PDPT FRAMEWORK

Building Information System with Wireless Connected Mobile Devices

Ondrej Krejcar

Centre for Applied Cybernetics, VSB Technical University of Ostrava, 17. listopadu 15, Czech Republic

Keywords: Information system, mobile device, PDA, WiFi, PDPT framework.

Abstract: The proliferation of mobile computing devices and local-area wireless networks has fostered a growing

interest in location-aware systems and services. Additionally, the ability to let a mobile device determine its

location in an indoor environment at a fine-grained level supports the creation of a new range of mobile

control system applications. Main area of interest is in model of radio-frequency (RF) based system

enhancement for locating and tracking users of our control system inside buildings. The framework

described here joins the concepts of location and user tracking in an extended existing control system. The

experimental framework prototype uses a WiFi network infrastructure to let a mobile device determine its

indoor position as well as to deliver IP connectivity. User location is used to data pre-buffering and pushing

information from server to user’s PDA. Experiments show that location determination can be realized with a

room level granularity.

1 INTRODUCTION

The usage of various wireless technologies that

enable convenient continuous IP-level (packet

switched) connectivity for mobile devices has

increased dramatically and will continue to do so for

the coming years. This will lead to the rise of new

application domains each with their own specific

features and needs. Also, these new domains will

undoubtedly apply and reuse existing (software)

paradigms, components and applications. Today,

this is easily recognized in the miniaturized

applications on network-connected PDA’s that

provide more or less the same functionality as their

desktop application equivalents. The web browser

application is such an example of reuse. Next to this,

it is very likely that these new mobile application

domains adapt new paradigms that specifically

target the mobile environment. We believe that an

important paradigm is context-awareness. Context is

relevant to the mobile user, because in a mobile

environment the context is often very dynamic and

the user interacts differently with the applications on

his mobile device when the context is different.

While a desktop machine usually is in a fixed

context, a mobile device goes from work, to on the

road, to work in-a-meeting, to home, etc. Context is

not limited to the physical world around the user, but

also incorporates the user’s behaviour, and terminal

and network characteristics.

Context-awareness concepts can be found as

basic principles in long-term strategic research for

mobile and wireless systems such as formulated in

(WWRF). The majority of context-aware computing

to date has been restricted to location-aware

computing for mobile applications (location-based

services). However, position or location information

is a relatively simple form of contextual information.

To name a few other indicators of context awareness

that make up the parametric context space: identity,

spatial information (location, speed), environmental

information (temperature), resources that are nearby

(accessible devices, hosts), availability of resources

(battery, display, network, bandwidth), physiological

measurements (blood pressure, hart rate), activity

(walking, running), schedules and agenda settings.

Context-awareness means that one is able to use

context information.

We consider location as prime form of context

information. Our focus here is on position

determination in an indoor environment. Location

information is used to determine an actual user

position and his future position. We have performed

a number of experiments with the control system,

focusing on position determination, and are

encouraged by the results. The remainder of this

162

Krejcar O. (2006).

PDPT FRAMEWORK - Building Information System with Wireless Connected Mobile Devices.

In Proceedings of the Third International Conference on Informatics in Control, Automation and Robotics, pages 162-167

DOI: 10.5220/0001215001620167

 SciTePress

paper describes the conceptual and technical details

of this.

2 BASIC CONCEPTS AND

TECHNOLOGIES OF USER

LOCALIZATION

The proliferation of mobile computing devices and

local-area wireless networks has fostered a growing

interest in location-aware systems and services. A

key distinguishing feature of such systems is that the

application information and/or interface presented to

the user is, in general, a function of his physical

location. The granularity of location information

needed could vary from one application to another.

For example, locating a nearby printer requires fairly

coarse-grained location information whereas

locating a book in a library would require fine-

grained information.

While much research has been focused on

development of services architectures for location-

aware systems, less attention has been paid to the

fundamental and challenging problem of locating

and tracking mobile users, especially in in-building

environments. We focus mainly on RF wireless

networks in our research. Our goal is to complement

the data networking capabilities of RF wireless

LANs with accurate user location and tracking

capabilities for user needed data pre-buffering. This

property we use as information ground for extension

of control system.

2.1 Location-Based Services

Location-based services (LBS) are touted as 'killer

apps' for mobile systems. An important difference

between fixed and mobile systems is that the latter

operate in a particular context, and may behave

differently or offer different information and

interaction possibilities depending on this context.

