05.083GPPRadio subsystem link controlTS
11.1 CTS idle mode tasks
Whilst attempting to attach to a CTS-FP, a CTS-MS shall implement the CTS cell selection procedure described in 3GPP TS 03.22. This procedure makes use of measurements and sub‑procedures described in this clause. The procedure ensures that the CTS-MS is CTS attached to a CTS cell from which it can reliably decode downlink data and where access to CTS service is allowed.
Whilst in CTS idle mode, the CTS-MS shall implement procedures reporting to the CTS-FP (AFA monitoring, BCCH detection and OFO measurement), described in 3GPP TS 03.22. These procedure makes use of measurements and sub-procedures described in this clause, and are used for the frequency control of the system, described in 3GPP TS 05.56 and 3GPP TS 05.10.
This clause makes use of terms defined in 3GPP TS 03.22.
For the purpose of CTS cell selection, the CTS-MS shall be capable of detecting and synchronizing to a CTSBCH carrier and read the CTSBCH-SB data at reference sensitivity level and reference interference levels as specified in 3GPP TS 05.05. A CTS-MS in CTS idle mode shall always fulfil the performance requirement specified in 3GPP TS 05.05 at levels down to reference sensitivity level or reference interference level.
For the purpose of CTS cell selection, the CTS-MS shall compute an average of received signal levels for the CTSBCH carrier. This quantity called ‘received level average’ shall be unweighted average of the received signal level measured in dBm. The accuracy of the signal level measurements for CTS cell selection and the other idle mode tasks shall be the same as for radio link measurements.
The tolerance on all the timing requirements in this subclause is ±10 %.
11.1.1 CTS cell selection
220.127.116.11 Synchronization and measurements for CTS cell selection
The CTS-MS shall store the CTSBCH ARFCN for each CTS-FP the CTS-MS is enrolled with.
In the modes where CTS cell selection is required (see 3GPP TS 03.22), for each CTS-FP the CTS-MS is enrolled with, the CTS-MS shall periodically attempt to synchronize to the stored CTSBCH carrier. When attempting to synchronize to the CTSBCH carrier, the CTS-MS shall attempt to detect the frequency correction burst of the CTSBCH-FB and when detected, to decode the synchronization burst of the CTSBCH-SB and read the CTSBCH-SB information. The CTS-MS shall calculate the received level average of the CTSBCH carrier, the averaging being based on at least five measurement samples taken on the CTSBCH bursts.
The maximum time allowed to synchronize to a CTSBCH carrier and read the CTSBCH-SB information shall be 5 seconds.
18.104.22.168 Initial sychronization of CTS-MS
In order to perform upper layer procedures, e.g. the enrolment of a CTS-MS (see 3GPP TS 04.56), a special procedure shall be implemented in the CTS-FP, by which the initial synchronization of a CTS-MS with the CTS-FP is eased. This procedure of initial synchronization of CTS-MS shall be triggered by the CTS upper layers.
The procedure consists in transmitting the CTSBCH in every TDMA frame with the following pattern :
if FN mod 52 = 25 then the CTSBCH-FB is transmitted
if FN mod 2 = 0 then the CTSBCH-FB is transmitted
if FN mod 2 = 1 then the CTSBCH-SB is transmitted
The first burst sent with this pattern shall be the next programmed CTSBCH-FB on the TDMA frame : FN mod 52 = 25. The above transmission pattern shall be repeated for a period of 120 52-multiframe. No CTSBCH shifting shall be allowed during the pattern: the CTSBCH timeslot number shall be the TNC, see 3GPP TS 05.02.
The CTS-MS shall attempt to synchronize to the CTSBCH transmitted with the above pattern. Once synchronized, the CTS-MS shall perform the non-hopping access procedure, e.g. for enrolment purpose (see 3GPP TS 04.56). Upon reception of the access request message by the CTS-FP, the pattern transmission shall be stopped.
11.1.2 Criterion for CTS cell selection
The path loss criterion parameter C1_CTS used for CTS cell selection is defined by:
C1_CTS = Received Level Average ‑ CTS_RXLEV_ACCESS_MIN
where: CTS_RXLEV_ACCESS_MIN = Minimum received level at the CTS-MS required for access to the system ; this parameter shall be given by the CTS-FP to CTS-MS during the enrolment procedure (see 3GPP TS 04.56) and shall be stored in the CTS-MS for each CTS-FP it is enrolled with. The parameter can be updated on request of the CTS-FP.
