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Overview
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Frequency Bands
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IEEE 802.11a (Wi-Fi)
channels: 12
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5.125 GHz to 5.850 GHz
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IEEE 802.11b (Wi-Fi)
channels: 11 (USA) / 13 (Europe)
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2.4 GHz to 2.4835 GHz
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IEEE 802.11g (Wi-Fi)
channels: 14
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2.4 GHz to 2.4835 GHz
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IEEE 802.16d (WiMAX)
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Sub 11 GHz
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IEEE 802.16e (WiMAX)
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2 GHz to 6 GHz
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Channel Bandwidth
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10 to 30 MHz
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Modulation
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FHSS (Frequency Hopping Spread Spectrum):
- 2GFSK (2-Level Gaussian Frequency Shift
Keying): 1 Mbps
- 4GFSK (4-Level Gaussian Frequency Shift
Keying): 2 Mbps
DSSS (Direct Sequence Spread Spectrum):
- DBPSK (Differential Binary Phase Shift
Keying): 1 Mbps
- DQPSK (Differential Quadrature Phase Shift
Keying): 2, 5.5, 11 Mbps
OFDM (Orthogonal Frequency Division Multiplexing): 6, 9, 12, 18, 24, 36, 48, 54, 75 Mbps
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Maximum link length
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WiFi: 30 to 300 feet
WiMAX: 1 to 6 miles
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Access format
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CSMA - CA (Carrier Sense Multiple Access with Collision Avoidance)
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Data rate
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802.11a: 54 Mbps max; 1 to 2 Mbps common
802.11b: 11 Mbps max; 4 to 10 Mbps common
802.11g: 54 Mbps max
802.16d: 75 Mbps max
802.16e: 30 Mbps max
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Transmit power rate
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100 mW to 1 W
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Applications
Wireless LAN according to IEEE 802.11 is the most common standard for wireless local area networks. It supports data rates up to 54 Mbps at a range of about 30 to 300 m.
It allows users to simply connect to a network without the need of cables. This is accomplished through Access Points (Hot Spots). Such an Access Point can handle up to three unique connections at the same time. The bandwidth is shared. Multiple Access Points communicate via roaming to compensate the limits in range.
Beneath the connection through Access Points, devices can be connected directly to each other. This is sometimes called Ad-hoc Networking.
Furthermore it is used for wireless internet access or for connecting different networks through WLAN bridges (802.11c).
WiMAX according to IEEE 802.16 is an emerging technology that will deliver broadband last mile connectivity in a larger geographic area than Wi-Fi. It will allow greater mobility with higher data rates.
Technology in brief
Wireless LAN was first approved in 1997 by the IEEE Group after seven years of development. 802.11b/g uses the ISM band (Industrial, Scientific and Medical) at 2.4 GHz which is free of license; whereas 802.11a is allocated in the FCC U-NII band at 5 GHz. 802.11b uses either FHSS or DSSS while 802.11a and g as well as WiMAX utilize OFDM.
Frequency Hopping Spread spectrum appears to be random, but this is not the case. It is part of the hardware encoding of the transmitter and receiver. This schedule of frequency hops is nearly impossible to determine by simply intercepting broadcast.
Direct Sequence Spread Spectrum refers to pseudo noise (PN). Redundant data is added while spreading the signal. These so-called Chips cause the information to be nearly unreadable for devices not knowing the right PN Code.
Orthogonal Frequency Division Multiplexing is a multi-carrier modulation method. It divides the data over the available spectrum. Therefore interference will only degrade a small portion of the signal. It is similar to conventional Frequency Division Multiplexing. The difference lies in the way the signals are modulated and demodulated. Priority is given to minimizing the interference among the channels.
Additional encryption provides even more security for wireless networks.
The IEEE 802.11e standard provides QoS-(Quality of Service) and Streaming-Additions for 802.11a/g. IEEE 802.11i adds encryption and authentication to 802.11a/b/g.
802.11n is a future standard yet-to-be-ratified by the IEEE 802.11 Group. It shall propose a raw throughput of up to 500 Mbps including strong QoS and will be situated in the 5 GHz band.
UWB (Ultra Wideband) according to IEEE 802.15.3a is a future wireless personal area network (WPAN) technology capable of high data rates (up to 480 Mbps) at short distances (max 30 feet). It is currently under development by the IEEE 802.15 Group.
Typical measurements
Numerical measurements: signal strength, noise level, SNR, carrier to noise, RF interference, adjacent channel rejection, channel power
Graphical representations: power vs. time, power vs. frequency, modulation spectrum
Willtek Test Instruments
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