Positioning in GSM. Date: 14th March 2003

Transcription

1 Positioning in GSM Date: 14th March 2003

2 Overview of seminar Potential applications in cellular network Review of localization system and techniques Localization in GSM system Progress of the project with Smartone

3 Potential Applications Location Sensitive Billing 1. The price of call in cellular network is related to location of caller. 2. Localization is available, operators can provide different prices for different locations. 3. Example: price of call at home is less expensive than in the street. a. Completive to the fixed line network b. No need to use fixed network even at home

4 Potential Applications Increased Subscriber Safety 1. More and more people have cellular phones so more and more emergency calls from MS. 2. However, most callers can t provide accurate position a. Too scared b. Don t know their location. c. Involved in the accident and not able to tell. 3. Localization of MS a. fast to help the caller b. efficient dispatch of emergency vehicles

5 Potential Applications Intelligent Transport system 1. Store real-time traffic and all buildings information of different locations. 2. MS user make a cellular call and request for traffic information, it provides the traffic information according to the location of the caller. 3. Caller asks for entertainment information, it provide relevant information around the area. a. Especially suitable for visitors

6 Potential Applications Enhanced Network Performance 1. Monitor caller location, more efficient for handoff BS1 MS BS2 2. Gather information of caller location, help design of the cellular network

7 Potential Applications When localization technique is employed in the cellular network. Enhances subscribers. Benefits cellular operators.

8 Positioning system and techniques Positioning System Signal Measurements Estimation System TOA TDOA AOA Positioning Finding System Co-ordinate of the MS (x,y)

9 Positioning system and techniques Estimated MS location: 1. Derived measurements from signals in GSM system. (Measurement Estimation System) 2. Each measurement form a locus of MS 3. Loci s intersection is the MS location Locus 1 Locus 2

10 Positioning system and techniques Classfication 1. Self-positioning: GPS / Mobile-Based 2. Remote Positioning: Radar / Network Based 3. Indirect Positioning: Mixed of above / Hybrid BS2 BS1 MS BS3

11 Positioning system and techniques Measurements : 1. Propagation time or Time of Arrival (TOA) 2. Time Different of Arrival (TDOA) 3. Angle of Arrival (AOA) Assumption, 2D scenario, i.e.bs and MS on the same plane. D2 D1

12 Positioning system and techniques Propagation Time / Time of Arrival (TOA) 1. The time which signal travels between a transmitter and a receiver. a) FindthetimeBStoMSorviceversa. b) Send signal from BS to MS and then MS send it back to BS or vice versa. BS1 Synchronization MS BS1 MS

13 Positioning system and techniques TOA1, TOA2.. Speed of light c Distance between MS and each BS BS3 Distance formula BS1 form a set of loci BS2 Intersection is the MS location Circular-Circular Method

14 Positioning system and techniques Time different of arrivals (TDOA) 1. Difference of time of signal travel from one transmitter relative to another transmitter. 2. All TDOAs also relative to the same transmitter BS1. TDOA21 = t2 t1 t3 BS3 TDOA31 = t3 t1 BS1 t1 t2 BS2 MS Synchronized BS

15 Positioning system and techniques TDOA12, TDOA13.. Speed of light c Distance difference between MS and each BS relative to BS1 L3 BS4 Distance formula BS3 form a set of loci BS1 L1 L2 BS2 Intersection is the MS location Hyperbolic-Hyperbolic- Method

16 Positioning system and techniques Angle of Arrival (AOA) 1. Angle of the signal arrived from the transmitter relative to the receiver. θ1 BS1 BS2 θ2 MS

17 θ1, θ2.. Positioning system and techniques m1 = tan(θ1) Form a set of slopes By point slope point form a set of loci θ1 θ2 Intersection is the MS location Angle-Angle- System

18 Positioning system and techniques Performance analysis Root Mean Square: RMS= E[(ˆ x x) 2 + ( yˆ y) 2 ] RMS affects by theaccuracy of measurement, relative geometry between BS and MS and Algorithm

19 Localization in GSM BS2 BS1 Sectored cell The severing BS knows the MS is in which sector but not in others BTS

20 Localization in GSM two 25MHz blocks of frequency spectrum uplink downlink 125 carrier frequencies 200kHz f f

21 Localization in GSM GSM system use TDMA in each frequency band. In time domain each frequency band is structured in time slots of 577µs duration. Group of 8 slot called a frame. TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 frame

22 Localization in GSM Logical Channels: 1. Traffic channels Voice data transmission. 2. Associated and Dedicated channels co-ordinate BS and MS 3. Common channels establish links 4. Broadcast channels transmit BS parameters Data in logical channels is fitted into time slot by different burst structure.

23 Localization in GSM Interested burst structure in Traffic Channel Normal Burst bit PN training sequence in the middle 2. Channel estimation Total =148bits, 577µs guard data TS data guard 1 bit = 3.90µs

24 Localization in GSM Add a correlator in the receiver Find the correlation of the received PN training sequence and stored PN sequence. The time which gives the maximum correlation function is the time of propagation. Assumption: Synchronization. Received PN sequence correlator stored PN sequence Correlation function

25 Localization in GSM Only accuracy of 1 bit which is ±585m. 1 bit = 3.90µs 1170m The resolution is not enough for some application which needs high accuracy Using PN training sequence in traffic channels, thus only the distance between the serving BS and MS can be estimated

26 Time Advance(TA) Localization in GSM TDMA, arrival of signal should be at appropriated time slot. In order to do so, thereisatainthegsmsystem. BS1 TS1 TS1 TS1 MS Only1bit accuracy, which is 585m Only serving BS provide TA TA

27 Localization in GSM Force handover BS2 BS1 MS Degrade voice quality and the capacity of the system

28 Localization in GSM Power strength of signal from the BSs are measured in the dummy time slot. BS2 P 2 PG G λ = t t r r 2 2 ( 4π ) d L BS1 Power strength with Power Loss Model then estimated distance between MS and each BS Use Circular Circular Method

29 Summary: 1. Sectoring Localization in GSM a. provide acceptable accuracy when the cell s size is small. Too rough when using cell size is large. b. suitable for solving ambiguity. 2. Training sequence data burst in traffic channel. a. only the distance between serving BTS and MS b. Modification of MS c. 1 bit accuracy

30 Localization in GSM Summary: 3. TA with forcing handover a. Modify the MS b. Can be use with circular circular method c. Only 1 bit accuracy d. Degrade voice quality 4. Power strength measurements with the help of power loss model can be used for MS localization.

31 Project with Smartone 2 meetings with Smartone. The BS locations near CU Available measurements, power strength Change the BS from latitude and longitude to Cartesian Coordinate (x,y) 2D scenario. Use Power Loss model to estimate the distance between source and BS and then use circular circular method to estimate MS location

32 Project with Smartone Offline experiments e.g. all measurements and estimation processes are not real time Then evaluate the results and performance by finding RMS.

33 Project with Smartone NextPhase: 1. Get more positioning related measurements to do analysis. 2. Develop special algorithm based on analyzed results.

34 Question and Answer Thanks