Lecture 1: Communication Systems 1st semester 1439 - 2018 By: Elham Sunbu

OUTLINE: What is a Communication Systems? long Distance Communication Electrical Communication Systems Aim of Communication System How to Build a Communication System? Communications System Model Input Transducer

What is a Communication Systems? A communication system is a way of transferring information from one source to another. Transference can occur between two humans, a human and an animal or a human and a machine.

Characteristics of Communication Systems must be a Sender and Receiver A protocol is a set of rules which governs the transfer of data between computers. Protocols allow communication between computers and networks. Handshaking is used to establish which protocols to use. Handshaking controls the flow of data between computers protocols will determine the speed of transmission, error checking method, size of bytes, and whether synchronous or asynchronous Examples of protocols are: token ring, CSMA/CD, X.25, TCP/IP

Long Distance Communication Communicating over long distances has been a challenge throughout history. Man has been seeking different ways of doing this since the beginning of time. The transmission of signals over a distance for the purpose of communication began thousands of years ago. Early methods of long-distance communication included runners to carry important messages, smoke signals, chains of searchlights, drums, carrier pigeons, the Pony Express and the telegraph.

Electrical Communication Systems These methods of communication have been superseded by electrical communication systems, where the communication is by using electrical signal.

Communication System Communication System Communication System: Is a combination of circuits and devices put together to accomplish a reliable transmission of information from one point to another. Communication System Source Destination

Aim of Communication System The purpose of a communication system is to carry information from one point to another.

How to Build a Communication System? Source Destination Transmitter Receiver Channel Source Destination

Communications System Model A typical communication system can be modeled as:

Source 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 Discrete: Finite set of outcomes. “Digital ” Continuous: Infinite set of outcomes. “Analog”

Input Transducer If the input message is nonelectrical ( e.g. voice), it must be converted by an input transducer to an electrical signal. A transducer: 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 processing; e.g., a microphone and a camera.

Transmitter The transmitter converts the electrical signal into a form that is suitable for transmission through the transmission medium or channel by a process called modulation. Data form depends on the channel.

Channel Channel: medium used to transfer signal from transmitter to receiver Channel 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’. 

Noise The 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 Noise 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).

Receiver The 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.

Output Transducer The 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.

Mode of Communication There are two basic mode of communication: 1- Broadcasting  single transmitter and numerous receiver. 2- Point to point communication  single transmitter and single receiver. Point to point Broadcasting

Data Transmission Mode Data transmission between two devices can be: In simplex mode, the communication is unidirectional. Only one of the two devices on a link can transmit; the other can only receive. Simplex Half-duplex Full-duplex 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.

Effectiveness of Communications System The effectiveness of a communications system depends on four fundamental characteristics: Delivery Accuracy Timeliness Jitter

Effectiveness of Communications System Delivery: 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.

Effectiveness of Communications System Timeliness: 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. Jitter: 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.

The Rate and Quality of Data Transmission The fundamental parameters that control the rate and quality of data transmission in the communication system are: Channel bandwidth . Signal power .

Channel Bandwidth The 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.

The rate of data transmission is directly proportional to B. Channel Bandwidth If 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?   The rate of data transmission is directly proportional to B.

Signal Power The 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).

Signal Power The 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.

Communication System Resources So, in a communication system there are two primary resources : Channel bandwidth. Power A general system design objective is to use these resources as efficiently as possible.

Communication System Resources Based on the channel bandwidth, the communication system can be classified as: Baseband communication system  channel bandwidth 0 to f Bandpass communication system  channel bandwidth f1 to f2

Communication System Resources There are two types of power in a communication system: Transmit power : is the average power of the transmitted signal Received power : the average power of the received signal

Communication 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

Review What is a communication system? Explain the functions of the three main parts of an electronic communication system. Draw the communication system model. What is the purposes of modulation?

Thank You