Hotspot Me Tod

7/27/2019 Hotspot Me Tod

1/17

Hotspot Verification MethodologyEdition 01 9.12.1997

MCD hp01_pp.doc 3DF 00993 6000 PGZZA 1

Site

Stuttgart

CELLULAR OPERATIONS DEPARTMENT

Originator(s)

U. Birkel

Hotspot Verification Methodology

Domain : MCD

Division : Operations

Rubric : Radio Network Planning

Type : Guideline

Distribution codes :

Predistribution:

To: cc:

Mr. G. Hellstern ACS/EFP Mr. H. Derrey OC

Mr. B. Viviand ACS/SR2

Mr. R. Collmann ACS/SR2

Mr. J. Kozlik ACS/SR1

Mr. R.-M. Grner ACS/SR2

Mr. W. Kllmar ACS/OAD

Abstract:

This document describes concept and methodology for verfication of traffic hotspots.

Approval

Name

Signature

C. Brechtmann K. Eckert R. Collmann

Name

Signature


2/17



Table of Contents

1 HISTORY.................................................................................................. 3

2 REFERENCES............................................................................................. 3

3 SCOPE...................................................................................................... 3

4 INTRODUCTION....................................................................................... 4

5 CONCEPT................................................................................................. 4

6 INSTALLATION STEPS.............................................................................. 7

7 POSTPROCESSING METHODOLOGY........................................................12

8 SUMMARY...............................................................................................16

9 ABBREVIATIONS.....................................................................................16

10 ANNEX A LIST OF REQUIRED HW AND SW MODULESFehler! Textmarke nicht definiert.


3/17



1 History

Date Edition Origin Comments

9.12.1997 Draft OC/NPL

2 References

[1] 3BK 11202 0014 DSZZA Power Control and Handover Algorithms, Release 3

[2] M. Hellebrandt, R. Mathar, M. Scheibenbogen: Estimating Position and Veloc-ity of mobiles in a Cellular Radio Network, IEEE Transactions on VT, Vol.46,No.1,Feb. 1997, pp. 65-71

[3] G. Hellstern, Detector of High Traffic Areas for Microcellular Network Plan-ning, internal paper

[4] G. Hellstern, MicroBTS Demonstrator Description, internal paper

[5] 3DC 20008 0001 UZZZA Hardware Commercial Configurator for AntennaSystems

[6] 3DF 00995 0000 UCZZA Antenna Engineering Rules

[7] A955 Product Description, to be released

[8] W. Kllmar, Hotspot Trial, internal report

[9] 8BL 00601 0000 MPZZA, BSS-Definition of Quality of Service Indicators

[10] B. Viviand, Hotspot Verificator 1.0 Users Guide, to be released

3 Scope

The intention of this paper is to give an overview about the Alcatel concept of hotspotverification. Several methodologies for postprocessing will be described.


4/17



4 Introduction

The required amount of sites of cellular networks is either determined by coverage orby traffic requirements. In low traffic areas this amount is primarily determined by theachievable cell ranges based on the link budget and the terrain. In high traffic areas,

cell ranges become smaller in order to reduce the maximum amount of traffic per cell.Thus two layer microcellular networks are introduced in order to handle high trafficareas and local traffic hotspots. The aim of the microcellular layer is to handle asmuch traffic as possible, but keeping fast moving mobiles in the umbrella cell. Accord-ing handover algorithms are implemented within the Alcatel microcellular concept [1].

Microcells are either installed to provide continuous coverage in high traffic areas or inorder to cover local traffic hot-spots. In the latter case the MicroBTS is a quick and ef-fective way of solving local capacity problems, especially in regions where no carrierupgrading is possible in the macrocellular layer.

The traffic in dense areas is usually inhomogeneous. In order to install MicroBTSs mosteffectively within the network, it is important to know how much and where high trafficdensities will occur. Since no exact traffic data bases are available with a sufficientresolution, a methodology for hotspot detection and verification is necessary.

The most promising methodology for hotspot detectionis a triangulation approach [2]based on RXLEV downlink field strength measurements and field strength prediction,which is currently under development within Alcatel.

