wcdma radio access network dimensioning for multiple services

8/22/2019 WCDMA Radio Access Network Dimensioning for Multiple Services

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WCDMA Radio Access Network Dimensioning for Multiple Services

Igor S. Simi, Ericsson d.o.o, V. Popovia 6, Beograd

[email protected]

I. INTRODUCTION

One of the most important characteristics of WCDMA is the

fact that power is the common shared resource. This makes

WCDMA very flexible in handling mixed services and

services with variable bit-rate demands. Other aspect of the

pooled downlink output power resource is an impact on the

radio access network (RAN) design. To diverse users

different amount of maximum output power can be assigned

depending on its service and its downlink interference

situation.

Since all the users share the same power and the same

frequency, the origination of new calls, or the re-negotiation

of the existing ones modifies the transmitted power in the

uplink and downlink affecting the quality of service (QoS)

of all the users. The power and frequency sharing results in a

soft capacity characteristics; no block exists in the system. In

principle new users can be accepted in the system, tolerating

a QoS degradation at cell edge. For this reason in WCDMA,

the radio network planning and radio resource management

algorithms are intended to minimize the transmitted power in

the uplink and in the downlink, in order to achieve the full

exploitation of system capacity and performance.

The RAKE receiver attempts to recover as much power as

possible from the cells in the mobile's active set(the cells it is

in soft handoff with). Any non-recovered power is

interference as far as the connection in question is concerned

and will degrade the achieved QoS. Power control outer

loops will attempt to compensate, thus increasing

interference and lowering capacity.

When there is low load in the system, the users do not

generate much interference. The majority of the interference

is non-power controlled, i.e. background noise or

interference from the non-power controlled downlink

broadcast channels. For the low load cases, the coverage is

higher since the users in a cell do not generate much

interference. During high load on the other hand, the power-

controlled interference from the users constitutes the majority

of the total interference and the maximum coverage is

reduced. Further, since the majority of the interference is

power controlled, changes in number of users will now have

a larger impact on the system. The quality based power

control leads to a trade-off between coverage and capacity.

Different operators will use UMTS to solve their diverse

needs. The usage of data services will depend on services

and terminals available, operators profile including theirchoice of charging and the competing media at that time.

From end-user and application point of view four major

service classes can be identified and separated into:

Real time applications Conversational class, where the QoS have to preserve

time relation (variation) between information entities and

to have a low delay (voice, video, CS data);

Streaming class, where the QoS have to preserve time

relation between information entities (video or audio

streaming);

Non-real time applications Background class, where the destination is not expecting

the data within a certain time but with preserved payload

content (email, messaging);

Interactive class, where a request/response pattern is of

importance and the payload content must be preserved

(WWW, ftp, telemetry).

When a user equipment (UE) wants to establish a connection

to the core network (CN), regardless of which applications to

be used, the UE will ask for a RAB with a set of Quality of

Service (QoS) attributes. The RAB is a point-to-point

connection between a UE and the core network. The mostimportant attributes are:

QoS class: Conversational, streaming, interactive or

background

Maximum bit rate: Highest bit rate desired

Guaranteed bit rate: Lowest bit rate acceptable

The RAB connection is realized as a radio bearer connection

between the UE and RNC and an Iu bearer connection

between RNC and CN. Table 1 shows a method of how

applications can be mapped onto radio bearers.

Application RAB class Radio bearer UL/DLVoice Conversational 12.2 kbit/s + 3.4 kbit/s SRBVideo

telephonyConversational

Conversational1 64 kbit/s +

3.4 kbit/s SRB

Packet data

(web, e-mail

ftp, etc)

Interactive,

background,

streaming

32 kbit/s (FACH)

64/64 kbit/s+3.4 kbit/s SRB



V.90

ModemConversational 57.6 kbit/s + 3.4 kbit/s SRB

Voice +

packet data

Conversational

+ (interactive or

background)

12.2 kbit/s + 64/64 kbit/s +

+ 3.4 kbit/s SRB

Table 1 Mapping of typical applications to available radio

access bearers (RAB)

There are strong relation between network costs and services

used in dimensioning. Therefore RAN design strategy is very


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important and should be considered first. Several concepts

could be used:

1) For 2G operators the best solution is reuse of existing

sites. It might be very inefficient to begin with a network

for low-date rate services and make it tighter later on.

