1. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 1 Computer Networks PHY

2. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 2 Physical Layer Mechanical –Medium –Connectors Electrical/optical –Band –Modulation Procedural –Timing, etc.

3. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 3 Practical Limits Nyquist –Noiseless –Dual of Sampling Theorem C (bps) = 2H (Hz) log 2 M (symbol el’ts) Shannon –White noise (e.g., thermal) C (bps) <= H (Hz) log 2 (1+S/N) S = signal power, N = noise power

4. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 4 Decibels Logarithmic measure –Addition of logs = multiplication SNR in dB SNR (dB) = 10 log 10 (S/N)

5. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 5 Mechanical Medium –Ribbon, UTP, STP, Cat 5, … –Coax (50 , 75  ) –Optic fiber (SM, MM, …) –Wireless Connectors –BNC, RJ11, RJ45, Coax, Fiber termination,…

6. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 6 Dividing Bands SDM – space (different wire, direction,…) FDM - frequency TDM – time CDM – code division multiplexing (spread spectrum) MF/TDM – First divide frequency, then time time frequency time frequency time frequency chan A chan 1 chan B A1 A2A3A1 C1 chan C chan D chan 2chan 3 chan 1 chan 4 B1B2B1B2 FDM TDMMF/TDM

7. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 7 Electrical/Optical Band –Range of frequencies used –Amplitude range Modulation –Analog signal (AM, FM) –Digital ASK FSK PSK phase amplitude

8. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 8 Modulation ASK – amplitude Angle Shift Keying –FSK – frequency –PSK - phase QAM – hybrid combination of PSK, ASK OFDM – Orthogonal FDM PPM – Pulse Position Modulation

9. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 9 Constellations 00 01 11 10 00011110 Q-ASK Q-PSK 8-QAM Note use of the Gray Code to minimize received bit errors in the presence of noise

10. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 10 OFDM Frequency Time Sub-carrier k - BPSK Sub-carrier j – 8-QAM Sub-carrier m – not used2.3 0.7 0.5 Sub-carrier l - QPSK1.5 Sub-carrier n – BPSK2.5 Especially useful for frequency selective fading channels Select modulation, which subcarriers to use, FEC rate Bit loading – select modulation per subcarrier Multiple subcarriers

11. CEN 5501C - Computer Networks - Spring 2007 - UF/CISE - Newman 11 Pulse Position Modulation One pulse per symbol frame Uses position of pulse in symbol frame If N positions, then log 2 N bits/pulse Very power efficient Symbol Frame i ………… 0xA70x1FSymbol = position Time Symbol Frame i+1 0x02