BSSPAR- Measurement Processing

BSSPAR

BSSPAR - Measurement Processing

Training DocumentBSSPAR - Measurement Processing

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Contents

1 Module Objectives........................................................4

2 Introduction To Measurements...................................52.1 Measurement Coding......................................................62.2 Mobile Station Measurements In Idle Mode....................72.3 Mobile Station Measurements In Dedicated Mode.........8

3 Measurement Processing..........................................103.1 Measurement Pre-Processing In BTS..........................113.2 Averaging And Sampling In BSC..................................123.3 Fast Averaging for Handover........................................13

4 DTX And Weighting....................................................19

5 Processing and Book Keeping In BSC.....................20

6 FER Measurement Feature.........................................22

7 Key Learning Points...................................................24

8 Review Questions.......................................................27

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1 Module Objectives

At the end of the module, the participant should be able to:

Explain the measurements carried out by the BTS and MS

State how measurements are coded for transmission

Show why and how pre-processing is performed at the BTS

Explain the fast averaging method and associated parameters

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2 Introduction To Measurements

The Mobile Station and Base Station perform measurements as part of the Radio Subsystem Link Control. These measurements include received signal level and channel quality. The measurements are sent to the BSC via BTS.

The Base Station is continuously measuring all the time slots in the uplink direction in every TRX. Thus, there is nothing special in the uplink measurements, because the Base Station knows the frequencies that it measures, and the measurement process is continuous.

The Mobile Station has to measure the downlink direction, and that is a little more complicated. In addition to the serving cell, the Mobile Station is also required to measure all the adjacent cells. The measurements carried out by the Mobile can be divided into two classes according to the status of the Mobile Station:

1. Idle mode measurements and

2. Dedicated mode measurements

Idle mode measurements are primarily used for are used to select the best base station from the neighbourhood.

In the dedicated mode i.e. on a TCH or SDCCH with respective SACCH/FACCH, measurement data is transmitted as measurements report on the SACCH to the base station. These reports are used for handover and power control purposes (to be discussed in subsequent modules).

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2.1 Measurement Coding

GSM uses two parameters to describe the levels and quality of a channel:

1. Received Signal Level (RXLEV) is measured by MS and BTS in each burst and expressed in dBm. It has a range of -110 dBm to -48 dBm.

2. Received Signal Quality (RXQUAL) is measured as Bit Error Rate (BER) percentage before any error correction techniques are applied. This can be estimated from the training sequences

Measurements transmitted in dBm or BER in measurement reports will require large bandwidth. Hence, the measurements are coded into levels as shown in Figure 1.

LEVEL QUALITY

P (dBm) FS (dBuV/m) LEV

-110 27 32 0-109 28 33 1-108 29 34 . . . . . . . . .-49 88 61-48 89 62-47 90 95 63

BER (%) BER (%) QUAL

RANGE MEAN< 0.2 0.14 00.2-0.4 0.28 10.4-0.8 0.57 20.8-1.6 1.13 31.6-3.2 2.26 43.2-6.4 4.53 56.4-12.8 9.05 6> 12.8 18.1 7

P=PowerFS= Field StrengthLEV= Level

BSC BSC

FS (dBuV/m) = RxLev (dBm) +77,2+20Log[freq(MHz)]

Figure 1. Coding of Received Signal Level and Quality

A received signal level, which is between -110 and -109 dBm, will be coded as Level 1. Similarly, if the BER of a received signal between 0.4-0.8%, it will be coded as signal quality of 2.

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2.2 Mobile Station Measurements In Idle Mode

In Idle mode, the Mobile receives information of the frequencies of the adjacent cells, which is sent on BCCH. The main purpose is to assign a mobile station to a cell whose BCCH carrier it can decode reliably.

The Mobile has to decode the BCCH of the serving cell every 30 s, and the BCCH of the adjacent cells every 5 min. The Mobile also has to pre-synchronise and decode the BSIC of the serving cell once in 30 s. The list of the Adjacent cells (six best adjacent cells) is updated every 60 s, and if a new cell appears in the list, the Mobile has to decode the BCCH of this new cell in 30 s.

