ETSI EN 300 912 V7.3.1 (2000-10)

SLOVENSKI STANDARD
SIST EN 300 912 V7.3.1:2003
01-december-2003
'LJLWDOQLFHOLþQLWHOHNRPXQLNDFLMVNLVLVWHPID]D±6LQKURQL]DFLMDUDGLMVNHJD
SRGVLVWHPD*60UD]OLþLFDL]GDMD
Digital cellular telecommunications system (Phase 2+) (GSM); Radio subsystem
synchronization (GSM 05.10 version 7.3.1 Release 1998)
Ta slovenski standard je istoveten z: EN 300 912 Version 7.3.1
ICS:
33.070.50 Globalni sistem za mobilno Global System for Mobile
telekomunikacijo (GSM) Communication (GSM)
SIST EN 300 912 V7.3.1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 300 912 V7.3.1:2003

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SIST EN 300 912 V7.3.1:2003
ETSI EN 300 912 V7.3.1 (2000-10)
European Standard (Telecommunications series)
Digital cellular telecommunications system (Phase 2+);
Radio subsystem synchronization
(GSM 05.10 version 7.3.1 Release 1998)
R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS

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SIST EN 300 912 V7.3.1:2003
2 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
Reference
REN/SMG-020510Q7R1
Keywords
Digital cellular telecommunications system,
Global System for Mobile communications (GSM)
ETSI
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Copyright Notification
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The copyright and the foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 2000.
All rights reserved.
ETSI

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SIST EN 300 912 V7.3.1:2003
3 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
Contents
Intellectual Property Rights.5
Foreword.5
1 Scope .6
1.1 References .6
1.2 Definitions and abbreviations.7
2 General description of synchronization system.7
3 Timebase counters.8
3.1 Timing state of the signals.8
3.2 Relationship between counters .8
4 Timing of transmitted signals.9
5 BTS Requirements for Synchronization.9
5.1 Frequency source.9
5.2 Timebase counters.9
5.3 Internal BTS carrier timing .9
5.4 Initial Timing advance estimation.10
5.5 Maximum timing advance value .10
5.6 Delay tracking .10
5.6.1 For circuit switched channels.10
5.6.2 For packet switched channels .10
5.6.3 Delay assessment error .10
5.6.4 Pico-BTS delay tracking.10
5.7 Timeslot length.11
5.8 Range of Timing advance.11
6 MS Requirements for Synchronization .11
6.1 MS carrier frequency.11
6.2 Internal timebase .11
6.3 Assessment of BTS timing .11
6.4 Timing of transmission.12
6.5 Application of Timing Advance.12
6.5.1 For circuit switched channels.12
6.5.2 For packet switched channels .12
6.6 Access to a new BTS.13
6.7 Temporary loss of signal .13
6.8 Timing of intracell channel change .13
6.9 Application of new Timing Advance value.13
6.10 Definition of "ready to transmit within x ms" .13
6.11 Definition of additional reaction times for GPRS mobile stations .14
6.11.1 Uplink and downlink assignment reaction times .14
6.11.2 Change in channel coding scheme commanded by network.14
6.11.3 Contention resolution reaction time.14
6.11.4 Reaction time in response to other commanding messages .14
6.12 Observed Frequency Offset (OFO) reported by the CTS-MS.14
7 CTS-FP Requirements for Synchronization.15
7.1 Frequency source default requirements.15
7.2 Frequency source for a CTS-FP assisted by a CTS-MS.15
7.3 Internal CTS-FP carrier timing.15
7.4 Timeslot length.15
7.5 Assessment of CTS-MS delay.15
ETSI

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SIST EN 300 912 V7.3.1:2003
4 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
Annex A (normative): Additional requirements for pseudo-synchronization, synchronized
handovers and pseudo-synchronized handovers.16
A.1 General descriptions and definitions .16
A.1.1 Conventions.16
A.1.2 Definitions.16
A.1.3 Details of operations.16
A.2 BTS requirements.17
A.2.1 The pseudo-synchronization scheme.17
A.2.1.1 BTS a time difference estimate.17
A.2.1.2 The reception epoch criterion .17
A.2.1.3 Pseudo-synchronized handover .17
A.2.2 The synchronization requirement .17
A.3 MS requirements .18
A.3.1 Provision of time difference information .18
A.3.2 After each successful handover.18
A.3.3 Synchronized or a pseudo synchronized handover.18
Annex B (informative): CTSBCH timeslot shifting properties for CTS-MS synchronization.19
B.1 Determination of TN by the CTS-MS when CTSBCH shifting is not active .19
B.2 Determination of TN by the CTS-MS when CTSBCH shifting is active .19
Annex C (informative): BTS frequency source stability and E-OTD LMU reporting periods
for LCS .20
C.1 BTS frequency source stability and E-OTD LMU reporting periods .20
C.2 Frequency source stability.20
C.3 Relationship to E-OTD reporting periods .20
Annex D (informative): Change control history .22
History .23
ETSI

