Slide 1

Chapter1 : Introduction

2nd semester 1434-1435

1nalhareqi-2014King Saud University College of Applied studies and Community Service1301CTBy: Nour Alhariqi

OutlineCommunication systemCommunication system modelMode of communicationData transmission modeEffectiveness of a communications system.Channel bandwidth.Signal power.Communication system resources.

nalhareqi-20142Long Distance Communication

Communication is the transmission of information. Some examples of past communication methods:3nalhareqi-2014Communication SystemThese methods of communication have been superseded by electrical communication systems, where the communication is by using electrical signal.Communication system is a combination of circuits and devices put together to accomplish the transmission of information from one point to another.i.e. the purpose of a communication system is to carry information from one point to another.

4nalhareqi-2014Examples of Communications Systems

5nalhareqi-2014Communications System ModelA typical communication system can be modeled asInputTransducerTransmitterChannelReceiverOutputTransducerDistortionAndNoiseSourceInputmessageInputsignalTransmittedsignalReceivedsignalOutputsignalOutputmessageDestinationSender/ TransmitterReceiver6nalhareqi-2014SourceSource: Produces an input message( voice, picture, computer data etc ).There are many different types of sources and there are different forms for messages. In general, input messages may be classified as analog or digital.Analog messages (such as voice, music, temperature, ) are represented by continuous-time variables while discrete messages (such as text or numeric data) are represented by discrete symbols

7nalhareqi-20147Input TransducerIf the input message is nonelectrical ( e.g. voice), it must be converted by an input transducer to an electrical signal (theBaseband signal / Message Signal)A transducer, in simple terms is a device that converts one form of energy into another.In the communication system, it convert the output of a source into an electrical signal that is suitable for transmission; e.g., a microphone and a camera.

8nalhareqi-2014TransmitterThe transmitter converts the electrical signal (theBaseband signal/Message Signal) into a form that is suitable for transmission through the transmission medium or channel by a process called modulation.

9nalhareqi-2014ChannelChannel: medium used to transfer signal from transmitter to receiverChannel can be wired or wireless.While the signal is travelling through the channel(the medium) it is always attenuated (and the level of attenuation increases with distance).Also, the signal shape may be changed during the transmission i.e. become distorted.

10nalhareqi-2014NoiseThe signal is not only distorted by a channel, but it is also contaminated along the path by undesirable signals lumped under the broad term noise, which are random and unpredictable signals from causes external ( such interference from signals transmitted on nearby channels) and internal ( such noise resulted from thermal motion of electrons in conductors). 11nalhareqi-2014ReceiverThe function of the receiver is to recover the message signal contained in the signal received from the channel (received signal).The received signal is a corrupted version of the transmitted signal. So, the receiver reconstruct a recognizable form of the original message signal.It reprocess the received signal by undoing the signal modifications ( demodulation) made at the transmitter and the channel.12nalhareqi-2014Output TransducerThe receiver output is fed to the output transducer, which convert the electrical signals that are received into a form that is suitable for the final destination; e.g., speaker, monitor, etc.13nalhareqi-2014Mode of CommunicationThere are two basic mode of communication:1- Broadcasting single transmitter and numerous receiver.2- Point to point communication single transmitter and single receiver.14nalhareqi-2014BroadcastingPoint to point Data Transmission ModeData transmission between two devices can be:

15nalhareqi - 2013Data Transmission ModeIn simplex mode, the communication is unidirectional. Only one of the two devices on a link can transmit; the other can only receive.In half-duplex mode, each device can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.In full-duplex mode (also called duplex), both devices can transmit and receive simultaneously.16nalhareqi - 2013Effectiveness of Communications SystemThe effectiveness of a communications system depends on four fundamental characteristics:

17nalhareqi - 2013Effectivenessof a Communications SystemDelivery:The system must deliver information to the correct receiver. Information must be received by the intended device or user and only by that device or user.Accuracy: The system must deliver the information accurately.Information that have been altered in transmission and left uncorrected are unusable.

18nalhareqi - 2013Effectivenessof a Data Communications SystemTimeliness: The system must deliver information in a timely manner. Information delivered late are useless. In the case of video and audio, timely delivery means :delivering data in the same order as they are produced,and without significant delay. This kind of delivery is called real-time transmission.19nalhareqi - 2013Effectivenessof a Data Communications SystemJitter:Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 3 ms. If some of the packets arrive with 3 ms delay and others with 4 ms delay, an uneven quality in the video is the result.20nalhareqi - 2013The Rate and Quality of Data TransmissionThe fundamental parameters that control the rate and quality of data transmission in the communication system are:Channel bandwidth .Signal power .

21nalhareqi-2013Channel BandwidthThe channel can transmit a range of frequencies with reasonable fidelity.The bandwidth of a channel (B) is the width of the frequency band used to transmit the data.It is the difference between the highest and lowest frequencies which the channel can carry.

22nalhareqi-2013Channel BandwidthIf a channel can carry a signal which its frequency range from 0 to 5000 Hz (5 khz), the channel bandwidth B is 5 khz. If a channel can carry frequencies between 200Hz and 4kHz, its bandwidth (the difference between those two frequencies) is 3.8kHz.If a channel can carry frequencies between 10MHz and 100MHz, what is the channel bandwidth? 23nalhareqi-2013Channel BandwidthThe rate of data transmission is directly proportional to B.24nalhareqi-2013Signal PowerThe power of a signal is defined as the average energy over time.The signal power is related to the quality of transmission.Increasing the signal power ( S ), reduces the effect of channel noise, and the information is received more accurately.We measure noise relative to a signal in terms of the signal-to-noise ratio (SNR).

25nalhareqi-2013Signal PowerThe SNR is the ratio of the average signal power to the average noise power.A larger SNR also allows transmission over a longer distance. In any event, a certain minimum SNR is necessary for communication.

26nalhareqi-2013Communication System Resources So, in a communication system there are tow primary resources : Channel bandwidth.Power

A general system design objective is to use these resources as efficiently as possible. 27nalhareqi-2013Communication System Resources Based on the channel bandwidth, the communication system can be classified as:

Baseband communication system channel bandwidth 0 to fBandpass communication system channel bandwidth f1 to f2nalhareqi-201428Communication System Resources There are two types of power in a communication system: Transmit power : is the average power of the transmitted signalReceived power : the average power of the received signalnalhareqi-201429Communication System Resources Generally, system performance will be better if there is high transmitted power.Practical constraints on cost, properties of the transmission medium, battery life imply low transmitted power.The received power is a function of the transmitted power and the channel.A larger distance between the transmitter and the receiver lower received power

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