Location Services » History » Version 1
laforge, 03/28/2020 06:56 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 | * 3GPP TS 48.031 (SMLCPP) |
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| 19 | |||
| 20 | h2. Procedures |
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| 21 | |||
| 22 | See 8.5.3 of TS 43.059 |
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| 23 | |||
| 24 | h3. TA based positioning in CS domain for A interface |
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| 25 | |||
| 26 | See Section 9.3 of 3GPP TS 43.059 |
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| 27 | |||
| 28 | h4. MS in idle state |
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| 29 | |||
| 30 | * MSC sends @BSSAP Perform Location Request@ |
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| 31 | * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ to SMLC |
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| 32 | * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ |
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| 33 | * BSC sends PAGING REQUEST via BTS to MS |
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| 34 | * MS sends PAGING RESPONSE via BTS to BSC; BTS adds timing offset information |
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| 35 | * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ |
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| 36 | * SMLC returns @BSSAP-LE Perform Location Response@ to BSC |
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| 37 | * BSC returns result to MSC in @BSSAP Perform Location Response@ |
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| 38 | |||
| 39 | |||
| 40 | h4. MS in dedicated state |
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| 41 | |||
| 42 | * MSC sends @BSSAP Perforl Location Request@ |
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| 43 | * BSC sends @SCCP-CR(BSSAP-LE Perform Location Request)@ |
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| 44 | * SMLC asks BSC to determine TA of MS via @SCCP-DT1(BSSMAP-LE Connection Oriented Info (TA Request))@ |
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| 45 | * BSC checks current TA (as per measurement processing) for lchan of MS |
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| 46 | * BSC reports CellID + TA value to SMLC @BSSMAP-LE Connection Oriented Info (TA Response)@ |
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| 47 | * SMLC returns @BSSAP-LE Perform Location Response@ to BSC |
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| 48 | * BSC returns result to MSC in @BSSAP Perform Location Response@ |
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| 49 | |||
| 50 | |||
| 51 | h2. Functionality in BSC |
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| 52 | |||
| 53 | * BSC receives requests for LCS information from CN via A interface |
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| 54 | * BSC passes those requests to the SMLC via Lb interface |
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| 55 | ** BSSAP-LE protocol stack (on top of SCCP) implementatioon |
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| 56 | |||
| 57 | h2. Functionality in SMLC |
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| 58 | |||
| 59 | Protocol stack looks like this: |
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| 60 | * BSSLAP (TS 48.071) |
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| 61 | * BSSAP-LE |
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| 62 | |||
| 63 | h3. Communication with MS |
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| 64 | |||
| 65 | Protocol stack looks like this: |
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| 66 | * RRLP (TS 48.031) |
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| 67 | * BSSLAP (TS 48.071) |
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| 68 | * BSSAP-LE (TS 49.031) |
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| 69 | |||
| 70 | h3. Communication with peer SMLC |
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| 71 | |||
| 72 | * SMLCPP (TS 48.031) |
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| 73 | * BSSAP-LE (TS 49.031) |
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| 74 | |||
| 75 | h3. Message Segmentation |
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| 76 | |||
| 77 | LCS messages can be segmented either |
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| 78 | * at the SMLCPP layer |
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| 79 | * 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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| 80 | |||
| 81 | |||
| 82 | h2. Functionality in SMLC |
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| 83 | |||
| 84 | * |
