C1 Wireless Systems - hawa.work Wireless Systems.pdf · Why Wireless? • Wireless ... This is because digital transmissions can be packed into adjacent channels, while analog ones

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Lecture 1: Wireless Systems

Dr. Mohammed HawaElectrical Engineering Department

University of Jordan

EE529: Simulating Wireless Networks.

Copyright © Dr. Mohammed Hawa Electrical Engineering Department, University of Jordan

Why Wireless?• Wireless communications have several advantages

over wired communications:• Mobility: Mobile phones can be used anywhere,

while landline phones are tethered to the wall.• Lower Cost: No need for expensive physical

infrastructure or excessive maintenance. – Compare connecting to Wi-Fi access point versus

installing wires to Ethernet switch. – Compare cellular towers versus twisted copper

infrastructure in the last mile of PSTN (digging streets).

• Seamless connectivity: The same mobile phone number at home, work, during travel.

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Copyright © Dr. Mohammed Hawa Electrical Engineering Department, University of Jordan 3

There are also disadvantages!

• Security issues: Personal or sensitive information (e.g., passwords) can be sniffed if encryption is not used.

• Wireless channels have high attenuation levels.

– More power is added to radio signals at the transmitter to overcome attenuation.

– More frequent transmitters or repeaters are used.

• When there is no adequate power, data rate is constrained (exchanging SNR for bandwidth).

• Other impairments: Noise, Fading, Shadowing, Doppler shift, Frequency-reuse interference, etc, require complex solutions.

• Radio transmission can harm humans if power is high.

• Microwave requires line-of-sight (LOS).

• Hence, wired and wireless are BOTH useful.


Examples of Wireless Systems

• Cellular Telephony:– 2G, 3G, 4G, 5G (coming soon).

• Wi-Fi wireless local area networks (LAN).• Bluetooth, Zigbee and NFC personal area

networks (PAN).• WiMAX metropolitan area networks (MAN).• Radio broadcasting (AM, FM, DAB).• TV broadcasting (NTSC, PAL, DVB-S,

DVB-T, ATSC). • More in the future: V2V, V2I, IoT, WSN, …

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Wireless Growth (4G LTE)

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Wireless Growth (Wi-Fi)

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Radio Waves

• Wireless channels can only carry electric and magnetic fields (EM).

• Converting voltage/current to electric/ magnetic field is performed by an antenna.

• Antenna length is proportional to signal wavelength (� � �/�).

• To allow reasonable antenna lengths, the baseband signal modulates a high frequency carrier (baseband to carrier).

• Low carrier frequency is RF transmission. Higher frequency is Microwave transmission.


Antennas

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Radio Signal Frequency

• Modulation (analog or digital) has advantages:– Allows the use of reasonable antenna lengths.

– Allows Multiplexing (FDM). As well as CDMA and OFDMA in digital systems.

– Allows exchanging SNR for Bandwidth.

• Radio signal frequency typically refers to carrier frequency, not bandwidth.

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Broadcast Frequencies (Depends on Country)

Technology Frequency

AM radio 535 kHz to 1.7 MHz

FM radio 88 MHz to 108 MHz

Television stations (VHF) 54 MHz to 88 MHz

174 MHz to 220 MHz

Television stations (UHF) 470 MHz to 806 MHz

Wi-Fi (we say 2.4 GHz) 2.412 GHz to 2.484 GHz

5.15 GHz to 5.725 GHz

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GSM band ƒ (MHz) Uplink (MHz)

(Mobile to Base)

Downlink (MHz)

(Base to Mobile)

Equivalent

LTE band

T-GSM-810 810 806.2 – 821.2 851.2 – 866.2 27

GSM-850 850 824.2 – 849.2 869.2 – 893.8 5

P-GSM-900 900 890.0 – 915.0 935.0 – 960.0

E-GSM-900 900 880.0 – 915.0 925.0 – 960.0 8

DCS-1800 1800 1710.2 – 1784.8 1805.2 – 1879.8 3

PCS-1900 1900 1850.2 – 1909.8 1930.2 – 1989.8 2


Satellite Systems

• Satellite TV uses broadcast frequencies within the ranges (Uplink/Downlink):

• C band: 6/4 GHz

• Ku band: 14/10-12 GHz

• Ka band: 27-31/18-20 GHz

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Spectrum Allocation

• Use of radio frequency bands is regulated by governments in most countries.

