Fundamental of Radio Frequency communications.ppt

There are two aspects of networking which must be considered
when installing either an NCL or LMS product:
1. Ethernet Networking (IP)
2. Radio Networking (RF)
This presentation will focus on the RF side of the NCL and
LMS products.

RF Terminology
Wavelength is the distance between identical points in the
adjacent cycles of a waveform. In wireless systems, this
length is usually specified in meters, centimeters, or
millimeters

The size of the wavelength varies depending on the frequency
of the signal. Generally speaking, the higher the frequency
the smaller the wavelength.
The WaveRider family of products operate in the 2.4000 -
2.4835 GHz range (NCL and LMS2000) as well as the 905 -
925 MHz range (LMS3000).
At 2.4 GHz the wavelength is 12.5cm
At 905 MHz the wavelength is 33cm

These values are calculated using the following formula:
Wavelength = 3 x 102
f (frequency in MHz)
This calculation is important to remember, especially when
installing antennas. Ideally, the antenna should be installed no
closer than 10 wavelengths to the nearest reflective surface.

Frequency
Frequency is the number of complete cycles per second in
alternating current direction. The standard unit of frequency is
the hertz, abbreviated Hz. If a current completes one cycle per
second, then the frequency is 1 Hz.
Kilohertz (kHz)
Megahertz (MHz)
Gigahertz (GHz)
Terahertz (THz)

Spectrum
800 850 900 960
DAMPS 869 894
GSM/NMT 890 915 935 960
EGSM 870 915 925 960
TACS 890 905 935 950
ETACS 872 905 917 950
PDC 940 958
AMPS 824 849 869 894
iDEN 806 821 851 866
ESMR 806 824 851 869
UP-SMR
896-
901
940 -
945
NPCS
901-
902
930-
931
940 -
941
PAGING 929 932
ISM 902 928
1700 1800 1900 2000 2500
PCN/DCS 1710 1785 1805 1880
PCS 1850 1910 1930 1990
ISM 2400-2483.5

Tx Power
Tx is short for “Transmit”
All radios have a certain level or Tx power that the radio
generates at the RF interface. This power is calculated as the
amount of energy given across a defined bandwidth and is
usually measured in one of two units:
1. dBm – a relative power level
referencing 1 milliwatt
2. W – a linear power level
referencing Watts

dBm = 10 x log[Power in Watts / 0.001W]
W = 0.001 x 10[Power in dBm / 10 dBm]
The NCL and LMS radios have Tx power of +18dBm, which
translates into .064 W or 64 mW.

Rx Sensitivity
Rx is short for “Receive”
All radios also have a certain ‘point of no return’, where if they
receive a signal less than the stated Rx Sensitivity, the radio
will not be able to ‘see’ the data.
This is also stated in dBm or W.
The NCL and LMS radios have a receive sensitivity of –82 dBm.
At this level, a Bit Error Rate (BER) of 10-5 (99.999%) is seen.
The actual level received at the radio will vary depending on
many factors.

Radiated Power
In a wireless system, antennas are used to convert electrical
waves into electromagnetic waves. The amount of energy the
antenna can ‘boost’ the sent and received signal by is referred to
as the antennas Gain.
Antenna gain is measured in:
1. dBi: relative to an isotropic radiator
2. dBd: relative to a dipole radiator
0 dBd = 2.15 dBi

There are certain guidelines set by the FCC that must be met in
terms of the amount of energy radiated out of an antenna. This
‘energy’ is measured in one of two ways:
1. Effective Isotropic Radiated Power (EIRP)
measured in dBm = power at antenna input [dBm] +
relative antenna gain [dBi]
2. Effective Radiated Power (ERP)
measured in dBm = power at antenna input [dBm] +
relative antenna gain [dBd]

Energy Losses
In all wireless communication systems there are several factors
that contribute to the loss of signal strength. Cabling,
connectors, lightning arrestors can all impact the performance of
your system if not installed properly.
In a ‘low power’ system (such as the NCL and LMS products)
every dB you can save is important!! Remember the “3 dB
Rule”.
For every 3 dB gain/loss you will either double your power
(gain) or lose half your power (loss).

