ETSI TS 145 010 V15.2.0 (2020-04)

TECHNICAL SPECIFICATION
Digital cellular telecommunications system (Phase 2+) (GSM);
GSM/EDGE Radio subsystem synchronization
(3GPP TS 45.010 version 15.2.0 Release 15)

R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS
3GPP TS 45.010 version 15.2.0 Release 15 1 ETSI TS 145 010 V15.2.0 (2020-04)

Reference
RTS/TSGR-0645010vf20
Keywords
GSM
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3GPP TS 45.010 version 15.2.0 Release 15 2 ETSI TS 145 010 V15.2.0 (2020-04)
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ETSI
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Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
1.1 References . 6
1.2 Definitions and abbreviations . 6
2 General description of synchronization system . 8
3 Timebase counters . 9
3.1 Timing state of the signals . 9
3.2 Relationship between counters . 9
4 Timing of transmitted signals . 9
5 BTS Requirements for Synchronization . 10
5.0 General . 10
5.1 Frequency source . 11
5.2 Timebase counters . 11
5.3 Internal BTS carrier timing . 11
5.4 Timing advance estimation. 11
5.4.1 Initial timing advance estimation . 11
5.4.2 BTS Timing Advance Estimation for Positioning . 11
5.5 Maximum timing advance value . 13
5.6 Delay tracking . 13
5.6.1 For circuit switched channels. 13
5.6.2 For packet switched channels . 13
5.6.3 Delay assessment error . 14
5.6.4 Pico-BTS and Local Area multicarrier BTS delay tracking . 14
5.7 Timeslot length . 14
5.7.0 Implementation options . 14
5.7.1 Regular implementation with timeslot lengths of non-integral symbol periods . 14
5.7.2 Implementation option for reduced symbol period bursts when integral symbol period option is used
for normal symbol period bursts . 16
5.8 Range of Timing advance . 17
6 MS Requirements for Synchronization . 17
6.0 General . 17
6.1 MS carrier frequency . 17
6.2 Internal timebase . 17
6.3 Assessment of BTS timing . 18
6.3.1 General . 18
6.3.2 MS Assessment of BTS timing for Positioning . 18
6.4 Timing of transmission . 19
6.5 Application of Timing Advance . 19
6.5.1 For circuit switched channels. 19
6.5.2 For packet switched channels . 20
6.6 Access to a new BTS . 20
6.7 Temporary loss of signal . 21
6.8 Timing of channel change . 21
6.9 Application of new Timing Advance value . 22
6.10 Definition of "ready to transmit within x ms" . 22
6.11 Definition of additional reaction times for GPRS mobile stations . 22
6.11.1 Uplink and downlink assignment reaction times . 22
6.11.2 Change in channel coding scheme commanded by network . 23
6.11.3 Contention resolution reaction time . 23
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6.11.4 Reaction time in response to other commanding messages . 24
6.11.5 PAN related reaction times . 24
6.11.6 DTR related reaction times . 24
6.12 Observed Frequency Offset (OFO) reported by the CTS-MS . 25
6.13 Timing of inter-RAT channel change from GSM to UTRAN . 25
6.13a Timing of inter-RAT channel change from GSM to E-UTRAN . 26
6.14 Timing of combined intracell channel change and packet assignment . 26
7 CTS-FP Requirements for Synchronization . 27
7.1 Frequency source default requirements . 27
7.2 Frequency source for a CTS-FP assisted by a CTS-MS . 27
7.3 Internal CTS-FP carrier timing . 27
7.4 Timeslot length . 27
7.5 Assessment of CTS-MS delay . 27
Annex A (normative): Additional requirements for pseudo-synchronization, synchronized
handovers and pseudo-synchronized handovers . 28
A.1 General descriptions and definitions . 28
A.1.1 Conventions . 28
A.1.2 Definitions . 28
A.1.3 Details of operations . 28
A.2 BTS requirements . 29
A.2.1 The pseudo-synchronization scheme . 29
A.2.1.1 BTS a time difference estimate . 29
A.2.1.2 The reception epoch criterion . 29
A.2.1.3 Pseudo-synchronized handover . 29
A.2.2 The synchronization scheme . 29
A.3 MS requirements . 29
A.3.1 Provision of time difference information . 29
A.3.2 After each successful circuit-switched handover . 30
A.3.3 Synchronized or a pseudo synchronized handover . 30
Annex B (informative): CTSBCH timeslot shifting properties for CTS-MS synchronization . 31
B.1 Determination of TN by the CTS-MS when CTSBCH shifting is not active . 31
B.2 Determination of TN by the CTS-MS when CTSBCH shifting is active . 31
Annex C (informative): BTS frequency source stability and E-OTD LMU reporting periods
for LCS . 32
C.1 BTS frequency source stability and E-OTD LMU reporting periods . 32
C.2 Frequency source stability . 32
C.3 Relationship to E-OTD reporting periods . 32
Annex D (informative): Change history . 34
History . 38

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Foreword
rd
This Technical Specification has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
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1 Scope
The present document defines the requirements for synchronization on the radio sub-system of the digital cellular
telecommunications systems GSM. 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.
