Enhanced Location Based Services Support in ...

TITLE:

Enhanced Location Based Services Support in cdma2000

SOURCE:

Shu Wang, Jungwon Min, Li-Hsiang Sun, LGE [email protected], [email protected], [email protected] ABSTRACT: The overview of mobile positioning technologies is presented. reverse link

enhancements are proposed for cdma2000 LBS support. RECOMMENDATION:

Review and adopt

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Outline •

Location based services (LBS) service level requirements and technologies • Positioning technologies

•

cdma200 positioning technologies and LCS architecture • Tradeoffs between forward link and reverse link positioning methods • Reverse link position approaches: TOA and TDOA

•

Access channel enhancements for cdma2000 • • • •

Preamble only access probe Extended access probe Extended access offset Reverse link positioning example for cdma2000

Location Based Service Levels • Applications require different service levels. • Basic service level: 400-1500m • Enhanced service level: 40-150m • Extended service level: less than 40m [Source: Location Interoperability Forum (LIF), now a part of Open Mobile Alliance (OMA)]

Call Routing Asset Tracking

Friend Finder Local News

Safety and Emergency Service

Fleet Management Family Tracking

Local Weather

Navigation Local Advertising

Roadside Assistance Emergency Call

Medical Assistance

Network Optimization Safety Alert

Location Sensitive Billing

Traffic Alert

Basic Service Level

Enhanced Service Level

Extended Service Level

LBS Technologies •

Mobile measures/Mobile determines: • Positioning is carried out in handset and sent back to network. • Examples: cell ID, timing advance, Rx signal strength level, GPS, AGPS

•

Network measures/Network determines: • Measurement and positioning are done by network itself. • Examples: U-TDOA, AOA

•

Mobile measures/Network determines: • Handset does measurements and network calculates the position. • Examples: EOTD, OTDOA, EFLT, AFLT, A-GPS

Existing Positioning Technologies Attributes

Network

Handset

Accuracy

All

All

GSM

All

CDMA

All

250-350m

All

All

100-200m

Cell ID

Cell ID based on pilot measurements

Cell ID + TA

Combines Cell ID with time advance.

EFLT

MS measures the forward link pilot.

AOA

NW measures the angle of arrival.

EOTD

MS measures time difference.

GSM

Upgrade

50-200m

AFLT

MS measures the forward link pilot timing.

CDMA

Upgrade

50-200m

UTDOA

NW measures the time difference.

All

Upgrade

50-80m

GPS/AGPS

GPS receivers embedded in the handsets and network.

All

Upgrade

5-30m

100m-3km (Depending on cell size and density)

500m (Depending on bandwidth)

cdma2000 Positioning Technologies •

•

•

Enhanced Forward Link Trilateration (EFLT) • Mobile uses existing pilot signal measurement message (PSMM) to transmit measurements to BS. • EFLT is typically used as a backup for non-AFLT/AGPS phones Advanced Forward Link Trilateration (AFLT) • AFLT is a TDOA-based technique. • It uses IS-801 message to transmit location data from mobiles. • Mobile receives 3 or more BS signals to perform trilateration its position. • AFLT is commonly used as a hybrid with A-GPS. Assisted GPS • GPS positioning gets assisted by network. • Assisted data can be transmitted using IS-801 messages.

Reverse Link Time (Difference) of Arrival • The time of arrival (TOA) or the time difference of arrival (TDOA) on the reverse link. • The location estimation schemes are similar to cdma2000 AFLT. • In TOA approach, one TOA measurement by a BTS determines a circle. • In TDOA approach, the difference in TOA measures by two different BTS determines a hyperbola.

• The mobile needs to be signaled to send out reverse link probes.

Preamble Only Access Probe Transmit Power P t0 P0

Enhanced Preamble/Pilot Channel (I Phase or Q Phase)

Configurable or Fixed

Time t

• In a new access probe, no data will be carried. • The pilot channel is transmitted either on the I phase or Q phase. • The length of preamble is defined by an extended AccessParameters message. • 4 slots, if PreambleLengthEx == 0 • PreambleLengthEx frames, if PreambleLengthEx > 0 • The output power of the preamble is configurable and the default value is set equal to the sum of data and pilot transmitted at 9.6 kbps as the current EV-DO standard states.

