drive testing_using tems investigation

Prepared by Mirza Baig

Optimization using Optimization using TEMS InvestigationTEMS Investigation

Prepared by Mirza BaigPrepared by Mirza Baig

Understanding The Network StrategyUnderstanding The Network Strategy

900/1800 Dual Band Network900/1800 Dual Band Network

Two layers 900 and 1800 using Two layers 900 and 1800 using SIEMENSSIEMENS Hierarchical Cell Hierarchical Cell Structure (HCS) FeatureStructure (HCS) Feature

1800 is the priority layer for Cell Reselection and for 1800 is the priority layer for Cell Reselection and for handovers.handovers.


CBQCell bar qualifyis used to assign a priority to a cell for the cellselection process. A suitable cell with low priority is only selected ifno suitable cell of normal priority can be found. The assignment ofCBQ is useful in hierarchical cell structures

CELLRESHCell reselect hysteresis, indicates the value of the receiver RFpower level hysteresis required for cell reselection (MS in idle mode)

on the basis of the path loss criterion C1.

C1 = (A - Max(B,0))where,A = <receive level average> - RXLEV_ACCESS_MIN= RLA_P - RXLEVAMI

B = MS_TXPWR_MAX_CCH - P= MSTXPMAXCH - P

P = Maximum RF output power of the MS

Max (B,0)= MSTXPMAXCH - P if MSTXPMAXCH > P

Max (B,0)= 0 if MSTXPMAXCH < P

Cell Selection & Re-Selection


The MS calculates the path loss criterion for the serving and the nonservingcell at least every 5 seconds

The calculation result determines the priority of these cells within the list of the six strongest neighbour cells which is dynamically managed in the MS in idle mode.

The path loss criterion is satisfied if

(A) C1 > 0 (If C1 has been < 0 for a period of 5 s the path tothe cell is regarded as lost).

(b) If C1 of the non-serving cell is higher than C1 of the serving cell for a period of 5 s then the MS performs a cell reselection

Exception: If the current cell and the new cell belong to different location areas the new cell shall only be selected if the path loss criterion C1 on the new cell exceeds C1 on the old serving cell by at least CELLRESH for a period of 5 seconds. This

mechanism is used to avoid unnecessary location update procedures

Note: The value of CELLRESH is sent on the BCCH (SYSTEMINFORMATION Type3 and Type 4


The criterion C2 is an optional feature that can be enabled on a cell basis. It is an enhancement of the cell selection C1. C2, however, is useful for microcell configurations since it prevents fast moving MSs from performingunnecessary cell reselections

CRESPARICell reselection parameter indicatorIndicates the presence of C2 cell reselection parameters

CRESOFF

Cell reselection offset

It applies an offset to the cell reselection criterion C2

Cell Reselection C2Cell Reselection C2


General Principle of the C2 algorithm:

If the MS places a non-serving cell on the list of six strongest carriers it starts a timer the value of which has been broadcast on the BCCH

Equation A: C2 = C1 + CRESOFF - TEMPOFFAs long as the timer runs C2 is increased by a permanent offset (see parameter CRESOFF) and decreased by a temporary offset (see parameter TEMPOFF). By this temporary offset the C2 of the non-serving cell is artificially made worse and the cellreselection is not executed

Equation B: C2 = C1 + CRESOFFOn expiry of the timer the temporary offset is disregarded and thus - if the C2 of a non-serving cell still exceeds the one of the serving cell for a period of 5 s the MSperforms a cell reselectionFor 1800 CRESOFF=10; FOR 900: CRESOFF=0

Equation C: C2 = C1 – CRESOFF ;if PENTIME = 31If the penalty time is set to 31 (i.e. 260s) the permanentoffset (CRESOFF) is not added to but subtracted, i.e. settingPENTIME to 31 results in a permanent decrease of priority

Exception: If the current cell and the new cell belong to different location areas the new cell shall only be selected if the C2 of the new cell exceeds C2 of the old serving cellby at least the cell reselect hysteresis (see parameter CELLRESH) for a period of 5 seconds. This mechanism is used to avoid unnecessary location update procedures.


