6 MS Requirements for Synchronization

05.103GPPRadio subsystem synchronizationTS

The MS shall only start to transmit to the BTS if the requirements of subclauses 6.1 to 6.4 are met.

The conditions under which the requirements of subclauses 6.1 to 6.4 must be met shall be 3 dB below the reference sensitivity level or input level for reference performance, whichever applicable, in 3GPP TS 05.05 and 3 dB less carrier to interference ratio than the reference interference ratios in 3GPP TS 05.05.

In discontinuous reception (DRX), the MS should meet the requirements of subclauses 6.1 to 6.3 during the times when the receiver is required to be active.

For CTS, the CTS-MS shall fulfil all the requirements of subclauses 6.1 to 6.4, 6.7, 6.8, 6.10 and 6.11 where «BTS» designates the CTS-FP. The CTS-MS shall always use a TA value of zero. The CTS-MS shall only start to transmit to the CTS-FP if the requirements of subclauses 6.1 to 6.4 are met. The conditions under which the requirements of subclauses 6.1 to 6.4 must be met shall be 3 dB below the reference sensitivity level or input level for reference performance, whichever applicable, in 3GPP TS 05.05 and 3 dB less carrier to interference ratio than the reference interference ratios in 3GPP TS 05.05. In discontinuous reception (DRX), the CTS-MS should meet the requirements of subclauses 6.1 to 6.3 during the times when the receiver is required to be active.

6.1 MS carrier frequency

The MS carrier frequency shall be accurate to within 0.1 ppm, or accurate to within 0.1 ppm compared to signals received from the BTS, except for GSM 400 where 0.2 ppm shall apply in both case (these signals will have an apparent frequency error due to BTS frequency error and Doppler shift). In the latter case, the signals from the BTS must be averaged over sufficient time that errors due to noise or interference are allowed for within the above 0.1 ppm and 0.2 ppm figure. The MS shall use the same frequency source for both RF frequency generation and clocking the timebase.

6.2 Internal timebase

The MS shall keep its internal timebase in line with that of signals received from the BTS. If the MS determines that the timing difference exceeds 2 µ seconds, it shall adjust its timebase in steps of 1/4 symbol period. This adjustment shall be performed at intervals of not less than 1 second and not greater than 2 seconds until the timing difference is less than 1/2 symbol periods.

6.3 Assessment of BTS timing

In determining the timing of signals from the BTS, the timings shall be assessed in such a way that the timing assessment error is less than 1/2 symbol periods. The assessment algorithm must be such that the requirements of 6.2 can be met.

6.4 Timing of transmission

The MS shall time its transmissions to the BTS according to signals received from the BTS. The MS transmissions to the BTS, measured at the MS antenna, shall be 468,75‑TA symbol periods (i.e. 3 timeslots‑TA) behind the transmissions received from the BTS, where TA is the last timing advance received from the current serving BTS. The tolerance on these timings shall be ± 1 symbol period. For CTS, the tolerance on these timings shall be ± 1/2 symbol period.

In case of a multislot configuration, the MS shall use a common timebase for transmission of all channels. In this case, the MS may optionally use a timeslot length of 157 symbol periods on timeslots TN = 0 and 4, and 156 symbol periods on timeslots with TN = 1, 2, 3, 5, 6 and 7, rather than 156,25 symbol periods on all timeslots. In case of a circuit switched multislot configuration, the common timebase shall be derived from the main channel and the TA values received on other channels shall be neglected. In case of a packet switched multislot configuration the common timebase shall be derived from all timeslots monitored by the MS. In this case, the MS may assume that the BTS uses a timeslot length of 156,25 symbol periods on all timeslots. In the case of a combination of circuit and packet switched channel configuration the MS may derive the common timebase from the circuit switched channel only.

6.5 Application of Timing Advance

6.5.1 For circuit switched channels

When the MS receives a new value of TA from the BTS on the SACCH, it shall implement the new value of TA at the first TDMA frame belonging to the next reporting period (as defined in 3GPP TS 05.08), after the SACCH frame containing the new TA value. On channels used for a voice group call, the TA value sent by the BTS applies only to an MS currently allocated the uplink.

The MS shall signal the used TA to the BTS on the SACCH.

6.5.2 For packet switched channels

The following requirements apply for all MS in packet transfer mode, except MS class A in dedicated mode:

The MS shall transmit access bursts with TA value=0.

Within the packet resource assignments (see 3GPP TS 04.08 and 3GPP TS 04.60) for uplink or downlink messages the MS gets the Timing Advance Index (TAI). The MS shall send access bursts on the subchannel defined by the TAI on the PTCCH. These access bursts received on PTCCH are used by the BTS to derive the timing advance.

When the MS receives the updated value of TA from the BTS on the downlink PTCCH, it shall always use the last received TA value for the uplink transmission of normal bursts.

