Location Services » History » Version 2
laforge, 03/29/2020 09:57 AM
1 | 1 | laforge | h1. Location Services |
---|---|---|---|
2 | |||
3 | *NOTE: This page describes our current understanding of the 3GPP specification; +none of this is implemented so far in Osmocom!+* |
||
4 | |||
5 | LCS includes a variety of different methods, such as |
||
6 | * Timing Advance |
||
7 | * E-OTD |
||
8 | * GNSS |
||
9 | * U-TDOA |
||
10 | * Multilateration TA |
||
11 | * Multilateration OTD |
||
12 | |||
13 | The most simple and hence most wide-spread approach is _Timing Advance_ |
||
14 | |||
15 | h2. Relevant specs |
||
16 | |||
17 | * 3GPP TS 43.059 "Functional stage 2 description of Location Services (LCS) in GERAN" |
||
18 | 2 | laforge | * 3GPP TS 48.031 "SMLC-SMLC Protocol" (SMLCPP) |
19 | ** Based on ASN.1 PER; transferred via BSSAP-LE |
||
20 | * 3GPP TS 49.031 BSSAP LCS extension (BSSAP-LE) |
||
21 | ** spoken on Lb (BSC-SMLC) and Lp (SMLC-SMLC) interface |
||
22 | *** Lp uses connectionless SCCP only |
||
23 | *** Lb uses connection-oriented SCCP and is very much like BSSAP/BSSMAP/DTAP on A interface |
||
24 | * 3GPP TS 48.071 "SMLC-BSS interface Layer 3" |
||
25 | ** On Lb interface, encapsulated as APDU IE of BSSLAP |
||
26 | |||
27 | |||
28 | 1 | laforge | |
29 | h2. Procedures |
||
30 | |||
31 | See 8.5.3 of TS 43.059 |
||
32 | |||
33 | h3. TA based positioning in CS domain for A interface |
||
34 | |||
35 | See Section 9.3 of 3GPP TS 43.059 |
||
36 | |||
37 | h4. MS in idle state |
||
38 | |||
39 | * MSC sends @BSSAP Perform Location Request@ |
||
40 | * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ to SMLC |
||
41 | * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ |
||
42 | * BSC sends PAGING REQUEST via BTS to MS |
||
43 | * MS sends PAGING RESPONSE via BTS to BSC; BTS adds timing offset information |
||
44 | * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ |
||
45 | * SMLC returns @BSSAP-LE Perform Location Response@ to BSC |
||
46 | * BSC returns result to MSC in @BSSAP Perform Location Response@ |
||
47 | |||
48 | |||
49 | h4. MS in dedicated state |
||
50 | |||
51 | * MSC sends @BSSAP Perforl Location Request@ |
||
52 | * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ |
||
53 | * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ |
||
54 | * BSC checks current TA (as per measurement processing) for lchan of MS |
||
55 | * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ |
||
56 | * SMLC returns @BSSAP-LE Perform Location Response@ to BSC |
||
57 | * BSC returns result to MSC in @BSSAP Perform Location Response@ |
||
58 | |||
59 | |||
60 | h2. Functionality in BSC |
||
61 | |||
62 | * BSC receives requests for LCS information from CN via A interface |
||
63 | * BSC passes those requests to the SMLC via Lb interface |
||
64 | ** BSSAP-LE protocol stack (on top of SCCP) implementatioon |
||
65 | |||
66 | h2. Functionality in SMLC |
||
67 | |||
68 | Protocol stack looks like this: |
||
69 | * BSSLAP (TS 48.071) |
||
70 | * BSSAP-LE |
||
71 | |||
72 | h3. Communication with MS |
||
73 | |||
74 | Protocol stack looks like this: |
||
75 | * RRLP (TS 48.031) |
||
76 | * BSSLAP (TS 48.071) |
||
77 | * BSSAP-LE (TS 49.031) |
||
78 | |||
79 | h3. Communication with peer SMLC |
||
80 | |||
81 | * SMLCPP (TS 48.031) |
||
82 | * BSSAP-LE (TS 49.031) |
||
83 | |||
84 | h3. Message Segmentation |
||
85 | |||
86 | LCS messages can be segmented either |
||
87 | * at the SMLCPP layer |
||
88 | * 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) |
||
89 | |||
90 | |||
91 | h2. Functionality in SMLC |
||
92 | |||
93 | * |