Interview and drive test tips tips
WCDMA Introduction and Overview
WCDMA concept and Architect Architecture ure Spreading and Scrambling Codes and Channels Code tree Rake Receiver Soft, Softer and Hard hand over Power control - fast and slow slow
WCDMA Driv Drive e test Overview Overview using using TEMS Investigation
TEMS Parameter for WCDMA Optimization Tips for WCDMA WCDMA Tools Tools for Drive Test Test 3G Voice Call Ca ll Testing Testing 3G Packet call & Video call testing 3G Drive test KPI overview 3G Optimization overview
WCDMA
Frequency and Spectrum
Uplink=1920MHz -1980 MHz Downlink= 2110 MHz -2170MHz Bandwidth=60 MHz Actual B. B.W W assign to operator is 5MHz And out of that 3.84 MHZ is utilize. In WCDMA f requency requency reuse f act actor =1 because time and f requency requency remains constant.
WCDMA
Frequency and Spectrum
Uplink=1920MHz -1980 MHz Downlink= 2110 MHz -2170MHz Bandwidth=60 MHz Actual B. B.W W assign to operator is 5MHz And out of that 3.84 MHZ is utilize. In WCDMA f requency requency reuse f act actor =1 because time and f requency requency remains constant.
In WCDMA f irst irst following process is done before Reading BCCH f requency requency. Slot Synchronization Frame Synchronization Scrambling Code
CPICH is pilot
which will read BCCH information Af ter ter Synchronization .
In WCDMA following Channels use for various f uncti unction in UL/DL. Downlink:-
Uplink:-
1.DL DPCH
1.UL DPDCH
2.DL CCPH
2. UL DPCCH
3. P-CCPH
3. UL CPCH
4. S-CCPH
4. UL PRACH
5. SCH
5. HS-DPCCH
6. PICH 7. CPICH (primary and secondary) 8. AICH
WCDMA
Spreading process
Spreading:- This is used to increase the B.W of the signal beyond the bandwidth n ormally required to accommodate information. For Spreading OVSF code are used which is kn own as Orthogonal variable spreading f actor code . Spreading f actor=chip rate/symbol rate . Scrambling Scrambling is used on top of the spreading s o , it does not change the signal bandwidth but only makes the signal f rom diff erent source separable f rom each other. Process gain = 10 l og (chip rate/bit rate) As bit rate increase pr ocess gain decrease . Cell breathing is situati on where cell foot print decrease due t o large amount of user access the network beyond the capacity of that particular cell .
Eb /NO= Bit energy/Noise energy
Ec/No = Chip Energy /N oise Energy.
Ec/No= Eb/No - process gain
As per Eb/No
is f ixed for each service for Ex: voice =2 and
video=4
Ec/N0= 2- 10= -8 for voice(for voice -8 is good limit)
Ec/N0= 4-18= -14 for video(for video -14 is good limit)
Process
gain(voice) = chip rate/bit rate= 10d B
Process
gain (video) = chip rate /bit rate= 18d B
Chip rate = 3 .84Mchips
in WCDMA.
WCDMA codes
Code
tree
Rake Receiver
Sof t Handoff
Power Control
types
For Speech drive Test
Mobile TX power
Received signal strength indicati on Target Signal to interf ere ratio Signal to interf ere ratio Speech quality mean opinion square Dedicate
channel
GSM/WCDMA
Speech quality
SQI MOS Algorithm
Downlink Dedicate
channel BLER%
Active Set- Currently serving Cell Measured neighb or- Def ined
Neighbor Detected Neighbor- Undef ined strong detected server UARFCN DL- UMTS Absolute radio f requency channel number
Ranges for Radio Parameter
1. CPICH EC/No- 0 to -34 dB.
2. CPICH RSCP -
3.Ms TX power -44 dBm to 60 dBm
4. UTRA Carrier RSSI - -20 dBm to -140 dBm for each rake f inger.
5. SQI MOS - 1 to 5
6. SQI - -20dBQ to 30 dBQ
7 . SIR - -30 t0 20 db (signal interf ere ratio measured on DPCCH )
-15 dBm to -140 dBm for each rake f inger.
12.2 Kbit/s: 30 dBQ 10.2 Kbit/s: 28 dBQ 7.95 kbit/s: 28 dBQ 7.40 kbit/s: 27 dBQ 6.70 kbit/s: 27 dBQ 5.90 kbit/s: 24 dBQ 5.15 kbit/s: 21 dBQ 4.75 kbit/s: 19 dBQ
Drive
Test KPI
Parameter-
RSSI In Between -75 to -85 dbm
RSCP In Between -75 to -85 dbm
Ec /Io In Between -8 to -10 db
FER 1% or 2%
Ms
Sof t
TX Power Handoff
Between
-5 to -10
35% of total time
Use f ull Plots
Server Plot Usef ul to f ind out Swap or Overshooting.
UE Plot - To Check Neighbour Relation.
