Mobile Computing

Sujesh P Lal FISAT

Module - 1

• Topics to be Covered – Introduction to Communication Technologies

• Mobile handsets • Wireless Communication • Server Applications

– Components of a Wireless Communication System – Architecture of a mobile telecommunication system – Wireless Standards – WLANs – Bluetooth Technology

• Bluetooth Low Energy(BLE), NFC

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Mobile handsets, Wireless Communication,

Server Applications

• Wireless Communication

• Wireless Networking

• Terrestrial radio system

• Satellite radio system

• Cellular communication technology

– “A technology that has revolutionized the human society and impacted almost everybody, is the cellular communication technology.”

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Components of a Wireless Communication System

1. Transmitter

2. Receiver

3. Antenna

4. Filters

5. Amplifiers

6. Mixers

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Transmitter • The input to a wireless transmitter may be voice, video,

data or other types of signal meant to be transmitted to one or more distant receivers, called baseband signal.

• The basic function of the transmitter is to modulate, or encode several baseband signals onto a high frequency carrier signal.

• A modulated high frequency signal can be radiated and propagated more effectively and helps make more efficient use of the radio frequency(RF) spectrum than what we direct transmission of the individual baseband signals can achieve.

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Receiver • The receiver receives the modulated signals

and reverses the functions of the transmitter component and thereby recovers the transmitted baseband signal.

• The antenna of the receiver is usually capable of receiving the electromagnetic waves radiated from many sources over a relatively broad frequency range.

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Antenna

• The function of the antenna is to convert the electric signal from a transmitter to a propagating electromagnetic RF wave, or viz.

• In a transceiver, a transmitter and a receiver is co-located for supporting full duplex communications.

• The same antenna is shared by both the transmitter and receiver.

• There are mainly two types of antennas that are used on wireless networks: – Omni-directional – Directional

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Filters

• Filters are key component present in all wireless transmitters and receivers.

• Used to reject interfering signals lying outside the operating band of receivers and transmitters.

• Filters also reject unwanted noise signals generated by the amplifier circuitry.

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Amplifiers

• Amplifier amplifies the strength (usually voltage) of a signal

• The important specification of an amplifier include power gain and the noise figure.

• The noise figure of an amplifier is a measure of how much noise is added to the amplified signal by the amplifier circuitry.

• This is most critical in the front-end of the receiver where the input signal is very weak and it is desirable to minimize the noise added by the receiver circuitry.

• It is necessary that the first amplifier in the receiver circuit has as low a noise figure as possible.

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Mixers

• A mixer is typically used to achieve frequency conversion at the transmitters and receivers.

• Frequency conversion is required because it is advantageous to transmit signals at a higher frequency, this is achieved by modulating a carrier wave form using the original baseband frequency.

• When a baseband signal is mixed appropriately with a high Fz on a carrier, it can be easily and efficiently radiated and becomes less susceptible to noises and attenuation.

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Architecture

• Mobile handsets communicate over the radio access network.

• The radio access N/W is primarily composed of the base stations which communicate with the mobile phones using radio Fz. electromagnetic waves.

• The coverage area is decomposed into hexagonal cells, in each cell, a base station is located.

• Two types of radio channels are usually involved in the communication between the base station and the mobile handsets: – Control channels and – Voice Channels

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Architecture

• Control Channel

– Typically use frequency shift keying (FSK) and are used for transferring control messages (data) between the base station and mobile phones.

• Voice Channel

– Typically use frequency modulation (FM).

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Architecture

• A base station typically has two antennas of different characteristics, one for receiving and the other for transmitting.

• Which increases the ability of the base station to receive the radio signals from the mobile phones that use very low transmitter power levels.

• On the other hand, mobile handsets typically use the same antenna for both receiving an transmitting.

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Architecture

• The core n/w interconnects the base stations, switches the mobile switching centre (MSC), and also provides an interface to other networks such as the traditional telephone n/w (PSTN) and the internet.

• The interconnect used in the core n/w is required to provide high speed connectivity, therefore, usually fibre optic cables are used as the interconnect in the core n/w.

• Based on the terrain conditions, microwave communication is also used.

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