All values are expressed in dBm.
The path loss criterion (3GPP TS 03.22) is satisfied if C1_CTS > 0.
11.1.3 Monitoring of CTSBCH and CTSPCH
22.214.171.124 Monitoring of received signal level
Whilst in CTS idle mode, the CTS-MS shall measure the received signal level of the CTSBCH and shall calculate the received level average of the CTSBCH carrier, the averaging being a running average on at least five collected measurement samples and a maximum time of 11 seconds (5*9*52 frames). The criterion C2_CTS defined below shall be calculated every time the CTS-MS decodes the CTSBCH in its CTS paging group :
C2_CTS = C1_CTS + CTS_CELL_RESELECT_OFFSET
If the criterion C2_CTS falls below zero for a period of 15 seconds, the CTS-MS shall considered itself as de-attached with the CTS-FP and shall perform the CTS cell selection specified in subclause 11.1.1.
126.96.36.199 Downlink beacon failure
The downlink beacon failure criterion is based on the downlink beacon failure counter DBC. Whilst in CTS idle mode on a CTS cell, DBC shall be initialized to a value equal to the nearest integer to 90/N where N is the number of paging groups defined for the CTS-FP (see 3GPP TS 05.02 subclause 6.5.7). Thereafter, whenever the CTS-MS attempts to decode CTSBCH-SB information bits (see 3GPP TS 05.02): if the information bits are successfully decoded DBC is increased by 1, however never beyond the initial value, otherwise DBC is decreased by 4. When DBC 0, a downlink beacon failure shall be declared.
If a downlink beacon failure occurs, the CTS-MS shall consider itself as de-attached with the CTS-FP and shall perform the CTS cell selection specified in subclause 11.1.1.
188.8.131.52 Downlink paging failure
The downlink paging failure criterion is based on the downlink paging failure counter DPC. Whilst in CTS idle mode on a CTS cell, DPC shall be initialized to a value equal to CTSPCH_DECOD (this parameter shall be given by the CTS-FP to the CTS-MS during the attachment procedure, see 3GPP TS 04.56). Thereafter, each time the CTS-MS is required to decode a paging message on the CTSPCH (see 3GPP TS 05.02 subclause 6.5.1 ix)): if the paging message is not successfully decoded (BFI = 1) DPC is decreased by 1, otherwise DPC is re-initialized to CTSPCH_DECOD. When DPC 0, a downlink paging failure shall be declared.
If a downlink paging failure occurs, the CTS-MS shall consider itself as de-attached with the CTS-FP and shall perform the CTS cell selection specified in subclause 11.1.1.
11.1.4 Procedures with reporting to the CTS-FP
Whilst in CTS idle mode, the CTS-FP may order to the CTS-MS to complete the procedures defined hereafter. The order for each procedure is sent to the CTS-MS during a dedicated connection (see 3GPP TS 04.56).
For each of the procedures, a maximum time of processing is allowed. When multiple procedures are ordered in a single dedicated connection, the results shall be ready to be reported to the CTS-FP when the time corresponding to the sum of the maximum time of each procedure has expired.
184.108.40.206 AFA monitoring
The reporting of the AFA monitoring procedure is used by the AFA algorithm for the frequency management of the CTS (see 3GPP TS 05.56).
The parameters sent by the CTS-FP to the CTS-MS in the AFA monitoring order message shall be a list of n carriers : AFA monitoring frequency list, AMFL(1,…,n), together with the number of AFA monitoring cycles NAMC to perform.
For each carrier of the AMFL, the CTS-MS shall perform NAMC basic measurements, where a basic measurement shall be the average received signal level on the 8 timeslots of the TDMA frame. The delay between two consecutive basic measurements shall be at least 5 seconds. The received interference level of the carrier shall be the maximum of the NAMC basic measurements.
The maximum processing time for this procedure shall be (NAMC x 10) seconds.
