network planning siemens

Network Planning Basics Siemens

TM2100EU03TM_0001 © 2002 Siemens AG

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Contents

1 First Steps & Factors affecting Network Planning 3

2 Cellular Networks and Frequency Reuse 15

3 Example of Network Optimization 27

Network Planning Basics

Siemens Network Planning Basics

TM2100EU03TM_0001

© 2002 Siemens AG

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1 First Steps & Factors affecting Network Planning

Network Planning

First Steps and Factors affecting Network Planning

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Introduction

Nowadays the end users of a mobile network consider seamless coverage all over the country as an obvious and fundamental feature of a cellular network. Cellular network operators will try to offer their services in every spot where a customer could wish to access them. Nevertheless still end users may experience total, partial or temporary lack of coverage in certain areas. There are several factors influencing how operators implement their networks and the resulting coverage is a compromise between those factors.

The very first step in the Network planning process is studying the topographical configuration of the territory. Local regulations and laws need to be known. Numbering and addressing plans must be evaluated and developed. For an efficient transmission planning existing networks and their substructure shall be considered. In particular the connection points to the PSTN, the possible existing lines that could be leased and the available microwave frequencies.

Furthermore statistical information are also necessary to determine the possible density of traffic of an area. Inhabitants of areas having similar population density could behave in very different ways in use of mobile phones according to their average income, education, and acceptance of technology. This kind of information must be very accurate and up to date and usually are retrieved from specialized third party geographical and statistical institutes.

Finally the future expansion plans of the network must be considered including possible new services.

Once the expected traffic density and the existing substructure have been evaluated a CAD system for radio network planning is used and the MSC, BSC and BTS sites are determined. Of course the locations need to be visited to verify if they are suitable for mounting the necessary equipment.

Siemens has a several years long experience in network planning with the Unix based tool Tornado.



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Very first steps

• Studying the topographical maps,

• the relative statistical relevant informations,

• local regulations and laws,• existing networks and numbering plans• future expansion plans

Introduction

Network

Planning

•evaluation of

expected traffic

density

• use of CAD network

planning tool (Tornado)•determination of suitable MSC, BSC, BTS sites

Transmission

Planning

• connection points to

the PSTN

• possible leased lines

• frequencies available for microwave links

Fig. 2


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Topography

Networks operating on a national level are divided by location into servicing areas, so-called cells, in which a Base Transceiver Station BTS supplies the mobile subscribers of the area concerned. The cells represent the smallest service area in the PLMN network.

A big number of cells ensure service of the total PLMN service area. The cells are theoretically arranged in a so-called honeycomb pattern. Adaptations to the population/ traffic density and the topography of the service area lead to a more irregular pattern. In a deserted flat area, as for example a salt lake, the radio network planning is mainly a geometry exercise: what is the minimum number (base stations have a cost!) of circular cells of a certain radius required for completely covering the area without leaving holes?

Things become more complicated if we introduce obstacles as for Example Mountains or forests, shadowing our transmitted signal. The area covered by the base station will not be circular anymore, forcing us to deal with a more complicated coverage patterns. Some rocky mountain walls, some lakes, or the sea in coastal areas could reflect our signal introducing additional factors to be considered.

Finally some areas could be more densely populated, having a higher density of traffic. It will be seen in this chapter how the higher the traffic density, the smaller the cell area since a limited number of HF channels can only cope with a limited traffic volume. This can be carried out via a reduction of the cell radius or by dividing the cells into sectors, complicating our pattern even more.

The presence of major streets and bridges also can influence dimensioning and shape of cells in the network.

Unfortunately it is not always possible placing the BTS on that ideal spot calculated with the network planning tool, not all rooftops can carry the weight of a base station or have enough place. Sometimes local administrations could also deny the permission for mounting a site. This is why in our urban areas we may discover some rooftops populated by base stations and antennas of more than one or all of the local operators. That is probably the only place suitable for a BTS in that area where it is permitted to place base stations, too.



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Relevant

Topographical

Factors• obstacles

(mountains,forests,...)

