A.3 Measure Position Response

04.313GPPLocation Services (LCS)Mobile Station (MS) - Serving Mobile Location Centre (SMLC) Radio Resource LCS Protocol (RRLP)TS

A.3.1 General

The Measure Position Response is a RRLP component from the MS to the network. It is the response to the Measure Position Request. It contains the following elements. One of the three elements containing measurement data or location estimate (E-OTD Measurement Information, Location Information or GPS Measurement Information) or Location Information Error element must be included.

Table A.2: Measure Position Response component content

Element

Type/Reference

Presence

Multiple Sets

Multiple Sets 3.2.1

O

Reference BTS Identity

Reference BTS Identity 3.2.2

O

E-OTD Measurement Information

E-OTD Measurement Information 3.2.3

O

Location Information

Location Information 3.2.4

O

GPS Measurement Information

GPS Measurement Information 3.2.5

O

Location Information Error

Location Information Error 3.2.6

C

GPS Time Assistance Measurements

GPS Time Assistance Measurements 3.2.6a

O

A.3.2 Elements

A.3.2.1 Multiple Sets Element

This element indicates how many E-OTD Measurement Information sets or GPS Measurement Information sets, and Reference BTS Identities are included to this element. This element is optional. If this element is absent, a single measurement set is included.

Number of E-OTD/GPS Measurement Information Sets

This field indicates the number of Number of E-OTD/GPS Measurement Information sets included to this component. This field is mandatory. If both types of measurement elements are present, then there are the equal number of them, and each pair has the same reference BTS.

Range: 2 – 3

Number of Reference BTS

This field indicates the number of reference BTSs used in this component. This field is mandatory.

Range: 1-3

Reference BTS relation to Measurement Elements

This field indicates how the reference BTSs listed in this element relate to measurement sets later in this component. This field is conditional and included only if Number of E-OTD/GPS Measurement Information Sets is ‘3’ and Number of Reference BTSs is ‘2’.

‘0’ = First reference BTS is related to first and second E-OTD/GPS Measurement Information Sets, and second reference BTS is related to third E-OTD/GPS Measurement Information Sets.

‘1’ = First reference BTS is related to first and third E-OTD/GPS Measurement Information Sets, and second reference BTS is related to second E-OTD/GPS Measurement Information Sets.

‘2’ = First reference BTS is related to first E-OTD/GPS Measurement Information Sets, and second reference BTS is related to second and third E-OTD/GPS Measurement Information Sets.

If this field is not included, the relation between reference BTS and Number of E-OTD/GPS Measurement Information Sets is as follows:

– if there are three sets and three reference BTSs -> First reference BTS relates to first set, second reference BTS relates to second set, and third reference BTS relates to third set;

– if there are two sets and two reference BTS -> First reference BTS relates to first set, and second reference BTS relates to second set;

– if there is only one reference BTS and 1-3 sets -> this reference BTS relates to all sets.

A.3.2.2 Reference BTS Identity Element

This element identifies the reference BTS(s). This element is conditional to the number of reference BTSs. It is mandatory, if there is more than one reference BTS, and optional otherwise. If this element is not included, the Reference BTS, used in other elements, is the current serving BTS of MS. If this element is included, the BTSs defined here are used as Reference BTSs in all other elements.

The following fields are repeated for the number of reference BTSs included in the Number of Reference BTS field.

CellIdType

This field indicates is the identity method of the Reference BTS. This field is mandatory within this element.

‘0’ = Cell identity is told using BSIC and BCCH carrier.

‘1’ = Cell identity is told using CI, and the LAC is the same as the current serving BTS.

‘2’ = Cell identity is told using an index referring to the BTS listed in the Measure Position Request component (the indicated reference BTS is 1)

‘3’ = Cell identity is told using an index referring to the BTS listed in the BCCH allocation list (System Information Neighbor Lists) of the serving BTS. This type of reference identity shall not be used by the MS unless it has received the “E-OTD Measurement Assistance Data for System Information List Element” from the SMLC for this cell.

