Week 4 Flashcards
Spread Spectrum (14 cards)
Explain Modulation
Process where information signal is modulated with carrier signal to generate a encrypted signal to be sent.
Type of Modulation
- Analog
- Digital
In Analog modulation, what type are there with explaination
- Amplitude: Tweak carrier signal to fit information signal amplitude
- Frequency: Increase frequency on part of signal with information
- Phase:
In Digital modulation, what type are there, with explaination
- Amplitude Shift Keying: If there is bit 1, increase amplitude, else maintain
- Phase Shift keying: Binary, Quadrature, 16-256
Name the factor which affect maximum data rate
- Data rate limitation
- Bandwidth: Limited by transmitter and nature of communication medium
- Noise: Noise surrounding network
- Error rate
What is Nyquist Bandwidth and formula
- Use to explain free-noise channel
C=2B *Log_2(L)
C = Channel Capacity
B is the available Bandwidth
L is the number of signal levels (elements)
What is Shannon Channel capacity and formulaw
- Explain no noise free channel
- C=B*log_2(1+2/n)
C is the channel capacity in bits per second;
B is the bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal);
S is the total received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e.
modulated carrier), measured in watt or volt2;
N is the total noise or interference power over the bandwidth, measured in watt or volt2; and
S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the
Gaussian noise interference expressed as a linear power ratio (not as logarithmic decibels)
What is the frequency ranges of 2.4Ghz
2.400-2.4835 Ghz
Higher bandwidth means more data
What is FHSS
Frequency Hopping Spread Spectrum
What FHSS does
FHSS is a radio transmission technique used to allow carrier signal rapidly switches between different frequency channels in a pseudorandom sequence
When there is interference happen in a frequency, it will hop to the next available frequency instead, preventing interference, security
What is DSSS
Direct-sequence Spread Spectrum
What DSSS does
Modulation technique used, spread data over wider frequency band.
It does two process, Tx and Rx.
Tx focuses on encoding the digital signals, goes through multiplier with code bits, then pass through RF modulator to be spread
Rx focuses on decoding the frequency, pass through code bits and multiplier to get back digital signal
What is OFDM
Orthogonal Frequency-Division Multiplexing
How OFDM works
OFDM distributes data over large number of
carriers that are spaced apart at precise
frequencies to provide ”Orthogonality”
This allows frequency sent to not interfere with each other at the receiver, making it a efficient technique. Used in 5Ghz
