umts predictions-dominant path model

7/28/2019 UMTS Predictions-Dominant Path Model

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UMTS Predictions

Dominant Path Model


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Introduction

For the installation of mobile radio systems, wave propagation models are necessary to determine thepropagation characteristics. The path loss predictions are required for the coverage planning, thedetermination of multipath effects as well as for interference and cell calculations, which are the basis for thehigh-level network planning process.

Generally this planning process includes the prediction of the received power in order to determine theparameter sets of the base transceiver stations (or access points). With the introduction of wirelessbroadband services in third generation systems (UMTS) or in Wireless Local Area Networks (W-LAN), thewideband properties (e.g. delay spread, angular spread and impulse response) of the mobile radio channelbecome more and more important for the planning process.

The environments where these systems are intended to be installed, are ranging from large rural areas(macrocells) down to indoor environments (picocells). Hence wave propagation prediction methods arerequired covering the whole range of macro-, micro- and pico-cells including in-building scenarios and

situations in special environments like tunnels or along highways.

Predicted Results

The ProMan software package is designed to predict the

important parameters of the mobile radio channel:

Field strength / Power / Path loss

Delay spread / Delay window / ....

Channel impulse response (CIR)

Direction of arrival (DoA) at MS and BS incl. phase information

Propagation Paths

ProMan includes a convenient interface to generate the

projects and to supervise the computation (online display

output during computation). It also offers a huge number of

postprocessing features (filter, zoom,...) to edit the predicted

results.


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Size of Active Set

This maps indicates for each pixel the number of links in the active set. The active set is determined by using

algorithms with the three parameters: Window_Add, Window_Drop, Window_Replace. These windows are

relative to the strongest cell at each location. The maximum active set size can also be specified. In the

following example it can be see, that the maximum of 5 links for the active set is the hardly reached due to the

cell isolation.


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Base Station Power

This map indicates the required downlink power per single link that is required to connect a mobile station

located at the considered pixel. If several snapshots are considered the maximum of the BS power per pixel

can additionally be written. In this simulation example the maximum downlink power was limited to 33dBm

per single link.


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Cell Area

This map gives an graphical representation of the resulting cell area (cell footprint). It may be useful to

estimate cell sizes as well as the cell isolation. The probability for handovers in case of mobility is obviously

closely related to these cell areas, and so the cell layout gives also a first important information about

handover characteristics.


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Probability for Coverage

This map indicates the coverage probability per pixel for a certain service. For each simulation interval a scan UE

evaluates the simulation area and tries to connect to the network. Therefore the downlink as well as the uplink and

the CCH availability is checked for the given interference situation. All common channels and the active dedicated

traffic channels contribute to the interference. Furthermore coverage maps can be generated for the common

channels. In this case it just indicates the areas where the CCH Ec/Io is above the specified threshold.


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CPICH Ec/Io

This map indicates the predicted Ec/Io for the specified common channel. All CCH and all DCH currently active

are taken in to account in the interference calculation. Furthermore, CDMA signal orthogonality is considered.

The results can be compared with the CCH Ec/Io target (e.g. -14dB) to estimate CCH or Pilot coverage.


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Channel Quality Indicator

In case of HSDPA a channel quality indicator is send back from the mobile station to the network side (Node B). Thischannel quality indicator (CQI) is based on pilot channel measurements with a granularity of 30 discrete steps. Thesevalues can be used on the network side to decide about the applied modulation and coding scheme for thecorresponding mobile (adaptive MCS). It can also be used for the scheduling algorithms (e.g. serve mobiles with the

best channels first). The following example map shows very good CQI (>20) in LOS areas, and poor CQI in difficultareas.


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Type of Handover

Different modes of soft/softer handover are possible and a map can be written to indicate the areas where each handover modeoccurs. Four modes are possible.soft HO: link to several sectors each located at a different site

softer HO: links to several sectors at one site

softer/soft HO: combination of soft and softer handover links

no HO: only one active link per pixel

The soft/softer handover algorithms can be tuned with the active set parameters: Window_Add, Window_Drop, Window_Replace. Forthe analysis with the scan UE, the mean of Window_Add and Window_Drop is used to generate the handover areas for themaps.