‘4’ = Cell identity is told using CI, and the LAC.

Reference LAC

This field indicates the Location Area Code of the reference BTS. The purpose of the Location Area Code is to identify a location area. This field is conditional, and included, if CellIDType field is ‘4’.

Range: 0 – 65535

Reference CI

This field indicates the Cell Identity value of the reference BTS. The purpose of the Cell Identity value is to identify a cell within a location area. This field is conditional, and included, if CellIDType field is ‘1’ or ‘4’.

Range: 0 – 65535

Reference BCCH Carrier

This field indicates the absolute RF channel number of the BCCH of the reference base station. BCCH carrier field is conditional and is included only if CellIdType is set ‘0’.

Range: 0 – 1023

Reference BSIC

This field indicates the BSIC (Base Station Identity Code of the base station).

BSIC field is conditional and is included only if CellIdType is set ‘0’ or ‘3’.

Range: 0 – 63

Request Index

This field indicates an index identifying the reference BTS by referring to the BTSs listed in the Measure Position Request component (the indicated reference BTS in the Measure Position Request component has the index value 1, and possible next BTS ‘2’, and so on )

This field is conditional and included only if CellIdType is set to ‘2’.

Range: 1-16

System Info Index

This field indicates an index identifying the reference BTS by referring to the BCCH allocation list (System Information Neighbor List) of the serving BTS.

This field is conditional and included only if CellIdType is set to ‘3’.

Range: 1-32

A.3.2.3 E-OTD Measurement Information Element

The purpose of the E-OTD Measurement Information element is to provide OTD measurements of signals sent from the reference and neighbor based stations. The length of this element depends on the number of neighbor cells for which OTD measurements have been collected. This element is optional in the Measure Position Response component. It is included in the Measure Position Response component, if the network has requested the mobile to perform the MS assisted E-OTD method. BTSs which cannot be measured or whose measurements are excessively inaccurate need not be reported. The MS may include measurements for other BTSs not given in the assistance data by the SMLC.

The E-OTD and 51 multiframe offset values are reported relative to the reference BTS as defined in the previous clauses.

The following fields are repeated for each measurement set.

Reference Frame Number

This field indicates the frame number of the last measured burst from the reference BTS modulo 42432. This information can be used as a time stamp for the measurements. This field is mandatory.

Range: 0 – 42431

Reference Time Slot

Reference Time Slot indicates the time slot modulo 4 relative to which the MS reports the reference BTS measurements. This field is mandatory.

Range: 0 to 3

NOTE: If MS does not know timeslot scheme, the MS reports the used timeslot. MS can only report results based on one time slot (N) or two time slots (N and N+4). If the MS knows the timeslot scheme, it can make measurements from several timeslots and reports that the used timeslot is zero (and makes correction).

Reference Quality

Reference Quality field includes the standard deviation of the TOA measurements from the reference BTS with respect to TRef (where TRef is the time of arrival of signal from the reference BTS used to calculate the OTD values). This field is optional. The Reference Quality field can be used to evaluate the reliability of E-OTD measurements in the SMLC and in weighting of the E-OTD values in the location calculation.

Following linear 5 bit encoding is used

‘00000’ 0 – (R*1-1) meters

‘00001’ R*1 – (R*2-1) meters

‘00010’ R*2 – (R*3-1) meters

‘11111’ R*31 meters or more

where R is the resolution defined by Std Resolution field. For example, if R=20 meters, corresponding values are 0 – 19 meters, 20 – 39 meters, 40 – 59 meters, …, 620+ meters.

Number of Measurements

Number of Measurements for the Reference Quality field is used together with Reference Quality to define quality of the reference base site TOA. The field indicates how many measurements have been used in the MS to define the standard deviation of the measurements. Following 3 bit encoding is used

‘000’: 2-4

‘001’: 5-9

‘010’: 10-14

‘011’: 15-24

‘100’: 25-34

‘101’: 35-44

‘110’: 45-54

‘111’: 55 or more

This field is optional.

