Time and Power Based Positioning Scheme for Indoor Location Aware Services

學生 :佑任老師 :劉宏煥

Reference

A. El Moutia , Kia Makki , ” Time and Power Based Positioning Scheme for Indoor Location Aware Services,” CCNC 2008. 5th IEEE , 10-12 Jan. 2008 , page(s) : 868 - 872

Outline

• Indoor location schemes and range estimation techniques

• Network model• Time-and-power based positioning scheme Step1:range detection Step2:location computer• Performance evalution

Indoor positioning scheme

• Ultrasound:– Calculates location using some triangulation from

short pulses of ultrasound emitted from a transmitter worn on the body to beacons installed in the roof

• Radio Frequency:– Use wireless network infrastructure to determine

location – Low setup cost,long range

Range estimation techniques

• RSS:computes distance based on the transmitted and received power lavels

Apha=path loss coeffient

C=const (antenna gain,height)

• TDoA using RF and Ultrasound:• sends a radio and an ultrasound simultaneously• When RF arrivaled ,start measuring the time until

ultrasound transmission arrivaled

Vs is the speed of sound in air at 21 ℃

Network model• The system models augments the existing IEEE

802.11 access protocol

• The overlay network is composed of three types of sensor nodes– Manager node:attached to the access point,it initializes the

sensor relays by conveying information about the associated access point

– 45it serves as the data aggregation server where reassociation requests from mobile nodes are gathered, and reassociation responses are sent back

– The relays are fixed sensors uniformly placed throughout the coverage area of an access point

– the relays are used to route messages between the manager and the sensor agents. They are also responsible for sensing the frequency bands

– The agents are sensors attached to the mobile nodes. They communicate with the relay sensors upon entering the transmission area

Time-and-Power based Positioning Scheme

• TPPS is based on time difference of arrival TDoA and RSS using RF and US signals to detect range difference from wireless mobile terminal to three sensors nodes

Step 1: Range Detection

• Now, let the received power at the master sensor be:

C = const (consider carrier frequency and transmitted power)α = attenuation exponentrA = the distance between the mobile terminal and master sensor A

sensor A estimates the received power levels and stores thisinformation to perform averaging with a deep of I samples toincrease the accuracy

The distance at time instant i can be estimated from the average received power using equation like:

•Consider channel fadingMultiplied Factor (accounting for the fading amplitude) Rayleigh pdf

Step 2: Location Computation

• Based on trilateration and Pythagorean Theorem

Subtracting second and third from first

minimizes the mean square error by

That is

PERFORMANCE EVALUATION• 12 sensor nodes uniformly distributed in the

coverage area of 100mx100m and 20 mobile terminals

• each MT picks a random destination and a speed, ranging from 0 to 10 m/s

• After a MT arrives at the destination, it pauses for a period of time ranging from 0s to 500s

The effect of the number of sensor nodes