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RF Considerations for wireless communications Jose Antonio Echenique.

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Presentation on theme: "RF Considerations for wireless communications Jose Antonio Echenique."— Presentation transcript:

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

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 = (D pl +D ao +D ro )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: D ao would be 32 bits and D ro 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) + SNR min  Nt is the thermal noise floor  Ns is the system noise figure  BW is the symbol rate  SNR min 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 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 101 t 101 t 101 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: “Unlicensed Wireless Data Communications, Part II: Specifying RF Parameters” by Tim Cutler

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