GSM vs CDMA

HISTORY

The GSM was originated in Europe (Global System for Mobile Communications) in the year 1987 and gained world wide popularity because of its modern network features which are available to the individual mobile phone user. CDMA or code division multiple access was developed by Qualcomm Inc. and it became an international standard in 1995.
TECHNICAL ISSUES
As you know the mobile personal communication systems uses microwave frequencies above 800MHz for their transmission and reception purposes. They all are operating in some predefined or pre allocated frequency bands according to the international standards.For operating in these microwave frequencies they all need some access methods. And these methods are: 1. Frequency division multiple access (FDMA) 2.Time division multiple access (TDMA) 3.Code division multiple access (CDMA) Thus CDMA is one access technology which cell phones uses to transmit and receive data. You can understand the meaning of FDMA, TDMA and CDMA eazily by just noting the word meaning for ezch letter. That is FDMA puts each call on a separate frequency and TDMA assigns each call a certain portion of time on a designated frequency for the above mentioned purpose. But CDMA gives a unique code to each call and spreads it over the available frequencies. All these are multiple access systems because more than one user can use the specified CELL ( not cell phone!) at a time.But GSM or Global System for Mobile uses the above mentioned TDMA ( Time Division Multiple Access ) for mobile communication purposes ! In other words GSM is a global standard based on TDMA and a very popular one in the entire Europe, Middle East, Asia and Africa and not an access code as CDMA but one global standard.( Remember it always....CDMA vs GSM is really misleading! it is CDMA vs TDMA..!)GSM operates in the 900 MHz band (890 MHz - 960 MHz) in Europe and Asia and in the 1900 MHz band in the United States. Besides these facts we must know the limitations and advantages of each systems in a brief way. All these facts are highly technical but i will try my best to write the details suite for all the mouthshut readers. First TDMA of GSM.The data transmission in TDMA is actually not continuous. It occurs in bursts. But the time between these bursts for a single mobile phone user is very very short, so that he never knows that the speech of the other person is discontinuous!As TDMA uses different time slots for transmission and reception your handset never need a duplexer. But it simply need a switch to transfer between transmission and reception sesseions!But the CDMA system has a soft capacity limit. That is increasing the number of users will decreases the system performance.( any comments Reliance users..?..!!).Channel data rates are very high in CDMA systems. But sel-jamming is a major problem.

AND NOW SOME INTERESTING FACTS

Above are the technical facts you must know. But as you are very familiar with GSM of BSNL, AIRTEL, ESCOTEL etc. and the CDMA of Relience i know you are also eager to know about some commonly misunderstood things.GSM is a widely spread standard and CDMA is a patented technology. That is you must pay a royalty for using CDMA! Also GSM covers the entire Europe , Asia except Korea, Africa and Middle East. So being a GSM user you have virtually an international roaming. You can eazily use a GSM phone in any of these countries while roaming. GSM users are almost 8 times in number than CDMA users worldwide. By being a GSM user you will be part of the largest mibile community. And coming to voice quality GSM is far better than CDMA, as i mentioned it earlier. CDMA base stations consumes less power than GSM and also covers a large distance. That is the cell size in CDMA is larger compared to GSM.In general both GSM and CDMA are frontier technologies and both have good and bad qualities. And in the case of mobile handsets the fact is that GSM handsets are very popular and many of the new facilties are readily available in GSM phones with lesser price. The reason is simple...nokia and motorola needs profit...and they will invest more in GSM because GSM has 8 times more users than CDMA.

Subscriber Identity Module (SIM) cards
The removable SIM card allows phones to be instantly activated, interchanged, swapped out and upgraded, all without carrier intervention. The SIM itself is tied to the network, rather than the actual phone. Phones that are card-enabled can be used with any GSM carrier.
The CDMA equivalent, a R-UIM card, is only available in parts of Asia but remains on the horizon for the U.S. market. CDMA carriers require proprietary handsets that are linked to one carrier only and are not card-enabled. To upgrade a CDMA phone, the carrier must deactivate the old phone then activate the new one. The old phone becomes useless.

How Mobile Networks Work

Introduction
This document is designed to give a very brief explanation of how today's mobile phone networks work. It explains what is meant by radio communication, and describes how mobile phone networks, using the cellular radio concept, operate.