The most simple approach of hotspot detectionis based on experience. Planning re-sults, statistical evaluation of the operating network or site surveys can be used as aninput for this task.

Using a traffic verificationapproach is then the appropriate method in order to quan-tify the traffic amount at the presumed hotspot and to estimate the offload of the mac-roBTS, which can be achieved by installation of the MicroBTS.

The benefit of a hotspot verificator depends on the reliability of the results. Thus theaim of this document is to define an accurate hotspot verification concept and meth-odology.

5 Concept

The aim of the verificator is to allow traffic measurements at presumed traffic hotspotswithout complete installation of a base station. As a result of the measurement we getthe traffic share, which could have been handled by a real BTS at the same location asthe verificator without disturbing the actual traffic [3].

Figure 1 summarises the key modules of the hotspot verificator. A standard MicroBTSwith a specific software, which requires no Abis connection is installed at the locationof the presumed area of high traffic within the coverage range of one or several Mac-roBTS as the potential umbrella cell(s). This MicroBTS transmits a BCCH carrier on a


5/17



specific ARFCN but does not handle any traffic, since it is not connected to the net-work. For the selection of the ARFCN either a test frequency is available or the fre-quency of an existing cell can be reused. This ARFCN is defined as a neighbour of theumbrella cell at the OMC-R. Thus mobile stations moving in the coverage range of the

MicroBTS will report every 480ms the received downlink RXLEV value to the BSC of theumbrella cell. This level information will be used for traffic evaluation. Several post-processing methodologies will be described in chapter 7.

MMIBox

MMIC

Cable

Micro BTSdemonstratorwith special

SW

Feedercable

CoverageRangeof Umbrellacell

Coverage Rangeof MicroBTSdemonstrator

220V Powersupply or24V battery

BCCH

BSC

Abisinterface

K1103

Macro BTSas the potentialumbrella cell

adjustableMast

Postprocessing of Abistrace files, to deteminethe MicroBTS traffic

share

microcell

antenna220V/24V

Laptop with Terminalemulation for BTSconfiguration:ARFCN, BSIC, Power,status barred

Abis interfacenot connected

OMC

Figure 1 Modules of the hotsp ot verif icator

The BSIC (=NCC,BCC) is transmitted on the BCCH carrier. In order to avoid hando-vers of mobiles located in the coverage range of the microcell, the transmitted BSIChas to differ from the BSIC which is defined for that cell at the OMC-R. Thus for mo-biles in the connected mode, the received downlink power level will be reported withinthe measurement report, but handover attempts towards this MicroBTS will be avoided

due to the wrong BSIC.In order to avoid cell selection in idle mode the MicroBTS has to be configured in thestatus barred.

As shown in figure 1, a laptop with terminal emulation is used to configure the Mi-croBTS. The following parameters need to be adjusted for a hotspot verification meas-urement: ARFCN, BSIC (=NCC,BCC) and output power.

The laptop is connected to the MicroBTS via the MMI Cable and the MMI Box.


6/17



The MicroBTS needs to be connected to a 220V power supply. If no power supply isavailable a 24V battery unit can be used by removing the E-Box.

The MicroBTS operates with a special software, making operation without a connectionto the Abis interface possible. The following two operation modes are possible:

MicroBTS demonstrator

Hotspot verfication

The concept of the MicroBTS demonstrator allows mobile to mobile calls without anAbis connection as described in more detail in [4]. Within this document only the con-cept of the Hotspot verification mode will be considered.

The recorded power levels and messages are reported on the Abis interface and canbe traced with a protocol analyzer (e.g. K1103). The Abis trace files will be postproc-essed and the MicroBTS traffic share will be evaluated.

The described concept of the hotspot verificator can be used for the following taskswithout having an impact on the operating network:

Verification of presumed traffic hotspots

Optimization of parameters like antenna type, position, output power etc.

Performance analysis of the future cell for the selected parameters


7/17



6 Installation steps

The following sections describes the required steps and methods of the hotspot verifi-cation process. The postprocessing methodology will be described more detailed inchapter 7.

