RF-for-WirelessComm-Jose.ppt
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Transcript of RF-for-WirelessComm-Jose.ppt
RF Considerations for wireless communications
Jose Antonio Echenique
Agenda Introduction to wireless communications
Wireless link implications Medium: the radio spectrum
The three main parameters that define radio–frequency: Over-the-air data rate Receive Sensitivity Transmit power
Other Considerations
Barriers to Future Growth
Introduction
Wireless Communication System: Any electrical communication system that uses a naturally occurring communication channel, such as air, water, earth.
Examples: Sonar Broadcast: Radio, TV, pagers, satellite TV, etc. Two Way: walkie talkie, cell phones, satellite phones, Wireless Local Area Networks, etc.
Wireless link implications
Communications channel is natural (air) poor quality: fading, shadowing, weather, etc.
Medium regulated by governments frequency allocation, licensing, etc.
Security issues
Medium: the radio spectrum
Wireless communications use the electromagnetic spectrum, which is regulated by government institutions such as the Federal Communications Commission (FCC).
Regulations specify what bands of frequency can be used for different applications. For instance: FM radio has 88-108MHz and AM radio has 540-1600KHz .
Medium: the radio spectrum
SOURCE: JSC.MIL
SOUND LIGHTRADIO HARMFUL RADIATION
VHF = VERY HIGH FREQUENCYUHF = ULTRA HIGH FREQUENCYSHF = SUPER HIGH FREQUENCY EHF = EXTRA HIGH FREQUENCY
4G CELLULAR56-100 GHz
3G CELLULAR1.5-5.2 GHz
1G, 2G CELLULAR0.4-1.5GHz
Frequency and wave length: = c/f :wave length , speed of light c 3x108m/s, frequency f
RF CONSIDERATIONS
The three main parameters that define radio–frequency: Over-the-air data rate Receive Sensitivity Transmit power
Range is a result of these three RF parameters and can be used to define them
RF CONSIDERATIONS
Over-the-air data rateDetermined by data throughput requirementsSpeed calculation:
In point-to-point systems: RF data rate = (Dpl+Dao+Dro)x(1+rt)/time
In a multipoint application, unless a polling scheme or time-division multiple access (TDMA) scheme is used, the calculation is more complicated.
RF CONSIDERATIONS Over-the-air data rate (Example)
Assume a remote unit needs to send 1000 bytes of payload data in a response to a 2-byte access point command every 75 milliseconds:
Dao would be 32 bits and Dro 80 bits The total amount of data for both transmissions must occur in
75 millisecondsRF data rate =
[((16b+32b+80b)+(8000b+32b+80b))x1.1]/0.075sec= 120.853 Kb/sec
RF CONSIDERATIONS
Receive Sensitivity Indicates the level of signal strength that must be
present to correctly receive data at a specified bit-error rate.
Receive Sensitivity = Nt + Ns + 10log(BW) + SNRmin Nt is the thermal noise floor Ns is the system noise figure BW is the symbol rate SNRmin is the minimum signal-to-noise- ratio required for a given
bit-error rate
RF CONSIDERATIONS
Transmit power It is usually driven by regulatory and power-
consumptions considerations For example, FCC allows up to 1 W of transmit power in
the United States in the 2.4 Ghz band
Other Considerations Antenna Selection
Directionality Omni (360 degree coverage) directional Directional (limited range of coverage)
Gain More gain means more coverage
Polarization
Other Considerations Modulation Techniques
Amplitude Shift Keying (ASK): very simple low bandwidth requirements very susceptible to interference
Frequency Shift Keying (FSK): needs larger bandwidth
Phase Shift Keying (PSK): more complex robust against interference
1 0 1
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1 0 1
t
1 0 1
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Range Depends On... Frequency Transmit power Radio sensitivity Processing gain from access technique and redundancy Interference effects
Barriers to Future Growth
Irreducible size of antennas Rising level of RF emissions -
interference problems and safety concerns Finite spectrum Lack of standards and interoperability of
hardware
THANK YOU …
Reference:
http://www.ce-mag.com/archive/02/Spring/cutler2.html
“Unlicensed Wireless Data Communications, Part II: Specifying RF Parameters” by Tim Cutler