B1P3 Flashcards
What is the difference between noise and interference
Noise is from natural sources – which tends to be unavoidable
Interference is from unwanted transmissions. This is a particular problem with radio, as radio depends on a shared medium
What is fading
Slow and fast fading refers to how quickly the signal changes as the receiver or transmitter moves or due to obstacles and reflections
slow fading is caused by …. movements
large
fast fading is caused by … movements
small
Rayleigh fading is…
A model describing fast fading, used when signals are received through multiple paths but there is no predominant line-of-sight signal
Rician fading is…
A model describing fast fading, used when there is a predominant line-of-sight signal together with signals from other paths
What is the doppler shift
a shifting of frequency when a transmitter and receiver are moving relative to each other
What is beam steering
also called beamforming, is a technique that uses multiple transmitter antennas. In this technique relative amplitudes and phases of the signals from each antenna are adjusted so that when they arrive at the target receiver, they add together.
What is MIMO, multiple input multiple output
MIMO, multiple input multiple output - The use of multiple antennas at the transmitter and receiver, to provide a diversity of signal paths in space
What is power density
A term describing the distribution of power over a section of spectrum.
Power density (in W Hz-1) = power (in W) / bandwidth (in Hz).
What is the signal to noise ratio
The signal to noise ratio, is the signal power divided by the noise power. the higher the S/N ratio, the less the signal is affected by noise.
What is the sampling theorem
puts a lower limit on the rate at which samples must be taken if a signal is to be accurately reconstructed. The sampling theorem states that the signal can be exactly reconstructed from its samples if they are taken at a rate exceeding 2f samples per second
How do you find the data rate in a noise free channel
To find the data rate in bits per second, the symbol rate is multiplied by the numbers of bits that can be represented by a single symbol. 16 QAM which has 24 = 16 different symbols, can send four bits as one symbol. 64 QAM with 26 = 64 symbols can send 6 bits
How do you find the data rate in a noisy channel
As the number of symbols increases, the more difficult they are to distinguish and the more susceptible they become to corruption by noise.
Shannons equation – the theoretical max rate at which data can be transmitted in a noisy communications channel at a low error rate
What is the shannon limit
theoretical upper bound to data rate