Std Resolution

Std Resolution field includes the resolution used in Reference Quality field and Std of EOTD Measurements field. Encoding on 2 bits as follows

’00’ 10 meters

’01’ 20 meters

’10’ 30 meters

’11’ Reserved.

This field is mandatory.

TA Correction

This field indicates the estimate of the time difference between the moment that the MS uses to adjust its internal timing for reception and transmission (e.g. corresponding to maximum energy) and the estimate of the reception of the first arriving component from the serving BTS. This value can be used as a correction by the SMLC to the Timing Advance (TA) value when the distance between the MS and the serving BTS is estimated based on TA.

The value TACor in this field corresponds to the TA Correction in bit periods as follows:

TA Correction in bit periods = TACor/64 –8.

TA Correction has the resolution of 1/64 bit period, and the range – 8 … +7 bit periods. Negative TA Correction in bits indicates that the first signal component from the serving BTS is estimated to arrive before the moment used for communication. This field is optional.

Range: 0-960

Number of Measured Neighbors

This field indicates the number of different neighbor BTSs. This field is mandatory.

Range: 0 – 10

NOTE: If the MS can not measure any neighbor BTSs, then this value is set to ‘0’.

The following fields are repeated for the number of BTSs included in the Number of Measured Neighbors field.

Neighbor Identity Present

The presence of this field is conditional, it shall not be present in the first set. It is mandatory for the other sets. This field indicates whether the identity information (i.e. CellIDType and possibly Neighbor CI / Neighbor BCCH Carrier / Neighbor BSIC / Neighbor Multiframe Offset / Request Index / System Info Index fields) concerning a certain BTS is present or whether the BTS identity is given as reference to the first measurement set.

‘0’ Identity information not included, and identity of this BTS is same as the identity of BTS in first set with same sequence number

‘1’ Identity information is included

CellIdType

This field indicates is the identity method of the cell. This field is conditional, and included if Neighbor Identity Present is ‘1’. If CellIdType field is not present, the following fields can not be present either: Neighbor CI, Neighbor BCCH Carrier, Neighbor BSIC, Neighbor Multiframe Offset, Request Index, System Info Index.

‘0’ = Cell identity is told using BSIC and BCCH carrier.

‘1’ = Cell identity is told using CI, and the LAC is the same as the current serving BTS.

‘2’ = Cell identity is told using 51 Multiframe offset and BCCH carrier.

‘3’ = Cell identity is told using an index referring to the BTS listed in the Measure Position Request component (the indicated reference BTS is 1).

‘4’ = Cell identity is told using an index referring to the BTS listed in the BCCH allocation list (System Information Neighbor Lists) of the serving BTS. This type of neighbor identity shall not be used by the MS unless it has received the “E-OTD Measurement Assistance Data for System Information List Element” from the SMLC for this cell.

‘5’ = Cell identity is told using CI and the LAC.

NOTE: The MS can decide which of these methods to use. The CellIdType ‘3’ and ‘4’ are preferred.

Neighbor LAC

This field indicates the Location Area Code of the neighbor BTS. The purpose of the Location Area Code is to identify a location area. This field is conditional, and included, if CellIDType field is ‘5’.

Range: 0 – 65535

Neighbor CI

This field indicates the Cell Identity of the particular neighbor cell. The purpose of the Cell Identity value is to identify a cell within a location area.

Neighbor CI field is conditional and is included only if CellIdType is set ‘1’ or ‘5’ and the CI value of the given cell is available.

Range: 0 – 65535

Neighbor BCCH Carrier

This field indicates the absolute RF channel number of the BCCH of the neighbor base station. BCCH carrier field is conditional and is included only if CellIdType is set ‘0’ or ‘2’.

Range: 0 – 1023

Neighbor BSIC

This field indicates the BSIC (Base Station Identity Code of the base station).

