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A.F. C OSME . UMTS C APACITY SIMULATION STUDY

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Figure 12: Wines WWW traffic model parameters configuration window

The parameterization of the (different) traffic models for the defined services

of this study (WWW, FTP, Video-call, Speech and Mobile TV) was an activitydone in close cooperation with France SFR and it is shown in the appendix 3

(Traffic Models parameters).

Also the parameterization of the System Parameters was done in cooperationwith SFR. The assumptions regarding the propagation conditions are

explained in the next two chapters (for each corresponding scenario:homogeneously and non-homogeneously distributed traffic), as well as the

other system parameters, which mostly were mapped from the real-settingsof the Vodafone UMTS network to try to reflect as close as possible theconfiguration of RNCs and Node B’s of the company. These parametersappear in the appendix 4 (confidential: system parameters).



55 Beneficiario COLFUTURO 2003

4.5 Summary of chapter 4

Static simulation vs. Dynamic simulation

Static simulations don’t have a time reference and therefore are not suitableto simulate algorithms that have a strong dependence of time (like RRM

algorithms). However, the degree of abstraction in the Static Simulations isstill enough to allow for meaningful statistical evaluations of the network

KPIs. In fact, this is the method currently used for initial dimensioning forlarge networks because they are more efficient in terms of time required to

complete a simulation (given its more simplistic modeling approach).

The Dynamic simulator, on the other hand, is a tool that is able to track thenetwork status as it evolves over time. Dynamic simulator is therefore an

ideal tool for:

-) Design and Test of RRM algorithms

-) RRM parameter optimization, specially those based on time (e.g. handovertimers), which is not possible with Static Simulation because the lack of the

time reference of that approach

-) Detailed Capacity, Coverage and Quality Analysis of specific areas

-) Tests of the capacity-coverage tradeoff with different service mixes andwith different user profiles

-) Analyze packet data throughput

The disadvantage of the dynamic approach is that requires high

computational resources due to the complexity of the necessary algorithmsand therefore the time required to perform dynamic simulations isconsiderably higher, which means that for networks with several hundreds or

thousands of sites, the Dynamic Simulation is not the best approach at the

present time.




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5. Description of the First

Simulation Scenario andGeneral Setup of the Simulation

Experiments

This chapter describes the Radio Network Layout and Environment chosen forthe 1st simulation scenario, including the assumptions made for the definedservices, the traffic mix of the services and the assumed traffic distribution

matrices. It also includes the simulation plan, which describes what has to be

done in each of the proposed experiments per each scenario. The completelist with all the configured system parameters and traffic model parameters isgiven in the confidential annexes [system parameters] and [traffic model

parameters] respectively.

5.1 Simulation and Analysis areas

Figure 13: First Simulation Scenario, simulation (red) and analysis (yellow) area




The Figure above illustrates the first Simulation Scenario. The NetworkLayout (including RNC, Node B’s, Antennas) as well as the path-loss

prediction was imported from a Project created in ATOLL radio planning Tool,and it is based on a real scenario (it is an area taken from the radio planning

map of the city of Bordeaux, France). This scenario was selected because itwas defined as the Base for common capacity dimensioning studies between

the branches of Vodafone in different countries, including The Netherlands.

The network layout itself consists on:

-) 7 node Bs in the Analysis Area (with 3 cells each one = 21 cells)-) 19 node Bs in total in the simulation Area.

-) Inter-site distance = 900 meters

The Simulation Area represents the area in where the users are createdand once created they are moving in. This Area is represented in the Figure

13 with red borders and has an area of 12 Km2.

The Analysis Area, which is the area where data is collected, is shown inthe Figure 13 with yellow borders. It has an area of 5 Km2.

5.2 Environment Assumptions

The main assumptions for this first scenario are a flat landscape (No DigitalElevation Model is used) and the Homogeneously-distributed traffic for

each of the defined services, therefore no clutter definition and neither traffic

maps based on clutter data were used for this scenario.

This assumption results in identical sites per simulation area, and given the

symmetry in the geometrical distribution of the nodes regarding their inter-site distances, each one may be considered a “prototype” site at the initial

dimensioning stage, as it is correctly mentioned in [Jaber].

