Monday, 13 July 2015

Skill - 1 : Mobile Hardware and Servicing - Unit I Notes


Introduction to Mobile Phone.

Cellular telephone systems are a way of providing portable telephone services. Each phone is connected by a radio link to a base station. In turn, this is linked to the telephone network, which is the largest machine on the planet.

There is nothing special about radio links - they've been used for scores of years. What is clever is that with a cellular system, each base station covers a limited area, and if a phone moves away, the connection is passed across to an adjacent base. This is called a hand-off, and allows mobility of phones, whilst permitting re-use of frequencies by base stations in nearby, but not adjacent, 'cells'.

In addition to telephony, modern mobile phones also support a wide variety of other services such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, gaming, and photography. Mobile phones that offer these and more general computing capabilities are referred to as smartphones.

In the year of 1973, a former general manager from the systems division of Motorola,   Dr. Martin Cooper, became who is thought to be the inventor of the first portable handset.     Dr. Cooper was also the first person to make a call using a portable cell phone.

COMMUNICATION SYSTEMS:

Simplex:  Simplex communication refers to communication that occurs in one direction only.

Examples:

  •  Commercial radio broadcast (not walkie-talkies, etc.)
  •  Television broadcast
  • Internet multicast.
 
Half-duplex:
A half-duplex system provides for communication in both directions, but only one direction at a time (not simultaneously). Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying.

Examples:

Walkie-talkie (since, it is two-way radio, wherein one must use "Over" or another previously-designated command to indicate the end of transmission, and ensure that only one party transmits at a time, because both parties transmit on the same frequency.)

Full-duplex :

A full-duplex, or sometimes Double-duplex system, allows Communication in both directions,  and, unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full-duplex, since they allow both callers to speak and be heard at the same time. A good analogy for a full-duplex system would be a two-lane road with one lane for each direction.

Examples:

  • Telephone,
  • Mobile Phone, etc

For Complete Unit I Notes : Visit Downloads Section

2 comments:

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