2) Key service dimensioning strategy where key

service is typical service the company has based its 3G

strategy upon. Key service should be significantimprovement over 2G services and have to be available

everywhere. Since coverage area depends strongly of the

service, it must also be taken into account when

choosing the key service (Vodafone data services and

3s video telephony).

3) RAN planning for predicted traffic demand and multiple

services - variable load dimensioning methodology.

Method is presented in section III.

II COVERAGE AND CAPACITY ESTIMATION

UPLINK CAPACITY

Derivation of system capacity on generic basic become

increasingly difficult with variability of services. The time

consuming simulation are usually used for obtaining capacity

figures. In this section rough capacity estimate is presented

mainly for dimensioning purposes.

Each mobile user equipment (UE) m, must be received in the

base station with a signal Sm that produces the target (S/I)m. It

is assumed that all mobiles requires the same target (S/I)m =

m and have perfect power control.

mthothown

mm

mtot

m

m SNII

S

SI

S

I

S

++==

=

(1)

whereNth is thermal noise power spectral density,Iown is total

received power from mobiles in own cell andIoth is total

received power from mobiles in other cells + interference

from other sources.

UE is performing transmitting power update in order to

maintain theEb/Io ratio constant. The ratio betweenEb/Ioand

signal to interference ratio (S/I)m can be expressed by:

p

b

m G

IE

I

S 0/=

(2)

where required Eb/I0 is ratio between energy per bit and

spectral interference density. From (1) and (2) can be

expressed:

tot

b

p

I

IE

GS

0/

1

1

+= (3)

Further ifMmobiles is connected to own cell

tot

b

pth

M

i

ithtot I

IE

G

MFNSNI

0

1

/1

)1(

+++=+=

=

(4)

where F is the ratio between the interference coming from

neighbouring cells and the own cell interferenceIoth/Iown.

From (4) it is possible to calculate the noise rise, the ratio

between interference caused by other UEs and the thermal

noise:

th

thoth

pole

th

totul

N

NI

MMN

II

+

==

1

1 (5)

Mpole is a theoretical maximal number of UEs attached to a

cell. This number can not be reached since the interference in

the cell would be infinite. From (4) and (5) with assumption

Iulis infiniteMpole is expressed as:

+

=ob

p

poleIE

G

FM

/1

1. (6)

For several services i.e. to several different targets noise

rise expression can be generalised:

th

thoth

Kpole

K

polepole

th

totul

N

NI

M

M

M

M

M

MN

II

+

==

,2,

2

1,

1 ...1

1 (7)

In WCDMA analysis, it is expected to define the cell loading.

For single service load is defined as:

poleM

MLoading= (8)

whereMis the number of simultaneous users in the cell.

For a multi-service system where the services utilize different

types of RABs, the equation can be written as:

...M

MM

MM

MLoading,pole,pole,pole

+++=3

3

2

2

1

1 (9)

where

Mn is the number of simultaneous users for the n RAB

Mpole,n is the uplink pole capacity for the n RAB.

UPLINK COVERAGE

Conventional link-budget (maximum path-loss for which a

system should be planned) could be determined for uplink.

lpathmax = PUE Bsens. + PCmarg IUL - LNFmarg Gb (10)

where

lpathmax is the maximum path loss due to propagation [dB].

PUE is the maximum UE output power [dBm].

Bsens is the Node B sensitivity [dB]

PCmarg is the power control margin [dB]

LNFmarg is the log-normal fading margin [dB].

IUL is the noise rise [dB]

Gb is the sum of all UL gains and loses at Node-B and

terminal, including antenna gains and body loss.

The unloaded Node B has the sensitivity level without any

interference contribution from other UEs, and can be

expressed as:

0/log10 NERNNB bInfoftsens +++= [dBm] (11)


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where

Eb/N0 is the ratio between bit energy and noise spectral

density [dB]

Nt is the thermal noise power density (174 dBm/Hz)Nf is the noise figure

RInfo is the information bit rate

From (10) and (11) it can been seen that bit-rate and noiseraise have strongest influence on the uplink budget.

