1. TRANSMISSION MEDIA SYSC 4700 Telecommunications Engineering
David Falconer and Halim Yanikomeroglu
Carleton University
January 30 & February 01, 2017

2. Transmission Media Objectives
To learn some basic vocabulary: e.g. channels, circuits, trunks, dB, dBm, dBw.
To have an idea of the relative bandwidths of some common signals.
Link budget.
To learn the basic characteristics, advantages and limitations of common transmission media.

3. Channels, Circuits, Trunks
Channel: Refers to the medium (such as copper wire, radio, coaxial cable, satellite, or optical fiber) used to convey information from a transmitter to a receiver.
Circuit: The complete path between two terminals over which one-way or two-way communications may be provided. A circuit may involve several channels. Ex: Twisted-pair copper + coax + fiber + coax + twisted-pair copper.
Trunk: A single transmission channel between two switching centers or nodes, shard by many users.

4. Typical Bandwidths and Bit Rates Required
Analog Voice
POTS (plain old telephone system): 300 to 3400 Hz (baseband)
AM broadcasting: 10 KHz (modulated)
FM broadcasting: 200 KHz (modulated)
Digital Voice
PCM DS0: 64 Kb/s
Compressed voice: < 64 Kb/s; ex: 8, 16, 32 Kb/s
Mobile cellular: ~10 Kb/s
CD: Mb/s (2-channel, 16-bit PCM sampled at 44.1 KHz) MP3 (MPEG-1 Audio Layer 3): 96 Kb/s (FM quality)
192 Kb/s (DAB quality)

5. Typical Bandwidths and Bit Rates Required
Analog TV video: 6 MHz
Digital compressed TV video: ~1.5 MHz (~1 Mb/s)
HDTV: 8-15 Mb/s (with MPEG-4 compression)
Video teleconferencing: 384 Kb/s.
Dial-up PC modem: v.34: 28.2 Kb/s; v.90: 56 Kb/s
High speed data: at least several Mb/s
Blu-ray: 40 Mb/s (max)
IEEE a (1999), .11g (2003): 54 Mb/s (shared peak rate)
IEEE ac (2013): 780 Mb/s (shared peak rate)
IEEE ad (2012): 6.75 Gb/s (shared peak rate)
3G Cellular: Mb/s (shared peak rate)
4G Cellular, LTE (20 MHz ch): ~ Mb/s (shared peak rate)
4G Cellular, LTE-A (100 MHz ch): ~1 Gb/s (shared peak rate)
5G Cellular (2020): 20 Gb/s ? (shared peak rate)

6. Two Wire and Four Wire Circuits
Subscriber loop:
Two-wire twisted copper pair.
Four-wire trunk
Multiplexing and switching node
Two-wire circuit: A full-duplex communications circuit that utilizes only two metallic
conductors, e.g., a single twisted pair.
Four-wire circuit: A two-way circuit using two paths so arranged that the respective signals are
transmitted in one direction only by one path and in the other direction by the other path.
Note: The four-wire circuit gets its name from the fact that, historically, two conductors were
used in each of two directions for full-duplex operation.
[Wikipedia] A two-wire circuit is characterized by supporting transmission in two directions simultaneously, as opposed to four-wire circuits, which have separate pairs for transmit and receive. In either case they are twisted pairs. Telephone lines are almost all two wire, while trunks and switching are almost entirely four wire.
A four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path. Late in the 20th century, almost all connections between telephone exchanges were four-wire circuits, while conventional phone lines into residences and businesses were two-wire circuits.

7. Key Points
Nowadays four wire circuits are used for all circuits except for most subscriber loops.
Four wire circuit can be 4 physical wires or a pair of frequency channels or time slots (depending on transmission medium).
Four wire digital transmission is prevalent today.
Media: each type of transmission medium is advantageous in a particular situation.