• Called spectrum management or spectrum allocation or frequency allocation.

• Federal Communications Commission (FCC) in U.S.

• Ofcom (Office of Communications) in UK.

• Telecommunications Regulatory Commission (TRC) in Jordan.


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Not all frequencies are the same!

• Higher frequencies suffer more attenuation (much more attenuation).

• Hardware running at higher frequency is expensive.

• Operating only in lower frequencies limits bandwidth (and hence, data rate).

• Wave propagation characteristics are also different for different frequencies (wavelengths).

• The choice is limited and spectrum is fast depleted.

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Frequency Band Names

Frequency Wavelength Designation Abbreviation

300–3000 Hz 103–100 km Ultra low frequency ULF

3–30 kHz 100–10 km Very low frequency VLF

30–300 kHz 10–1 km Low frequency LF

300 kHz – 3 MHz 1 km – 100 m Medium frequency MF

3–30 MHz 100–10 m High frequency HF

30–300 MHz 10–1 m Very high frequency VHF

300 MHz – 3 GHz 1 m – 10 cm Ultra high frequency UHF

3–30 GHz 10–1 cm Super high frequency SHF

30–300 GHz 1 cm – 1 mm Extremely high frequency EHF

300 GHz – 3 THz 1 mm – 0.1 mm Tremendously high frequency THF


Radio Wave Propagation

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Surface Wave (Ground Wave)

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• Long wavelength radio waves (low frequency).

• Follows curvature of the earth (runs parallel to earth’s surface).

• Subject to surface attenuation.

• Frequency (up to 3 MHz, VLF, LF, MF): Primarily surface wave, although sky waves are used for longer distances.


Sky Waves

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• Medium wavelength radio waves.• Reflected or refracted by the

ionosphere. Sky waves will continue to reflect or refract between the earth’s surface and the ionosphere until complete attenuation occurs.

• Ionosphere: Layers of ionized gas caused by solar radiation, located between 60 and 200 miles above the earth’s surface, and varies daily and with seasons and latitude.

• Frequency (3 to 30 MHz, HF): Sky waves are predominant.

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Space Waves

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• Short wavelength radio waves.

• Can pass through the ionosphere (without reflection or refraction) into space.

• Space waves neither follow the curvature of the earth, nor bend around obstructions.

• Can also travel as line-of-sight from TX to RX.

• Frequency (above 30 MHz, VHF, UHF, SHF, EHF): Propagation is by line-of-sight (space waves). Ground waves are rapidly attenuated, and sky waves rarely exist.


Satellite Communications

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Suitable frequencies are limited!

• Again: Higher frequencies suffer more attenuation.

• Again: Hardware running at higher frequency is expensive.

• Again: Operating only in lower frequencies limits bandwidth (and hence, data rate).

• The popularity of wireless systems and their exponential growth requires more spectrum allocation.

• Remember: 5G, Wi-Fi, WiMAX, DAB, DVB, V2V, V2I, IoT, WSN, …

• Spectrum is a scarce resource!


Where do we get new spectrum?

• White spaces refer to frequencies allocated to a broadcasting service but not used locally.

• Governments license the rights to broadcast over certain frequencies. However, radio spectrum can end up being unused because there is no business interest, or is becoming free as a result of technical changes.

• In the U.S., switchover to digital TV freed up large spectrum chunks between about 50 MHz & 700 MHz.This is because digital transmissions can be packed into adjacent channels, while analog ones cannot.

• In many countries, the number of terrestrial TV stations or FM stations or AM stations is less than the allocated spectrum.

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Spectrum White Space!


Can we use white space?

• Cognitive radio is a promising wireless technology.

• Allows users to harness spectrum that is assigned to licensed users, but is not being fully utilized at a specific place or time.

• Devices in a cognitive radio network sense the spectrum around them for unused portions and then dynamically utilize empty spectrum bands they can find.

Documents

C1 Wireless Systems - hawa.work Wireless Systems.pdf · Why Wireless? • Wireless ... This is because digital transmissions can be packed into adjacent channels, while analog ones