BSIC field is conditional and is included only if CellIdType is set ‘0’ or ‘4’.

Range: 0 – 63

Neighbor Multiframe Offset

This field indicates the frame difference between the start of the 51 multiframes frames arriving from this BTS and the reference BTS. The multiframe offset is defined as TBTS – TRef, where TBTS is the time of the start of the 51 multiframe in the BTS in question, and TRef is the time of the start of the 51 multiframe in the reference BTS. This field is conditional and included only if CellIdType is set to ‘2’.

Range: 0 – 51

Request Index

This field indicates an index identifying the reference BTS by referring to the BTSs listed in the Measure Position Request component (the indicated reference BTS in the Measure Position Request component has the index value 1, and possible next BTS ‘2’, and so on).

This field is conditional and included only if CellIdType is set to ‘3’.

Range: 1-16

System Info Index

This field indicates an index identifying the reference BTS by referring to the BCCH allocation list (System Information Neighbor List) of the serving BTS.

This field is conditional and included only if CellIdType is set to ‘4’.

Range: 1-32

Neighbor Time Slot

Neighbor Time Slot indicates the time slot modulo 4 relative to which the MS reports the neighbor BTS measurements. This field is mandatory.

Range: 0 to 3

NOTE: If the MS does not know the timeslot scheme, the MS reports the used timeslot. MS can only report a result based on one time slot (N) or two time slots (N and N+4). If the MS knows the timeslot scheme, the MS can make measurements from several timeslots and reports that the used timeslot is zero (and makes correction).

Number of EOTD Measurements

Number of Measurements field is used together with Std of EOTD Measurements field to define quality of a reported EOTD measurement. The field indicates how many EOTD measurements have been used in the MS to define the standard deviation of these measurements. Following 3 bit encoding is used.

‘000’: 2-4

‘001’: 5-9

‘010’: 10-14

‘011’: 15-24

‘100’: 25-34

‘101’: 35-44

‘110’: 45-54

‘111’: 55 or more

This field is mandatory.

Std of EOTD Measurements

Std of EOTD Measurements field includes standard deviation of EOTD measurements. This field is mandatory. It can be used to evaluate the reliability of EOTD measurements in the SMLC and in weighting of the OTD values in location calculation.

Following linear 5 bit encoding is used

‘00000’ 0 – (R*1-1) meters

‘00001’ R*1 – (R*2-1) meters

‘00010’ R*2 – (R*3-1) meters

‘11111’ R*31 meters or more

where R is the resolution defined by Std Resolution field. For example, if R=20 meters, corresponding values are 0 – 19 meters, 20 – 39 meters, 40 – 59 meters, …, 620+ meters.

OTD

This field indicates the measured OTD value between the receptions of signals from the reference and the neighbor BTS. The OTD is defined as TNbor – TRef (modulo burst length) where TNbor is the time of arrival of signal from the neighbor BTS, and TRef is the time of arrival of signal from the reference BTS. The reporting resolution of the OTD value is 1/256 bit. This field is mandatory.

Range: 0 – 39999

A.3.2.3a E-OTD Measurement Extended Information Element

The purpose of the E-OTD Measurement Ext Information element is to provide OTD measurements of signals sent from the reference and neighbor base stations. The length of this element depends on the number of neighbor cells for which OTD measurements have been collected. This element is optional in the Measure Position Response component. It is included in the Measure Position Response component, if E-OTD measurements didn’t fit in the E-OTD Measurement Information Element.

The E-OTD and 51 multiframe offset values are reported relative to the reference BTS as defined in the previous clauses.

The following fields are valid only for the first set of measurements

Number of Measured Neighbors

This field indicates the number of different neighbor BTSs. This field is mandatory.

Range: 0 – 5

NOTE: If the MS can not measure any neighbor BTSs, then this value is set to ‘0’.