In Idle mode, the Mobile has enough time to measure the adjacent cells, because there is no traffic between Mobile Station and Base Station. Actually, the Mobile measures the serving cell only when the Base Station sends paging messages to the paging group of Mobile Station.

In summary, MS Measurements in Idle Mode (GSM Specs) are

MS has to decode BCCH of serving (camped)cell every 30 s

MS has to decode BCCH of 6 best neighbours cells at least every 5 min

Pre-synchronization and BSIC-decoding of 6 best neighbours cells

Once in 30 s

List of 6 best neighbours is updated every 60 s

New neighbour

BCCH decoding in 30 s

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2.3 Mobile Station Measurements In Dedicated Mode

In the Dedicated mode, channel measurements of the mobile station occurs over an SACCH interval, which comprises of 104 TDMA Frames in the case of TCH channel. The Mobile Station does not have so much time to make adjacent cell measurements, because the Mobile has to transmit and receive data to and from the serving Base Station, as shown in Figure 2.

• Measures the Lev and Qual of the Server

• Detects whether DTX is used

26-FRAME MULTIFRAME 120 ms

TDMA FRAMES:

TCH SACCH IDLE

• Measures the BA frequencies (System Info 5)

• BSIC decoding of at least one neighbour

• Pre-Synchronization on SCH

TDMA FRAME 4.615 ms

SACCH PERIOD = 480 ms

RX TX RX TX RX TX

MEAS

MEASMEAS

Figure 2. Mobile Station Measurements in Dedicated mode

The Mobile Station measures the receiving level of the serving cell and receives data from serving cell simultaneously. When receiving the data from the serving Base Station, the Mobile also detects if DTX is used or not. After receiving the data, the Mobile in its turn transmits data to the serving Base Station. After transmitting and before receiving the next frame, the Mobile has a short time to measure the adjacent cell frequencies. The Mobile gets a list of them on System Info 5. During the idle slot, the Mobile has a longer time to make the adjacent cell measurements, and during this time, the Mobile pre-synchronises itself to the frequency of the adjacent cell and tries to decode the BSIC of the adjacent cell.

In Dedicated mode the Mobile has to pre-synchronise and decode the BSIC of the adjacent cells once in 10 s. When a new adjacent cell is taken in the list, pre-synchronisation and BSIC decoding has to happen in 5 s. If it is not successful, the Mobile will use the old neighbour list and again try to decode the BSIC of the new adjacent cell.

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The Mobiles sends a list of the six best adjacent cells every half second (exactly every SACCH period, i.e. 480 ms) to the Base Station, which pre-processes and sends the measurement results to the Base Station Controller (BSC).

In summary:

Pre-synchronization and BSIC-decoding of adjacent cells once in 10s

New neighbour

5s decoding BSIC + Pre-synchronization

If not successful -> Old neighbour list + New try

Measurement results of 6 best neighbours sent to BSC every SACCH period 480 msec

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3 Measurement Processing

The measurement reports transmitted by the BTS and MS need to be processed further before they can be used by handover and power control algorithms. Most measurement processing takes place in the BSC. However, some pre-processing, to reduce signalling and processing the load in the BSC, is carried out by each BTS.

Measurements Measurements

BtsMeasAverage

AveragingWindow SizeAdjCellAllAdjacentCellsAveragedNumberOfZeroResults

AveragingAveraging

AveragingAveraging

BookkeepingBookkeeping

ho/pc_Averaging_Lev/Qual_UL/DLWindowSize

WeightmsDistanceAveragingParameter

WIndowSize

DTXMode

Measurements Measurements

Handover ?

