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

Process Scheduling handles the selection of a process for the processor on the basis of a scheduling algorithm and also the removal of a process from the processor. It is an important part of multiprogramming operating system.There are many scheduling queues that are used in process scheduling. When the processes enter the system, they are put into the job queue. The processes that are ready to execute in the main memory are kept in the ready queue. The processes that are waiting for the I/O device are kept in the I/O device queue.The different schedulers that are used for process ... Read More

A process is an active program. It can also be said as a program that is under execution. It is more than the program code as it includes the program counter, process stack, registers, program code etc. Compared to this, the program code is only the text section.A process passes through different states as it executes. These states may be different in different operating systems. However, the common process states are explained below with the help of a diagram −NewThis is the state when the process has just been created. It is the initial state in the process life cycle.ReadyIn ... 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

Message switching is a connectionless network switching technique where the entire message is routed from the source node to the destination node, one hop at a time. It was a precursor of packet switching.ProcessPacket switching treats each message as an individual unit. Before sending the message, the sender node adds the destination address to the message. It is then delivered entirely to the next intermediate switching node. The intermediate node stores the message in its entirety, checks for transmission errors, inspects the destination address and then delivers it to the next node. The process continues till the message reaches the ... Read More