19

Chapter 3

GSM Technology

This chapter presents technical details related to use of GSM-SMS

technology for remote data access and also describes two applications

designed using this technology. The first application is an auto-

responder which is an inquiry response mechanism designed for

educational institutes. The application maintains the database related

to student’s daily attendance, exam results, etc., and allows parents or

other stack holders to remotely access this information 24x7 on their

mobile phones through SMS request. The second application is related

to customize bulk messaging. This application facilitates sending SMS

to number of students at one go with each SMS having distinct

information relevant to each student.

3.1 Review of GSM-SMS technology for remote access

GSM is the most popular standard for mobile phones in the world. Deployed

first in year 1991, GSM system is a second generation (2G) cellular phone

technology. In over twenty years of development, GSM has been continually

evolved to provide platform to deliver broad range of mobile services as per

market demands. Examples of newer version of this standard are GPRS,

Enhanced data rates for GSM evolution (EDGE), 3G, etc. that in addition to

voice telephony supports applications with higher data rates like mobile

internet, video calls and mobile TV. Long-term evolution (LTE), marketed as

4G LTE, is now at the door step and claims to increase capacity and speed of

mobile communication network drastically.

GSM technology provides one possible solution for remote access for

embedded system. It being an off-the-shelf technology is ready to use and

20

with time as the number of mobile phone users are increasing, its

infrastructure is evolving and its prices are sinking. GSM technology can be

used for data transfer in two different ways – circuit switching data transfer, a

method comparable to voice calls, or packet switching data transfer, one

comparable to internet technology. GPRS service available over GSM

networks is based on packer switching and its use for data transfer is

discussed in the following chapter.

SMS is a text messaging service available on GSM networks. It

provides a mechanism for transmitting short message to and from a wireless

device registered in a GSM network. SMS has its first commercial deployment

in 1993. Voice conversations in GSM network is primarily using circuit

switched approach reserving a physical channel. On the contrary, SMS

makes use of control channel of GSM network that is independent of the voice

channel and allows user to transmit and receive SMS in parallel to voice

conversation. When user is engaged in voice conversation GSM renders

slow associated control channel (SACCH) for the SMS and when voice

conversation is not there GSM renders a standalone dedicated control

channel (SDCCH) for the SMS. In both the scenarios, SMS always uses a

lower power transmission channels. Figure 3.1 depicts basic network

structure for SMS service [5]. Short messaging entity (SME) represents an

entity that may receive or send a SMS. SME may be located in either fixed

network, a mobile station (MS) or another service center. Typical example of

SME can be a mobile handset or a GSM modem. When SME sends out an

SMS, short message service center (SMSC) relay this data to SMS-gateway

mobile switching center (SMS-GMSC). SMS-GMSC accesses the home

location register (HLR) to search the current location of destination number

and send the route information to mobile switching center (MSC). On basis of

this data MSC identifies SMSC to be contacted and relays the message. In

case if SMS source or the end destination is in roaming mode, SMS-

interworking mobile switching center (SMS-IWMSC) will come into picture.

Also visitor location register (VLR) is used to provide information about the

visiting subscribers that may be needed by MSC. SMS makes use of mobile

application part (MAP), that defines methods and mechanism of

21

communication in wireless network and uses SS7 protocol [53]. As per this

protocol the length of the message is limited to 140 octets (140 x 8 bits = 1120

bits). Thus depending on the encoding technique used in GSM device like

GSM 7-bit alphabet (default), 8-bit data alphabet or 16-bit UCS-2 the size of

the text message is limited to 160, 140 or 60 characters respectively.

Contents larger then this are generally sent as multiple concatenated SMS

using the feature of user data header (UDH). In such a case it becomes the

responsibility of the receiving device to reassemble the message.

Figure 3.1: Short message service network architecture.

Designing an embedded system with remote access capabilities using

GSM-SMS technology primarily requires connecting a GSM modem to the

existing system and adding necessary software modules for data

communication to the existing firmware. Here, GSM modem is used as a

generic term that refers to any modem that supports one or more of the

protocols of GSM or related evolutionary technologies like GPRS or 3G. It is a

subscriber identity module (SIM) based device that acts as an interface

between the application and GSM network to send and receive messages like

a mobile phone. They are available from number of manufacturers like

Wavecom, Multitech, Falcom, Simcom, etc. and also with number of

interfacing options like serial, USB or Bluetooth. Various functionalities that

GSM modem is capable of performing can be handled using set of AT

commands as defined in the European telecommunications standards

institute (ETSI) GSM 07.05 and 3GPP TS 27.005 specifications [54]. In

Appendix B some of commonly used AT commands for text messaging using

SIM300 GSM modem from SIMCOM are discussed [55].

