Wireless Spectrum
in the USA
Jiapeng Zhao
Yingfei Wang
Gautam Rajagopal
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Regulation of the Radio Spectrum
Federal Communications Commission (FCC)
https://transition.fcc.gov/files/logos/fcc-logo_black-onwhite.jpg
Private citizens, businesses, state and local governments
National Telecommunications and Information Administration (NTIA)
Federal government
International Telecommunication Union (ITU)
UN agency
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http://www.spectrumwiki.com/wp/allocations101.p
df
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Explaining the Chart
Radio spectrum is all frequencies below 3000 GHz
Only allocated up to 275 GHz (scientific and engineering applications)
Application
Frequency
AM broadcast
530 - 1700 kHz
FM broadcast
88 - 108 MHz
Satellite radio
~2.3 GHz
Satellite TV
~12 GHz
http://www.spectrumwiki.com/wp/allocations101.pdf
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Explaining the Chart
Amateur (satellite): not for financial gain
FM voice communication, Morse code, digital comm.
Broadcasting (satellite): meant for general public
AM: 530 - 1700 KHz, FM: 88 - 108 MHz
TV: 54 - 72, 76 - 88, 174 - 216 MHz
Fixed (satellite): communication between two points
radio towers
Maritime Mobile: between coast and ship stations.
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Distress signal (Channel 16): 156.8 MHz
Why do we care?
Efficient use of spectrum
Interference
Extremely high frequency: 30-300 GHz
New technologies
Competition
All for the public’s benefit
FCC and NTIA work together
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Why do we need to regulate the spectrum?
Interference!
http://people.csail.mit.edu/fadel/timo/
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Digital Signal Communication
(Shannon Capacity, 1948)
● Theoretical limit of how fast you can transmit data
● We are near it (for low power communication)
● Capacity-approaching codes:
○ Turbo code (1993) (3G, 4G)
○ Low-density parity-check code (1996,
rediscover)
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Digital Signal Communication (Bandwidth)
fast
slow
Frequency
data rate ≤ bandwidth * log2(1 + power / noise)
● bandwidth proportional to data rate
● not linear in practice but close to linear
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Digital Signal Communication (Noise)
data rate ≤ bandwidth * log2(1 + power / noise)
● Non-human source noise
● Interference!
Interference happens when 2 services operate in the same frequency
range
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Spectrum regulation
Reduced interference!
http://computernetworkingsimplified.com/physical-layer/overview-channel-multiplexing-techniques/
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Digital Signal Communication (Power)
power transmitted
to the receiver
data rate ≤ bandwidth * log2(1 + power / noise)
● Power fades as signal travels
● Lower frequency signal travels further (better range!)
○ Just like red light travels further than blue light
● Signal range determined by: data rate, frequency, total
transmission power, ...
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Example: two models of XBee
normal model operate @ 2.4Ghz
model @900Mhz: BETTER RANGE(6 mi vs 1 mi) but LARGER ANTENNA!
2.4Ghz:
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900Mhz:
The Crowded and Narrow 2.4Ghz frequency
WiFi, ZigBee, Bluetooth concentrated on 83Mhz bandwidth
(2.400Ghz~2.483Ghz)
Coexistence could be a PROBLEM!!!
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The Coexistence Problem - ZigBee and WiFi
ZigBee
16 channels
2Mhz
width
(slow data rate)
WiFi
3 channels
22Mhz width
(high speed)
Interference can happen when a ZigBee
channel slip in between WiFi channels.
Imagine a motorcycle slips in between trucks
in a stuck traffic.
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The Coexistence Problem - Bluetooth and WiFi
Bluetooth
(Frequency Hopping Spread Spectrum or FHSS)
WiFi
FHSS idea: spreading a narrowband signal by “hopping” across a given frequency band.
What happens when bluetooth signal HOP ONTO WiFi’s channel?? Interference!
Bluetooth WiFi Interference
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The Coexistence Problem
“To summarize, Wi-Fi devices are scarcely affected by the presence of other wireless technologies operating
concurrently such as ZigBee and Bluetooth devices. Conversely, Bluetooth and ZigBee suffers conspicuously from
the presence of Wi-Fi” (R. Challoo, 2012)
Solutions:
Time Division Multiplex (one device talks at one time)
Spatial Isolation (separate devices far apart)
Frequency Isolation (use a different spectrum)
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Frequency Isolation
5 Ghz
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2.4 Ghz
Questions???
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References
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1.
Information about frequency chart: http://www.spectrumwiki.com/wp/allocations101.pdf
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Shannon Capacity https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem
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xBee specs and pictures from www.sparkfun.com
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ZigBee WiFi pictures: https://www.anaren.com/air-wiki-zigbee/Zigbee_Wifi_Coexistence
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Bluetooth WiFi coexistence pictures: https://www.digikey.com/Web%20Export/Supplier%20Content/Laird_776/PDF/laird-wireless-bluetoothwifi-coexistence.pdf?redirected=1 http://1.bp.blogspot.com/NaHr4FmZn7Q/VXMuT2V4l4I/AAAAAAAAADk/Sp3PebHtqr8/s1600/03%2BZigbee%2Bchart.png
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5Ghz WiFI picture: http://www.broadcom.com/blog/wp-content/uploads/2013/07/120104_broadcom_5G_logo_MASTER_RGB.png
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LTE image: http://4f4k0612jn953kln3h2oofxd.wpengine.netdna-cdn.com/wp-content/uploads/2014/03/4G_LTE.png
Spectral leakage
frequency
range
● Spectral leakage will cause interference
○ unavoidable
○ good for bandwidth utilization
○ very little interference
● Don’t test your project right under a
radio tower!
98%
2%
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http://www.ldark.club/tower.gif