Abstract:
The word mobile comes from a Latin word “mobilis” which means to able to move freely. The history of mobile phone is derived from the idea of two-way radios used by taxi cabs, police mobiles and other service vehicles. But the main difference between them and mobiles is that they were not connected to a main telephone network as like the mobile phones of today. In the 1940’s Motorola developed a large hand held two way radios for US military. [1]
By 1967, mobile phone technology was available for the users but they have to stay within one cell area. On April 3, 1973, Motorola employee Dr. Martin Cooper placed a call to Dr. Joel S. Engel, head of research at AT&T's Bell Labs, while walking the streets of New York City talking on the first Motorola DynaTAC prototype in front of reporters. [2]
When talking about the generations of mobile technologies, they are divided into three main technologies which we are using nowadays namely 1G, 2G, 3G. We will now discuss seperately each and every technology now.
1.2: First Generation of mobile technologies
1G is the name of mobile technology which uses analog signals as compared to 2G which is digital. They were introduced in 1980’s and continued their working until they were being replaced by 2nd generation of mobile technologies [3]. The underlying technology behind 1G was AMPS (Advanced Mobile Phone system).
AMPS use separate frequencies, or "channels", for each conversation and therefore required considerable bandwidth for a large number of users [4]. In AMPS, the cell centers could flexibly assign channels to handsets based on signal strength, allowing the same frequency to be re-used in various locations without interference. This allowed a larger number of phones to be supported over a geographical area.
The frequencies allocated to AMPS by the FCC range between 824 to 849 MHz in reverse channels (mobile to base) and 869 to 894 MHz in forward channels (base to mobile) [5].
In terms of overall connection quality, 1G compares unfavorably to its successors. It has low capacity, unreliable handoff, poor voice links, and no security at all since voice calls were played back in radio towers, making these calls susceptible to unwanted eavesdropping by third parties.
However, 1G has few advantages over 2G. In comparison to 1G's analog signals, 2G's digital signals are very reliant on location and proximity. If a 2G handset made a call far away from a cell tower, the digital signal may not be strong enough to reach it. While a call made from a 1G handset had generally poorer quality than that of a 2G handset, it survived longer distances. This is due to the analog signal having a smooth curve compared to the digital signal, which had a jagged, angular curve [6]. As conditions worsen, the quality of a call made from a 1G handset would gradually worsen, but a call made from a 2G handset would fail completely.
1.3: Second generation of mobile technologies
After the success of mobile phones throughout the world there comes the era of 2nd generation of mobile technologies which actually revolutionize the mobile industry. It was based on GSM standard which uses TDMA (time division multiple access) scheme. It is estimated that around 80% of the world population uses GSM as a mobile standard. [7]. GSM also provides an alternative to voice calls which is low in cost and is more reliable. This is called SMS or short messaging service.
GSM is a cellular network which means that mobile phones connected to it for the searching of cells available in immediate vicinity. When coming to the frequencies used by GSM, it uses 890–915 MHz to send information from the mobile station to the base station (uplink) and 935–960 MHz for the other direction (downlink), providing 125 RF channels spaced at 200 kHz. Duplex spacing of 45 MHz is used. [8]. There is also an extension band of 15 MHz in both directions.