-3 dB = 1/2 power
-6 dB = 1/4 power
+3 dB = 2x power
+6 dB = 4x power
Sources of loss in a wireless system: free space,
cables, connectors, jumpers, obstructions

FCC Guidelines
The ISM Bands are defined as follows:
902 to 928 MHz
2400 to 2483.5 MHz
5725 to 5850 MHz
FCC Part 15, Class B
Unlicensed operation from 2400 to 2483.5 MHz
P2P - EIRP : +36 dBm (4 Watts)
: 3:1 i.e. +24 dBm into 24 dBi
P2MP - EIRP : +36 dBm (4 Watts)
: 3:1 at subscriber (considered P2P)

System must be installed by a “Professional Installer” as defined in
FCC Document 15.247 Part 15;
Complete understanding of FCC emissions regulations for
unlicensed operation in the 2.4 GHz ISM Band.
Installer must have a full understanding of the impact of various
types of antennae, amplifiers and other active and passive
components on the compliance of the equipment under FCC
regulations.
FCC - Installer

An external Power Amp cannot be used in conjunction with WR
radio components, in order to comply with FCC regulatory
emissions requirements. Use of an external PA device with a
WaveRider system is deemed illegal and may result in significant
penalty to the manufacturer, seller, and customer.
Unique connectors provide means of compliance.
Standard connectors require professional installation to ensure
compliance.
FCC - Installation

WaveRider High Speed
Wireless Systems
The NCL and LMS systems are designed to support terrestrial fixed
links in an outdoor environment. Typical distances achieved while
staying within FCC guidelines are:
Point to Multipoint: up to 8km
Point to Point: up to 15km
These distances may vary depending on the installation, antennae
chosen, cabling, etc.

Direct Sequence Spread Spectrum
Also known as Direct Sequence Code Division Multiple Access (DS-
CDMA), DSSS is one of two approaches to spread spectrum
modulation for digital signal transmission over the air.
The stream of information to be transmitted is divided into small
pieces, each of which is allocated to a frequency channel across the
spectrum.
When transmitted, the data is combined with a higher data-rate bit
sequence (also known as a chipping code) that divides the data
according to a spreading ratio.

The transmitter and the receiver must be synchronized with the
same spreading code.
The chipping code helps the signal resist interference and also
enables the original data to be recovered if data bits are damaged
during transmission.
22 MHz wide

Frequency Hopping Spread
Spectrum
Also known as Frequency Hopping Code Division Multiple Access
(FH-CDMA), FHSS radios transmit "hops" between available
frequencies according to a specified algorithm which can be either
random or preplanned.
The transmitter operates in synchronization with a receiver, which
remains tuned to the same center frequency as the transmitter.

TIME
1 2 3 4 5 6 7 8 9 10 11 12
f1
f2
f3
f4
f5
Each
channel
1MHz wide
Hopset
FHSS – an example

Signal Propagation
As the signal leaves the antenna it propagates, or disperses, into
space. The antenna selection will determine how much
propagation will occur.
At 2.4 GHz it is extremely important to ensure a that a path (or
tunnel) between the two antennas is clear of any obstructions.
Should the propagating signal encounter any obstructions in the
path, signal degradation will occur.
Trees, buildings, hydro poles, and towers are common
examples of path obstructions.

The greatest amount of loss in your wireless system will be from
Free Space Propagation. The Free Space Loss is predictable
and given by the formula:
FSL(dB) = 32.45 + 20Log10F(MHz) + 20Log10D(km)
The Free Space Loss at 1km using a 2.4 GHz system is:
FSL(dB) = 32.45 + 20Log10(2400) + 20Log10(1)
= 32.45 + 67.6 + 0
= 100.05 dB

Line of Sight
Attaining good Line of Sight (LOS) between the sending and
receiving antenna is essential in both Point to Point and Point to
Multipoint installations.
Generally there are two types of LOS that are used discussed
during installations:
1. Optical LOS - is related to the ability to see one
site from the other
2. Radio LOS – related to the ability of the receiver
to ‘see’ the transmitted signal

To quantify Radio Line of Sight, the Fresnel Zone theory is
applied. Think of the Fresnel Zone as a football shaped tunnel
between the two sites which provides a path for the RF signals.
At WaveRider acceptable Radio Line of Sight means that at
least 60% of the first Fresnel Zone plus 3 meters is clear of any
obstructions.

2nd* 1st*
3rd*
* Fresnel Zones
Fresnel Zones

Site A
Site B
• Fresnel Zone diameter depends upon
Wavelength, and Distances from the sites
along axis
• For minimum Diffraction Loss, clearance of
at least 0.6F1+ 3m is required
d2
d1
Radius of n th
Fresnel Zone given
by:
2
1
2
1
d
d
d
d
n
rn
+
=
l
The First Fresnel Zone

When obstructions intrude on the first Fresnel Zone many issues
can arise which will affect the performance of the system. The
main issues are:
1. Reflection
– incident wave propagates away from smooth scattering
plane
– multipath fading is when secondary waves arrive out-of-
phase with the incident wave causing signal degradation