EnaFastAveCallSetupEnaFastAvePCEnaFastAveHOMS + BTS

MS

BSC

Figure 3. Measurement Processing

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3.1 Measurement Pre-Processing In BTS

Pre-processing is the task of the BTS and means that the measurement results (both uplink and downlink) can be averaged over 1, 2, 3 or 4 SACCH periods. This averaging is carried out to reduce the signalling load and the BSC processing load. Reducing the signalling load is necessary in the A-bis interface where 16-kBit signalling is used.

The parameter btsMeasAver (BMA)(BTS) is used to set the number of SACCH periods used for the averaging process. If this parameter is set to 1, then pre-processing (averaging) is not performed at the BTS.

Pre-processing also causes delay (btsMeasAver-1) x 480 ms in the final measurement processing in the BSC.

btsMeasAver 1 ... 4 SACCH

Parameter Value

• For MS and BTS measurements

• Average measurements over 1, 2, 3 or 4 SACCH-period

• Cause a delay (btsMeasAver-1) x 480 ms

• Reduce a transmission load and a processing load in BSC

• Needed in Abis interface when 16 kbit signalling is used with Half Rate

(decreases load on A-bis - not a sliding window process)

Figure 4. Pre-processing in the BTS

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3.2 Averaging And Sampling In BSC

After the pre-processing, the results are sent to the BSC where the final processing is carried out. An important phase in the processing in the BSC is averaging and sampling.

Averaging can be controlled by the parameters:

ho/pcAveragingLev/QualDL/UL which included

windowSize (1 .. 32):

weighting (1 .. 3): which tells how samples are averaged and weighted due to the DTX

msDistanceAveragingParam (MSWS)(HOC) for handover due to distance

Averaging is done after each measurement result (after each SACCH period) so that the averaging window is sliding. An example of the averaging process is shown in Figure 5. The parameters used in this example are given below. In this example, no pre-processing is performed at BTS, which means that all averaging is performed at BSC. The first average is worked out after 5 measurements are received, as the window size is 5. This average (40) is above the Handover Threshold Level of 33 dBm, so the P value is set to 0. This averaging process is repeated on the next 5 measurements resulting in an average of 35dBm. Px represents the number of parameters that have to be lower than or equal to a threshold before handover or power control is initiated. Thus after 3 averages in which P=1 has been observed, a handover attempt can be initiated.

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HoThresholdLevDL = 33 (= -77 dBm) WindowSize = 5, Weighting = 1Px = 3, Nx = 4btsMeasAver = 1 (no pre-processing in BTS)

30 2550 3545 40 1520 10

480 ms AVERAGE=40, P=0

AVERAGE=35, P=0

AVERAGE=30, P=1

AVERAGE=25, P=2

AVERAGE=20, P=3

Handover trigger

ho/pc_Averaging_Lev/Qual_UL/DL WindowSize………………1 … 32 Weight………………1 … 3

msDistanceAveragingParameter WindowSize………………1 … 32

Parameter Value

Figure 5. Averaging and Sampling

3.3 Fast Averaging for Handover

Fast averaging for handover is a feature that became available in software release S6. As the cells become smaller and smaller (microcells), a faster handover algorithm is needed. The need for a quick handover decision, particularly in a handover between adjacent microcells, resulted in the development of this technique.

This method allows faster handover decisions especially where power control commands are normally being executed. The newer method is an alternative, it is based on the existing handover algorithm and parameters, and even the same values can be used.

The newer handover measurement averaging method for serving cell can be used the following situations:

a) In the call setup phase (SDCCH) by enabling the parameters:

enaFastAveCallSetup (EFA)(HOC)(Yes/No)

b) After a power control command by enabling the parameter:

enaFastAvePC (EFP)(HOC)(Yes/No)

c) At the start of a new channel (TCH) by enabling the parameter:

enaFastAveHO (EFH)(HOC)(Yes/No)

The newer handover measurement-averaging method for neighbouring cell measurements is always used and is very useful for IUO and DR.

