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Conversions

1 MHz = 1,000,000 Hz
1 GHz = 1,000 MHz
1 GHz = 1,000,000,000 Hz

I.E.
- 2400 MHz is the same as 2.4 GHz
- 5800 MHz is the same as 5800 GHz

Hz = Radio Spectrum
Bits = data
M = 1,000,000
G = 1,000,000,000
There is a total of 83.3 MHz of Spectrum available in the 2.4 GHz Band

LICENSE FREE BANDS

ISM
ISM: Industrial, Scientific, and Medical
UNI-I (or UNII)
Unlicensed National Information Infrastructure
  • 902 to 928 MHz
  • 2,400 to 2,483.5 MHz
  • 5,725 to 5,850 MHz
  • 5,150 to 5,250 MHz
  • 5,250 to 5,350 MHz
  • 5,725 to 5,825 MHz

900 MHz Band

  • (902 to 928 MHz)
  • Data Rates are up to 3 Mbps ( Typical 2 Mbps throughput)
  • Non Line of Sight
  • Unaffected by weather
  • Only few Manufacturers for the products – proprietary technology
  • Expensive – Compared to IEEE 802.X technologies

2.4 GHz Band

  • Large bandwidth available (83.5 MHz)
  • High data rates possible (up to 11 Mbps)
  • With the 11g – 54 Mpps is possible
  • Equipment reasonably priced
  • Unaffected by weather
  • Line of Sight required for long range (greater the several hundred yards)
  • Used world-wide

5 GHz Band

  • 5.725 – 5.850 GHz Spread Spectrum Band
  • Virtually unlimited ERP on Point-to-Point links makes long range practical
  • Very high data rates possible
  • Equipment more expensive then 2.4 GHz equipment
  • Still greatly underutilized
  • High gain directional antennas focus signals
  • Ideal for point-to-point wireless backbone
Unlicensed National Information Infrastructure

Band 1
Band 2
Band 3
FREQUENCY
5.15 - 5.25 GHz
5.25 - 5.35 GHz
5.725 - 5.825 GHz
TX POWER
23 dBm EIRP
(200 mW)
30 dBm EIRP
(1 Watt)
36 dBm EIRP
(4 Watts)
APPLICATION
INDOOR USE ONLY
CAMPUS LINKS
LONG RANGE
(Several Miles)

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RF FUNDAMENTALS

RF Communication

Full Duplex

  • Radio TX and RX data simultaneously
  • Requires a pair of Frequencies (one for TX and one for RX)
  • Fastest means of data transfer
Both radios are transmitting and receiving at the same time on different radio frequencies.


Half Duplex

  • Used by IEEE 802.11a,b,g and others
  • Time Division Duplex (TDD)
  • Bi-directional system
  • Only one radio transmits at a time
  • Radio buffers the data until it is its turns to transmit
  • Operates only on one radio channel
  • Typically less then half thru-put of the over-the-air data rate
Radios alternate transmit and receive on the same radio channel.


DEFINITIONS

dB
Difference (or ratio) between two signal levels. Generally used used to describe the effect of system devices on signal strength.
dBm
A signal strength level. 0 dBm is defined as 1 mW of power. Small signals are negative numbers. (e.g. - 83 dBm)
dBi
The gain of an antenna relative to an isotropic radiator. Used in calculating ERP and range.

NOTE: dB, dBm and dBi are used because systems’ powers, gains and losses can be calculated by simply adding and subtracting.
ERP
Effective Radiated Power, equal to the antenna gain added to the power into that antenna. (Technically, called EIRP.)

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Gain and Loss

Amplification
Signal Loss


Remote Amplifier System



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Effective Radiated Power (ERP)

dBm vs. Watts

dBm
0
1
2
3
6
10
15
20
30
33
36
40
50
60
Power
1.0 mW
1.3 mW
1.6 mW
2.0 mW
4.0 mW
10.0 mW
32.0 mW
100 mW
1 Watt
2 Watts
4 Watts
10 Watts
100 Watts
1.000 Watts
dBm = 10 log
dBm = 10 log
dBm = 10 log

Example: Convert 250 mW to dBm
10 log
250
= 10 x 2.39 = 24dBm
1 mW
Rule Of Thumb
Double/Half Power:
Add/Subtract 3dB
Ten Times/One-tenth Power:
Add/Subtract 10dB
Spread Spectrum Technologies

Frequency Hopping (FHSS)
  • The radio carrier hops around the band.

Direct Sequence (DSSS)

  • The radio carrier signal is “spread out” on a specific channel

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Channels For FHSS

Each data packet sent on one of 82 channels.
  • Next packet randomly hops to another channel.
  • Signal itself not “spread” - occupies narrow bandwidth.
  • Signals “hop” around interfering signals.

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Channels For DSSS System

802.11 Radio Channels
All Radios in One Network Operate on a Single Channel

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DSSS Spectrum - IEEE 802.11b

Direct Sequence Spread Spectrum (DSSS)
Frequency Channel in 2.4 GHz (IEEE 802.11)

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Overlapping Channels

802.11 Radio Channels Overlap

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802.1 Protocol Summary

Standard
Modulation
Air Data Rate
Frequency Band
802.11
FHSS
DSSS
2 Mbps
2.4 GHz
802.11a
OFDM
54 Mbps
UNII
802.11b
DSSS
11 Mbps
2.4 GHz
802.11g
OFDM
DSSS
54 Mbps
11 Mbps
2.4 GHz
802.1x
N/A
Authentication and
Access Control
All

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Int'l: 1.631.588.3877
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Please Note:
We are closed November 27 and 28 for Thanksgiving. During this time, you can still place orders online and over our fax line. These orders will be processed promptly when we return. Additionally, any technical or sales-related questions can be e-mailed or left on our voicemail system. They will be answered when we reopen.

All Of Us At
HD Communications Corp.
Wish You And Yours A Safe & Happy Holiday!