Location is often the principal aspect determining

the context. Many different technologies are used to

provide location information. Very common is the

GPS system, which uses a network of satellites and

provides position information accurate within 10–20

m. However, due to its satellite based nature, it is not

suited for indoor positioning. In cellular

telecommunication networks such as GSM, the cell

ID gives coarse-grained position information with an

accuracy of about 200 m to 10 km. For fine-grained

indoor location information, various technologies

are available, based on infrared, RF, or ultrasonic

technologies often using some type of beacon or

active badge. Given the ubiquity of mobile devices

like PDAs, however, active badges will probably be

superseded by location technologies incorporated in

these devices.

In the context of our experimental setup, we need

indoor position information accurate enough to

determine the room in which the user is located. We

must deploy a separate location technology, where

we use the information available from a WiFi

network infrastructure to determine the location with

room-level accuracy. By this information possible

user track is estimate.

2.2 WiFi - IEEE 802.11

The Institute of Electrical and Electronics Engineers

(IEEE) develops and approves standards for a wide

variety of computer technologies. IEEE designates

networking standards with the number 802. Wireless

networking standards are designated by the number

11. Hence, IEEE wireless standards fall under the

802.11 umbrella. Ethernet, by the way, is called

802.3 (Reynolds, 2003).

The 802.11b is an updated and improved version

of the original IEEE 802.11 standard. Most wireless

networking products today are based on 802.11b.

802.11b networks operate at a maximum speed of 11

Mbps, slightly faster than 10-BASE-T Ethernet,

providing a more than fivefold increase over the

original 802.11 spec. The 802.11 standard provided

for the use of DSSS and FHSS spread-spectrum

methods. In 802.11b, DSSS is used.

We use only 802.11b infrastructure (PDA has

only this standard) so other standards (802.11a or g)

is not needed to describe. However, it can be

possible to develop a PDPT framework with it.

2.3 Data Collection

A key step in the proposed research methodology is

the data collection phase. We record information

about the radio signal as a function of a user’s

location. The signal information is used to construct

and validate models for signal propagation. Among

other information, the WaveLAN NIC makes

available the signal strength (SS) and the signal-to-

noise ratio (SNR). SS is reported in units of dBm

and SNR is expressed in dB. A signal strength of s

Watts is equivalent to 10*log10(s/0.001) dBm. A

signal strength of s Watts and a noise power of n

Watts yields an SNR of 10*log10(s/n) dB. For

example, signal strength of 1 Watt is equivalent to

30 dBm. Furthermore, if the noise power is 0.1 Watt,

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163

the SNR would be 10 dB. The WaveLAN driver

extracts the SS and the SNR information from the

WaveLAN firmware each time a broadcast packet is

received. It then makes the information available to

user-level applications via system calls. It uses the

wlconfig utility, which provides a wrapper around

the calls, to extract the signal information.

2.4 Localization Methodology

The general principle is that if a WiFi-enabled

mobile device is close to such a stationary device –

Access Point (AP), it can “ask” the location

provider’s position by setting up a WiFi connection.

If the mobile device knows the position of the

stationary device, it also knows that its own position

is within a 100-meter range of this location provider.

Granularity of location can improve by triangulation

of two or several visible WiFi APs as described on

figure [Fig. 1].

Figure 1: Localization principle - triangulation.

Figure 2: PDA Locator – AP intensity & Positioning.

The PDA client will support the application in

automatically retrieving location information from

nearby location providers, and in interacting with the

server. Naturally, this principle can be applied to

other wireless technologies.

The application (locator) based on .NET

language is now created for testing. It is

implemented in C# using the MS Visual Studio

.NET 2003 with compact framework and a special

OpenNETCF library enhancement (Tiffany, 2003)

and (WWRF). Current application [Fig. 2] records

just one set of signal strength measurements. By this

set of value the actual user position is determined.

2.5 WiFi Middleware

The WiFi middleware implements the client’s side

of location determination mechanism on the

Windows Mobile 2005 PocketPC operating system

and is part of the PDA client application. The

libraries used to manage WiFi middleware are:

AccessPoint, AccessPointCollection, Adapter,

AdapterCollection, AdapterType, ConnectionStatus,

Networking, NetworkType, and SignalStrength.

Methods from the Net library are used for example

to display Visible WiFi AP. See figure [Fig. 3].

dtVisibleAP = new DataTable("Visible

AP");

DataRow drDataRow;

adptrColection =

networking.GetAdapters();

foreach (Adapter adptr in

adptrColection)

{

Application.DoEvents();

if (adptr.Type==AdapterType.Ethernet)

{

foreach (AccessPoint ap in

adptr.NearbyAccessPoints)

{ drDataRow = dtVisibleAP.NewRow();

drDataRow["BSSID"] =

(ap.Name.ToString());

drDataRow["Signal [%]"] =

((ap.SignalStrength.Decibels).ToString(

));

dtVisibleAP.Rows.Add(drDataRow);

}

Figure 3: Sample code – signal strength from AP.