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After a PC command the power control comparison is started again, but handover comparison is continued and only measurements before PC are initialised. The trigger thresholds remain and a newer averaging method is used, as in Figure 6, which shows the difference between the older and newer methods.

DL power control (RR)

0 1 1 1 0...

0 1 1 1 0...Px 4Nx 60 1

DL handover (RR)

DL power control (RR)

0 1 1 1 0...

0 0 0 0 0...Px 4Nx 60 1

DL handover (RR)

1 1 10 0

a. New method

b. Old method

0 = HO threshold not triggered1 = HO threshold triggered

Old triggered thresholds

Triggered thresholds after PC

Figure 6. Initialisation of the triggered thresholds

The existing Handover & Power Control algorithm uses a sliding window technique in order to average the measurements. The sliding window technique takes into account up to a maximum of 32 most recent measurement samples. The averaging procedure can start as soon as possible as the required number of samples is available.

However, in some cases, it is reasonable to calculate the averaging value before the measurement averaging window size is fulfilled.

The newer technique enables the Handover & Power Control algorithm to calculate averaging values beginning from the first measurement, and enables reliable averaging values for the handover algorithm (e.g. for Channel Allocation to Super-reuse Channel in IUO-feature (C/I calculation)). The following example (Figure 7.) presents the newer method.

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Figure 7. Newer averaging method

The newer averaging method averages new measurements before the averaging window size is fulfilled as an average value of new measurements. By using this method new measurements can be averaged although the averaging window size is not fulfilled The newer method enables faster handover decisions and prevents consecutive PC commands where handover is needed. After the averaging window is fulfilled, the averaging algorithm works as before (the average window is used).

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Nokia's Fast Averaging for Handover feature introduces a new handover algorithm capable of makingfaster handover decisions in environments where quick decisions need to be made, e.g. handoversbetween neighbouring microcells.

Feature Evaluation

• Algorithm based on existing handover algorithm and parameters

• After a handover the averaging process can start as soon as the first measurement is received from the new cell without having to wait for the averaging window to fill up before the first averaged measurement is available for the comparison process

• Measurements are averaged over the number of measurements available

• Algorithm works until the averaging window is full after which the normal sliding window technique is re-employed

AVERAGE = -72

Handover executed

AVERAGE = -73

AVERAGE = -72

AVERAGE = -72

-73 -70 -73 -77 -79 -74 -69 -65 -67 -68 -70 -73

AVERAGE = -79/1

AVERAGE = (-79 + -74)/2

AVERAGE = (-79 + -74 + -69)/3

Normal slidingwindow averagingprocess resumes

Averaging window full

n(x)=3

n(x)=1

n(x)=2

Figure 8. Enable Fast Averaging for Handover

Nokia's Fast Averaging for Power Control feature use a new handover algorithm capable of (i)introducing fast averaging for signal quality measurements and (ii) scaling of signal levelmeasurements, just after the increase/decrease in MS/BTS power

Feature Evaluation - Scaling of Signal Level

• BSC scales the signal level measurement results preceeding the power change so that they correspond to the new power level of the MS/BTS. (e.g uplink signal level measurements scaled by 4dB after MS pc step of 4dB)

• BSC does not need to start averaging of signal level measurement results from the beginning - process can continue without interruption

• Handover threshold comparison continues without interruption - PC threshold comparison starts from beginning

• Feature enabled using enaFastAveraingPC parameter

AVERAGE = -79 : p=0

PC step due to RXLEV (4dB inc.)

