the network is

also able to cater to the needs of the subscribers

during periods of heavy load.

This method however does not allow for the close

monitoring and optimisation of cell load across the

network, as it ideally has to be done at the

individual cell level or across groups consisting of a

few cells at a given point in time. There is an

inherent drawback in using one or two time

dependent tariffs to enhance utilisation levels across

all cells of the network. In other words all the cells

in the network will not behave in a similar manner


so that one global peak and off peak tariff is

applicable throughout the network at a particular

moment in time. This requires that the cellular

utilization is optimised in a dynamic way

considering groups of cells in particular localities as

opposed to a global or on a network wide basis.

At the present time there are Dynamic Discount

Systems (DDS) that attempt to increase cellular

yield by making discounted offers to subscribers in

selected cells. The workings of these systems are

proprietary and not disclosed to operators or the

public. This paper describes how such systems may

be implemented in-house at a mobile operator. As

such this paper presents a method by which the

cellular utilisation can be enhanced by encouraging

subscribers by way of incentives to use mobile

services in situations of low cellular load measured

in individual or groups of cells. This technique can

even be extended to situations of high load where

subscribers are given incentives to delay making

use of the telecommunications services until the

peaks in the utilisation level has passed. As

individual cells or groups of cells can be selected

from any part of the network at any given moment

in time for this utilisation enhancement, there is no

temporal or geographic limitation in the choice of

cells selected. It therefore presents vast

opportunities for the operator to gain additional

revenue by increasing the utilisation levels

Thus under conditions of light cellular load the

subscribers can be urged to make use of the

telecommunications services that take up large

bandwidth like video calls, streaming services and

network games. And under conditions of high load

a message could be broadcast to users in the

respective cells with offers to delay the use of

bandwidth intensive services for a later time at

lower tariffs. This type of system is already

deployed in certain markets under the broad

classification of Dynamic Discount Systems (DDS)

the workings of which are confidential and

proprietary. There are at present several equipment

manufactures like Ericsson of Sweden and Huawei

and ZTE of China that offer complete DDS

solutions, [5], [6].

This paper presents the means for making such a

system in house at a particular network operator

using existing network infrastructure. We also

describe the measurements needed for triggering

events based on cellular load, an algorithm for

selecting suitable cells for utilisation enhancement

and the requirements placed on the cell broadcast

server that will communicate the dynamic offers to

the subscribers in selected cells.

This scheme therefore illustrates techniques for

measuring the load of Universal Mobile

Telecommunications System (UMTS) cells across

the network. These measurements are then

transferred to a measurement processing system in

near real time. This system can be an external server

running an algorithm for processing cellular load

measurements and selecting suitable cells for

enhancing utilisation levels. These cells may be

selected based purely on their utilisation levels and

or considering other business and geographic

criteria. The algorithm thus gives the operator much

flexibility in the selection of cells for optimising

utilisation levels and thereby its revenues .

2. UMTS MECHANISMS FOR EFFICIENT

USE OF RADIO AND CELLULAR

RESOURCES [4]

UMTS employs several techniques to ensure that

radio and cellular resources are used efficiently.

Principal among them are Admission Control,

Transport Channel Switching, Radio Access Bearer

downsizing and Pre-emption, each of which are

briefly described below.

Admission Control: This algorithm controls the

allocation of new bearers and services carried in a

cell. It allows the allocation of new radio resources

to support new users and the allocation of new

bearers (reconfiguration of existing bearers) to

existing users as long as the resources allocated to

existing users of similar or higher priority are

unaffected.

Transport Channel Switching: This algorithm

changes the rate of the radio bearer allocated to a

particular user based on traffic volume and quality

measurements (such as error rate). Thus a user who

is initially assigned a high rate radio bearer may be

subsequently downgraded to a lower rate bearer if

for example the volume of traffic utilized by that

user is low freeing up resources for allocation to

other users.