Handover Parameter SettingHandover Parameter Setting

Power Budget Handover:From 900 to 900: From 900 to 900: Handover Margin= 5 dBmHandover Margin= 5 dBmFrom 900 to 1800: From 900 to 1800: Handover Margin= -20 dBmHandover Margin= -20 dBmFrom 1800 to 1800:From 1800 to 1800: Handover Margin= 5 dBmHandover Margin= 5 dBmFrom 1800 to 900: From 1800 to 900: Handover Margin= 20 dBmHandover Margin= 20 dBm

A Power budget (Better Cell) handover is triggered if:A Power budget (Better Cell) handover is triggered if:

PBGT(n) > HO_MARGIN(n)

Where:PBGT(n) = RXLEV_NCELL(n) - (RXLEV_DL + PWR_C_D) + Min (MS_TXPWR_MAX, P) - Min (MS_TXPWR_MAX(n), P)

Parameter Unit Default Urban Highway Name Definition

RXLEVAMI 1dB 8(-102dB) 8(G900),12(G1800) 6(G900),10(G1800)Minimum received

Level (Idle Mode)

Minimum received level at the MS

required for access to the network

on the RACH

RXLEVMIN 1dB 12(-98dBm)

G9=15(-95 dBm),G18=25(-85 dBm)

Source cell is G9

G9=12(-98 dBm),G18=20(-90 dBm)

Rxlevel minimum(Dedicated Mode)

The minimum received signal level

the adjacent cell must provide to

be regarded as a suitable target

cell for handover.

G9=15(-95 dBm),G18=20(-90 dBm)

Source cell is G18

G9=12(-98 dBm),G18=15(-95 dBm)


PBGT (n) = power budget of the neighbor cell (n)

HO_MARGIN(n) = HOM (CREATE ADJC) = handover margin of the neighbour cell (n) in [dB]

RXLEV_NCELL(n) = received level average of the neighbour cell (n)(the averaging is done according to the setting of HOAVPWRB (SET HAND))

RXLEV_DL = received level average downlink of the serving cell

PWR_C_D = BS_TXPWR_MAX - BS_TXPWR= averaged difference between the maximum downlink RF power and

the actual downlink due to Power Control

MS_TXPWR_MAX = MSTXPMAXGSM or MSTXPMAXDCS or MSTXPMAXPCS value in [dBm]= max. allowed transmit power of serving cell (n)

MS_TXPWR_MAX(n) = MSTXPMAXGSM/DCS/PCS [dBm]= max. allowed transmit power of neighbour cell (n)

P = power capability of the mobile in [dBm]

Min(MS_TXPWR_MAX,P) = MS_TXPWR_MAX if MS_TXPWR_MAX < P

Min(MS_TXPWR_MAX,P) = P if MS_TXPWR_MAX > P


Imperative Handover:Imperative Handover:1. Bad up- and downlink quality 2. Bad up- and downlink level 3. Exceeding maximum distance

ParameterUnit

Default Urban Highway Name Definition

HOTDLINT 1 dB 35(-75 dBm) 35(-75 dBm) 35(-75 dBm)

HO threshold level

downlink intra Cell

This parameter defines the max interference level from BTS to MS direction for the quality intracell handover decision.(Interference HO)

HOTULINT 1 dB 35(-75 dBm) 35(-75 dBm) 35(-75 dBm)

HO threshold level uplink

intra Cell

This parameter defines the max interference level from MS to BTS direction for the quality intracell handover decision.(Interference HO)

HOLTHLVDL 1 dB 10(-100 dBm)

13(-97 dBm) G900, 15 (-95 dBm)

G1800

10(-100 dBm) G900, 15 (-95 dBm)

G1800

HO lower threshold level

downlink

defines the receive signal level threshold on the downlink for inter-cell level handover decision.

HOLTHLVUL 1 dB 8(-102 dBm)10(- 100 dBm) G900, 12(-98 dBm)g1800

10(- 100 dBm) G900, 12(-98 dBm)g1800

HO lower threshold level uplink

defines the receive signal level threshold on the uplink for inter-cell level handover decision.