• reflections (mountain

walls, water...)• traffic density (population density)• streets, bridges•local regulations

Topography

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Financial Aspects

To guarantee a GSM coverage aiming to 100% of the population, in a country like Germany more than 35000 base stations are needed. A big investment is necessary if we consider that apart from the cost of a base station, each site needs:

��an engineers evaluation for suitability to understand if there are all of the necessary stability and security conditions on the ground or rooftop to mount a base station and eventually a mast for the antennas,

��a local administration permission, which sometimes can be obtained only after some expenses or a longer legal dispute, or in some cases can result in the payment of a fee if totally or partially ignored,

��sometimes a compensation payment to the owner of the ground or rooftop, also here it is not unusual that some mediation skills are required,

��cables for power supply which must be pulled to the site and wired respecting the local security regulations

��cables or radio links for transmission, which need specialized mounting and commissioning

��antennas and power amplifiers

��specialized workers to mount the site

In the densely populated and economically strong urban areas this kind of investments is easily recovered, this is the reason why network operators always start implementing their networks there. In these areas operators know that investing in capacity of the network and in quality of services translates into revenue.

In the deserted salt lake area of our previous example, radio network planning maybe easy and also relatively cheap, but the amount of traffic is too low to make the investment financially viable. In these areas the operator will in any case lose money. Nevertheless the operator probably will cover that area because he must cover a minimum percentage of the country’s area according to his frequency licensing agreement with the local government. Once this percentage of territory is reached only the economically less interesting areas will be left with no coverage at all.



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• cost of the base station

• engineers evaluation of the area

• local administration permission

• compensation to ground owner

• cablings (power, transmission)

• specialized workers

Financial Aspects

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Quality of Service

We shall distinguish between quality of service (QOS) perceived by the end user and QOS from the network operators point of view.

The QOS perceived by the end user can be defined as the difference between the service the user expects and the service he actually gets. The perceived quality of service will determine the degree of satisfaction of the end user and his loyalty to the network operator. So quality of service is a fundamental factor for the long-term success of an operator.

From the point of view of the operator quality of service means principally two things:

��Providing all the services promised to the customer by allocating a sufficient number of resources to satisfy all the requests. There can be exceptions as for example available traffic channels on new years day, or coverage in nearly unpopulated areas. The permanent costs for providing the service is in this cases very often far beyond the benefits. In any case customers have lower expectations in this occasions and the perceived QOS is not much influenced.

��End user friendliness with an easy to access customer hotline service. Employees being contacted by the customer shall transmit interest for the end user questions, courtesy and knowledge, providing an immediate and, if necessary, individual response.

Quality of service results a compromise between wanting to satisfy the end user and on the other hand to save costs. During the phase of network planning the desired QOS to be provided will be a fundamental factor for deciding the amount of material and human resources to employ.



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Quality of Service

Difference

between

expected and

reiceived

service

Determines

user

satisfaction

and loyalty

Provide all

promised

services

User:

Operator:

User

friendliness with efficient

customer

hotline

Fig. 5


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Erlang Tables

An important aspect of quality of service is the so-called grade of service. The grade of services is usually indicated as a percentage number. A grade of service of 3 % means that during a certain monitoring period 3 phone call attempts out of 100 failed due to lack of available traffic channels.

Once an operator has decided what kind of grade of service he wants to offer, the question reduces to how many traffic channels (TCH) or time slots are necessary to provide it. This is a typical dimensioning problem. Here the previously mentioned statistical studies come into action. A statistical evaluation of the amount of traffic is needed. The unit of measurement of this quantity is called the Erlang and is calculated by using the following formula:

seconds) in (time

] time) onconversati (average x calls) phone of (number [Erlangs n �

A certain monitored area could present during a period of 24 hours for example 3600 calls with average duration of 120 seconds. The traffic in that area measured in Erlangs would result:

Erlangs 5 3600 x 24

120 x 3600�

Now the Erlang tables are used, on the column corresponding to the desired grade of service e.g. 3% we look for a value major than 5 Erlang, it results to be 5.53, corresponding to 10 TCH or time slots. This means that being there 8 time slots in one frequency, we need to allocate two frequencies in that area.

Of course during 24 hours the amount of traffic will fluctuate very much, and during peak hours these resources could be insufficient, this is why more accurate measurements during different time intervals over the day are necessary.



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C h an n e l s 1 % 2 % 3 % . . . . . . . .

1 0 .0 1 0 .0 2 0 .0 3 . . . . . . . .

2 0 .1 5 0 .2 2 0 .3 8 . . . . . . . .

3 0 .4 6 0 .6 0 .7 3 . . . . . . . .

