umts predictions-dominant path model
TRANSCRIPT
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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.