HOLTHQUDL 5 5

HO lower threshold quality downlink

defines the receive signal quality threshold on the downlink for inter-cell quality handover decision.

HOLTHQUUL 5 5

HO lower threshold quality uplink

defines the receive signal quality threshold on the uplink for inter-cell quality handover decision.

HOTMSRM 1km 34 34

Handover threshold MS range maximum

the threshold for the maximum permitted distance between MS and the BTS in 1km step size which is used for intercell handover due to distance.


Antenna System:Antenna System:1- Sector Swap (Rx / Tx Line)2- Loose or Open Connector Connection at BTS/Line/Antenna Port

Observations: Bad Up/Dl, Drop Calls, Handover Failures

Troubleshooting: Drive Test; Path Loss/Path Balance (Up/Dl Losses) [RF Loopback]

BTS Cabinet:BTS Cabinet:1- Faulty Radio/TS (Drop Calls/Handover Failure)2- Other Hardware like Coupling System, Band Pass Filter

Observations: Bad Up/Dl, Drop Calls, Handover Failures

Troubleshooting: Drive Test; Path Loss/Path Balance (Up/Dl Losses) [RF Loopback]

Hardware Related

Tracing out Issues during Drive Test


DATABASE Related:DATABASE Related:

1- Missing/Wrong Neighbor definition2- Co-Channel Neighbor (Handover Failure)

RF Related:RF Related:

1- Co-Channel Interference (Overshoot)2- Adjacent Channel Interference3- Logical Server and Handover Boundary (TA, Obstacle, Antenna Tilt)4- Interference on Hopping

RF Related

Tracing out Issues during Drive Test


Case Studies

The carrier-over-interference ratio is the ratio between the signal strength of the current serving cell and the signal strength of undesired (interfering) signal components

In dedicated mode, average C/I (-5 dB to 25 dB)is presented twice a second, which is equal to the ordinary measurement interval. If frequency hopping is employed, the average C/I for each frequency is presented

C/I is not the measure of Speech Quality. Although it’s of course generally true that severe interference problem tends to degrade speech quality

C/I Worst(0): 0 gives the C/I of the worst channel

Co- Channel Interference: (C/I >= 9dB)

Co-Channel interference is meant interference from other network cells usingCo-Channel interference is meant interference from other network cells usingthe same transmission frequencythe same transmission frequency

How to reduce Co-Channel Interference:i- Improvement of Cell Planningi- Improvement of Cell Planning

ii-Shrinking the interfering cell, for example by lowing it’s output power orii-Shrinking the interfering cell, for example by lowing it’s output power or tilting the antennas of that particular celltilting the antennas of that particular celliii- Activating DL DTX on the Traffic Channelsiii- Activating DL DTX on the Traffic Channels

iV- Activating DL Power Control on Traffic ChannelsiV- Activating DL Power Control on Traffic Channels

Interference


Case Studies

Adjacent Channel Interference: (C/A >= -9 dB)

Adjacent Channel interference is always originates from other carriers than the oneAdjacent Channel interference is always originates from other carriers than the onemobile is transmitting on.mobile is transmitting on.

C/A-1 >= -9 dB at +/- 200 kHzC/A-1 >= -9 dB at +/- 200 kHzC/A-2 >= -41 dB at +/- 400 kHzC/A-2 >= -41 dB at +/- 400 kHz

Interference


Full vs. SUB Values:Full vs. SUB Values:

In GSM, there are two types of values presented for RXQual and RXLev i.e. RXQual Full, RxQual Sub, RxLev Full, RxLev Sub.

The Full values are based upon all frames on the SACCH multiframe, whether they have been transmitted from the base station or not. This means that if DTX DL has been used, the Full values will be invalid for that period since they include Bit Error Measurements at periods where nothing has been sent resulting in very high BER.

In Total, 100 bursts (i.e. 25 blocks) will be used for the Full values

The Sub Values are based on the mandatory frames on the SACCH multiframe i.e. frames that always must be transmitted.

