Global System for Mobile Communication

WHAT IS GSM : Global System for Mobile Communication (GSM) is a popular method used in the whole word for voice and data communication. GSM became popular over other existing wireless s widely adopted in a short span of time because of its superior speech quality and its uniform international standard which made sure that a single telephone number and mobile station could be used throughout the world. GSM is used in over 135 countries. (Harte, 2004). GSM was the world’s first cellular system to specify digital modulation and the world’s most popular 2G technology.

Before GSM, European countries used different cellular standards throughout the continent, and it was not possible to a customer to use a single subscriber unit throughout Europe. GSM was originally developed to serve as the pen-European cellular service and promised a wide range of network service through the use of ISDN. GSM’s success has exceeded the exception of virtually everyone, and it is now the world’s most popular standard for new cellular radio and personal communications equipment throughout the world. As of 2001, there were over 350 million GSM subscribers worldwide.

GSM works in 2 bands commonly 900 MHz or 1800 MHz bands. GSM was first introduced into the European market in 1991. But but the end of 1993 several non-European countries in south America, Asia and Australia has adopt GSM for its greater services. GSM services follow ISDN standardars and its services are classified as either tele or data services. Tele services include standard mobile telephony and mobile originating and base-originating traffic. Data services include computer-to-computer communication and packed switched traffic. User services may be divided into three major categories.

1). Telephone Services: including emergence calling and facsimile. GSM also supports video text and tele, through they are not integral parts of the GSM standard. 2). Data Services: GSM supports packet switched protocols and data rates from 300 bps to 9. 6 kbps. 3). Supplementary ISDN Services: are digital in nature and includes the Short Messaging Services (SMS) which allows GSM subscribers and base stations to transmitting alphanumeric pages of limited length (160 7-bit ASCII characters) while simultaneously carrying normal voice traffic.

It can be used to send emergency messages to the subscribers What distinguishes GSM from other systems such as AMPS is the Subscriber Identity Module (SIM), which is a small chip that stores information about the subscriber (user) such as the subscriber’s identification number, the network ,privacy keys, and other user specification information. Without a SIM installed, all GSM mobiles are identical and no operational. It is the SIM that gives GSM subscriber units their identity. A second remarkable feature of the GSM is the on-the-air privacy which provided by the system.

It is not possible to eavesdrop on a GSM radio transmission. GSM offers wide range of services such as • Support for international roaming • Extensive security features • Distinction between user and device identification • Excellent speech quality • Telephony • E-mail and Internet connections • Interworking (e. g. with ISDN, DECT) • Extensive security features • Telephony • Asynchronous and synchronous data services (2. 4/4. 8/9. 6 kbit/s) • Access to packet data network (X. 25) • Telematic services (SMS, fax, videotext, etc. )

• Wide range of value-added features (call forwarding, caller ID, voice mailbox) GSM MODEM GSM modem is used to access GSM, all the cell phones operating in GSM mode have a GSM modem built-in and hence they are able to access the services that the GSM offers. GSM modem is also be made to work as an stand alone application when a GSM modem or phone is connected to a PC serial port. When a GSM SIM card is inserted into this modem, it can be made to send and receive data over the GSM cellular service protocols. The GSM modem finds applications widely in remote data transfer .

GSM modems allow for real-time monitoring and control of remote data loggers and other sensor systems by simply dialing into cellular or land phone networks. AT COMMANDS All the GSM modems are programmable using a windows program HyperTerminal by AT commands. Using these AT commands operations such as dialing, hanging up, and changing the parameters of the connection could be done. AT commands are instructions used to control a GSM modem. AT is the abbreviation of ATtention. All the AT commands start with “AT”. This is the reason why the modem commands are called AT commands.

There are two categories of AT commands, basic commands which are used on all kinds of modems and GSM/GPRS modems specific AT commands specific to the GSM technology, Basic AT commands are the ones that that do not start with “+”. For example, D (Dial), A (Answer), H (Hook control) and O (Return to online data state) Extended AT commands always begin with “+”. All GSM AT commands are extended commands. For example, +CMGS (Send SMS message), +CMSS (Send SMS message from storage), +CMGL (List SMS messages) and +CMGR (Read SMS messages).

The starting “AT” is the prefix that informs the modem about the start of a command line. It is not part of the AT command name. For example, D is the actual AT command name in ATD and +CMGS is the actual AT command name in AT+CMGS. Here are some of the tasks that can be done using AT commands with a GSM/GPRS modem or mobile phone: 1. Get basic information about the mobile phone or GSM/GPRS modem. For example, name of manufacturer (AT+CGMI), model number (AT+CGMM), IMEI number (International Mobile Equipment Identity) (AT+CGSN) and software version (AT+CGMR). 2.