GSM-SMS technology provides simple and cost effective solution for

remote data access in embedded system particularly where the intended

22

communication is not continuous and does not require high data rate. Further,

GSM encryption inherently provides data security in SMS transmission and

features like delivery report; automatic retransmission in case of transmission

failure etc. makes it more effective. Further limitation of SMS in terms of

number of characters that can be transmitted is quite admissible in many

remote monitoring and controlling operations. Because of all these benefits

GSM-SMS technology is found to be successfully used for remote data

access in number of embedded applications as discussed in Chapter 2. In the

following sections of this chapter two applications based on GSM-SMS

technology, designed for educational institutes are discussed along with the

experimental results.

3.2 Design of Auto-responder – An inquiry response mechanism

Parents are important stack holders for any educational institute and acts as

an important catalyst in academic growth of a student as well as institute’s

brand building. Most of the educational institutes have parent-institute

interaction cell, which work towards providing regular update to parents about

their wards academic development, regularity and behavioral patterns.

However, it is found that parents, in general, in spite of their willingness, are

not able to be in regular interaction with institute due to number of reasons

like geographical distance, busy schedule, etc. Many institutes maintain their

website and try to keep parents informed about their ward’s performance by

making related data available online or posting the same through e-mail.

Doing this is easy, but in context of Indian society, this does not serve the

purpose much as most of the parents are not comfortable with use of internet

or sometimes even a computer. Many institutes also follow a practice of

regularly sending student’s information to parents by post. However, this

involves lot of physical work, stationary and recurring cost. Further, timely

execution of this practice and its accountability always remains in the

question. On the other hand parents also many a time try to inquire about

their ward’s progress by calling the concerned person at institute. However,

23

effectiveness of this interaction totally depends on the sincerity of the

concerned person in terms of the amount of handy information he/she holds.

Inspired by these considerations, as a part of the present work, a GSM-

SMS based auto-responder has been designed that primarily acts as an

inquiry response mechanism for effective parent-institute interaction. The

designed system maintains the database of student’s details like attendance,

exam results, etc. and allows parents to remotely access this information 24x7

on their mobile phones through a simple SMS request. Parents have to send

a SMS containing enrollment number and branch of the student along with

information request code (e.g. A for attendance, R for result) and the system

will extract the requested information from the database and automatically

convey it back in form of an SMS. Architecture and system software of the

auto-responder are discussed in the following part of this section.

3.2.1 System architecture

The system architecture of the auto-responder as shown in Figure 3.2

consists of mainly the central data server, GSM modem, remote GSM

enabled mobile phone and GSM network. The central data server represents

an ordinary computer server or a workstation that runs an application to

maintain the database of student related details and respond to the local and

remote queries. It is responsible for following functions.

1. To receive, classify and save the data related to attendance,

examination results etc. that is feed to it on daily basis.

2. To extract required information and generate desired reports on basis

of local queries.

3. To automatically respond to the valid request received over GSM link

from the remote user.

4. To log details of all communication done over the GSM network.

GSM modem is used as an interface between the central server and

GSM network. It acts as data terminal equipment that combines traditional

modem and GSM wireless mobile communication system. The modem used

in the design is SIMCOM SIM300 based device that is a tri-band GSM/GPRS

24

engine [56]. It provides a serial TTL (Rx/Tx) interface option and auto-baud

rate support from 1200 bps to 115200 bps. It supports set of AT commands

for configuration and operation. It also supports various short message

services viz. mobile terminated (MT), mobile originated (MO) and cell

broadcast (CB) and also support message formats viz. text and packet data

unit (PDU). The modem also supports SMS transmission alternatively over

circuit switched data (CSD) or packet switch data i.e. GPRS that can be

selected using AT commands. Modem does not support any on-board

memory except the SIM card memory to store SMS. In the design modem via

Max-232 driver is connected to the central server over standard RS-232 serial

interface.

Figure 3.2: System architecture of auto-responder.

3.2.2 System software

System software of auto-responder consists of four major modules as shown

in Figure 3.3. These modules are as follows.