If an MS is allocated different TAI values for simultaneous uplink and downlink packet transfer, the MS may chose to use any one or both PTCCH subchannels. If two subchannels are used, the MS shall always use the received TA value corresponding to the last transmitted PTCCH uplink burst.

If the MS receives a packet resource assignment or power control/timing advance message (see 3GPP TS 04.08 and 3GPP TS 04.60) without a TAI, the MS shall not use the continuous timing advance procedure.

Upon initiation of the continuous timing advance procedure the MS shall disregard the TA values on PTCCH until it has sent its first access burst on PTCCH.

The network may request the MS to send 4 access bursts to calculate a new TA value. For this purpose the network sets the system information element CONTROL_ACK_TYPE to indicate that the MS is to respond with a PACKET_CONTROL_ACKNOWLEDGEMENT consisting of 4 access bursts (see 3GPP TS 04.60), and sends a PACKET_POLLING_REQUEST to the MS. In this case, the MS shall transmit 4 consecutive access bursts on the assigned resources.

If the MS receives a packet resource assignment or power control/timing advance message (see 3GPP TS 04.08 and 3GPP TS 04.60), the MS shall use the included TA value for normal burst transmissions until it receives a new value on PTCCH. If the message does not contain a TA value, the MS shall not change its TA value.

When entering packet transfer mode, the MS is not allowed to transmit normal bursts until it has received a valid TA value by any of the methods described above.

A MS class A in dedicated or dual transfer mode shall follow the procedures described in subclause 6.5.1.

6.6 Access to a new BTS

When the MS accesses a new BTS or the serving BTS is changed, or the MS initiates a packet transfer, the MS shall change the TA as follows:

Random access and Packet random access:

– the MS shall use a TA value of 0 for the Random Access burst sent. When a TA is received from the BTS that TA shall be used.

Synchronized or Pseudo Synchronized handover:

– after the Handover Access bursts which shall be sent with a TA value of 0 the MS shall use a TA calculated as specified in annex A. When a TA is received from the new BTS that TA shall be used. The transmission of the Handover Access burst is optional if so indicated by the BTS.

In those cells that support extended TA values if TA value in new cell is greater than 63 and the HANDOVER COMMAND message indicates that the transmission of four HANDOVER ACCESS messages is optional the MS shall not transmit these four messages.

Non‑synchronized handover:

– the MS shall use a TA value of 0 for the Handover Access bursts sent. When a TA is received in a physical information message that TA shall be used. Before a TA is received from the new BTS no valid "used TA" shall be signalled to the new BTS.

Pre‑synchronized handover:

– after the Handover Access bursts which shall be sent with a TA value of 0 the MS shall use a TA as specified in the HO command by the old BTS, or a default value of 1, if the old BTS did not provide a TA value. The transmission of the Handover Access burst is optional if so indicated by the BTS.

In those cells that support extended TA values if TA value in new cell is greater than 63 and the HANDOVER COMMAND message indicates that the transmission of four HANDOVER ACCESS messages is optional the MS shall not transmit these four messages.

6.7 Temporary loss of signal

During a temporary total loss of signal, of up to 64 SACCH block periods, the MS shall update its timebase with a clock which is accurate to within 0,2 ppm, or to within 0,2 ppm of the signals previously received from the BTS.

6.8 Timing of channel change

When the MS receives an intracell channel change command or a handover command (see 3GPP TS 04.08), it shall be ready to transmit on the new channel within T_GSM_Delay of the last timeslot of the message block containing the command, unless the access is delayed to an indicated starting time, in which case it shall be ready to transmit on the new channel at the designated starting time, or within T_GSM_Delay, whichever is the later. The time between the end of the last complete speech or data frame or message block sent on the old channel and the time the MS is ready to transmit on the new channel shall be less than T_GSM_Interrupt.

T_GSM_Delay and T_GSM_Interrupt are defined in table 1.

Table 1: Channel change delay and interruption times.

Target cell

T_GSM_Delay (ms)

T_GSM_Interrupt (ms)

Synchronized GSM cell

120 ms

20 ms

Not Synchronized GSM cell

Under good radio conditions

220 ms

120 ms

6.9 Application of new Timing Advance value

When the MS receives a new TA value in response to a handover access burst, the MS shall be ready to transmit using the new TA value within 40 ms of the end of the last timeslot of the message block containing the new TA value.

When the MS receives a new or updated TA value on the downlink PTCCH or downlink PACCH, the MS shall be ready to transmit using the new TA value within 40 ms of the end of the last timeslot of the message block containing the new TA value.