2.6 Predictive Data Push

Technology

This part of project is based on model of location-

aware enhancement, which we used in created

control system. These information about are useful

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in framework to increase real dataflow from wireless

access point (server side) to PDA (client side).

Primary dataflow is enlarged by data pre-buffering.

These techniques form the basis for predictive data

push technology (PDPT). PDPT copies data from

information server to clients PDA to be on hand

when user comes at desired location.

The benefit of PDPT consists in reduction of

time needed to display desired information requested

by a user command on PDA. Time delay may vary

from a few seconds to number of minutes. It

depends on two aspects. First one is the quality of

wireless Wi-Fi connection used by client PDA. A

theoretic speed of Wi-Fi connection is max 825

kB/s. However, the test of transfer rate from server

to client’s PDA, which we have carried out within

our Wi-Fi infrastructure provided the result speed

only 160 KB/s. The second aspect is the size of

copied data. The application (locator) based on .NET

language is now created for testing. Current

application (see figure [Fig. 2]) records just one set

of signal strength measurements. By this set of value

the actual user position is determined.

2.7 Framework Design

PDPT framework design is based on most

commonly used server-client architecture. To

process data the server has online connection to the

control system. Data from technology are

continually saved to SQL Server database (Tiffany,

2003) and (Reynolds, 2003). The part of this

database (desired by user location or his demand) is

replicated online to client’s PDA where it is

visualized on the screen. User PDA has location

sensor component which continuously sends to the

framework kernel the information about nearby

AP’s intensity. The kernel processes this information

and makes a decision if and how a part of SQL

Server database will be replicated to client’s SQL

Server CE database.

The kernel decisions constitute the most

important part of whole framework because the

kernel must continually compute the position of the

user and track and make a prediction of his future

movement. After doing this prediction the

appropriate data (part of SQL Server database) are

pre-buffered to client’s database for future possible

requirements. The PDPT framework server is

created as Microsoft web services to handle as

bridge between SQL Server and PDPT PDA Clients.

Figure 4: System architecture – UML design.

3 EXPERIMENTS

We have executed a number of indoor experiments

with the PDPT framework, using the PDPT PDA

application. WiFi access points are placed at

different locations in building, where the access

point cells partly overlap. We have used

triangulation principle of AP intensity to get better

granularity. It has been found that the location

determination mechanism selects the access point

that is closest to the mobile user as the best location

provider. Also, after the loss of IP connectivity,

switching from one access point to another (a new

best location provider) takes place within a second

in the majority of cases, resulting in only temporary

loss of IP connectivity. This technique partially uses

a special Radius server (RADIUS) to realize

“roaming” known in cell networks. User who loss

the existing signal of AP must ask the new AP to get

IP. This is known as “renew” in Ethernet networks.

At the end of this process, user has his same old IP

and connection to new AP. Other best technique to

realize roaming is using of WDS (Wireless Decision

System).

Currently, the usability of the PDPT PDA

application is somewhat limited due to the fact that

the device has to be continuously powered. If not,

the WiFi interface and the application cannot

execute the location determination algorithm, and

the PDPT server does not receive location updates

from the PDA client.

PDPT FRAMEWORK - Building Information System with Wireless Connected Mobile Devices

165

Battery Power Consumption for PDPT Locator

338

327

255

140

128

100

223

215

165

50 100 150 200 250 300 350

Test [No]

Time [min]

Figure 5: Battery power consumption graph.

3.1 Battery Power Consumption

Tests

We have executed a number of tests of battery

power consumption with three PDA devices running

PDPT Locator. The tests were executed from 100 %

battery level to 20 % battery level with balanced

load. The first was HTC Blue Angel PH20B which

is known also as MDA III from T-Mobile (Intel

XScale PXA263 CPU, MS WM2005 OS). The

second one was iPAQ h4150 from Hewlett &

Packard Company (H&P) (Intel XScale PXA255

CPU, MS WM2003 OS). The third one was iPAQ

hx4700 from H&P (Intel XScale PXA270 CPU, MS

WM2003 SE OS). These devices have Li-Ion battery

with different capacity (1490 mAh, 1000 mAh and

1800 mAh). MDA III device has integrated GSM

module in addition.

Test Type CPU [MHz] Scan WiFi Backlight

1 400 2 s ext. 50%

MDA

III

400 10 s norm. off

3 100 2 s norm. off

4 h4150 400 2 s ext. 50%

5 400 10 s norm. off

6 100 2 s norm. off

7 hx4700 624 2 s ext. 50%

8 624 10 s norm. off

9 104 2 s norm. off

Figure 6: Battery tests description.

The test chart [Fig. 5] shows number of results. The

first, most evident and expected result is caused by

different battery packs. The power consumption is

worse for h4150 model and the best for hx4700

model. The second aspect is evident as well. The

score is better when the backlight is turned off.

