# RF and Radio Technology Fundamen

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```					Radio Frequency (RF) and Radio Technology
Fundamentals
The Concept of Wireless Point-to-Point (PTP, PP)

 One location to one location
 Dedicated access
> Full bandwidth between two locations

2
The Concept of Wireless Point-to-Multipoint
(PTMP, PMP)

 One location to many locations;
Many locations to one location
 Shared access
> Shared bandwidth between multiple locations
Indoor Wireless LAN

Outdoor Point-to-Multipoint

3
The Concept of Line-of-Sight (LOS)

 No obstructions between each end
> No trees
> No buildings
> No mountains
 Can you go through a window?
Probably, but with added losses that are hard to predict:
» Plan on 10dB as an initial guess, can be greater for
reflective (metallic) tinted glass

Note: The lower the frequency, the better it will travel through obstacles

4
The Line-of-Sight Issue - raising one side

 A structure can be erected to establish line-of-sight over
obstacles

5
The Line-of-Sight Issue – raising two sides

 Two structures can be erected to establish line-of-sight over
obstacles

6
The Line-of-Sight Issue – using a repeater

 A system approach called a “repeater” can establish line-of-sight
to go around or over obstacles
> Active repeaters (two radio systems back-to-back)
> Passive repeaters (one radio system redirected)

7
The Hertz Measurement of Frequency

 1 Hertz (Hz) = 1 cycle/second
> 1,000 Hz = 1 kHz
> 1,000,000 Hz = 1 MHz
> 1,000,000,000 Hz = 1 GHz

time

period
(cycle)
8
Wavelength

 Directly related to frequency
 Wavelength = the distance required to complete one
cycle at a particular frequency
> The distance from Point A to Point B represents one
wavelength
> Wavelength is normally measured relative to meters
(such as cm, or mm)

A      B

9
Phase

 The location of the traveling wave at a fixed point
in time
 Measured in degrees or radians, related to Pi ()
 360 Degrees = 1 Cycle                               90°

0°     180°   360°

270°

10
Watts & Decibels: Measurement of Power

 Watt (W)
 Decibel reference to 1 mW (dBm)
 Decibel (dB) - a ratio or difference in power
> e.g. 20dBm is 3dB less than 23dBm

Conversion equations
x(dbm) = 10logy(mW)
y(mW) = 10x(dBm)/10

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Watts vs. dBm

100 W   50 dBm

10 W    40 dBm
2W     33 dBm
1W     30 dBm

100 mW      20 dBm

1 mW    0 dBm
100 uW      -10 dBm

0.001 nW     -80 dBm
12
Power and Directivity

 Without obstructions and with high intensity and beam focus, RF can
travel long distances
> Power is measure of strength
> Gain is measure of amplification

13
How Much Power is a Watt?

   A standard microwave oven has an
output power of 700 to 1500 Watts
   A typical cell phone has an output
power in the range of 0.1 to 0.2 Watts
   Proxim's highest output power radio
devices are our outdoor radios that
operate at 2.4 GHz and have no
greater than 1 Watt output power
   Proxim‟s indoor wireless systems and
our 5 GHz outdoor systems have
substantially less power, typically in the
range of 0.01 to 0.2 Watts

14
Concept: Microwaves Behave Similar to
Visible Light & Sound

 They propagate in air similar to light and sound
> Reflect off surfaces
> Absorbed by surfaces
> Diffuse and refract through substances

Transmitting source
Signal is more concentrated
Point A       Point B   at Point A than at Point B

15
RF Refraction and Scattering

 RF can pass through materials which will change it‟s direction of
travel (called „refraction‟)
 RF can pass through materials which will diffuse the energy (scatter)
to a wider beam

Away from
Air (medium 1)          Perpendicular

Observer

Apparent
Position
Water (medium 2)
Actual Position

16
Reception:RF ~ Vision:Light

 Reception of RF can be affected by “vision-related” components
> “Blinders”
> Angle of attack
> Focus
> Obstructions
> Weather

17
RF is Attenuated (Relative to Frequency)
by Rainfall

 Signals above 11 GHz can be
severely affected
 Most of Proxim‟s products operate
11GHz
below 6 GHz and are virtually
Cloudburst
unaffected by rainfall in most parts
=7dB/mile                   of the world

6GHz
Cloudburst

18
Obstructions Will Stop or Seriously
Attenuate Signals

 Some RF can travel easily
through walls, stone, etc. and
some will be immediately
dampened
 Partial obstructions can
dramatically reduce wave
energy

19
RF Reflection and Multipath

 RF can “bounce” off objects like
buildings and mountains, water
and atmosphere

 Different paths of RF will arrive
at destination at different times -
this is called „multipath‟

20
The Importance of Signal Phase

Best Case: Even number of ½ Wavelengths

x
_

2x
_
-x
_

+                 =
x
_
-2x
_

-x   _

21
The Importance of Signal Phase

Worst Case: Odd number of ½ Wavelengths

x
_

-x
_

+                =
x   _

-x   _

22
Fresnel Zone

 The Fresnel zone is additional path clearance that is required to
 There are an infinite number of points where reflected signal arrives
exactly ½ wavelength out of phase for a given frequency

23
Earth Curvature and k factor

 One factor for line-of-sight includes earth curvature and the
effects of the atmospheric refraction due to the curve of the
earth‟s surface
> The earth‟s bulge between the end points must be considered when
determining if LOS and proper path clearance exists, including Fresnel
zone
> The k factor (refraction index) is a mathematical figure that will help
determine the effect on path clearance
 Not much of a factor under 10 miles

24
Polarization

 Polarization describes the orientation of the E (electrical) and H
(magnetic) components of an RF wave front.
> Linear polarization (horizontal, vertical, slant linear)
> Circular polarization (right-hand, left hand)