When ordered by the CTS-FP, the CTS-MS shall report in the next AFA monitoring report message a table of received interference level of the carrier of the AMFL, INTERF_LEV (1,…,n), together with the minimum of the numbers of performed AFA monitoring cycles, NAMC_REAL ; the procedure shall be stopped.
220.127.116.11 BCCH detection
The reporting of the BCCH detection procedure may be used by the CTS-FP by the AFA algorithm and for the OFO request.
The parameters sent by the CTS-FP to the CTS-MS in the BCCH detection message shall be a list of m carriers : BCCH detection frequency list, BDFL(1,..,m).
For each carrier of the list, the CTS-MS shall attempt to synchronize to it and decode the SCH. The BCCH detection shall be failed (BCCH not detected) if the CTS-MS fails to decode the SCH.
The procedure shall be completed in maximum (m x 10) seconds
When ordered by the CTS-FP, the CTS-MS shall report in the next BCCH detection report message a table of BCCH detection status of the carriers of the list, BCCH_DETECT (1, …, m) ; the procedure shall be stopped.
18.104.22.168 Observed Frequency Offset (OFO) measurement
The reported OFO measurements shall be used by the CTS-FP to correct its frequency source (see 3GPP TS 05.10).
The parameters sent by the CTS-FP to the CTS-MS in the OFO measurement message shall be a list of k BCCH carriers : OFO measurement BCCH list, OMBL(1,..,k).
For each BCCH carrier of the list, the CTS-MS shall attempt to assess the frequency offset between the BCCH carrier and the CTS-FP. The measurement status shall be “failed” if an offset measurement accuracy better than 0.2 ppm cannot be ensured.
The procedure shall be completed in maximum (k x 15) seconds
When ordered by the CTS-FP, the CTS-MS shall report in the next OFO measurement report message the table of OFO measurements and measurement status of the BCCH carriers of the list : OFO_MEAS(1,…,k), OFO_STATUS(1, …,k) ; the procedure shall be stopped.
11.2 Intra-cell handover
11.2.1 Overall process
The overall intra-cell handover process is implemented in the CTS-MS and CTS-FP. Measurement of radio subsystem downlink performance is made in the CTS-MS. These measurements are signalled to the CTS-FP for assessment. The CTS-FP measures the uplink performance for the CTS-MS being served. Initial assessment of the measurements in conjunction with defined thresholds and intra-cell handover strategy shall be performed in the CTS-FP.
11.2.2 CTS-MS measurement procedure
A procedure shall be implemented in the CTS-MS by which it monitors the downlink RX signal level and quality from its serving CTS cell. The requirements for the CTS-MS measurements are given in subclause 11.5.
11.2.3 CTS-FP measurement procedure
A procedure shall be implemented in the CTS-FP by which it monitors the uplink RX signal level and quality from each CTS-MS being served by the CTS cell.
The intra-cell handover strategy employed by the CTS-FP for radio link control determines the handover decision that will be made based on the CTS measurement results reported by the CTS-MS and made by the CTS-FP, and on various parameters set for each CTS-FP.
Due to the Total Frequency Hopping applied to the traffic channels in CTS, intra‑cell handover can only occur to a different timeslot of the CTS cell.
Intra‑cell handover from one timeslot in the CTS cell to another timeslot in the same CTS cell will normally be performed if the CTS measurement results show a low RXQUAL, but a high RXLEV on the serving CTS cell. This indicates a degradation of quality caused by interference even though the CTS-MS is situated within the coverage area of the serving CTS cell. The intra‑cell handover should provide a timeslot with a lower level of interference.
11.3 RF power control
11.3.1 Overall process
RF power control is employed to minimize the transmit power required by CTS-MS or CTS-FP whilst maintaining the quality of the radio links. By minimizing the transmit power levels, interference to co‑channel users is reduced.
11.3.2 CTS-MS implementation
RF power control shall be implemented in the CTS-MS.
The power control level to be employed by the CTS-MS on the uplink channel is indicated by means of the power control information sent either in the layer 1 header of each SACCH message block (see 3GPP TS 04.04) on the corresponding downlink channel, or in a dedicated signalling block (see 3GPP TS 04.56).
The CTS-MS shall employ the most recently commanded power control level (parameter CTS_MS_TXPWR_REQUEST) for all transmitted bursts on either a TCH, FACCH or SACCH.
