B1P3 - The real world: noise, interference and coexistence

Question 1

additive white Gaussian noise (AWGN)

Answer 1

additive noise that is normally distrubuted over the spectrum and which can also model real noise;

Question 2

aliasing

Answer 2

when the sampling frequency < 2*f;

‘alias’ not real name of a person)A.to(bad sample not real rep of frequency

Question 3

beam steering

Answer 3

where multiple-transmitter-antennas ‘steer’ signals in such a way that they constructively interfere thereby improving reception at the receiver;

Question 4

channel capacity

Answer 4

how many bits can be transmitted through the channel per second;

Question 5

cognitive radio

Answer 5

a device that can find free spectrum and avoid other radio signals;

Question 6

Doppler shift

Answer 6

the frequency shift that occurs in the signal when a transmitter and receiver are moving towards or away from each other;

Question 7

electromagnetic compatibility (EMC)

Answer 7

where electronic devices can coexist without interference;

Question 8

fast fading

Answer 8

where a signal takes different paths but with the paths destructively interfering with each other;

Question 9

frequency diversity

Answer 9

where the signal is spread over a range of frequencies thereby increasing the signal’s resilience;

Question 10

hidden station problem

Answer 10

where two stations both transmit to a third station without being aware of each other’s transmissions;

Question 11

log-normal fading

Answer 11

use of the log-normal distribution (_|_) to model slow fading;

Question 12

multiple input multiple output (MIMO)

Answer 12

where multiple antennas are used at transmitter and receiver to provide a diversity of signal paths;

Question 13

power density

Answer 13

describes the distribution of power over an interval of spectrum; units = W Hz^-1;

Question 14

Rayleigh fading

Answer 14

models a subset of fast fading where there is no predominant line-of-sight signal;

Question 15

Rician fading

Answer 15

models a subset of fast fading where there is a predominant line-of-sight signal;

Question 16

sampling theorem

Answer 16

if we sample an analogue signal with frequency f at a rate of >= 2*f, then the original signal can be reconstructed from the samples;

Question 17

Shannon limit

Answer 17

the maximum rate at which bits can be transmitted in a noisy communications channel:

C = W*log_2(1+(S/N)) bit s^-1

Question 18

slow fading

Answer 18

where the signal strength varies due to receiver moving around and hence varying the quality of the signal path;

Question 19

spatial diversity

Answer 19

where there are multiple paths between transmitter and receiver;

Question 20

spatial multiplexing

Answer 20

where 2+ streams of data can be sent via multiple paths between transmitter and receiver without using additional spectrum;

Question 21

spectral envelope / mask

Answer 21

a limit on the power that can be transmitted in and around a channel; set by the government to reduce interference;

Question 22

white space

Answer 22

unused or freed-up spectrum;