ERICSSON GSM SYSTEM HIGH FREQUENCY LOAD PLANNING (FLP) GUIDELINE

ERICSSON GSM SYSTEM

EAB/RNG-03:0045 Rev F 2005-03-28 COMMERCIAL IN CONFIDENCE 1(42)

HIGH FREQUENCY LOAD PLANNING (FLP) GUIDELINE

Ericsson AB 2005

The contents of this document are subject to revision without notice due to continued progress in methodology, design and manufacturing.

Ericsson shall have no liability for any error or damages of any kind resulting from the use of this document.


2(42) COMMERCIAL IN CONFIDENCE EAB/RNG-03:0045 Rev F 2005-03-28

Revision history

Rev Date Description

A 2003-04-19 Document created. This document is the result of

merging the three previous FLP guidelines:

Fractional Load Planning (FLP) Guideline,

ERA/LVR/D-99:0201 Rev A

FLP implementation cook book, ERA/SV-

01:0632 Rev A

Frequency Planning Strategies, ERA/SV-01:0633

Rev B

The document is also updated to an R9.1-R10

perspective.

B 2003-08-29 Updates of all areas.

C 2003-11-10 Updates of examples in chapter 3.5.2.

D 2003-11-11 Further updates of chapter 3.5

E 2004-01-23 Change of name of the document from Fractional

Load Planning (FLP) Guideline to High

Frequency Load Planning (FLP) Guideline.

Change of scope to only cover the preferred

frequency plan strategy: 1/1.

New “Operator benefit” chapter with a

commercial view of FLP.

General updates of the entire document.

F 2005-03-28 Update of 4.2.1 to point out the lower limit of

number of hopping frequencies for FLP.

Also some editorial changes and a new reference

to “Guideline for Activating Synchronized Radio

Networks”

ERICSSON GSM SYSTEM


Contents

1 Introduction........................................................................ 5

1.1 Background ........................................................................................... 5

1.2 How to read this guideline ..................................................................... 5

1.3 Concepts ............................................................................................... 6

1.4 Abbreviations ......................................................................................... 7

2 Operator benefits summary .............................................. 7

2.1 Minimized frequency planning and flexible network expansion ............. 8

2.2 High frequency load .............................................................................. 8

2.3 Installed base of filter combiners ........................................................... 8

3 Technical background ...................................................... 9

3.1 General .................................................................................................. 9

3.2 Frequency load Planning (FLP) definition ............................................. 9

3.3 Frequency hopping – a basic pre-requisite for FLP ............................ 10

3.4 Hardware constraints .......................................................................... 11

3.5 Utilizing the frequency hopping gain .................................................... 11

3.6 Operation & maintenance in FLP networks ......................................... 13

4 The FLP method .............................................................. 13

4.1 1/1-frequency planning method ........................................................... 13

4.2 Frequency allocation of BCCH & TCH frequencies ............................ 14

4.3 Effects of uneven traffic distribution .................................................... 18

4.4 TRX dimensioning by using the frequency load .................................. 18

5 Radio Network optimization ........................................... 20

5.1 General ................................................................................................ 20

5.2 Common mistakes when implementing FLP techniques .................... 21

5.3 Features .............................................................................................. 23

5.4 Parameters .......................................................................................... 33

6 Datacom aspects ............................................................. 36

7 Load and reuse definitions ............................................. 37

7.1 Frequency load .................................................................................... 38

7.2 HW load .............................................................................................. 39

7.3 Frequency Utilization ........................................................................... 40

7.4 Physical Frequency reuse ................................................................... 40

7.5 Equivalent (TCH) reuse ....................................................................... 41

8 References ....................................................................... 42

ERICSSON GSM SYSTEM


1 Introduction

1.1 Background

High frequency loaded networks, planned with extremely tight reuse such as 1/1

have shown to be a very competitive method in order to achieve high spectrum

efficiency. This is especially true for operators with little spectrum available,

where traditional frequency planning cannot use to full advantage the interference

averaging/diversity effects of frequency hopping. The high capacity potential,

together with a simplified process of frequency planning and a decreased cost for

operation and maintenance have made High Frequency Load Planning (FLP) a

very attractive alternative for many operators.

The FLP method is based upon frequency hopping together with a number of

radio network features in order to enhance the network capacity and quality. Each

frequency is only used a fraction of the time for each connection. As FLP

requires synthesizer hopping, the base stations need to be equipped with hybrid

combiners.

The message to the operator to implement FLP successfully is:

• Plan for having mobiles experience one dominant server.

• To utilize the Ericsson functionalities to achieve a “Robin Hood effect”

(see 3.5). This means more Erlang for a given spectrum.

This guideline has been produced in order to spread knowledge of how to plan

and dimension systems with high frequency load.

1.2 How to read this guideline

The “Operator benefits summary” chapter is written on a high level to give a

commercial view for market-oriented readers. The gain figures are in this part of

the document not described in detail. They are presented only to give a market

message of what can be achieved in most networks. Of cause, variations

depending on local network qualities are expected.

The “Technical background” chapter serves as a basic introduction on how and

why the FLP method should be used. This chapter gives a brief overview on the

benefits of using the FLP method.

In the “FLP method” chapter the reader will get a deeper knowledge on different

frequency planning issues to be used in different situations.

The “Radio Network optimization” chapter will explain different radio network

features and common mistakes when implementing FLP techniques and will

serve as a guide on how to understand the behavior of an FLP network. Also, in

this chapter, the product names/numbers are stated.

Packet data aspects are described in the “Datacom aspects” chapter.



Different load and reuse measure definitions used throughout this guideline are

presented in the final chapter.

1.3 Concepts

Cell Area covered by one BCCH. A cell can have a

subcell structure using only one BCCH. In R10 two

system types, i.e. two frequency bands, can be

defined in one cell but on different subcells. See

figure 1.

Channel Group The channel group is a group of frequencies from

one system type, i.e. one frequency band. There can

be more than one CHGR defined in a cell/subcell.

CHGRs are identified by a local channel group

number defined per cell, see figure 1. CHGR 0

contains the BCCH and is defined automatically at

cell definition. A frequency may (from R10) be

defined in more than one CHGR per cell (except

for the BCCH carrier).

Frequency Load With frequency hopping each frequency is used by

a connection a fraction of the time. This fraction is

dependent by the number of hopping frequencies.

When the traffic load increases in a network the

fraction of time a frequency loads the air interface

increases, i.e. the probability of interference

increases. The maximum achievable frequency load

is dependent on the acceptable quality standards set

for a network and thereby defines how effectively

the frequencies are used. The quality can be

maintained/kept low by the usage of features.

FLP Planning Method of combining GSM functionality such as

Frequency Hopping, MAIO Management, Power

Control, DTX and more, to use each frequency as

effectively as possible.

Subcell A cell can be divided into an overlaid/underlaid

subcell structure, see figure 1. A subcell contains

one or more CHGRs using the same system type

(i.e. one frequency band).

ERICSSON GSM SYSTEM


Figure 1. A cell divided into subcells and CHGRs.

1.4 Abbreviations

AMR Adaptive Multi Rate

CHGR Channel Group

DTX Discontinuous Transmission

DTQU Deci Transferred Quality Unit

EDGE Enhanced Datarates for GSM Evolution

EFR Efficient Full Rate

E-GPRS Enhanced General Packet Radio Service

FLP (High) Frequency Load Planning

MAIO Mobile Allocation Index Offset

MRP Multiple Reuse Patterns

OL/UL Overlaid/Underlaid Subcells

OSS Operation and Support System

RNO Radio Network Optimization

SCLD Subcell Load Distribution

TCH Traffic Channel

TRU Transceiver Unit

TSC Training Sequence Code

2 Operator benefits summary

Usage of the FLP planning method can result in major benefits for an operator.

The benefits can be sorted into two major areas; Minimized frequency planning

and flexible network expansion support, and High frequency utilization. The

capacity gain by using FLP is specifically useful for operators with a narrow

frequency band, and sometimes maybe the only reasonable alternative. Practically

all operators will benefit from the reduced effort spent on TCH frequency

planning.

CHGR 3

CHGR 2

CHGR 1

CHGR 0

Overlaid subcell

Cell

Underlaid subcell



In addition to the above-mentioned benefits a result of the FLP method will be a

general quality increase in terms of better quality calls in most radio

environments.

2.1 Minimized frequency planning and flexible network expansion

When using the FLP method, retuning the TCH frequency plan at network

expansion, is avoided. A saving of roughly 50% of the total frequency retuning

cost is estimated.

A cell in the FLP network is able to handle large traffic variations (in e.g. up to a

3*4 TRX RBS configuration) without any activities other than adding &

deploying TRXs. This can be compared to a non-FLP network where expanding a

cell from e.g. 2 to 3 TRXs mostly leads to tedious frequency planning work.

The flexibility in traffic handling capacity can be used for areas that suddenly

require more capacity than planned for, e.g. a shopping mall is established in the

area. This can easily be handled by adding more TRXs to the basestations in the

area. TRXes from low traffic cells may even be moved to the cells covering the

“Shopping mall area”, see 3.6. This flexibility is applicable to both circuit

switched and packet switched traffic.

New cells can also be added, with effort spent on frequency planning only for the

BCCH frequencies

2.2 High frequency load

With FLP, experience has shown that frequency load figures of significantly

more than 10 % can be reached. The large variation depends on the FLP features

used and the general radio conditions. The radio conditions are mainly dependant

on the quality of the cell plan.

The recommendation is to use all available high capacity radio network features

and functions when operating a FLP network.