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. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 25.123: "Requirements for support of radio resource management (TDD)".
[3] 3GPP TS 25.133: "Requirements for support of radio resource management (FDD)".
[4] 3GPP TR 43.030: "Radio network planning aspects".
[5] 3GPP TS 43.052: "Lower layers of the Cordless Telephony System (CTS) Radio Interface; Stage
2".
[6] 3GPP TS 43.059: "Functional stage 2 description of Location Services (LCS) in GERAN".
[7] 3GPP TS 43.064: "Overall description of the GPRS radio interface; Stage 2".
[8] 3GPP TS 44.018: "Mobile radio interface layer 3 specification, Radio Resource Control Protocol".
[9] 3GPP TS 44.060: "General Packet Radio Service (GPRS); Mobile Station (MS) - Base Station
System (BSS) interface; Radio Link Control/ Medium Access Control (RLC/MAC) protocol".
[10] 3GPP TS 45.002: "Multiplexing and multiple access on the radio path".
[11] 3GPP TS 45.005: "Radio transmission and reception".
[12] 3GPP TS 45.008: "Radio subsystem link control".
[13] 3GPP TS 45.050: "Background for RF Requirements".
[14] 3GPP TS 45.056: "CTS-FP Radio Sub-system".
[15] 3GPP TS 45.004: "Modulation".
[16] 3GPP TS 36.133: "Evolved Universal Terrestrial Radio Access (E-UTRA); Requirements for
support of radio resource management".
[17] 3GPP TS 36.211: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and
Modulation".
[18] 3GPP TS 49.031: "Location Services (LCS); Base Station System Application Part, LCS
Extension (BSSAP-LE)".
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1.2 Definitions and abbreviations
In addition to those below, abbreviations used in the present document are listed in 3GPP TR 21.905.
BTS: Base Transceiver Station.
BTTI: Basic TTI.
Coverage Class: see definition in 3GPP TS 43.064.
CTS-FP: CTS Fixed Part.
CTS-MS: MS operating in CTS mode.
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.
EC: Extended Coverage, see definition in 3GPP TS 43.064.
EC operation: see definition in 3GPP TS 43.064.
EC-GSM-IoT: Extended Coverage GSM for Internet of Things.
FANR (Fast Ack/Nack Reporting): Fast Ack/Nack Reporting enables the use of a PAN field within an RLC/MAC
block for EGPRS data transfer or for EGPRS2 data transfer. FANR enables the mobile station to transmit in the uplink
direction a PAN field corresponding to a downlink TBF. Similarly FANR enables the network to transmit in the
downlink direction a PAN field corresponding to an uplink TBF.
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 symbol, 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 symbols, but with a timing advance of T symbols, the reported timing offset will be P-T quantized to the
nearest symbol. For GPRS the MS timing offset is not reported.
Normal Symbol Period: duration of a symbol for bursts using a modulating symbol rate of 1625/6 ksymb/s (see 3GPP
TS 45.004); it is equal to 48/13 µs. This symbol duration is used for transmission of GMSK, 8PSK, 16QAM and
32QAM modulated bursts on downlink and GMSK, 8PSK and 16QAM modulated bursts on uplink (see 3GPP TS
45.004).
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).
