Wireless - Telecommunications - Lecture Slides, Slides of Telecommunication electronics

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Wireless

What is wireless

• Free space communication (no wire, no waveguide, no

fiber optic cable)

• Indoor/outdoor/space

• Concentrating on most active frequency bands - RF

and microwave frequencies

• RF – “radio frequency” - hundreds of MHz to several GHz
• Microwave - several GHz to approx 30 GHz
• Circuit theory / transmission lines / electromagnetics all

needed

• Circuit dimensions d ≈ λ for RF and microwave circuits.
• Question: what relationship between d and λ exists for low

frequency circuits?

Why Wireless

• Mobility
• Available channels
• Cost
  • 1 in 5 in U.S. live in areas too remote for fast wire-line internet access
  • Construction:equipment =
    • 20:80 for wireless
    • 90:10 for burried line
• Half new fixed phone lines installed by 2003 will be wireless

Design Issue

• Operating Frequency
• Propagation
• Radiated Power

Allocated Spectra

• Operating frequency:
  • Frequencies allocated by international standards

bodies (e.g. FCC, CTRC, IEEE, etc.)

Typical Frequencies Approximate Band Designations

AM Broadcast Band 535 −1605 kHz L-band 1 − 2 GHZ

Shortwave radio 3 − 30 MHz S-band 2 − 4 GHz

FM broadcast band 88 − 108 MHz C-band 4 − 8 GHz

VHF TV (2 − 4) 54 − 72 MHz X-band 8 − 12 GHz

VHF TV (5 − 6) 76 − 88 MHz Ku-band 12 − 18 GHz

UHF TV (7 − 13) 174 − 216 MHz K-band 18 − 26 GHz

UHF TV (14 − 83) 470 − 890 MHz Ka-band 26 − 40 GHz

Microwave Oven 2.45 GHz U-band 40 − 60 GHz

Propagation

• Certain frequencies are very poor for

long range communication.

Propagation (cont.)

• Power density of propagating wave in free space decreases as

1/R^2 , where R is the distance from the source.

• Atmosphere and other objects may cause much faster decrease

in power density

• Reflections may interfere with direct line-of-sight path,

leading to multipath interference or fading

• Spread spectrum systems, multiple antennas, and error-

correcting codes can be used to reduce fading

Case Study: PCS

• Second generation cellular protocol
• North American PCS systems use IS-136 (TDMA), IS-

95 (CDMA, QPSK) or European Global System Mobile

(GSM) (which is also TDMA) systems

• Most modern cell phones are dual mode, meaning

that they can not only communicate on digital PCS

networks, but also the older first generation

Advanced Mobile Phone Service (AMPS) system

Case Study: GPS

• Global Positioning Satellite (GPS) system uses 24 satellites in medium

earth orbit (MEO) 20,200 km above the Earth to provide position

information

• A minimum of four satellites must have a line-of-sight view of the

positioning receiver

• Propagation delay between satellites and receiver used to determine

position of receiver relative to the satellites (for which position is known)

• Low gain antennas are used for the receivers, so receivers must be able to

receive signals around -130 dBm

• Timing pulses transmitted as spread spectrum signals with BPSK

modulation.

Case Study: Bluetooth

• Bluetooth specifications (cont.)
  • Transmitter
    • Three power levels (1, 2.5, 100 mW)
    • In-band and out-of-band spurious emissions
    • Frequency accuracy of ±75 kHz from center of channel
  • Receiver
    • Sensitivity ≤ −70 dBm
    • Maximum usable level −20 dBm

Block Diagram Symbols

• Block diagram symbols for commonly used RF

and microwave components

Component Symbol Component Name

Antenna

Amplifier

Mixer

∼ Oscillator

Filter Block Symbols