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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. In RF
area 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 mobile
control system to exceed the data transfer speed
limits.
2.1 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), which is reported
in units of dBm. A signal strength of Watts is
equivalent to 10*log10(s/0.001) dBm. For example,
signal strength of 1 Watt is equivalent to 30 dBm.
The WaveLAN driver extracts the SS information
from the WaveLAN firmware each time a broadcast
packet is received. Then the information is make
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.
2.2 Localization Methodology
The general principle is that if a Wi-Fi-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 Wi-Fi connection.
If the mobile device knows the position of the
stationary device, it also knows that its own position
is within a range of this location provider (100
meters app.). Granularity of location can be
improved by triangulation of two or several visible
Wi-Fi APs. 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) is now implemented in C#
using the MS Visual Studio .NET 2005 with .NET
compact framework and a special OpenNETCF
library enhancement (OpenNETCF, 2007). Schema
on figure 1 describes a runtime localization process.
The stars points are exactly measured and computed
points of suppose user position. The real track on
figure presents real movement of user during the
time. The exact track mean computed track from
measured Wi-Fi intensity level.
Figure 1: Localization principle - triangulation.
2.3 Predictive Data Push Technology
This part of project is based on a model of location-
aware enhancement, which we used in debug control
system. These info-data are used in developed
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 push 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 687 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 from 43 to
160 KB/s on three various type of PDA (HTC
Roadster, Blueangel and Universal). The second
aspect is the size of copied data. We advice to use
partitioned blocks from original data files or blocks.
2.4 Data Artefact Management
The PDPT Server SQL database manages the
information (for example data about Ethernet
hardware such as Ethernet switch, UTP socket,
CAT5 cable lead, etc.) in the context of their
location in building environment. This context
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