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HSDPA Data Rate

For each pixel the maximum achievable HSDPA data rate is calculated. For this calculation it is assumed that all

HSDPA resources of a given cell can be assigned exclusively to the Test-Mobile at the considered point of time.

Due to the sporadic traffic characteristic of typical PS services this is a tolerable assumption for and and

medium traffic densities.


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Mobile Station Power

For each pixel the power required to establish an uplink connection is shown in this map. In the following map

the indoor penetration loss can be clearly seen. If several snapshots are considered the maximum of the MS

power per pixel can additionally be written.


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Mobile Station Histograms

For each mobile station the transmission power (UL) and the Active Set size is recorded every slot. Histograms

considering all mobile stations in the simulation area can be plotted based on this data. The following figures

show the MS power histogram for a outdoor simulation. Furthermore the Active Set size histogram is shown.

In this case the maximum number of links in the active set was limited to three. Furthermore it can be

calculated that on average for all mobiles 1.45 links were active.


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Blocking and Dropping Rates

During the dynamic simulation the rates of blocked and dropped mobiles are recorded. A mobile is blocked if

not enough resources are available to serve this new mobile (e.g. power limit, code limit, pilot coverage).

These conditions are checked for a certain period of time after the mobile has come up (connection

establishment phase). On the other hand if the required link quality in terms of received Eb/N0 target is

missed for a certain period of time (connection hold time) the mobile station is dropped. This happens for

example if a mobile station leaves the coverage area or if it enters a new cell without enough resources.

The following figure depicts the blocking and dropping rate for a series of simulations with increasing traffic

load. The strong increase in blocking is due to the fact that the network capacity is nearly reached and it is still

tried to fill the system. In this case a large part of the traffic increase is blocked.


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Carried and Offered Traffic

The traffic (in MBit/s), which is generated and offered to the network, is recorded for each simulation interval, for each sector. In

case of CS services this is done based on the service bit rate and the planned duration for each individual call. The traffic that is

actually carried by the network is also recorded. In the CS case this can be done for all active mobiles based on the service bit

rate. So in CS simulations the difference between offered and carried traffic is related to the dropping and blocking

characteristics. In PS simulations the offered traffic is measured based on the generated packet data and the carried traffic isrecorded based on the successfully transmitted packets. In contrast to CS simulations the offered traffic of PS services is not only

determined by the traffic settings (a-priori) but it depends also on the network performance and load. This is because of the

possible feedback-loop in the PS traffic model (page reading time).

The following figure depicts the Carried-Offered-Traffic curve for a CS service simulation. The traffic is accumulated for several

cells. The maximum system capacity can be clearly seen in this example as the point where the carried traffic does not increase

significantly for increasing offered traffic. Furthermore the ratio between carried and offered traffic can be depicted depending

on the number of mobile stations per cell. In the example figure below a cell capacity of approximately 38 mobiles per cell can

be estimated for a tolerated carried/offered traffic efficiency of 90%


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TFRC / CQI

These measurement quantities are recorded during HSDPA simulations.

The CQI value is the channel quality measurement (based on pilot channel evaluation) generated in fixed intervals at each mobile

station. The CQI generation interval can be specified and for all generated CQI values a histogram output is written per sector.

The lifetime of a UE depends on the generated amount of data (session), system capacity, system load, and the serving process

(e.g. scheduling). Therefore it might happen that it takes longer to serve UEs with poor channel conditions (C/I scheduling). Inthis case there might be many CQI measurements with bad channel conditions and consequently low CQI values.

During data transmission the transport format and resource combination (TFRC) has to be selected according to the actual channel

conditions and other parameters. For each generated Transport Block the corresponding TFRC number is included in a histogram.

Retransmitted Transport Blocks are not considered in the statistic. Each time a HSDPA UE performs a CQI measurement the

determined CQI value is added to this statistic. The CQI measurement interval can be defined in multiples of a TTI for each

HSDPA UE type individually.


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HS-PDSCH codes / HS-SCCH codes / DCH codes

To get an overview about the code resource allocation during dynamic PS simulation (e.g. HSDPA) the allocation of HS-

PDSCH, HS-SCCH, and DCH codes is recorded continuously for each sector in the simulation area. The number of HS-

SCCH codes per cell indicate the number of UE served in parallel in the considered cell. The number of HS-SCCH and

HS-PDSCH codes are given as absolute values while the DCH codes are given in multiples of SF512 codes units. This

enables the consideration of mobiles with different spreading factors (e.g. different services).