AVERAGE = -81 : p=1

-78 -80 -81 -83 -79 -78 -76 -75 -73 -76 -77

pcLowerThresholdLevUL = -80dBmnx(1) : px(1)

AVERAGE = -78 : p=0

AVERAGE = -79 : p=0

AVERAGE = (-77 + -79 + -79)/3

AVERAGE = (-79 + -79 + -78)/3

Preceeding measurementsscaled by 4dB

Averaging process continueswithout

interuption & pc thresholdcomparison

process starts again

Figure 9. Enable Fast Averaging for PC

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Nokia's Fast Averaging for Power Control feature use a new handover algorithm capable of (i)introducing fast averaging for signal quality measurements and (ii) scaling of signal levelmeasurements, just after the increase/decrease in MS/BTS power

Feature Evaluation - Fast Averaging of Signal Quality

• BSC initialises signal quality measurements preceeding MS/BTS pc step and starts averaging process from beginning using fast averaging

• Averaging process can start as soon as the first measurement after pc step is received without having to wait for the averaging window to fill up before the first averaged measurement is available for the comparison process

• Handover threshold comparison continues without interruption - PC threshold comparison starts from beginning

• Feature enabled using the enaFastAvePC parameter

AVERAGE = 2

PC step due to RXQUAL

AVERAGE = 1

AVERAGE = 0

AVERAGE = 2

3 0 1 1 2 0 0 1 3 6 7 7

AVERAGE = 2/1

AVERAGE = (2 + 0)/2

AVERAGE = (2 + 0 + 0)/3

Normal slidingwindow averagingprocess resumes

Averaging window full

Figure 10. Enable Fast Averaging for PC

•Length of averaging window size is changed according to MS speed information•Fast mobile has short averaging window size -> mobiles may hand over to target cell faster•Slow mobile has long averaging window size

msSpeedDetectionStatemsSpeedDetectionState0:0: ho between macro - ho between macro -

micro layermicro layer1.. 100:1.. 100:the scaling factor for the scaling factor for

averaging window size (%).averaging window size (%).

slow MSs

Slow mobile

Fast mobile

Time

CellBTS

fast MSs

BSC

BTS

meas_res

meas_res

4

2

Scaling is 50%

Figure 11. Various Window Sizes with MS_SPEED_DETECTION

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The BSC may use the information on the speed of the mobile station to do the followingby means of the parameter MsSpeedDetectionState:

0 MS speed information is used to control traffic between separate layers

1 - 100 MS speed information is used to scale the values of the averaging parameters. The range is from 1% to 100%. That is, if the value is, forexample, 80% it means that the averaging window is 80% of the normalwindow size.

Figure 12. Parameter Range

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4 DTX And Weighting

When DTX is used, only "SUB" measurement results are reported to the BSC, which means that averaging is done over 12 time slots (or 3 data blocks). This "SUB" measurement averaging process is controlled by the parameter weighting (1 .. 3) as in the following example.

• DTX is allowed just on TCH (only for speech call, not for data call)

• “SUB”- measurement results are reported when DTX is used

AV_RXLEV_UL_PC = 2x35 + 1x42 + ... + 2x35 2+1+2+2+1+1+1+2

= 36

Sample: 1 2 3 4 5 6 7 8

DTX used: 0 1 0 0 1 1 1 0

uplink level: 35 42 33 36 39 40 39 35

pcAveragingLevULwindowSize = 8weighting = 2

DTXMode 0 MS may use DTX1 MS shall use DTX2 MS shall not use DTX

Parameter Value

Figure 13. DTX and Weighting Example

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5 Processing and Book Keeping In BSC

The BSC gets all the serving cell and adjacent cell measurement results from the BTSs after pre-processing. It makes averaging calculations and comparisons to thresholds such as the parameter hoThresholdsLevDL (-110- -47 dBm), including px (1. 32) and nx (1 .. 32). Threshold comparisons are always made in the BSC as a part of the BSC processing. All the handover and power control thresholds will be given in the subsequent Modules on Handover Processing and Power Control.

The capacity of the BSC is related to the number of the adjacent cells processed in the BSC simultaneously. The Nokia BSC can simultaneously maintain measurements from up to 32 samples of 32 different adjacent cells. This is referred to as book keeping. All the adjacent cells can be averaged, or just the six best ones controlled by the parameter:

allAdjacentCellsAveraged (AAC)(HOC)(Yes/No)

The BTS sends only the six best measurement results to BSC, and the rest is being given a zero level (-110 dBm). Thus, even some good adjacent cells can be given a zero result, as shown in the example below. These adjacent cells however can still be taken into account (up to 7 zero results) with the parameter

numberOfZeroResults (NOZ)(HOC)(0 .. 7).