6.10 Definition of "ready to transmit within x ms"

The phrase "ready to transmit within x ms" means that the MS shall transmit no later than the first allowed transmission opportunity that occurs after the x ms, e.g.:

‑ the first burst of the first TCH or control channel block that occurs after the x ms, in case of an intracell channel change;

‑ the first burst of the TCH or control channel that occurs after the x ms, in case of a handover;

– the first burst of the PDTCH or control channel that occurs after the x ms;

– the first allowed uplink frame (see 3GPP TS 25.212 and 3GPP TS 25.214 for FDD and 3GPP TS 25.222 for TDD), that occurs after the x ms, in case of an inter-RAT handover to a UTRAN cell.

NOTE: The MS shall keep the timings of the neighbour GSM cells that it is monitoring (according to 3GPP TS 05.08) to an accuracy of ± 1 symbol periods.

6.11 Definition of additional reaction times for GPRS mobile stations

6.11.1 Uplink and downlink assignment reaction times

An MS shall be ready to transmit and receive using a new assignment no later than the next occurrence of block B((x+3) mod 12) where block B(x) is the last radio block containing the assignment message. This applies also for the reception of the first USF for dynamic uplink assignment.

If the MS is required to transmit a PACKET CONTROL ACKNOWLEDGEMENT subsequent to an assignment message (see 3GPP TS 04.60), the MS shall be ready to transmit and receive on the new assignment no later than the next occurrence of block B((x+2) mod 12) where block B(x) is radio block containing the PACKET CONTROL ACKNOWLEDGEMENT.

6.11.2 Change in channel coding scheme commanded by network

Upon receipt of a command from the network to change the channel coding scheme, the MS shall begin to transmit blocks using the new channel coding scheme no later than the next occurrence of block B((x+3) mod 12) where block B(x) is the radio block containing the command.

6.11.3 Contention resolution reaction time

Upon contention resolution during one phase access, the mobile station shall start transmitting RLC data blocks without the TLLI field no later than the next occurrence of block B((x+3) mod 12) where block B(x) is the radio block containing the contention resolution message (see 3GPP TS 04.60).

6.11.4 Reaction time in response to other commanding messages

Upon a receipt of a commanding message or indication from the network requiring an action by the mobile station, if the reaction time for such action is not specified elsewhere, the mobile station shall begin to perform the required action no later than the next occurrence of block B((x+6) mod 12), where block B(x) is the radio block containing the commanding message or indication form the network.

6.12 Observed Frequency Offset (OFO) reported by the CTS-MS

When required the CTS-MS shall compute the Observed Frequency Offset between the CTS-FP and a specified BTS (see 3GPP TS 05.08). The CTS-FP and BTS received signals frequencies shall be estimated with an accuracy of 0,1 ppm, averaging the signals over sufficient time. The conditions under which this requirements must be met shall be 3 dB below the reference sensitivity level or input level for reference performance, whichever applicable, in 3GPP TS 05.05 and 3 dB less carrier to interference ratio than the reference interference ratios in 3GPP TS 05.05.

6.13 Timing of intersystem channel change from GSM to UTRAN

When the MS receives an INTER SYSTEM TO UTRAN HANDOVER COMMAND (see 3GPP TS 04.18), it shall be ready to transmit on the new channel within Tdelay of the last timeslot of the message block containing the command, unless the access is delayed to an indicated starting time, in which case it shall be ready to transmit on the new channel at the designated starting time, or within Tdelay, whichever is the later. The time between the end of the last complete speech or data frame or message block sent on the old channel and the time the MS is ready to transmit on the new cell shall not exceed Tinterrupt. Tdelay and Tinterrupt are defined in table 2 for the case of intersystem handover to a single UTRAN cell assuming good radio conditions.

Table 2: Intersystem handover delay and interruption times.

Target cell

Tdelay (ms)

Tinterrupt (ms)

Known FDD cell
(see 3GPP TS 25.133)

220

120

Not known FDD cell
(see 3GPP TS 25.133)

320

220

Known TDD cell
(see 3GPP TS 25.123)

190

90

Not known TDD cell
(see 3GPP TS 25.123)

350

250

6.14 Timing of combined intracell channel change and packet assignment

When the MS receives a combined intracell channel change command and packet assignment in either dedicated mode or dual transfer mode (see 3GPP TS 04.18), the requirements specified in sub-clause 6.8 shall apply to the new dedicated channel.

In addition, the MS shall be ready to transmit and receive using the packet assignment within T_GSM_delay of the last timeslot of the message block containing the command, unless the access is delayed to an indicated starting time, in which case it shall be ready to transmit on the new channel at the designated starting time, or within T_GSM_Delay, whichever is the later. This applies also for the reception of the first USF for dynamic uplink assignment.

The requirements for using the packet assignment apply also when the MS receives a stand-alone packet assignment (on the main DCCH), causing the transition from dedicated mode into dual transfer mode (see 3GPP TS 04.18).

T_GSM_delay is defined in sub-clause 6.8, table 1.