Step 1: Identify a potential traffic hotspot as a measurement location

The hotspot verificator approach can be used in order to evaluate the efficiency of asite, related to the expected amount of traffic. Before this measurement can be per-formed the potential hotspots need to be detected and an according site needs to beselected. In order to find hotspots the following methods can be used

Local environment knowledge is still the most effective way to identify traffic hot-spots, by the usage of maps or personal investigation of the location: Look for pub-

lic squares, junctions, railway stations, shopping or business centres etc. Take into account the experience of the operator, the planning team and the results

of site surveys.

Analyze cells of the operating network with high load and/or quality problemsbased on cellular statistics, e.g sites with a high call block/drop rate (e.g. OMC-Rcounter type 5, Quality of Service Indicators [9] and Dico evaluation, e.g. BSC trafficand call evolution per day).

Especially macrocells, where no further carrier upgrading is possible to solve ca-pacity problems are ideal for an installation of a hotspot MicroBTS.

The hotspot traffic characteristic can be time and season dependant, evaluate theperiod of peak hour traffic based on experience or available measurements (OMC-R counter).

Take into account the cell boundaries based on field strength predictions and/ormeasurements in order to determine which MacroBTS is covering the potential hot-spot. It can be possible, that the presumed hotspot area is within the coveragerange of two MacroBTS. In that case two Abis traces need to be performed andevaluated.

When selecting the sites, general aspects of site acquisition should also be taken

into account (possibility for installation of a real BTS). Timing advance measurements allow a resolution of 550m. This technique is cer-

tainly most effective when using directive antennas on large sector sites. The resultwill be a ring area, where the subscribers are located.

RXLEV measurements also provide information on the distance of the mobiles, butare difficult to interpret, since indoor/outdoor mobiles cannot be distinguished.


8/17



The amount of incoming and outgoing handovers between a pair of macrocellsprovides information, which can be used for the evaluation of the traffic distributionwithin a macrocell (based on A interface measurements processed with Aglae, the.THO-File or OMC Counter evaluation).

Step 2: Parameter Definition

The following parameters need to be defined and will be set at the OMC-R or down-loaded via the laptop as will be described in Step 4.

1. Selection of ARFCN and definition of microcell and handover relationship

For the selection of the channel there are two possible cases, either a test frequency isavailable, or a frequency of the operating network will be reused. A test frequency is a

frequency which belongs to the operators band but is not in use within the network.If a test frequencyis available, the microcell needs to be defined as a new cell at theOMC-R. The microcell needs to be defined as a neighbour of the umbrella cell. Theadvantage of the usage of a test frequency is, that the verificator can be installed any-where in the network without a risk of interference, provided that the test frequencyhas a minimum separation of at least two channels to the channels in use. Thus noanalysis of the frequency plan is required.

Ifno test frequencyis available a frequency of the operating network will be reused.The used frequency needs to be selected carefully for each measurement site, in orderto prevent active or passive interference. An according analysis of the frequency planis required. The cell reusing this frequency needs to be sufficiently far away. Since acell with this frequency is already defined at the OMC-R, no new cell needs to be de-fined. It is sufficient to define this cell as a neighbour of the umbrella.

The coverage range of the hotspot can be within the coverage range of two potentialumbrella cells. In that case the Abis interface measurements have to be performed atboth macrocells and the neighbourhood relationship from the macrocell towards themicro BTS has to be defined at both macrocells, if the measurement is performed si-multaneously.

2. Definition of output power, antenna type, height and position

The antenna type, height, position and the output power has to be defined in a way,that the intended coverage range or the intended indoor coverage is achieved. It isrecommended to combine the hotspot verification with fieldstrength predictions (beforeMicroBTS installation) or measurements (after MicroBTS installation) in order to deter-mine the area, where the measured traffic occured. The result of a measurementcampaign should be the measured traffic in combination with an according power or


9/17



best server plot. Based on a simulation the antenna type, height, position and the out-put power can be optimized and defined.

The hotspot verificator is equipped with an omnidirectional standard microcellular an-tenna with an antenna gain of 5dBi. If a different antenna type is intended to be used

for that site, it should be used instead.

The installation height of microcellular antennas should be in between 5 to 12 m ac-cording to [6].

