Digital Advanced Mobile Phone System (D-AMPS)is a digital version of Advanced Mobile Phone Systems (AMPS), the original analog standard for cellular phones. D-AMPS uses a combination of time division multiple access (TDMA) and frequency division multiple access (FDMA). It adds TDMA to get three channels per AMPS channel, thus tripling the number of calls on a channel. Features They are standardised by IS-54 and IS-136. As in AMPS, D-AMPS also uses frequencies from 800 to 900MHz for transmission. Half of the spectrum is used for sending signals and the other half is used for receiving signals. The frequency ... Read More

Second generation (2G) mobile phones switched from analog system of 1G to digital system. It was commercially launched in 1991 as GSM standard in Finland. As with 1G phones, 2G phones didn’t have any worldwide standardizations. 2G systems were also known as personal communications services (PCM). Advantages of 2G over 1G It allows voice signals to be digitized and compressed. So, they are more efficient on frequency spectrum than 1G. They introduced data services for mobile in form of SMS text messaging. Data and voice signals are digitally encrypted. So, security against eavesdropping and fraud increased manifold. Digital signals ... Read More

Frequency division duplex (FDD) is a communication technique where the connected parties can communicate with each other in both directions through use of separate frequency bands for transmitting and receiving. Since FDD uses different frequency bands for upstream data and downstream data, the sending and the receiving signals do not interfere with each other. FDD in Cellular Networks Cellular networks use FDD to separate the channels. One block of the electromagnetic spectrum is allocated for uplink, which carries data from mobile phones to a base station. A different block of the spectrum is allocated to downlink, carrying data ... Read More

Cellular architecture is constituted of the following −A network of cells each with a base station.A packet switched network for communication between the base stations and mobile switching centers.The public switched telephone network to connect subscribers to the wider telephony networkCellular ConfigurationIn all cellular systems, land area is divided into a number of cells each with its radio service. In AMPS the area is large which in digital services, the area is much smaller.Conventionally cells are hexagonal in shape.Each cell uses a frequency range that is not used by its adjacent cells. However frequencies may be reused in non-adjacent cells.At ... Read More

Advanced mobile phone system (AMPS) was a standard for analog cellular phone system developed by Bell Labs and officially introduced by AT&T in 1983.FeaturesIt is an analog system based on the initial electromagnetic spectrum allocation for cellular service by the Federal Communications Commission.It uses frequency division multiple access (FDMA) for multiple simultaneous conversations.Frequency ranges within the 800 and 900 MHz are allocated for cellular telephones in AMPS. Half of the signal is used for sending signals and half is used for receiving signals.It has a high bandwidth requirement particularly when the number of conversations is very high.It was the first ... Read More

Improved Mobile Telephone System (IMTS) was a radio system that linked to public switched telephone networks (PSTN) before the era of cellular mobiles. It was introduced in 1964 and was the wireless equivalent of landline dial up telephones. Features IMTS was a radio system for mobile telephones that was an improvement over the previous Mobile Telephone System (MTS). MTS supported half duplex communication. So, the communicating parties could not communicate simultaneously. IMTS supported full duplex communication, thus allowing both the user to talk and hear simultaneously. IMTS required a high power transmitter to be installed, preferably on the ... Read More

Wireless cellular technology or mobile communications started with first generation mobile phones, popularly known as 1G. It was an analog telecommunications system, introduced in 1979 and continued to mid of the 1980s. History 1G mobile communication system was introduced in Japan in 1979 by Nippon Telegraph and Telephone (NTT). Initially, it started in Tokyo and within next five years expanded to cover the whole of Japan. In 1981, Nordic Mobile Telephone (NMT) was launched in European countries. In 1983, Ameritech launched 1G mobiles in the USA using Motorola mobile phones. Use of mobile communication system was then followed by several ... Read More

Mobile telephone service (MTS) connects mobile radio telephones with other networks like public switched telephone networks (PSTN), other mobile telephones and communication systems like Internet.Basic Mobile Communications SystemMobile phones and other mobile devices, called mobile stations are connected to base stations. Communication between the mobile stations and the base stations are done by wireless radio signals, which may be both data signals and voice signals. Each base station has a coverage area around it, such that mobile stations within this area can connect provided they have access permissions. Base stations contain transmitters and receivers to convert radio signals to electrical ... Read More

Packet switching is a connectionless network switching technique. Here, the message is divided and grouped into a number of units called packets that are individually routed from the source to the destination. There is no need to establish a dedicated circuit for communication. Process Each packet in a packet switching technique has two parts: a header and a payload. The header contains the addressing information of the packet and is used by the intermediate routers to direct it towards its destination. The payload carries the actual data. A packet is transmitted as soon as it is available in a node, ... Read More

Circuit switching is a connection-oriented network switching technique. Here, a dedicated route is established between the source and the destination and the entire message is transferred through it.Phases of Circuit Switch ConnectionCircuit Establishment : In this phase, a dedicated circuit is established from the source to the destination through a number of intermediate switching centres. The sender and receiver transmits communication signals to request and acknowledge establishment of circuits.Data Transfer : Once the circuit has been established, data and voice are transferred from the source to the destination. The dedicated connection remains as long as the end parties communicate.Circuit Disconnection ... Read More