4 0 .8 7 1 .0 9 1 .2 6 . . . . . . . .

5 1 .3 6 1 .6 6 1 .8 8 . . . . . . . .

6 1 .9 1 2 .2 8 2 .5 4 . . . . . . . .

7 2 .5 2 .9 4 3 .2 5 . . . . . . . .

8 3 .1 3 3 .6 3 3 .9 9 . . . . . . . .

9 3 .7 8 4 .3 4 4 .7 5 . . . . . . . .

1 0 4 .4 6 5 .0 8 5 .5 3 . . . . . . . .

1 1 5 .1 6 5 .8 4 6 .3 3 . . . . . . . .

1 2 5 .8 8 6 .6 1 7 .1 4 . . . . . . . .

1 3 6 .6 1 7 .4 7 .9 7 . . . . . . . .

1 4 7 .3 5 8 .2 0 8 .8 0 . . . . . . . .

1 5 8 .1 1 9 .0 1 9 .6 5 . . . . . . . .

1 6 8 .8 8 9 .8 3 1 0. 5 . . . . . . . .

1 7 9 .6 5 1 0 .7 1 1. 4 . . . . . . . .

1 8 1 0. 4 1 1 .5 1 2. 2 . . . . . . . .

1 9 1 1. 2 1 2 .3 1 3. 1 . . . . . . . .

2 0 1 2 1 3 .2 1 4 . . . . . . . .

2 1 1 2. 8 1 4 1 4. 9 . . . . . . . .

2 2 1 3. 7 1 4 .9 1 5. 8 . . . . . . . .

2 3 1 4. 5 1 5 .8 1 6. 7 . . . . . . . .

2 4 1 5. 3 1 6 .6 1 7. 6 . . . . . . . .

2 5 1 6. 1 1 7 .5 1 8. 5 . . . . . . . .

2 6 1 7 1 8 .4 1 9. 4 . . . . . . . .

2 7 1 7. 8 1 9 .3 2 0. 3 . . . . . . . .

2 8 1 8. 6 2 0 .2 2 1. 2 . . . . . . . .

2 9 1 9. 5 2 1 2 2. 1 . . . . . . . .

3 0 2 0. 3 2 1 .9 2 3. 1 . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Erlang tables

[ (number of phone calls) x (average conversation time) ]

n Erlangs = ---------------------------------------------------------------------------------

(time in seconds)

Grade of

service: 3%

=> 3 out of

100 call

attempts fail

Channels:

number of

time slots

necessary for

providing the

desired grade

of service

Elangs

Fig. 6


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2 Cellular Networks and Frequency Reuse

Network Planning

Cellular Networks and Frequency Reuse

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Cellular Network

In order to guarantee a seamless coverage, in a cellular network the service areas of the individual cells partially overlap. As a consequence, if the same frequency is used in these overlapping areas, interferences between neighboring cells will occur. The subscribers’ mobile stations will not be able to distinguish the different signals reaching that area from different base stations. For this reason all cells surrounding one cell in the cell structure must use frequencies differing from those used in the one central cell.

Frequency channels are a limited resource, each operator has only a limited number of channels, so there cannot be used different channels in all cells over the whole network. For these reason cellular networks are commonly organized according to the principle of cellular systems, frequency re-use. Examples of cellular networks not using frequency re-use are the IS-95 and the UMTS network. They are CDMA networks, where cells are distinguished by codes and not by frequency.

In GSM the narrow available frequency range is divided into individual frequencies (channels). Only some of these channels are used in a certain cell, the remaining channels are used in the adjacent cells. The same frequency is used again in cells, which are sufficiently far apart from each other to avoid inter-channel interference. This means that any area can be covered and thus an enormous increase in network capacity can be achieved with a small supply of channel frequencies.



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The Cellular

Network

Principle:• Many cells (BTS)

• Ful l coverage

• Partia l overlap of cel ls• Distribution of frequency resources

• Only a few frequencies per cell

• Frequency re-use

Solution:

cell,radio cell

r = cell ra dius(cell parameter)

Principle:

~ 4 r

cha nnelsu, v, w

channels

x,y, z

r

channels

x,y, zco-ch annel int erference zone

= cluster area

re-use distancefor HF channel frequen cy

re-use distancefor

HF channel frequency

Fig. 8


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Cluster

A certain minimum distance must be maintained between cells using the same frequencies in order to prevent interference or at least keep it to a bare minimum. This minimum distance, the so-called frequency re-use distance, depends on the concrete network planning and corresponds to approximately 4 times the cell radius. On this principle, the available channels can be divided e.g. into 7 parts and distributed over the PLMN area in such a way that each cell contains one of these 7 sets of frequency channels. The minimum area in which the whole range of HF channels are used is described as a cluster. Planning a concrete network implies that the population/traffic density, the topography of the area to be supplied, etc. must be taken into account.

