Network_optimisation.doc

CCELLULARELLULAR N NETWORKSETWORKS OOPTIMISATIONPTIMISATION

Course « Mobile Communications »

ALTTC (Ghaziabad) - February 18th – 22nd 2002

Sami Tabbane (ITU)

SSUMMARYUMMARY

- 1 – Network structure and basic equipment

- 2 – Cellular engineering basics- 3 – Network tuning- 4 – Quality of service monitoring process and equipment

- Cellular networks optimisation - Sami Tabbane – p. 2 -

- 5 – Decision process


- 1 GSM - 1 GSM NETWORKNETWORK STRUCTURESTRUCTURE ANDAND BASICBASIC

EQUIPMENTEQUIPMENT


GSM GSM NETWORKNETWORK INFRASTRUCTUREINFRASTRUCTURE ANDAND INTERFACESINTERFACES


AANTENNANTENNA CHARACTERISTICSCHARACTERISTICS

Antenna: one of the most critical elements in a RF communications system. Antenna used for receiving and transmitting: 1 dB gain = 2 dB gain for the system (1 dB in each way). It is a passive element: Cannot transmit more power than received (in each direction), Can concentrate energy in a specific direction and thus, shows a gain.


RRADIATIONADIATION PATTERNSPATTERNS

The radiation pattern: polar diagram: Horizontal plane: azimuth radiations (i.e., according to the direction N-E-S-W), Vertical plane: radiations according to the height (i.e., up, down and horizontally). Antennas can be compared through their diagram characteristics:

Points at -3 dB, -6 dB, -10 dB, Front to back ratio, Zeros angles, minor lobes, etc.


EEXAMPLESXAMPLES OFOF A ANTENNANTENNA D DIAGRAMSIAGRAMS (1) (1)

Sector antenna

EEXAMPLESXAMPLES OFOF A ANTENNANTENNA D DIAGRAMSIAGRAMS (2) (2)

Omnidirectional antenna


GGAINAIN OBTENTIONOBTENTION

Optical-based methods:- Reflectors used to focus the radiations. Works well

for the micro-waves where the reflectors have small sizes (parabolic reflector).

Array-based antennas (discrete elements):- Power feeded to multiple elements,- The radiations of the elements are on-phase in

some directions.

AARRAYRRAY ANTENNASANTENNAS FORFOR SECTORSECTOR SITESSITESSector antennas: Dipoles, yagis, or log-periodic

elements vertical combinations with reflectors in the back.


SSOMEOME ANTENNAANTENNA SELECTIONSELECTION CRITERIACRITERIA

Before chosing an antenna, check: The radiation patterns of the vendor:

Radiating pattern in the low, central and upper frequencies of the band, Minor beams and zeros, Symetry.

Test: Physical integrity, water resistance, Type of power, Measurements.

Ask other users.


UUSUALSUAL ANTENNASANTENNAS

Type Gains (in dB)

Dipole 0Omni 0

Gain omni 3 to 12Helicoidal 5 to 15

Yagi 3 to 20Parabolic 10 to 30


RRADIATINGADIATING CÂBLESCÂBLES

Classical solution to cover indoor tunnels.

Signal remains constant over several hundreds of meters.

The use of radiating cables allows to smooth the signal variations and to extend the coverage.


BTS BTS ARCHITECTUREARCHITECTUREA BTS contains: A transmission board (TRU), A unit for combining, filtering and duplexing functions, … A TRX for: digital/analog processing, power amplifying, main receiver and diversity, frequency hopping (synthesized and baseband).


BTS BBTS BASICASIC A ARCHITECTURERCHITECTURE


BTS BTS TRANSMISSIONTRANSMISSION//RECEPTIONRECEPTION CHARACTERISTICSCHARACTERISTICS

Receiver sensitivityWith duplexerWithout duplexerWith diversity

- 106 dBm- 105 dBm- 111 dBm

Transmitter output powerWithout combinerWith combiner

42 dBm39 dBm


RBS 2000 (ERBS 2000 (ERICSSONRICSSON) ) EXAMPLEEXAMPLEElements:- DXU, Distribution Switch Unit (interface between

PCM links and the TRU, LAPD multiplexing),- TRU, Transceiver Unit (management of the 8 time

slots, include A5/1 or A5/2 protocols),- CDU, Combining and Distribution Unit (combining

the signals transmitted by the different TRU),- PSU, Power Supply Unit (+24V),- BFU, Battery Fuse Unit (safety power),- ECU, Energy Control Unit (supervises and controls

the power and the cooling of the equipment).