DOWNLINK CAPACITY

In downlink, the number of scrambling codes and the power

are limiting capacity. In an interference limited case both

single code power and total base station power can limit the

capacity. However, if flexible power allocation is assumed,

the total power will become the main limiting factor. This

concept of capacity estimation is given in [1] and presented

in this section.

The downlink in WCDMA consists of dedicated andcommon channels. Dedicated channels are power controlled

with rate of 1500 Hz, while the common channels are

transmitted with a constant power. The common channels

can be divided into two groups: a no orthogonal

synchronisation channels and rest referred as orthogonal

common channels. Interference could be seen as sum of

powers from other cells and the synchronisations channels.

Due to multipath propagation a fraction of the receivedown cell power is experienced as intracell interference.

lm

PTOT, Ptch,m Im

other

UEm

Figure 1. Downlink power distribution.

It is possible to derive some simplified expressions for (S/I)and the total power consumption,PTOT.

The (S/I)k experienced by mobile m in a position with

attenuation lk

is given by simplified equation:

m

thotherm

mTOTm

mm

m NIlP

lP

I

S

++

=

)(

(12)

PTOT

is the total power transmitted by the base station

mis a parameter that models the orthogonally with respectto all other channels in own cell

Pm is the power transmitted on the channel referred to mobilem

Im

otheris the interference from other cells (and other sources

of interference)

mis the target (S/I)m for mobile m. and

lmis the path loss for mobile m

For the traffic channelPtch,m is

m

m

thotherm

mTOTmmtch

l

NIlPP

)(,

++= (13)

The total power consumption from the base station is equal to

m

m

thotherm

mTOTmM

m

cch

M

m

mtchcchTOT

l

NIlPP

PPP

)(

1

1

,

+++=

=+=

=

= (14)

and

capm

thothermM

m

cch

TOT PM

l

NIP

P

++

==

1

)(

1 (15)

where PCCHis the power allocated to orthogonal downlink

common control channels. It is assumed that all UEs require

the same (S/I), i.e.m=and that the orthogonally factor is

position independent i.e. m = . It is obvious thatM < 1/= Mpolebut also that the total power consumption (Ptot)cannot be higher than the maximum of the node-B output

power(Pcap),

Including soft handover (macro-diversity) gain in (13),m,Ptch,mbecomes

mm

b

m

thotherm

mTOTmmtch

l

NIlPP

)1(

)(, +

++= (16)

where

sm

nmb

snn

b

m

I

SI

S

,

,

,1 )(

)(

=

=

b indicates the number of legs in the soft handover and s is

the node-B with the best (S/I) arriving at UE position. The

total power consumption from the base station then becomes

mm

b

m

thotherm

mTOTm

SHOM

m

AS

b

cch

SHOM

m

mtch

AS

b

cchTOT

l

NIlPbP

PbPP

b

b

)1(

)(

11

1

,

1

+++

+=

=+=

==

== (17)

where

Mis the number of simultaneous users in cell;

AS is the active set size;

SHOb is the fraction of users that are in soft/softer

handover with b node-Bs.

Total required power is


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capAS

bb

b

mb

k

thotherkSHOM

m

AS

b

cch

TOT PSHOb

M

l

NIbP

P

b

+

++

+=

=

==

1

11

11

)1(

)(

(18)

forPTOT= M=Mpoleand it is

= +

++

=AS

bb

b

b

polebSHO

F

M

2

)1

)1(1)((

1

(19)

whereFis a ratio between the received intercell and intracell

powers assumed to be constant for all users in the cell.

When expressingMpole it is assumed that total node-B power

is unlimited. However, in reality this is not the case. There

are two kinds of power limitation: a maximum value of total

node-B output power, and maximum value for single

dedicated channel.

