9 TOA based positioning

03.713GPPFunctional descriptionLocation Services (LCS)Release 1999Stage 2TS

After receiving the ‘BSSMAP-LE Connection Oriented Information (TOA Request) ‘ from VMSC/SMLC, the BSC shall initiate procedures for position the MS with TOA po sitioning method.

9.1 TOA procedures

9.1.1 Successful TOA Positioning Procedure for NSS based SMLC

Figure 52: TOA measurement flows

Positioning Preparations:

1. VMSC receives a ‘BSSMAP-LE Connection Oriented Information (TOA Request)’ message from SMLC, which contains the BSC delta timer value and an indication of the preferred type of handover (intra-cell to same channel, intra-cell to new channel or inter-cell). The message also contains the cell ID and TDMA frame number of the serving cell, and depending on the preferred handover type, also contains the cell ID and TDMA frame number for candidate (maximum six) cells for positioning handover.

2. The MSC sends the BSSMAP Connection Oriented Information (TOA Request) ‘ message to BSC with the same information received in step 1.

3. The BSC specifies the physical channel information (frequencies, hopping sequence, channel type, time slot for access burst etc.), cell ID, TA, measurement report, MS output power, and handover reference number in the ‘BSSMAP Connection Oriented Information (TOA Response) ‘ message to the VMSC. The BSC also starts the delta timer.

NOTE: If the BSC selects to use a different channel, this channel is reserved internally within the BSC, i.e. no additional signaling or delay is required. Based on the request information from SMLC, the BSC can choose between requesting an intra-cell handover (to same channel or to a new channel) or an inter-cell handover. If BSC decides to make an inter-cell handover the BSC selects a neighbor cell based on the measurement reports received from the MS (only neighbors for which the MS has been able to decode BSIC are possible to specify since the MS needs to know the timing of the target base station).

4. The VMSC forwards the information to the SMLC in ‘BSSMAP-LE Connection Oriented Information (TOA Response) ‘ message. SMLC uses this information for the configuration of the LMUs.

5. The SMLC selects which LMUs should measure and sends ‘DTAP-LE Register or Facility (LLP TOA Command)’ messages for each of these LMUs to the MSC according to the procedure defined in section7.8.1.1. Each DTAP-LE message is targeted to one LMU and specifies Radio Frequency List, Hopping Sequence Information, HO reference number, BSIC, Starting Time, Measurement Options, Starting Time Uncertainty, GPS Time Stamping Request.

6. The MSC sends the DTAP message, which reaches the LMUs over the air interface. It has been assumed here that the DTAP connection is already established at this point (refer to section7.8.1.1).

Positioning Establishment:

7. At expiration of the delta timer (note 1), the mobile is instructed to perform non-synchronized handover from the current radio channel (e.g. SDCCH or TCH) to a specified traffic channel with HANDOVER COMMAND message. A TDMA frame number at which the sending of ACCESS burst should begin is specified.

8. The MS starts sending the access burst in HANDOVER ACCESS message. At the same time, configured LMUs measure the Time of Arrival of access bursts.

9. The MS continues to send the access bursts until the timer T3124 expires when the MS returns to the old channel.

10. The MS sends the HANDOVER FAILURE message to the BSC.

11. LMUs report their measurement results in a ‘DTAP-LE Facility or Release Complete (LLP TOA Measurement Response)’ message to the VMSC.

12. The measurement results will be forwarded to the SMLC as a ‘DTAP-LE Facility or Release Complete (LLP TOA Measurement Response)’ message with measured TOA, TOA quality estimate, and Used Time Stamping. SMLC shall keep track of the number of expected measurement results from LMUs in the network. If a location estimate satisfying the requested QoS was not successfully obtained, the SMLC may initiate another TOA location attempt by restarting the TOA procedure at step 1.

NOTE 1: BSC starts the delta timer when received from the MSC in (2). The purpose of this timer is to allow enough time for MLC to initialize and configure all the LMUs for the TOA measurement. This timer value should be long enough for this task. When the BSC timer runs out, the BSC starts the handover process (step7).

NOTE 2: After a radio channel is allocated to the MS to be positioned, the MS starts sending measurement reports to the serving BTS. Based on these measurement reports the BSC would normally order handovers when considered necessary. If a radio related handover would take place between message 1 and 7, this would invalidate the information sent to the LMUs and positioning would fail. After the initialization of the delta timer in the BSC (step 3), the BSC shall cancel the ongoing positioning if a radio related handover has been requested. On the other hand, the BSC shall never allow any radio-related handover during steps 7 to 10.