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SIST EN 300 912 V7.3.1:2003
5 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://www.etsi.org/ipr).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This European Standard (Telecommunications series) has been produced by ETSI Technical Committee Special Mobile
Group (SMG).
This European Standard (Telecommunications series) has been produced by ETSI Technical Committee Special Mobile
Group (SMG), and is now submitted for the ETSI standards One-step Approval Procedure.
The contents of the present document may be subject to continuing work within SMG and may change following formal
SMG approval. Should SMG modify the contents of the present document it will then be re-submitted for formal
approval procedures by ETSI with an identifying change of release date and an increase in version number as follows:
Version 7.x.y
where:
7 GSM Phase 2+ Release 1998.
x the second digit is incremented for changes of substance, i.e. technical enhancements, corrections, updates,
etc.;
y the third digit is incremented when editorial only changes have been incorporated in the specification.
National transposition dates
Date of adoption of this EN: 29 September 2000
Date of latest announcement of this EN (doa): 31 December 2000
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 30 June 2001
Date of withdrawal of any conflicting National Standard (dow): 30 June 2001
ETSI

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SIST EN 300 912 V7.3.1:2003
6 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
1 Scope
The present document defines the requirements for synchronization on the GSM radio sub-system. However, it does not
define the synchronization algorithms to be used in the Base Transceiver Station (BTS), CTS Fixed Part (CTS-FP) and
Mobile Station (MS). These are up to the manufacturer to specify.
The present document is for GSM, DCS 1 800 and PCS 1 900.
1.1 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
• References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies.
• A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same
number.
• For this Release 1998 document, references to GSM documents are for Release 1998 versions (version 7.x.y).
[1] GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations and
acronyms".
[2] GSM 03.60: "Digital cellular telecommunications system (Phase 2+); General Packet Radio
Service (GPRS); Service Description Stage 2".
[3] GSM 03.64: "Digital cellular telecommunications system (Phase 2+); General Packet Radio
Service (GPRS); GPRS Radio Interface Stage 2".
[4] GSM 04.08: "Digital cellular telecommunications system (Phase 2+); Mobile radio interface
layer 3 specification".
[5] GSM 04.60: "Digital cellular telecommunications system (Phase 2+); General Packet Radio
Service (GPRS); Mobile Station (MS) - Base Station System (BSS interface; Radio Link Control
(RLC) and Medium Access Control (MAC) Layer Specification".
[6] GSM 05.02: "Digital cellular telecommunications system (Phase 2+); Multiplexing and multiple
access on the radio path".
[7] GSM 05.05: "Digital cellular telecommunications system (Phase 2+); Radio transmission and
reception".
[8] GSM 05.08: "Digital cellular telecommunications system (Phase 2+); Radio subsystem link
control".
[9] GSM 03.30: "Digital cellular telecommunications system (Phase 2+); Radio network planning
aspects".
[10] GSM 03.52: "Digital cellular telecommunications system (Phase 2+); GSM Cordless Telephony
System (CTS), Phase 1; Lower layers of the CTS Radio Interface; Stage 2".
[11] GSM 05.56: "Digital cellular telecommunications system (Phase 2+); GSM Cordless Telephony
System (CTS), Phase 1; CTS-FP Radio subsystem".
ETSI