3. Definition of BSIC

The BCCH carrier transmits the BSIC, which consists of two figures, the Base StationColour Code (BCC) and the Network Colour Code (NCC). In order to prevent hando-ver attemps towards this cell, the BSIC transmitted by the MicroBTS has to differ fromthe BSIC which is defined for that MicroBTS at the OMC-R.

The recommended way to define the different BSICs is, to use a wrong NCC and awrong BCC. If a wrong NCC is used it will be more easy for postprocessing purposesto identify, the Dummy BTS within the measurement report.

4. Definition of measurement time and period

It should be taken care, that the measurement period is long enough and the meas-urement is performed during the peak hour traffic. The longer the measurement themore reliable will be the results, on the other hand, the higher will be the effort for

postprocessing related to calculation time and required disk space. It is recommendedto perform measurements for the period of 24 hours. With these results it is possible toevaluate the traffic profile versus time.

Available traffic measurements of the operating network can also support the decision,by the evaluation of the according OMC-R counters, Dico evaluation or Quality ofService Indicators .

Step 3: MicroBTS installation

The Abis interface is not connected to the MicroBTS.

If no 220V power supply is available, the MicroBTS can be connected to a 24V batteryunit instead.

The adjustable mast can be set at the defined position and height. The antenna will beconnected to the MicroBTS with a feeder cable.

For the download of the MicroBTS parameters in step 4 the MicroBTS is connected tothe laptop via the MMI cable and the MMI Box.


10/17



It is recommended to setup the equipment in a car in order to be more flexible. Theadjustable antenna mast can also be car mounted.

Step 4: OMC-R Modifications and Parameter Download to MicroBTSThe parameters which have been defined in step 2 have to be input at the OMC-Rand downloaded from the laptop to the MicroBTS via the MMI Interface.

1. Modifications at the OMC-R

If a test frequency is used, a new cell and a handover relationship from the umbrellacell towards this cell has to be defined at the OMC-R. The BSIC defined for this cell isinput.

If an ARFCN of the operating network is reused, no new cell needs to be defined. Ahandover relationship from the umbrella cell to an existing cell, which is sufficiently faraway, using this frequency is defined at the OMC-R.

2. Parameters for Download to the MicroBTS

The following parameters which have been defined in step 2 will be downloaded viathe MMI interface:

The defined BSIC, which will be transmitted on the BCCH carrier and which has todiffer from the BSIC defined at the OMC-R above.

The defined ARFCN, output power and the parameter setting the MicroBTS in thestatus barred in order to prevent handover attemps towards this cell.

After parameter download, the MicroBTS will transmit the BCCH carrier according tothe parameter settings.

It is recommended to use a spectrum analyzer or a test mobile in order to make sure,that the MicroBTS is operating correctly.

Step 5: Recording of Abis traces and measurement of coverage area

For configuration and method of measurement of Abis traces, refer to the manual ofthe appropriate protocol analyzer (e.g. K1103). The protocol analyzer is connected tothe Abis interface of the umbrella cell. The measurement will be performed during theperiod, which has been defined in step 2. The aim of the Abis interface trace is to rec-ord the RXLEV values of the serving cell and the neighbouring cells, which are re-ported by the MS within the measurement report. One of the neighbouring cells is thereceived BCCH power level of the hotspot verificator.

The following messages have to be recorded for postprocessing purposes:


11/17



Measurement Results (UL&DL Measurement Reports)

Channel Activation Messages

RF Channel Release Messages

However it is recommended to record all Layer3 messages.

In addition to the fieldstrength prediction, measurements can be performed for theevaluation of the coverage area.

Step 6: Postprocessing

Postprocessing is based on the Abis trace evaluation of the measured RXLEV values ofthe serving cell (potential umbrella cell) and the hotspot verificator MicroBTS. Thereare three methods for the evaluation of the traffic share, the according methodologieswill be described and discussed in chapter 7.

Step 7: Repetition of measurements for one potential hotspot

When the measurements according to step 1 to 5 have been performed, the amountof traffic, which would be handled by a MicroBTS at the selected location with the se-lected coverage range has been evaluated. In order to optimize these parameters orin order to get a better overview on the traffic distribution of the hotspot, it can beusefull to repeat the measurement with modified parameters or to perform severalmeasurements simultaneously:

Perform the measurement for one potential hotspot at different locations in order toget an overview on the whole hotspot area. If sufficient frequencies are available,perform simultaneous measurements at different loacations.