The honeycomb structure represented here would apply to the deserted flat area of our example only, in real life frequency planning is such a difficult matter that in any case a sophisticated network planning software is needed.



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• Frequency re-use distance: avoid inter-channel interferences

• Cluster: smallest domain within which all frequency resource is used

(GSM900: typ. 7/9 cells)

• Network planning: difficult

The Cellular Network / Principles of Network Planning

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Cell Size

The size and shape of the cell depend on:

��The range of the MS radio contact (MS output peak power); topography (e.g. mountains, buildings, vegetation etc) and climate play a role here.

��Traffic density

The maximum radius of a cell broadcast channel is 35 km in the GSM900 system, 8 km in the GSM1800 system. The possibility of setting up "extended range cells" with a radius of up to 100 km has been integrated into GSM Phase 2+ for GSM900 systems. This should allow coverage of sparsely populated areas and especially coastal regions. The extended cell concept results in a reduced capacity.

Transmit power is limited for higher traffic densities in order to achieve a high degree of re-use of frequencies over smaller cells: The size of clusters is inversely proportional to the capacity of the radio system.

Cell Coverage

��Omni Cells: The BTS is equipped with omni-directional antennae and serves a 360° angle.

��Sector Cells: The BTS supplies the cells with directional antennae. The cell shape is a circular segment. Sectors of e.g. 180° or 120° but also 60° are covered.

Omnicells are often employed in the countryside or in general in areas with a low traffic density.

180° sector cells are usually employed along major communication roads as highways or urban thoroughfares.

120° sector cells are typical for urban areas

60° sector cells have been developed for extreme traffic situations as for example urban hotspots like railway stations or particular indoor solutions.



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Cell Size and Coverage

GSM 1800: 8km

GSM 900: 35km (100 km)360° omnicellcountryside

deserted and coastal areas (100 km)

180° sector cellalong roads

120° sector cellurban areas

60° sector cellareas with dense traffic

hotspots (e.g. railway

stations)

Fig. 10


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Hierarchical Cellular Structures

A Hierarchical Cell Concept (Rec. 05.22) is planned for towns, with an extremely high density of mobile subscribers.

��Macro-Cell: The "normal" cells are called Macro Cells. They have ranges from approximately one km to several (extended cell concept: 100 km).

��Micro Cell: Typical urban cell. Sometimes used in restricted areas with very high mobile user density, e.g. shopping malls, railway and subway stations, airport terminals. Their radius ranges from some 100 meters to approximately 1 km.

��Pico Cell: Cells for the support of indoor applications, e.g. offices. Their range should be several 10m.

Velocity dependent Handover are necessary in the Hierarchical Cellular Structures.

A macro cell superimposed to an existing network structure such that it covers a certain number of cells is commonly appealed as umbrella cell. Umbrella cells are hierarchically floating above the network and can be used as a traffic buffer for urban network cells. In case of a traffic overflow in one or more cells, some running traffic connection can be handed over to the umbrella cell so that the exceeding connection requests can be accepted by the hierarchically lower cell.

A Pico cell can be implanted inside a hierarchically lower position in a micro or macro cell. This is typically done in high traffic density locations where a micro cell is not sufficient for handling all the connection requests. This kind of implantation can also be temporary, by using mobile base stations. A typical example could be the Oktoberfest, where for a limited period the amount of traffic rises dramatically in a restricted area. After that period the mobile base station are uninstalled again.