9.1.2 Successful TOA Positioning Procedure for BSS based SMLC

FigureĀ 53: TOA measurement flows for BSS based SMLC

Positioning Preparations:

1. BSC receives a ‘BSSMAP-LE Connection Oriented Information (TOA Command)’ message from SMLC, which contains the BSC delta timer value and an indication of the preferred type of handover (intra-cell to same channel, intra-cell to new channel or inter-cell). The message also contains the cell ID and TDMA frame number of the serving cell, and depending on the preferred handover type, also contains the cell ID and TDMA frame number for candidate (maximum six) cells for positioning handover.

2. The BSC specifies the physical channel information (frequencies, hopping sequence, channel type, time slot for access burst etc.), cell ID, TA, measurement report, MS output power, and handover reference number in the ‘BSSMAP-LE Connection Oriented Information (TOA Response)’ message to the SMLC. The BSC also starts the delta timer. SMLC uses this information for the configuration of the LMUs

NOTE: If the BSC selects to use a different channel, this channel is reserved internally within the BSC, i.e. no additional signaling or delay is required. Based on the request information from SMLC, the BSC can choose between requesting an intra-cell handover (to same channel or to a new channel) or an inter-cell handover. If BSC decides to make an inter-cell handover the BSC selects a neighbor cell based on the measurement reports received from the MS (only neighbors for which the MS has been able to decode BSIC are possible to specify since the MS needs to know the timing of the target base station).

3. The SMLC selects which LMUs should measure and sends ‘DTAP-LE Resister or Facility (LLP TOA Command)’ messages for each of these LMUs according to the procedure defined in section 7.8.4.1Each LCS Information Request message is targeted to one LMU and specifies Radio Frequency List, Hopping Sequence Information, HO reference number, BSIC, Starting Time, Measurement Options, Starting Time Uncertainty, GPS Time Stamping Request. It has been assumed here that the DTAP connection is already established at this point (refer to section 7.8.4.1).

Positioning Establishment:

4. At expiration of the delta timer (note 1), the mobile is instructed to perform non-synchronized handover from the current radio channel (e.g. SDCCH or TCH) to a specified traffic channel with HANDOVER COMMAND message. A TDMA frame number at which the sending of ACCESS burst should begin is specified.

5. The MS starts sending the access burst in HANDOVER ACCESS message. At the same time, configured LMUs measure the Time of Arrival of access bursts.

6. The MS continues to send the access bursts until the timer T3124 expires when the MS returns to the old channel.

7. The MS sends the HANDOVER FAILURE message to the BSC.

8. The measurement results will be forwarded to the SMLC as a ‘DTAP-LE Facility or Release Complete (LLP TOA Measurement Response)’ LCS Information Response message with measured TOA, TOA quality estimate, and Used Time Stamping. SMLC shall keep track of the number of expected measurement results from LMUs in the network.

NOTE 1: BSC starts the delta timer when received from the SMLC in (1). The purpose of this timer is to allow enough time for SMLC to initialize and configure all the LMUs for the TOA measurement. This timer value should be long enough for this task. When the BSC timer runs out, the BSC starts the handover process (step 4).

NOTE 2: After a radio channel is allocated to the MS to be positioned, the MS starts sending measurement reports to the serving BTS. Based on these measurement reports the BSC would normally order handovers when considered necessary. If a radio related handover would take place between message 1 and 4, this would invalidate the information sent to the LMUs and positioning would fail. After the initialization of the delta timer in the BSC (step 2), the BSC shall cancel the ongoing positioning if a radio related handover has been requested. On the other hand, the BSC shall never allow any radio-related handover during steps 4 to 7.

9.1.3 Successful TOA positioning procedure in BSC

There are three messages defined to handle error scenarios during positioning procedure in BSC.
The messages are 1) Reject, 2) Abort and 3) Reset . Please refer to GSM 8.71 for details.

After receiving the BSSLAP TOA Command in BSC (message 2 in section 9.1.1 and message 1 in section 9.1.2), a Reject will be sent with proper cause value from BSC to SMLC in "BSSMAP Connection Oriented Information" if TOA positioning cannot be performed in BSC at that time for reasons other than handover or another ongoing RR management procedure.

Between messages 3 and 7 in section 9.1.1 and between messages 2 and 4 in section 9.1.2 (i.e the duration of delta timer in the BSC), an Abort or Reset is possible if the TOA positioning can not be done in BSC during that time. Reset is sent to SMLC to indicate when the positioning needs to be restarted after temporary interruption due to an intra BSC HO or other intra-BSC RR management procedure. If the Handover Complete or Handover Failure is not received before the delta timer expires, Abort may be sent at the expiration of delta timer from BSC to SMLC. Abort is used to indicate to SMLC the failure of the current TOA positioning attempt (e.g. due to inter-BSC handover) and allowing a new one from application level.