The following fields are repeated for the number of BTSs included in the Number of Measured Neighbors field. They are defined in the previous subclause :

CellIdType, Neighbor LAC, Neighbor CI, Neighbor BCCH Carrier, Neighbor BSIC, Neighbor Multiframe Offset, Request Index, System Info Index, Neighbor Time Slot, Number of EOTD Measurements, Std of EOTD Measurements, OTD

A.3.2.4 Location Information Element

The purpose of Location Information element is to provide the location estimate from the MS to the network, if the MS is capable of determining its own position. Optionally, the element may contain the velocity parameters computed by the MS.

This element is optional. This element contains the following fields.

Reference Frame

This field specifies the reference BTS Reference Frame number during which the location estimate was measured. The time of the Reference Frame boundary is as observed by the MS, ie without Timing Advance compensation. This field is mandatory. However, if the Reference Frame number is within (42432..65535), the value of this field shall be ignored and in that case the MS should provide GPS TOW if available.

Table A.3: Reference Frame field contents

Parameter

# of Bits

Resolution

Range

Units

Reference Frame

16

0 – 65535

frames

Note that expected values for Reference Frame are in range 0 – 42431.

GPS TOW

This field specifies the GPS TOW for which the location estimate is valid , rounded down to the nearest millisecond unit. This field is optional but shall be included if GPS Time Assistance Measurements are included. If GPS Time Assistance Measurements are included in the RRLP Measure Position Response, the MS shall align GPS System time (as defined by the GPS TOW and the GPS TOW Subms fields) with the reported GSM frame boundary observed by the MS at that time.

Table A.4: GPS TOW field contents

Parameter

# of Bits

Resolution

Range

Units

GPS TOW

24

1 ms

0 – 14399999

ms

The 24 bits of GPS TOW are the least significant bits. The most significant bits shall be derived by the Serving Mobile Location Center to unambiguously derive the GPS TOW.

Fix Type

This field contains an indication as to the type of measurements performed by the MS: 2D or 3D. This field is mandatory.

‘0’ = 2D fix

‘1’ = 3D fix

Position Estimate

This field contains the calculated position estimate in the format defined in 3GPP TS 03.32. The allowed shapes are:

– ellipsoid Point;

– ellipsoid point with uncertainty circle;

– ellipsoid point with uncertainty ellipse;

– ellipsoid point with altitude and uncertainty ellipsoid.

A.3.2.5 GPS Measurement Information Element

The purpose of the GPS Measurement Information element is to provide GPS measurement information from the MS to the SMLC. This information includes the measurements of code phase and Doppler, which enables the network-based GPS method where position is computed in the SMLC. The proposed contents are shown in table A.5, and the individual fields are described subsequently. See also Figure A.1 for an illustration of the relation between some of the fields.

Figure A.1. Exemplary definitions of GPS measurement information fields.

This element is included in the Measure Position Response component if the network has requested the mobile to perform mobile-assisted location measurements using a GPS location method.

Following fields are repeated a number of times told in Number of E-OTD/GPS Measurement Sets field if Multiple Sets element is included. If Multiple Sets element is not included, the default value for sets is one (i.e. the following fields are present only once).

Table A.5: GPS Measurement Information element content

Element fields

Presence

Occurrences

Reference Frame

O

1

GPS TOW

M

1

# of Satellites (N_SAT)

M

1

Measurement Parameters

M

N_SAT

The following paragraphs describe the content of each information field of this element.

Reference Frame

This field is optional.

Table A.6: Reference Frame field contents

Parameter

# of Bits

Resolution

Range

Units

Reference Frame

16

0 – 65535

frames

Note that expected values for Reference Frame are in range 0 – 42431. If Reference Frame and GPS Time Assistance Measurements both are included in the RRLP Measure Position Response, the code phase measurements shall be aligned with the reported GSM frame boundary observed by the MS at that time, as indicated in Figure A.1. The time of the Reference Frame boundary is as observed by the MS, ie without Timing Advance compensation.