• BSC is able to maintain up to 32 last measurement results of 32 adjacent cells

• Mobile reports to BSC 6 best results and the rest are 0 (= -110 dBm)

• Zero results can be eliminated from averaging ( up to 7 )

• All adjacent cells can be averaged or just 6 best (reported by the MS in lastmeasurements)

averagingWindowSizeAdjacentCells 1 … 32numberOfZeroResutlts 0 … 7allAdjacentCellsAveraged Y / N

Parameter Value

Example

allAdjacentCellsAveraged = NonumberOfZeroResults = 2WindowSize = 8

Sample: 1 2 3 4 5 6 7 81 -65 -67 -71 -69 -72 -70 -73 -712 -73 -75 -74 -75 -76 -77 -75 -773 -77 0 -80 -79 -81 -79 0 -804 -85 -83 -87 -88 -84 0 -86 -875 -90 -94 -91 -90 -95 -93 -92 -906 -97 -99 -98 -99 -96 -97 0 0

Figure 14. Book Keeping

Now, even if there are two zero results in the samples of the adjacent cell 3, the average of that cell can still be calculated, and the cell remains in the group of the six best adjacent cells.

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• MS DATA (MEASURED BY BTS)

0 1 0 0

3 2 2

0 0 1

3

1 0 1 0

54

0 0

5 4 4 4 4 5 6

56545450

0 0 0

485145

2

43474441

00

3632

2 1 0 3 0 4 5

1 1 1 0

5 6 7 6

33302832

5 1 0 0

0 0 0 0 1 1 1 0 0 0 0 0 0

54545252

0 1 0

464840

0

42444445

00

4035

1 2 2 3 5 6 4

0 0 0 0

33343536

4 3 2 2

4049484645434240403938

025303232403842444348506058565456

3335384042444851535456LEV_NCELL(n)

AV_RXLEV_NCELL(n)

• BTS DATA (MEASURED BY MS)

• ABTS DATA (MEASURED BY MS)

DTX USEDQUAL_DLRXLEV_DLAV_RXLEV_DL_HO

DTX USEDQUAL_ULRXLEV_UL

TIMING ADVANCE EXAMPLES:

1. HO AVERAGING AND COMPARISON

Window Size = 8, Weighting = 2

HoThresholdLevDL = 38 (-72 dBm), Px = 1 Nx = 1

2. ABTS AVERAGING AND PBGT COMPARISON

WindowSizeAdjaCell = 7

hoPeriodPBGT = 8 SACCH (= 4 s)

hoMarginPBGT = 6 dB

Figure 15. BSC Measurement Data Processing

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6 FER Measurement Feature

FER measurement provides an ability to report the UL FER from the BTS to the BSC. This provides more realistic measure of voice quality in the system and enables to perform handovers and power control based in FER rather than BER-based RxQuality. This feature can then provide more capacity and better quality.

Additionally, DL FER is estimated using the correlation between UL FER and UL BER values and applying these to the DL BER values. Both UL FER values and estimated DL FEP (Frame Erasure Probability) values are available in the new FER measurement. In addition to handover and power control algorithms, feature provides also significant improvements to network quality statistics.

Frame Erasure Rate is the best available indicator in a GSM system to assess the Voice Quality provided in a network. It represents the percentage of frames being dropped due to high number of non corrected bit errors in the frame.

The BER figure currently reported to the system is not a good indication of the quality of the network, especially when efficiency of the error correction mechanism changes due to functionality introduced in the network such as frequency hopping or dynamic channel coding:

Frequency Hopping spreads out the fading and interference problems, effectively allowing the decoding mechanism to restore the original information via the Error Correction process. Not only the correlation between BER and FER will change when Frequency Hopping is in use, but different frequency hopping schemes (depending in the reuse and number of frequencies to hop over) will have a different BER to FER correlation. The figure below shows this effect measured in an operational network for the DL path. The area of interest is the one showing the correlation of RXQUAL 4 to 6 and the voice quality degradation (FER>5%).