RSCP Plot- Coverage wholes
Ec /No- for good Throughput and removing pilot pollution. 4th best Server Echno should be > -10db 5th
best Server Echno should be > -10db
Condition for
Pilot Pollution
Radio Environment
RSCP >= -85dBm & Ec /Io =< -10 dB Coverage
Limited
RSCP <= -85dBm & Ec /Io => -10 dB Poor
Radio Condition-
RSCP <= -85dBm & Ec /Io =< -10 dB Good Coverage RSCP >= -85dBm & Ec /Io => -10 dB
3G voice call testing
SCFT-Single Cell Functional Test Before the single site verif ication, we should only ensure the following conditions have been met. ±
Alarm Check
±
Cell
±
Status Check Parameter Check
Alarm Check / Cell ±
Status Check
The product support engineer will be resp onsible for checking and res olving all the alarms. It is important for the optimization engineer prior to any f ield test to check with product support engineer regarding any alarms especially intermittent alarms.
Parameter Check ±
The optimization engineer need to ensure the radio part parameters conf iguration list has been achieved . In the list the radio part parameters includes: the scrambling code, power setting, neighbor cell list, handover parameter etc.
3G voice call testing
Site Verif ication Items: ±
±
±
Installations: CPICH RSCP, CPICH Ec/Io, Rx Antenna Swap Test Settings: Frequency & SC, Cell reselection parameters, LAC/RAC, Neighbor List. Functions: LA/RA update, 3G<->2G Cell reselection, SMS (MT & MO), Voice (MT & MO), VP (MT & MO), PS Attach & Detach, PS service, Voice/VP/PS sof t handover, Voice 3G>2G handover
Testing On CELL site ±
Items: Voice Call (MT & MO)
±
Purpose: Verify the voice call function is normal and the voice call quality is good
±
Method: Make the dialing test of 3G voice service between two 3G mobiles, one for the terminating call and another one for the originating call. Test the voice communication quality
±
Items: Voice Call (MT & MO)
±
Purpose: Verify the voice call function is normal and the voice call quality is good
±
Method: Make the dialing test of 3G voice service between two 3G mobiles, one for the terminating call and another one for the originating call. Test the voice communication quality
Feeder Connection Check Test Process Items: Antenna swapping test Purpose: Verif y the Rx f eeder installation is right. Method: Switch the transmitter f rom one f eeder to another, check the RSCP changed or not. If no change happened, it means that the f eeder is correct. Notes: Check the RSCP f rom scanner
Problem
and Solution
In the site verif ication, following problems have been found ±
Scrambling Code Setting is wrong: The scrambling code f rom scanner and mobile is diff erent f rom the planning
±
is 20dB lower than before.
Scrambling Code Setting is wrong The Scrambling Code may be wrong in RNC, check the datasheet in RNC. If the Scrambling Code f rom scanner is the same as that of another sector in same site planned, maybe the TX/RX f eeder is crossed to the another sector. Af ter f eeder swapped, the CPICH RSCP is 20dB lower than before: The RX f eeder is crossed to the antenna of another sector. In this case, the CPICH RSCP will be high in the c overage area of the other antenna. Check the connection between the f eeder and the antenna. ±
±
Af ter f eeder swapped, the CPICH RSCP
±
DATA drive wind ow
Data Drive Parameter with low
through. put
Channel quality
index
Modulation
technique As
64 Q AM is utilized so less HSDPA throughput is less.
Case-2
with high throughput
In this case 16 Q AM is used 100% and Throughput is high
Data Drive
There is 3 modulation technique Q PSK,16Q AM,64Q AM. For high through put 16Q AM and 64Q AM should be utilized high Utilization So, if There is less Utilization of Q PSK in downlink than data throughput is also high CQI is like SQI in speech which ensure good channel quality for data transf er. Retransmission of HS- DSCH(High-Speed Downlink Shared Channel) packet is high than also throughput is decreases. In case of stationary Data Test- 2Mbits speed can be achieved In case of moving Vehicle 800kbits to 1.2 Kbits speed can be achieved. Application throughput is always 85% of physical layer data rate throughput because at application level IP inclusion and overhead information will be there. Latency time is round trip time f rom server and for 3G it should be 150 ms for 32 bit data .
The modulation scheme and coding is changed on a per-user basis depending on signal quality and cell usage . The initial scheme is Quadrature phase-shif t keying (Q PSK), but in good radio conditions 16Q AM and 64Q AM can signif icantly increase data throughput rates. With 5 Code allocation, Q PSK typically off ers up to 1.8 Mbit/s peak data rates, while 16Q AM off ers up to 3.6. Additional codes (e.g. 10, 15) can als o be used to improve these data rates or extend the network capacity throughput signif icantly.
Data
Throughput will be also depend on MS class which supp ort 5,10 and 15 codes resp.
CQI- Channel
Channel quality indicators
quality information may include carrier level received signal strength indication (RSSI) and bit error rate (BER). I are messages that are sent on a communication system (such as a m obile communication system) that provide the remote connection (e.g. base station) with channel quality information
Drive Test tool for
drive
Sony Ericsson C702
(capable of Scanning)
Sony Ericsson Z750i
(capable of Scanning)
PCTel
SeeGull LX WCDMA 2100
PCTel
SeeGull LX Plus WCDMA 2100
Global Sat BU-353 (NMEA-0183)
Garmin 10 Mobile Bluetooth (NMEA-0183)