Using capacity and coverage formulas above for rural area

and different Node-B power capabilitiesPcap number of voice

users (12.2 kbps) as function of path-loss is calculated in

Figure 2. For path-loss calculations Okumura-Hata model is

used. Common pilot channel power is 10% of Pcap. It is

assumed: log normal fading margin for rural area and 90%

coverage probability, UL power control margin of 1.5 dB,

antenna gain 19.5 dB, Node-B antenna height 25 m and UL

load limit 60%, and LNA used for UL coverage

improvement.

05

1015202530354045

143.3 146.2 148.6 150.5 152.6 154.3 155.5 157.2Path-loss [dB]

Voiceusers

60W 30W 20W UL

Figure 2 . Capacity-coverage curves for up and down link.

III. VARIABLE LOAD DIMENSIONING METODOLOGY

In GSM there was time slot and frequency separation

between users, therefore co-interference caused by other

service users did not exist. In 3G inherent flexibility in

handling data rates and service types has to be considered in

network dimensioning process.

In a WCDMA system the cell breathes, which means that

when loaded with a certain amount of traffic the coverage

decreases due to the increased interference in the cell. Aninitial value for the cell load can be determined by comparing

the traffic volume of the different bearer services to the initial

number of sites. The resulting cell load will give a new link

budget and thereby result in a corrected number of cells, and

again a corrected load factor. This process converges at a

certain number of node-B sites.

The ratio access network dimensioning intends to find the

required amount of sites, the capacity per cell and the load,

based on the constraints in the air interface. Depending on

the given input parameters and the degree of freedom in the

dimensioning there are a number of approaches available.

In this section the most common method is presented. In

general the output from dimensioning should be: number of

sites, site configuration, traffic carried per site/cell, capacity

per site/cell. Design input constants are: offered network

traffic, area coverage and site configuration.

This is the classical dimensioning method where there is full

freedom to find the optimal number of sites by varying the

load per cell. Two series of calculations with varying load

per cell are performed. In one, only the requirement on

coverage degree is taken into consideration, in the other only

the requirement on network capacity. A high load yieldsmany sites to fulfil the coverage requirement but few sites for

the capacity requirement, and vice versa for low loads. By

modifying the number of users per cell it is possible to find

the required amount of sites to fulfil both the coverage and

capacity requirements. This is the optimal number of sites.

An example is shown in Figure below.

10% 20% 30% 40% 50% 60% 70% 80%Load

Numberofsites

UL Cov erage DL Cov erage Capacity

Optimal site count

Figure 3. The number of sites required for coverage andcapacity as a function of cell load.

Calculate start

values

Subs/cell

Balanced?

Calculate DL Load

END

Calculate DLSites for covera e

Calculate UL Load

Calculate ULSites for covera e

No

Yes

Calculate capacity

Max (UL,DL)

Input data

Figure 4. Method to find the optimal site count, balancingUL and DL coverage and capacity

This approach is quite useful even if sites are not evenly

distributed. The diagram in Figure 4 illustrates a step-by-step

approach in order to find the optimal site count.


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IV. TRAFFIC MODEL AND MONTE CARLO SIMULATOR

In the design of a WCDMA network, where services with

different service capacity requirement occur, the Erlang B

tables are not valid, because it assume that every user

requires the same constant capacity amount. The capacity

requirement of service will not necessarily be constant,

activity profiles are unknown and it makes trafficdimensioning more difficult. This especially occurs in packet

services, where the user is not constantly active. If capacity

requirement of service is based on the peak capacity, this

would lead to a heavily over dimensioned network.

There are several methods available that make it possible to

calculate the amount of traffic that can be carried in the

system. These method can generally be divided into two

groups: methods that apply exact models to make it possible

to calculate the grade of service at an amount of traffic in

multirate system (Kaufman-Roberts method) and methods

that make it possible to approximate the grade of service in

multirate system. Using this methods traffic mix usuallyexpressed in mE and Kbytes, is translated into simultaneous

users per RAB necessary for RAN planning.

For final radio network design of WCDMA multi service

network, the link budget calculations and capacity estimation,

given in previous section, are not accurate enough. RAN

planning tool based on Monte Carlo simulator should be

used. The principal aim behind the Monte Carlo approach to

WCDMA system modelling is to obtain "snapshots" of

potential configurations (trial) of the desired system.