PAN: Piggy-backed Ack/Nack.
Quarter symbol number: timing of quarter symbol periods (12/13 µs or 10/13 µs depending on the actual symbol
period used) within a timeslot. A symbol can represent 1 to 5 bits depending upon modulation.
Reduced Latency: refers to the use of FANR either in BTTI configuration or in RTTI configuration for EGPRS and
EGPRS2.
Reduced Symbol Period: duration of a symbol for bursts using a modulating symbol rate of 325 ksymb/s (see 3GPP
TS 45.004); it is equal to 40/13 µs. This symbol duration is used for transmission of QPSK, 16QAM and 32QAM
modulated bursts on uplink and downlink (see 3GPP TS 45.004).
RTTI: Reduced TTI.
Symbol Period: symbol period is the duration of a symbol and shall refer to normal symbol period unless explicitly
clarified to be the reduced symbol period.
TDMA frame number: count of TDMA frames relative to an arbitrary start point.
Timebase counters: set of counters which determine the timing state of signals transmitted by a BTS or MS.
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Time group (TG): used for compact, time groups shall be numbered from 0 to 3 and a particular time group shall be
referred to by its time group number (TG) (see 3GPP TS 45.002).
Timeslot number (TN): timing of timeslots within a TDMA frame.
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.
Timing Advance Index: Timing Advance Index TAI used for GPRS, which determines the position of the subchannel
on PTCCH (see 3GPP TS 45.002) used by the MS to send an access burst, from which the network can derive the
timing advance.
TTI: Transmission Time Interval.
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 carrier or, for COMPACT on the CPBCCH carrier, 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, control channel frames, and (for COMPACT) the rotation of
time groups 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".
Additionally, synchronization functions may be implemented in both the MS and the BTS to support the so-called
pseudo synchronization scheme for circuit-switched handovers. 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 for circuit-switched handovers are included in annex A.
While in dual transfer mode an MS performs all the tasks of dedicated mode. In addition, upper layers can require the
release of all the packet resources, which triggers the transition to dedicated mode, or the release of the RR resources,
which triggers the transition either to idle mode and packet idle mode or, depending upon network and MS capabilities,
to packet transfer mode.
When handed over to a new cell, the MS leaves the dual transfer mode, enters the dedicated mode where it switches to
the new cell, may read the system information messages sent on the SACCH and may then enter dual transfer mode in
the new cell (see 3GPP TS 44.060).
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.
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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 (for normal symbol period), a MS (for normal symbol period), a
CTS-FP, or an Compact BTS and MS is defined by the following counters:
- Quarter symbol number QN (0 - 624)
- Symbol 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); or
- for Compact, TDMA frame number FN (0 to (52 x 51 x 1024) -1 = 2715647).
In CTS, the CTS-MS shall manage different sets of counters for CTS operation and GSM operation.
Alternatively, in case of transmission using reduced symbol period, for a BTS or an MS the following counters have the
following ranges:
- Quarter symbol number QN (0-749)
- Symbol number BN (0-187)
3.2 Relationship between counters
The relationship between these counters is as follows:
- QN increments every 12/13 µs for normal symbol period and every 10/13µs for Reduced Symbol Period;
- BN = Integer part of QN/4;
- TN increments whenever QN changes from count 624 to 0 for normal symbol periodand whenever QN changes
from count 749 to 0 for reduced symbol period;
- 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.
4 Timing of transmitted signals
The timing of signals transmitted by the MS, BTS and CTS-FP is defined in 3GPP TS 45.002.
i) 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;
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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).
ii) For Compact, 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;
FN = (R1 x 51 + R2) x 52 + 51 when the synch burst is received (where R1 and R2 are contained in
information fields in synchronization burst);
TN is determined from TG as described in 3GPP TS 45.002, where TG is contained in information fields in
synchronization burst.
iii) 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.
iv) For EC-GSM-IoT, the MS can use the timing of receipt of the synchronization burst on EC-SCH to set up its
timebase counters as follows:
QN is set by the timing of the training sequence;
TN = 1 when the synch burst is received
FN = RFN + 51 x 26 x 512 x QUARTER_HYPERFRAME_INDICATOR
QH
where,
RFN = FN within a quarter hyperframe = (51 x 52 x T1') + (4 x 51 x T2' + 51 x T2'') + T3 when the synch
QH
burst is received,
T1', T2' are contained in information fields in the synchronization burst, and,
T2'' is signalled through the cyclic shift pattern used on the EC-SCH, see 3GPP TS 45.003.