2.3 Installed base of filter combiners

Because of the FLP benefits an operator should consider moving installed filter

combiners from urban and suburban areas that are interference limited, to rural

areas where good coverage is most important. This is most important for

operators with a narrow frequency band. Hybrid combiners and the FLP method

should then be deployed in High capacity, interference limited areas. There are of

course other considerations when using hybrid combiners compared to using

filter combiners (filter loss, capacity etc).

ERICSSON GSM SYSTEM


3 Technical background

3.1 General

FLP offers a very simple and powerful way to achieve good quality in a network

with very little effort for frequency planning. As long as the traffic is within

certain limits the network can grow and TRXs can be added with very little

operation & maintenance. The exception is the BCCH frequencies, which still

have to be planned according to the traditional method of e.g. 4/12.

3.2 Frequency load Planning (FLP) definition

An FLP network is characterized by pseudo random synthesizer hopping being

used in combination with other Ericsson features to achieve an effective usage of

the available frequencies. The key is to use as many frequencies as possible for

each connection, but each frequency only for a fraction of time. When the traffic

load increases in a network the probability of co-channel collisions between cells

increases as all use the same set of hopping frequencies. Increased traffic load

makes the frequency load increase. The maximum achievable frequency load is

dependent on the acceptable quality standards set for a network and thereby sets a

measure on how effectively the frequencies are used. The quality can be

maintained/kept low by the usage of features.

Compared to traditional frequency planning, the tight frequency reuse method of

FLP gives more hopping frequencies per cell in a 1/11 frequency reuse planned

network. The interference variation becomes larger since the interfering cells are

closer. The radio network can cope with such tight frequency reuse as 1/1 since

each frequency is only used a fraction of time for each connection. Another

advantage with an extremely tight reuse is that the interference originates from

many more sources. The mobile receives interference from a larger number of

base stations in the downlink, and the uplink interference originate from mobiles

located in a large number of cells. The large number of interferers, each only

transmitting a fraction of the time, evens out the interference in the network,

thereby lowering the risk that some areas are very badly interfered. Severe

interference hits occur sufficiently seldom due to the fractional loading and

frequency hopping. The channel coding and interleaving schemes can thereby

limit the bit errors in the received speech frames. The increased hopping gain, i.e.

frequency- and interference diversity gain, cater for that a connection can be held,

with sufficient quality, at a lower C/I (i.e. higher RXQUAL2, see further 5.2.2).

Frequency hopping also increases coverage as the impact of multipath fading is

diminished.

1 1/1 means that all available TCH frequencies are used in all cells. Note that 1/1 can only be applied on the TCH frequencies. The

BCCH frequencies must still use a sparse reuse for satisfactory control channel performance. 2 The RXQUAL distribution is very much correlated with the variance of the bit error rate on burst level. The higher variance the

more is the RXQUAL distribution moved towards higher values. The variance of the bit error rate increases primarily with the

physical frequency re-use and the number of hopping frequencies.



Figure 2. FLP principle from cell 1A perspective:

Area a: The C (in C/I) is much stronger than the total I.

Area b: The C is equal to I. The C/I is dependent on the traffic and number of

hopping frequencies.

Area c: The C is less than the total I. The frequency load is too high and a lot of

harmful co-channel collisions will occur.

Area d: The C is equal to I from cell 1B, but as the cells are synchronized this I

can (with MAIO Management) totally be avoided and give no contribution to C/I.

It is important in FLP networks that all voice mobiles are connected to the

strongest server. This Means:

• No HCS between cells using the same frequencies.

• Low hysteresis (2-3) and/or short filter lengths for handovers.

• Enable CLS to offload mobiles in high load situations.

• “All neighbors should be defined”. Use antenna tilts instead of inhibiting

a handover from being performed by undefining the relation.

3.3 Frequency hopping – a basic pre-requisite for FLP

FLP uses frequency hopping. Frequency hopping means that the connection will

change frequency between each TDMA frame, i.e. every 4.6 ms. The benefit of

this is that frequency hopping will have an averaging effect on the interference

for all connections in a cell. There will be no very bad connections or very good

connections compared to a non-hopping cell. The averaging of the interference

will improve the total performance of the cell due to that the GSM coding can

handle interference from time to time and no really bad connections are left in the

cell.

The frequency hopping method for FLP networks is called Synthesizer frequency

hopping. Synthesizer frequency hopping means that one TRX handles all bursts

that belong to a specific connection. Therefore the number of frequencies used

for hopping is not dependent on the number of TRXs. This leads to the possibility

of an increased interference- and frequency hopping diversity in cells with few

Cell 1A

Cell 3

Cell 2

a b

cd

b

a b

cd

b

Cell 1B

ERICSSON GSM SYSTEM


TRXs. This is especially true for operators with narrow spectrum allocation, e.g.

below 6 MHz. For more information regarding synthesizer hopping see [3].

FLP maximizes the frequency diversity gain, since FLP allow hopping over 32

frequencies for each connection. In practice the maximum gain is achieved at 14-

15 pseudo random hopping frequencies. However, for the interference diversity

there is no upper limit of number of frequencies used. This leads to maximal

coverage if the hopping channels are used at the cell border increasing the

coverage 5-6dB.

3.4 Hardware constraints

FLP methods are restricted to be used together with synthesizer frequency

hopping. Synthesizer hopping requires hybrid combiners (CDU A, C, C+, G).

It is recommended to consider BTS alarm handling if constant adjacent channels

are used within a CDU since alarms might be triggered.

3.5 Utilizing the frequency hopping gain

Traditional frequency planning such as 4/12 is based upon a worst case planning

where full traffic load is assumed. The radio network must be dimensioned for

full traffic load since the interference in most cases comes from mainly one or a

few interfering connections. Thus, the fact that the radio resources are merely

used a fraction of the time can NOT be utilized.

In an FLP network, even at full traffic load when all available timeslots are

occupied by traffic, each frequency allocated to a cell is only transmitted a

fraction of the time. However, the reuse of the BCCH still has to be planned

according to traditional methods.

By spreading the interference both in time and space with FLP (figure 3) the

network does not need to be planned for full traffic, i.e. less TRXs than

frequencies for each cell. This is why the FLP method gives higher spectrum

utilization without introducing additional frequencies to the network.



Figure 3. Each one of the frequencies in the hopping sequence has different

interferers, which are spread out, in different parts of the cell.

In figure 4, the distribution of the Carrier to Interference Ratio (C/I) for all

connections in a network is schematically shown. Note that this is a theoretical

picture, not from a real radio network. In a radio network utilizing the FLP

functionality step by step the quality becomes more and more equal for all

connections because of the interference averaging, see the “FHOP” curve in

figure 4. This is the “Robin Hood effect”, i.e. take from the rich and give to the

poor. The more FLP related features that are used the more narrow the curve

becomes.

In non-hopping networks there are connections with interference and some

connections without interference, which leads to a very large spread in the C/I

distribution, see the “nothing” curve in figure 4. Nothing means no radio network

features are utilized.

C/I

MS

dis

trib

uti

on

FHOP

FHOP+BTSPC

FHOP+BTSPC+DTX

Nothing

Acceptable C/I

no FHOP

Acceptable C/I

FHOP

Figure 4. The impact of frequency hopping on the C/I distribution (Probable

Distribution Function). Nothing means no radio network FLP-features are

utilized.

Note that the full benefits from frequency hopping only can be utilized when

sufficiently high interference diversity is achieved.

f2

f1

f3

f1,

f2,f3

f3 interfered

f2 interfered

f1 interfered

f2 and f3 interfered, but

log normal fading

is not correlated

f2

f1

f3

f1,

f2,f3

f3 interfered

f2 interfered

f1 interfered

f2 and f3 interfered, but

log normal fading

is not correlated

ERICSSON GSM SYSTEM


3.6 Operation & maintenance in FLP networks

One major driver for implementing the FLP technique in a network is the

decreased effort for frequency planning and decreased operation and maintenance

when adding new TRXs and cells.

The frequency planning can be performed in an easy way without any decrease in

network performance compared to other more complex methods. With a very

simple 1/1 scheme, the planning can be made manually for a large area in a very

short time. When doing TRX expansions no frequency planning considerations

have to be done at all for the hopping CHGR. Note that the load/reuse in the area

must be monitored so that the traffic and thereby quality are kept within

acceptable limits.

An example of a simplified roll out could be that less consideration can be taken

to uneven traffic. If there is a shopping centre in the middle of a planned area and

1/1 planning is used, more TRXs can easily be installed without frequency

replanning in these cells after congestion or high load is detected. E.g. TRXs can

be moved from the low traffic cells, see figure 5.

Figure 5. With FLP a fast roll out can be done with less consideration to uneven

traffic load as capacity adjustments easily can be done. TRXs can be moved from

low traffic areas to high traffic areas with no frequency retuning. The dots mark

where the traffic is.

4 The FLP method

4.1 1/1-frequency planning method

1/1 planning means that all hopping TCH frequencies are used in all cells. It is

required to use the features synthesizer frequency hopping, MAIO Management,

DTX UL, MS and BTS power control. It is further recommended to use the

features OL/UL, Subcell Load Distribution, BCCH in OL, Intra Cell Handover

TRX

TRX

TRX

TRX

TRX



and DTX DL. 1/1 cannot be utilized fully unless the cells within a site are

synchronized and MAIO management is utilized (see 5.3.2). In this way, the same

HSN should be used within the site, or in clusters of synchronized cells, in order

to achieve orthogonal frequency hopping within a site or between synchronized

cells. The Training Sequence Codes, TSCs, can be the same for clusters of cells

with perfect frequency hopping, or orthogonal hopping, i.e. cells that are never

using the same frequency at the same instant in time. Read about TSC planning in

[6].

