group1 intro micro comm

7/31/2019 Group1 Intro Micro Comm

1/17

August 17, 1951 The firsttranscontinental microwave radio systembegan operation

- 107 relay stations- 30 miles apart

- radio link between New York and San

Francisco- cost $40 Million (Bell System)


2/17

Intrastate or feeder service : short haul

Interstate and backbone route

applications : long haul

System capacity : less than 12 voice-bandchannels to more than 22,000 channels

Early microwave : FDM voice-band

circuits/ FMRecently developed microwave : PCM-

TDM/ PSK or QAM


3/17

The next higher part of the radioelectromagnetic spectrum, where thefrequencies are above 30 GHz and below 100GHz

Radio waves in this band are usually stronglyattenuated by the Earthly atmosphere andparticles contained in it, especially duringwet weather.

The electronic technologies needed in themillimeter wave band are also much moredifficult to utilize than those of themicrowave band.


4/17

Suitable over line-of-sight transmission linkswithout obstacles

Provides large useful bandwidth when

compared to lower frequencies (HF, VHF,UHF)

Affected by the refractive index(temperature, pressure and humidity) of the

atmosphere, rain, snow and hail, sandstorms, clouds, mist and fog, stronglydepending on the frequency.


5/17

[Wireless]] transmission of information

One-way (e.g. television broadcasting) andtwo-way telecommunication using

communications satellite Terrestrial microwave radio broadcasting

relay links in telecommunications networksincluding e.g. backbone or backhaul carriers

in cellular networks linking BTS-BSC


6/17

Radio systems do not require a right-of-way

acquisition between stations

Each station requires the purchase or leaseof only a small area of land


7/17

High frequencies mean short wavelengths,which require relatively small antennas.

Because of their high operating frequencies,microwave radio systems can carry largequantities of information


8/17

Fewer repeaters are necessary foramplification.

Radio signals are more easily propagatedaround physical obstacles such as water andhigh mountains

Distance between switching centers are less.


9/17

Minimum delay times are introduced.

Minimal crosstalk exist between voicechannels.

Increased reliability and less

maintenance are important factors.

Underground facilities are minimized.


10/17

It is more difficult to analyze anddesign circuits at microwavefrequencies.

Measuring techniques are moredifficult to perfect and implement atmicrowave frequencies

It is difficult to implementconventional circuit components atmicrowave frequencies.


11/17

Transient time is more critical atmicrowave frequencies.

It is often necessary to use specializedcomponents for microwave frequencies.

Microwave frequencies propagate in astraight line, which limits their use toline-of-sight applications.


12/17

Analog : FM


13/17

Digital : PSK or QAM

BPSK


14/17

QAM


15/17

FM is used in microwave radio system

FM signals are less sensitive to

random noise.FM can be propagated with lower

transmit power.

In FM, intermodulation noise is afunction of signal amplitude and themagnitude of frequency deviation


16/17

AM signals are more sensitive to

amplitude nonlinearities.In AM, intermodulation noise is

caused by repeater amplitude

nonlinearity.In AM, intermodulation noise is a

function of signal amplitude.


17/17

Letter Frequency Band HF 3 - 30 MHz

VHF 30 - 300 MHz

UHF 300 - 1000 MHz

L 1000 - 2000 MHz

S 2000 - 4000 MHz

C 4000 - 8000 MHz

X 8 -12 GHz

Ku 12 -18 GHz

K 18-27GHz

Ka 27 - 40 GHz

V 40 - 75 kHz

W 75 -110 GHz

group1 intro micro comm

Documents