1. Database creation and amendment module

2. Data collection and classification module

3. Data analysis and report generation module

4. GSM communication module.

25

All these four modules are encapsulated in an easy-to-use GUI. Complete

system software including front end GUI has been designed using MATLAB.

Though MATLAB is not tailor made platform for database management and

design of front end interface, it provides effective ways to define data structure

in terms of multi-dimensional matrices. Further it supports ways to handle

serial communication and to design attractive GUI [57]. The system software

modules are discussed in detail as follows and list of MATLAB function

designed is given in Appendix A along with its brief description.

Figure 3.3: System software modules of auto-responder.

Database creation and amendment module

This module allows defining a fresh database structure generally required at

the beginning of an academic term. It also allows editing and amending the

created database as required later on. Creation of the database consists of

two processes. First is defining an empty database structure with required

fields and second is feeding data to the database. On selection of create new

database option from GUI a fresh database structure is created. For example,

for an institute with six branches having two divisions in each branch the

26

database structure defined for attendance module will be as shown in Figure

3.4.

Figure 3.4: Database structure for attendance module: (a) data tables (b)

indexes.

Any database primarily consist of two main structures tables

(commonly referred as arrays in MATLAB) and indexes. Tables are structures

that store data in database and indexes store information related to features

of database that helps to access the data from database easily. As shown in

Figure 3.4, in this database module an individual table with required fields is

created for each branch. The structure of each table (empty) created is

illustrated in Figure 3.5 (a) and (b) for Computer engineering branch. Each

27

table is defined as an array of structures with dimension defined by number of

semesters and number of division. In this case these are eight and two

respectively. Each item in the table is a structure containing fields like Name,

Roll number, Enrollment number and Attendance. In addition to these data

tables two indexes are also created viz. Branch details and Active entity

reference table as shown in Figure 3.4. The index Branch details helps to

relate branch name with data structure table. The index Active entity

reference table is a simple 6 x 8 x 2 (branch x semester x division) dimension

matrix of data type logical that keeps the summary of currently active

semesters and divisions in the data structure. For example, in odd semesters

fields in the table related to odd semesters are only used and hence these are

marked as active. Date table is another index that is used to keep the record

of dates when attendance data are feed to the data base. All these indexes

help to validate of any database query and quickly point to the requested data

in database.

Figure 3.5: (a) Table of CE in database; (b) Empty table fields corresponding

to CE semester 2, division 2; (c) Populated table fields corresponding to CE

semester 2, division 2; First four entries in the fields (d) name and (e)

attendance of CE semester 2, division 2.

28

For populating the database with relevant data update/edit database

option has to be selected from GUI. On selection of this option GUI presents

an interface as shown in Figure 3.6. This interface allows user to load a

Microsoft Excel file containing details of Name, Roll number and Enrollment

number of students with details of semester, branch and division. On

submission of details the software module extracts data from .xls file and

stores it in appropriate fields of the related table. MATLAB supports inbuilt

function xlsread() that allows reading data from a Microsoft Excel file; however

when the Excel sheet consist of data that is mix of numeric and text, use of

this command is not convenient. In this module a unique function csv2struct()

[58] is used that efficiently extracts the data from .csv or .xls file and stores it

as a structure. The database on MATLAB platform after populating data is

shown in Figure 3.5 (c). It represents second division in semester two of CE

having total of 67 students. Figure 3.5(d) exemplifies how required data can

be addressed. In MATLAB, MAT is the default data file format used to save

the data on the system disk. All data tables and indexes are thus stored in this

format.

Figure 3.6: GUI interface for feeding data into database.

29

Data collection and classification module

This module handles day-to-day data entry in the database. For example,

daily cumulative attendance of lectures and laboratories of each division can

be given to the database in form of a Microsoft Excel file. The file is expected

to have a standard format with sequential column head defined as: Name,

Roll number, Enrollment number, Total attended, Total conducted. The

system generates warning or error if the file is not in standard format or if the

details are incomplete. The file can be uploaded to the database using Data

entry option in GUI. This option presents the interface as shown in Figure 3.7.

Attendance of a student is stored in the attendance matrix in terms of two

entries viz. total sessions attended and total sessions conducted till date.

Information of date is stored in the index Date table. Thus every time an Excel

file is submitted two columns are added in attendance matrix and relevant

date is added in Date table. Entries in the attendance table are exemplified in

Figure 3.5(e). Data in attendance matrix is not purposely overwritten but

maintained date wise so that track record of student’s attendance over the

entire semester duration remains available.