2. Refraction
– incident wave propagates through scattering plane but at an
angle
– frequencies less than 10 GHz are not affected by heavy
rains, snow, “pea-soup” fog
– at 2.4 GHz, attenuation is 0.01 dB/Km for 150mm/hr of
rain
3. Diffraction
– incident wave passes around obstruction into shadow
regions

Antenna - How it Works
The antenna converts radio frequency electrical energy fed to it (via
the transmission line) to an electromagnetic wave propagated into
space.
The physical size of the radiating element is proportional to the
wavelength. The higher the frequency, the smaller the antenna size.
Assuming that the operating frequency in both cases is the same,
the antenna will perform identically in Transmit or Receive mode

The type of system you are installing will help determine the
type of antenna used. Generally speaking, there are two ‘types’
of antennae:
1. Directional
- this type of antenna has a narrow beamwidth; with the
power being more directional, greater distances are usually
achieved but area coverage is sacrificed
- Yagi, Panel, Sector and Parabolic antennae
- an EUM, NCL Station/Master will use this type of antenna
in both Point to Point and Point to Multipoint

2. Omni-Directional
- this type of antenna has a wide beamwidth and radiates
3600; with the power being more spread out, shorter
distances are achieved but greater coverage attained
- Omni antenna
- a CCU or an NCL Master will use this type of antenna

Yagi
- better suited for shorter links
- lower dBi gain; usually between 7 and 15 dBi

Parabolic
- used in medium to long links
- gains of 18 to 28 dBi
- most common

Sectoral
- directional in nature, but can be adjusted anywhere from 450 to
1800
- typical gains vary from 10 to 19 dBi

Omni
- used at the CCU or Master NCL for wide coverage
- typical gains of 3 to 10 dBi

Antenna Radiation Patterns
Common parameters
– main lobe (boresight)
– half-power beamwidth (HPBW)
– front-back ratio (F/B)
– pattern nulls
Typically measured in two planes:
• Vector electric field referred to E-field
• Vector magnetic field referred to H-field

An antennas polarization is relative to the E-field of antenna.
– If the E-field is horizontal, than the antenna is Horizontally
Polarized.
– If the E-field is vertical, than the antenna is Vertically Polarized.
Polarization
No matter what polarity you choose, all antennas in the same RF
network must be polarized identically regardless of the antenna
type.

Polarization may deliberately be used to:
– Increase isolation from unwanted signal sources (Cross
Polarization Discrimination (x-pol) typically 25 dB)
– Reduce interference
– Help define a specific coverage area
Horizontal
Vertical

Antenna Impedance
A proper Impedance Match is essential for maximum power
transfer. The antenna must also function as a matching load for
the Transmitter ( 50 ohms).
Voltage Standing Wave Ratio (VSWR), is an indicator of how
well an antenna matches the transmission line that feeds it.
It is the ratio of the forward voltage to the reflected voltage. The
better the match, the Lower the VSWR. A value of 1.5:1 over the
frequency band of interest is a practical maximum limit.

Return Loss is related to VSWR, and is a measure of the
signal power reflected by the antenna relative to the forward
power delivered to the antenna.
The higher the value (usually expressed in dB), the better. A
figure of 13.9dB is equivalent to a VSWR of 1.5:1. A Return
Loss of 20dB is considered quite good, and is equivalent to a
VSWR of 1.2:1.

VSWR Return Loss Transmission Loss
1.0:1  0.0 dB
1.2:1 20.83 dB 0.036 dB
1.5:1 13.98 dB 0.177 dB
5.5:1 3.19 dB 2.834 dB

Environmental Effects
Ice and wind loading, Salt spray
Radomes used to improve performance in icy, windy
conditions (more common with larger solid parabolic
dishes). Wind loading can be reduced substantially by
using a radome.
Wind loading can produce vibration, which in turn can
produce azimuth errors. For longer paths, this can be critical.
Installation - pay close attention to proper sealing of all
connector junctions.

Fundamental of Radio Frequency communications.ppt

The Transmission Line
The type of cable selected depends mostly on the length of that
cable required. Generally, the longer the cable run the better
the cable must be in terms of attenuation.
Attenuation refers to the degradation of the signal as it travels
through the cable. This is usually stated as a loss in dB per 100
feet.

