Actions
Location Services¶
NOTE: This page describes our understanding of the 3GPP specification; only parts of this (such as TA based positioning) are implemented so far in Osmocom!
LCS includes a variety of different methods, such as- Timing Advance
- E-OTD
- GNSS
- U-TDOA
- Multilateration TA
- Multilateration OTD
The most simple and hence most wide-spread approach is Timing Advance
Relevant specs¶
- 3GPP TS 43.059 "Functional stage 2 description of Location Services (LCS) in GERAN"
- 3GPP TS 48.031 "SMLC-SMLC Protocol" (SMLCPP)
- Based on ASN.1 PER; transferred via BSSAP-LE
- 3GPP TS 49.031 BSSAP LCS extension (BSSAP-LE)
- spoken on Lb (BSC-SMLC) and Lp (SMLC-SMLC) interface
- Lp uses connectionless SCCP only
- Lb uses connection-oriented SCCP and is very much like BSSAP/BSSMAP/DTAP on A interface
- spoken on Lb (BSC-SMLC) and Lp (SMLC-SMLC) interface
- 3GPP TS 48.071 "SMLC-BSS interface Layer 3" (BSSLAP)
- On Lb interface, encapsulated as BSSLAP APDU IE
Procedures¶
See 8.5.3 of TS 43.059
TA based positioning in CS domain for A interface¶
See Section 9.3 of 3GPP TS 43.059
MS in idle state¶
- MSC sends
BSSAP Perform Location Request
- BSC sends
SCCP-CR(BSSAP-LE Perform Location Request)
to SMLC - SMLC asks BSC to determine TA of MS via
SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))
- BSC sends PAGING REQUEST via BTS to MS
- MS sends PAGING RESPONSE via BTS to BSC; BTS adds timing offset information
- BSC reports CellID + TA value to SMLC
BSSMAP-LE Connection Oriented Info (TA Response)
- SMLC returns
BSSAP-LE Perform Location Response
to BSC - BSC returns result to MSC in
BSSAP Perform Location Response
MS in dedicated state¶
- MSC sends
BSSAP Perforl Location Request
- BSC sends
SCCP-CR(BSSAP-LE Perform Location Request)
, including a BSSLAP APDUTA Layer 3
with current TA - SMLC may decide to use the received TA, or to do another TA request:
- SMLC asks BSC to determine TA of MS via
SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))
- BSC checks current TA (as per measurement processing) for lchan of MS
- BSC reports CellID + TA value to SMLC
BSSMAP-LE Connection Oriented Info (TA Response)
- SMLC asks BSC to determine TA of MS via
- SMLC returns
BSSAP-LE Perform Location Response
to BSC - BSC returns result to MSC in
BSSAP Perform Location Response
Functionality in BSC¶
- BSC receives requests for LCS information from CN via A interface
- BSC passes those requests to the SMLC via Lb interface
- BSSAP-LE protocol stack (on top of SCCP) implementatioon
Functionality in SMLC¶
Protocol stack looks like this:- BSSLAP (TS 48.071)
- BSSAP-LE
Communication with MS¶
Protocol stack looks like this:- RRLP (TS 48.031)
- BSSLAP (TS 48.071)
- BSSAP-LE (TS 49.031)
Communication with peer SMLC¶
- SMLCPP (TS 48.031)
- BSSAP-LE (TS 49.031)
Message Segmentation¶
LCS messages can be segmented either- at the SMLCPP layer
- At RR layer (TS 44.018) and BSAP-LE Layer (TS 4.031) for segmentation of RRLP (TS 44.031) for legacy MS (<= Release 4)
Functionality in SMLC¶
*
Updated by laforge about 3 years ago · 7 revisions