The CTS-MS shall confirm the power control level that it is currently employing in the SACCH L1 header on the uplink (parameter CTS_MS_TXPWR_CONF). The indicated value shall be the power control level actually used by the CTS-MS for the last burst of the previous SACCH period.
When accessing a cell on the ARCH (CTS access request) and before receiving the first power command during a communication on a TCH (after a CTS immediate assignment message), the CTS-MS shall use the power control level defined by the CTS_MS_MAX_TXPWR parameters ; this parameters shall be given by the CTS-FP to the CTS-MS during the enrolment procedure, and can be updated on request of the CTS-FP.
If a power control level defined in 3GPP TS 05.05 is received but the level is not supported by the CTS-MS, the CTS-MS shall use the supported output power which is closest to the output power indicated by the received power control level.
11.3.3 CTS-MS power control range
The range over which a CTS-MS shall be capable of varying its RF output power shall be from its maximum authorized output power CTS_MS_MAX_TXPWR, down its lowest nominal output power (as defined in 3GPP TS 05.05), in steps of nominally 2 dB.
3GPP TS 05.05 gives a detailed definition of the RF power level step size and tolerances for a CTS-MS.
11.3.4 CTS-FP implementation
RF power control shall be implemented in the CTS-FP.
11.3.5 CTS-FP power control range
The range over which a CTS-FP shall be capable of varying its RF output power shall be from its maximum authorized output power CTS_FP_MAX_TXPWR down its lowest nominal output power (as defined in 3GPP TS 05.56), in steps of nominally 2 dB.
3GPP TS 05.56 gives a detailed definition of the RF power level step size and tolerances for a CTS-FP.
The RF power control strategy employed by the CTS-FP determines the ordered power control level that is signalled to the CTS-MS, and the power control level that is employed by the CTS-FP.
The power control level to be employed in each case shall be based on the CTS measurement results reported by the CTS-MS and made by the CTS-FP, and on various parameters set for each CTS-FP.
If the CTS-MS reports in each CTS measurement results a RXQUAL_0 and a RXLEV greater or equal to 31, for a period of 30 seconds, the CTS-FP RF output power shall be at the end of this period the lowest nominal output power specified in 3GPP TS 05.56.
Under static interference free conditions, if the CTS-MS signal level received by the CTS-FP is greater or equal to -85 dBm for a period of 30 seconds, the CTS-FP shall command the CTS-MS to reduce its RF output power, so that the CTS-MS RF output power is at the end of this period the lowest nominal output power specified in 3GPP TS 05.05.
Upon receipt of a command from an SACCH to change its power level, the CTS-MS shall change to the new level at a rate of one nominal 2 dB power control step every 60 ms (13 TDMA frames), i.e. a range change of 15 steps should take about 900 ms. The change shall begin at the first TDMA frame belonging to the next reporting period (as specified in subclause 11.5.4). The CTS-MS shall change the power one nominal 2 dB step at a time, at a rate of one step every 60 ms following the initial change, irrespective of whether actual transmission takes place or not.
In case of intra-cell handover, the commanded power control level shall be applied on the new timeslot immediately.
11.4 Radio link failure
The criterion for determining Radio Link Failure in the CTS-MS shall be based on the success rate of decoding messages on the downlink SACCH.
11.4.2 CTS-MS procedure
The aim of determining radio link failure in the CTS-MS is to ensure that calls with unacceptable voice/data quality, which cannot be improved either by RF power control or intra-cell handover, are either re‑established or released in a defined manner.
The radio link failure criterion is based on the radio link counter S_CTS. If the CTS-MS is unable to decode a SACCH message (BFI = 1), S_CTS is decreased by 1. In the case of a successful reception of a SACCH message (BFI = 0) S_CTS is increased by 2. In any case S_CTS shall not exceed the value of CTS_RADIO_LINK_TIMEOUT. If S_CTS reaches 0 a CTS radio link failure shall be declared. The action to be taken is specified in 3GPP TS 04.56. The CTS_RADIO_LINK_TIMEOUT parameter is transmitted by the CTS-FP to the CTS-MS during the attachment procedure (see 3GPP TS 04.56). For the attachment or enrolment procedure, the CTS_RADIO_LINK_TIMEOUT shall be set to 64.