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SIST EN 300 912 V7.3.1:2003
7 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
1.2 Definitions and abbreviations
In addition to those below, abbreviations used in this EN are listed in GSM 01.04.
For the purposes of the present document, the following terms and definitions apply:
BTS: Base Transceiver Station.
CTS-FP: CTS Fixed Part.
CTS-MS: MS operating in CTS mode.
Timing Advance: signal sent by the BTS to the MS which the MS uses to advance its timings of transmissions to the
BTS so as to compensate for propagation delay.
Quarter bit number: timing of quarter bit periods (12/13µs) within a timeslot.
Timeslot number: timing of timeslots within a TDMA frame.
TDMA frame number: count of TDMA frames relative to an arbitrary start point.
Current Serving BTS: BTS on one of whose channels (TCH, DCCH, CCCH or PDCH) the MS is currently operating.
Current Serving CTS-FP: CTS-FP on one of whose channels (TCH or CTS control channels) the CTS-MS is
currently operating.
Timebase counters: set of counters which determine the timing state of signals transmitted by a BTS or MS.
MS timing offset: delay of the received signal relative to the expected signal from an MS at zero distance under static
channel conditions with zero timing advance. This is accurate to ± 1 bit, and reported once per SACCH or after a
RACH as. required (i.e. at the same rate as timing advance). For example, for an MS with a round trip propagation
delay of P bits, but with a timing advance of T bits, the reported timing offset will be P-T quantized to the nearest bit.
For GPRS the MS timing offset is not reported.
Timing Advance Index: Timing Advance Index TAI used for GPRS, which determines the position of the subchannel
on PTCCH (see GSM 05.02) used by the MS to send an access burst, from which the network can derive the timing
advance.
Observed Frequency Offset (OFO): difference of frequency of signals received by a CTS-MS from a CTS-FP and a
BTS. The Observed Frequency Offset is measured and reported by the CTS-MS on CTS-FP requirement. The Observed
Frequency Offset is expressed in ppm with an accuracy of 1/64 ppm (i.e. about 0,016 ppm).
2 General description of synchronization system
This clause gives a general description of the synchronization system. Detailed requirements are given in clauses 3 to 7.
The BTS sends signals on the BCCH to enable the MS to synchronize itself to the BTS and if necessary correct its
frequency standard to be in line with that of the BTS. The signals sent by the BTS for these purposes are:
a) Frequency correction bursts;
b) Synchronization bursts.
The timings of timeslots, TDMA frames, TCH frames and control channel frames are all related to a common set of
counters which run continuously whether the MS and BTS are transmitting or not. Thus, once the MS has determined
the correct setting of these counters, all its processes are synchronized to the current serving BTS.
The MS times its transmissions to the BTS in line with those received from the BTS. The BTS sends to each MS a
"timing advance" parameter (TA) according to the perceived round trip propagation delay BTS-MS-BTS. The MS
advances its timing by this amount, with the result that signals from different MS's arriving at the BTS and compensated
for propagation delay. This process is called "adaptive frame alignment".
ETSI

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SIST EN 300 912 V7.3.1:2003
8 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
Additionally, synchronization functions may be implemented in both the MS and the BTS to support the so-called
pseudo synchronization scheme. The support of this scheme is optional except that MS shall measure and report the
Observed Timing Difference (OTD), which is a mandatory requirement. The detailed specifications of the
pseudo-synchronization scheme are included in annex A.
In CTS, the CTS-FP sends signals on the CTSBCH to enable the MS to synchronize itself to the CTS-FP and if
necessary correct its frequency standard to be in line with that of the CTS-FP.
The signals sent by the CTS-FP for these purposes are:
a) frequency correction bursts;
b) synchronization bursts.
The timings of timeslots, TDMA frames, CTSBCH, CTSARCH, CTSAGCH and CTSPCH frames are all related to a
first common set of counters which run continuously whether the CTS-MS and CTS-FP are transmitting or not. Thus,
once the CTS-MS has determined the correct setting of these first counters, the CTS-MS is able to attach to the current
serving CTS-FP. In addition, during CTS-MS attachment, the CTS-FP sends to the CTS-MS the remaining counters for
SACCH and TCH frames. Then, all processes of the CTS-MS are synchronized to the current serving CTS-FP.
The CTS-MS times its transmissions to the CTS-FP in line with those received from the CTS-FP. The timing advance
parameter is set to zero for CTS.
Additionally, the CTS-FP may be assisted by a CTS-MS to adjust its frequency source. When required by the CTS-FP,
the CTS-MS estimates if possible and reports the Observed Frequency Offset of the CTS-FP with a specified BTS. The
CTS-FP may then adjust its frequency source according to this value.
3 Timebase counters
3.1 Timing state of the signals
The timing state of the signals transmitted by a BTS, a MS or a CTS-FP is defined by the following counters:
- Quarter bit number QN (0 - 624)- Bit number BN (0 - 156);
- Timeslot number TN (0 - 7);
- TDMA frame number FN (0 to (26 x 51 x 2048) - 1 = 2715647); or
- for a non attached CTS-MS, TDMA frame number modulo 52 T4 (0 - 51).
In CTS, the CTS-MS shall manage different sets of counters for CTS operation and GSM operation.
3.2 Relationship between counters
The relationship between these counters is as follows:
- QN increments every 12/13µs;
- BN = Integer part of QN/4;
- TN increments whenever QN changes from count 624 to 0;
- FN increments whenever TN changes from count 7 to 0; or
- for a CTS-MS, T4 increments whenever TN changes from count 7 to 0.
ETSI