Perform the measurement with different coverage ranges (output power, antennaheight), to find a relation between the percentage of traffic and coverage range asshown in figure 2.

MeasuredHotspotTraffic

Output power of Dummy BTS

Figure 2: Evaluation of the optimum output power


12/17



7 Postprocessing Methodology

The aim of the postprocessing methods is to determine the percentage of traffic share(related to the traffic of the umbrella cell), which would be handled by a real Mi-croBTS, if it were installed instead of the hotspot verificator. Three different methods

based on the measured downlink power levels will be described within this section.Method 1 and 2 is based on a fieldstrength analysis and is recommended to use for arough estimation. Method 3 is the most accurate method, based on a complete simu-lation of the Alcatel handover algorithm, but is on the other hand the most time con-suming approach.

The result of each method is the percentage of traffic share, but it gives no informationon the coverage range of the MicroBTS. This information can be derived from an ac-cording fieldstrength prediction using the Alcatel RNP tool A955.

Method 1: Fieldstreng th analysis based on RXLEV Threshold

This is the most simple approach, which can be used for a first approximation of thetraffic share of a site. Depending on the postprocessing effort, which is planned to beinvested, one can use this method to preselect only sites with a sufficient high percent-age, which can then be further investigated with the methods mentioned below. Themethod is based on the following principle:

Within the measurement report of the Abis trace, the downlink fieldstrength levels ofthe serving umbrella cell and the declared neighbourcells are reported every 480ms.

The traffic of the umbrella cell can be determined by:

Traffic umbrella cell [Erlang]=N total ms

PErlang

( )[ ]

480[Eq. 1]

With:

N(total)=Total amount of valid measurement samples reported on the Abis interface

P=Measurement period

As soon as the signal of the dummy BTS is recognized by a mobile, it will be reportedwithin the measurement report. Thus the recorded amount of samples, where thedummy BTS was recognized as a neighbour will be N(dummy)


13/17



Traffic share in MicroBTS =Amount of samples above threshold

[%]( )N total

100 % [Eq.2]

Figure 3 summarizes an example of this method:

The total amount of measurement reports (=samples) during the observation period Pwas 664491. Within 152591 measurement reports, the Dummy BTS was recognizedas a neighbour. The fieldstrength distribution of these samples is shown in figure 2.Considering only samples with fieldstrength levels above -90dBm, gives us the estima-tion of the MicroBTS traffic share accordingly:

Traffic share MicroBTS[%]=79079/664491*100%=11.9%

As a result of the measurement the distribution of measurement samples of the macro-and microcells over the observation time can be displayed as shown in Figure 3. Basi-cally the information of the traffic distribution within time is also available with theOMC-R counters. But with the graph in figure 3 the influence of the microBTS duringbusy and low traffic hour can be seen. This information can also be used for furtherpreselection of measurement results: The more time consuming simulation of method

Total amount of samples: 664491Samples dedicated to MicroBTS 152591Samples > -85 dBm 62824Samples > -90 dBm 79079 =>11.90%Samoles >-95 dBm 94977

Fieldstrength distribution

0

1000

2000

3000

4000

5000

6000

-110

-107

-104

-101

-98

-95

-92

-89

-86

-83

-80

-77

-74

-71

-68

-65

-62

-59

-56

-53

-50

-47

RXLev [dBm]

Samples

Traffic share of -BTS

Makro

Figure 3: Evaluation of MicroB TS traff ic share based on Method 1 - RXLEV Threshold


14/17



3, should be done at least during the period of busy hour. This period can be definedby the curve shown in figure 4.