The CTS-MS shall continue transmitting as normal on the uplink until S_CTS reaches 0.
The algorithm shall start after the assignment of a dedicated channel and S_CTS shall be initialized to CTS_RADIO_LINK_TIMEOUT.
The detailed operation shall be as follows:
– the radio link time‑out algorithm shall be stopped at the reception of a CTS intra-cell handover command;
– (re‑)initialization and start of the algorithm shall be done whenever the CTS-MS switches to a new timeslot, at the latest when the main signalling link (see 3GPP TS 04.56) has been established;
– the CTS_RADIO_LINK_TIMEOUT value used at (re‑)initialization shall be that used on the previous timeslot (in the CTS immediate assignment case the value stored by the CTS-MS during the attachment procedure), or the value received on SACCH if the CTS-MS has received a CTS_RADIO_LINK_TIMEOUT value on the new channel before the initialization;
– if the first CTS_RADIO_LINK_TIMEOUT value on the SACCH is received on the new channel after the initialization, the counter shall be re‑initialized with the new value.
11.4.3 CTS-FP procedure
The criteria for determining radio link failure in the CTS-FP should be based upon either the error rate on the uplink SACCH or on RXLEV/RXQUAL measurements reported by the CTS-MS.
11.5 Radio link measurements
Radio link measurements are used in the intra-cell handover and RF power control processes.
The measurements are made over each SACCH multiframe, which is 104 TDMA frames (480 ms) for a TCH.
11.5.1 Signal strength
The received signal level may be employed as a criterion in the RF power control and intra-cell handover processes.
22.214.171.124 Physical parameter
As specified in subclause 8.1.2, measured by the CTS-MS and CTS-FP.
126.96.36.199 Statistical parameters
For each channel, the measured parameters (RXLEV) shall be the average of the received signal level measurement samples in dBm taken on that channel within the reporting period of length one SACCH multiframe defined in 11.5.4. In averaging, measurements made during previous reporting periods shall always be discarded.
When assigned a TCH, the CTS-MS shall make a received signal level measurement on all bursts of the associated physical channel (see 3GPP TS 05.02), including those of the SACCH.
For any TCH assigned to a CTS-MS, the CTS-FP shall make a received signal level measurement on all bursts of the associated physical channel including those of the SACCH.
188.8.131.52 Range of parameter
As specified subclause in subclause 8.1.4.
11.5.2 Signal quality
The received signal quality shall be employed as a criterion in the RF power control and intra-cell handover processes.
184.108.40.206 Physical parameter
As specified in subclause 8.2.2, measured by the CTS-MS and CTS-FP.
220.127.116.11 Statistical parameters
For each channel, the measured parameters (RXQUAL) shall be the received signal quality, averaged on that channel over the reporting period of length one SACCH multiframe defined in subclause 11.5.4. In averaging, measurements made during previous reporting periods shall always be discarded.
18.104.22.168 Range of parameter
As specified in subclause 8.2.4.
11.5.3 Aspects of discontinuous transmission (DTX)
The use of DTX is mandatory for the CTS-MS and the CTS-FP on a TCH. Not all TDMA frames may be transmitted, however, the subset specified in subclause 8.3 shall always be transmitted, and hence can be employed to assess quality and signal level during DTX.
11.5.4 Measurement reporting for the CTS-MS on a TCH
For a TCH, the reporting period of length 104 TDMA frames (480 ms) is defined in terms of TDMA frame numbers (FN) as follows:
Timeslot number (TN)
TDMA frame number (FN) modulo 104
SACCH Message block
0 and 1
0 to 103
12, 38, 64, 90
2 and 3
26 to 25
38, 64, 90, 12
4 and 5
52 to 51
64, 90, 12, 38
6 and 7
78 to 77
90, 12, 38, 64
When on a TCH, the CTS-MS shall assess during the reporting period and transmit to the CTS-FP in the next SACCH message block the following:
‑ CTS_RXLEV_FULL_SERVING_CELL and CTS_RXQUAL_FULL_SERVING_CELL : RXLEV_FULL and RXQUAL_FULL for the full set of TCH and SACCH TDMA frames. The full set of TDMA frames is 100 (i.e. 104 ‑ 4 idle) frames for a full rate TCH;
‑ CTS_RXLEV_SUB_SERVING_CELL and CTS_RXQUAL_SUB_SERVING_CELL: RXLEV_SUB and RXQUAL_SUB for the subset of 4 SACCH frames and the SID TDMA frames/L2 fill frames defined in 8.3. If no FACCH frames have been received at the corresponding frame positions, the RXQUAL_SUB report shall include measurements on the 4 SACCH frames only. The performance requirements of subclause 8.2.4 do not apply in this case for RXQUAL_SUB.