Sufficient snapshots are generated to allow the compilation

of significant statistics on the RAN system performance. For

a voice-only system, the main variable "indexing " thedifferent snapshots in a run is the geographic configuration of

the mobile users (Figure 5).

Figure 5. Monte Carlo snapshots obtained by simulator.

For each trial, the power control processes all the mobiles

and cells are run to convergence. After convergence has

been attained, the number of mobiles able to achieve their

performance targets and the number of mobiles failing to

achieve their targets can be determined. The relativeproportions of these good and bad mobiles could vary

significantly between trials, hence it is important to perform

sufficient trials to give a statistically representative sample of

the geographic configurations.

The essence of the simulator is the function modelling of the

convergence of the power control processes in the cell and

mobile. Each iteration of the power control model begins

with the calculation of "best serving cell", i.e. a

determination of which cell or cells each mobile is incommunication with. In this process, the signal to noise

ratios of the candidate set of pilot channels are evaluated and

on the basis of these, a decision is made whether or not to

establish a link to the appropriate cell. This is followed by a

call to the measurement process which performs the

following tasks:

1. computes the intracell and intercell interference at each

cell

2. computes, for each mobile, the pilot signal to noise ratio

("Ec/Io") from each cell and ranks the pilots accordingly

3. computes, for each mobile, the forward link RAKE

finger signal to noise ratio for each finger assigned to acell in the previous cell ownership process

4. attempts to allocate remaining fingers to secondary

multipath components on the chosen cells

5. calculates the reverse link RAKE finger signal to noise

ratio for each active finger on the reverse links

6. Calculates the finger-combinedEb/No for the forward

and reverse links

On completion of the measurement process, the power

control process begins. Power control looks up the target

Eb/No based on a number of parameters - service type, speed,

QoS. It then adjusts the forward and reverse link powers

according to the difference between the achieved Eb/Nofigures calculated in the measurements process and the target

Eb/N0 figures. Upper and lower transmit power constraints

in the mobile and base station are respected.

After power control, the metric calculation process is

invoked to decide whether or not the power control loop has

converged. If the metric calculation determines that

subsequent power contol loop iterations will not significantly

improve the system performance, convergence is supposed to

have occurred and the power control loop is exited. At this

point, various statistics are recorded and the process is

repeated for a new Monte Carlo trial.

Simulating coverage and capacity in the TEMS Cell Planer

Universal for planned WCDMA network with Monte Carlo

simulator gives results shown on the pictures below.

Coverage for different service RAB in unloaded system is

dependent only on node-B power and propagation losses. In

Figure 6 could be seen coverage for RAB in an unloaded

WCDMA system. Adding traffic amount for 384 kbps

service RAB lead to coverage reduction as it can be seen in

Figure 7.


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Figure 6. DL coverage for mixed radio access bearers 384kbps - red, 128 kbps - blue, 64 kbps - green, voice 12.2 kbps

- yellow.

Figure 7. DL coverage for mixed radio access bearers 384kbps - red, 128 kbps - blue, 64 kbps - green, voice 12.2 kbps yellow when 384 kbps traffic demand is 20 times higher

while other bearers intensity demand stayed unchanged.

V. POWER BALANCING

Pilot power balancing

A balanced system means that the uplink and downlink

handover regions coincide. More precisely, a balanced

system is achieved when uplink and downlink path loss in a

cell is equal at the handover border, and this equality is validin every cell. The handover region and the serving cell are

determined by the received common pilot channel (CPICH)

power from the cells in the area. The soft handoff algorithms

for WCDMA are based on measurements made by the UE on

the pilot channel. The uplink is not considered in the

decision.

There are several benefits by maintaining a balanced system:

Minimizing uplink interference at call set up an unbalanced

system may cause a cell to be selected in idle mode which

appears wrong from an uplink point of view. This can

generate an excessive uplink power at call set up causinguplink interference.