Figure 3.7: GUI interface for feeding daily attendance into database.

30

Data Analysis and Report Generation Module

This module helps to respond to database queries generated either from local

interface or from remote user. Local database quires can be submitted using

Report generation option available in GUI. This option presents the interface

as shown in Figure 3.8. Module supports generation of variety of reports like

1. attendance report of whole division till date or for duration between

specific dates

2. attendance of individual student till date or for duration between

specific dates.

Report generated on basis of the query is in form of a Microsoft Excel file that

can be save and/or printed as per the need.

When GSM communication is enable this module also responds to

database quires received through SMS from the remote user. Message

requesting the information should be in a specific format. The prescribed

format is <student’s branch> <student’s enrollment number> <requested

information code>. The requested information code can be A for attendance,

R for result, E for examination schedule etc. for different database that exist.

For example, a valid query for attendance can be a message like - CE

90010056 A. On receiving a valid database query from the GSM

communication module the data is extracted from the database and

information is returned to GMS communication module which in turn

generates an answering SMS.

GSM Communication Module

This module is responsible for receiving and responding to SMS request

received from the remote user over GSM network. The module becomes

active only when the Auto-responder is enabled through Enable Auto-

responder option available in GUI. As discussed above, the request SMS

needs to be in a valid standard format. If the received message is not in

standard format or the details given in it is wrong then an error message is

returned. In case of a valid message database query is forwarded to Data

analysis and report generation module and the information received in return

31

is appropriately framed in a text message and replied to the mobile number

from which the request was received. Various functions performed by this

module are discussed as follows.

Figure 3.8: GUI interface for local database queries.

Initialization of serial port: This is a code for getting access to the serial port of

central data server where GSM modem is connected. In MATLAB serial port

is treated as an object similar to a file [59]. Once the serial port object is

created for selected serial port various object properties are required to be

configured. These includes baud rate, data packet format, size of input and

output buffers, mode of reading serial port (asynchronous or synchronous),

timeout while attempting to read, message termination character etc

Initialization of GSM modem: This code is responsible for configuring GSM

modem using AT commands that are communicated over the serial port.

Detailed list of AT commands is given in Appendix B and some of them used

for initial configuration of GMS mode are given in Table 3.1.

For sending and receiving message modem can be configured in two

possible modes viz. text mode and PDU mode. In PDU mode the message is

framed using a special encoding scheme where as in text mode it is framed

as a plain text. .PDU is generally the default mode in most of the mobile

32

phones and modems as it provides flexibility in terms of encryption, encoding

and data compression [60]. However using PDU mode in embedded

applications requires implementing its compression and decompression

algorithms in application program thus increasing the code footprint on the

controller. Further, in text mode header fields like senders address, message

length, etc. are available in plain text along with the sent message and hence

are relatively easy to handle. In this application GSM modem has been

configured in text mode. Other thing to be configured in modem includes

method for buffering the message and notifying arrival of new message [55].

In this application, the modem is configured such that when a new message is

arrived location of the memory where the message is stored is forwarded by

modem. This information can then be used to read the message from the

memory.

Table 3.1 Principal AT commands for GSM modem initialization.

AT commands Operation

AT check successful connection between PC and GSM modem

AT+CPIN detect valid SIM card

AT+CREG check network registration of GSM modem

AT+CMGF set preferred message format, text or PDU

AT+CNMI select procedure for message reception from the network

In the initialization code, the response received for each AT command

sent to modem is verified and in case of failure user is intimated on GUI

through an error message. After modem is initialized serial port object in

MATLAB is configured in an asynchronous mode so that the software is not

required to poll the input buffer but receives an interrupt for any request

received from modem.

Reading serial port and receiving SMS: This is an interrupt call-back function

executed when modem sends an intimation of some new activity. The

execution flow of this code is shown in the flow chart of Figure 3.9. The

function is called primarily due to either arrival of a message or a voice call.

The function continues further if the intimation is due to new message

otherwise leaves the call-back function. As discussed earlier, the modem is

33

configured to send the intimation of arrival of new message by sending the

memory location where the message is stored. The function reads message

from the SIM memory and extracts information like sender’s phone number,

date, time and text message from it. If the details in the message are found to

be valid then the requested information is extracted from the database

through Data analysis and report generation module. For example, in inquiry

related to attendance, on basis of the enrollment number and branch

mentioned in receive message, information like students name, semester,

current attendance and the date when attendance was last updated in the

database are extracted. This information is passed to the next stage that will

send a return message. In case message is not valid or the details in the

message are not correct, it reports received message to be invalid to the next

stage.