Another consequence of the assumption is that as the model is considered tobe flat, it doesn’t make sense then to include the shadowing model (i.e. the

fading in the signal caused by the varying nature of particular obstructionsbetween Node Bs and UEs, particularly tall buildings or dense woods). This

phenomenon is well described in [anntena-saunders] and it has more

importance in the coverage studies (because it affects directly the path-loss).

The difference in performance terms between this symmetric andhomogeneously distributed scenario and another more “realistic scenario” (i.e. scenario including clutter, DEM and traffic matrices based on clutter

data) is going to be studied further in chapter 9 of this thesis.




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5.3 Defined Services and Traffic Mix

In Wines simulator, several services can be created based on the definedradio bearers in the TRIPS settings (as it was described in the previous

chapter).

For the purpose of this study, five services were defined because theycorrespond with the current UMTS services offered by Vodafone, although

only four of them were considered in the study. The defined services were:

-) Speech: circuit-switched symmetrical service (12.2 Kbps UL/DL)

-) FTP: packet switched asymmetrical service (64 Kbps UL/384 Kbps DL)

-) Web: packet switched asymmetrical service (64 Kbps UL/384 Kbps DL)

-) Video-call: circuit-switched symmetrical service (64 Kbps UL/DL)

-) Mobile TV: circuit-switched symmetrical service (64 Kbps UL/DL)

The traffic mix, i.e. the percentage of usage of each service relative to the

total usage of services, was defined as it is shown in the following Figure.

This traffic mix was based on internal discussions within members of Vodafone in different countries and it is assumed to approximately reflect the

current service mix (year 2005). As the users are becoming familiar with thenew Data Services, this traffic mix is expected to change, as it is mentionedin [umts-forum6].

Service percentage

Voice 77,00%

Video-call 7,50%

Web 12,50%

Ftp 3,00%

MobileTv 0.00%

Traffic Mix [% ]

77,00

7,50

12,50

3,000,00

Voice

Video calls

www

ftp

Mobile Tv

Figure 14: Traffic Mix assumption




Additionally, within each service, 2 kinds of users were assumed:

• Indoor Users (with an additional penetration loss of 18 dBs).• Outdoor users.

The Indoor Users were defined as the 2/3 (66.7%) of the total of users of thecorresponding service, and the Outdoor users were defined as the remaining

1/3 (33.3%). This was conveniently modeled in Wines defining two differentUser Terminals per each service (each one with different additional losses)and the different service portion (i.e. the corresponding 2/3 and 1/3) was

modeled by creating two UE Profiles (indoor, outdoor) per each one of the

defined services.

About mobility types, all simulations were performed with pedestrian mobilitytype, except in the specific experiments dealing with the differences between

the two mobility types pedestrian-vehicular (the experiments are specified in

the simulation plan to be presented also in this chapter), a vehicular mobilitytype was applied to the Outdoor users.

5.4 Service Configuration

Continuing with the Service Configuration, each service has to be defined in

terms of the following data:

5.4.1 Radio Bearer Properties

The Radio Bearer is the service provided by the RLC for the transfer of user

data between the UE and the UTRAN [21.905]. The Radio Bearer containsRLC parameters, MAC parameters, Transport Format Set(s) (TFS), physicalchannel parameters, and the information bit rate. Upon reception of a service

request, the RNC performs a mapping of UMTS service parameters to Radio

Bearer parameters – called Radio Bearer Translation. According to thespecifications, a UMTS service may be mapped to a signaling Radio Bearer or

a combination of a (service-specific) Radio Bearer and a signaling RadioBearer [34.108].

As Wines is focused on the performance of the user data transmission, it is

dominated by modeling the non-signaling Radio Bearers which carry the userdata. Nevertheless, signaling Radio Bearers associated with user data

transmission are considered, e.g., for resource allocation. The non-signalingRadio Bearer configurations required to support the UMTS services areprovided in the Trip Settings.




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Among the radio bearer properties, these have to be defined in the Serviceconfiguration Tab:

• The switching type: either circuit or packet switched

• The Transport Channel and the Maximum Data Rate (UL/DL): these

have to be selected from the list of the Service Configuration Dialog.This list is based on the values defined on the TRIPS which can be also

modified by the user of the simulator.• The RLC Mode (Transparent, Acknowledged, Unacknowledged). For

circuit-switched services, the transparent mode it is the only possiblemode. This mode means that the system accepts the information

coming from the transmitter and delivers it to the receiver in anunchanged form. For packet-switched services, Transparent,

Acknowledged or unacknowledged mode are available.

