22650243 Network Quality
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Transcript of 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%
2 TRX 15 speech channels 9.0 Erlang 60%
3 TRX 22 speech channels 14.9 Erlang 68%
4 TRX 30 speech channels 21.9 Erlang 73%
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Radio network capacity
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
Radio network capacity
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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