Writing serial port and sending SMS: This code segment is responsible for

replying SMS request on basis of the information received from the previous

stage. The information extracted from the database is framed into appropriate

text message and it is sent using AT+CMGS command. Example of a typical

message replied against a query related to attendance will be like “Vamja

Vishal B., Branch:CE, Sem:2, Attd:73.9%, upto:2/06/2010.” In case if the

message received is in the correct format but the content is incorrect then a

reply message is sent informing the user to verify the content.

Deleting the served message from SIM memory and updating log file: As

modem does not support additional memory, received messages are stored in

SIM memory. If the SIM memory becomes full then new messages cannot be

received. Thus, received SMS once replied is deleted from SIM memory using

AT+CMGD command. Further, each communication between the central data

server and GSM modem is recorded into a log file. Microsoft Excel file is used

as a log file in which information like requester’s phone number, request date

and time, branch and enrollment of student, requested information code are

noted. If the request has been replied then replied message and date & time

of reply is also registered.

34

Figure 3.9: Execution flow for reading serial port and receiving SMS.

3.2.3 Experimental results and discussion

In this section various operations performed to verify functioning of

attendance module of auto-responder is discussed. For experimentation,

required data was taken from Atmiya Institute of Technology & Science,

Rajkot. As per the needs of the institute auto-responder was initialized with

data of six branches viz. IT, CE, EC, IC, EE and ME with two divisions in each

branch. The database was selectively populated with student’s data being

feed using Microsoft Excel file. Example of such a file is shown in Figure 3.10.

Number of data entries related to student’s attendance was made in database

again in form of Microsoft Excel file. Example of such a file is shown in Figure

3.11. While feeding data, for the purpose of verification, various error

situations were created like feeding incomplete information, feeding

35

information not in proper format, duplicating information, etc. In all such cases

the errors were successfully trapped and required warnings/error messages

were generated.

Figure 3.10: Microsoft Excel file of populating student’s data in database.

Figure 3.11: Microsoft Excel file of updating student’s attendance in database.

Report generation and analysis module of auto-responder was

functionally verified through local database queries. Various types of reports

as discussed in section above were generated. System generates reports in

form of Microsoft Excel file. Two such reports are illustrated in Figure 3.12.

36

(a)

(b)

Figure 3.12: Report of attendance of (a) whole division till date (b) individual

student between dates.

Operation of GSM communication module of auto-responder that

serves remote request was tested in two stages. First using specially

designed test bench for offline testing and second through hours of online

operation. Test bench was primarily a MATLAB code that generates various

text messages acting as a GSM module. For all such test vectors response of

auto-responder was verified. This was very much useful in debugging the

code. In the second stage the system was tested online for total of around 20

Hrs. With an aim to test system under different GSM network traffic conditions

the system was kept online in time slots of 1Hr to 4 Hrs durations on different

days of the week and at different time. Statistics of system response to SMS

37

request either intentionally sent or received naturally are discussed below in

Table 3.2.

Table 3.2

Statistics related to auto-responder’s response during online testing.

1 GSM service providers whose SIM were used in testing

a) Vodafone

b) BSNL

55%

45%

2 Percentage distribution of SMS request received

a) Correct SMS

quires related to initialized data fields

quires related to uninitialized data fields

b) SMS with incorrect information

incorrect enrollment number

incorrect branch code

c) Irrelevant messages

incorrect format

incomplete message text

marketing SMS

72%

12%

16%

3 System response to SMS request

a) Correct SMS

b) SMS with incorrect information

c) Irrelevant messages

100%

100%

0%

4 Approximate average time in responding to SMS < 15 sec.

5 Failure in deleting SMS after responding 0%

6 Failure in recording data in log file 0%

7 Effect of voice calls received during operation

(voice calls were not responded)

No effect

8 Effect on operation at different time or days Not

significant

9 Effect of using different GSM services Not

significant

Important observations made during the experimental stage are as

follows

1. Working with GSM modem configured in text mode is more convenient

compared to that in PDU mode as decoding and encoding of

messages can be easy handled using string operations. Further, as the

data to be communicated in the application is relatively of limited size

38

and not confidential additional compression and decompression is not

needed.