8. TRANSMISSION MEDIA Subscriber loop: Twisted copper pair cable.
Optical fibre.
Radio
Twisted copper pair cable.
Coaxial cable
Optical fibre
Microwave radio
Satellite
Multiplexing and switching node

9. What is wrong with the below figure?

10. What is wrong with the below figure?
The detail is lost for the small values of the vertical axis!

11. What is wrong with the below figure?
The detail is lost for the small values of the vertical axis!
Want to show large and small values on the same scale?

12. Logarithmic versus Linear Scale
What is wrong with the below figure?
The detail is lost for the small values of the vertical axis!
Want to show large and small values on the same scale?
Use logarithmic scale (not linear scale) in the vertical axis.

13. dB Notation Linear dB 5000 37 400 26 10 8 9 5 7 2 3 1 0.5 -3 0.125 -9
logc(a x b) = logc(a) + logc(b) logc(a / b) = logc(a) – logc(b)
Decibel notation: Field quantities: 20 log10 (./.)
Power quantities: 10 log10 (./.)
In this course: 10 log10 (.)
x  + (increased by 1,000,000 times  increased by 60 dB)
÷  - (decreased by 50 times  decreased by 17 dB)
A [unitless] = (10 log10 A [unitless]) [dB]
A [u] = (10 log10 A[u]) [dBu]
Linear dB
5000 37
400 26 10 8 9 5 7 2 3 1
0.5 -3
0.125 -9
0.01
-20
0.0005
-33

14. dB Notation Linear dB 5000 37 400 26 10 8 9 5 7 2 3 1 0.5 -3 0.125 -9
logc(a x b) = logc(a) + logc(b) logc(a / b) = logc(a) – logc(b)
Decibel notation: Field quantities: 20 log10 (./.)
Power quantities: 10 log10 (./.)
In this course: 10 log10 (.)
x  + (increased by 1,000,000 times  increased by 60 dB)
÷  - (decreased by 50 times  decreased by 17 dB)
A [unitless] = (10 log10 A [unitless]) [dB]
A [u] = (10 log10 A[u]) [dBu]
P [W] = (10 log10P[W]) [dBW] Ex: 2 [W] = 3 [dBW]
P [mW] = (10 log10P[mW]) [dBm] Ex: 2 [mW] = 3 [dBm]
P [dBW] = (P+30) [dBm] Ex: 5 [dBW] = 35 [dBm]
10 log10SNR = (10 log10(Psignal [mW] / Pnoise [mW])) [dB]
10 log10SNR = (10 log10Psignal) [dBm] – (10 log10Pnoise) [dBm]
X [dBm] – Y [dBm] = Z [dB]; X [dBm] + Y [dB] = Z [dBm]
Linear dB
5000 37
400 26 10 8 9 5 7 2 3 1
0.5 -3
0.125 -9
0.01
-20
0.0005
-33

15. Decibel Unit
A power ratio X/Y, expressed in decibels (dB) is 10 log(X/Y) = 10logX-10logY (note: X and Y must be proportional to power)
dBm means power relative to 1 milliwatt; i.e. 10log(power in milliwatts)
dBw means power relative to 1 watt; i.e., 10log(power in watts).
0 dBw (meaning 1 watt) = 30 dBm.

16. Link Budgets Gain GTX dB GRX dB Transmitter Channel Receiver Noise
Path loss PL dB (attenuation)
Noise
Transmit
power PTX dBW
Received power in dBW: PRX = PTX + GTX – PL + GRX (all quantities in dB scale)
Received power in watts: PRX = PTX GTX GRX /PL (all quantities in linear scale)
Note: Attenuation PL usually depends on distance and frequency.

