WIRELESS NETWORKS
Performance predictions valid for indoor and outdoor paths
Roger Freeman
12.14.2004
Rating: -2.00- (out of 5)
In this tip we briefly cover basic performance prediction
methods needed for planning and installing wireless (radio) systems in
the enterprise environment. These wireless systems are popular examples
of
indoor/outdoor wireless communication links covered under the umbrella
term WLAN (wireless LAN). IEEE 802.11 series variants and Wi-Fi
standing for
wireless
fidelity which is tied to IEEE 802.11b in particular.
Another popular acronym is WiMax standing for
worldwide interoperability for microwave access.
The IEEE 802.16 standard governs
WiMax. These are just several among a host
of
indoor-outdoor radio (wireless) systems.
The model used is our own.
Practical applications include radiolinks in offices and
factory buildings, production and laboratory floors covering one or
multiple
stories. Connectivity may also wish to
be extended campus-wide. Here we mean that communication may also be
desired over and around several buildings and adjacent properties. IEEE 802.16 documentation gives the maximum
bit rate supported as 155 Mbps. Let us
assume a receiver noise figure of 5 dB and transmitter output power of 2.0 W or +6 dBW, transmission line losses of
3 dB and an antenna gain of 0 dBi, what kind of performance can we
expect on an
LOS path 1 km distant? The model link is
set out in a tabular form beginning with the transmitter power output
placed at
the top of the column. The abbreviation RSL
means the "receive signal level." This
term is widely used on RF systems. RSL
is conventionally measured in dBW or dBm.
We also establish a performance requirement expressed as BER
at 1X10-10. where the Eb/No = 17 dB
including
2 dB of modulation implementation loss.
Eb/No is energy per bit (Eb)
per noise density ratio (No).
In our table below Eb = RSL divided by the bit rate. No = thermal noise in 1 Hz of
bandwidth and is calculated as –204 dBW + 10Log(noise figure). The noise figure of the model receiver is 5
dB, then No = -204 dBW + 5 dB = -199 dBW/Hz.
Model outdoor-indoor link power budget
| ITEM
|
PARAMETER
VALUE |
COMMENTS
|
| Transmitter
power output |
+6 dBW
|
4 W equiv.
|
| Trans line
losses |
-3 dB |
Approx
|
| Trans ant
gain |
0 dBi
|
|
| EIRP
|
+3 dBW
|
|
| LOS free
space loss at 1 km, @ 2.5, 5.2 GHz |
-100.36 dB
(2.5 GHz)
-106.72 dB (5.2 GHz)
|
|
| Rec ant gain
|
0 dBi
|
|
| Miscl line
losses |
-3 dB
|
|
| Rec signal
level (RSL) |
-97.36 dBW
|
((Content component not found.)) .5 GHz
|
| Rec signal
level (RSL) |
-103.72 dBW
|
((Content component not found.)) .2 GHz
|
| Link bit rate
|
155x106
bps |
81.9 dB equiv
|
Eb,
(RSL = -106.36 dBW)
Eb (RSL = -112.72 dBW)
|
-179.26 dBW
-185.62 dBW
|
((Content component not found.)) .5 GHz
((Content component not found.)) .2 GHz |
| Eb/No
|
19.74 dB
(2.5 GHz)
13.38 dB (5.2 GHz)
|
No=
-199 dBW/Hz |
FSL
= 32.4 + 20Log2500 = 32.4 + 67.96 =
100.36 dB at 1 km, 2.5 GHz
32.4 + 20log5200 = 106.72
dB at 1 km, 5.2 GHz
About the author:
Roger Freeman has worked in telecommunications since 1946 when he
joined the Navy and became an aviation radioman. Later, Roger served as
a radio officer in the merchant marine for nearly 10 years. He then
held several positions with ITT assigned to their Spanish Standard
Electrica subsidiary. He also served the International
Telecommunication Union as Regional Planning Expert for Northern Latin
America based in Quito, Ecuador. Roger is bilingual. His last employee
position was principal engineer with the Raytheon Company, Marlboro, MA
where he took early retirement in 1991 to establish Roger Freeman
Associates, Independent Consultants in Telecommunications. He has been
giving seminars in telecommunication disciplines at the University of
Wisconsin, Madison for nearly 20 years. Roger has been writing books on
various telecommunication subjects for John Wiley & Sons since
1973. There are seven titles which he keeps current including the
two-volume work, Reference
Manual for Telecommunication Engineers, now in 3rd edition. He
holds two degrees from NYU. His Web site is www.rogerfreeman.com and his
e-mail address is rogerf67@cox.net.
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