22650243 network quality

7/29/2019 22650243 Network Quality

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Network Quality

Technology for executives,

Moscow - 13 September 2004Author: Morten RaaumPresenter: Hans Myhre


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Network Quality,

as perceived by customer

Coverage

Capacity Speech quality

Services quality

Customer care..


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GSM in the field

BTS

BTS

BTS

BTS

To BSC / MSC

To BSC / MSC

To BSC / MSC

To BSC / MSC

Handover

Handover


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Some practical experiences..

No network access (= no Telenor in the display) Lack of coverage

Network overload situation (users barred from access)

Network failure.

3 beeps/3-tone beeps at call setup

Blocking/error situations somewhere in the network User error (e.g. non-existent number)

Poor speech quality Marginal coverage

Interference between base stations

Dropped call Poor quality of radio link Blocking in target cell (moving mobile, handover situation)

Network failure (transmission)

The mobile is the weakest link in the chain:

Mass production units

Internal antenna

Increased software andprocessing complexity (WAP/GPRS/HSCSD/games&features)


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GSM in the field

BTS

BTS

BTS

BTS

To BSC / MSC

To BSC / MSC

To BSC / MSC

To BSC / MSC

Handover

Dropped call

Poor speech

quality

Handover tonon-optimal cell

No traffic channelsavailable


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How is Network Quality

monitored by the operator? Coverage

Measurements by technical staff. Test telephone + laptop.

Measurements by remotely controlled test systems

(installed in bus, taxi etc). Customer complaints and performance stats as input.

Capacity Network Maintenance Center / Operations center

The network counts # of events (pos./neg.)

Post processing in Performance Management tool. Tools for prognosis on capacity needs vs. required quality

of the network (Grade of Service)


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How is Network Quality

monitored by the operator? Speech quality

The network counts Dropped calls and to some extentreport on speech quality

Measurements by remotely controlled test systems /tech.staff.

Services quality Services are built up by combining equipment and software

External tools needed to ensure quality of delivery

Correct content / Response time

3rd party content delivery

3rd party Service Level Agreements (SLA)


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Capacity and quality a trade off at a given funding


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Capacity in the GSM radio network

Base station with antennas connected in a mast BTS contains a number of TRX based on the need for capacity.

UPLINK

DOWNLINK

Tx

Rx

Tx

Rx

BTS cabinet

TRX TRX

TRX


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Radio network capacity

Building blocks for capacity at the base stations: TRX 8 channels that are used for signalling (SMS, suppl.services etc) and speech/data.

Call duration -> Erlang

1 Erlang = 1 hour of speech for 1 user Call duration 90 sec: 90s / 3600s = 0,025 Erl = 25 mErl

I.e. 1 Erlang: 40 calls of 90 seconds each. (1 Erl = 40 x 25 mErl)

Theoretical capacity: Erlangs model and chosen Grade of Service. GoS (%) Number of call attempts that may meet blocking in a busy hour.

Typical values used: 2-5%

Example, GoS=2%

1 TRX 7 speech channels 2.9 Erlang 41%





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Base station configuration example:

3 TRXes, Omni directional cell 1 cell with 3 TRX, GoS=2%: Capacity = 14.9 Erl

90 sec call duration (25mErl)

14.9 / 0.025 = 596 calls in a busy hour(theoretical max!)

If we accept higher blocking figures we can carry more traffic withless customer satisfaction.

5% GoS used in this example => 17.1 Erl capacity => 684 calls (+15%)

BTS

TRX TRX TRX


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Base station configuration example:

3 TRXes, Sectorised 1/1/1. 3 cells with 1 TRX each: Capacity = 3 x 2,9 Erl = 8,7 Erl

90 sec call duration

8,7 / 0,025 = 348 calls in a busy hour

If we accept higher blocking figures we can carry more traffic with lesscustomer satisfaction.

5% GoS used in this example => 11.1 Erl capacity => 444 calls (+28%)

BTS

TRX TRX TRX



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Frequency planning

Re-use of GSM channels isnecessary. In this example afrequency is re-used in every12th cell => reuse factor 12


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Resource: Frequency spectrum

Spectrum size strongly affect base station roll out. Re-use of GSM channels is necessary. 1 TRX use 1 GSM channel

Example, Malaysia: 24.8 MHz => 124 GSM channels

# of TRX per cell: >6. Good capacity per base station (xx Erlang).

Example, Russia: 4 MHz => 20 GSM channels

Maximum ~1,5 TRX per cell = a denser base station network will be needed for servingincreasing traffic (xx Erlang)

Good radio/frequency planning and use of smart features enables atight re-use of GSM channels

Power control

Mobile and BTS adjust their output power as low as possible, adjustment 2 times per sec.

Discontinuous Transmission (DTX)

Mobile and BTS only transmit when user actually speak. (User benefit: less power consumption)

Frequency hopping

Mobile and BTS jump from GSM channel to GSM channel (480ms), less affected by interference.


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Area= 50km2

Population= 1 MSubscribers= 346k

15 mErl/sub

Traffic= 5190 Erl

Spectrum vs. investmentsCapacity case

Malaysia case.. 6TRX/cell= 34,6 Erl/cell

900TRX, 150 cells and 50 BTS needed

Russia case.. 1,5 TRX/cell= 5,8 Erl/cell

1343TRX, 895 cells and 299 BTS needed

We need 6 times as many sites for

capacity reason!

For illustration purpose onlythe conclusions and calculations are simplified


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Network Quality,

some KPIs Minutes per dropped call

Summary of all traffic minutes divided by number of dropped callsduring a period of time (e.g. Week/month)

Typical values: 50-150 minutes.

Blocking/Congestion Call attempts that meet blocking, all resources are occupied.

The network is dimensioned to meet a certain traffic level in thebusy hour.Typical dimensioning values (GoS): 2 - 5 %Typical values measured in the networks: 0 - 50+ %


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Network Quality, some KPIs

Network UtilisationCell utilization

0

20

40

60

80

100

120

140

160

1%

4%

7%

10%

13%

16%

19%

22%

26%

29%

32%

35%

38%

41%

44%

47%

50%

53%

57%

60%

63%

66%

69%

72%

75%

78%

81%

84%

88%

91%

94%

97%

100%

Cell utilization distribution

Utilization(%

About 22% of the cells in the network are utilised > theoretical max =

customers experience more blocking than acceptable in these cells!


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Technical KPIs

PSTN

Access network OSS Core network OSS

Technical

KPIsFinancial

Market

HR

Technical

Benchmarking

Report

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

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

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

BTS BSC

MSC

MSC

MSC

MSC

Events

& alarmsEvents

& alarms


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Network Quality,

challenges How to measure customer perceived quality?

Unmanned active measurement units.

New and advanced services Fast development and deployment of new services.

Increased complexity, both for network and mobile. 3.party content providers

Timeout... Not available...

Service Level Agreements. How do you know what is delivered?

New and advanced measurement systems for test&monitoring.

Roaming How well are we able to keep foreign roamers in our network

and how are our roamers abroad doing?

Advanced measurement systems (signalling) fortest&monitoring.


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Environment

Base station location:


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Trndelag theatre


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Tree-mountedantenna..


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Antenna

Vindern


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Vindern

Typical antenna-installation in a cityenvironment


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Mini-BTS mounted on apole by the fjord

22650243 network quality

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