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Hierarchical Cellular StructuresA macro cell

as umbrella

cell over

several micro cells

(traffic buffer)

A pico cell

inside a

micro cell

(hotspots)

Hierarchical Cellular Concept:

• Macro cells: min. 500 m

• Micro cells: some 100 m

• Pico cells: some 10 m

speed-dependent allocation

Fig. 11


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BSS Transmission Planning

Connecting a base station to the local BSC may become a challenging task in certain areas. The necessary bandwidth must be estimated, and then a convenient transmission line must be determined. In urban areas microwave links with directional antennae are very popular as an alternative to leased lines but, for example, they have a poor performance in areas characterized by frequent heavy rainfalls or their use in certain areas is forbidden by local regulations. In some very particular cases as for example in deserts, also satellite connections are used.

When connecting all base stations of one area to a BSC, several possible configurations can be chosen:

��Star: All base stations are connected one by one to the BSC

��Multidrop Chain: One base station is connected to the BSC and all the other base stations are connected one to another forming a chain. This configuration is used mainly for road coverage and helps saving on connection lines. Connecting the same base stations with a star configuration would be much more expensive.

��Loop: Similar to the multidrop chain, but with the particularity that the chain ends at the BSC again. This configuration is safer than the multidrop chain. If in the multidrop chain one link is down all of the following base stations in the chain will be disconnected and the traffic lost. With the loop, those base stations will be still connected to the BSC on the other end and the traffic will not be lost.

��Redundant: Same as Star, but with loop advantage. For very important sites.

��Cross Connect: A hub or similar cross-connect equipment can be integrated at the BTS site to allow the connection of more base stations over that one site.

��Multidrop Loop: Another possible use of cross-connect equipments, with loop advantages.

All combinations of this configurations are possible.



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BSS Transmission Planning

Cross-

connect

Multidrop chain

BSC

Star

Loop

• leased lines

• microwave links

• satellite

Multidrop

Loop

Redundant

Fig. 12



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3 Example of Network Optimization

Network Planning

Examples of Network Optimization

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Change of Initial Conditions

A network is always planned and then rolled out using topographical maps, statistical information and local regulations that are in a certain sense a photography of the actual situation. Some forecasts can be done on how the given situation will develop in time and a network shall be always planned in such a way that it can easily adapt to the changing conditions. Nevertheless sudden changes in habits of population and related traffic densities in well restricted areas are quite common and operators are constantly forced to re-plan parts of their networks. Here some examples are listed in which additional base stations must be placed and integrated. The whole network planning process must be repeated for that area. A certain number of frequencies must be employed and carefully chosen according to the actual frequency reuse patterns of that area, lines must be leased for BSC connections, available microwave frequencies found etc. etc.

��Nightlife changes in unpredictable ways, masses of people may in few weeks abandon completely certain facilities crowding some others simply following the wave of fashion.

��Changes in local urban regulations or long term street maintenance works can influence traffic flows heavily, urban thoroughfares can change from one day to the other from characterized by constant traffic jams (dense phone traffic, relatively few handovers) to fast flowing (low phone traffic, relatively frequent handovers) or vice-versa

��It is not unusual that new shopping malls are opened in almost deserted areas in the outskirts of urban conglomerates creating a confluence of customers towards areas previously of low interest

For these reasons network monitoring tools have been developed, able to provide cell by cell performance and quality of service information. These tools are commonly included in the OMC-B for the Base Station Subsystem and in the OMC-S for the Network Switching Subsystem.



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Change of Initial Conditions

• fashion & nightlife

• changed city traffic

• new shopping malls

network monitoring tools are needed

network planning process must be repeated

Fig. 14


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Canyoning

Optimization of a cellular network means improving the efficiency of an existing situation and very often results in tangible economical benefits for the network operator. Network monitoring information are compared with the results of field measurements performed in the area to be optimized. These measurements may be of various nature (power, direction of arrival, polarization, etc. etc.) depending on the particular environment and require professional tools and well trained personnel.

A typical example of how misleading network monitoring information can be if not compared to adequate field measurements is the phenomenon of street canyon scattering or more simply canyoning. A cell can assume undesired propagation shapes modeled on the surrounding environment, these shapes are highly influenced by how the antennas are directioned, both in the horizontal and in the vertical sense.

The example presented shows how in a given urban environment the actual propagation shapes of two cells A and B can differ very much from the intentions of the network planner. Cell A has to cover part of Square 1. Cell B has to cover Street 2. The network monitoring tool will report traffic statistics related to the cells A and B associating them to the supposed coverage areas (Intention of the network planner). The output information at this point will be that cell A presents a much higher traffic density than expected and needs additional capacity. Cell B has almost no traffic and seems to have been over-dimensioned. More money needs to be invested in cell A, for supporting additional frequencies and larger transmission means. The initial investments on cell B are nearly wasted.