MMICROICRO-BTS (A-BTS (ALCATELLCATEL))


TMA (TTMA (TOWEROWER M MOUNTEDOUNTED A AMPLIFIERMPLIFIER)) Amplifier which compensate the power losses in the

feeder link of the antenna and reduces the noise level.

If a usual antenna is provided for reception and transmission with a TMA installed on the mast, a duplexor filter must be installer on the mast.

External alarms: RBS2000 provided the necessary connections for the external alarms. These are defined by the operator and transmitted to the BSC through the LAPD signaling link on the Abis interface.

16 types of different alarms can be defined.- Cellular networks optimisation - Sami Tabbane – p. 20 -

MMICROICRO-W-WAVEAVE L LINKSINKS

BTSs to BSC links can be insured by micro-waves (MW).

Example of MINI-LINKs:

- Bitrates: 2, 22, 42 or 8, 28 or 82, 34+2 or 172 Mb/s.

- Frequency bands: 7, 14-15, 17-19, 21-23, 25-26 and 37-39 GHz.


EEXAMPLEXAMPLE OFOF MW MW USEUSE


BSCBSCExample of Ericsson BSC and TRC equipment

BSC/TRC BSC TRCNumber of TRX Up to 1020 Up to 1020 -Number of cabinets

2 to 8 1 to 5 3 to 11

Number of cells 512 512 -Number of BSCs 16 - 16BHCA 200 000 200 000 700

000Capacity in Erlangs 6 400 1 000 6 400


Power 48 – 54.5 V - -


RREPEATERSEPEATERS

Transmission-Reception equipment: To fill coverage holes (indoor, …). Amplify the signals in these areas. To extend the service area of a cell beyond its normal coverage.

Not visible by the system. Passive function of signal regeneration in both ways. Channel management remains under BTS complete control.


RREPEATEREPEATER EXAMPLEEXAMPLE OFOF USEUSE


- 2 C- 2 CELLULARELLULAR ENGINEERINGENGINEERING BASICBASIC

CONCEPTSCONCEPTS


SSOMEOME BASICBASIC RULESRULES

Urban areas coverage: Define regular pattern (reals sites located within 10 to

20% radius distance from the theoretical position). Homogeneous antennas azimuths in the same area

(for example, 0°, 120° and 240°). Similar antennas heights in the same area (15 meters

for example). Choice of the BTSs sites: buildings of (n+1 or n+2)

floors compared to the mean neighbouring buildings height (n floors) in the area, that is, about 6 to 8 meters. Do not use quasi-bi or quasi-tri sites in urban areas. Use

only tri-sector sites.


AAERIALERIAL INSTALLATIONINSTALLATION

Diversity techniques Horizontal space diversity: put two antennas

separated by a certain distance (1 to 2.5 meters typically). Gains: 5 dB on the uplink.

Vertical space diversity: put two antennas one above the other with a separation (1 meter typically, a too large distance gives rise to different coverages). Gains: 4 dB on the uplink.

Note: The BCCH should be transmitted on the lowest antenna.


Polarisation diversity: use a cross-polar antenna which transmits and receive with polarisation angles of +45° and –45°.


HHORIZONTALORIZONTAL DIVERSITYDIVERSITY

The most current one.If it cannot be used polarisation diversity in urban environment and vertical space diversity in rural environment.Diversity antennas must have:

Same height, Same azimuths, Same tilts, Coplanar (i.e., in the same plan).


AANTENNASNTENNAS

In the transmission system, feeders must be of same type and length, antennas must be similar.Antennas types: 65° or 85° horizontal aperture and 4.5° and 7° vertical aperture with an electrical tilt. Mechanical tilt: physical inclinaison of the antenna. An important downtilt up shifts the back lobes of the antenna pattern. Electrical tilt: Allows to gather the lateral lobes of the horizontal radiations towards the center of the radiating area.