Radio Access Bearer (RAB) downsizing: This

algorithm allocates a lower rate bearer at the

initiation of the call than requested depending on

the available resources as reported by the admission

control algorithm. Thus if the admission control

algorithm indicates that there is code/power

resource available for a 64kbit/s bearer when a

384kbit/s service has been requested the lower rate


may be allocated instead of rejecting the request

altogether due to the inability to meet the original

request. (this is particularly true in the case of

Interactive/Background class services)

Pre-emption: The allocation/ retention priority of a

radio link in a cell can be set to pre-empt users of

lower priority and admit users of higher priority in

to cell. These attributes are typically set based on

the Quality of Service (QOS) profile of a user.

Power reservation: When allocating power for High

Speed Downlink Packet Access (HSDPA) users in a

cell, certain schemes accomplish this objective by

modifying the data rates of interactive/ background

class services. A certain amount of cell power is

also reserved for use exclusively by HSDPA users.

Maximum Power Per Code: Limits the maximum

power transmitted to a user on a per service basis

with the objective of ensuring that a subscriber in

bad radio conditions does not end up consuming a

large amount transmit carrier power, leaving

capacity to serve other users.

3. ESTIMATING CELL LOAD

Techniques for measuring cell load levels in CDMA

systems typically depends on the direction of

transmission. The measurements for this purpose

are available from the Radio Network Controller

(RNC) and the messages passed over the Iub via

NBAP protocol (3GPP 25.433).

3.1 Cell Load on the Downlink

In the down link (DL) the typical cell load

measurements are transmitted carrier power, and

channelization code usage. Additionally aggregate

transmitted bit rates are also some times used to

determine a throughput based estimate of cell load.

In the case of power measurements the load is

commonly expressed as a proportion of the total DL

transmitted carrier power capability of the cell.

(Typically a proportion of the transmit power is also

reserved for HSDPA users.)

The proportion of the code tree utilized also

provides a measure of the load in the cell and is

related to the total transmitted data rates relative to

the total data rate capacity of the cell.

In throughput based estimation of load, the ratio

between the sums of the total data rates to all users

to the maximum allowed throughput of the cell

forms such a measure

3.2 Cell Load on the Uplink

In the up link the cell load measure is one of noise

rise, calculated from measurement of received total

wide band power (RTWP) in the cell. Noise rise is

typically computed as the ratio between the total

received wider band power to the noise floor (noise

floor may be a parameter or dynamically estimated

when the cell is not supporting any users).

Throughput based load estimation can also be

derived here as well, utilizing a construct that

defines it to be the ratio between the received power

at the cell from any given user to the total

interference power received at the cell (RTWP).

3.3 Cell Load Measure via the Admission

Control Algorithm

The admission control algorithm operating in the

RNC determines whether a call is admitted in to a

cell by checking the available resources of

transmitted carrier power and code on the down link

and expected rise in the interference levels on the

uplink. If both the expected load on the downlink

and uplink are within tolerable limits upon the

admission of the call the new call is admitted in to

the cell.

The admission control algorithm determines the

load contribution of each potential call by

calculating a load factor for each service which is

typically a function of EbNo target, bit rate, and

activity factor.

Thus one way of estimating cell load and potential

capacity of a cell is through this algorithm. Access

to statistics and logs relating to this algorithm will

be implementation dependent. So there us no

guarantee that all vendors will be able to provide

measurements internal to the admission control

algorithm.

Other factors like backhaul capacity on Iub and

channel element usage that are not directly related

to cell load in the classical sense also determine

whether a call is allowed in to a cell or not.

4. KEY PERFORMANCE INDICATORS FOR

TRIGGERING CELL LOAD EVENTS

The following Key Performance Indicators (KPIs)

can be used to determine when the cell load falls

below a certain suitable limit to activate the “Event

Triggered CYM” algorithm.


4.1 Cell Load on the Uplink

1. A measure of the Noise Rise in the cell can be

estimated by the ratio between RTWP and noise

floor. The noise floor (on the order of -108dbm) can

be used as a parameter or if a measurement via the

RNC is available at a suitable load level/time of

day.

2. Average Channel Element Utilization:

4.2 Cell Load on the Downlink

1. Transmitted Carrier Power as a proportion of

total transmitted carrier power capability of the cell.

MAX

TX

P

P

2. Transmitted carrier power of all codes not used

for HSDPA transmission as a proportion of total

transmitted carrier power capability of cell .