Cable Type Attenuation at 2.4 GHz
per 100 feet
RG8 10
LMR400 6.8
Heliax 3/8" 5.36
LMR600 5.4
Heliax 1/2" 3.74
Heliax 5/8" 2.15
Attenuation Table

Transmission Line Selection
Physical Characteristics:
Bend radius
Diameter - transition considerations (interface ‘jumper
cable’ use)
Environmental considerations
Plenum installation (fire retardant)
Special weather-resistant types
UV resistance very important in tropics

Line Loss or Attenuation paramount – refer to your Link Budget
Calculations to determine how much loss is acceptable and still
have a viable link.
Foam dielectric, Air Dielectric, Pressurized types of Coaxial
Cable. Waveguide use also possible but typically not cost-
effective

Connectors
Your connector selection will be determined based on the
following:
- connector gender at antenna
- type of cable being used
- use of lightning protection
- gender of jumpers being used

For the most part the cabling manufacturers also manufacture
the connectors that go on the cables. ‘Knock off’ connectors
are available, but don’t always fit the cable the way the
manufacturers connectors do.
Generally the only decision that needs to be made is what
gender of connector to install…Male or Female
Antennas – usually Female
Lightning Arrestors – usually Female

Connectors
N-male
RP-SMA-female
RP-SMA- male
N-female

The Lightning Arrestor
To avoid the potential for damage during a lightning strike, the
use of lightning is highly recommended.
For maximum protection, ground must be connected close to
point of entry into building - within 2ft.
Typically structural steel OK for ground connection
Typical
Lightning
Arrestor
Do not use Gas Lines or
Water pipes.
Check Electrical Code for
grounding restrictions.

Network Feasibility Assessment
Through WaveRiders Professional Services Group (PSG), a
Network Feasibility Assessment can be done to establish the
viability of a proposed wireless network with either the NCL or
LMS products.
- System and Program Planning
- Implementation Management
- Application engineering
- Network engineering
- Backhaul Design

- Electrical Inspection
Certified electrician, equipment grounding
- Primary Power Sources
- Site Lease / Costs
Antenna
Floor space

Link Budget Calculations
To establish the viability of a link prior to installing any
equipment, a Link Budget Calculation needs to be made.
Performing this calculation will give you an idea as to how much
room for path loss you have, and give you an idea as to link
quality.
Using the WaveRider Link Path Analysis Tool (LPA Tool), the
Fade Margin and other link criteria can be mathematically
calculated to determine link quality.

Fade Margin
– Defined as the difference between the Receive Signal
Level RSL, and the Rx Threshold or other chosen
reference Level.
– For path lengths of 16km or less, a minimum 10dB
Fade Margin is recommended
Ie. If you have an RSL of –60dB and a Rx Threshold of –72dB,
than your fade Margin would be 12dB

–Path Loss (dB)
–Field Factor (dB)
–Antenna Gain
–(dBi)
–Cable Losses
–(dB)
–Connector
–Losses
–(dB)
–Connector
–Losses
–(dB)
–Cable Losses
–(dB)
–A –B
–Received Signal Level – (dBm) = Tx Output (dBm) - Path
–Loss(dB) - Field Factor (dB) + Total Antenna Gains (dB) - Total
–Cable Losses (dB) - Total Connector Losses (dB)
–Antenna Gain
–(dBi)
–Tx Output (dBm)
–Tx Output (dBm)

Customer CAP1 Subscriber1
Elevation (ft)
Latitude
Longitude
Azimuth
Antenna Type TA-2404-2 TA-2436
HAAT (ft) 50.00 40.00
Antenna Gain (dBi) 14.50 24.00
Tx Line Type LMR600 LMR600
Tx Line Length (ft) 70.00 60.00
Tx Line Loss (dB/100 ft) 4.42 4.42
Tx Line Loss (dB) 3.09 2.65
Connector Loss (dB) 1.50 1.50
Amplifier Type HA-2401E-100/10 HA-2401E-100/10
Amplifier Tx Gain (dB) 0.00 0.00
Frequency (MHz)
Path Length (mi)
Free Space Loss (dB)
Diffraction Loss (dB)
Net Path Loss (dB) 116.36 116.36
Radio Type Model CCU2000 EUM2000
Tx Power (mW) 31.62 31.62
Tx Power (dBm) 15.00 15.00
Effective Isotropic Radiated Power (dBm) 24.91 34.85
Effective Isotropic Radiated Power (W) 0.31 3.05
Amplifier Rx Effective Gain (dB) 10.00 10.00
Rx Sensitivity for max. Throughput (dBm) -72.00 -72.00
Rx Signal Level (dBm) -61.60 -61.60
Fade Margin (dB) 10.40 10.40
2450.00
4.00
116.36
0.00

Interference Countermeasures
1. Short Paths
2. Narrow Beam Antennas (high gain)
3. Frequency Selection
4. Antenna Polarization
5. Antenna Azimuth
6. Equipment/Antenna Location

Fundamental of Radio Frequency communications.ppt

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