Alcatel Optimization

2.3 Radio measurements data processing neighbor cell measurement book-keeping ▼ BUILDING

A BOOK-KEEPING LIST OF NEIGHBOR CELLS

 The MS reports the measurements of the

NO_NCELL_M (≤ 6) best cells every multi-frame  The adjacent cells reported by the MS can change from one measurement to another  The book-keeping function keeps a table of the last 32 reported adjacent cells  Clearing process of non-reported neighbors during 10s (signal level=0)

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An MS is required to measure the BCCH power level of a number of BCCH frequencies. These measurements are used for the power budget computation in the BSC and the candidate cell evaluation in the BSC. The MS reports to the BTS, in the MEASUREMENT REPORT message, the measurements of the NO_NCELL_M (NO_NCELL_M <= 6) best cells it receives (RXLEV_NCELL, BCCH frequency index and BSIC number) for each multiframe. In case of multiband capability, the mobile reports the best cells of each supported frequency band (if available). This reporting is allowed at BSS level by the flag EN_INTERBAND_NEIGH and it is specified by the parameter MULTIBAND_REPORTING. The adjacent cells reported by an MS can change over the averaging interval. The book-keeping function keeps a table composed of the last 32 reported adjacent cells, the maximum number of which is NBR_ADJ. The total number of adjacent cells for which measurements reported by the MSs are available within the average interval is BTSnum. The BSC G1 maintains a table of up to 150 cells, from which up to 64 can be declared as adjacent cells to a given cell. The BSC G2 maintains a list of up to 1000 cells, from which up to 64 can be declared as adjacent cells to a given cell. Because the maximum number of adjacent cells may be greater than 32, the number of adjacent BCCH frequencies is limited to 32. Moreover, a mechanism for overwriting obsolete entries in the bookkeeping table, when new cells are reported, is provided. When the variable BTSnum reaches its maximum value of 32 and at least one new cell has to be entered in the list, then the BSC sorts out all cells in the bookkeeping list, which have been reported with signal level = 0 for the last 20 measurements (10 seconds). This is done by summing the raw measurement values over the last 20 samples. All the corresponding cell entries are cleared from the bookkeeping list, BTSnum is decreased by the number of cleared entries and some of the vacant entries are used to include the new cells. The end of the comment is on the next page...

© Alcatel University - 8AS902001485 VH ZZA Ed 02

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2.3 Radio measurements data processing Training exercise  Measurements averaging With ‘averaging window’ excel

sheet... • Compute averaging on quality, distance and level • Make charts with different sliding averaging windows

Time allowed: 10 minutes 1.62 w

Fill up the table with average function. The chart will be automatically processed

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The fact that there may not be enough cleared entries to store new measurements is excluded, see justification below: Because the MS must resynchronize at most every 10s with the neighbor cells it monitors, it is useless to keep cells in the bookkeeping list which have not been reported for more than 10s, it will be impossible to makkes an handover towards these cells. Therefore, the overwriting mechanism described above will function correctly if there are less than 32 cells reported in every 10s, which makes an average rate of 3 new cells per second. The potentiality of overflow of the book-keeping list is therefore excluded. The book-keeping is performed according to the BSIC and BCCH frequency couple. This function updates the table every multiframe except if the measurement report is missing or Measurement Valid Bit is set to not valid. When the level of a cell is not reported, a zero must be entered as measurement value. For each multiframe and for each of the NO_NCELL_M cell measurements it receives, the function has to check the BSIC number and the BCCH frequency index (FREQ(n)). When the couple (BSIC, BCCH frequency) is not in the reference list (received from the OMC), the corresponding measurements should be discarded. The BTSnum variable is updated every multiframe except if the measurement report from the MS is missing. It is incremented by the number of new couples (BSIC number, BCCH frequency index) registered as described above. Remark: Two cells can have the same BSIC number or the same BCCH frequency index. Therefore, the couple of these parameters is needed to define a cell.

