4. Transmission Media

1. 4. Transmission Media

2. Contents • Transmission Media • Guided Transmission Media • Wireless Transmission

3. Transmission Media • Physical path between Tx and Rx • Guided or Unguided (wireless) • Communication in the form of electromagnetic waves • Characteristics and quality of data transmission are determined by characteristics of medium and signal • In guided media, medium characteristics is more important, whereas in unguided media, signal characteristics is more important.

4. Design factors to determine the data rate and distance. • Bandwidth: the greater the bandwidth of a signal, the higher he data rate that can be achieved. • Transmission impairments: limit distance • Interference: distort signal • Number of receivers: attenuation and distortion on the line.

6. Guided Transmission Media • Twisted pair • The oldest, least-expensive, and most widely-used medium • Physical Description • Pair of insulated wires twisted together to reduce susceptibility to interference(two straight parallel wires tend to act as an antenna and pick up extraneous signals) • Quite highly susceptible to noise & interference

7. Guided Transmission Media • Application • May be already installed (telephone usage) • Transmission Characteristics • Need repeater every 2-3 km (digital), and amplifier every 5-6 km (analog) • Up to 250 kHz analog and few Mbps digital signaling( for long-distance point-to-point signaling ) • Much efforts are undergoing to use it for high-speed (10-100 Mbps) LAN • UTP vs. STP • Category 3 (16MHz) and Category 5 UTP (100MHz)

8. Guided Transmission Media

9. Outer conductor Guided Transmission Media • Coaxial Cable • Physical Description • Because of shielding, much less susceptible to noise than twisted pair • Operate over a wider range of frequencies

10. Guided Transmission Media • Application • Most versatile medium LANs, Cable TV, Long-distance telephones, VCR-to-TV connections • Transmission Characteristics • Noise immunity is better than twisted pair • Attenuation, thermal noise, intermodulation noise (e.g. FDM) • Need amplifier/repeater every few kilometer or so

11. Guided Transmission Media • Optical Fiber • Physical Description • Thin (2~125m), flexible medium capable of conducting an optical ray

12. Guided Transmission Media • Application • Greater capacity • Extremely high bandwidth : more than 2Gbps (=31,250 voice channels) • Smaller size and lighter weight • Lower attenuation (Fig 3.3) • Electromagnetic isolation • Not effected by external electromagnetic fields. • Neither radiate energy nor cause interference • Difficult to tap • Greater repeater spacing • Lower cost and fewer sources of error

13. Guided Transmission Media • Transmission Characteristics • Multimode step-index • Variety of angles will reflect • The limited data rate due to multiple paths

14. Guided Transmission Media • Single mode • By reducing the radius of the core to the order of a wavelength • Superior performance

15. A travels a greater distance but faster than B A B Guided Transmission Media • Multimode graded-index • Varying the index of refraction of the core

16. Guided Transmission Media • Light source • LED vs. injection laser diode (ILD) • Cost/Data rate

17. LED/ILD • Light Emitting Diode (LED) • Cheaper • Wider operating temp range • Last longer • Injection Laser Diode (ILD) • More efficient • Greater data rate • Wavelength Division Multiplexing

18. Wireless Transmission • Wireless transmission • Directional • Be carefully aligned • Omnidirctional • Frequencies • 2GHz-40GHz: microwave frequencies (directional point-to-point) • 30MHz-1GHz: omnidirectional (broadcast radio) • 300GHz-200THz: Infrared (short-range communication)

19. Incoming signals Parabolic arc (reflector) Parabola’s focus (receiver) Incoming signals Wireless Transmission • Terrestrial Microwave • Physical Description • Maximum distance between antennas in km

20. Wireless Transmission • Application • Transmission Characteristics • Attenuation loss • Interference

21. Wireless Transmission • Satellite Microwave • Physical Description • Uplink & Downlink • Stationary with respect to its earth station : 35,784 km • Limited number of possible satellites : 3-4 o spacing

22. Wireless Transmission • Application • Television distribution • Long-distance telephone transmission • Private business network • very small aperture terminal (VSAT) system • Transmission Characteristics • Optimal to 1~10GHz • Significant propagation delay • Broadcast facility : from many stations to many stations

23. Wireless Transmission • VSAT • Business data application • Connection with central hub • Low cost small antenna dishes ( 5ft )

24. Wireless Transmission • Broadcast Radio • Physical Description • Omnidirectional • Application • Transmission Characteristics • 30MHz ~ 1GHz • Multipath interference • Infrared • Do not penetrate walls • No security and interference problem • No government license issue

25. Cellular Radio • Paging Systems • One way, require little bandwidth • Cordless Phones • Two way, short range • Base is the phone itself • Analog Cellular • Push-to-talk systems • IMTS – two way system • AMPS • Frequency reuse • Small cells • Handoff

26. Cellular Radio • Digital Cellular • IS-54 and IS-135 compatible with AMPS frequency • IS-95 based on Direct Sequence Spread Spectrum • GSM • Started Europe • Uses a combination of FDM and TDM • TDM within each 200 kHz FDM band • Personal Communication System (PCS)