Measurement results - Macro / Micro

0

10000

20000

30000

40000

50000

60000

08:47:07

09:47:07

10:47:07

11:47:07

12:47:07

13:47:07

14:47:07

15:47:07

16:47:07

17:47:07

18:47:07

19:47:07

20:47:07

21:47:07

22:47:07

23:47:16

00:47:15

01:47:15

02:47:18

03:47:29

04:47:48

05:47:33

06:47:33

07:47:33

Figure 3 Amount of samp les distributet over observation time

Method 2 :Fieldstrength analysis based on Power Budget Evaluation

Another rather simple approach is the evaluation of the pathloss between

Mobile/serving cell PL1 = PwrUmbr - RXLEVDL

Mobile/MicroBTS PL2 = PwrMicro - RXLEVNcell

The traffic share of the MicroBTS can be evaluated based on the percentage of sam-ples, which fulfil the following condition:

PL1 > PL2 + HO_Margin [Eq. 3]

This method simulates a power budget handover with a handover margin, which canbe adjusted for postprocessing purposes. This method could be applied for hotspotverification of a homogenous microcellular network, evaluating the amount of traffic

performing a PBGT-handover from one microcell towards the dummy BTS.

Method 3: HO -Simulation

Based on the measured fieldstrength levels of each individual call the post-processingmethod simulates the handover algorithm, taking into account the incoming and out-going HO causes. Thus the amount of incoming handovers and the holding time ofthe MS within the dummy BTS can be determined for traffic evaluation.


15/17



For this simulation the defined BSS parameter, e.g. T_Dwellmin, Level thresholds andaveraging windows sizes are required as an input.

The postprocessing time of this method is higher compared to the upper methods. Theevaluation is based on the evaluation of individual calls. Therefore the available

measurements samples need to be sorted per call. A call is defined by all TCH eventsbetween the Channel activation message and the RF Channel Release message.

Figure 5 summarizes the considered HO types.

Figure 5: Considered HO types for the HO simulation

Incoming handovers from the umbrella cell towards the microcellular layer are basedon the velocity dependant handover cause 14 (high level in neighbour microcell). Thereceived fieldstrength level of the target microcell needs to be higher then a giventhreshold (RXLEV_MCHO_Ncell) for a sufficient amount of time (T_DWell_Min).

For the outgoing handover from the microcell towards the macrocell, the following HOcauses are taken into account:

Cause 18: level downlink microcell - high threshold

Cause 9: level downlink microcell - low threshold

Cause 7: N consecutive bad SACCH frames

Cause 0: End of call

Intracell HO and quality HO causes are not taken into account.

For more detailed information on the HO causes and on the implemented simulationrefer to [1] and [10].

The method provides the following two basic informations as a result:

Percentage of calls, which will perform a handover towards the microcell based onthe cause 14 handover condition.

Coverage Range ofUmbrella cellCoverage Range

of Dummy BTS

Incoming HO

cause 14

Outgoing HOCauses:18, 9 and 7or End of call


16/17



Percentage of call time, during which a mobile will remain in the microcellularlayer, taking into account the incoming handovers (cause 14), the outgoing (cause18, 9, 7) handovers or the end of a call.

With the introduction of the next BSS Software Release B4, new handover algorithms

will be defined. Small macrocells, so called minicells are introduced. The handoveralgorithm for microcells differs from release 3 algorithm. For hotspot verification thesehandover algorithms need to be taken into account accordingly for postprocessing.

8 Summary

A hotspot verfication methodology is described. The concept can be applied for out-door or indoor traffic measurements. The concept has successfully been tested withinfieldtrials [8].

The concept (chapter 5) is based on downlink fieldstrength measurements of a stan-dard MicroBTS and requires no Abis connection. The result of the measurement is thepercentage of traffic, which will be allocated to a MicroBTS, if it were installed insteadof the verficator.

The required installation steps are described in chapter 6, three appropriate post-processing methodologies are defined within chapter 7. The most accurate post-processing method takes into account the microcellular handover algorithms of Re-lease 3 (method 3). For the next BSS software release B4, this method still needs to bedefined for microcells and minicells.

9 Abbreviations

ARFCN Absolute Radio Frequency Channel Number

BCC Base Station Colour Code

BCCH Broadcast Control Channel

BSIC Base Station Idendity Code

BSS Base Station Subsystem

BTS Base Transceiver Station

DLS Data Load Segment

HW Hardware

NCC Network Colour Code

MMI Man Machine Interface


17/17



OMC-R Operation and Maintenance Centre - Radio

RNP Radio Network Planning

SW Software

END OF DOCUMENT

Documents

Hotspot Me Tod