 RF can be transmitted (and received) with dominant polarization

> Polarization provides a level of discrimination (attenuation) against
different polarization signals, especially “opposite” polarization (e.g.
horizontal versus vertical)

 Weather and multipath can “de-polarize” RF

25
Terrain Effects on RF

 Mountainous terrain is best
> Many multipath reflections will not
reach the other end, thus reducing
the potential for out-of-phase
reflected signals that may have
degraded the integrity of the direct
signal

 Flat, smooth terrain is worst
> Many multipath reflections may reach
the other end, thus increasing the
potential for out-of-phase reflected
signals that may degrade the integrity
of the direct signal

26
Climate Effects on RF

 Humid climate is worst
> More moisture = more ducting and refraction = more attenuation

 Dry climate is best
> Reduced moisture = less ducting and refraction = less attenuation

27
Overall Spectrum

AM
550 - 1700kHz    460-600MHz       100GHz-500THz Medical X-ray

VLF    LF   MF   HF   VHF   UHF   SHF   EHF   Infrared   Visible   UV   X   Gamma   Cosmic

Sound     88-108 MHz                              Light
20Hz - 20kHz   VHF TV                           700THz - 1000THz
54-220 MHz

Cellular 800-900 MHz
PCS 1.8-2 GHz
Terrestrial Microwave 1–18 GHz
Indoor Wireless 900 MHz, 2 & 5 GHz

28
USA Frequency Allocations

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Types of Spectrum

> Anyone can use
> No coordination or registration required
> Opportunity for interference, which the user must work around
> Coordination required
> Registration required
> Interference is better controlled, but not completely eliminated
 Regulatory agency will assist with any interference cases
 Owned
> Purchased spectrum, usually in a given region, usually by auction
> Owner needs to self-coordinate intra-system interference potential
> Some coordination may be needed with neighboring owners

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 Three primary ISM (Industrial, Scientific, Medical) bands:
> “900” MHz
 902-928 MHz
> “2.4” GHz
 2400-2483.5 MHz
> “5.7” or “5.8” GHz
 5725-5850 MHz
 Three primary U-NII (Unlicensed National Information Infrastructure)
bands:
> “5.2” GHz (or “Lower 5”)
 5150-5250 MHz, indoor only
> “5.3” GHz (or “Middle 5”)
 5250-5350 MHz, indoor and low-power outdoor
> “5.7” or “5.8” GHz (or “Upper 5”)
 5725-5825 MHz (higher power, outdoor)
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The Concept of Interference

 Interference is the reception of signals from sources other than the
intended source
> The source of the interference may be from a closer and/or stronger
signal level compared to the desired signal impacting the ability of the
system to receive the desired signal properly

 Interference can be caused by energy that is at the same frequency
as the signal that you wish to receive, or can be at a nearby frequency
with enough energy to „leak‟ into the receiver
 Interference can also be caused by energy that is a completely
different frequency from that which you wish to receive. High-powered
transmitting energy that is a multiple of the intended transmitter
frequency

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Methods of Two-Way Communications

 Frequency Division Duplex (FDD)
> Communications in one direction are at a different frequency than in the
other direction, transmitting and receiving in both directions at the same time
 Can establish high speeds in both directions (usually equivalent speed)
 No substantial time delays (latency) for communication, as no information
is buffered
 The difference in frequency can be small (a few MHz) or large (100‟s of
MHz), in the same frequency band or different bands altogether
 Time Division Duplex (TDD – or „Ping Pong‟)
> Communications in one direction are at a different time than in the other
direction, transmitting and receiving at the same frequency but in succession
 Can provide unbalanced communications when desired (e.g. more
 Has an impact on latency

33
Connected or Connectorized Antenna

 Some Proxim products have built-in antennas that cannot be removed
or bypassed
 Some Proxim products have built-in antennas that can be bypassed
and an alternate antenna connected instead
 Some Proxim products do not have a built-in antenna; an antenna
must be connected, usually with a cable between the antenna

Connectorized Antenna Configurations
Connected Antenna Configurations

34
One-Piece and Two-Piece Construction

 For Proxim‟s outdoor wireless solutions,
of one or two distinct boxes
> One-piece radios are designed for all-indoor
mounting (or mounting in a weatherproof
container)
> Two-piece radios give the flexibility of
mounting part of the system closer to the             2-piece configuration
antenna
 In some cases, the antenna may be
integrated as part of the radio to help ease
cabling and minimize attenuation of the
cable between the antenna and the radio
1-piece configuration

35
Antenna Performance Parameters

 Gain
 Beamwidth/Coverage Pattern
 Polarization

36
What Governs Distance or Coverage?

 The “strength” of the transmitted signal
 The radio‟s frequency of operation
 Output power regulations
 Obstacles between the end points
 Climate/Terrain
 The antenna pattern

37
Basic Distance Planning:
A Series of Gains and Losses

Antenna     Path    Antenna
(Gain)    (Loss)    (Gain)

Transmission                           Transmission
Line (Loss)                          Line (Loss)
RSL

(Output Power)             (Threshold)

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Margin”

 System Gain
> The difference between the output     Output
power and the threshold               Power
> The difference between the received
signal level and the threshold

System
Gain

Margin
Threshold

39
Understanding “Availability”

 The predicted amount of time the system will be operating above
threshold
> Availability is the primary design criteria for outdoor wireless
systems

Examples:
99.999% = 5.26 minutes/year outage
99.995% = 26.28 minutes/year outage
99.950% = 262.8 minutes/year outage

40

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 views: 40 posted: 4/27/2010 language: English pages: 40