It is very important to have a good cell plan with this tight reuse. This means that

all areas with poor coverage or no dominant servers will suffer from bad quality

and dropped calls. Antenna down tilt must be used extensively in order to create

dominant servers and limit areas of overlapping coverage. It is devastating for the

network quality and capacity to have high sites overlapping to a large number of

surrounding sites. Most important in FLP networks is therefore to work with the

cell plan, thus to decrease the cell overlap and to contain all cells in order not to

interfere with each other. The uplink seems to suffer more than the downlink

when the frequency reuse is tightening. This indicates that networks with high

frequency utilization are uplink limited rather than downlink limited.

In R9.1 up to 32 frequencies per CHGR can be used to hop over, or in practice 31

as the BCCH needs one frequency and 32 is the limit of frequencies per cell. In

R10 up to 128 frequencies can be assigned per cell, which means that the

practical hopping limit is 32 frequencies per CHGR. Releases earlier than R9.1

up to 16 frequencies could be used to hop over. In this guideline R10 is assumed,

in which also the possibility to reuse a frequency in more than one CHGR is done

whenever is needed.

4.2 Frequency allocation of BCCH & TCH frequencies

4.2.1 Split spectrum between non-hopping BCCH and hopping TCH

In an FLP network it is recommended to split the frequency band into a dedicated

BCCH and a dedicated hopping TCH band, which means that a BCCH frequency

is never used as a hopping TCH frequency and vice versa. The BA lists then

become shorter, which improves BSIC decoding performance and measurement

accuracy of neighbouring cells. It is also a good solution from a practical O&M

point of view as there is less consideration to be taken to the frequency plan at

expansions. But, it is of course good to be flexible with this issue and it is

actually rather easy in an FLP system to temporarily steal hopping TCH

frequencies and use as non-hopping BCCH carriers for new sites etc.

When splitting the frequency spectrum between BCCH and hopping TCHs, the

goal is to achieve a good balance between the speech quality on the non-hopping

BCCH speech channels, and the speech quality on the hopping TCHs. The BCCH

have to be good enough to secure the handover performance and also good

enough to secure the quality of the non-hopping traffic channels on the BCCH

carrier. On the other hand, as many frequencies as possible should be used as

hopping TCHs. However, it is for example not optimal to have a 12 reuse BCCH

ERICSSON GSM SYSTEM


if the equivalent TCH reuse is as high as 18, i.e. 18 hopping frequencies on in

average 1 TRX/cell, or 36 on 2 TRX/cell. With a tight BCCH frequency reuse the

BCCH frequencies will be very difficult to plan with a risk of possible

interference and handover problems, whereas the hopping TCHs easily could

handle more traffic and thus interference. There is no gain to hop over less than

four frequencies.

The feature BCCH in Overlaid Subcell will help tightening the BCCH to a 12

reuse as the speech connections are allocated closer to the cell core in the BCCH

channel group compared to the underlaid, speech only, subcell. It has been shown

in some networks that the BCCH can be pushed down to 11-12 reuse with

maintained locating performance. This is dependent whether the BCCH is

staggered or blocked, see chapter 4.2.2.

Note that a 12 frequency reuse on BCCHs is much more difficult to plan than a

12 frequency reuse on the hopping TCHs. The average interference level on the

BCCH frequency is much higher than on a hopping TCH planned with the same

reuse. This is because the BCCH always have a frequency load on the downlink

of 100 % as all BCCH-carrier timeslots are always transmitting. Dummy bursts

are transmitted if there is no ongoing traffic on a timeslot. In addition to this, the

hopping TCH channels benefit from the use of power control and DTX on the

downlink that decreases the interference significantly.

It is essential to realize that there is a trade-off between the physical frequency

reuse (see 7.4) and the frequency hopping gain. The frequency gain must be

sufficient in order to achieve high interference diversity. Thus, the spectrum

available for the hopping TCH frequencies determines the physical frequency

reuse that should be considered. As there is no gain to hop over less than four

frequencies, the minimum required frequency spectrum for FLP is 3 MHz

(= 11 BCCH frequencies + 4 TCH frequencies).

Recommendation:

Plan, if possible, for a 12 reuse on the BCCH even if there are plenty of

frequencies. The reason is that if the traffic is expected to increase a lot in the

near future, it might be a good idea to plan the BCCH frequency plan a little

tighter in favor of hopping TCH than what is really necessary at the moment. The

network plan can then cope with additional traffic, and TRXs can be added

without any need to change the frequency plan.

4.2.2 Staggered or blocked BCCH/TCH frequency plan

In an FLP network, it is recommended to use a staggered BCCH/TCH frequency

plan unless the spectrum available for the blocked TCH is alone much higher

than 2 MHz, which is the outdoor coherence bandwidth3. Indoors the coherence

bandwidth is 5 MHz.

3 The coherence bandwidth can be thought of as the bandwidth within which the fading dips will occur at the same locations. A

broader spectrum to hop over will eliminate the risk of having the same fading dips for all hopping frequencies.



Example of staggered BCCH/TCH frequency plan:

22 frequencies in total divided into12 BCCH frequencies & 10 hopping TCH

frequencies.

The BCCH frequencies are allocated staggered as:

2,3,5,7,9,11,13,14,16,18,20,21.

A staggered configuration of the TCH carriers would then be:

1,4,6,8,10,12,15,17,19,22.

Example of blocked BCCH/TCH frequency plan:

22 frequencies in total divided into12 BCCH frequencies & 10 hopping TCH

frequencies.

The BCCH frequencies are allocated blocked as:

1,2,3,4,5,6,7,8,9,10,11,12.

A blocked configuration of the TCH carriers would then be:

13,14,15,16,17,18,19,20,21,22

For narrow spectrum (~6 MHz) operators the recommendation is to spread the

frequencies in order to hop wider than the coherence bandwidth. If, for example,

hopping over two adjacent frequencies in one end of the spectrum and two

adjacent frequencies in the other end of the spectrum the performance result will

be closer to hopping over two frequencies than hopping over 4 frequencies in

total. The conclusion should be that hopping over adjacent frequencies will give

less frequency diversity gain. A staggered BCCH/TCH is also simpler to plan as

no considerations have to be made regarding adjacent channel interference

between BCCHs.

The benefits of using a staggered BCCH in an FLP system:

• Easier to plan BCCH layer

• Might manage on less BCCH carriers than blocked, maybe 12 instead of 13-

15 in the case of blocked BCCH.

• More MAIOs available with maintained interference diversity since

adjacent MAIOs can be used without any drawbacks, see 5.3.2.

• If the uplink interference is limiting, then the uplink quality on the TCH

carriers becomes relatively better than the downlink since there is no/less

adjacent channel interference.

• Wider spectrum to hop over. It is recommended to have at least 2 MHz

between the lowest and highest frequency at synthesizer hopping.

The benefits of using a blocked BCCH in an FLP network:

• Possible to support higher frequency utilization on the TCH hopping

carriers since there are no adjacent BCCH carriers.

• Supports more efficient use of BTS Power control, thereby increasing the

possibility to load the hopping TCH channel group even higher.

ERICSSON GSM SYSTEM


The benefits of staggered BCCH/TCH strategy due to the wider hopping

spectrum are more important than the benefits from using a blocked BCCH/TCH

strategy. Especially when the available spectrum is small. It is not determined

how big difference in loading there is between a staggered and a blocked

BCCH/TCH plan since it is hard to perform good comparisons.

A higher gain from downlink power control strategy can be used in a blocked

TCH plan. The downlink connections will not suffer from the adjacent BCCH

channels and can thereby be down regulated much more. However, as power

control down regulation is done close to the cell core rather than close to the cell

border, the adjacent channel interference from a BCCH carrier to a hopping TCH

carrier within the cell has less impact in the more interfered area at the cell border

than closer to the site (see figure 6). The conclusion is that staggered planning

can be done without too much consideration on the power control issue.

Figure 6. Own BCCH interference when using staggered BCCH/TCH.

In a staggered BCCH/TCH plan, the hopping TCH carriers suffer from adjacent

channel interference on the downlink from BCCH frequencies. In a high

frequency loaded network there are many interferers, which means that the

interference comes from many different connections. The additional residual bit

errors that occur due to adjacent BCCH frequencies to the TCH hopping

frequencies then adds to the co-channel hits.

Several factors impact the choice of BCCH allocation strategy, e.g. capacity

issues or that the whole country has a staggered plan, which means that the

border areas between urban and suburban will be hard to manage if a blocked

BCCH plan is used in the city areas, or vice versa.

RxLev from TCHRxLev from TCH

RxLev from BCCHRxLev from BCCH

Cell border

Total Inter-cell interference

Power ControlPower Control

C/A Robustness: +9 to +15 dB



4.3 Effects of uneven traffic distribution

FLP 1/1 can handle large differences in traffic between cells with minor impact

on network performance, i.e. networks with uneven transceiver distributions. For

example, 1/1 can handle a network with traffic between 2 and 20 Erlang4 per cell

quite well. It is thus easy to add more transceivers to the network when needed.

This can be done until the average load reaches the acceptable limit.

FLP can handle high load in individual cells. With 1/1, the number interfering

neighbours become many. The interference comes from many different cells, and

is cumulative. If there is a lot of interference from one single high traffic

neighbour, the performance will not be dramatically worse, it will merely degrade

the performance slightly. This is of course valid up to the point where the co- and

adjacent channel hits becomes too many from a particular neighbour and the

channel coding can’t handle all bit faults.

As the traffic increases and more TRXs are installed, there is a point when MAIO

values start to run out. This means interference problems as all available hopping

frequencies are used on the air interface simultaneously. A cell split according to

traditional routines should be performed as FLP does not solve this problem. This

is merely to explain that FLP methods can cope with uneven traffic distributions.

