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Test

Digital Communication

Rebecca Perriment 7 preguntas

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Preguntas del test (7)

  1. 1Pulse Width Modulation PWM
    As the amplitude varies, the width of the pulse varies
    Add a [blank_start]sawtooth[blank_end] wave to the PAM signal and use the [blank_start]reference[blank_end] [blank_start]voltage[blank_end] to get the PWM signal
    1. Asawtooth
    2. Breference
    3. Cvoltage
  2. 2Pulse Positon Modulation (PPM)
    As the amplitude varies, the position of the pulse varies
    Put the PWM signal through [blank_start]monostable[blank_end] [blank_start]multivibrator[blank_end] (2 transistors) to get PPM
    1. Amonostable
    2. Bmultivibrator
  3. 3Pulse Coded Modulation (PCM)
    PCM signal is a sequence consisting of binary bits
    Take PAM signal amplitudes, [blank_start]quantise[blank_end] them and use a [blank_start]discrete[blank_end] set of quantisation levels to get PCM signal
    1. Aquantise
    2. Bdiscrete
  4. 4Multiplexing
    Allows more than one message to be transferred via the same [blank_start]communication[blank_end] channel
    Frequency division multiplexing - signals have different frequency [blank_start]bands[blank_end] in the same line, messages [blank_start]share[blank_end] channel bandwidth, messages occupy [blank_start]narrow[blank_end] bandwidth at all time
    Time division multiplexing - messages occupy [blank_start]all[blank_end] the channel bandwidth for [blank_start]short[blank_end] intervals of time, messages [blank_start]share[blank_end] channel time
    1. Acommunication
    2. Bbands
    3. Cshare
    4. Dnarrow
    5. Eall
    6. Fshort
    7. Gshare
  5. 5Time Division Multiplexing
    Due to the gaps in PAM signals, they can be inserted together to achieve TDM
    A lower pulse width (funny T) in PAM signals means [blank_start]more[blank_end] signals can fit in the [blank_start]same[blank_end] time period Ts, however this [blank_start]increases[blank_end] bandwidth
    1. Each message filtered to remove [blank_start]alias[blank_end] frequencies
    2. [blank_start]Commutator[blank_end] takes narrow sample of each and [blank_start]interleaves[blank_end] them with sample period Ts
    3. Messages converted to PAM, PWM, PPM or PCM signal
    4. Messages transmitted
    5. At [blank_start]receiver[blank_end], inverse process to recover original message
    The bandwidth can be defined as up to the first [blank_start]null[blank_end] in the frequency spectrum
    A [blank_start]narrower[blank_end] pulse width means [blank_start]larger[blank_end] bandwidth but [blank_start]more[blank_end] messages can be multiplex in the [blank_start]same[blank_end] time period
    To get TDM bandwidth:
    1. Use Nyquist sampling theorem (fs=2fmax) to get [blank_start]minimum[blank_end] sampling rate
    2. Calculate [blank_start]Ts[blank_end]
    3. Calculate Tm using Tm = [blank_start]Ts[blank_end]/[blank_start]n[blank_end] where n is the number of signals
    4. Calculate funny T (pulse width) using given equation in question
    5. Bandwidth = 1/[blank_start]2funny T[blank_end]

    1. Amore
    2. Bsame
    3. Cincreases
    4. Dalias
    5. ECommutator
    6. Finterleaves
    7. Greceiver
    8. Hnull
    9. Inarrower
    10. Jlarger
    11. Kmore
    12. Lsame
    13. Mminimum
    14. NTs
    15. OTs
    16. Pn
    17. Q2funny T
  6. 6Line Coding
    Line coding is applied before the [blank_start]modulator[blank_end] and convers the [blank_start]PCM[blank_end] signal to an [blank_start]electrical[blank_end] signal
    Unipolar return-to-zero (RZ): when 1, [blank_start]+A[blank_end] for half, [blank_start]0[blank_end] for half
    when 0, [blank_start]0[blank_end]
    Polar nonreturn-to-zero (NRZ): when 1, [blank_start]A[blank_end]
    when 0, [blank_start]-A[blank_end]
    Bipolar return-to-zero (BRZ): when 1, [blank_start]+A[blank_end] for half, [blank_start]0[blank_end] for half or [blank_start]-A[blank_end] for half, [blank_start]0[blank_end] for half
    when 0, [blank_start]0[blank_end]
    Split phase (Manchester code): when 1, [blank_start]+A[blank_end] to [blank_start]A[blank_end]
    when 0 [blank_start]-A[blank_end] to [blank_start]A[blank_end]
    The DC component is [blank_start]removed[blank_end] with AC couples transmission to avoid [blank_start]distortion[blank_end], however this causes the signal to [blank_start]exponentially[blank_end] [blank_start]decay[blank_end] after each transition.
    1. Amodulator
    2. Belectrical
    3. CPCM
    4. D+A
    5. E0
    6. F0
    7. GA
    8. H-A
    9. I+A
    10. J0
    11. K-A
    12. L0
    13. M0
    14. N+A
    15. OA
    16. P-A
    17. QA
    18. Rremoved
    19. Sdistortion
    20. Texponentially
    21. Udecay
  7. 7Channel Capacity
    Channel capacity is the [blank_start]maximum[blank_end] rate at which information can be [blank_start]transmitted[blank_end]
    Measured in [blank_start]bits[blank_end] per [blank_start]second[blank_end] (bps)
    C = [blank_start]Blog2(1+S/N)[blank_end] where S/N is the signal-to-noise ratio
    log2(x) = log10([blank_start]x[blank_end])/log10([blank_start]2[blank_end])
    1. Amaximum
    2. Btransmitted
    3. Cbits
    4. Dsecond
    5. EBlog2(1+S/N)
    6. Fx
    7. G2

Información

Descripción
(Digital Communication) Signals and Communications 1 Test sobre Digital Communication, creado por Rebecca Perriment el 22/05/2018.
Idioma
English
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