Part 2: Communication System PDF

Part 2: Communication System Model of a Communication System  Model of a Communication System 1- The information Source - The message produced by the information source may not be electrical in nature such as voice. - An input transducer converts the message to a time-varying el...

Part 2: Communication System Model of a Communication System  Model of a Communication System 1- The information Source - The message produced by the information source may not be electrical in nature such as voice. - An input transducer converts the message to a time-varying electrical quantity called a message signal. - At the destination, output transducer converts the electrical waveform to the appropriate message.  Model of a Communication System 2- The Transmitter - Data generated by a source can not transmitted directly. - A transmitter transforms information to EM signals that can be transmitted across the transmission system. - It processes and modifies the input for efficient transmission over a channel. - Signal processing operations performed by the transmitter include amplification, filtering, and modulation.  Model of a Communication System 3- The Communication Channel - The channel provides the electrical connection between the distant source and destination user. - The channel may be wired or wireless. - During transmission, the signal gets distorted due to noise. - Noise is always random in character and has a great effect on the signal.  Model of a Communication System 4- The Receiver - The receiver extracts the input signal from the degraded version coming from the channel. - The receiver performs this function through the process of demodulation in addition to amplification and filtering.  Classification of a Communication System Analog - It is designed to transmit analog data using analog modulation. Systems - The AM, FM and TV transmissions are examples. - May be wired or wireless. - It is designed to transmit digital data using digital or analog Digital modulation. Systems - The data may be binary or binary coded of analog data. - It is termed as data communication system.  Criteria for Communications Systems 1. Data delivery: The data should be delivered to the correct destination to assure confidentiality and privacy. 2. Data integrity: Data should be delivered accurately without no errors, no loss, no addition and no duplication. 3. Timeliness of data transfer: Data should be delivered without violating the delay constraints specific for each service. - Uneven jitter in packet arrival may be annoying to the user.  Digital Communications Systems 1- Use of modern digital technology Advent of VLSI technology reduces cost, size and reliability of digital transmission circuitry. 2- Data integrity Due to repeaters, signal impairments does not affect digital transmission as analog. 3- Ease of multiplexing and robust transmission Efficient utilization of link capacity can be achieved with digital rather than analog techniques.  Digital Communications Systems 4- Security and privacy Encryption can be readily applied to digital signals. 5- Integration of diverse services By treating all signals digitally, transmission system does not have to provide special attention to individual services. 6- Performance monitorability Quality of digital received signal can be ascertained with no knowledge of the nature of the traffic. Elements of Digital Communication System  Elements of Digital Communication System 1- Information source Based on its output, it may be analog or digital. i- Analog information source Like a microphone actuated by speech or a TV camera. It emits continuously varying amplitude signals. It can be transformed into digital format. ii- Discrete information source Its output consists of a sequence of binary bits. A familiar example of discreet data is text or character strings.  Elements of Digital Communication System 2- Source encoder/decoder - Its input is a string of symbols at a rate rs symbols/sec. - It converts input to a binary sequence of 0‟s and 1‟s. - The source decoder converts this back to a symbol sequence. 3- Channel encoder/decoder - Channel encoder adds extra bits to output of the source encoder to detect or correct errors at the channel decoder. - Channel encoder/decoder can realize high transmission  Elements of Digital Communication System 4- Modulator/demodulator - The modulation process serves several purposes in communication systems. (Next) - Modulator accepts a bit stream and converts it to an electrical waveform suitable for transmission over channel. - Demodulator extracts the message from the information- bearing waveform.  Elements of Digital Communication System Why modulation? 1- Overcoming some equipment limitations - It may be difficult to design a system at a specific frequency. - With modulation we translate to a practicable band. - When wireless transmission is applied, we need antenna. - Antenna dimension should be comparable to operating λ.  Elements of Digital Communication System 2- Removing interference - Most signals occupy the same frequency range. - For transmission without modulation interference will occur. 3- Reducing noise - The limitation of communication is the unavoidable noise. - Modulation schemes could minimize the effect of noise. 4- Allowing efficient capacity utilization - With modulation, multiplexing results in efficient and cost-effective utilization of the communication link.  Elements of Digital Communication System 5- Matching signal to channel - Modulation allows matching the signal characteristics to the channel characteristics. - Consider for example electrical signal to be transmitted over an optical fiber or wireless medium.  Line Configuration - It refers to the way through which two or more communicating devices attach to the transmission line. Point-to-point Line Configuration Types Multipoint  Line Configuration Point-to-point - It provides a dedicated link between two devices. - Entire link capacity is reserved for transmission between two devices. - Infrared remote control is a p-t-p connection. - It utilized in star and ring topology of computer networks.  Line Configuration Multipoint - It is also called multidrop. - More than two specific devices share a single link. - The capacity of the channel is shared between multiple devices. - This type of connection is employed in the bus network topology.  Direction of Data Flow Two linked devices can communicate with each other by sending and receiving data. Direction of Data Flow Simplex Half duplex Full duplex Direction of Data Flow  Direction of Data Flow 1) Simplex - The transmission is unidirectional. - Only one station can transmit; the other can only receive. - There is no ACK of reception, so errors cannot be conveyed to transmitter. - The paging systems, TV, and FM radio are examples of this mode.  Direction of Data Flow 2) Half-duplex - Each station can both transmit and receive, but not at the same time. - When one station is sending, the other can only receive and vice versa. - Entire capacity is taken over by transmitting station at the time. - The “Push-to-talk” walkie-talkies is half-duplex systems.  Direction of Data Flow 3) Full-duplex - Both stations can transmit and receive at once. - Signals going in either direction share the capacity of the link. - Two people can talk and listen at the same time. - Also, videoconferencing. - One example is telephone network.  Transmission Modes The transmission of binary data across a link can be accomplished in either parallel or serial mode. Parallel Transmission Modes Serial  Transmission Modes 1) Parallel transmission - Multiple bits are sent with each clock tick. - Data are organized into groups of n bits transmitted through n wires.  Transmission Modes Advantages of Parallel transmission + It is characterized by high speed of data transmission. + It can increase the transfer speed by a factor of n over serial transmission. Disadvantages of Parallel transmission - High cost as it requires n lines just to transmit data stream. - It is practical only for short distances. - Consequently, parallel transmission is usually limited to shorter distances.  Transmission Modes 2) Serial transmission - One bit follows another, so it needs only one channel. - It is designated as synchronous or asynchronous depending on how the timing and framing information is transmitted.  Transmission Modes Advantages of Serial transmission + Only one channel is required; consequently, cost is reduced. + It has few errors and is practical for long distances. Disadvantages of Serial transmission - It is slow. - There is a need for serial to parallel conversions. - Consequently, serial transmission is usually practical for long distances. Thanks [email protected] Faris A. Almalki @EngFarisAlmalki