J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 1 Telecommunications Concepts Chapter 1.5 Communications Media

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 2 Contents Optical fibers Coaxial cables Twisted pairs Wireless communications

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 3 Contents Optical fibers Coaxial cables Twisted pairs Wireless communications

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 4 Snell’s Law sin  1 sin  2 = n2n1n2n1 22 11 n2n2 n1n1   cc n2n2 n1n1 >c>c n2n2 n1n1 n2 < n1

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 5 Optical Fibers (step index) n1n2 n2 < n1 Protective coating

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 6 Multimode Fiber Diameter : > 50  Low cost but limited bandwidth * distance due to multimode dispersion Step index fiber Graded index fiber

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 7 Multimode Dispersion Step index fiber : < 50 MHz.Km Graded Index Fiber : < 1000 MHz.Km (1990) < 5000 MHz.Km (2000) t t

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 8 Monomode Fiber Diameter : < 5  Only one propagation mode possible Higher cost due to end equipment but enormous bandwidth*distance product 10 Gb/s over 500 Km optical sections (1995)

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 9 Wave Domain Multiplexing Each color can carry an independent data flow. In colors carrying each 10 Gb/s or 80 colors carrying each 2.5 Gb/s were commercially available

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 10 Optical amplifiers Pump laser Erbium doped fiber Erbium atoms are pumped into a higher energy state by the light of the pump laser, they fall back in synchronism with the incoming light, amplifying it.

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 11 Optical Switching From IEEE Com.Mag.V39,N1, Jan 2001.

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 12 Contents Optical fibers Coaxial cables Twisted pairs Wireless communications

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 13 Coaxial Cables Protective coating Insulator Conductor Monomode propagation for all data applications Transmission rates up to some Gb/s Distance limited by electrical attenuation

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 14 Contents Optical fibers Coaxial cables Twisted pairs Wireless communications

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 15 Twisted Pairs Performance highly dependant on cable quality Transmission speed up to several 100 Mb/s for distances of up to 100 m. with better cables (class 5 or 6)

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 16 Contents Optical fibers Coaxial cables Twisted pairs Wireless communications

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 17 Wireless Communications Why ? Mobile terminals Cost of wiring Why Not ? Lower data rates Lower reliability Potential Lack of Security

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 18 Wireless Communications Main restrictions: Limited available bandwidth Uncontrolled sources of noise Some solutions: Displace some heavy users (TV) Reuse of frequencies at different locations (Cellular radio, Point to point links, …) Sharing of a set of frequencies (spread spectrum radio)

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 19 Reuse of Frequencies P r /S a = P t /r 2 r transmitter P r = Power at receiver S a = Area of receiver antenna P t = Power at transmitter r = Distance At some distance, a transmitter can no longer be received and the same frequency can be reused

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 20 Cellular Radio Ideally, 3 different frequency sets are sufficient

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 21 The Mobile Access Network Second Generation Handover When a receiver is between two cells, the receiver has to disconnect from one cell and connect into the next one. Circuit routing has to be adapted accordingly.

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 22 Cellular Radio k = number available frequencies per cell S = Area of a cell =  *r 2 n = Number of simultaneous calls per km 2 p t = Power of transmitter P 0/ S a = Minimal field strength at receiver input n = k / S p t = p 0 /S a * r 2 With smaller cells, - more antenna sites are needed... - more simultaneous calls are possible - transmitted power can be reduced

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 23 Cellular Radio in practice FlandersArdennes Propagation conditions depend heavily on geography

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 24 Cellular Radio In practice, seven or more different sets of frequencies are needed

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 25 Digital Cellular Phones Name Freq.(MHz) # rad.ch. P.max.(W) r.max.(Km) Voicerate (Kb/s) Capacity (E/Km 2 ) DECT GSM DCS

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 26 Cellular Radio and frequency hopping Problem : Propagation conditions are extremely variable in function of location and frequency, especially in cities Solution : Use a set of different frequencies and switch at a high rate between them. e.g. In GSM every 20 mS frequencies change.

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 27 Wireless Communications Main restrictions: Limited available bandwidth Uncontrolled sources of noise Some solutions: Displace some heavy users (TV) Reuse of frequencies at different locations (Cellular radio, Point to point links, …) Sharing of a set of frequencies (spread spectrum radio)

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 28 Wireless Interference Margins Cause considerable loss in transmission capacity Considerable room for improvements by controlling interferences –Signal hardening –Signal recovery –Signal expansion =Third generation mobile networks (UMTS) Frequency Space Time

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 29 The Mobile Access Network Data combined with known higher frequency pseudo random sequence Resulting modulated radio signal has high bandwidth Shannon : low data rate combined with high bandwidth = excellent noise margins! Fast hopping Spread Spectrum n b/s Data Pseudo- random sequence m * n b/s xor HF carrier Modulated signal Large bandwidth ≈ m times bandwidth needed for data

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 30 The Mobile Access Network Spread Spectrum and CDMA D1D1 S1S1 xor HF Tx1 D2D2 S2S2 xor HF Tx2 D2D2 S2S2 HF Correl -ator Rx2 D1D1 S1S1 HF Correl -ator Rx1 For radio link Tx1-Rx1, emission by Tx2 is just another source of noise

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 31 The Mobile Access Network Multi-path Interference GSM : interference = noise UMTS : correlator adds similar input signals with appropriate delays so that they reinforce each other Different paths have different lengths and different delays

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 32 The Mobile Access Network Third Generation Handover When a receiver is between two cells, both transmitters send the same signal. These two signals reinforce each other, as multipath propagation does.

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 33 Multi-path Interference 2 nd generation (GSM) : interference = noise 3 rd generation (UMTS) : add similar input signals with appropriate delays so that they reinforce each other Different paths have different lengths and different delays

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 34 Wireless Local Loop Radio is sometimes cheaper than digging the streets ! Used for telephony and for Internet access (WiMax)

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 35 Microwave Point to Point Links Highly directive antennas limit spatial spreading High transmission capacity (several Mb/s) transmission impaired by heavy rain Cost effective for line of sight communications

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 36 Satellite Communications Km Geostationary Round trip Delay = 240 ms High power ground stations

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 37 Satellite Communications Low Orbit Short round trip delaysLow power ground stations In fact, a cellular system with mobile base- stations

J.Tiberghien - VUB K.Steenhaut & J.Tiberghien - VUB 38 Introduced concepts Optical communications are becoming dominant. –Low cost, high throughput fixed communications. Wireless communications are growing: –For replacing local wiring –For mobile communications Geostationary satellite communications: –One way broadcasting –low traffic point to point but high delays Low Orbit satellites: –Cellular system for global mobile application.