Location Services » History » Version 4
laforge, 08/21/2020 04:07 PM
| 1 | 1 | laforge | h1. Location Services |
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| 2 | |||
| 3 | *NOTE: This page describes our current understanding of the 3GPP specification; +none of this is implemented so far in Osmocom!+* |
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| 4 | |||
| 5 | LCS includes a variety of different methods, such as |
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| 6 | * Timing Advance |
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| 7 | * E-OTD |
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| 8 | * GNSS |
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| 9 | * U-TDOA |
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| 10 | * Multilateration TA |
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| 11 | * Multilateration OTD |
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| 12 | |||
| 13 | The most simple and hence most wide-spread approach is _Timing Advance_ |
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| 14 | |||
| 15 | h2. Relevant specs |
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| 16 | |||
| 17 | * 3GPP TS 43.059 "Functional stage 2 description of Location Services (LCS) in GERAN" |
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| 18 | 2 | laforge | * 3GPP TS 48.031 "SMLC-SMLC Protocol" (SMLCPP) |
| 19 | ** Based on ASN.1 PER; transferred via BSSAP-LE |
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| 20 | * 3GPP TS 49.031 BSSAP LCS extension (BSSAP-LE) |
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| 21 | ** spoken on Lb (BSC-SMLC) and Lp (SMLC-SMLC) interface |
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| 22 | *** Lp uses connectionless SCCP only |
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| 23 | *** Lb uses connection-oriented SCCP and is very much like BSSAP/BSSMAP/DTAP on A interface |
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| 24 | 3 | laforge | * 3GPP TS 48.071 "SMLC-BSS interface Layer 3" (BSSLAP) |
| 25 | ** On Lb interface, encapsulated as _BSSLAP APDU IE_ |
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| 26 | 1 | laforge | |
| 27 | h2. Procedures |
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| 28 | |||
| 29 | See 8.5.3 of TS 43.059 |
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| 30 | |||
| 31 | h3. TA based positioning in CS domain for A interface |
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| 32 | |||
| 33 | See Section 9.3 of 3GPP TS 43.059 |
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| 34 | |||
| 35 | h4. MS in idle state |
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| 36 | |||
| 37 | * MSC sends @BSSAP Perform Location Request@ |
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| 38 | * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ to SMLC |
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| 39 | * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ |
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| 40 | * BSC sends PAGING REQUEST via BTS to MS |
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| 41 | * MS sends PAGING RESPONSE via BTS to BSC; BTS adds timing offset information |
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| 42 | * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ |
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| 43 | * SMLC returns @BSSAP-LE Perform Location Response@ to BSC |
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| 44 | * BSC returns result to MSC in @BSSAP Perform Location Response@ |
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| 45 | |||
| 46 | |||
| 47 | h4. MS in dedicated state |
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| 48 | |||
| 49 | * MSC sends @BSSAP Perforl Location Request@ |
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| 50 | * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ |
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| 51 | * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ |
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| 52 | * BSC checks current TA (as per measurement processing) for lchan of MS |
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| 53 | * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ |
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| 54 | * SMLC returns @BSSAP-LE Perform Location Response@ to BSC |
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| 55 | * BSC returns result to MSC in @BSSAP Perform Location Response@ |
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| 56 | |||
| 57 | |||
| 58 | h2. Functionality in BSC |
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| 59 | |||
| 60 | * BSC receives requests for LCS information from CN via A interface |
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| 61 | * BSC passes those requests to the SMLC via Lb interface |
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| 62 | ** BSSAP-LE protocol stack (on top of SCCP) implementatioon |
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| 63 | |||
| 64 | h2. Functionality in SMLC |
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| 65 | |||
| 66 | Protocol stack looks like this: |
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| 67 | * BSSLAP (TS 48.071) |
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| 68 | * BSSAP-LE |
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| 69 | |||
| 70 | h3. Communication with MS |
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| 71 | |||
| 72 | Protocol stack looks like this: |
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| 73 | * RRLP (TS 48.031) |
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| 74 | * BSSLAP (TS 48.071) |
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| 75 | * BSSAP-LE (TS 49.031) |
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| 76 | |||
| 77 | h3. Communication with peer SMLC |
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| 78 | |||
| 79 | * SMLCPP (TS 48.031) |
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| 80 | * BSSAP-LE (TS 49.031) |
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| 81 | |||
| 82 | h3. Message Segmentation |
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| 83 | |||
| 84 | LCS messages can be segmented either |
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| 85 | * at the SMLCPP layer |
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| 86 | * 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) |
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| 87 | |||
| 88 | |||
| 89 | h2. Functionality in SMLC |
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| 90 | |||
| 91 | 3 | laforge | * |