There is a trade-off between the money spent on cell plan optimization compared

to the cost of for example a cell split. This cost relation varies between operators

and different countries.

4.4 TRX dimensioning by using the frequency load

4.4.1 General

In this chapter some basic rules on how high load or how low reuse can be

expected by a given planning method. Basically, how much traffic, and thereby,

how many TRXs/cell can be installed for a given frequency band.

When dimensioning a network the number of TRXs per cell have to be

dimensioned according to the peak traffic in each cell. Thus, when estimation of

the number of TRXs is done, the peak traffic figures should be used.

4.4.2 Using the frequency load

The recommended way of calculating the number of TRXs per cell is to look at

the frequency load. The frequency load measure is defined as:

)(#*8 cell

cell

FRQ

ErlangFRQLoad =

4 A three-sector site with a 2x06 has capacity of 4 TRXs per cell. 4 TRXs gives 20 Erlang with 2% GoS. Expansion above this has to

be done with a new cabinet. In these cases a new site for this new RBS should be considered.

ERICSSON GSM SYSTEM


…where the average busy hour Erlang figure per cell is estimated from an area

with around 10-30 cells. With 1/1 it is not possible to look at only one cell,

instead many should be considered. It is possible to have a very high load in one

cell. But that cell will cause interference to surrounding cells, which can take less

traffic due to that. Therefore an area of cells must be used for the calculation.

Note that the frequency load figure has to be estimated from a network average or

a large area for the busy hour period of a couple of hours. The reason is that some

cells might carry much more traffic than average, especially during short periods

of time, giving a frequency load of much more than 10 %.

If the cell plan is fairly good and if all Ericsson BSS features are used and tuned

correctly a network average frequency load of around 10 % should be possible

with sufficient quality. This requires that the time and effort put into the tuning of

the cell plan is higher than average.

Example:

An operator has 5 MHz, 25 carriers, available. The frequency spectrum is split to

12 BCCH and 12 TCH carriers. It is possible to or plan for a frequency load of

10%.

)(#*8 cell

cell

FRQ

ErlangFRQLoad = =>

)12(*81.0 cell

Erlang= =>

cellErlang = 9.6

The TCH traffic on the BCCH is estimated to almost the number of TCH TS

available, i.e. 5 Erlang (this is an estimate). This means that each cell can carry

5 Erlang on BCCH + 9.6 Erlang on TCH, thus 14.6 Erlang/cell in total.

14.6 Erlang in average gives 22 TCHs with 2% GoS, i.e. 22 TS for TCH in total

for the cell.

If 2 TSs are used for BCCH and SDCCH on the non-hopping CHGR then there

are 6 TS left for TCH traffic on the BCCH TRX.

22 TS – 6 TS = 16 TS for TCH on hopping CHGR =>

=> 16 TCH / 8 TS per TRX = 2 TRXs

1 BCCH TRX + 2 hopping TRXs = 3 TRXs.

This means that it is be possible to install up to almost 3 TRXs per cell in

average.



5 Radio Network optimization

5.1 General

In FLP networks, the interference, and therefore also quality in the network, is

strongly related to the traffic load. However, the number of installed TRXs

controls the traffic that can be carried by a radio network. The frequency load is

the maximum allowed traffic, i.e. the maximum number of TRXs, per frequency.

The maximum frequency load in a 1/1 network can be very different for different

networks because of different radio network topology and cell plan. Important

factors that determine how high load that can be carried with obtained quality are:

• Low / high sites (confined coverage)

• Antenna direction and tilt

• How the BCCH frequencies are chosen (staggered/blocked BCCH/TCH

plan)

• Microcells between FLP hopping cells in the same area

• Dedicated or shared TCH band (with e.g. microcells)

• The relation between outdoor and indoor traffic (especially traffic in high

rise buildings can be critical)

• Available spectrum (as the hopping gain depends on it)

• Quality standards for the operator (accessibility, retainability, integrity)

Thus, the acceptable frequency load is very operator/network dependent.

The design of the cell plan will significantly affect the radio network quality

and/or capacity. In a network with well-contained cells with few handover

relations, thus cell that interfere with few other cells, characterize a “good” cell

plan. I.e. ideally flat terrain and even antenna heights just above the average

clutter height. All sites should be on an even regular grid with no areas with bad

coverage or lack of a dominant server. There are no high-rise buildings with

elevated traffic in an ideal cell plan.

On the other hand, the characteristics of a “bad” or “difficult” cell plan are cells

that have many handover relations and thus interfere with many different

neighbors. The quality of a radio network with such a cell plan will suffer from a

higher level of interference for a given traffic. The network will therefore have a

significantly lower capacity.

ERICSSON GSM SYSTEM


5.2 Common mistakes when implementing FLP techniques

When FLP is implemented it is very important to understand that the radio

network behaves in a different way compared to the case when more traditional

methods are used. Many operators have tested FLP methodology and concluded

that the network deteriorates and that FLP is a bad method. This is however not

always true since these conclusions often are made without a proper analysis. The

following chapters describe the most common mistakes.

5.2.1 Cell planning considerations

The most common problem is that the cell plan is not adapted to synthesizer

hopping and tight physical reuse. The quality with FLP solutions will therefore be

lower than expected. If 1/1 is used it is important to have a confined cell plan, see

[10]. Otherwise, e.g. with high sites with no tilts, the quality and capacity will

suffer. The high sites need to be addressed when FLP is implemented. This often

happens when an operator evaluates FLP without understanding why and where

the quality deteriorates in an FLP environment.

This implies that there is a trade-off between the money spent on cell plan

optimization in order to get high frequency load within quality standards

compared to the cost of for example a cell split. The most important factor is

however the available spectrum. For a low spectrum allocation, e.g. below 6 MHz

it is probably beneficial to make a good cell plan in order to use FLP and to

squeeze the most out of the spectrum.

5.2.2 The RXQUAL measure change behavior

The RXQUAL measure drastically changes behavior when FLP is used and

should be interpreted and evaluated in a different way. Thus, RXQUAL must be

interpreted and evaluated differently in a BB hopping, non-hopping or a

synthesizer hopping environment. There are two reasons to the change in

RXQUAL behavior:

1 Fewer calls have RXQUAL 0 because of interference averaging.

This yields that the RXQUAL distribution will look much worse

just by turning hopping on. Also note that it is easy to stay

connected at RXQUAL 5, 6 and 7 when hopping over many

frequencies. In a non-hopping case it’s very probable to drop the

call at high RXQUAL values. This implies that the number of

RXQUAL 5-6-7s increase in the case of hopping due to this

phenomenon which gives a higher RXQUAL average. Note that

the speech quality still is acceptable with RXQUAL 5-6 and

even 7 during short periods when SY hopping over many

frequencies.

2 Because of the logarithmic behavior of RXQUAL (the mapping

between BER and RXQUAL). This applies both within a



SACCH measurement period in the mobile/BTS as well as

during the filtering process of measurement results. See table 2.

Table 2. Example of the influence of frequency hopping on RXQUAL. In case of

non hopping there are 1 bad and 3 good connections. If hopping there are 4 good

connections in this case.

NON hopping Frequency hopping

Frequency BER RXQUAL BER RXQUAL

F1 (call 1) 0% 0 2% 4

F2 (call 2) 0% 0 2% 4

F3 (call 3) 8% 6 2% 4

F4 (call 4) 0% 0 2% 4

AVERAGE RXQUAL 6/4 = 1.5 4

The RXQUAL distribution will change when using FLP and thus the average

RXQUAL. This will introduce a higher ratio of intra-cell handovers and bad

quality handovers. Thus, the levels for the quality-triggered events such as Intra-

cell handover and bad quality handovers have to be adjusted. Note that the

subscriber perceived quality does not degrade because of the increased number of

quality-triggered events.

It is hard to measure the speech quality performance by means of RXQUAL,

especially if comparative measurements between different kinds of frequency

planning methods are performed. It is however crucial to use the RXQUAL

measure anyway since the RXQUAL is the ONLY measure within the GSM

standard that can be measured with good statistical confidence by means of

system tools (NOTE, not by means of drive testing). It is thus important to make a

good estimate of the speech quality as possible by means of the RXQUAL

measure. Table 3 is a proposal of how RXQUAL can be used for approximate

comparative speech quality measurements:

Table 3. RXQUAL usage.

Frequency planning strategy Proposed type of measurement

Non frequency hopping Percentage RXQUAL 4+5+6+7

Baseband hopping over 2-5

frequencies, e.g. MRP

Percentage RXQUAL 5+6+7

Synthesizer hopping over 16

frequencies, e.g. FLP-1/1

Percentage RXQUAL 6+7

NOTE: This is not claimed to be the best way but it is a recommended way based

upon experience.

The RXQUAL distribution for different hopping networks or different network

configurations will not truly reflect the difference in subjective speech quality of

the networks. The RXQUAL measure can thus not be used for benchmarking

ERICSSON GSM SYSTEM


when comparing different radio network configurations utilizing different number

of hopping frequencies. However, RXQUAL is still interesting when comparing

own network e.g. before and after changes to the network and also for comparing

cells.

5.2.3 The BCCH carriers are non-hopping

In a synthesizer-hopping network there are two different kinds of traffic channels,

non-hopping TCHs on the BCCH carrier and hopping TCHs. The coverage

performance on a non-hopping TCHs is worse than any kind of frequency

hopping channel due to frequency diversity. Thus, the coverage performance

might decrease for TCHs on the BCCH carrier when going from baseband

hopping to synthesizer hopping, if not catered for in a proper way. I.e. the non-

hopping TCHs on the BCCH carrier might be used at the cell border.