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HS-DSCH power / HS-SCCH power / DCH power

In the dynamic HSDPA simulation the amount of transmission power assigned for the individual Transport

Blocks (TB) is recorded in form of a histogram for each cell of the simulation area. Furthermore the requiredHS-SCCH power is also collected in a separate statistic. The HS-SCCH transmission power is determined based

on the given HS-SCCH SNIR target values and the actual channel condition between mobile and serving

station. If additional DCH traffic mobiles are present the corresponding output power for these mobiles is also

collected in a histogram. The example below shows a HS-DSCH power histogram.


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Page Throughput / Page Throughput (UE average)

In PS service simulations for each successfully transmitted page the page throughput is collected. This statistic

is given per PS service per sector [in KBytes/s]. That means for each sector there is one histogram reported. It

is determined by the page size (amount of data) and the transmission time, i.e. the time between the arrival

of the first packet of the current page at the air interface (network side) and the time of successful reception

of the last packet belonging to the current page at the mobile side. There are two different histograms

available: one contains one value for each completed page. For the second one (UE average page throughput)

the mean page throughput of a UE is determined at the end of the UEs session and this mean value is inserted

in the histogram, i.e. there is one value for each completed session (UE). An example figure for a simulation

series with increasing traffic load and the mean page throughput taken from the histogram is depicted in the

following figure.


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RLC transmission / TB transmission

During dynamic HSDPA simulations the number of transmission attempts on transport bock (TB) level as well as

on RLC level is recorded in form of histograms for each cell. The statistic is updated every time a transport block is

finished, i.e. it was successfully transmitted or the last possible retransmission was not successful. The number of

TB retransmissions is limited by the chosen parameter settings.

To transport data that was not successfully transmitted on TB level (even with fast retransmissions) a higher level

retransmission mechanism can be enabled (RLC retransmission). For these retransmissions there is also a statistic

collected. The statistic is updated every time a RLC Block transmission was successfully finished. In contrast to the

TB retransmissions the number of RLC retransmissions is not limited.


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PS OTA cell throughput

During dynamic PS simulations the Over The Air (OTA) throughput is determined and statistically recorded.

The OTA throughput is defined as the amount of successfully transferred (HSDPA) data (all successfully

transferred Transport Blocks (TB) including its padding and header bits) divided by the activity time of thecorresponding cell. I.e. silent periods are not considered in this measurements. The OTA is given for each cell.

An example OTA simulation result is visualized in the following figure.


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Packet Delay and Packet Transfer Delay

In PS service simulations (esp. HSDPA) the delay of all successfully transmitted packets are recorded. There aretwo different quantities: The Packet Delay is measured from the generation of the packet (corresponds to the

arrival of the packet at the Node B) to the successful reception at UE side. This includes scheduling delays,

transmission delays, and retransmission delays (on packet level or transport block level). An example

histogram output is shown below. It contains several data lines, whereof each corresponds to one sector.


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Sector Packet Throughput

For PS services (e.g. using HSDPA) the total throughput is recorded for each sector based on the size of alltransport blocks transmitted in the current TTI. This throughput includes the overhead caused by physical

layer retransmissions and header sizes. The data is given in form of histograms with additional information

about minimum, maximum and mean values. This histogram data can also be used to approximate the

cumulative density function (CDF). An example simulation result is depicted in the following figure.


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PS service cell throughput

The PS service throughput is defined as the total amount of successfully transferred user data (i.e. packets) per

service divided by the complete simulation time. These measurements are carried out per sector


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Session Duration / Session Size

During dynamic packet traffic simulation a packet generator is used to generate the data units to be transmitted. The

generator can be parameterized with a three stage model. The highest layer is the so called session level, whichcorresponds to the lifetime of a single mobile. During simulation the quantities for the session sizes and the durationof the individual sessions are recorded in form of histograms. The session duration starts with the generation of thefirst packet for the considered UE and ends after successful reception of the last packet. It depends on the networkload and the channel quality of the mobile station, and both quantities may vary over time.

umts predictions-dominant path model

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