20101 The Physical Layer Chapter 2

20102 Bandwidth-Limited Signals

20103 Maximal Data Rate Shannon –Hartley law (1948): a channel with a bandwidth of H Hz and random noise maximum bps (bits per second) is: H log 2 (1+S/N) S/N: signal power to noise power (dB: 10 log 10 (S/N) ) current coding techniques approaches the limit To achieve higher speed: better cables and electronics higher bandwith (less attenuation of higher frequencies) lower internal noise decrease influence of external EM radiation light via fiber optics

20104 Coax, Twisted Pair, fiber Category 5 UTP Category 3 UTP Signal is difference in voltage

20105 The Electromagnetic Spectrum

20106 The Telephone Local Loop: Modems The use of both analog and digital transmissions for a computer to computer call. Conversion is done by the modems and codecs.

20107 Modems Binary signal Amplitude modulation Frequency modulation Phase modulation Modern methods combine these modulation modes and use more amplitudes, frequencies and phases to approach the Shannon limit

20108 (Asymmetric)Digital Subscriber Lines A typical (A)DSL equipment configuration.

20109 ADSL frequency bands Operation of ADSL using discrete multitone modulation. gap, larger for ISDN In each channel a “modem: of maximal 56 kbps, reduced automatically when S/N is too high ADSL2+ goes upto 2,2 GHz

Internet over Cable

TV Cable Spectrum Allocation Frequency allocation in a typical cable TV system used for Internet access

Wireless Local Loops Architecture of an LMDS (IEEE ) system. Superseded by ADSL and cable TV WiMAX (IEEE ) is more promising now

Frequency Division Multiplexing (a) The original bandwidths. (b) The bandwidths raised in frequency. (b) The multiplexed channel. With fibers: different wavelength of light

Time Division Multiplexing

CDMA – Code Division Multiple Access Each sender has an unique code of m bits, called chips “1”: chip sequence is send “0”: complement of it is send

CDMA – Chip decoding (a) Binary chip sequences (b) Bipolar chip sequences (c) Six transmissions (d) Recovery of C’s signal

The Mobile Telephone System First-Generation Mobile Phones: Analog Voice Second-Generation Mobile Phones: Digital Voice (GSM) Third-Generation Mobile Phones: Digital Voice and Data (UMTS) Fourth-Generation: based on LTE ?

Global System for Mobile Communications GSM uses 2 * 124 frequency channels, each of which uses an eight-slot TDM system

GSM data framing other framing: Control (base to mobile) to manage the system Paging (base to mobile) to alert users to calls for them Access (bidirectional) for call setup and channel assignment

Neighbouring cells Different frequencies for neighbouring cells (fixed sender / receiver)

Energy, environment Prediction over 4 year: 1/3 of IT budget goes to energy bills 2/3 of that for cooling How to dispose of 512 million old PC’s