2. When a message is read from the SIM, the details forwarded depends

on whether the message is from number stored in SIM contact list or

from unknown number. If a message is received from the number

whose details are stored in SIM then the message will typically have

following format (that includes the details of contact).

+CMGR: "REC UNREAD","+919925209452","A A Vyas", "10/09/19,

11:48:46+22”

CE 90001112 A

However, if a message is received from an unknown number then

messages will not have details of contact other than its number and

would typically look like

+CMGR: "REC READ","+919879522686","10/09/01,11:26:21+22"

IT 90000020 A.

This requires careful decoding while extracting details like phone

number, date and time and message text. Response of SIM when the

message is read may also change with SIM from different GSM service

providers.

3. In the current design provision is not made to respond SMS received

when auto-responder is not online, e.g. instances when the data is

being updated in the database or reports are generated for local use.

However, this can be easily handled by modifying a code such that

every time GSM modem is enabled, list of unread SMS is first read

from the SIM (using AT+CMGL command) and request of all valid SMS

is catered.

4. As modem does not support any memory for storing SMS, all received

SMS are stored in SIM memory which is limited. In case SIM memory

is full the messages are not received. Thus, it is also necessary that

when GSM modem is enabled for the first time there should be room in

SIM memory for receiving messages. As the designed system follows

39

the practice of deleting messages once responded problem of memory

in run time would not occur.

3.3 Design of customized bulk SMS system

Bulk SMS, also known as bulk messaging, is a mobile messaging service that

allows sending high volume of SMS to mobile phone terminals. It is mainly

used by media companies, small and big enterprises, banks, etc. for variety of

purposes like entertainment, marketing, alerts, reminders, information, etc. It

is a very convenient way of sending large number of SMS quickly and

efficiently. Bulk SMS can be both standardized as well as customized.

Standardized messages will have same message text sent to all recipient

numbers where as customized messages will have recipient specific details in

each message sent. Generally the service of bulk SMS is provided by

registered telemarketers and they are in good numbers in the market today.

Bulk SMS services provided by these service providers follows regulations

laid by Telecom Regulatory Authority of India (TRAI). In order to curb

unsolicited commercial communication through bulk SMS service TRAI has

enforced National Do Not Call register (now renamed as National Customer

Preference Register) popularly known as DND service [61]. As per this bulk

SMS service has been divided into two categories namely transactional

messages and promotional messages. Transactional messaging covers

messages related to services delivered to valid customer in areas of banking,

insurance, airlines, railways, educational institutes, and government

authorities. Messages other then this purpose are considered as promotional

messages. Promotional messages are not be delivered to DND activated

numbers whereas this is not the case for transactional messages. Further,

transactional messages can be delivered 24 x 7, whereas promotional

messages have to be delivered only in specific time slot of the day. For any

organization who wants to use bulk SMS service under transactional message

category has to register itself and has to enter into an agreement with access

provider. It is also required for the organization to deposit security deposit as

a part of the agreement and there are strict penalties for the defaulters [62].

40

For an educational institute bulk SMS service can prove to be very

efficient approach to reach to students and particularly parents in number of

instances. For example, communicating internal examination results to

parents, communicating overall attendance of students periodically, notifying

student’s absence to parents on daily basis, important announcements to

students etc. However, as discussed above, for using bulk SMS service

institute will have to register itself, sign an agreement and pay security

deposit. Further, in an educational institute the quantum of SMS to be done

on daily basis is generally limited. This is relatively larger only at the time of

examination results or monthly updates to parents. Generally, bulk SMS

services that are available in the market starts with a minimum package of

10,000 SMS and offers limited period validity and thus many a times does not

fit into the needs of an institute. This is especially true for institutes or

academic organizations that have limited students mass. In contrast to this,

most of the GSM service providers offer cheap schemes for SMS allowing

reasonably good number of free SMS per day. This motivates the need of

one’s own bulk SMS system that can be tailored as per one’s need.

Inspired by these considerations a customized bulk SMS system has

been designed as a part of the present work. It is an easy to use GUI based

application designed in MATLAB that allows sending customized bulk SMS.

Application runs on a personal computer connected to a GSM modem via

serial port. Details of GSM modem has been discussed in Section 3.2. Design

of system software is discussed as follows. List of MATLAB function designed

for the application is given in Appendix C along with brief description.

3.3.1 System software

GUI designed for bulk SMS system is shown in Figure 3.13. Various fields

provided in the GUI are discussed as follows.

