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Takács György

Infokommunikációs rendszerek – Infocommunication Systems Lecture 4 . előadás Kódolás, nyalábolás, kapcsolás Coding, multiplexing, switching. Takács György. Where we are now in study (tele -, info- ) communications systems?. Networks are working systems of terminals, nodes and links

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Takács György

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  1. Infokommunikációs rendszerek – Infocommunication SystemsLecture 4. előadásKódolás, nyalábolás, kapcsolásCoding, multiplexing, switching Takács György Infocom. 4. ea 2014. 09. 29.

  2. Where we are now in study (tele-, info-) communications systems? • Networks are working systems of terminals, nodes and links • The basic technologies in links (wireline and wireless) have been discussed • Node functions (multiplexing, switching, signalling, demultiplexing) will be discussed today Infocom. 4. ea 2014. 09. 29.

  3. Infocom. 4. ea 2014. 09. 29.

  4. Infocom. 4. ea 2014. 09. 29.

  5. Analog modulation systems- (AM) • Amplitude modulation • The momentary amplitude of the carrier is proportional to the momentary amplitude of the modulating signal Infocom. 4. ea 2014. 09. 29.

  6. Analog modulation systems- (AM) Infocom. 4. ea 2014. 09. 29.

  7. The spectrum of the AM in the case of discrete fm modulation frequency Infocom. 4. ea 2014. 09. 29.

  8. Frequency modulation systems- (FM) • The momentary frequency of the carrier is proportional to the momentary amplitude of the modulating signal Infocom. 4. ea 2014. 09. 29.

  9. Frequency modulation systems- (FM) Infocom. 4. ea 2014. 09. 29.

  10. The spectrum of FM modulated signal in the case of discrete fm modulation frequency Infocom. 4. ea 2014. 09. 29.

  11. Digital modulation methods – Amplitude Shift Keying (ASK) Infocom. 4. ea 2014. 09. 29.

  12. Digital modulation methods – Binary Phase Shift Keying (BPSK) Infocom. 4. ea 2014. 09. 29.

  13. Generation of BPSK  Carrier signal ~ x BPSK 1 0 0 1 +1 -1 t Infocom. 4. ea 2014. 09. 29.

  14. Digital modulation methods – Constellation Diagram / BPSK Infocom. 4. ea 2014. 09. 29.

  15. Eye diagram as a basis for demodulation of BPSK signal Eye diagram Received BPSK signal 1,0,1,0 comparator x ∫ Carrier signal Infocom. 4. ea 2014. 09. 29.

  16. Digital modulation methods –Qadrature Phase Shift Keying (QPSK) • Two carriers: sine wave (Q) and cosine wave (I) • The modulated signal is the sum of the two components • One symbol is two bits Infocom. 4. ea 2014. 09. 29.

  17. Digital modulation methods –Qadrature Phase Shift Keying (QPSK) Infocom. 4. ea 2014. 09. 29.

  18. Digital modulation methods –Qadrature Phase Shift Keying (QPSK) Infocom. 4. ea 2014. 09. 29.

  19. Digital modulation methods –Qadrature Phase Shift Keying (QPSK) 1 Infocom. 4. ea 2014. 09. 29.

  20. Digital modulation methods –Qadrature Amplitude Modulation (QAM) • Two carriers: sine wave (Q) and cosine wave (I) • The modulated signal is the sum of the two components • Different amplitude and differnt phase values for one symbol • 16QAM means: one symbol is four bits Infocom. 4. ea 2014. 09. 29.

  21. Digital modulation methods –Qadrature Amplitude Modulation (16QAM) Infocom. 4. ea 2014. 09. 29.

  22. Digital modulation methods –Qadrature Amplitude Modulation (16QAM) Infocom. 4. ea 2014. 09. 29.

  23. Digital modulation methods –Qadrature Amplitude Modulation with channel noise Infocom. 4. ea 2014. 09. 29.

  24. Why to use sophisticated modulations -- like QAM? • To put more bits into the standard medium • twisted pair cable –ADSL, Gigabit Ethernet, • coaxial cable – digital TV, HDTV, INTERNET, • Radio – GSM, satellite TV and radio program broadcasting • Efficient use of spectum (the radio spectrum is a limited resource) Infocom. 4. ea 2014. 09. 29.

