Unformatted text preview: e - Signaling at frequencies up to
500 mhz up to about a kilometer distance.
Optical Fiber - multimode, 50 microns, or
single mode, 8-10 microns.
We saw that optical fiber allows the 10
Gb/second Ethernet, with plans to go to 100
Light signals described in terms of wavelengths,
ë = c/f,
where c is the speed of light, 3*108
1.3 and 1.55 micron bands: attenuation - 0.2 dB per
kilometer. The bands are about 25,000-35,000 gigaherz
wide. UNGUIDED MEDIA Free space propagation - Excluding losses, received
signal power falls inversely with square of distance.
Inverse square law does not correspond to dB per
kilometer - 6 dB per doubling of the distance.
Long distance radio transmission.
At low carrier frequencies, signals propagate around
earth’s curvature, increasing the range.
At higher frequencies, propagation is mostly line-of-sight.
microwave transmission between tall towers.
Use of electromagnetic spectrum is highly regulated
Also power limits. The cellular concept in mobile
communication W ithin a cell, the division can be frequency
multiplexing, time multiplexing, or CDMA (Code
Division Multiple Access). CDMA has different codes for different senders,
preferably orthogonal or near ortogonal. Public Switched Telephone Network (PSTN)
Local loops were Analog transmission in about the 3003300 hz range.
All trunks and switches use digital transmission.
Connections coaxial cable, microwave, fiber optic. Digital important for regeneration advantages.
Sending data over voice channels (older method)
Data must be modulated to imitate a signal bandlimited to
about the 300-3300 hz range. The modulator of a modem
does this. Can send 4 - 10+ bits per pulse - 9600, 28,800,
and more bits pre second.
Very high speed modems have to test the line first. To raise rates, eliminate filters for the twisted pair local
loops; The wires themselves can handle much higher rates.
xDSL - DSL for...
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This note was uploaded on 04/03/2014 for the course EE 362 taught by Professor Laporta during the Fall '08 term at Penn State.
- Fall '08