AANTENNANTENNA INSTALLATIONINSTALLATION ONON THETHE ROOFTOPROOFTOP - - IINSTALLATIONNSTALLATION ONON AA CENTRALCENTRAL MASTMAST


AANTENNANTENNA INSTALLATIONINSTALLATION ONON THETHE ROOFTOPROOFTOP - I- INSTALLATIONNSTALLATION ONON SEPARATESEPARATE 3 3 MASTSMASTS


AAERIALERIAL CLEARINGCLEARING RULESRULES (1) (1)

Antennas close obstacles (horizontal or vertical plan) Importante reduction of the signal and thus of the site role.Horizontal clearing:Avoid obstacles located within an angle of 120° from the antenna.


AAERIALERIAL CLEARINGCLEARING RULESRULES (2) (2)Vertical clearing: Angle between obstacles and the lower part of the antenna 30°.

Antenna height (Hm) = d.tg(30°) + h + L/2.


AAERIALERIAL INSTALLATIONINSTALLATION

BTS to aerials connection includes: A jumper between the output of the BTS and the feeder connector. A feeder. A jumper between the feeder connector and the antenna connector. The connectors.To avoid important losses: Minimise the BTS to antennas distance. Maximum acceptable value: 3 dB.


Curvature radius cables indicated by the vendor must be respected to avoid an increase in the value of the SWR (Stationary Wave Ratio).


CCONNECTIONONNECTION OFOF THETHE BTS BTS TOTO THETHE AERIALSAERIALS


FFEEDERSEEDERS SIZESSIZESFor a 3 dB maximum loss.

Feeder Link Maximum length½ super flex

1 feeder 17 m

½ 1 feeder + 1 jumper

23 m

7/8 1 feeder + 2 jumpers

35 m

1 ¼ 1 feeder + 2 jumpers

47 m

1 5/8 1 feeder + 2 55 m- Cellular networks optimisation - Sami Tabbane – p. 40 -

jumpers


BTS BTS INSTALLATIONINSTALLATION

Some basic rules: BTS cabinet must be installed close to each others with an easy access. Transmission equipement (MW or HDSL) installed on the same line as the BTS or the closest possible. A/C installed front of the BTS equipment. Backup power supply (rectifier and battery) installed the farest possible from the BTS cabinets. Cabling (energy, ground, transmission) on the cable tray. Patch pannel with multipoints connection to fixed half-way from the BTS equipment and power equipment, directly connected to the ground.

Feeder cables outgoing path must be waterproofed.


BTS BTS SITESITE INSTALLATIONINSTALLATION PLANPLAN

BTS BTS CONNECTIONSCONNECTIONS WITHWITH NETWORKNETWORK EQUIPMENTEQUIPMENT


- 3 N- 3 NETWORKETWORK PPARAMETERARAMETER SETTINGSETTING


NNETWORKETWORK PARAMETERPARAMETER SETTINGSETTING

Working parameters setting is one of the main tasks to realize when putting a network into operation.

Essential task of the network operator for:

Activate or desactivate some fonctionnalities,

Quality of Service,

Network optimisation.


DDIFFERENTSIFFERENTS TYPESTYPES OFOF PARAMETERSPARAMETERS Equipment related parameters: Specific to the equipment.

System parameters (activation of certain fonctionalities such as ciphering, power control, …).

Product related parameters (software versions). Engineering parameters (almost fifteen for optimising the network): Can be modified by the operators at the OMCs.

Numbering (BSC number, …). Network design (sites numbers, …).


Optimisation for system tuning (handover margins, access thresholds, …).

Operation (barred cells, …).


BSS BSS PARAMETERSPARAMETERS (1) (1)

Cell selection/reselection parameters

- Cell_Reselect_Offset: Favor the cells of a frequency band.

- Temporary_Offset: Avoid Ping-Pong cell reselection.

- Cell_Reselect_Hysteresis: Avoid the reselection of cells belonging to different LAs


and reduces the unsuccessful paging rate. Example: 6 dB.



Access related parameters- Max_Number_Retransmission: Maximum

number of retransmissions on the access channel (example: 1, 2, 4, 7). Default value: 2.

- Number_of_Slots_Spread_Trans: Maximum number of slots between 2 successives retransmissions (3 to 12, 14, 16, 20, 25, 32, 50).