17. Link Budgets Gain GTX dB GRX dB Transmitter Channel Receiver Noise
power PTX dBW
Path loss PL dB (attenuation)
Received power in dBW: PRX = PTX + GTX – PL + GRX (all quantities in dB scale)
Received power in watts: PRX = PTX GTX GRX /PL (all quantities in linear scale)
Note: Attenuation PL usually depends on distance and frequency.
Noise power in watts: k T B F (all quantities in linear scale)
where k = 1.38 x (Boltzmann’s constant); T = 273+°C
Noise power in dBW: N = log10(273 + C°) + 10log10(B) +F
where °C = temp. in degrees centigrade; B = signal bandwidth in Hz; F=noise figure in dB

18. Link Budgets Gain GTX dB GRX dB Transmitter Channel Receiver Noise
power PTX dBW
Path loss PL dB (attenuation)
Received power in dBW: PRX = PTX + GTX – PL + GRX (all quantities in dB scale)
Received power in watts: PRX = PTX GTX GRX /PL (all quantities in linear scale)
Note: Attenuation PL usually depends on distance and frequency.
Noise power in watts: k T B F (all quantities in linear scale)
where k = 1.38 x (Boltzmann’s constant); T = 273+°C
Noise power in dBW: N = log10(273 + C°) + 10log10(B) + F
where °C = temp. in degrees centigrade; B = signal bandwidth in Hz; F = noise figure in dB
Signal to noise ratio (SNR) in dB = PRX - N
SNR in linear: PRX/N

19. Link Budgets
Gain
GTX dB
GRX dB
Transmitter Channel Receiver
Noise
Transmit
power PTX dBW
Path loss PL dB (attenuation)
Received power in dBW: PRX = PTX + GTX – PL + GRX (all quantities in dB scale)
Received power in watts: PRX = PTX GTX GRX /PL (all quantities in linear scale)
Note: Attenuation PL usually depends on distance and frequency.
Noise power in watts: k T B F (all quantities in linear scale)
where k = 1.38 x (Boltzmann’s constant); T = 273+°C
Noise power in dBW: N = log10(273 + C°) + 10log10(B) + F
where °C = temp. in degrees centigrade; B = signal bandwidth in Hz; F = noise figure in dB
Signal to noise ratio (SNR) in dB = PRX - N
SNR in linear: PRX/N
Link budget: Determine minimum transmit power etc. which satisfy these
equations and give a required minimum SNR.

20. VF (Voice Frequency) Cable - Paired Metallic Conductors
Aerial (on poles): exposed to damage and environment
Buried: more expensive to install; trouble locating
Pro
Compact, fairly high capacity (up to 1000 pairs per cable) - but low compared to coax and optical fiber
Quality controlled in factory
Con
High loss
Subject to crosstalk interference from neighbouring pairs in same cable

22. Coaxial Cable Aerial or buried
Large bandwidth (~1000 MHz), high capacity
Self shielding
Relatively expensive

23. Attenuation of 0.375 in. coax cable
Attenuation (dB\km.)
[Fig from “Telecommunication System Engineering” 2nd ed., by R.L. Freeman, Wiley, Ny. 1989]
Frequency (MHz)
Attenuation of in. coax cable

24. Summary Twisted copper pairs used in telephone subscriber loop plant:
Attenuation and usable bandwidth depends on length and thickness.
Many pairs in a cable in close proximity - subject to crosstalk interference.
Coax used in CATV plant:
Much lower attenuation and much higher usable bandwidth for same length.
Insulated - little or no interference.
More expensive and bulky, but can carry more payload.

25. Radio Microwave Line of Sight (LOS)
Cellular, WLAN, WiMax, sensor, ad hoc, PAN
Dispatch, paging
Pro
Low real estate and installation cost (don’t need to install wires or fibers to every possible customer), good coverage
Mobility
Con
Subject to interference and propagation disturbances
Security, privacy a concern

26. Line of Sight (LOS) Radio Propagation
Free space path loss in linear scale: (4πd/λ)^2
Free space path loss (FSPL) in dB
=10 log10 (input power/output power)
= log10 f + 20 log10 d
where frequency f is in Hertz and distance d is in metres.
PL is terrestrial radio links: PL = A + 20 log10 f + 10n log10 d
where n (>2) is the propagation exponent.