Proposed Access Probe Enhancements • Extended access probe with payload • Preamble: 4 slots, 1~15 frames • Payload: 1~CapsuleLengthMax frames • Preamble only access probe • Preamble: 4 slots, 1~15 frames • Payload: 0 • Extended access probe offset. • It will be sent with extended access probe offset. • The possible access probe offset values include 16 slots, 32 slots, 48 slots, 64 slots, 80 slots, 96 slots, 112 slots, 128 slots.

Positioning Procedure w/ New Access Probes 1. AN pages AT. (This step is only for the network initiated LCS.) 2. After receiving page message, AT sends an access probe. •

3.

4.

5.

Inside the data capsule, there may be pilot signal measurement message (PSMM), route update message (RUM) information, and so on, in addition to MAC header. After successfully receiving access probes, the serving AN acknowledges the AT. • If the AT has been successfully positioned at the required PQoS with the regular probes, the positioning procedure is terminated. • Otherwise, inside the AN acknowledge message, AN specifies extended access parameters for continuing positioning. AT sends preamble only access probes for continuing positioning. • The access probe offset is specified by accessProbeOffsetEx • Additional PQoS related parameters may be provided, including duration, periodicity, etc. After enough AN measurements are received by PDE and the PQoS requirement is satisfied, the positioning will be terminated. • AN sends additional acknowledge message to the AT.

Conclusions •

With different positioning technologies, different positioning quality of services (PQoS) are achievable. • PQoS: horizontal accuracy, response time, etc. • LBS in general requires different service levels.

•

Currently, mobile assisted positioning technologies on forward link have been implemented for cdma2000. • EFLT, AFLT: 1X only • A-GPS

•

Reverse link LCS approaches provides • • • •

•

less mobile complexity EV-DO compatibility higher signal processing capability provided by the network almost no impact on air interface.

The enhancements to the EV-DO reverse link access probe are proposed for enhanced support of LBS in cdma2000 network. • Preamble only access probe • Extended access probe with payload • Extended access probe offset

References • • • • •

Shu Wang, Jungwon Min and Byung K Yi, “Location Based Services for Mobiles: Technologies and Standards”, Tutorial#25, IEEE International Conference on Communication (ICC), May 23, 2008, Beijing, China. Shu Wang, Jungwon Min and Li-Hsiang Sun, “Extended AccessParameters Message for Enhanced LBS Support”, 3GPP2 TSG-C WG2, Osaka, Japan, May 2008. Jialin Zou, David Rossetti and Subramanian Vasudevan, “HRPD Enhancements for Improved Support of Location Based Services”, 3GPP2 TSG-C WG2, Montréal, Canada, April, 2008 3GPP2 TSG-X, “MAP Location Services Enhancements”, X.S0002-0 v2.0 (TIA881-1). 3GPP2 TSG-X, “IP Based Location Services”, X.S0024.

FYI: EV-DO Access Probe • Access channel is usually used by the AT

to initiate communication with the AN or to respond to an AT directed message.

• Access channel consists of pilot channel and data channel. • The default data rate of the access channel is 9.6 kbps

• Access probe consists of preamble and one

or more access channel physical layer packet. • Only pilot channel during the preamble transmission • Pilot and data channel during the physical layer packet transmission

• On the access channel, AT sends a series

of access probes until it receives a response from AN or the timer expires.

FYI: Extended Access Probe

• The first PreambleLengthEx frame of pilot (I-channel or Q-channel) functions as a preamble. • After PreambleLengthEx frames, the probe data is enabled for up to CapsuleLengthMax.

FYI: cdma200 LCS Architecture •3GPP2 X.S0002-0 v2.0 (TIA-881-1): “MAP Location Services Enhancements” •3GPP2 X.S0024: “IP Based Location Services” D

2

E3

E1

3GPP2 LCS User Plane

E9

E9

L1

Home PS

WNO IP Network

Network LCS Client

Internet

External LCS Client

Home Network

Visited Network

3GPP2 LCS Control Plane

WNO IP Network

LCS Client Network LCS Client PDSN

MS

Server

Serving PS PDE(s)