22-06-2012, 01:48 PM
A Theoretical Model of GSM Network Based Vehicle Tracking System
[attachment=25068]
INTRODUCTION
Theft of vehicle has become a major concern now a day. A
statistics reveals that in 2008 approximately one million
vehicles were stolen in USA causing property losses of $6.4
billion [1], [2]. Apart from avoiding theft, there may be
security and other reasons for monitoring and/or tracking a
vehicle. Presently many wireless sensor network, GPS and
internet based tracking system are proposed and being used
which provides a pretty good range of precision in the
tracking system [3], [4]. However, some of the major
limitations of these systems are the cost of implementation
and system complexity. For example, a major limitation of
the GPS-based tracking system is that it works pretty well for
outdoor only. It does not work at indoor environments where
GPS satellite signal is not present. In addition, implementing
a GPS-based tracking system requires good amount of
investment, the operation cost is also considerably high.
Similarly, for wireless sensor networks, the initial
implementation of the gateway nodes requires high level of
investment that hinders the accessibility of these technologies
to mass people.
In this paper a novel method of a vehicle tracking system
is proposed, where the existing GSM cellular network will be
used to perform the required tracking. No additional cost will
be incurred to implement the system. Only small scale
software will have to be developed to incorporate with the
cellular operators’ BSC (Base Station Controller) to collect
the required data, execute necessary commands and display
the results. Besides a small call receiving kit costing a few
dollars will be used inside each vehicle or object to be
tracked. The cellular network based tracking system would
not only be very efficient in terms of cost-benefit perspective
but also will be very much effective at indoor environments,
as cellular radio signal can penetrate the walls and is
available inside the building.
II. GSM BASIC ARCHITECTURE
A cellular network consists of many base stations called
Base Transceiver Stations (BTS) in GSM topology. BTS
handles the radio interface to the mobile station (MS). The
BTS includes antennas that serve honey comb like cells.
Generally a BTS serves three cells which are designed in
hexagonal sectors where each of the three sectors cover 120º.
Each cell is configured with one or more radio frequencies
generally termed as TRx depending on the capacity
requirements under each cell. A group of BTS is controlled
by a BSC while number of BTS under each BSC depends on
total TRx capacity to be handled or maximum traffic load
handling capability of the BSC.
The basic function of a BSC is to provide all the control
functions and physical links between the MSC (Mobile
Services Switching Center) and BTS. It is a high-capacity
switch that provides functions such as handover, cell
configuration data and controls the radio frequency power
levels in BTS. A number of BSCs are connected with MSC.
The MSC performs the telephony switching functions of the
system. It controls calls to and from other telephone and data
systems. It also performs such functions as toll ticketing,
network interfacing, common channel signaling, and others.
VLR (Visitor Location Register) is a database that contains
temporary information of a subscriber which is needed by
MSC. Generally, VLR is integrated with the MSC. MSC is
connected with the other related components such as HLR
(Home Location Register), AUC (Authentication Center),
III. RADIO TRANSMISSION ASPECTS
The 25MHz GSM band (890-915MHz in UL and 935-
960MHz in DL) are divided into 124 pairs of duplex channels
with 200 kHz carrier spacing using Frequency Division
Multiple Access (FDMA). Using TDMA (Time Division
Multiple Access) each of the 200 kHz radio channels are
divided into 8 Time Slots (TS) of length 0.577 ms each. Thus
a TDMA frame is 4.615 ms in length. The recurrence of one
particular timeslot in every 4.615ms makes up one basic
channel. By employing these TSs each channel transmits the
digitized speech in a series of short bursts. Fig. 2 shows the
TDMA frame structure in GSM.
Traffic Channels (TCH) are defined using a 26-frame
multi-frame (i.e. a group of 26 TDMA frames). The length of
a 26-frame multi-frame is 120ms (26 X 8 X 0.577ms). Out of
the 26 frames, 24 are used for traffic, one is used for Slow
Associated Control Channel (SACCH) and one is kept as idle.
During this idle time the MS reads the information of the
BCCH frequency (i.e. FCCH channel) of the neighboring
cells.
Data are transmitted in bursts placed within the TSs with a
transmission bit rate of 271 kbps. The burst is the
transmission quantum of GSM. Its transmission takes place
during a time window lasting for only 0.577 ms, i.e. 156.25
bit duration. A normal burst contains two packets of 58 bits
(57 data bits + 1 stealing bit) surrounding a training sequence
code (TSC) of 26 bits and 3 tail bits. The 26-bit training
sequence is of a known pattern that is compared with the
received pattern in order to reconstruct the rest of the original
signal (multipath equalization). From the reception of TSC
the BSC calculates Timing-Advance (TA), meaning how far
the MS is from the cell center. This is required for frame
synchronization and transmitter power adjustment. Each TA
corresponds to a physical distance of 550 m. Accordingly, the
TA value ranges from 0 to 63 meaning a distance between
550 m to 35.2 km.
IV. METHODOLOGY
A SIM (Subscriber Identity Module) will be kept inside the
vehicle to be tracked with the special kit, capable to receive
incoming calls. With the specially designed software, the
SIM number will be dialed form the interface connected with
the MSC and BSC. As mentioned earlier, the call will be
established immediately as the kit is capable of receiving a
call automatically. While in calling mode, the channel
measurement of the MS occurs over an SACCH interval,
which comprises 104 TDMA frame (i.e. 480ms). For the
channel at hand two parameters determined: the received
signal level RXLEV and the signal quality RXQUAL. The
two values are averaged over an SACCH interval (480ms)
and transmitted to the BSC through BTS on the SACCH as
measurement report.
