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311 introduction to communication system

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311 introduction to communication system

  1. 1.  Electronic communication system Transfer info from one place to another Is the transmission, reception and processing of information between two or more locations using electronic circuits  3 main components of communication system: Transmitter Channel Receiver
  2. 2.  Transmitter – circuit/device which converts original source info to a form more suitable for transmission  Medium/channel – provides means of transporting signal between transmitter and receiver  Noise – unwanted signals that interfere with the info signal  Receiver – circuit/device which accepts transmitted signals and converts them back to their original form
  3. 3.  Two types:  Guided propagation  Free propagation
  4. 4.  Signal = set of information/data represented by mathematical functions of time  System will process a set of signals (i.e. inputs) to produce another set of signals (i.e. outputs)
  5. 5. 1. Continuous-time and discrete-time signals 2. Analog and digital signals 3. Periodic and non-periodic signals 4. Even and odd signals
  6. 6.  Continuous-time signal: Specified at every value of time t. Represented by x(t).  Discrete-time signal: Specified at separate values of time. Represented by x[n]. Continuous-time signal Discrete-time signal
  7. 7.  Binary signal Is a type of digital signal Has only two possible levels (‘high’, or ‘low’)
  8. 8.  Periodic signal: Signal that repeats itself over a time period T. Otherwise, it is non-periodic  A continuous-time periodic signal satisfies the condition x(t) = x(t ± T), where T is the period  A discrete-time periodic signal satisfies the condition x[n] = x[n + N], where N is the period
  9. 9.  Relationship between period, T and frequency, f: frequency, f = 1 T
  10. 10.  Even Signal A signal that is identical to its reflection about the origin Symmetric about the vertical axis x(-t) = x(t), or x[-n] = x[n]  Odd signal Symmetric about a line midway between the vertical axis and the negative horizontal axis and passing through the coordinate origin Signal is zero at the origin, and -x(-t) = x(t) or -x[-n] = x[n]
  11. 11.  Decibel (dB) – to define power ratios, voltage ratios or current ratios  Note: ö ÷ ÷ø æ dB P ç çè = 1 P 2 10log10 Power levels P1 and P2 must be in same units + dB  power gain - dB  power loss (attenuation) 0 dB  unity power gain (i.e. P1 = P2)
  12. 12.  Given P1/P2 = 100. Convert this absolute power ratio to dB
  13. 13.  Convert 23 dB to absolute power ratio
  14. 14.  Decibel milliwatt (dBm) – a unit of measurement to indicate the ratio of a power level with respect to a fixed reference level i.e. 1 mW dBm P ö çè ÷ø = æ mW 1 10log10
  15. 15.  Convert 200 mW to dBm

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