T3 is determined e.g. by the device through the identification of the mapping of the FCCH, or EC-SCH,
onto the specific TDMA frames within the 51-multiframe.
QUARTER_HYPERFRAME_INDICATOR is obtained in the immediate assignment, see 3GPP TS
44.018.
NOTE: Depending on the coverage condition, the MS may optionally use the timing of receipt of the
synchronization burst (SCH) to set up its timebase counters as described in i).
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).
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5 BTS Requirements for Synchronization
5.0 General
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 or input level for reference performance, whichever applicable, in 3GPP TS 45.005 and 3 dB less
carrier to interference ratio than the reference interference ratios in 3GPP TS 45.005.
For EC-GSM-IoT, the conditions shall be met at the input level for reference performance of EC-RACH, and at the
reference carrier to interference ratios of the EC-RACH, for the highest coverage class, as defined in 3GPP TS 45.005
for the supported TS option(s) of EC-RACH.
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 and Local Area multicarrier BTS classes 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.
For COMPACT inter base station time synchronization is required such that timeslot number (TN) = i (i = 0 to 7) and
frame number (FN) with FN mod 208 =0 shall occur at the same time in all cells. The timebase counters of different
BTSs shall be synchronized together such that the timing difference between different BTSs shall be less than 1 symbol
period, 48/13 μs (which can be 1 or 3 bits depending upon modulation) measured at the BTS antenna.
If a cell defines a COMPACT cell in its neighbour list, time synchronization is required such that timeslot number
(TN) = i (i = 0 to 7) and frame number (FN) with FN mod 208 =0 shall occur at the same time in both cells.
When extended DRX (eDRX) is supported in a routing area (RA) time synchronization is required such that any given
timeslot number (TN) and frame number (FN) shall occur at the same time in all cells within the RA subject to an
allowed tolerance. The timebase counters of different BTSs shall be synchronized together such that the timing
difference between different BTSs (allowed tolerance) shall be less than 4 seconds measured at the BTS antenna.
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 ¼ normal symbol periods, measured at
the BTS antenna.
For pico-BTS and Local Area multicarrier BTS, the timing difference between different carriers shall be less than
2 symbol periods, measured at the BTS antenna.
5.4 Timing advance estimation
5.4.1 Initial timing advance estimation
When the BTS detects an access burst transmission on RACH, PRACH, or one or a sequence of access burst(s) on EC-
RACH, it shall measure the delay of this signal relative to the expected signal from an MS at zero distance under static
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channel conditions. This delay, called the timing advance, shall be rounded to the nearest normal symbol period and
included in a response from the BTS when applicable.
For the pico-BTS and Local Area multicarrier 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.
5.4.2 BTS Timing Advance Estimation for Positioning
A higher level of accuracy of the timing advance estimation by the BTS (reported to the SMLC, see 3GPP TS 43.059
[6]) is desired when the following positioning procedures are used:
- Multilateration Timing Advance procedure for assessing the timing advance in the serving cell and in non-
serving cells, and
- Multilateration Observed Time Difference procedure for assessing the timing advance in the serving cell,
The actual algorithms and methods for estimation of the timing advance value are implementation dependent.
Moreover, a BSC that reports a timing advance value based on transmissions from an MS (e.g. the EC Multilateration
Request message or EGPRS Multilateration Request message, see 3GPP TS 44.018 [8] and 3GPP TS 44.060 [9]) using
the RLC Data Block or the Extended Access Burst method, shall establish a reported timing advance value = .