- RXLEV_Access_Min: Defined the cell area. A change of 3 dB corresponds to 21% of the cell radius and 46% of the cell coverage area.



Handover

Their tuning is done to meet the following goals:

Minimise the number HO/distance, HO triggered off the closest to the cell border, Target cell correctly selected, Link quality maintained during the HO phase.



HandoverTo meet these constraints, we shall minimise: The number of HO attempts, The HO failure probability or call dropping rate, Ping-pong effect, Handover duration (handover triggering target BS link successful establishment), Resource consumption.


BSS BSS PARAMETERSPARAMETERS (5) (5)Handover related parameters

- L_RXQUAL_H: Maximises the quality of the communication and minimises the HO rate. Typical value: 1.6 to 3.2%.

- L_RXLEV_XX_H: Determined by radio engineering, so that the HO triggering occurs at the cell border. If too low, the HO will be triggered too soon (ping-pong effect), if too large, HO triggered too late (call dropping). Default value: -101 to –110 dBm.

- MAX_MS_RANGE: Determined according to cell sizes (fixed during the cellular engineering phase).


- HO_MARGIN(n): Hysteresis allowing to meet a tradeoff between the ping-pong handover rate and the quality of service.


HO_MHO_MARGINARGIN ADJUSTEMENTADJUSTEMENT (1) (1)


HO_MHO_MARGINARGIN ADJUSTEMENTADJUSTEMENT (2) (2)


- 4 M- 4 MEASUREMENTSEASUREMENTS


IINTERFACESNTERFACES TYPESTYPES

Air Interface (Um): Provide information on the downlink as well as on the exchanged messages during the protocols operation (calls, lcoation updates, …). Tools (mobiles with trace and associated tools) such as Ericsson TEMS. BTS-BSC Interface (Abis): Allows evaluate radio performance of one or several calls in both ways (uplink and downling). Allows observe resource allocation mechanisms (TCH or SDCCH) as well as intra-BSC handovers operation. Tools (protocol analysers) such as Siemens K11XX or K12XX series.


BSC-MSC Interface (A): FoAllows capture additional information on the protocol operation and BSS - NSS problems. Tools such as Siemens K11XX or K12XX series.


Radio interface analysis Radio interface analysis tools: essential to identify the origins of the problems (handover failures, coverage holes, bad quality due to interference, call drop, …). Mobiles with trace: display the serving cell frequency, the allocated time slot number, RXLEV and RXQUAL, neighbouring cells list, neighbouring cells BCCHs, timing advance, ... Data can be stored in a laptop. GPS receiver connection allows to display on a map (for instance in MAPINFO) the mobile trajectory and the evolutions of the indicated parameters.


EERICSSONRICSSON TEMS TEMS TOOLTOOL EXAMPLEEXAMPLEA measurement chain using TEMS includes:

PC software with a serial port for the data, TEMS mobile with trace including the related software,

GPS receiver.


TEMS collected information- Serving cell and neighbouring cells identities (BSICs) and BCCH frequencies.- Radio parameters: RXLev, RXQual, TXPower, DTX, Timing Advance, FER, SQI (voice quality), C1, C2, …- Current channel: CGI (MCC, MNC, LAC, CI), BSIC, BCCH ARFCN, TCH ARFCN, Time slot, Channel type, Channel mode (FR, EFR, HR), Hopping Channel, Hopping Frequencies, HSN (Hopping Sequence Number).- Map to display the measurement itinerary with: parameters values, main events (handover, call drop, …) and sites position. A GPS receiver is required for this feature.- Level 2 messages (RR-RSP, DISC-CMD, UA-RSP, SABM-CMD, …) and 3 (Synch Channel Information, System Information Type 6, Measurement Report, Synch Channel Information, Paging Request, Assignement Complete, Handover Complete, …).


- Frequency scanning.


Voice quality analysisQVOICE example (Ascom)

This tool allows:- To recognize FR and EFR types of coding.- To measure the voice quality of several networks in

parallel.- Store the differents voice effects (live recording),- To detect blank, mettalic voice, Ping-Pong effect, echos

problems.


OMC-R counters analysis to partir des

Counters transmitted by the BSCs to the OMC-R. Essentials to analyse the quality, to detect problems, to realize statistics, … at the system side. Analysis tools use these counters (generally, these are specific). Example: Alcatel RNO or NPA, Metrica.