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2 ALGORITHMS AND ASSOCIATED PARAMETERS 2.4 Radio Link Supervision and Power Control

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© Alcatel University - 8AS 90200 1485VH ZZA Ed.02

Theoretical presentation Radio measurements principles Radio measurements data processing Radio Link Supervision and Power control Handover Detection Handover Candidate Cell Evaluation Handover Management Exercise


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2.4 Radio link supervision and power control Functional entities

BTS

BSC

Radio Link Supervision

Radio Link Measurements

Radio Link Command

Active Channel Pre-processing

PC Threshold Comparison

PC Command

Assignment of PC functions in the ALCATEL BSS

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The two main functions specified in this document and implemented in the ALCATEL BSS are:  Radio link supervision and radio link comman d:  These functions handle the detection of the radio link failure so that calls which fail either from loss of radio coverage or unacceptable interference are satisfactorily handled by the network. The radio link supervision is responsible for detection of the loss of the radio link, based on incorrectly received SACCH frames. The radio link command is responsible for commanding to set the power at a maximum level for radio link recovery or to clear the call when the radio link has failed.  The radio link recovery can be activated or not, depending on a configuration flag (EN_RL_RECOV). The radio link failure procedure is always running and clears the call when the radio link has failed.  Power control:  This function handles the adaptive control of the RF transmit power from the MS and the BS. The RF

power control aims at minimizing the co-channel interference and also at reducing the DC power consumption of the MS. This function is in charge of detecting a need for a power command and then of applying this power command. Therefore it can be divided into two processes: PC threshold comparison and PC command. MS and BS power control are operating independently, they can be activated or not, depending on configuration flags (EN_MS_PC and EN_BS_PC). w w

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All these functions require directly or indirectly input parameters provided by the function in charge of the radio link measurements. Most of the input data required by the power control functions are provided by Active channel pre-processing function. The figure depicts in a general way:  the interconnections between all these functions,  the implementation of these functions in the ALCATEL BSS.


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1 TYPICAL RADIO PROBLEMS Session presentation ▼ Objective:

to be able to characterize typical radio problems in order to trigger an intervention of the appropriate team

▼ Program:

1.1Theoretical presentation 1.2 Coverage problem 1.3 Interference problem 1.4 Unbalanced power budget problem 1.5 TCH Congestion problem 1.6 Deducing the right team for intervention 1.7 Exercises

1.4 S1: TYPICAL RADIO PROBLEMS S2: ALGORITHMS AND ASSOCIATED PARAMETERS S3: OMC-R RADIO PARAMETERS S4: ALGORITHMS DYNAMIC BEHAVIOR S5: CASE STUDIES


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2.4 Radio link supervision and power control Radio link supervision ▼

Principles  Detection (by BTS) of a radio link failure with an MS  notification to BSC for radio resource release  Try to recover an MS when radio becomes poor  optional mechanism “radio link recovery”  by requiring BTS and MS to transmit at maximum power  Equivalent mechanism in MS for Radio Link Failure detection

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The determination of the radio link failure is based on a counter. According to the GSM Technical Specification 05.08 for the BSS, the criterion for incrementing/decrementing this counter should be based:  either on the error rate on the uplink SACCH,  or on RXLEV/RXQUAL measurements of the MS. In the ALCATEL BSS, it is based on the number of SACCH frames which cannot be decoded. It must be stressed that this criterion is related to the first one recommended above but it is not exactly the same. The ALCATEL criterion is in fact the one recommended by the GSM Technical Specification 05.08 for the MS.


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2.4 Radio link supervision and power control Principles of radio uplink supervision  For each active radio channel, a counter “S” is  decremented by 1 each time an SACCH frame

cannot be decoded (BFI=1)  incremented by 2 each time a valid SACCH

frame is received

 The value of S gives a measure of the “quality”

S B _ O T L R

of uplink radio link

18 16 SACCH block lost: - 1

 Initial value of S = BS_RADIO_LINK_TIMEOUT  if S reaches N_BSTXPWR_M, a radio link

recovery is triggered (optional)  if S reaches 0, a radio link failure is detected

 RADIOLINK_TIMEOUT_BS ≥

RADIOLINK_TIMEOUT is important because the mobile must release the radio channel first.

) 0 O 0 T L 1 T R (

M _ R W P X T _ S B _ N

13 Radio link Recovery

SACCH block received: + 2

S

S 0

0 Radio link Failure

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The radio link supervision function is performed in the BTS and it uses three parameters given to the BTS in the TRX configuration data message:  EN_RL_RECOV: flag enabling/disabling the sending of CONNECTION FAILURE INDICATION by the BTS when the need for radio link recovery is detected,  N_BSTXPWR_M: threshold for the radio link recovery,  RADIOLINK_TIMEOUT_BS: threshold (number of SACCH messages) for the radio link failure.