5.4.2 Signal to Interference Ratio

• Initial Target Eb/N0 UL: The target Eb/N0 value in uplink for therespective service. This value is used as target for the inner loop

Power Control as long as no outer loop Power Control is applied.• Initial Target Eb/No DL: The target Eb/No value in uplink for the

respective service.

The values used for Downlink values for this study are based on ameasurement study performed by Vodafone UK [Moret] and appear in the

confidential appendix 3.

For the Uplink values, an adaptation from the appendix 3 was used.

The adaptation of values for Uplink had into account the followingcharacteristic of the UL and DL characteristics:

Target Eb/No Uplink < Target Eb/No Downlink ( 5-1)

This is given because the better reception techniques in the Node B (in

Uplink, Tx = mobile, Rx = Node B), and it is in line with the assumptions

presented in [Alcatel], [25.942] and Wines default values.

If the target values for UL and DL need to be given in terms of the target SIR(as is the case of another Simulation Tools as Prismo), the target Eb/No can

easily converted into a corresponding target SIR according to the followingrelationship:

SIR [dB] = Eb/N0 [dB] - 10 * log10(3840 / (spreading factor * user datarate [kb/s])). (5-2)




5.4.3 Service Prioritization

This value determines the order how services are processed by theCongestion Control and the Inter-Frequency Handover Control. This is a

value between 1 and 15 where 1 gives the highest priority. The defaultservice priority is 3. In this study the default value was used, in order to not

interfere with the admission and congestion control implemented in theEricsson P3 RRM algorithms.

5.4.4 Optional Semi-Dynamic Mode

This mode, applicable only to circuit-switched services, allows us to generate

a traffic load (service arrival process) where the users are not moving butstatic. It is useful when one wants to test the soft capacity when an already-

known hard-capacity (e.g. voice users) is already present in the system. As itis also a simplification of the interference modeling, it also helps to reduce

simulation times. In some simulations (as it is going to be explained in the

simulation plan), this mode was used.

5.4.5 Physical Layer parameters

Decoding Limit Offset UL[dB]: The Eb/N0 threshold for correct (i.e. error-

free) detection of signaling messages in uplink for the respective service,given as an offset to the target Eb/N0. This value should be negative (in dB)

such that a received data packet that meets the target Eb/N0 condition is

detected correctly. The reference for this Decoding limit was the CapacityStudy performed in Vodafone Germany by Peter Schneider [Schneider-2]

Decoding Limit Offset DL[dB]: The Eb/N0 threshold for correct (i.e. error-free) detection of signaling messages in downlink for the respective service.

This value should be negative (in dB) such that a received data packet that

meets the target Eb/N0 condition is detected correctly. The reference for thisDecoding limit was the Capacity Study performed in Vodafone Germany byPeter Schneider [Schneider-2]

Both definitions are in line with the “satisfied user” definition presented in[25.942] where a user is “satisfied” when the measured Eb/No of his

connection is higher than a value equal to Eb/No target – 0.5 dB. Otherwise,if it is lower than this limit, the user is considered in outage.

Target BLER UL: It is the target BLER for the outer loop Power Control inuplink. The value ranges between 0 and 1.




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Target BLER DL: It is the target BLER for the outer loop Power Control inDownlink. The value ranges between 0 and 1.

The target BLER levels in Downlink were based on the same document fromVodafone UK [Moret] where the DL Eb/No levels were based. For the Uplink

direction the same values for Downlink were assumed.

5.4.6 Traffic Model parameters

The traffic model parameters were first defined according to the selection of

the corresponding traffic models implemented in Wines according to theservice. The following Table summarizes this first characterization step. Acomplete description of each one of the traffic models is provided in

[Winestechref].

Service Wines Traffic Model

Speech Speech/video

Web WWW

FTP File

Video-call Speech/video

Mobile TV Speech/video

Table 2: Defined Services and Wines Traffic Models used

Once the corresponding traffic model was selected, its parameterization was

the outcome of discussions with colleagues in SFR (France). The agreedvalues are presented in the corresponding appendix 3, together with thedescription of the source taken to establish the value. Some of them were

based on existing measurements from the GPRS network.

One thing to mention here is the association that Wines makes between a

Service and ASE values which is slightly different than the definition of ASE

provided by Ericsson.