If the next SACCH message block is used for a different Layer 3 message, the averaged data which would otherwise be sent in that block is discarded and a new average started for the current block. i.e., any SACCH message will report the average data for the previous reporting period only.
The CTS-MS shall also transmit a bit (CTS_DTX_USED) in the next SACCH message block, which indicates whether or not it has employed DTX during the reporting period. This bit shall be set even if just one burst in a TDMA frame in the reporting period was not transmitted due to DTX.
NOTE: A speech frame subject to DTX may cross the "border" between two reporting periods, in which case both of the associated SACCH message blocks will have the CTS_DTX_USED flag set.
11.6 Control of CTS-FP service range
In order to restrict the CTS-FP service range, the CTS-FP shall monitor the delay of the signal sent by from the CTS-MS. For each CTS-MS the CTS-FP has allocated a TCH, a range measurement of the CTS-MS shall be computed by the CTS-FP every five reporting period by averaging over five reporting periods the assessed delay (as specified in 3GPP TS 05.10) for each received TCH burst of the subset always to be transmitted, specified in subclause 8.3, and for each received SACCH burst.
The TCH shall be released by the CTS-FP if two consecutive range measurements are greater than 1 bit period.
11.7 Control parameters
The parameters employed to control the radio link are shown in table 4, 5 and 6.
Table 4: Radio subsystem link control general parameters
The maximum authorized output power control level the CTS-FP shall use (downlink)
The maximum authorized output power control level a CTS-MS shall use with this CTS cell (uplink)
Minimum received level at the CTS-MS required for access to the system : coded as a RXLEV value (see subclause 8.1.4)
Applies an offset to the C2_CTS criterion : 0-63 dB in 63 steps of 1 dB
The maximum value of the radio
link clounter : 4‑64 SACCH blocks, in 15 steps of 4 SACCH blocks
Number of non-decoded paging messages before declaring a downlink paging failure
Table 5: AFA monitoring, BCCH detection and OFO measurement
control parameters – dedicated connection
AFA monitoring frequency list : contains n carriers represented by their ARFCN
AFA monitoring order
Number of AFA monitoring cycles
AFA monitoring order
Received interference level per carrier of the AMFL : coded as a RXLEV value (see subclause 8.1.4)
AFA monitoring report
Minimum of the numbers of performed AFA monitoring cycles
AFA monitoring report
BCCH detection frequency list : contains m carriers represented by their ARFCN
BCCH detection order
BCCH detection status :
00 : detected
01 : not detected
11 : not attempted
BCCH detection report
OFO measurement BCCH list : contains k BCCH carriers represented by their ARFCN
OFO measurement order
OFO measurements list : 0.05 – 6.4 ppm in 127 steps of 0.05 ppm
OFO measurement report
OFO measurement status :
00 : measurement OK
01 : measurement failed
11 : measurement not attempted
OFO measurement report
Table 6: Intra-cell handover and power control parameters – SACCH
The power level to be used by a
(ordered MS power level)
Indication of the power
(actual CTS-MS power level)
level in use by the CTS-MS.
The power level to be used by a
CTS-MS on the indicated channel
The RXLEV in the current
serving CTS cell accessed over
all TDMA frames
The RXLEV in the current
serving CTS cell accessed over
a subset of TDMA frames
The RXQUAL in the current
serving CTS cell, assessed over
all TDMA frames.
The RXQUAL in the current
serving CTS cell, assessed over
subset of TDMA frames.
Indicates whether or not the CTS-MS
used DTX during the previous
NOTE 1: RXLEV and RXQUAL fields are coded as described in subclause 11.6.
NOTE 2: For the details of the CTS Measurement Result message see 3GPP TS 04.56.