EEXAMPLEXAMPLE OFOF AA QUALITYQUALITY REPORTREPORT TABLETABLE Operator quality monitoring teams may developp applications (Excel based typically) to extract the required information.

BSC OUARDIA1CELL TBLOCTCH TBLOCS

DTRUPTCH

TRUPTSD

THBETERC TEHOSintra

TEHOSinter

TEHOEintra

TEHOEinter

TEHO/cel

HODROP

Aeroport_Tunis_M_12_2

1,0% 0,1% 2,3% 0,3% 90,0% 2,2% 13,6% 6,5% 33,3% 2,1% 0,3%

Aeroport_Tunis_M_51

0,0% 0,0% 1,3% 0,0% 15,7% 3,0% 0,0% 10,1% 0,0% 0,0%

Asdrubal_13_3 0,0% 0,4% 1,0% 0,3% 64,6% 2,5% 72,5% 3,0% 5,9% 6,7% 0,6%Asdrubal_7_1 0,0% 0,0% 0,6% 0,3% 69,1% 3,3% 17,6% 2,5% 10,6% 4,5% 0,2%Asdrubal_7_2 0,4% 0,0% 0,8% 0,4% 59,7% 3,8% 19,4% 5,0% 8,9% 1,3% 0,2%Bardo_10_1 0,0% 0,3% 1,3% 0,5% 52,2% 12,3% 34,8% 9,3% 7,2% 7,1% 0,4%Bardo_10_2 5,9% 0,9% 0,7% 0,4% 26,5% 9,0% 42,5% 17,6% 13,9% 0,0% 0,2%Bardo_10_3 0,2% 0,0% 0,6% 0,3% 41,6% 12,4% 32,5% 5,2% 3,3% 0,0% 0,1%Belvedere1_1 0,0% 0,0% 0,5% 0,2% 48,4% 3,5% 10,3% 2,1% 5,0% 1,0% 0,2%Belvedere1_2 0,0% 0,0% 0,9% 0,2% 55,3% 4,1% 45,1% 4,7% 11,1% 2,2% 0,5%Belvedere2_3 0,0% 1,0% 0,6% 0,3% 46,1% 6,5% 14,4% 46,0% 95,5% 1,0% 0,2%

Quality of service indicators

Indicator Meaning Indicator MeaningTBLOCTCH TCH blocking rate (TCH congestion) TBLOCSD SDCCH bloking rate (SDCCH congestion)TRUPTCH TCH dropping rate TRUPTSD SDCCH dropping rateTHBETERC Best cell criterion HO rate TEHOSintr Intra-BSC outgoing HO failure rate


aTEHOSinter Inter-BSC outgoing HO failure rate TEHOEintr

aIntra-BSC incoming HO failure rate

TEHOEinter Inter-BSC incoming HO failure rate TEHO/cel Intra-cell HO failure rateHODROP Call drop due to HO problem


- 5 D- 5 DECISIONECISION PPROCESSROCESS


AANALYSISNALYSIS PROCESSPROCESS


DDECISIONSECISIONS EXAMPLESEXAMPLESProblem Detection Solutions

Coverage - Access failure rate- Call drop rate- Important RXLEV HO

rate

- New sites- Antennas (tilt, azimuths,

aperture)- TMA installation

Interference

- Communication quality - RXQUAL HO rate- Call dropping

- Frequency change- Power control tuning- Antennas action

Capacity - Blocking rate- HO failure rate

- TRX adjunction- Cell load distribution- HO thresholds and cell access

parameters adjustmentHandover

Ping Pong

- Bad quality- Micro-communication

interruption

- HO parameters adjustement- BTSs power adjustment


CCONCLUSIONSONCLUSIONS

Network optimisation is a continuous process. Requires well-trained and experienced staff. Many problems can have various origins (maintenance, parameters tuning, features activation, frequency planning, equipment installation, …). Close interaction between Quality Monitoring Team, Engineering Department and Maintenance Teams is necessary.


Date post:	09-Feb-2016
Category:	Documents
Upload:	chidhuro-owen
View:	12 times
Download:	2 times

Network_optimisation.doc

Documents