WCDMA Radio Access Network Dimensioning for Multiple Services

Igor S. Simić, Ericsson d.o.o, V. Popovića 6, Beograd

igor.simic@ericsson.com 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 their choice 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 most important 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/DL Voice Conversational 12.2 kbit/s + 3.4 kbit/s SRB Video

telephony Conversational 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

64/128 kbit/s+3.4 kbit/s SRB 64/384 kbit/s+3.4 kbit/s SRB

V.90 Modem Conversational 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

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 significant improvement 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 “3”s 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 = γm and have perfect power control.

mthothown

mm

mtot

m

m SNIIS

SIS

IS

−++==

−=

γ (1)

where Nth is thermal noise power spectral density, Iown is total received power from mobiles in own cell and Ioth is total received power from mobiles in other cells + interference from other sources. UE is performing transmitting power update in order to maintain the Eb/Io ratio constant. The ratio between Eb/Io and signal to interference ratio (S/I)m can be expressed by:

p

b

m GIE

IS 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

pI

IEGS

0/1

1

+= (3)

Further if M mobiles is connected to own cell

tot

b

pth

M

iithtot I

IEG

MFNSNI

0

1

/1

)1(+

++=+= ∑=

(4)

where F is the ratio between the interference coming from neighbouring cells and the own cell interference Ioth/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 Iul is infinite Mpole is expressed as:

+=

ob

ppole IE

GF

M/1

1 . (6)

For several services i.e. to several different γ targets noise rise expression can be generalised:

th

thoth

Kpole

K

polepole

th

totul N

NI

MM

MM

MMN

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:

poleMMLoading = (8)

where M is 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)

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 noise raise 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 and common 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 α of the received own cell power is experienced as intracell interference.

lm

PTOT, Ptch,m Imother

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:

mthother

mmTOTm

mm

m NIlPlP

IS γ

α≥

++⋅⋅⋅

=

)( (12)

PTOT is the total power transmitted by the base station αm is a parameter that models the orthogonally with respect to all other channels in own cell Pm is the power transmitted on the channel referred to mobile m Im

other is the interference from other cells (and other sources of interference)

γm is the target (S/I)m for mobile m. and lm is the path loss for mobile m For the traffic channel Ptch,m is

mm

thotherm

mTOTmmtch l

NIlPP γα )(,

++⋅⋅= (13)

The total power consumption from the base station is equal to

mm

thotherm

mTOTmM

mcch

M

mmtchcchTOT

lNIlPP

PPP

γα )(1

1,

++⋅⋅+=

=+=

∑

∑

=

= (14)

and

capm

thothermM

mcch

TOT PM

lNIP

P ≤−

++

=∑

=

γα

γ

1

)(1 (15)

where PCCH is the power allocated to orthogonal downlink common control channels. It is assumed that all UEs require the same (S/I), i.e. γm = γ and that the orthogonally factor is position independent i.e. αm = α. It is obvious that M < 1/γα = Mpole but 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), δm, Ptch,m becomes

mm

bm

thotherm

mTOTmmtch l

NIlPP γδ

α)1(

)(, +⋅

++⋅⋅= (16)

where

sm

nmb

snn

bm

ISIS

,

,

,1 )(

)(∑

≠=

=δ

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

bm

thotherm

mTOTmSHOM

m

AS

bcch

SHOM

mmtch

AS

bcchTOT

lNIlPbP

PbPP

b

b

γδ

α)1(

)(11

1,

1

+⋅++⋅⋅

+=

=+=

∑∑

∑∑⋅

==

⋅

== (17)

where M is 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

capAS

bb

b

mb

k

thotherkSHOM

m

AS

bcch

TOT PSHObM

lNIbP

P

b

≤

+⋅

−

+⋅+

+=

∑

∑∑

=

⋅

==

1

11

11

)1()(

δγα

δγ

(18)

for PTOT=∞ M=Mpole and it is

∑= +

−−++

=AS

bb

bb

pole bSHOFM

2

)1

)1(1)((

1

δδαγ

(19)

where F is a ratio between the received intercell and intracell powers assumed to be constant for all users in the cell. When expressing Mpole 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 capabilities Pcap 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.

0 5

10 15 20 25 30 35 40 45

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

Voic

e us

ers

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. An initial 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 yields many 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

Num

ber o

f site

s

UL Coverage DL Coverage Capacity

Optimal site count

Figure 3. The number of sites required for coverage and capacity as a function of cell load. Calculate start

values

Subs/cell

Balanced?

Calculate DL Load

END

Calculate DL Sites for coverage

Calculate UL Load

Calculate ULSites for coverage

No

Yes

Calculate capacity

Max (UL,DL)

Input data

Figure 4. Method to find the optimal site count, balancing UL 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.

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 traffic dimensioning 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 usually expressed 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 " the different 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 relative proportions 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 in communication 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 a cell 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-combined Eb/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/No figures 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.

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

Figure 7. DL coverage for mixed radio access bearers 384 kbps - 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 valid in 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 causing uplink 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 – an unbalanced 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 AFeeder loss: 1 dBprimaryCpichPower: 33 dBmASC

Cell BFeeder loss: 5 dB

primaryCpichPower: 29 dBmASC

UL

DL

Reference point

Cell border defined as Ec/N0 of CPICH

Region of soft handover gain

Figure 8. Example of an unbalanced system where there is a mismatch between uplink path loss between cell A and cell B at the cell border

Cell AFeeder loss: 1 dBprimaryCpichPower: 30 dBmASC

Cell BFeeder loss: 5 dB

primaryCpichPower: 30 dBmASC

UL

DL

Reference point

Cell border defined as Ec/N0 of CPICH

Region of soft handover gain

Figure 9. The same system as in Figure 8. , but after balancing. 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 services Taking 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

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 cover the 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

DCH

PP

γγ

= (20)

where γDCH is the target value for the DCH

γCPICH 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 behaviour could 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 a highly 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.

Upl

ink

inte

rfere

nce

Load Planned

Planned coverage

Noise floor

User added

New users blocked above 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 decision have 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 required quality 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 are

insensitive to increased delays (channel switching). This is 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

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 is low 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 strategy affect 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”, VCT’98, 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., VTC’98, 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 of WCDMA 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 MREŽE ZA VIŠESTRUKE SERVISE

Igor S. Simić