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RF Considerations for wireless communications

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

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RF Considerations for wireless communications

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  1. RF Considerations for wireless communications Jose Antonio Echenique

  2. 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

  3. 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.

  4. Wireless link implications • Communications channel is natural (air) • poor quality: fading, shadowing, weather, etc. • Medium regulated by governments • frequency allocation, licensing, etc. • Security issues

  5. 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 .

  6. 4G CELLULAR 56-100 GHz 3G CELLULAR 1.5-5.2 GHz 1G, 2G CELLULAR 0.4-1.5GHz Medium: the radio spectrum HARMFUL RADIATION LIGHT RADIO SOUND VHF = VERY HIGH FREQUENCY UHF = ULTRA HIGH FREQUENCY SHF = SUPER HIGH FREQUENCY EHF = EXTRA HIGH FREQUENCY Frequency and wave length:  = c/f :wave length , speed of light c  3x108m/s, frequency f SOURCE: JSC.MIL

  7. 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

  8. RF CONSIDERATIONS • Over-the-air data rate • Determined by data throughput requirements • Speed 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.

  9. 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 milliseconds RF data rate = [((16b+32b+80b)+(8000b+32b+80b))x1.1]/0.075sec = 120.853 Kb/sec

  10. 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

  11. 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

  12. Other Considerations • Antenna Selection • Directionality • Omni (360 degree coverage) directional • Directional (limited range of coverage) • Gain • More gain means more coverage • Polarization

  13. Other Considerations 1 0 1 • 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 t 1 0 1 t 1 0 1 t

  14. Range Depends On... • Frequency • Transmit power • Radio sensitivity • Processing gain from access technique and redundancy • Interference effects

  15. 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

  16. 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

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