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Figure 16. RX Quality / FER Correlation for hopping and non-hopping cases

The Channel Coding algorithm in use has a direct impact in the Error Correction performance. Depending how robust the channel coding is, it associated performance will vary. A clear example of this will take place when different coding schemes are implemented simultaneously in AMR networks. Again the correlation between BER and FER will change, and this time it will potentially do it dynamically according to the conditions.

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7 Key Learning Points

The Mobile Station and Base Station perform measurements as part of the Radio Subsystem Link Control. These measurements include received signal level and channel quality. The measurements are sent to the BSC via BTS.

The Base Station is continuously measuring all the time slots in the uplink direction in every TRX.

The MS measurements can be classified into:

(a) Idle mode measurements, which are primarily used to select the best base station from the neighbourhood.

(b) Dedicated mode measurements, which are used for handover and power control purposes.

GSM uses two parameters to describe the levels and quality of a channel:

Received Signal Level (RXLEV), is measured by MS and BTS in each burst and expressed in dBm. It has a range of -110 dBm to -48 dBm

Received Signal Quality (RXQUAL), is measured as Bit Error Rate (BER) percentage before any error correction techniques are applied

In idle mode, the Mobile receives information of the frequencies of the adjacent cells, which is sent on BCCH. The Mobile has to decode the BCCH of the serving cell every 30 s, and the BCCH of the adjacent cells every 5 min. The Mobile also has to pre-synchronise and decode the BSIC of the serving cell once in 30 s. The list of the Adjacent cells (six best adjacent cells) is updated every 60 s, and if a new cell appears in the list, the Mobile has to decode the BCCH of this new cell in 30 s.

In Dedicated mode the Mobile has to pre-synchronise and decode the BSIC of the adjacent cells once in 10 s. When a new adjacent cell is taken in the list, pre-synchronisation and BSIC decoding has to happen in 5 s. If it is not successful, the Mobile will use the old neighbour list and again try to decode the BSIC of the new adjacent cell.

The Mobiles sends a list of the six best adjacent cells every half second (exactly every SACCH period, i.e. 480 ms) to the Base Station, which pre-processes and sends the measurement results to the Base Station Controller (BSC).

Pre-processing at BTS is carried out to reduce the signalling load and the BSC processing load. The BTS parameter btsMeasAver (BMA)(BTS) is used to set the number of SACCH periods used for the averaging process. If this parameter is set to 1, then pre-processing (averaging) is not performed at the BTS.

Averaging at BSC is done by computing the average of window size measurement samples from BTS with appropriate weighting if DTX is used. Averaging can be performed for handover and power control, receiver levels and quality, downlink and uplink. It can be controlled by the following parameters:

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ho/pcAveragingLev/QualDL/UL which includes

windowSize (1 ... 32):

weighting (1 ... 3): which tells how samples are averaged and weighted due to the DTX

msDistanceAveragingParam (MSWS)(HOC) for handover due to distance

The fast averaging method averages measurements as they are received before the window size is filled with measurements. The new method enables faster handover decisions and prevents consecutive PC commands where handover is needed. After the averaging window is filled, the conventional averaging algorithm starts working.

Fast averaging is used for a number of tasks using the following parameters:

enaFastAveCallSetup (EFA)(HOC)(Yes / No): for call set-up phase

enaFastAvePC (EFP)(HOC) (Yes / No): for power control command

enaFastAveHO (EFH)(HOC)(Yes / No):

When DTX is used, only "SUB" measurement results are reported to the BSC, which means that averaging is done over 12 time slots (or 3 data blocks). This "SUB" measurement averaging process is controlled by the parameter weighting (1 .. 3).