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SIST EN 300 912 V7.3.1:2003
9 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
4 Timing of transmitted signals
The timing of signals transmitted by the MS, BTS and CTS-FP are defined in GSM 05.02.
The MS can use the timing of receipt of the synchronization burst to set up its timebase counters as follows:
QN is set by the timing of the training sequence;
TN= 0 when the synch burst is received;
FN = 51 ((T3-T2) mod (26)) + T3 + 51 x 26 x T1 when the synch burst is received,(where T3 = (10 x T3') + 1, T1,
T2 and T3' being contained in information fields in synchronization burst).
For CTS, the timebase counters are set as follows:
QN is set by the timing of the training sequence;
TN is set according to the CTSBCH-SB position (see Annex C);
T4 = 51 when the CTSBCH-SB is received (prior to attachment);
FN = (51 ((T3-T2) mod (26)) + T3 + 51 x 26 x T1) mod (2715648) when the CTS-MS receives the last CTSAGCH
burst of the non-hopping access procedure, where T2 = T4 mod (26), and T1 and T3 being contained in this
CTS immediate assignment message.
Thereafter, the timebase counters are incremented as in subclause 3.2.
(When adjacent BTS's are being monitored for handover purposes, or for cell reselection purposes in group receive
mode, the MS may choose to store the values of QN, TN and FN for all the BTS's whose synchronization bursts have
been detected relative to QN, TN and FN for its current serving BTS).
5 BTS Requirements for Synchronization
The conditions under which the requirements of subclauses 5.4 and 5.6 must be met shall be 3 dB below the reference
sensitivity level in GSM 05.05 and 3 dB less carrier to interference ratio than the reference interference ratios in
GSM 05.05.
5.1 Frequency source
The BTS shall use a single frequency source of absolute accuracy better than 0,05 ppm for both RF frequency
generation and clocking the timebase. The same source shall be used for all carriers of the BTS.
For the pico BTS class the absolute accuracy requirement is relaxed to 0,1ppm.
NOTE: BTS frequency source stability is one factor relating to E-OTD LCS performance and the reader is
referred to Annex C for the relationship between BTS frequency source stability and E-OTD LCS
performance characteristics.
5.2 Timebase counters
It is optional whether the timebase counters of different BTS's are synchronized together.
5.3 Internal BTS carrier timing
The channels of different carriers transmitted by a BTS shall be synchronized together, i.e. controlled by the same set of
counters. The timing difference between the different carriers shall be less than 1/4 bit periods, measured at the BTS
antenna.
ETSI

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SIST EN 300 912 V7.3.1:2003
10 ETSI EN 300 912 V7.3.1 (2000-10)
(GSM 05.10 version 7.3.1 Release 1998)
For pico-BTS, the timing difference between different carriers shall be less than 2 bit periods, measured at the BTS
antenna.
5.4 Initial Timing advance estimation
When the BTS detects an access burst transmission on RACH or PRACH, it shall measure the delay of this signal
relative to the expected signal from an MS at zero distance under static channel conditions. This delay, called the timing
advance, shall be rounded to the nearest bit period and included in a response from the BTS when applicable.
For the pico-BTS there is no requirement to measure this timing advance. However, either this measured value or a
programmable value of timing advance shall be included in the response from the BTS when a timing advance value
needs to be sent.
5.5 Maximum timing advance value
The maximum timing advance value shall be 63. If the BTS measures a value larger than this, it shall set the timing
advance to 63. (GSM 03.30 defines how the PLMN deals with MS's where the delay exceeds timing advance value 63.)
5.6 Delay tracking
5.6.1 For circuit switched channels
The BTS shall thereafter continuously monitor the delay of the normal bursts sent by from the MS. If the delay changes
by more than one bit period, the timing advance shall be advanced or retarded 1 and the new value signalled to the MS.
Restricting the change in timing advance to 1 bit period at a time gives the simplest implementation of the BTS.
However the BTS may use a larger change than this but great care must then be used in the BTS design.
5.6.2 For packet switched channels
The BTS shall perform the continuous update timing advance mechanism for all MS working in packet transfer mode
for which an PTCCH subchannel is assigned, except for MS class A in dedicated mode. Therefore the BTS shall
monitor the delay of the access bursts sent by the MS on PTCCH and respond with timing advance values for all MS
performing the procedure on that PDCH. These timing advance values shall be sent via a downlink signalling message
on PTCCH.
The BTS shall update the timing advance values in the next downlink signal
...