Radiocommunication
Mobile phones may be a relatively new technology, but radio has been used as a means of communication for over a hundred years. Marconi made the very first radio transmission in 1895. Within thirty years radio was being used on a daily basis for broadcasting and for two-way radio communication by the military and the police.

What is a radio wave?
Mobile phones and their base stations transmit and receive signals using electromagnetic waves (also referred to as electromagnetic fields, or radio waves). Electromagnetic waves are emitted by many natural and man-made sources and play a very important part in our lives. We are warmed by the electromagnetic emissions of the sun and we see using the part of the electromagnetic spectrum that our eyes detect as visible light. All electromagnetic radiation consists of oscillating electric and magnetic fields and the frequency, which is the number of times per second at which the wave oscillates, determines their properties and the use that can be made of them. Frequencies are measured in hertz or Hz, where 1 Hz is one oscillation per second, 1 kHz a thousand, 1 MHz is a million, and 1 GHz, is a thousand million. Frequencies between 30 kHz and 300 GHz are widely used for telecommunication, including broadcast radio and television, and comprise the radio frequency band.Waves at higher frequencies but within the RF region, up to 60 GHz, are referred to as microwaves and have a wide variety of uses. These include radar, telecommunication links, satellite communications, weather observation and medical diathermy.

How radio communication works

A radio frequency wave used for radio communication is referred to as a carrier wave. The radio frequency carrier wave of any system is produced by the transmitter as a sine wave. A sine wave conveys very little information since it simply repeats over and over. However, it can be switched on and off and this was the technique used in the earliest radio transmissions which used Morse code.
If the radio wave is to convey more information, such as speech or computer data etc., this information has to be added to the carrier wave in some way, a process known as modulation. The modulation process involves some feature of the carrier wave being varied in accordance with the information transmitted. For example, for AM (amplitude modulation) transmission, the electrical signal from a microphone produced by speech or music is used to vary the amplitude of the carrier wave, so that at any instant the size or amplitude of the RF carrier wave is made proportional to the size of the electrical modulating signal.

There are many different types of modulation technique, each with different characteristics, and each suitable for different applications. You might be familiar with the frequency modulation (FM) used for radio broadcasting, or the digital techniques used by mobile phones. All work by varying some property of the carrier wave in a way by which the information to be communicated can be conveyed or carried by the radio frequency carrier wave.


Mobile Phone Networks
Base Station and handsets
A mobile phone sends and receives information (voice messages, fax, computer data, etc) by radio communication. Radio frequency signals are transmitted from the phone to the nearest base station and incoming signals (carrying the speech from the person to whom the phone user is listening) are sent from the base station to the phone at a slightly different frequency. Base stations link mobile phones to the rest of the mobile and fixed phone network.
Once the signal reaches a base station it can be transmitted to the main telephone network, either by telephone cables or by higher frequency radio links between an antenna (e.g. dish) at the base station and another at a terminal connected to the main telephone network.


'Cellular' Radio
Each base station provides radio coverage to a geographical area known as a cell. Base stations are connected to one another by central switching centres, which track calls and transfer them as the caller moves from one cell to the next. Diagram 2 below shows the cell structure of a mobile phone network . An ideal network may be envisaged as consisting of a mesh of hexagonal cells, each with a base station at its centre. The cells overlap at the edges to ensure the mobile phone users always remain within range of the base station. Without sufficient base stations in the right locations, mobile phones will not work.
The size of each cell depends on three factors. First, the local terrain; radio signals are blocked by trees, hills and buildings. Second, the frequency band in which the network operates (in general, the higher the radio frequency, the smaller the cell). Third, the capacity (i.e. number of calls) needed in any given area. Base stations are typically spaced about 0.2-0.5 km in towns and 2-5 km apart in the countryside.
If a person with a mobile phone starts to moves out of one cell and into another, the controlling network hands over communications to the adjacent base station.

(While cells are generally thought of as regular hexagons, making up a 'honeycomb' structure, in practice they are irregular due to site availability and topography. )

Why are so many base stations required?

Transmitted signal strength falls off rapidly with distance from base stations, and mobile phones require a certain minimum signal strength to ensure adequate reception. The current generation of GSM base stations cannot communicate over distances greater than 35 km because the delay in receiving radio signals becomes too great. However, the decline of signal strength with distance places a practical limit on coverage of around 10 km. For these reasons an extensive network of base stations is needed to ensure coverage.

