Physical Layer

Effective Bandwidth

Area of a Spectrum where most if the signal bandwidth is contained

Channel Capacity with out Noise

Nyquist Formula

C = W log2(M) W: bandwidth in hertz M: number of discrete signals C: theoretical maximum capacity in bits per second

Delay Distortion

when a signals frequency components arrive at the receiver with different delays from each other. these increase with badwidth

attenuation

an error where amplitude decreases with distance. amplifiers and reapeater are the solution

repeater

more expensive, only applicable in digital signals, tries to restore the original signal

amplifier

cheaper, simpler, amplifies all signals around so it is more prone to errors

inter symbol interference

when pulses signals are spread out so much so that it effect near by signals enough to distort them. adaptive equalization is the solution

adaptive equalization

the solution to inter symbol interface, applied to either side of the medium

multi path

when a signal reflects from surrounding objects and so the signal will arrive at the reviser at differnt times and with different frequencies

shadowing

the attenuation effect when signals pass through objects

chanel capacity with out noise

C = 10 B log2(1 + 10 ^(db/10)) B: Bandwidth in hertz

multifiber

more common, cheaper

singlefiber

expensive, but more common for longer distances

optical fiber

transmits singnals throught reflecting light in the wire

twisted cable

cross talk issue, tranmsits over a physical medium

NRZ

cheap, lack of synchronization

bipolar AMI and Psudeo

good error detection, lacking in synchronization canonization, middle expense

Manchester

expensive, good error detection and good synchronization

Multiplexing

combining signals onto one medium for a more efficient transmissions

Frequency Division Multiplexing

limited bandwidth and unlimited time, cross talk is an major issue

Time Division Multiplexing

Unlimited bandwidth limited time, multiple bandwidth combined together to be sent over the medium , inefficacy wasted time slots, pulse stuffing

TDMA

Multiple access, used for longer transmissions like satellite up link, buffer and burst method

Frequency Hoping Spread Spectrum

both transmitter and receiver must have synchonization to make sure that they both hop to the same freuquency. hard to hack this because it changes so much

DSSS

uses spreading code, single bits are spread out across a wider frequency band, similar performance to FHSS

Slow FHSS

bad an inefficient

Fast FHSS

better performance