Acquire information about the subscriber. For example, MSISDN (AT+CNUM) and IMSI number (International Mobile Subscriber Identity) (AT+CIMI). 3. Read (AT+CPBR), write (AT+CPBW) or search (AT+CPBF) phonebook entries. 4. Control the presentation of result codes / error messages of AT commands. For example, controlling whether to enable certain error messages (AT+CMEE) and whether error messages should be displayed in numeric format or verbose format (AT+CMEE=1 or AT+CMEE=2). 5. Establish a data connection or voice connection to a remote modem (ATD, ATA, etc). 6. Send and receive fax (ATD, ATA, AT+F*).

7. Send (AT+CMGS, AT+CMSS), read (AT+CMGR, AT+CMGL), write (AT+CMGW) or delete (AT+CMGD) SMS messages and obtain notifications of newly received SMS messages (AT+CNMI). 8. Perform security-related tasks, such as opening or closing facility locks (AT+CLCK), checking whether a facility is locked (AT+CLCK) and changing passwords (AT+CPWD). 9. Know the current status of the mobile phone or GSM/GPRS modem. For example, mobile phone activity status (AT+CPAS), mobile network registration status (AT+CREG), radio signal strength (AT+CSQ), battery charge level and battery charging status (AT+CBC). 10.

Control the presentation of result codes / error messages of AT commands. For example, controlling whether to enable certain error messages (AT+CMEE) and whether error messages should be displayed in numeric format or verbose format (AT+CMEE=1 or AT+CMEE=2). 11. Acquire or change the configurations of the mobile phone or GSM/GPRS modem. For example, change the GSM network (AT+COPS), bearer service type (AT+CBST), radio link protocol parameters (AT+CRLP), SMS center address (AT+CSCA) and storage of SMS messages (AT+CPMS). 12. Monitoring the signal strength. Monitoring the charging status and charge level of the battery.

13. Save and restore configurations of the mobile phone or GSM/GPRS modem. For example, save (AT+CSAS) and restore (AT+CRES) settings related to SMS messaging such as the SMS center address. SENSORS A sensor is a component that measures a physical quantity and converts it into different form usually electrical which can be then processed by the instrument or observed by an experimenter. For example this conversion of energy can be from mechanical to electrical. Sensors can be divided into several categories such as thermal, Electromagnetic, mechanical , chemical etc . each of these find various applications in real life.

For examples thermocouple sensor is used in industry and at home/clinics to find the exact temperature. Mechanical sensors such as pressure or humidity is used to measure the pressure of air, fluid flow etc. Without proper sensors the automatic systems are useless because they take the input from the sensor and then process that data to perform any action. Sensors have wide applications in data acquisition and logging systems and used for polling any device. (Fraden, 2003) ELECTRO CARDIOGRAPH An electrocardiogram abbreviated as EKG or ECG is a medical procedure that helps in determining the electrical activity of the heartbeat.

With each beat, an electrical impulse progresses through the heart producing waves which causes the muscle to squeeze and pump blood from the heart. An electrocardiogram is a recording of the electrical activity of the heart over the time that is being produced by an electrocardiograph; it is usually recorded through electrodes attached to the skin. Electrocardiograph (ECG) is one of the most extensively used biomedical sensing methods as the heartbeat is the best indicator for a wide range of physiological conditions. ( Dubin , 2000)

ECG SESNORS The EKG (Electrocardiogram) sensor measures electrical signals (voltages) produced during heart/ muscle contractions. An ECG sensor comes in a standard 3 or 12 lead package which can be used for standard 3-lead or 12 lead EKG tracings or to make surface EMG recordings(attached to the skin of the patient). Each of the three leads on the sensor connects to disposable electrodes. Using the readings produced by these eletrodes an EKG graph is displayed, demonstrating the contraction and repolarization of the heart’s chambers.

A large amount of research is underway in making these sensors more accurate since the whole system design depends on it. (Aehlert,2005) Almost all of these ECG sensors use some form of electrodes that must make electrical contact with the subject’s skin surface. An ECG senor can be studied with these typical specifications: Range, Resolution (8 bit or 12-bit), Sample Rate, Voltage Protection, Isoelectric Line (Gain): System design The proposed ECG monitoring system can be functionally divided into four subsystems: ECG Sensors, Data Sampling, Wireless Transmission using GSM , and Host Interface.

ECG signals are first digitized by ADCs and transmitted wirelessly to be received by the GSM modem. References Harte,L. (October 2004). Introduction to GSM: Physical Channels, Logical Channels, Network, and Operation. Althos Fraden, J. (2003). Handbook of Modern Sensors: Physics, Designs, and Applications, 3rd edition (Hardcover). Springer Dubin ,D. ( 2000) Rapid Interpretation of EKG’s, Sixth Edition (Paperback). Cover Publishing Company Aehlert,B . ( 2005) ECGs Made Easy – Book and Pocket Reference Package, 3 edition (Paperback). Mosby/JEMS

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