Pre-processed BTS data is sent to BSC, which makes averaging calculations and comparisons to thresholds. Nokia BSC can simultaneously maintain measurements from up to 32 samples of 32 different adjacent cells. All the adjacent cells can be averaged or just the six best ones controlled by the parameter allAdjacentCellsAveraged (AAC)(HOC)(Yes/No).

BTS sends only the six best measurement results to BSC, with the rest being given a zero level (-110 dBm). These adjacent cells however can still be taken into account using parameter numberOfZeroResults (NOZ)(HOC)(0 .. 7).

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btsMeasAver 1 ... 4 SACCH

Parameter Value

ho/pc_Averaging_Lev/Qual_UL/DL WindowSize……………… 1 … 32 Weight…………………… 1 … 3

msDistanceAveragingParameter WindowSize……………… 1 … 32 SACCH

EnaFastAveCallSetup Y / NEnaFastAvePC Y / NEnaFastAveHO Y / N

DTXMode 0 MS may use DTX1 MS shall use DTX2 MS shall not use DTX

averagingWindowSizeAdjacentCells 1 … 32numberOfZeroResutlts 0 … 7allAdjacentCellsAveraged Y / N

Figure 17. Parameter Overview

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8 Review Questions

Q1. Which of the following measurements are performed by the MS? …...

(a) Idle mode measurements to select the best base station.

(b) Dedicated mode measurements, which are used for handover and power control purposes.

(c) Averaging measurements to reduce load on the BTS.

(d) All of the above.

(e) Choices (a) and (b) only.

Q2. Which of the following is measured as BER?

(a) Received Signal Level (RXLEV)

(b) Received Signal Quality (RXQUAL)

(c) Voice quality.

(d) Handover failure rate.

(e) All of the above choices.

Q3. Which of the following is true in idle mode?

(a) The Mobile has to decode the BCCH of the serving cell every 30 s.

(b) The Mobile has to decode the BCCH of the adjacent cells every 5 min.

(c) The Mobile has to pre-synchronise and decode the BSIC of the serving cell once in 30 s.

(d) The Mobile has to decode the BCCH of every new cell in 30 s.

(e) All of the above.

Q4. Which of following is true about measurement pre-processing at the BTS?

(a) It is carried out to reduce the BTS signalling and processing load.

(b) The BTS parameter btsMeasAver (BMA)(BTS) is used to set the number of SACCH periods used for the averaging process.

(c) If btsMeasAver (BMA)(BTS) = 1, then weighted averaging is performed.

(d) All of the above.

(e) Choices (a) and (b) only.

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Q5. Which of the following dictates how many samples are used for averaging at the BSC?

a) ho/pcAveragingLev/QualDL/UL which includes

b) windowSize (1..32):

c) weighting (1..3):

d) msDistanceAveragingParam (MSWS)(HOC)

e) Px

f) All of the above.

Q6 What is the purpose of the fast averaging method?

a. It averages measurements as they are received before the window size is filled with measurements.

b. It enables faster handover decisions and prevents consecutive PC commands where handover is needed.

c. After the averaging window is filled, the conventional averaging algorithm starts working.

d. It is faster than the conventional algorithm.

Q7. Which of the following parameters are associated with fast averaging?

a) ho/pcAveragingLev/QualDL/UL

b) btsMeasAver (BMA)(BTS)

c) enaFastAveHO (EFH)(HOC)(Yes/No):

d) All of the above.

e) None of the above.

Q8. A Nokia BSC can average all 32 adjacent cells or just the six best ones controlled by the use of the parameter:

(a) allAdjacentCellsAveraged (AAC)(HOC)(Yes/No)

(b) numberOfZeroResults (NOZ)(HOC)(0..7)

(c) btsMeasAver (BMA)(BTS)

(d) enaFastAveHO (EFH)(HOC)(Yes/No)

(e) None of the above.

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BSSPAR- Measurement Processing

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