  25. Bit error rate as a function of signal to noise ratio using BPSK modulation Infocom. 4. ea 2014. 09. 29.

  26. Channel capacity as a function of signal to ratio at different modulation system. The reference is the BPSK Infocom. 4. ea 2014. 09. 29.

  27. Multiplexing vs. switching City A Trunks for active calls only City B 103 105 105 Infocom. 4. ea 2014. 09. 29.

  28. Multiplexing principles • To reduce transmission costs • To utilize higher bandwidth • „Framing” and „packing” of information • TDM -- Time Division Multiplexing • FDM -- Frequency Division Multiplexing • CDMA -- Code Division Multiple Access • WDM -- Wavelength Division Multiplexing • Mixed Infocom. 4. ea 2014. 09. 29.

  29. TDM principles I. PCM frame (Pulse Code Modulation) 4.50 ábra 125 µs Infocom. 4. ea 2014. 09. 29.

  30. TDM principles II. PDH hierarchy Plesiochronous Digital Hierarchy 4.51 ábra Infocom. 4. ea 2014. 09. 29.

  31. TDM principles III. PDH hierarchy 4.51 ábra Infocom. 4. ea 2014. 09. 29.

  32. SDH hierarchy • SDH – Synchronous Digital Hierarchy • VC – Virtual Container (multiplexing level) • STM-N Synchronous Transport Modules (line signal level) • POH – path overhead (control and supervisory information) • POH+Payload=VC • A number of VCs can packaged into a larger VC Infocom. 4. ea 2014. 09. 29.

  33. Transport modules • RSOH – Regenerator Section Overhead • MSOH – Multiplexer Section Overhead • AU Pointer – Administrative Unit Pointer (specifies where the payload starts) • Duration of STM-1 module is 125 µs Infocom. 4. ea 2014. 09. 29.

  34. General Transport Module 4.56. ábra Infocom. 4. ea 2014. 09. 29.

  35. Infocom. 4. ea 2014. 09. 29.

  36. Infocom. 4. ea 2014. 09. 29.

  37. SDH Network elements DXC – Digital Cross Connect ADM – Add-drop Multiplexer TM – Terminal multiplexer Infocom. 4. ea 2014. 09. 29.

  38. Example of a physical network Infocom. 4. ea 2014. 09. 29.

  39. FDM principles Infocom. 4. ea 2014. 09. 29.

  40. TDM/FDM channel architecture as used in GSM Infocom. 4. ea 2014. 09. 29.

  41. FDM in Cable TV network (US Standard) Infocom. 4. ea 2014. 09. 29.

  42. Variable bit-rate data transfer within TDM time-slots Infocom. 4. ea 2014. 09. 29.

  43. The Spread Spectrum Concept Infocom. 4. ea 2014. 09. 29.

  44. General Model of Spread Spectrum Digital Communication System Infocom. 4. ea 2014. 09. 29.

  45. Frequency_Hopping Spread Spectrum FHSS Infocom. 4. ea 2014. 09. 29.

  46. FHSS • A number of channels are allocated for FH • The transmitter operates in one channel at a time for fixed time interval (Tc) • During that interval, some number of bits or a fraction of a bit are transmitted (signal elements) • The time interval of signal elements Ts • The sequence of the channels used is dictated by spreading code • Both transmitter and receiver use the same code to tune into a sequence of channels in synchronisation Infocom. 4. ea 2014. 09. 29.

  47. Transmitter of the FHSS System Infocom. 4. ea 2014. 09. 29.

  48. Receiver of the FHSS System Infocom. 4. ea 2014. 09. 29.

  49. Slow FHSS using Multi Frequency Shift Keying Tc>Ts (in this case 4 subfrequencies for 2 bits) Infocom. 4. ea 2014. 09. 29.

  50. Fast FHSS using Multi Frequency Shift Keying Tc<Ts (in this case 4 subfrequencies for 2 bits) Infocom. 4. ea 2014. 09. 29.

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