At a more detailed analysis (actual situation revealed by measurements) a strong canyoning effect is detected. The cell A has a shape such to cover greatest part of the area cell B had to cover. Almost all users in Street 2 use cell A instead of B. In lucky cases adjusting the mounting angle of the antennae of cell A and B, can drastically reduce canyoning of cell A, and improve the efficiency of cell B.



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CanyoningA

B

A

B

Intention of the network planner

Actual situation revealed by measurements

Network monitoring tool:

• cell A presents unexpected high density

• cell B is almost unused

Invest in capacity

expansion of AOR

Try network

optimization

• equipment

• transmission

means

• A is

overdimensioned

• B is still unused

The angles of the

antennae of cell A

and B are slightly

changed so to

reduce cell A

canyoning and

• better

approximate the

intention of the

network planner

• use cell B

efficiently

• no further

expenses needed

Square 1

Street 2

Fig. 15


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Handover Margins

The handover procedure is of extreme importance for the correct functioning of a cellular network. For this reason it is standardized very in detail in the ETSI recommendations. This doesn’t mean that there is no possibility of optimization of handovers. For example the algorithm used by the BSC together with the received measurement reports to take the handover decision is completely in the hands of network developers and can change deeply depending on the network parameters and the state of the art in network measurement technologies. One of the editable parameters in these algorithms is the handover margin.

During a conversation the mobile station measures the RXLEV of its serving BTS and that one of the neighboring ones, the delta between those is constantly calculated by the BSC. As the mobile moves on the neighboring signal will become stronger until it is bigger than that of the serving cell. The delta is now considered negative and when it reaches a certain threshold the handover is performed, that threshold is, simplifying, the handover margin. If a handover margin is set too low, a Ping-Pong effect can occur, the handover will be performed in a very restricted area between the two BTSs, and the probability of being re-handovered back is high. On the other hand too high handover margins will cause the BSC to perform the handover when the connection quality is already very poor, or in worst case the connection has already dropped.

Power is the quantity used for the measurement, but quality of service is what the operator wants to preserve. The handover margin must be placed in any case within the limits of an acceptable (according to the operator’s market and traffic strategy) quality of service. These limit is defined as lower threshold in the handover process and represents the strength level at which the connection reaches the lowest quality allowed.

The handover margin values can be very different from area to area, and an optimization of them helps increasing:

��the network efficiency avoiding unnecessary Ping-Pong signaling

the QOS perceived by the end users by performing timely handovers.



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Handover Margins(moving from A to B)

signal strenght

distance

lower threshold

= 0

highest

handover

margin allowed

range for

handover

margins

A B

Fig. 16


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Frequency Hopping

Frequency Hopping means to change the frequency used for transmission is consequently changed every TDMA frame following a certain frequency hopping algorithm. The Time Slot of the physical channel is still fixed.

The logic behind frequency hopping is to guarantee that all channels have the same high degree of transmission quality by dividing possible short term interference over all channels of the cell.

So a narrow-band interference does not disrupt the total transmission on one carrier, i.e. on one frequency band, because the transmission is hopping from TDMA frame to TDMA frame to other frequencies.

Nevertheless, now interference occurs for all the carrier of the cell from time to time when transmitting on the disturbed frequency band. But this can be compensated in GSM, because in classical GSM there is always redundancy on the transmitted data. The redundant information is delivered in the next TS of the succeeding TDMA frame, i.e. on another frequency (which is not disturbed).

Frequency hopping is optional in GSM. It is on the PLMN operators decision to use frequency hopping or not. Frequency hopping significantly improves the quality / reliability of transmission.

The time slot transmitting the Broadcast Control Channel BCCH (carrying information necessary for MS synchronization to the network) does not participate in frequency hopping.

Frequency hopping is done in the MS and BS, managed from the BSC. The frequency hopping algorithm can be configured from an OMC.



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Frequency Hopping

f rame 0 frame 1 frame 2 frame 3 frame 4 frame 5

RFC 1

RFC2

RFC 3

RFC 4

RFC 5

TCH

Compensation of

narrow-band interference

� stable & reliable transmission

(redundant bits on different TDMA frames)

Fig. 17

network planning siemens

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