MAX

NonHS

P

P

2a. The ratio between Transmitted carrier powers of

all codes not used for HS transmission to the total

transmitted carrier power capability less

Transmitted carrier power plus the Transmitted

carrier power of all codes not used for HS

transmission can be considered.

TXMAXNonHS

NonHS

PPP

P

3. Ratio of Transmitted carrier power less

Transmitted carrier power of all codes not used for

HSDPA transmission to total transmitted carrier

power capability of cell.

MAX

NonHSTX

P

PP

3a. Ratio between Total transmitted carrier power

less Transmitted carrier power of all codes not used

for HS transmission to Total transmitted power

capability less Transmitted carrier power of all

codes not used for HS transmission.

NonHSMAX

NonHSTX

PP

PP

Note: In multi carrier environments with dedicated

carrier for HSDPA, direct ratio between HSDPA

power and max carrier power can be used to

estimate utilization. In dynamic power allocation

schemes all measures would be applicable. If

however fixed allocation is used for reserving

power for HSDPA measures 1,2,3 could be used

and additionally 2a and 3a could be used as is or by

accounting for the proportion that is reserved.

4. Level of Code tree utilization. The measurement

may not be available directly from all vendors and

so will need to be derived either from average data

rate/ bearer spreading factor measurements.

If the average spreading factors (SF) of the bearers

in use during a particular measurement period are

available, it would be possible to determine an

estimate for the code weight of each bearer by

dividing 512 by SF. Thus if two bearers of

spreading factor 128 and 64 were in use in the

measurement period, the code weight could be

considered to be 512/128 + 512/64 = 12, giving an

average utilization of 12/512. One must keep in

mind that the bearers won’t be active all the time

and a time weighted average is what should really

PNonHS

PHSDPA

PMAX

Figure 1: Shared Single Carrier

PTX


be used. If however the sampling intervals are

relatively short a fairly accurate estimate can be

obtained. In systems where dynamic code allocation

is implemented sharing of code resource between

R99 and HSDPA enables direct measure of

utilization, else the reserved portion can be counted

as part of the tree that is utilized.

5. Average Channel Element (CE) Utilization:

6. Iub resource availability: It may also be

necessary to factor in the backhaul capacity

depending on the current network planning.

5. FRAMEWORK FOR CELL SELECTION

The flow graph depicted in Figure 2, illustrates how

a candidate cell for cellular yield maximisation may

be selected. The thresholds utilised in the diagram

can be drawn from the triggering thresholds

described in “KPIs utilised for triggering cell load

events” of section 4. The measurements needed for

computing the KPIs can be obtained from the RNCs

on a near real time basis. It was found that Huawei,

Ericsson and ZTE equipment can provide the

measurements of power, noise rise, code and

channel element utilisation at a frequency of about

once every 15-20 minutes [7],[8],[9]. This time

interval is sufficient to obtain a realistic picture of

the cell load across the cells of interest on a near

real time basis.

As discussed earlier in the paper the cells may be

selected purely based on their utilisation levels or a

further consideration of the location of the cells may

also be taken in to account. Thus it may be that

certain zones could be established based on their

geographical locations where only certain types of

offers are made or it may be even that those zones

may be excluded entirely from the event based

cellular yield maximisation scheme. It may be that

those zones comprising certain groups of cells are

reserved entirely for campaigns utilizing the

location based service function of UMTS for

instance.

Determining the location of groups of users using a

location based server requires that they be

periodically paged so that the users transition in to a

Radio Resource Control (RRC) state that makes

their position available to the core network. For

example the network has no idea of the

geographical position of users in “Idle” Mode,

except at the “location area” level. The user will

have to be made to transition to “Connected” mode

in order to reveal its position. Paging a large

number of users regularly consumes a lot of

network resources so an intelligent paging

mechanism will have to be employed where once a

particular location of a user whose position is being

tracked is located, a further paging of its position

would not be made unless he happens to be near or

heading towards a particular zone of interest.

