Transmission Line Theory

1
Transmission Line Theory
MCS.145234551
Maj JW Paul
Refs lecture notes LFTSP 2003 Dr Smain Amari
lecture notes ACS 2003 Mr Josh Dore
2
(No Transcript)
3
Review - cellular systems

• What is the basic concept of cell systems?
• Frequency reuse
• What methods does it use?
• SDMA (TDMA, FDMA, CDMA)
• What are 3 methods to increase reuse?
• cell size - cluster size - sectorization
• can also use CDMA etc
• Why is CDMA limited?
• orthagonal pseudo-random

4
Review

• How do hand-offs work?
• Frequency reuse
• Explain Hard vs Soft hand-offs
• Soft keep the same frequency
• used to reduce delay (data comms)
• What is the principle behind cloning?
• copy MIN ESN
• How can it be defeated?
• PIN - Challenge/Response - RF Fingerprint

5
Todays Class

• Metallic Transmission Lines
• Types
• Losses
• High Speed Data Lines

6
Transmission Lines
7
Transmission Lines

• Two fundamental types
• Low Frequency
• used for power transmission
• High Frequency
• used for RF transmission
• wavelengths are shorter than or comparable
  to the length of cable
• Note - transmission line conductor - but only
  use surface

8
Types of Transmission Lines

• How many do you know of?
• Parallel Line
• Twisted Pair (Shielded Unshielded)
• Coaxial
• Waveguides

9
Parallel Pair
Spacers
Low loss dielectric
10
Parallel Line (aka Ribbon Cable)

• Simple Construction
• Used primarily for power lines, rural telephone
  lines or TV antenna cable
• Freq up to 200MHz over short distances
• High Radiation Loss
• moving current Ae
• need to be aware of other metalic conductors

11
Twisted Pair
metal cladding
Shielded
protective dielectric
Unshielded
coating is paper, rubber, PVC can also have
single pair, each wrapped individually
12
Twisted Pair

• Twists tend to cancel radiation loss
• Helps reduce crosstalk
• Still fairly inexpensive
• Frequency lt 100MHz
• Generally short distances
• analog 5-6 km
• digital 2-3 km
• Note - power line interference

13
CAT5 Cable

• UTP
• 4 pair
• terminating in RJ45
• 100MHz max frequency
• 1000 Mbps transmit rate
• Aside Wire Gauge (smaller is bigger)

14
Coaxial Cable
15
Coaxial Cable

• Geometry creates a shielded system
• no EM energy outside the cable
• Can support frequencies gt 100MHz
• Can support data rates gt 1GHz
• Low self-inductance allows greater BW
• Used for long-distance telephone trunks, urban
  networks, TV cables
• Expensive must keep dielectric dry

16
Waveguides aka plumbing

• width is wavelength

17
Waveguides

• Uses a different transmission method
• Ducting not conducting
• gt1GHz
• Expensive
• May need to be filled
• Cannot turn sharp corners
• Any defects will cause significant attenuation
  (sparking)

18
Microstrips

• Used for very high frequencies in semi-conductors

19
Transmission Losses
20
Transmission Theory

• Current and Voltage change with time along the
  line (the signal)
• superposition of waves in both directions
• but over short distances (lt?) are constant
• Energy is lost (heat - resistance) or
  stored (magnetic - inductance) / (capacitive -
  capacitance)

v Ri
Attenuation Losses
21
Attenuation is ? ?

• Problem...

22
Attenuation Distortion

• Attenuation increases with distance
• Frequency-dependent (? with frequency)
• Results in amplitude distortion

Attenuation dB
f (Hz)
300
1700
3300
23
Delay Distortion

• Speed is frequency

Delay ms
f (Hz)
300
1700
3300
24
Characteristic Impedence

• Depends on position on line
• If line terminates with Z Z0 then the line is
  matched
• If not - get reflection - standing waves - no
  energy is transmitted

25
Plus

• Crosstalk
• Plus still have noise
• (notice - no spherical attenuation)

26
High Speed Lines
27
Digital Channel Performance
Shannon's Equation
gives the maximum
digital capacity of an analogue channel in bps.
C B log (1SNR)
2
C Bit rate capacity (bps)
B Bandwidth in Hertz
SNR S/N (not in dB)
28
Example
The capacity of a telephonic voice- grade line
with a SNR of 30 dB and a bandwidth of 3000 Hz
is
C B log (1SNR)
2
C 3000 log ( 1 1000)
2
C 3000 log (1001)
log 2
C 30 kbps
29
Modem Evolution

• 1980 1200 bps
• 1984 2400 bps
• 1991 14.4 kbps
• 1994 28.8 kbps
• 1996 33.6 kbps
• 1997 56 kbps

30
But High Speed?

• How do we get data rates much higher than that
  predicted by Shannon?
• Based on Analogue
• Data compression
• Modulation (QSPK, 16-QAM)
• But need high quality lines...

31
How to get the signal back

• Repeaters, Amplifiers and Equalizers
• remember 2 km limit?
• Attenuation Equalizer adds losses to the power
  frequencies then amplifies all the frequencies to
  bring signal to original level
• Delay Equalizer introduces more delay to the
  higher frequencies to compensate for signal
  delays
• Line Conditioning

32
C-Conditioning

• Reduces effects of attenuation and delay
  distortion ( but does not remove them) - provides
  for more consistency across the BW.
• Attenuates high-amplitude signals
• Delays faster frequency components
• C1, C2 and C4 apply to leased lines
• C3 and C5 apply to companies' switching networks

33
D-Conditioning

• Deals with harmonic distortion (unwanted
  harmonics).
• Calls for high quality circuits and switches
• Improves SNR
• D1 applies to point-to-point lines
• D2 applies to multi-point lines

34
Transfer Rates
T1
T2
T3
T4
1.544 Mbps
6.312 Mbps
44.736 Mbps
274.176 Mbps
96 channels
672 channels
4032 channels
24 channels
DS4
DS1
DS2
DS3
DS0 64 kbps
(4 kHz baseband with 8 k samples/second and 8
Quantization levels)
35
High-speed Race

• Regular-speed phone .056 Mbps
• Digital Subscriber Line .90 Mbps
• High-speed wireless 10 Mbps
• Cable 30 Mbps
• Satellite .40 Mbps
• Why is ADSL as fast as cable?
• What does A stand for...

36
Questions
37
Review

• Name and describe 5 types of metallic
  transmission lines
• Give their advantages/disadvantages
• What causes attenuation/noise?
• How do you fix this?

38
Next Class

• Fibre Optics
• note start at 0750 Friday