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In addition, the function handles a counter named S. RADIOLINK_TIMEOUT_BS is the initial and maximum value of S.  For each SACCH not decoded, S is decremented by 1 while for each SACCH decoded, it is incremented by 2. The incrementation or decrementation is performed if the following condition is met: RADIOLINK_TIMEOUT_BS >= counter S >= 0.  As soon as the counter S is equal to the threshold N_BSTXPWR_M, the radio link recovery is triggered if EN_RL_RECOV = ENABLE. Therefore, in the case where the shadowing is so strong that all SACCH frames are lost, the radio link recovery will be triggered after (RADIOLINK_TIMEOUT_BS - N_BSTXPWR_M) SACCH periods.

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The parameter N_BSTXPWR_M must be set according this simple behavior. If the radio link recovery is not successful, as soon as S reaches 0, the radio link failure procedure is applied. As soon as a radio link failure is detected, the radio link supervision must be started again in the BTS.

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2.4 Radio link supervision and power control S counter for radio link supervision

S = f [ BFI(t) ]

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RADIO_LINK_TIMEOUT_BS

N_BSTXPWR_M 15

e u l a v

BFI S

S

10

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0 1

3

5

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13 15 17 SACCH number

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Received events 

Activate supervision: activation of the radio link supervision from the BTS telecom layer 3,

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SACCH, BFI = 1: not decoded SACCH frame,

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SACCH, BFI = 0: decoded SACCH frame,  Note: the BFI flag is internal to the BTS and does not deal with the BFI flag defined by the GSM.

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Deactivate supervision: deactivation of the radio link supervision by the BTS telecom layer 3.

Transmitted events 

Radio link recovery: indication sent to the radio link command function in order to set the BS and MS powers to

the maximum. 

Radio link failure: indication sent to the radio link command function in order to release the call.

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These events are sent to the BSC in the CONNECTION FAILURE INDICATION message:  In case of Radio link recovery, the BTS sends only once (to avoid overload of the Abis interface) the CONNECTION FAILURE INDICATION message to the BSC with cause "set MS/BS-TXPWR-M” (value: '001 1111', reserved for National use). This action (message formatting) is performed by the GSM layer 3.  In case of Radio link failure, the BTS sends the CONNECTION FAILURE INDICATION message with cause 'Radio link Failure' to the BSC.

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Thus, the CONNECTION FAILURE INDICATION message on Abis is not showing any call drop. One should look at the cause of CONFAIL.


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2.4 Radio link supervision and power control Radio link recovery ▼ The

BTS is sending a Connection Failure Indication message  cause ‘001 1111’ reserved for national usage

(ALCATEL: RLR)  On K1205: “set MS/ BS_TXPWR_MAX (Alcatel only)” ▼ The

BSC is sending BS and MS POWER CONTROL messages  required for maximum possible values  The MS required level is embedded in the SACCH

header in the downlink ▼ Optional

mechanism

 EN_RL_RECOV =ENABLE  useless without power control  “master” vs. power control 1.68 w w

The action consists in increasing the power of the MS and of the BTS to their maximum, in a single step, if the link is failing, i.e. the BTS is not able to decode the SACCH anymore for some period of time. This functionality is performed upon reception of the CONNECTION FAILURE INDICATION message (cause “set MS/BS-TXPWR-M”) from the BTS. This message can be sent by the BTS only if EN_RL_RECOV = ENABLE. Upon reception of this message, the radio link command function: 1. sends to the BTS a power increase command up to BS_TXPWR_MAX (BS_TXPWR_MAX_INNER if the MS is on the inner zone of a concentric or multiband cell) in the BS POWER CONTROL message. 2. sends to the MS a power increase command up to min(MS_TXPWR_MAX,P) (min (MS_TXPWR_MAX_INNER,P) if the MS is in the inner zone of a concentric or multiband cell) in the message MS POWER CONTROL.

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When a radio link recovery occurs, the radio link command function gives an indication to the power control function once the power increase has been commanded.

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The maximum power increase of the MS is 2dB per 60 ms. Thus, if MS_TXPWR_MAX=33dBm and MS_TXPWR_MIN=13dBm, the MS coming from MIN to Max will take 600 ms.


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Alcatel Optimization

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