[attachment=25068]
INTRODUCTION
Theft of vehicle has become a major concern now a day. A
statistics reveals that in 2008 approximately one million
vehicles were stolen in USA causing property losses of $6.4
billion [1], [2]. Apart from avoiding theft, there may be
security and other reasons for monitoring and/or tracking a
vehicle. Presently many wireless sensor network, GPS and
internet based tracking system are proposed and being used
which provides a pretty good range of precision in the
tracking system [3], [4]. However, some of the major
limitations of these systems are the cost of implementation
and system complexity. For example, a major limitation of
the GPS-based tracking system is that it works pretty well for
outdoor only. It does not work at indoor environments where
GPS satellite signal is not present. In addition, implementing
a GPS-based tracking system requires good amount of
investment, the operation cost is also considerably high.
Similarly, for wireless sensor networks, the initial
implementation of the gateway nodes requires high level of
investment that hinders the accessibility of these technologies
to mass people.
In this paper a novel method of a vehicle tracking system
is proposed, where the existing GSM cellular network will be
used to perform the required tracking. No additional cost will
be incurred to implement the system. Only small scale
software will have to be developed to incorporate with the
cellular operators’ BSC (Base Station Controller) to collect
the required data, execute necessary commands and display
the results. Besides a small call receiving kit costing a few
dollars will be used inside each vehicle or object to be
tracked. The cellular network based tracking system would
not only be very efficient in terms of cost-benefit perspective
but also will be very much effective at indoor environments,
as cellular radio signal can penetrate the walls and is
available inside the building.
II. GSM BASIC ARCHITECTURE
A cellular network consists of many base stations called
Base Transceiver Stations (BTS) in GSM topology. BTS
handles the radio interface to the mobile station (MS). The
BTS includes antennas that serve honey comb like cells.
Generally a BTS serves three cells which are designed in
hexagonal sectors where each of the three sectors cover 120º.
Each cell is configured with one or more radio frequencies
generally termed as TRx depending on the capacity
requirements under each cell. A group of BTS is controlled
by a BSC while number of BTS under each BSC depends on
total TRx capacity to be handled or maximum traffic load
handling capability of the BSC.
The basic function of a BSC is to provide all the control
functions and physical links between the MSC (Mobile
Services Switching Center) and BTS. It is a high-capacity
switch that provides functions such as handover, cell
configuration data and controls the radio frequency power
levels in BTS. A number of BSCs are connected with MSC.
The MSC performs the telephony switching functions of the
system. It controls calls to and from other telephone and data
systems. It also performs such functions as toll ticketing,
network interfacing, common channel signaling, and others.
VLR (Visitor Location Register) is a database that contains
temporary information of a subscriber which is needed by
MSC. Generally, VLR is integrated with the MSC. MSC is
connected with the other related components such as HLR
(Home Location Register), AUC (Authentication Center),
III. RADIO TRANSMISSION ASPECTS
The 25MHz GSM band (890-915MHz in UL and 935-
960MHz in DL) are divided into 124 pairs of duplex channels
with 200 kHz carrier spacing using Frequency Division
Multiple Access (FDMA). Using TDMA (Time Division
Multiple Access) each of the 200 kHz radio channels are
divided into 8 Time Slots (TS) of length 0.577 ms each. Thus
a TDMA frame is 4.615 ms in length. The recurrence of one
particular timeslot in every 4.615ms makes up one basic
channel. By employing these TSs each channel transmits the
digitized speech in a series of short bursts. Fig. 2 shows the
TDMA frame structure in GSM.
Traffic Channels (TCH) are defined using a 26-frame
multi-frame (i.e. a group of 26 TDMA frames). The length of
a 26-frame multi-frame is 120ms (26 X 8 X 0.577ms). Out of
the 26 frames, 24 are used for traffic, one is used for Slow
Associated Control Channel (SACCH) and one is kept as idle.
During this idle time the MS reads the information of the
BCCH frequency (i.e. FCCH channel) of the neighboring
cells.
Data are transmitted in bursts placed within the TSs with a
transmission bit rate of 271 kbps. The burst is the
transmission quantum of GSM. Its transmission takes place
during a time window lasting for only 0.577 ms, i.e. 156.25
bit duration. A normal burst contains two packets of 58 bits
(57 data bits + 1 stealing bit) surrounding a training sequence
code (TSC) of 26 bits and 3 tail bits. The 26-bit training
sequence is of a known pattern that is compared with the
received pattern in order to reconstruct the rest of the original
signal (multipath equalization). From the reception of TSC
the BSC calculates Timing-Advance (TA), meaning how far
the MS is from the cell center. This is required for frame
synchronization and transmitter power adjustment. Each TA
corresponds to a physical distance of 550 m. Accordingly, the
TA value ranges from 0 to 63 meaning a distance between
550 m to 35.2 km.
IV. METHODOLOGY
A SIM (Subscriber Identity Module) will be kept inside the
vehicle to be tracked with the special kit, capable to receive
incoming calls. With the specially designed software, the
SIM number will be dialed form the interface connected with
the MSC and BSC. As mentioned earlier, the call will be
established immediately as the kit is capable of receiving a
call automatically. While in calling mode, the channel
measurement of the MS occurs over an SACCH interval,
which comprises 104 TDMA frame (i.e. 480ms). For the
channel at hand two parameters determined: the received
signal level RXLEV and the signal quality RXQUAL. The
two values are averaged over an SACCH interval (480ms)
and transmitted to the BSC through BTS on the SACCH as
measurement report.