GPS TOW

This field specifies the GPS TOW for which the location estimate is valid, rounded down to the nearest millisecond unit. This field is mandatory.

Table A.7: GPS TOW field contents

Parameter

# of Bits

Resolution

Range

Units

GPS TOW

24

1 ms

0 – 14399999

ms

The 24 bits of GPS TOW are the least significant bits. The most significant bits shall be derived by the Serving Mobile Location Center to unambiguously derive the GPS TOW.

# of Satellites (N_SAT)

Number of Measurements

This field specifies the number of measurements for which measurements satellites are provided in the component. This value represents the number of satellites that were measured by the MS. This value of N_SAT determines the length of the payload portion of the component. Typical range for N_SAT is four to a maximum of 12. This field is mandatory and occurs once per set.

Table A.7a: # of Satellites field contents

Parameter

# of Bits

Resolution

Range

Units

N_SAT

4

1 – 16

Measurement Parameters

This field contains information about the measurements of code phase and Doppler, which enables the network-based method where position is computed in the SMLC. This field is mandatory and occurs N_SAT times per message.

Table A.8: Measurement Parameters field contents

Parameter

# of Bits

Resolution

Range

Units

Satellite ID

6

0 – 63

C/No

6

1

0 – 63

dB-Hz

Doppler

16

0.2

6553.6

Hz

Whole Chips

10

1

0 – 1022

chips

Fractional Chips

10

2-10

0 – (1-2-10)

chips

Multipath Indicator

2

see Table A.9

TBD

Pseudorange RMS Error

6

3 bit mantissa

3 bit exp

0.5 – 112

m

Satellite ID

This field identifies the particular satellite for which the measurement data is valid. This values 0 – 63 represent satellite PRNs 1 – 64, respectively.

C/N0

This field contains the estimate of the carrier-to-noise ratio of the received signal from the particular satellite used in the measurement. It is given in whole dBs and has a range of 0 to 63. Typical levels observed by MS-based GPS units will be in the range of 20 dB to 50 dB.

Doppler

This field contains the Doppler measured by the MS for the particular satellite signal. This information can be used to compute the 3-D velocity of the MS. The Doppler range is sufficient to cover the potential range of values measured by the MS.

Whole Chips

This field contains the whole value of the code-phase measurement made by the MS for the particular satellite signal at the time of measurement, in units of 1 GPS chip in the range from 0 to 1022 chips, where increasing binary values of the field signify increasing measured pseudoranges. The code phase measurement is divided into two fields, “Whole Chips” and “Fractional Chips”.

Fractional Chips

This field contains the fractional value of the code-phase measurement made by the MS for the particular satellite signal at the time of measurement. The resolution of the fractional portion is approximately 0,3 m.

Multipath Indicator

This field contains the Multipath Indicator value. This parameter is specified according to the representation described in table A.9.

Table A.9: Multipath Indicator values and associated indications

Value

Multipath Indication

00

Not measured

01

Low, MP error < 5m

10

Medium, 5m < MP error < 43m

11

High, MP error > 43m

Range: 0 – 3

Pseudorange RMS Error

This field contains a Pseudorange RMS Error value.

Range: 0,5 m to 112 m

NOTE: This parameter is specified according to a floating-point representation as described in Table A.10.

Table A.10: Pseudorange RMS Error representation

Index

Mantissa

Exponent

Floating-Point value, xi

Pseudorange value, P

0

000

000

0.5

P < 0.5

1

001

000

0.5625

0.5 <= P < 0.5625

I

x

y

0.5 * (1 + x/8) * 2y

xi-1 <= P < xi

62

110

111

112

104 <= P < 112

63

111

111

112 <= P

A.3.2.6 Location Information Error Element

The purpose of Location Information Error element is to provide the indication of error and the reason for it, when the MS can not perform the required location or the network can not determine the position estimate. The element may also indicate what further assistance data may be needed by the target MS to produce a successful location estimate or location measurements. This element is optional. This element has the following fields.