ASE (Air Speech Equivalent) is a measure of air-interface utilization relativeto the utilization of one Speech User (for instance, a connection using 3 ASEs

in DL generates the same interference level as the one generated by three

voice users). This definition is used by Ericsson within the CapacityManagement monitors (ASE UL/DL utilization); the ASE usage applies hard




limits to a cell’s and hence the network’s capacity. Technically, it is calculatedper radio link connection and defined according to [Ericsson-capacity] as:

ASErl = (max. rate DCH)/(max. rate DCH speech) * ( AF DCH )/(AF DCH speech ) (5-3)

Where:

• ASErl is the air interface speech equivalent for a radio link

• Max.rate DCH is the expected maximum DCH rate for the radio link

(DCH rate takes into account the overhead introduced by codingtechniques and it doesn’t corresponds directly to the information rate,

for the corresponding DCH Rate per Radio Link see appendix 3)

• Max.rate DCH Speech is the expected maximum DCH rate for aspeech radio link connection

• AFDCH is the activity factor of the considered DCH

• AFDCH,Speech is the activity factor of the voice service (assumed to be

0.67) The ASE for a radio connection is the sum of the ASE of all services on the

radio connection. For example, the Speech radio connection consists of boththe speech service (ASE=1) and the Dedicated Control Channel (DCCH)

service (ASE=0.61), so the ASE for Speech becomes ASEspeech= 1 + 0.61 =1.61.

The estimation of ASEs in the cell for monitoring purposes is performed as

follows:

ASE DL= Sum rl (ASE rl Dl ) ( 5-4)

ASE UL= Sum rl (ASE rl UL / nb radio links per RNC) (5-5)

Where:

• ASEDL is the air interface speech equivalent in downlink for the cell

• ASErl DL is the air interface speech equivalent in downlink for a radiolink

• ASEUL is the air interface speech equivalent in uplink for the cell

• ASErl ul is the air interface speech equivalent in uplink for a radio link

• nb radio links per RNC is the number of radio links within respective

RNC

The number of ASEs for a radio link per cell in uplink is divided by thenumber of radio links involved in the connection. The principle is that the

average uplink interference a UE creates in the respective cell, is proportionalto the number of cells to which it is connected. This means that if a UE is

connected to two cells, it only requires approximately half the ASEs in each

cell, compared to using one cell.




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This is something that it is not modeled in Wines as the number of ASEs isassociated to the Service, independent on the number of radio links (radio

bearers). For the next release of Wines, Radioplan is going to change thisapproach by separating the service and the radio bearer control. This is going

also to allow to model correctly the “slow start” mechanism defined inEricsson, where the packet oriented connections start with the lowest-defined

radio bearers for those connections (e.g. 64 Kbps) and progressively acquirebetter speed changing the bearer if and only if the radio conditions allow to

do that (i.e. if there is enough soft capacity). In the current version of thesimulator, the packet oriented connections still start asking for the highest

possible data rate (which is often 384 kbps). This leads to a very highblocking rate for those bearers if the Ericsson parameter sf8Adm (which

defines the maximum number of connections using SF-8, i.e. connections of

384 Kbps) is defined very low. In order to not affecting the simulationoutcomes because of this non-realistic implementation, this parametersf8Adm has been configured to its maximum value (8) which means no

limitation, only the soft-capacity limit. Anyway, the results are going to be

somewhat pessimistic for this kind of high-speed packet services because thementioned Slow Start mechanism is not correctly implemented nowadays inWines Simulator.

5.4.7 Traffic Matrices

A traffic matrix is location-based data of traffic density values. Each Service

has a Traffic associated to it. The traffic density values are given inErlang/km2. The traffic matrix assigns a traffic density value to each “pixel”

or minimum area unit (area size configurable within the simulator).

The traffic values in the traffic matrices are used for several purposes[WinesTechRef]:

• UE activation: New UEs are activated during a network simulation

according to the spatial distribution of the relative traffic values in thetraffic matrices. That is, UEs are created with higher probability atpositions with higher traffic values.

• Targeted movement: Users in a dynamic network simulation movepreferably along paths with higher traffic, if paths are defined (not in

this study). The relative traffic values in the traffic matrices are usedfor this directly.

• Inter-arrival time of the service arrival process: The mean inter-arrival time of UE activations for a certain service is calculated from

the given mean holding time (also known as the “service time”) of the

service and the total traffic density (given through the traffic matrix).

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