Why can't one base station serve my town?

Radio spectrum is a precious natural resource with many different demands upon it (for example, radio and TV broadcasting, emergency communication, navigation aids etc). Consequently the amount made available to each mobile phone operator is limited and this means base stations can only carry a limited number of calls at any one time.
To accommodate the steadily increasing volume of users, network operators have to use the limited number of radio frequencies licensed to them to support the maximum number of mobile phone users. This is achieved by re-using any given radio frequency many times in a network and carefully controlling base station power so that signals arising in different parts of the network do not interfere with each other. This concept of frequency re-use is illustrated in figure 3. The cells are grouped into clusters, with the frequencies allocated to a particular cell within a cluster not being re-used until the corresponding cell in adjacent clusters. This gives a repeating pattern of cells and clusters which can be expanded to provide national coverage.
To increase the capacity of their networks, operators have to build additional base stations and thus reduce cell size. It is for this reason that one large base station cannot serve a whole town.

Types of Mobile PhoneTechnology

Cellular radio networks operate using two different technologies:- GSM and CDMA.

GSM - Global system for Mobile Communications or Groupe Speciale Mobile.

CDMA- Code Division Multiple Access

Jammer

Cell Phone Jammer
A phone jammer transmits low power radio signals to cut off communications between cell phones and cell base stations. It does not interfere with any communications other than cellular phones within the defined regulated zone. Upon activating a phone jammer, all idle phones will indicate "NO NETWORK." Incoming calls are blocked as if the cellular hand phone were off.When the phone jammer is turned off, all cell hand phones will automatically re-establish communications and provide full service.

The jamming area is influenced by the location of the cell tower and the obstacles between cell tower and the cellular jammer. It means that in normal condition if the distance is close between the cell tower and the phone jammer, it will have less jamming area. Likewise, if there are obstacles and walls between the cell tower & the cellular phone, the jammer will give more jamming area.



Provides Acoustics Isolation
A phone jammer provides the ultimate solution in any area where cellular communications frequently cause nuisance either by loud incoming call rings or resulting loud telephone conversations. Examples of places where cell phones can be disruptive include:-
Public Transport (trains, busses, etc.).
Theatres (movie theatres, concert halls, playhouses, opera houses, etc.) .
Lecture rooms .
Libraries .
Museums .
Restaurants .
Schools and Universities (classrooms, lecture halls, auditoriums, etc.) cell phone jammers can prevent students from SMS cheating.
Places of Worship (mosques, shrines, churches, temples, etc.) .
Country Clubs . Sporting Events .
Recording Studios.
TV Stations, Radio Stations, etc.


Protects Against Breach Of Security Policy
Cell phones are innocent looking communication devices that enable continuous transmission of voice/data. In secured places, where policy does not warrant the use of mobile phones, it is almost impossible to detect a person conducting cell phone conversations or to spot other such misuse, especially when mobile phones are very small. Examples of places where cell phone use may not be allowed include:-
Businesses (conferences, board of directors rooms, seminars, meeting rooms) .
Government Building and Government Complexes .
Law Enforcement Facilities .
Police Stations .
Drug Enforcement Facilities .
Prison Facilities, Jails, Etc. .
Courts of Law and Court Houses .
Embassies .
Military Installations, Military Complexes, and Military Training Centres.


Addresses Safety Issues
In accordance with fire code regulations, mobile phones must be switched "off" in any area that has a potentially explosive atmosphere, including "petrol service stations" where sparks could cause an explosion or fire. These preventable accidents occur more frequently than most people are aware. Areas where mobile phone use is prohibited include:-
Petrol/ Gas Stations .
Oil Refineries and Storage Facilities .
Offshore Oil Platforms .
Petrol/Gas Transportation Vehicles .
Chemical Refineries and Storage Facilities. Chemical Transportation Vehicles .
Laboratories .
Fireworks Factories .
Liquefied Petroleum (LPG) Refineries and Storage Facilities. LPG Transportation Vehicles . Natural Gas Refineries and Storage facilities . Natural Gas Transportation Vehicles .
Power Plants .
Industrial Plants (or anywhere the air contains chemicals or particles such as grain, dust, or metal powders) .
Hospitals.

I think low power cell phone jammers for use in all the listed areas for obvious safety reasons.