Error Reason

This field indicates the reason for error. This field is mandatory.

‘0’: Undefined error.

‘1’: There were not enough BTSs to be received when performing mobile based E-OTD.

‘2’: There were not enough GPS satellites to be received, when performing GPS location.

‘3’: E-OTD location calculation assistance data missing.

‘4’: E-OTD assistance data missing.

‘5’: GPS location calculation assistance data missing.

‘6’: GPS assistance data missing.

‘7’: Requested method not supported.

‘8’: Location request not processed.

‘9’: Reference BTS for GPS is not the serving BTS.

’10’: Reference BTS for E-OTD is not the serving BTS.

Additional Assistance Data

This field is optional. Its presence indicates that the target MS will retain assistance data already sent by the SMLC. The SMLC may send further assistance data for any new location attempt but need not resend previous assistance data. The field may contain the following:

GPS Assistance Data:

necessary additional GPS assistance data (structure and encoding as for the GPS Assistance Data IE in 3GPP TS 09.31 excluding the IEI and length octets)

A.3.2.6a GPS Time Assistance Measurements Element

This IE contains measurements that are used to define an accurate relation between GSM and GPS time or to provide additional GPS TOW information for MS Assisted A-GPS. The contents are shown in Table A.10a, and the individual fields are described subsequently.

Table A.10a: GPS Time Assistance Measurements Information element content

Element fields

Presence

Reference Frame MSB

O

GPS TOW Subms

O

Delta TOW

O

GPS Reference Time Uncertainty

O

Reference Frame MSB

This field shall be included when GPS-GSM time association is provided for either MS Based A-GPS or MS Assisted A-GPS. It indicates the Most Significant Bits (MSBs) of the frame number of the reference BTS corresponding to the GPS measurement or location estimate. Starting from the complete GSM frame number denoted FN, the MS calculates Reference Frame MSB as

Reference Frame MSB = floor(FN/42432)

The complete GSM frame number FN can then be reconstructed in the SMLC by combining the fields Reference Frame with Reference Frame MSB in the following way

FN = Reference Frame MSB*42432+Reference Frame

Range: 0-63

GPS TOW Subms

This field is only applicable for MS-Based A-GPS. This field indicates in units of 100ns the submillisecond part of the GPS time of measurement. This field together with the GPS TOW field in the Location Information Element provides a more accurate time stamp of the location estimate for MS based AGPS Expressed in units of microseconds. The precise GPS time of measurements in milliseconds is thus equal to

GPS TOW + 0.0001*GPS TOW Subms

The estimation of precise GPS time of measurement using AGPS is vulnerable to millisecond ambiguities. Therefore the MS shall only report this field when it is confident that any millisecond ambiguities have been avoided.

Range: 0-9999

Delta TOW

This field is only applicable for MS-Assisted A-GPS. This field specifies the difference in milliseconds between the GPS TOW reported in the GPS Measurement Information Element and the millisecond part of the SV time tsv_1 of the first SV in the list reported from the MS. Figure A.1 shows an example of Delta TOW calculation. The Delta TOW is defined as Delta TOW = GPS TOW – fix(tsv_1) where fix() denotes rounding to the nearest integer towards zero. The estimation of tsv_1, which forms the basis for the calculation of Delta TOW, is vulnerable to millisecond ambiguities. Therefore the MS shall only report this field when it is confident that the correct millisecond event has been recovered.

Range: 0-127

GPS Reference Time Uncertainty

This element is optional. It provides the accuracy of the relation GPS and GSM time in the Location Information or GPS Measurement Information Element when GPS-GSM time association is provided. For MS Assisted A-GPS when GPS-GSM time association is not provided, even if GPS Time Assistance Measurement Request is not included in the Measure Position Request, this element can be included to provide the accuracy of the reported GPS TOW. The interval, range and treatment is as described in sub-clause 2.2.4b.