Even more important, the planning margins must be much bigger for a non-

hopping BCCH compared to planning a BCCH integrated in a baseband hopping

sequence. This problem can be removed if the feature BCCH in Overlaid Subcell

is used.

5.2.4 Radio Network features becomes more important

Accurate tuning of RN features becomes more important. Up- and downlink

power control and traffic distribution within a cell in particular. See chapter 5.3

for further information.

5.2.5 Non-realistic expectations of RN quality

Operators often have non-realistic expectations of network quality when testing

FLP techniques. Operators tend to expect decreased effort for planning,

optimization and O&M at the same time as the quality and capacity increase. This

will not always happen for medium and large spectrum allocations, especially if

the mistakes mentioned in this chapter have been made.

5.3 Features

5.3.1 Frequency Hopping

FAJ 122 288, Frequency Hopping

FAJ 121 054, Frequency Hopping on 32 Frequencies

FAJ 122 855, RBS 200 and 2000 in the same Cell

FAJ 122 854, RBS 2000 Synchronisation

FAJ 121 374, Re-Use of Frequencies within a Cell

Synthesizer frequency hopping is a prerequisite for FLP. To get the most out of

frequency hopping the cells should be synchronized, at least within a site, and

MAIO Management should be utilized.



When allocating frequencies to a cell there are limitation issues regarding the

maximum frequency spacing, i.e. the frequency range, especially when having a

wide spectrum or/and when using multi band cells. However there are

workarounds in R10 to meet these limitations. Read more in [3] for further

details.

If the hopping TRXs in a cell belong to different TGs (i.e. RBS cabinets) the

TRXs must belong to different CHGRs. In R10 a frequency (except the BCCH

carrier) can be reused in all CHGRs in the cell. This means that a split of the

spectrum between CHGRs is not longer necessary. However, there must be some

MAIO planning to these synchronized cabinets to avoid co-channel collisions

within the cell.

Recommendation:

Use synthesizer hopping with a tight frequency reuse to increase the capacity in

the network.

5.3.2 Mobile Allocation Index Offset (MAIO) Management

FAJ 122 870, Flexible MAIO Management

Mobile Allocation Index Offset (MAIO) is in the Ericsson GSM system

automatically assigned to each TRX in a predefined order within each cell. The

MAIOs are assigned in an “even then odd” manner. This means that no adjacent

channels in a blocked TCH configuration are used within a cell as long as the

number of hopping TRXs are equal or less than half the number of frequencies.

This is to avoid constant adjacent channel interference.

With the feature MAIO Management increased control of interference between

cells can be achieved in all reuse situations as long as the cells are synchronized.

For more information and recommendations regarding MAIO planning, see User

Description, MAIO Management.

Recommendation:

This feature is a prerequisite for 1/1 frequency reuse.

5.3.3 Synchronized Networks

FAJ 122 081, Synchronized Radio Networks

With a synchronized network a larger freedom of MAIO planning is achieved.

Network wide MAIO planning to can be done to minimize interference between

non co-sited cells. As can be seen in figure 7 the difference is that before R10

MAIO planning is restricted to be done within a site. In R10, by selecting the

worst few interferers, a MAIO planned cluster can be created. A nearby cluster

using the same frequencies can be created using a different HSN, or same HSN

but with a different FN offset value. For more information see [8] & [12].

ERICSSON GSM SYSTEM


Figure 7. R10 provides possibility to create MAIO planned clusters of non co-

sited cells. The HSN has to be same for all cells but a MAIO value should not be

reused (just like normal MAIO planning). 147 in the figure means that MAIO

values 1, 4 and 7 are used for that cell.

Recommendation:

Start off by making small clusters, preferably only reusing the previous “same-

site-only” cells. Cells interfering each other between the clusters should then be

selected to change cluster.

Close by clusters using the same frequencies should be differentiated a few frame

numbers with FNOFFSET rather than with HSN. The difference of FNOFFSET

between the clusters should be at least 4 from a multiple of 51.

Do not create too large clusters, e.g. whole network, if the cell plan in general has

many neighbour relations for all cells, as the measuring procedure for handover

candidates will take longer time.

5.3.4 Intra Cell Handover

FAJ 122 290, Intra-cell Handover

The intra cell handover, IHO, will move interfered connections to a channel,

which radio characteristics differs as much as possible. In an FLP network there

are at least two channel groups with very different interference pattern in each

cell. With two or several channel groups IHO can “rescue” connections with bad

quality, especially when OL/UL and SCLD is used which gives an even

distribution of idle TCHs in all CHGRs. IHO change channel group as first

choice if that is possible, which means that the connection will jump to a totally

different interference environment, e.g. from a 1/1 hopping TCH to a non

hopping TCH on the BCCH frequency.

- R10, all sites synchronized - MAIO plan between any cells

Before R10. I.e. only site

synchronization

FNOFFSET MAIO



A proper analysis of whether uplink or downlink triggered events should be

performed for BCCH and TCH channel groups. This might lead to that uplink

triggered IHOs from the TCH to BCCH channel group is good to use and that

downlink triggered IHOs from the BCCH to the TCH channel group is beneficial

to use more aggressive.

Intra cell handovers due to too low signal strength should be avoided in a 1/1

planned network. The reason for this is that the timer TINIT when active

(normally set to 5 seconds) will inhibit intra cell handovers, inter cell handovers

and subcell changes. Therefore, there is a risk that an intra cell handover will

“delay” the inter cell handover for a fast moving mobile moving into a

neighbouring cell and thereby cause interference.

Note that there are separate IHO parameters for EFR and AMR [9].

Recommendation:

In general, it is strongly recommended to use mainly uplink triggering of IHOs,

e.g. above 50 dtqu. Downlink triggered IHOs should be performed only if there is

very bad quality, e.g. above 55-60 dtqu. For AMR FR the IHO triggering should

be set 10 dtqu higher than the corresponding EFR setting as the AMR FR

connections will be able to handle speech at higher RXQUALs than EFR.

It is recommended to make zero or at the most one IHO within a hopping channel

group or between TSs on the BCCH frequency since the probability for a better

channel is much lower in this case. It might however be beneficial to perform one

IHO within a BCCH channel group if it is uplink triggered.

5.3.5 Power Control

FAJ 122 910, Dynamic BTS Power Control

FAJ 122 260, Dynamic MS Power Control

FAJ 121 055, Adaptive Multi Rate (AMR)

Power control is a very important feature in FLP networks, since the decreased

interference can be utilized in a more efficient way compared to a BB-hopping

network.

The correlation between signal strength and quality is of great importance for

tuning of many radio network features. The correlation between the signal

strength and the quality is more significant for the UL compared to the DL. Thus,

high signal strength on the UL often means good quality, which is the explanation

to the fact that the power control could be tuned differently for UL and DL.

BTS and MS Power Control can be implemented according to the parameter

settings below but might require some fine-tuning to adapt to the environment.

NOTE that before BSS R10 the algorithms for BTS and MS power control are

different.

BTS power control:

For BTS power control the recommended setting is SSDESDL=90,

LCOMPDL=5, QDESDL=30, QCOMPDL=57, UPDWNRATIO=300. Filters

should be set short (to 3 SACCH periods).

ERICSSON GSM SYSTEM


If the TCH carrier are in a blocked configuration, i.e. no BCCHs adjacent, it is

beneficial to use a more aggressive setting, e.g. QCOMPDL=65.

NOTE that it is recommended to only adjust the parameter QCOMPDL for the

fine-tuning of the algorithm to keep control over different settings used.

If OL/UL subcell structure is configured with the non-hopping channel group

(including BCCH) and the hopping channel group are placed in different channel

groups, a more aggressive power control can be used in the subcell containing the

hopping channel group. In this case QDESDL can be set to a higher value 35-40

depending on the number of frequencies in the hopping group.

MS power control before R10:

For MS power control the recommended setting is SSDES=90, LCOMPUL=50-

90, QDESUL=0, QCOMPUL=50-60.

The signal strength filters should be set short (to 3-5 SACCH periods). The

quality filters needs to be a bit longer (to 4-8 SACCH periods) in order not to

create an unstable situation.

A more aggressive strategy for high signal strength mobiles should be used if the

physical reuse is tight. This is controlled by means of the LCOMPUL parameter

and should be set to 50 (for reuse above 8, e.g. MRP), to 70-80 (for 1/3 reuse)

and to 80-90 (for 1/1 reuse).

NOTE that it is recommended to only adjust the parameters SSDES and

LCOMPUL for the fine-tuning of t1he algorithm.

MS power control R10:

In R10 the MS power control algorithm is changed and uses the same algorithm

as BTS power control. The same recommendation as for BTS power control are

applicable on MS power control: SSDESUL=90, LCOMPUL=5, QDESUL=30,

QCOMPUL=57, UPDWNRATIO=300. Filters should be set short (to 3 SACCH

periods). Note that the parameter values are completely different compared to the

old algorithm as the parameters have different meaning compared to R9.1.

However, if the UL suffers a lot from outdoor mobile to indoor mobile

interference, MS power control could be more aggressive. The same

recommendation for tuning of BTS power control also applies for MS power

control.

AMR FR and power control:

The increased robustness of AMR FR can be used to decrease interference in the

network by using a more aggressive power control, both uplink and downlink, for

a MS using AMR FR.

In R10 a set of new parameters are introduced to differentiate power control for

AMR FR capable and non-capable mobiles. The new parameters are for BTS

power control: QDESDLAFR and SSDESDLAFR, and for MS power control:

SSDESULAFR and QDESDLAFR

It is recommended to set QDESDLAFR and QDESULAFR to 40 to allow down

regulation at higher RxQual. SSDESDLAFR should be set to the same value as

SSDESDL and SSDESULAFR should be set to the same value as SSDESUL.