However, the very large score is at hx4700 test case

comparing to two other PDA. The last interested

result is however in 100 MHz CPU speed setting.

The speed decreasing was controlled by special

utility managing the core of operating system. When

the maximum speed of CPU was decreased, the

working time of PDA increased about several

percent. This result is last useful thing for enlarge

battery power consumption.

The practical type of PDA usage with PDPT

application is somewhere between minimum and

maximum score of these tests for such model of

PDA. For example the mean usage of the worse

PDA iPAQ h4150 is about two hours of working

time so it is not very comfortable, but it is usable for

many types of operations. Other two devices have

battery consumption time higher so practical use is

without remarkable limitation.

3.2 Data Transfer Increase Tests

Using PDPT Framework

The result of utilization of PDPT framework is

mainly at data transfer speed reducing. The second

test is focused on real usage of developed PDPT

Framework and his main issue at increased data

transfer. At table [Fig. 7] are summary of eighteen

tests with three type of PDA and three type of data

transfer mode. Each of these eighteen tests is

fivefold reiterated for better accuracy. At table are

only average values from each iteration.

Test Type Mode

Data

[kB] Time [s]

Speed

[kB/s]

1 SQl CE 257 0.4 643

2 SQl CE 891 0.4 2228

3 SQL 257 5 51

MDA III

SQL 891 13 69

5 PDPT 257 1.1 234

6 PDPT 891 3.2 278

7 SQl CE 257 0.5 514

8 SQl CE 891 0.5 1782

9 h4150 SQL 257 5 51

10 SQL 891 14 64

11 PDPT 257 1.2 214

12 PDPT 891 3.7 241

13 SQl CE 257 0.3 857

14 SQl CE 891 0.4 2228

15 hx4700 SQL 257 5 51

16 SQL 891 13 69

17 PDPT 257 0.9 286

18 PDPT 891 2.5 356

Figure 7: Data transfer tests description.

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The data mode column has three data transfer mode.

The SQL CE mode represents the data saved at

mobile device memory (SQL Server CE) and the

data transfer time is very high. The second mode

SQL means data which are stored at server (SQL

Server 2005). Primary the data are loaded over

Ethernet / Internet to SQL Server CE of mobile

device and secondary the data are shown to user.

The data transfers time consumption of this method

is generally very high and the waiting time for user

is very large. The third data mode PDPT is

combination of previous two methods. The PDPT

mode has very good results in form of data transfer

acceleration. Realization of this test consists at user

movement from location A to B at different way

direction. Location B was a destination with

requested data which are not contained at SQL CE

buffer in mobile device before test.

4 CONCLUSION

The main objective of this paper is in the

enhancement of control system for locating and

tracking of users inside a building. It is possible to

locate and track the users with high degree of

accuracy.

In this paper, we have presented the control

system framework that uses and handles location

information and control system functionality. The

indoor location of a mobile user is obtained through

an infrastructure of WiFi access points. This

mechanism measures the quality of the link of

nearby location provider access points to determine

actual user position. User location is used in the core

of server application of PDPT framework to data

pre-buffering and pushing information from server

to user PDA. Data pre-buffering is most important

technique to reduce time from user request to system

response.

The experiments show that the location

determination mechanism provides a good indication

of the actual location of the user in most cases. The

median resolution of the system is approximately

five meters. Some inaccuracy does not influence the

way of how the localization is derived from the WiFi

infrastructure. For the PDPT framework application

this was not found to be a big limitation as it can be

found at chapter Experiments. The experiments also

show that the current state of the basic technology

used for the framework (mobile device hardware,

PDA operating system, wireless network

technology) is now at the level of a high usability of

the PDPT application.

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Krejcar, O.: Predictive Data Push Technology Framework

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pp. 378-383, ISBN 80-214-3130-X

Krejcar, O.: Wifi User Localization for Intelligent Crisis

Management - Data Push Technology Framework,

Transaction on Environment and Development -

WSEAS, Issue 2, Volume 1, Venezia, Italy, 2005, pp.

319-326, ISSN 1790-5079

Reynolds, J.: Going Wi-Fi: A Practical Guide to Planning

and Building an 802.11 Network, CMP Books, 2003.

ISBN 1578203015

Wigley, A., Roxburgh, P.: ASP.NET applications for

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ISBN 073561914X

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the .NET Compact Framework, Apress, 2003. ISBN

1590591194

The Internet Engineering Task Force RADIUS Working

Group: http://www.ietf.org/

The Wireless World Research Forum (WWRF):

http://www.wireless-world-research.org/

OpenNETCF - Smart Device Framework:

http://www.opennetcf.org/

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