20101 The Physical Layer Chapter 2. 20102 Bandwidth-Limited Signals.

2010 1

The Physical Layer

Chapter 2

2010 2

Bandwidth-Limited Signals

2010 3

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 log2 (1+S/N)

• S/N: signal power to noise power (dB: 10 log10 (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

2010 4

Coax, Twisted Pair, fiber

Category 5 UTP

Category 3 UTP

Signal is difference in voltage

2010 5

The Electromagnetic Spectrum

2010 6

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.

2010 7

Modems

Binary signal

Amplitude modulation

Frequency modulation

Phase modulation

Modern methods combine these modulation modesand use more amplitudes, frequencies and phasesto approach the Shannon limit

2010 8

(Asymmetric)Digital Subscriber Lines

A typical (A)DSL equipment configuration.

2010 9

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 highADSL2+ goes upto 2,2 GHz

2010 10

Internet over Cable

2010 11

TV Cable Spectrum Allocation

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

2010 12

Wireless Local LoopsArchitecture of an LMDS (IEEE 802.16) system.

Superseded by ADSL and cable TV

WiMAX (IEEE 802.16) is more promising now

2010 13

Frequency Division Multiplexing

(a) The original bandwidths.

(b) The bandwidths raised in frequency.

(b) The multiplexed channel.

With fibers:different wavelength of light

2010 14

Time Division Multiplexing

2010 15

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

2010 16

CDMA – Chip decoding

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

2010 17

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 ?

2010 18

Global System for Mobile Communications

GSM uses 2 * 124 frequency channels, each of which uses an eight-slot TDM system

2010 19

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

2010 20

Neighbouring cells

Different frequencies for neighbouring cells (fixed

sender / receiver)

2010 21

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