27. Non-Line of Sight Radio Propagation
Diffraction
Reflection
Impulse response: Frequency response:
Obstruction
(shadowing)
Scattering,
diffraction
“Multipath”

28. Sample Link Budget for a Radio Link
Transmitter
Receiver
Noise
Distance d
Given: Signal centre frequency f = 4 GHz
Distance d = 20 km.
Total antenna gains and cable losses = Gt + Gr = 24 dB
Bandwidth = B = 10 MHz
Noise figure = 10 dB; Temp = 17°C
Required SNR = 20 dB

29. Sample Link Budget for a Radio Link
Transmitter
Receiver
Noise
Distance d
Given: Signal centre frequency f = 4 GHz
Distance d = 20 km.
Total antenna gains and cable losses = Gt + Gr = 24 dB
Bandwidth = B = 10 MHz
Noise figure = 10 dB; Temp = 17°C
Required SNR = 20 dB
Free space path loss (FSPL) in dB
= log10 f + 20 log10 d = dB [f is in Hz and d is in m.]
Noise power in dBW = log10(273 + C°) + 10log10(B) +F = -124 dBW Required received power in dBW = SNR + Noise Power = 20 – 124 = -104 dBW
Required transmit power = Required received power + Path Loss - Gains =
= 2.4 dBW = 1.74 watts

30. Shadowing
Path loss variation due to obstructions, combined with distance
Path loss (dB) =avg. path loss+random path loss
Avg. path loss
Path
Loss
(dB)
Measured path loss
Free space path loss
Distance (log scale)

31. Fiber Optic Cable
Most long-haul trunks in Canada and U.S. are now carried on optical fiber.
Huge capacity.
High installation cost (but low cost per circuit in large capacity systems).
Immune to electromagnetic interference.
Low attenuation.
Long life.
Small size - makes better use of cable ducts.
Excellent for digital signals.

35. Satellites
Microwave frequency repeaters in geostationary orbits (~40,000 km.)
Large coverage; e.g., all of Canada.
Large capacity, high quality.
Extensively used by TV networks.
Capacity shared by multiple access.
Excellent for providing fixed or mobile coverage in remote areas, across oceans (although fiber is taking over).

36. Orbits (LEO, GEO, MEO) Low Earth Orbit (LEO)
500km-1500km from earth  low delay
Non-stationary, satellites rise and fall (orbit time ~ 90 minutes)
Smaller satellites with less transponders (~100 kg to 500 kg)
Closer  lower launch costs and requirements
Closer  smaller antennas, lower power requirements (ground terminals, satellite)
Need many, many satellites to provide global, uninterrupted coverage (example: original Teledesic needed 800! Skybridge requires 80)
Hand-off required, complex signal routing needed
Geo-stationary Earth Orbit (GEO)
30,000 km - 40,000 km from earth  larger delay
Appear stationary to earth observer (Clarke’s orbit!)
Larger satellites with many transponders (~ 1 to 20 tons!)
Further  higher launch costs and requirements
Further  larger antennas, Kwatts of power requirements
Theoretically, can cover earth with 3 satellites
No-hand-off needed, simpler signal routing
Medium Earth Orbit (MEO)
4,000-12,000 km from earth

37. Satellite Types Bent Pipe Satellites Regenerative Satellites
Simple Repeaters in the sky
Receive a signal on frequency F1, amplify it, transmit it on frequency F2
Almost all of today’s commercial satellites are bent pipe
Regenerative Satellites
Deploy on-board processing (OBP)
Receive signals, demodulate them, make intelligent decision on where to send them, modulate them and transmit them
Restricted to a few military satellites, they are becoming the preferred type of the next generation communication satellites
Iridium is a Regenerative satellite

39. IEEE, Communications Magazine, Nov. 2016