Recommendation:



Make sure that the down regulation of power control does not occur within the

Intra Cell Handover permitted area (see figure 8).

Figure 8 Power control down regulation in relation to Intra Cell Handover and

Bad quality urgency trigger.

Power control is beneficial for reducing adjacent channel interference in the

uplink, due to near-far effects. For the downlink, the impact from adjacent

channel interference increase if BTS power control is used. Thus, a less

aggressive downlink power control setting should be used in a staggered plan,

e.g. a maximum down regulation of 10 or 12 dB.

5.3.6 OL/UL subcells

FAJ 122 430, Dynamic Overlaid/Underlaid Subcells

FAJ 121 53, BCCH in Overlaid Subcell

A wisely chosen sub-cell traffic distribution strategy will significantly increase

the total traffic/quality a cell can handle from just being the sum of “a BCCH

layer” and “a TCH layer”.

The OL/UL feature can increase the number of hopping frequencies when it is

used to tighten the BCCH reuse, i.e. BCCH in the OL subcell and hopping TCH

in the UL subcell. Use Subcell Load Distribution (SCLD) together with the

feature BCCH in OL in order to control the BCCH traffic dependent on the load

in the cell. The output power should be set the same for the two subcells to secure

the BCCH coverage for the cell, however the TCH traffic on the BCCH carrier

shall be kept close to the cell core.

With the BCCH in the overlaid subcell the hopping TCH carriers can serve all

traffic when the load is below a certain limit, with high quality in the UL subcell.

This also yields maximum coverage due to the hopping gain. When the load

1

11

21

31

41

51

61

01

2

3

4

5

6

7

0

2

4

6

8

10

12

14

Regulation (dB)

RXLev

RXQual

12-14

10-12

8-10

6-8

4-6

2-4

0-2

LDESDL

QDESDL

LCOMPDL

QCOMPDL

-97

30

0,05

0,55

IHO

BQ Urgency

ERICSSON GSM SYSTEM


increases, the BCCH starts to take traffic in the OL subcell. Thus at peak traffic

the BCCH is fully loaded close to the cell core which implies maximized

spectrum utilization

The different subcells and thereby the different channel groups, non hopping

BCCH and hopping TCHs, can have different parameter settings for power

control, BQ handover triggers and intra-cell handovers for non-hopping BCCH

and hopping TCHs, and also separate statistics for the OL and UL.

Recommendation:

Use the feature OL/UL and put the BCCH carrier in the OL subcell and the

synthesizer hopping in the UL. The reason for this is:

1 The traffic can be distributed with full flexibility to BCCH or

TCH first, by means of the dynamic OL/UL feature and BCCH

in OL.

2 Performance can be measured separately with STS for non-

hopping BCCH and hopping TCH channels.

3 Measurement Result Recording (MRR tool in the OSS/RNO

package) statistics such as RXQUAL, Signal strength, TA etc

can be measured system wide separately for non-hopping BCCH

and hopping TCH channels. In R10 MRR works on CHGR level.

4 Quality trigger thresholds for urgency handovers and intra-cell

handovers can be set differently for non-hopping BCCH and

hopping TCH channels.

The most robust channels should serve the traffic on the cell border and at low

signal strength. The BCCH reuse must be less tight if the BCCH should serve

traffic at the cell border, e.g. 14-20 (see figure 9).

BCCH, reuse 14-20UL

OL TCH SY hopping

Figure 9. BCCH used in underlaid subcell.

If hopping TCH channels are used at the cell border, and thus non-hopping

BCCHs at the inner parts of the cell, the BCCH reuse can be much tighter (see

figure 10). This is done with the feature BCCH in Overlaid Subcell.



1/1, 1/3 or non-uniform hopping

CHGRUL

OL BCCH, reuse 11-16

Figure 10. Tighter BCCH reuse with BCCH in Overlaid Subcell.

Handovers directly to OL, or between two OL subcells, is possible if CHAP 5 or

CHAP 6 is used. CHAP 10 can also be used if SCLD is used. See further [7]. 5.3.7 DTX

FAJ 122 287, Discontinuous Transmission (DTX) Downlink

FAJ 122 256, Discontinuous Transmission (DTX) Uplink

DTX is a very important feature in FLP networks, since the decreased

interference can be utilized in a more efficient way compared to a BB-hopping

network. The effects from DTX can be fully utilized in an FLP network since the

interference comes from several cells and thereby several connections. This

together with random frequency hopping makes the interference hits truly

random. Thus, the decreased interference by means of DTX can be planned for

and thereby gained from.

The voice activity is a bit different for different cultures but is usually around

50% to 55%. This together with the fact that some bursts are always sent yields

that the gain probably is 2 to 2.5 dB. This means that the number of co-channel

hits in a 1/1 plan is reduced by at least 40%. This gain with DTX might however

be decreased a bit due to that the network is non-synchronized. In a non-

synchronized network two bursts can be destroyed by one strong interfering

burst.

Recommendation:

DTX UL is always recommended to use since this feature gives better

performance in most situations.

DTX DL should only be used in networks with tight frequency reuse and high

load. This due to that there is a tradeoff between quality and gain when using

DTX DL. If the benefits of the decreased interference are higher than the

decreased accuracy of locating and the slightly worse speech quality, then this

feature should be used. This has to be decided on a case-by-case basis depending

on network performance and roadmap. In order not to have a large increase in

handovers, the locating filter length can be adjusted to a slightly higher value, or

the hysteresis can be set a bit higher, e.g. from 3 to 4.

ERICSSON GSM SYSTEM


5.3.8 Assignment to Another Cell

FAJ 122 286, Assignment to Another Cell

The assignment to worse cell at congestion should be used with care in a 1/1

situation since the connection might suffer very low C/I if set up on the wrong

cell. The benefit of being able to set up a connection in a weaker cell has to be

compared to the disadvantage of increased interference. The mobile will

handover back as soon as there is an idle TCH in the dominant server. This can

happen within a few seconds which means that the interference may only be a

short occurrence.

Recommendation:

AWOFFSET should be set equal or lower than the handover hysteresis.

The recommendation is to install more TRXs to solve congestion problems.

5.3.9 Cell load sharing

FAJ 122 911, Cell Load Sharing

There are no drawbacks to use Cell Load Sharing, CLS, in a 1/1 network. This

because CLS only works within the hysteresis area and that the connections that

are closest to the neighbouring cell are moved first. Thus, it is recommended to

use CLS to the full extent.

Recommendation

Set RHYST to 100%.

5.3.10 Multi Band Cells

FAJ 122 085, Multi Band Cell

Figure 11. Multi band cell with compensation for the different propagation of the

system types.

The Multi Band Cells (R10) functionality enables the possibility to have more

than one system type in a cell, e.g. 900 and 1800. One BCCH instead of two

BCCHs per sector is used. This means that less frequencies are used for the

TCH, 800TCH, 800OL subcell

BCCH, 1900UL subcell BCCH, 1900

TCH, 800

Cell border.

FBOFFS will compensate for different

frequency bands.

TCH, 800TCH, 800OL subcell TCH, 800OL subcell

BCCH, 1900UL subcell BCCH, 1900

TCH, 800

Cell border.


frequency bands.

TCH, 800

Cell border.


frequency bands.



BCCH plan in favor for the hopping CHGRs, i.e. if the BCCH plans are done

with 14 reuse for each system type, multi band cells will lead to 14 additional

hopping frequencies. The trunking gain will also be higher for packet data

services. Another benefit is that the BA list will be shorter meaning more

accurate measurements of the neighbours. The number of neighbour relations will

be smaller.

Figure 11 illustrates the parameter for deciding the cell border as the frequency

bands has to be compensated for different propagation characteristics.

5.3.11 Interference Rejection Combining

FAJ 122 0083, Interference Rejection Combining (IRC)

Figure 12. IRC - Use the difference of the received signals to filter out the

interference.

Interference Rejection Combining, IRC, is a feature that with its algorithm filters

out the interference by comparing signals from two antennas on the uplink. As an

extreme example to show the pinciple: if intf1 = intf2 in figure 12, then take

difference rx1 - rx2 to cancel interference. Mobiles suffering from high

interference benefit the most.

IRC does not help a noise limited network.

Live tests have shown that with IRC there is a significant improvement at high

traffic levels while there is no noticeable performance change at low traffic. A

30% reduction of RXQUAL=5-7 measurements on the uplink could be seen at

high traffic compared to no IRC usage. There were also less (around 30%) uplink

triggered bad quality urgency handovers after IRC was turned on.

Recommendation:

IRC is recommended to be used. The gain is highly dependent on

uplink/downlink balance.

Carrier

Interfererrx1=carr1+intf1

rx2=carr2+intf2

(rx ≡ received signal)

Lower BER at given C/I!

ERICSSON GSM SYSTEM


5.4 Parameters

5.4.1 EVALTYPE

The parameter EVALTYPE sets the locating algorithm, Ericsson1 or Ericsson3.

It is defined per BSC. See further [9].

Recommendation:

Use Ericsson3 as it uses only signal strength ranking. Ericsson1 uses path loss

which can result in MSs using a low signal strength cell instead of the strongest.

5.4.2 Bad quality urgency handover triggers

The limits for quality handovers should be set rather high for TCH hopping

carriers in an FLP system and the area where quality handovers are allowed,

BQOFFSET, should be restricted to the hysteresis area (0 to 5 dB). QLIM

(QLIMUL and QLIMDL) should be set between 50 to 60 (recommended value

is 55). The BQOFFSET and QLIM should be set accordingly because of two

reasons:

1. The voice quality is better at a given RXQUAL compared to the non-

hopping or BB hopping case. This because that the RXQUAL measure

behaves a bit different in a fractionally loaded system, see 3.5.