File: This field allows the user to upload Microsoft Excel file that contain

student’s details to be sent. Screenshot of one such file is shown in Figure

3.14. It is a file of internal examination result containing student’s details like

name, number of subjects in which passed, failed or absent, percentage

marks scored and phone number.

41

Message: This field is to enter the text message to be sent. Example of typical

message to be sent can be: “Mid-Sem Exam Result of #C1#: Pass in #C2#

subjects, Fail in #C3# subjects, Absent in #C4#. Percentage Scored #C5#”.

#Ci#s in above message are markers that define where the student related

data has to be inserted. Every time the message is framed these are

substituted by student’s detail present in the ith column of Excel file uploaded.

For example, first text message framed after extracting the details form Excel

file given in Figure 3.10 will be “Mid-Sem Exam Result of PADALIYA GOLDI

DAMJIBHAI: Pass in 2 subjects, Fail in 3 subjects, Absent in 1. Percentage

Scored 30.”

Column of phone number: This field allows user to specify the column in Excel

file that contains phone number on which the SMS is to be sent. For the Excel

file given in Figure 3.10 detail to be filled in this filed will be C6.

System Comments: After filling details in each field of GUI when the process

of sending SMS is started (pressing send SMS button) current status/progress

of execution is indicate to user in this field through system generated

comments.

Figure 3.13: GUI interface for bulk SMS system.

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Figure 3.14: Screenshot of Microsoft Excel file for bulk SMS.

Figure 3.15 describes the flow of execution when send SMS button is

pressed by the user initiating the process of sending SMS. In the code first the

details entered in various fields of GUI is extracted and verified. In case of

irrelevant or incomplete information (e.g. blank fields) an error message is

displayed in system comments field of GUI and execution is terminated. If all

fields are found with valid details then the code first initializes serial port of

computer followed by initialization of GSM modem. Procedure of initializing

serial port and GSM mode is same as that discussed in Section 3.2.2 under

GSM communication. If code fails to initialize either serial port or GSM

modem an error message is displayed in system comments field and

execution is terminated. Once GSM modem is initialized the processes of

sending SMS is initiated. Each row in an Excel file represents student specific

data that is extracted and a text message is framed. This message is sent on

mobile number mentioned in the Excel file. Time required in completing send

process depends on number of factors like network signal strength, network

traffic, correctness of recipient number, etc. Application waits for send

acknowledgement for fixed time before proceeding to next message. The

process is repeated for each row in the Excel file. Details of each message

are logged in log file. Log file is primarily an Excel file that records recipient’s

mobile number, message text, date, time and special remarks if message

could not be sent.

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Figure 3.15: Execution flow for transmitting bulk SMS.

3.3.2 Experimental results and discussion

Functioning of customized bulk SMS system has been verified through

number of operations. All the attempts to send SMS with correct data feed as

per the format were 100% successful. Number of operations with intentional

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errors was performed to identify if the error is properly trapped and required

warning is generated. The system was capable of trapping following errors.

1. Empty fields in GUI.

2. File type other then Microsoft Excel (.xls) file specified in GUI.

3. Microsoft Excel file not in proper format or with bank entries.

4. Number of columns specified in message and/or column number

specified in phone number filed of GUI do not match with the data

present in linked Microsoft Excel file.

5. Unable to initialize serial port.

6. Modem if not responding e.g. power not turned on.

7. SIM not responding e.g. PIN not enabled or SIM not properly inserted.

8. Problem in network registration due to weak network signal.

9. After successful initialization of modem, if modem stops responding

later on.

10. Modem taking more time in sending the SMS.

Designed system has been practically used number of times at Darshan

Institute of Engineering & Technology, Rajkot for sending SMS of student’s

mid-semester examination results to their parents. Before this was used the

result were sent by post. This used to involved lots of man hours as well as

expenses towards stationary and postages. Around 10% of post used to

return undelivered due to wrong or change in address may be because of un-

updated records or human errors. Further, the mechanism took its own time

and hence the timely response of parents was not achievable. Use of

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customized bulk SMS system was able to overcome all the mentioned

drawbacks and was also well appreciated by the parents.

Study of log file indicates that average time taken by the system to send a

SMS is less than 10 sec. This also includes time to record details into log file.

Information about messages that could not be sent present in log file helps to

verify the details so that the same can be sent after correction if any. Details

in typical log file have been illustrated in Figure 3.16.

Figure 3.16: Log file in customized bulk SMS system.