Mobile telephone technology entered the market in the 1980s. People could then talk to each other using their mobile handsets from wherever they wanted. Now if everyone made calls using the same frequency band then all the calls were likely to be confused with each other and the call would fail. So each call was divided into different frequency bands so that different people could make calls using completely different lines.
The system called Frequency Division Multiple Access (Frequency-division multiple access) or ephadiemae (FDMA). And this is how the previous phones worked. The general meaning of FDMA is that through this technology people will keep their calls separate by using different frequency bands for each call. FDMA phones worked much like landline phones and were called first-generation phones or 1G phones.
The biggest drawback to FDMA technology is that if many people started talking together in one area, it would not be possible to provide a separate band for everyone. So the engineers invented another new method, and they moved the whole system from analog to digital technology. In this technology, human voice samples are taken and the voice is converted to numeric code.
In FDMA, each call was sent to a different frequency band. But this time the engineers invented a whole new method. Instead of using a different frequency band for each call, they came up with a way to broadcast a call to a different band for a while. A call is broadcast on the same frequency in different bands for some time, making it possible to deliver multiple calls at once. The technology is called ” time-division multiple access ” (Time-division multiple access) or TDMA (TDMA). GSM-dependent mobile networks all use TDMA technology. And these phones are called 2G phones.
SIM card is the key feature of GSM network– The SIM card is mainly a small card — where a small chip is attached, and it is a must have item for every GSM phone to work. GSM phones can never top the network without a SIM card. Not only that, this card contains all the important information.
TDMA technology cannot be called perfect — because if mobile phone users grow too fast, the call quality in this technology will also deteriorate and the network will fail to deliver countless calls. So this time the engineers started thinking again, how to bring more users together in the system. And this time the system they created is called ” Code-Division Multiple Access ” (CDMA). CDMA is not a completely new technology, it is made with the ingredients of FDMA and TDMA.
CDMA phone does not require SIM. CDMA operators keep a complete list of all their phones so that they can give them access to use their network. These phones are tracked using their ESN ( Electronic Serial Number ), so no SIM-card is required on this phone later. After activating the phone, CDMA starts trying to connect the phone directly to its mobile network.
Most mobile operators in the United States offer CDMA-based services. However, some mobile operators offer both CDMA and GSM services simultaneously. Although CDMA services are offered in the United States, GSM is the most popular worldwide. Even Bangladesh’s mobile operator Citycell has been completely destroyed mainly due to non-provision of GSM services.