Maintaining macro diversity gain one of the main benefits

with soft handover is the macro diversity gain in uplink. The

soft handover area, i.e. the diversity area, is obtained as the

overlap between those two areas where the uplink and

downlink soft handover criteria are fulfilled. In an

unbalanced system this area will be unnecessarily restricted.

Minimizing uplink interference at soft handover anunbalanced system can cause new radio links to be added too

late (from an uplink perspective) which can generate

unnecessarily high uplink interference in the target cell.

Minimizing power control problems in uplink in extreme

cases, a large unbalance can cause one of two links in the

active set to lose its uplink synchronization. If this happens,

the diversity gain is lost and power control commands are

potentially distorted, causing also downlink power problems.

There is also a higher risk for dropped calls in this situation.

Cell A

Feeder loss: 1 dB

primaryCpichPower:33 dBm

ASC

Cell B

Feeder loss: 5 dB

primaryCpichPower:29 dBm

ASC

UL

DL

Reference point

Cell borderdefined asEc/N0 ofCPICH

Region of soft handover gain

Figure 8. Example of an unbalanced system where there is amismatch between uplink path loss between cell A and cell B

at the cell border

Cell A

Feeder loss: 1 dB

primaryCpichPower: 30 dBm

ASC

Cell B

Feeder loss: 5 dB

primaryCpichPower: 30 dBm

ASC

UL

DL

Reference point

Cell borderdefined asEc/N0 ofCPICH

Region of soft handover gain

Figure 9. The same system as in Figure 8. , but afterbalancing. Uplink and downlink ideal handover regions

coincide

When balancing, the pilot power is set equal in all cells at the

reference point. The total amount of power, however, is

limited to a maximum output power rating at the node-B

antenna port. Thus the ratio of pilot power to total output

power in one individual cell will vary between cells

depending on feeder loss.

Balancing coverage zones for different servicesTaking the service type into consideration during assignment

of the maximum power level, means that the users can be

assigned maximum output power in such a way that all


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services experience the same downlink coverage. In the

uplink, however, this is not the case, since each terminal has

an individual maximum output power.

DL traffic channels coverage varies with the cell load while

soft handover regions does not (due to constant pilot power

setting). Therefore, the main task in DL coverage balancing

is to make sure that DL traffic channel coverage can coverthe whole soft handover area. Otherwise, connection drop or

handover failure might occur.

The maximum downlink power per radio link is controlled

by the RAN parameter that is specified per radio bearer. To

achieve equal coverage at the cell border for all radio bearers

as well as for common pilot channel, traffic channel (DCH)

output power can be calculated using a SIR target value that

expresses the required sensitivity. Combining the expressions

for this ideal output power for the CPICH and DCH, the

following relationship is obtained, expressed in linear terms:.

CPICH

DCH

CPICH

DCHP

P

= (20)

where

DCH is the target value for the DCH

CPICH is the target value for the CPICH = 16 dB

Equation 20 leads to values of the DCH power relative to the

CPICH power for the different radio bearers.

VI. RADIO NETWORK FUNCTIONALITIES

Soft capacity and degradation of planned RAN behaviourcould be controlled with radio network functionalities such

as: admission control and congestion control.

Admission control

Admitting a new call will always increase the interference

level in the system. This interference increase will reduce the

cell coverage, so called cell breathing. In order to secure the

cell coverage when the load increases, the admission control

will limit the interference, see Figure below. The basic

strategy is to protect ongoing calls, by denying a new user

access to the system if the system load is already high, since

dropping is assumed to be more annoying than blocking. In ahighly loaded system, the interference increase may cause the

system to enter an unstable state and may lead to dropped

call.

Admission control is required in both links, since the

different services are served by the system. Furthermore,

different services demand different capacity as well as

different quality. Hence, service dependent admission control

thresholds will be employed. These services dependent

thresholds should preferably depend on load estimates, for

instance the received power level at the base station as an

uplink load estimate and the total transmitted power from a

base station as a downlink load estimate.

Uplin

k

interference

Load Planned

Planned coverage

Noise floor

User added

New users blockedabove this point

Figure 10. Uplink interference as function of traffic load.

The admission control guarantees the coverage.

