lecture.1-1.pdf

Broadband Communication Networks Assoc.Prof.Dr.ibrahim khider September 2021  Lecture 1 Communication Systems  Elements of a Communication System The system which specially deals with digital data and digitally pre-processed signals is a digital communication system....

Broadband Communication Networks Assoc.Prof.Dr.ibrahim khider September 2021  Lecture 1 Communication Systems  Elements of a Communication System The system which specially deals with digital data and digitally pre-processed signals is a digital communication system. The basic elements of a digital communication system are shown in next slide. First, the message generated by the information source is to be converted to binary bit stream. This process of efficiently converting analog or digital message generated from source, into a sequence of binary digits is called as source encoding. This process includes digital data compression. Elements of a Communication System On the receiver side, there is an antenna to receive a signal, which normally is low in strength and needs to be further amplified. The main issue faced by communication systems is that the channel is subject to additional noise, and may also introduce some distortions on the transmitted signal. Elements of a Communication System  Digital Communication Systems The system which specially deals with digital data and digitally pre-processed signals is a digital communication system. The basic elements of a digital communication system are shown in next slide. First, the message generated by the information source is to be converted to binary bit stream. This process of efficiently converting analog or digital message generated from source, into a sequence of binary digits is called as source encoding. This process includes digital data compression. Digital Communication Systems  Digital Communication Systems The sequence of bits is then passed through the channel encoder. The purpose of channel encoding is to introduce intentional redundancy into the information sequence to overcome the effects of noise encountered in the transmission channel. The channel codes, also called error correcting codes The channel encoded bits are then passed to a digital modulator. After passing through the channel, the received signal is passed through a digital demodulator  Digital Communication Systems The bit stream is passed then through the channel decoder to reconstruct correct information after removing the redundant bits from the knowledge of encoding scheme used in the channel encoder end. The last and final stage is source decoder. Like channel decoding, source decoder also decodes the input signal according to the source encoding scheme applied at the transmitter end. Advantages of digital communications Increased demand for data transmission. Increased scale of integration, sophistication and reliability of digital electronics for signal processing, combined with decreased cost. Facility to source code for data compression. Possibility of channel coding (line, and error control, coding) to minimize the effects of noise and interference. Ease with which bandwidth, power and time can be traded off in order to optimize the use of these limited resources. Standardization of signals, irrespective of their type, origin or the services they support, leading to an integrated services  Performance Evaluation The performance of a transmission system is evaluated by either computing or measuring the error probability per received information bit at the receiver, also called the bit error rate. The other major characteristics of a communication system are its complexity, its bandwidth, its consumed and transmitted power, and the useful data rate that it can transmit. Categories of Communication Systems A communication system can also be classied into three categories in respect of direction of communication as: Simplex: Simplex communication is a unidirectional communication system i.e., communication is possible in one direction only. Typically, the transmitter (the one talking or sending information in any ways) sends a signal and its up to the other receiving device (the listener) to figure out what was sent. Examples: Broadcast systems like the TV and radio signals, re alarm systems Categories of Communication Systems Half Duplex: Bi-directional communication is possible, but only in one direction at a time. That means one can either transmit or receive a signal at a particular instant of time in this system of communication. Examples: The walky-talky used in defense and by police Full Duplex: Here simultaneous two-way communication is achieved. Unlike half duplex communication system, one can both transmit and receive a signal simultaneously. Example: Telephone conversation is an appropriate example of Full Duplex communication system  Network Designs There are three basic design types in common use today for half and full duplex systems: direct, single site and cellular. Direct radio networks are those in which two or more radio transceivers are linked without the need for any intervening infrastructure. Single site radio networks are those in which two or more radio devices communicate with one fixed location transceiver. The fixed location transceiver, which often has a large antenna mast associated with it, might also serve as a gateway between the radio network and another, such as the public switched telephone network (PSTN). 3Cellular networks are based on two principles: small radio coverage zones known as cells  Mathematical Models for Communication Channels The Additive Noise Channel In this model, the transmitted signal s(t) is corrupted by an additive random noise process n(t). If the noise is introduced primarily by electronic components and amplifiers at the receiver, it may be characterized as thermal noise. This type of noise is characterized statistically as a Gaussian noise process. Mathematical Models for Communication Channels The Additive Noise Channel Hence, the resulting mathematical model for the channel is usually called the additive Gaussian noise channel Because this channel model applies to a broad class of physical communication channels and because of its mathematical tractability, this is the predominant channel model used in our communication system analysis and design. Mathematical Models for Communication Channels The Additive Noise Channel