It does so by first using the BTS estimated TA value = (based on the AB received on the RACH or on the
EC-RACH (including blind physical layer transmissions for CC2, CC3 and CC4) identified when the MS starts the
positioning procedure and using it as the assigned TA value = (i.e. the TA value sent to the MS using an
assignment message on the AGCH/EC-AGCH is the value of the rounded off to the nearest symbol). It then
adjusts the most recent estimated TA value as it receives subsequent updated timing advance estimation values from the
BTS (i.e. the BTS provides an updated timing advance estimation for each subsequent burst it receives from the MS for
the remainder of the positioning procedure wherein each burst sent by the MS uses the assigned TA).The final reported
TA value () is calculated by the BSC after it has received the last estimated TA value from the BTS based on
the last transmission from the MS for the current positioning procedure and takes into account the MS Transmission
Offset sent by the MS during the procedure (see 3GPP TS 44.018 [8] and 3GPP TS 44.060 [9] and 3GPP TS 43.059
[6]). This is shown in the formulas below.

= ∑ (1)
where
= + (2)
= ++ (3)  …
where corresponds to the time as reported by the MS in the "MS Transmission Offset IE" (see

3GPP TS 49.031 [18]).
For the Extended Access burst method the number of timing advance estimations is N= 2 wherein both the RACH burst
and the Extended Access burst are used for timing advance estimation. Similarly, for the RLC Data Block method the
number of timing advance estimations correspond to N=5 (for the case of no HARQ retransmissions needed on the (EC-
)PDTCH) wherein the AB received on RACH or EC-RACH and the 4 normal bursts used to receive the RLC data block
are used for timing advance estimation.
Moreover, a BTS estimating the timing advance value for an MS using the RLC Data Block or the Extended Access
Burst methods will be subject to an accuracy limitation inherent to its implementation and the radio conditions
applicable when receiving transmissions from the MS performing the Multilateration Timing Advance procedure. This
accuracy limitation is expressed as an assessment error of the reported TA value and shall be reported (to the
SMLC via the BSS) as the BTS Reception Accuracy Level (see 3GPP TS 43.059 [6] and 3GPP TS 49.031 [18])
wherein the assessment error corresponds to the variance of the reported timing advance value of multiple timing
advance estimations according to the equations below where N denotes the number of timing advance estimations and
t i=1.N denotes the estimated timing advance in estimation 'i'.
Ai,
The variance of the estimated timing advance value shall be evaluated using the formula:
ETSI
3GPP TS 45.010 version 15.2.0 Release 15 13 ETSI TS 145 010 V15.2.0 (2020-04)

()= (4) _
s is the unbiased sample variance

= ∑ − (5)
where and are calculated per the equations (1), (2) and (3) above.
For the Access Burst method the reported timing advance value corresponds to the estimated timing advance value
derived from receiving the AB containing the EC Multilateration Request message or EGPRS Multilateration Request
message.
When reporting the timing advance value to the SMLC the is rounded off to the nearest 1/64 of a normal
symbol period (see 3GPP TS 49.031 [18]).
Similarly, for the SMLC to be able to accurately estimate the number of required BTSs to be used during the
Multilateration Timing Advance procedure (in order to meet a targeted positioning accuracy) each individual BTS shall
provide the BSC with BTS Reception Accuracy Capability information (see 3GPP TS 49.031 [18]) as follows:
- with a guaranteed timing advance assessment error, it shall always be capable of supporting at radio conditions
down to the reference sensitivity level for RACH, if the BTS is capable of PEO operation, for all MTA radio
access methods supported by the BTS. The BTS Reception Accuracy Capability shall be evaluated at the
reference sensitivity level for PRACH/11 bits as specified in TS 45.005 [11].
- with a guaranteed timing advance assessment error, it shall always be capable of supporting at radio conditions
down to the input signal level for reference performance for EC-RACH (CC1), if the BTS is capable of EC
operation, for all MTA radio access methods supported by the BTS. The BTS Reception Accuracy Capability
shall be evaluated at the input signal level for reference performance for EC-RACH (CC1) as specified in TS
45.005 [11].
The BSC, in turn, reports this guaranteed timing advance assessment error value as the applicable BTS Reception
Accuracy Capability in the Assistance Information Response message sent to the SMLC in response to an Assistance
Information Request message (see 3GPP TS 43.059 [6]).
The BTS shall comply with the indicated BTS reception Accuracy Capability in 90 % of the timing advance
estimations.
5.5 Maximum timing advance value
The maximum timing advance value TA shall be 63. If the BTS measures a v
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