2. In an FLP system, especially in a 1/1 plan, there is no better cell. This

means that quality only gets worse if a handover to a cell with lower signal

strength takes place.

Note that QLIM preferably be set to 40 to 45 for the non-hopping BCCH channel

group. Also note that QLIMUL and QLIMDL are subcell parameters, which

means that they cannot be set differently for two channel groups within a subcell.

But, one solution might be to place the BCCH and the hopping TCH channel

groups in separate subcells, see 5.3.6.

The limits for QLIM are mostly dependent on the number of hopping

frequencies. The more frequencies to hop over the higher setting of QLIM. In a

1/1 FLP, QLIM should preferably be set between 55 and 65 since the probability

to get better quality is small. If the connection makes handover to a worse cell,

the call might be dropped.

Recommendation:

The recommendations are within the text above.

5.4.3 TINIT

Immediately after an assignment, a handover, a subcell change or a intra-cell

handover, it is desirable to remain on the same channel for a while. The reason is

that the filtering of measurements needs some time to produce reliable estimates

on which to base further action. Therefore, at initiation of a locating individual, a



timer TINIT is started. The timer inhibits intra cell handovers, inter cell

handovers and subcell changes, until it expires. After immediate assignment

handovers are inhibited before TINIT has expired, but assignment to own or

other cell are allowed.

Recommendation:

The timer is normally set to 5 seconds. A too long timer value increases the risk

of interference when delaying a handover to take place.

5.4.4 Hopping Sequence Number (HSN)

In order to spread the interference between all cells using the same hopping

TCHs, e.g. in a 1/1 plan, Hopping Sequence Number (HSN) planning is used.

HSN is planned in order to avoid correlation between closely located cells.

Without control over frame numbering between sites, it is best to avoid HSN

differences between proximate sites less than 3, i.e. allocate HSN=14 and

HSN=33 close to each other, not HSN=14 and HSN=16. The reason is that the

effects of bad FNOFFSET differences are most severe if deltaHSN<3 and if

frame numbering cannot be controlled, bad FNOFFSET differences may appear.

In a 1/1 plan using MAIO Management (see 5.3.2), perfect synchronization of the

frequencies can be achieved when using the same HSN in all synchronized cells.

In a 1/1 plan not using MAIO Management (see 5.3.2) within the sites, the cells

within a site should use different HSN. Otherwise, severe co-channel interference

might occur. This should be performed even if the cells are not synchronized.

Recommendation:

It is always recommended to use random frequency hopping (i.e. not using

HSN=0) together with MAIO Management since the interference averaging gain

is much higher in most cases. In special cases such as FLP 1/1 or it is NOT even

possible to use cyclic frequency hopping (HSN=0) since the risk of having

constant co-channel interference is rather high between co-channel cells.

5.4.5 BCCH as first or last choice (CHALLOC)

With the use of BCCH in Overlaid Subcell (see 5.3.6) the BCCH frequency plan

can be tightened in the favor of the hopping CHGR to get more frequencies to

hop over. This means that it is preferable to use the TCH channel groups first and

let the subcell load distribution algorithm handle traffic distribution towards the

BCCH CHGR at high traffic hours.

It is possible to control whether the traffic channels on the BCCH should be used

as first or last choice or with no preference by means of the BSC exchange

property CHALLOC. However, if there is a PSET on the BCCH CHGR traffic is

set up as if CHALLOC would have been set to “hopping TCH as first choice”.

Recommendation:

ERICSSON GSM SYSTEM


It is in most cases recommended to use the hopping TCH as first choice. A very

good way to achieve the BCCH last strategy is to use the dynamic OL/UL and to

use BCCH in OL, see [11].

5.4.6 Penalties

After a bad quality urgency handover is performed the originating cell can be

penalized with PSSBQ dB for PTIMBQ seconds.

Recommendation:

It is recommended to use low values for penalties (5 dB or preferably lower) for a

rather short time (less than 10 seconds).

5.4.7 Offsets and filters

The tighter the frequency plan gets the more important it becomes to use signal

strength ranking in locating, i.e. to be connected to the strongest server. This

implies that it also becomes harder to use offsets, assignment to worse cell, large

hysteresis areas, long filters etc.

In an area with bad quality, traditionally, the frequency plan can be utilized as a

tool to solve the problem area. In a tight FLP such as 1/1 there is not much to do

except to make some sort of “frequency planning”, tilt antennas, build a new site

and so on.

Recommendation:

It is recommended not to use offsets unless necessary. It is further recommended

to use shorter filters, low penalties and so on in order to stick to the best server to

a larger extent.

5.4.8 The SAS parameter

In the channel selection process there are different strategies to choose from to

prioritize channels as candidates prior to others. CHALLOC has been mentioned

for prioritizing between CHGRs, but prioritization can also be done within a

CHGR from R10. With the parameter SAS the order of the selection process can

be changed to e.g. select channels with the MAIO value that is first in the

operator defined MAIO list, and after that select the group of consecutive TCHs,

0-7, using the same frequency with the best quality and lowest traffic. The

parameter can be set to QUALITY, MAIO or MULTI. When using MAIO for

tight frequency reuse planning where few frequencies are used for hopping, two

co-sited/synchronized cells using adjacent MAIO values can be planned not to

use adjacent frequencies at low traffic simply by entering the MAIO values in an

order where the first MAIO values are not adjacent for the two cells. E.g.

MAIO=0&2&4 and MAIO=3&5&1 in this two cell site example.

For more information of the channel selection order, see [7].

Recommendation:



Set SAS to MAIO.

6 Datacom aspects

In general, it is very easy to implement GPRS / E-GPRS in a synthesizer hopping

network. E-GPRS capable TRXs can be added with full flexibility without any

impact on the current frequency plan and thus with no initial planning effort

whatsoever. Transceiver group synchronization between TRXs of different

capabilities may have to be done depending on hardware, see ref [5].

Due to the fact that GPRS / E-GPRS does not have downlink power control, the

ramp up of GPRS / E-GPRS traffic might cause interference. The interference

must be dealt with but the impact will probably be minor during the start-up time.

Especially E-GPRS could benefit from a separate CHGR in such a way that C/I

can be controlled and thus the throughput can be high. However the sharing of

frequencies between the CHGRs has to be done, i.e. it is “expensive”.

By introducing GPRS / E-GPRS on the BCCH CHGR there are no concerns for

increased interference on the hopping CHGRs. Packet data will not increase the

interference on the downlink as the BCCH is transmitting continuously anyway,

i.e. the interference environment on the downlink will not be dependent on

traffic. However, there is not a firm recommendation to put EDGE on BCCH or

not. EDGE has proven to work quite well in frequency hopping networks too. It

might even be advantages to have the GPRS / E-GPRS on hopping CHGR

considering low traffic hours. Also the number of frequencies for hopping / non-

hopping CHGR should be considered. When the traffic ramps up, in order to

maximize the total offered traffic mixing CS and PS in 1/1 can be done.

Recommendation:

The main activity is voice. Therefore it is recommended to plan for CS traffic.

Spectrum is a natural resource, which limits the capacity. CS can handle C/I

around 10dB with satisfactory quality while EDGE performs better with rising

C/I. Still, plan for CS capacity and prioritize CS traffic over PS. Let PS work in

the background with one or two dedicated. EGDE will also benefit from more

available timeslots.

Without taking PS/CS co-existence into consideration, there are only marginal

differences between frequency hopping or non-hopping for EDGE. If non-

hopping BCCH and hopping TCH CHGR have the same frequency reuse (12

BCCH frequencies + 12 TCH frequencies per TRX) then non-hopping BCCH is

marginally better for EDGE and in some areas hopping would be better for

EDGE. Therefore it is recommended to let CS considerations decide which

CHGR, non-hopping BCCH or hopping TCH, to use for EDGE.

For CS the first priority when tuning a network is the capacity, i.e. avoid

blocking. The radio quality, C/I, is the second priority.

ERICSSON GSM SYSTEM


When implementing EDGE the first priority is enough capacity, i.e. avoid sharing

PSET with another user. The second priorities are enough radio quality &

consecutiveness of timeslots.

When implementing GPRS the first priority is enough capacity, i.e. avoid sharing

PSET with another user. The second priority is consecutiveness of timeslots. For

GPRS the radio quality issue is not as important as for EGPRS.

The recommendation is therefore:

• If the radio quality is roughly the same in both (all) channel groups, then

configure GPRS/EDGE and voice in different channel groups.

• If the radio quality is significantly better in hopping CHGR than in non-

hopping CHGR then the capacity will decide:

-In a two-TRX cell, then it is recommended to direct voice to hopping

TCH and EDGE to non-hopping BCCH in order not to push away CS

from the good channels. Otherwise CS performance will suffer, and CS

more important than PS. -In e.g. six-TRX cell then there is sufficient amount of good radio

channels to consider EDGE and voice to be mixed in the hopping CHGR.

EDGE will occupy one TRX and PS has plenty of space for capacity. The

BCCH CHGR will be used for high traffic and at intra cell handovers.

7 Load and reuse definitions

There are several different ways to denote how spectrum efficient a frequency

plan is. In this chapter different measures are defined.

• Frequency load, based upon actual traffic load. For example a frequency

load of 12% per cell means that each frequency is used 12% of the time for

a cell.

• Hardware load, based upon number of TRXs. For example 20% HW load

means e.g. 10 frequencies hopping on two TRXs.

• Frequency utilization. This is a measure of the spectrum efficiency related

to the actual traffic (very similar to Frequency load measure).