6. COMMUNICATING THE OFFER VIA THE

CELL BROADCAST CENTER

Cell broadcast is the proposed method for

communicating the offers to subscribers in the

selected cells. The Cell Broadcast Center (CBC)

allows the broadcast of unacknowledged general

Cell Broadcast Short Message Service (CBS)

messages to be broadcast in what is known as a

service area. A service area is a single cell or a

collection of cells, or it could even encompass the

entire PLMN. Cell broadcast has the advantage that

Periodic Cell Measurements

Is UL Noise Rise (or RTWP) < Noise Rise Activation threshold

Is UL CE Utilization < UL CE Utilization Activation threshold

Is Code Utilization < Code Utilization Activation threshold

Is DL Power KPI < DL Power Activation threshold

Is DL CE Utilization < DL CE Utilization Activation threshold

Is Iub Utilization < Iub Utilization Activation threshold

Candidate Cell for CYM

Y

N

N

N

N

N

N

Y

Y

Y

Y

Y

Figure 2: Cell Selection for CYM


users in the RRC state of Idle Mode can receive the

message. It thus can reach the vast majority of

subscribers in a service area.

A CBS page consists of 82 octets that correspond to

93 characters when using the default character set

[1]. Up to 15 such pages can be concatenated to

form a single CBS message. Each page will have a

message identifier and a serial number. For a single

message the message identifier and serial number

will be the same across the pages allowing the user

equipment (UE) to ignore re-broadcasts of already

received messages. The operator/information

provider will determine the duration and frequency

of the cyclical broadcast of the CBS messages [1].

Uu

CellBroadcast

Center

(CBC)

UTRAN

RNCNode B

Node BUE

UE

1

Iub

IuBC

Figure 3, presents the network elements, the

interfaces and the position of the CBC as defined in

3GPP 23.041.

The display of the messages on the handsets is not

defined or standardized in the 3GPP standards and

is left to the handset manufacturer to arrive at a

suitable implementation.

The messages to be broadcast via the CBC can be

determined via a program running on a server and

provided to the CBC through an API. Thus the

messages can change from time to time, location to

location and the particular level of cell load

experienced in the cells of interest at a given point

in time. In this way the operator has access to a vast

array of strategies with which to broadcast offers

and incentives to the subscribers chosen from an

array of cells and established zones.

7. CONCLUS ION

Dynamic discount systems are already deployed in

several African and South Asian markets, but their

workings are confidential and proprietary. No

information on the inner workings of the system,

the measurements used, the cell selection methods

and the discount calculation techniques are

available to the operators. The solution is provided

literally as black box to the mobile network

operators. Thus certain operators have attempted to

develop solutions in-house as all the measurements

are available from existing RNCs and the

commercially available Cell Broadcast servers have

the necessary functionality and flexibility. Typically

such a solution devised at a network operator need

not be simulated in a network simulator as typically

such simulators only simulate the radio access

network or core network and not the interactions

between devices such as RNCs and cell broadcast

servers.

This paper presented a framework that can be used

to enhance the utilization of lightly loaded cells in

third generation mobile communications systems

and construct a dynamic discount system inhouse.

The measures of cell load on the up link and

downlink were studied with a view to defining

metrics that can be used to define triggering

thresholds. These triggering thresholds do not have

to be the same for all the cells across the network

and can take different values depending on the

specific situation of the cell or cells under

consideration.

The cells for utilization enhancement can be

selected based on their utilization levels or on their

specific geographic location or based on both

considerations. The time factor may also be taken in

to account where cells in certain zones may or may

not be impacted by the event based CYM depending

on the specific time of day. The event based CYM

technique allows for the deployment of a vast array

of strategies for the enhancement of utilization

levels in cells of interest and opens up new avenues

for revenue generation.

8. REFERENCES

[1] 3GPP TS 23.041, Release 5.



[4] Harri Holma and Antti Toskala, WCDMA for

UMTS, John Wiley & Sons Ltd, 2006, pp187-218

[5] Cell Broadcast Server, R5, description, Huawei

Technologies.

[6] Dynamic Discount Solution, R3.0, description,

Ericsson.

Figure 3: CBC interfaces [1]


[7] WCDMA RNC, BSC6800 v1.0 Description,

Huawei Technologies

[8] ZXWR RNC V3.0 Description, ZTE.

[9] 9370 V.10 Radio Network Controller

Description, Ericsson.

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Asoka_Korale_Event_based_CYM_IET_2013_submitted linkedin