Systems and Architecture Transmission Fundamentals Lecture 2 PDF

Systems and Architecture Transmission Fundamentals Lecture 2 Objectives  To explains the fundamentals Logical media: Microwave, Satellite Radio and Infrared communications  To discuss the operations of asynchronous and synchronous transmission...

Systems and Architecture Transmission Fundamentals Lecture 2 Objectives  To explains the fundamentals Logical media: Microwave, Satellite Radio and Infrared communications  To discuss the operations of asynchronous and synchronous transmission SYS.2 Unguided Media  Transmission and reception are achieved by means of an antenna  Configurations for wireless transmission Directional Omnidirectional SYS.3 Microwave  Microwave data communication exists in two forms: 1. Terrestrial (earth-based) systems, and 2. Satellite systems.  Functionally they are similar, but the abilities of each are somewhat different. SYS.4 General Frequency Ranges  Microwave frequency range 1 G H z to 40 G H z Directional beams possible Suitable for point-to-point transmission Used for satellite communications  Radio frequency range 30 M H z to 1 G H z Suitable for omnidirectional applications  Infrared frequency range 3×1011 to 2×1014 Hz Useful in local point-to-point multipoint applications within confined areas SYS.5 Terrestrial Microwave  Description of common microwave antenna Parabolic "dish", 3 m in diameter Fixed rigidly and focuses a narrow beam Achieves line-of-sight transmission to receiving antenna Located at substantial heights above ground level  Applications Long haul telecommunications service Short point-to-point links between buildings SYS.6 Satellite Microwave  Description of communication satellite Microwave relay station Used to link two or more ground-based microwave transmitter/receivers Receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink)  Applications Television distribution Long-distance telephone transmission Private business networks SYS.7  Multipath Interference Broadcast Radio  Radio frequency ( 3 kHz -300 GHz )  FM radio, UHF and VHF TV.  V H F and part of the U H F band; 30 M H Z to 1G H z  Covers F M radio and U H F and V H F television  Omni directional. Still need line of sight.  Less sensitive to attenuation from rainfall.  Suffered by multipath interference (Reflection from land, water, and natural or human-made objects eg ghosting on TV pictures). SYS.8 Multiplexing  Capacity of transmission medium usually exceeds capacity required for transmission of a single signal  Multiplexing - carrying multiple signals on a single medium with the help of a multiplexer More efficient use of transmission medium SYS.9 Reasons for widespread use of Multiplexing  Cost per kbps of transmission facility declines with an increase in the data rate  Cost of transmission and receiving equipment declines with increased data rate  Most individual data communicating devices require relatively modest data rate support SYS.10  Multiplexing Techniques  Frequency-division multiplexing (FDM) Takes advantage of the fact that the useful bandwidth of the medium exceeds the required bandwidth of a given signal  Time-division multiplexing (TDM) Takes advantage of the fact that the achievable bit rate of the medium exceeds the required data rate of a digital signal  Synchronous Time-division multiplexing (STDM) SYS.11 FDM and TDM SYS.12 Synchronous TDM System SYS.13 Infrared  Uses infrared light.  Transceivers must be within the line of sight of each other.  Infrared do not penetrate through the walls.  Furthermore, there is no frequency allocation issue with infrared, because no licensing is required.  typical uses TV remote control IRD port SYS.14 UNBOUNDED(unguided) MEDIA COMPARISON Types Area of EMI Coverage Sensitivity Terrestrial Directional Moderate Microwave beam Satellite Beam to small Moderate Microwave or large area Infrared Omnidirectional Low in relatively small area Radio Omnidirectional High in small or large area SYS.15 Asynchronous and Synchronous Transmission  The transmission of a stream of bits from one device to another across a transmission.  Transmit using cooperation and agreement between the two sides.  Synchronization: The receiver must know the rate at which bits are being received so that it can sample the line at appropriate intervals to determine the value of each received bit.  Two types: Asynchronous and synchronous SYS.16 Asynchronous - Behavior  In asynchronous transmission, each character of data is treated independently.  Data are transmitted one character at a time.  Each character begins with a start bit that alerts the receiver that a character is arriving.  The receiver samples each bit in the character and then looks for the beginning of the next character.  Works well for long blocks of data.  Simple and cheap but requires an overhead of two to three bits per character. SYS.17 Asynchronous Transmission SYS.18 Synchronous Transmission  For large blocks, synchronous transmission is used.  Each block of data is formatted as a frame that includes a starting and an ending flag (preamble and post amble).  Stream of bits without start and stop codes.  The block may be many bits in length.  To prevent timing drift between transmitter and receiver, their clocks must somehow be synchronized.  More efficient (lower overhead) than asynchronous. SYS.19 Reference  Chapters 4 and 5. Computer Networks and Internets, Douglas E. Comer, Prentice Hall. 3rd edition  Chapter 7 and 16. Data and Computer Communications, 8ed, by William Stallings SYS.20