In Total, 12 busrts (i.e. 2 blocks) will be used for Sub Values

Definitions


Why SQI?Why SQI? Traditionally, speech quality in GSM networks is measured by means of the RxQual parameter (which is also available in TEMS Investigation). RxQual, however, suffers from a number of drawbacks which make it an unreliable indicator of speech quality. SQI is a more sophisticated measure which is dedicated to reflecting the quality of the speech (as opposed to radio environment conditions). This means that when optimizing the speech quality in your network, SQI is the best criterion to use.

RxQual and Its Limitations:RxQual and Its Limitations:RxQual is obtained by transforming the bit error rate (BER) into a scale from 0 to 7.In other words, RxQual is a very basic measure: it simply reflects the average BER over a certain period of time (0.5 s). By contrast, a listener's assessment of speech quality is a complex process which is influenced by many factors. Some of these, all of which RxQual fails to take into account, are the following:(A)The distribution of bit errors over timeFor a given BER, if the BER fluctuates very much, the perceived quality is lower than if the BER remains rather constant most of the time. Different channel conditions give rise to radically different BER distributions. However, since RxQual just measures the average BER, it cannot capture this. (In fact, the logarithmic scale of RxQual gives rise to the opposite effect: a high BER variance gives a better RxQual than a low variance does. This is completely misleading from a speech quality point of view.)

Definitions


(B) Frame erasuresWhen entire speech frames are lost, this affects the perceived quality in a very negative way (C) Handovers Handovers always cause some frames to be lost, which generally gives rise to audible disturbances. This does not show at all in RxQual, however, since during handovers BER measurements are suppressed.(D) The choice of speech codecThe general quality level and the highest attainable quality vary widely between speech codecs. Moreover, each codec has its own strengths and weaknesses as regards types of input and channel conditions

In short, RxQual fails to capture many phenomena that have a decisive influence on a listener's judgment of speech quality. Using RxQual for optimization of speech quality in the network thus leads to suboptimal results

Definitions


Design of SQI: SQI has been designed to take into consideration all the phenomena

discussed in the preceding section. This ensures that it will produce an unbiased prediction of the speech quality, independently of channel conditions and other circumstances. Somewhat roughly, the computation of SQI involves : :i- The bit error rate (BER) ii- The frame erasure rate (FER)iii- Data on handover eventsiv- Statistics on the distributions of each of these parameters

Furthermore, for each speech codec, SQI is computed by a separate algorithm which is tuned to the characteristics of that codec. Like RxQual, SQI is updated at 0.5 s intervals.

FR (Full Rate): -19 ... 22 dBQEFR (Enhanced Full Rate): -20 ... 30 dBQ

Definitions


FER Frame Erasure Rate:The FER rate is the value between 0 and 100%, and it’s calculated and represented in

TEMS one each SACCH multiframe.

The FER value presented in the TEMS is based on the number of blocks that has beendiscarded due to error in the CRC, i.e.

FER(%)= (No. of blocks with incorrect CRC / total no. of blocks)*100

FER Full: The Total number of Blocks on a full rate TCH is 24 TCH + 1 SACCH=25 blocks.

FER Full= (No. of blocks with incorrect CRC / 25)*100

FER SUB (FER Actual): The Total number of mandatory Blocks on a full rate TCH is 1 TCH + 1 SACCH=2 blocks.

FER SUB (FER Actual)= (No. of blocks with incorrect CRC / 2)*100

Note: The Actual FER Sub values are limited to three values : 0, 50, 100%

Definitions


DTX Downlink Rate (0 to 96%):

The Information Element DTX Downlink Rate indicates in % that how many TCH framesthat were not sent to the Mobile station during the last SACCH Multiframe.

DTX DL Rate (%)= (number of silent blocks/total number of blocks)*100

Each SACCH multiframe hold 24 TCH frames, therefore, total number of blocks=24

• DTX Downlink Rate is not the measure of the Quality, instead it’s an indication whether DTX DL is used in the GSM Network.

• If DTX DL Rate is very high for a whole period of time during a call where there should have been speech, you could suspect a Silent Call problem in the Network.

Definitions

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