• Physical frequency reuse. This denotes the average number of cells within a

cluster where a frequency is used only once. Thus, a measure of the reuse

physical distance between frequencies. Neither traffic nor TRXs impacts

on this measure.

• Equivalent TCH reuse. This is an easy-to-understand measure of the

spectrum efficiency related to the number of TRXs installed.

The busy hour traffic load determines the network quality and thereby the

dimensioning of the network. It is therefore recommended to use the average

traffic load per cell/area during busy hour period (one or several hours) when

calculating the frequency load or frequency utilization The area considered for



load might be all cells in an area, for example a BSC. If the area is too large, the

average traffic load in that area will not reflect how high the interference level

will be in the areas where the traffic is more dense. If the traffic is unevenly

spread (which it, in most cases is) one should choose a smaller area. In order to

calculate the frequency load it is recommended to use at least 5 times physical

frequency reuse number of cells. For example in a 1/3 plan, 15 cells (5*3) should

be included in order to get a valid measure.

It is important to consider how the BCCH traffic, i.e. TCH traffic on the BCCH

carrier, is handled when calculating the load. If the HW- and frequency

load/utilization should be calculated it is the traffic that is carried by the hopping

TCHs that is interesting. The BCCH traffic should thus be estimated and

excluded.

It is also interesting to know the distribution of load in the area, i.e. the highest

loaded cells since most networks have a very large spread in traffic load for

different cells. Thus, relevant measures should be calculated for area average and

the most loaded cells/sites.

7.1 Frequency load

The frequency load, which is a specific measure for 1/1 planned networks,

reflects how effective the hopping frequencies are used in a cell. This is done by

measuring the actual traffic load and compare it with the number of assigned

frequencies. The upper limit of this measure is decided by the quality standards

for the network.

The quality can be improved by successfully using the FLP Planning method and

thereby give a margin for further increase of the frequency load measure, i.e.

more TRXs. The strategy to increase the quality can be to use Power Control in

order to decrease the energy of the transmitted bursts. This restricts the area in

the cell to where this energy is needed. In this way the air interface will be less

loaded close to the cell border compared to the cell core, and the cell border is

where co-channel collisions are most severe. An extreme version of this strategy

is to use DTX, which completely blocks most of the energy by not sending any

bursts of an ongoing connection when the users are silent. These strategies will

increase the upper traffic limits for the cells.

The frequency load measure is defined by first dividing the average full rate

traffic load per cell by 8 to get the average timeslot traffic. This is then divided by

the number of hopping frequencies to get the average traffic load per timeslot and

frequency. This measure can be written as:

)(#*8 cell

cell

FRQ

ErlangFRQLoad =

The average traffic load per cell can be calculated by measuring the average

traffic in an area and divide this by the number of cells in the area.

ERICSSON GSM SYSTEM


Example:

Two hopping TRXs carry 8 Erlang, i.e. in mean, 1 Erlang is used by each timeslot

in the TDMA frame. If there are 10 hopping frequencies the frequency load is:

)10(*8

8=FRQLoad = 10 %

7.2 HW load

The HW load reflects the number of installed TRXs per cell if the spectrum

allocation (number of frequencies) for TCH frequencies is given. This makes the

HW load very quick to use and easy to understand.

The hardware load is defined as the average number of hopping TRXs per cell

divided by the number of hopping frequencies per cell and can be expressed as:

cell

cell

FRQ

TRXHWLoad

#=

However, the hardware load does not take the trunking gain into account. The

same hardware load results in different served traffic loads depending on the

number of frequencies and thereby different frequency loads. Also, the safety

margin for GoS is different for different networks/operators and many networks

are over dimensioned with TRXs.

Due to the trunking gain the HW load becomes a bad measure when comparing

different networks (or different cells) since the HW utilization is very different

with different number of TRXs. Also note that many networks are over

dimensioned capacity wise or planned for a Grade of Service (GoS) higher than

2%, e.g. 0.5%.

Thus, the HW load gives a non-comparable measure for different networks since

the HW utilization is different for different networks.

And:

The HW load is NOT recommended to use because this measure differ depending

on the number of TRXs per cell (different carried traffic per timeslot at 2%

GOS).

One problem with the HW load measure is that a cell never utilizes the HW to the

full degree. For example a cell that carries 3,5 Erlang busy hour need two TRXs

even though it can carry more than 7 Erlang in average.

In order to make the HW load a bit more reliable the GoS compensated HW load

can be calculated. The real traffic is then taken into account and it’s expressed as:

cell

cell

cell

cell

ErlangGoS

Erlang

FRQ

TRXHWLoaddcompensateGoS

%2#×=



7.3 Frequency Utilization

The Frequency Utilization offers a measure of the true spectrum efficiency, based

upon the actual traffic and reuse in the network. It is recommended to use the

Frequency utilization in order to compare different networks or frequency

planning methods.

The Frequency Utilization is a way of describing the traffic load per frequency

and it’s defined accordingly:

)(

)(

# area

cell

FRQ

TrafficnutilisatioFrequency =

The higher the figure of Frequency Utilization, the more spectrum efficient the

plan is. Note that the total number of frequencies used in the area should be used.

It is of utter most interest to calculate the TCH frequency utilization. This means

the utilization of the TCH frequencies where the BCCH frequencies and the

traffic carried by the BCCH is excluded. Here is an example of the total

(BCCH+TCH) frequency utilization.

Example 1:

A BB FH network with 4/12 pattern and about 2.8 TRXs per cell in mean.

Assuming there are 2 and 3 TRX cells only. The maximum carried traffic is then

about 12 Erlang per cell according to the Erlang B table. In reality the traffic

might be about 9 Erlang per cell in average because of dimensioning reasons. The

number of BCCH frequencies is 12 and the number of TCH frequencies is 24.

Thus, the frequency utilization in the area:

9 Erl / 36 freq. = 0.25 Erl/freq.

Example 2:

The same network with 1/1 hopping over 15 frequencies. Same traffic and

configuration. The number of TCH frequencies used is in this case reduced from

24 to 15. The number of BCCH carriers are still 12.

Thus, the frequency utilization in the area: 9/27 = 0.33 Erl/freq.

This means that the spectrum efficiency has increased since the frequency

utilization increased from 0.25 to 0.33.

7.4 Physical Frequency reuse

The physical frequency reuse is basically a measure of the number of cells in a

cluster that use a frequency only once. Thus, the physical TCH reuse is a measure

that describes the distance between the frequencies in a network. Whether the

frequencies are loaded or not is not considered. The physical frequency reuse is

relevant to calculate for the BCCH and TCH separately in order to determine

what reuse scheme is used. It is defined according to:

)(

)(

#

#

cell

area

FRQ

FRQreusefrequencyPhysical =

ERICSSON GSM SYSTEM


Example 1:

A strict 1/3 plan would have a physical frequency reuse of 3 and a 1/1 plan would

accordingly have a physical frequency reuse of 1.

Example 2:

A fractionally loaded FL-MRP 12/8/6/4 (1 BCCH frequency + hopping over 3

frequencies) would have a physical TCH frequency reuse of:

63

18

)(#

)(#

===

cellFRQ

areaFRQ

reusefrequencyTCHPhysical

A BB hopping 12/8/6/4 MRP with an average of 2,5 TRXs per cell would have a

physical TCH reuse of 18/1,5 = 12.

Note that if there were 4 TRXs everywhere the equivalent TCH reuse (see 7.6)

and physical TCH reuse becomes the same (=6).

Example 3:

If there are 16 dedicated BCCH frequencies the physical BCCH frequency reuse

is 16.

7.5 Equivalent (TCH) reuse

The equivalent TCH reuse is, just as the frequency utilization, a measure of how

spectrum efficient the frequencies are used. The difference is that the Equivalent

TCH reuse is based on the installed hardware rather than the actual traffic. It is a

good measure to use in order to compare different frequency planning methods

within a network. Note that it is irrelevant whether baseband or synthesizer

hopping is used. It is defined accordingly:

HWload

reusePhysical

cellTRXTCH

areaaninusedfreqTCHoftotreuseTCHEquivalent ==

/

#

Note that the equivalent reuse can be calculated for all frequencies in the area as

well, thus including the BCCH.

But, due to the trunking gain the equivalent reuse becomes a bad measure when

comparing different networks (or different cells) since the HW utilization is very

different with different number of TRXs. Also note that many networks are over

dimensioned capacity wise or planned for a Grade of Service (GoS) other than

2 %, e.g. 0.5%.

Note that it is the actual traffic that is carried that is interesting from a

dimensioning point of view.

Example 1:

The network with 3.2 TRXs/cell with an MRP 16/6/5/4 have an Equivalent TCH

reuse of:

15 Freq / (3.2 - 1) TRX/cell = 6.8



The total equivalent reuse is 9.7 (31/3.2) and the BCCH equivalent reuse is 16

(16/1).

Example 2:

The same network with a BCCH (16 reuse) in one channel group and another

channel group with 1/1 hopping over 15 frequencies. The equivalent TCH reuse

is 6.8 (15/2.2) in this case also.

8 References

1. GSM Technical spec 05.02

2. User Description, MAIO Management

3. User Description, Frequency Hopping

4. Frequency planning of FH networks using multiplan in EET R2C, LVR/D-

98:0164.

5. Transceiver Group Synchronization Guideline

6. Training Sequence Code Planning Guideline

7. User Description, Channel Administration

8. User Description, Synchronized Radio Networks

9. User Description, Locating

10. Cellplan Characterization Guideline

11. User Description, Overlaid/Underlaid Subcells

12. Guideline for Activating Synchronized Radio Networks

ERICSSON GSM SYSTEM HIGH FREQUENCY LOAD PLANNING (FLP) GUIDELINE

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