Since the received power level as well as the transmitted

power level may change rapidly, event driven measuring and

signalling are preferred. The measurement values are

obtained at the base station, where the admission decisionhave to be made. Arrivals of high bit rate users, particularly

the ones that require a large amount of resources in the

downlink may demand global information in order to make

an efficient admission decision.

Congestion control

Even though an efficient admission control algorithm and an

efficient scheduling procedure, overloaded situation may still

occur. When reaching overload, the output powers are

rapidly increased by the fast closed loop power control until

one or several transmitters are using their maximum output

power. The connections unable to achieve their requiredquality are considered useless and are only adding

interference to the system. This is of course an unacceptable

behaviour. Hence, a procedure to remove the congestion is

needed. The congestion problem is particularly severe in the

uplink, where the high interference levels may propagate in

the system. The impact of the high uplink interference level,

due to overload, may be limited by integrating the uplink

power control with the uplink congestion control procedure.

This is achieved by slightly degrading the quality of the users

in the overloaded cell during the time it takes to resolve the

congestion. The congestion control consists of several steps:

Lowering the bit rate of one or several services that areinsensitive to increased delays (channel switching). Thisis the most preferred method.

Performing inter-frequency handovers. Removing one or several connections.

The congestion control is activated once the congestion

threshold is exceeded. Thus both the uplink and the downlink

thresholds correspond to a certain load. This means that the

same measurements as in the admission control are used.

However, to detect overload, these measurements have to be

updated continuously since the considered values varies very

rapidly when overload occurs. In order to make an efficient

decision regarding which connections to deal with, i.e.minimizing the number of altered connections, the

congestion control algorithm is likely to require global

information. This information is obtained by event driven


8/8

signalling, trigged by the occurrence of overload. Once the

connections to alter are identified, the required signalling is

typically the same as for altering bit rates, performing an

inter-frequency handover or call termination.

The Channel Switching function allows optimisation of

available resources by switching the UE data between

different channel types or different bit rates depending on

user activity and resource availability. When user activity islow the UE is switched from a dedicated channel to a

common channel so that the dedicated radio resources are

available for other users.

VI. CONCLUSION

In GSM cell separation and interference could be controlled

with frequency planning. It is an cheap, fast and effective

way of planning and optimizing a radio network. In

WCDMA there is no frequency planning at all, but its

inherent flexibility in handling data rates and service types

contributes to more demanding RAN design and tuning

activities. Traffic models and operators marketing strategyaffect RAN coverage and capacity performance indicators. In

initial network deployment optimal number of sites gives

good starting point in network dimensioning.

References

[1] K. Hiltunen, R.D.Bernardi, WCDMA Downlink Capacity

Estimation, VTC 2000, May 15-18, 2000

[2] B. Christer, B.Johansson,Packet Data Capacity in a

Wideband CDMA System, VCT98, pp.1878-1883[3] J. Knutsson, P. Butovitsch, M. Persson, and R. D. Yates,

Downlink Admission Strategies for CDMA Systems in a

Manhattan Environment, Proc. 48th IEEE Veh. Tech. Conf.,

VTC98, Ottawa, Canada, May 1998.

[4] H. Holma, A. Toskala, WCDMA for UMTS Radio Access for

Third Generation Mobile Communications, Wiley, March 2001

Abstract: In this paper method for dimensioning ofWCDMA radio access network with variable load is

presented. Optimal number of sites could be estimated. More

precise results and final RAN design check have to be

performed in Monte Carlo simulator. With common pilot

channel power balancing method handover regions for up

and down link is aligned in the same region. This step is

enough if UTRAN operate only voice service. Next step, DL

traffic channels coverage balancing has to be performed to

ensure equal coverage at the cell border for all radio bearers.

DL traffic channels coverage have to cover the whole soft

handover area. Otherwise, connection drop or handover

failure might occur. And finally to ensure planed coverage

regions with predicted amount of traffic per offered service,

network functionalities such as admission control, congestion

control and channel switching could be applied.

DIMENZIONISANJE WCDMA RADIO MREEZA VIESTRUKE SERVISE

Igor S. Simi

wcdma radio access network dimensioning for multiple services

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