Understanding Signal Conversion - Digital and Analog Conversion
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The document discusses the conversion between digital and analog signals, highlighting techniques such as Pulse Code Modulation (PCM) and various modulation methods for transmitting data. It explains the processes of sampling, data transmission modes, and different types of multiplexers while detailing the pros and cons of each modulation technique. Additionally, it covers transmission media, including guided and unguided mediums like twisted pair cables, coaxial cables, and fiber optics, emphasizing their characteristics and applications.
Understanding Signal Conversion - Digital and Analog Conversion
- 1. Digital and Analog Conversion PCM, Sampling, Modulation, and Bandwidth Utilization
- 2. Analog-to- digital Conversion A digital signal is superior to an analog signal because it is more robust and noise can easily be recovered, corrected, and amplified. For this reason, the tendency today is to change an analog signal to digital data. In this section, we describe two techniques: • Pulse Code Modulation (PCM) • Delta Modulation (DM)
- 3. Pulse Code Modulation (PCM) PCM is a method that is used to convert an analog signal into a digital signal so that the modified analog signal can be transmitted through the digital communication network. PCM consists of three steps to digitize an analog signal: • Sampling • Quantization • Binary encoding
- 4. Sampling Sampling is a process of measuring the amplitude of a continuous-time signal at discrete instants. Sampling is also recognized as Pulse Amplitude Modulation (PAM)
- 5. Types of Sampling Three different sampling methods for PCM Ideal sampling Amplitude Natural sampling Amplitude Flat-top sampling Amplitude
- 6. Nyquist theorem The sampling rate must be at least 2 times the highest frequency contained in the signal. Telephone companies digitize voice by assuming a maximum frequency of 4000 Hz. The sampling rate therefore is 8000 samples per second.
- 7. Digitize the human voice The human voice normally contains frequencies from 0 to 4000 Hz. The sampling rate and bit rate are calculated as follows: Sampling rate= 4000 X 2 = 8000 samples/s Bit rate = 8000X 8 = 64000 bps = 64 kbps
- 8. Transmission modes •Serial transmission •Parallel transmission Data transmission refers to the process of transferring data between two or more digital devices. There are two modes used to transmit data between digital devices:
- 9. Serial Transmission Serial data transmission sends data bits one after another over a single channel.
- 10. Serial transmission occurs in one of three ways Asynchrono us Synchronous Isochronous
- 11. Asynchronous Usually 1-byte of Data send at one time Start and Stop bit are exist Data transmission speed and cost slow and low
- 12. Synchronous Usually, Multiple bytes of Data send at one time Start and Stop bit do not exist Data transmission speed and cost slow and low fast and high
- 13. Isochronous Transmission occurs at regular intervals Fixed gap between transmission of two data items
- 14. Parallel Transmission Parallel data transmission sends multiple data bits at the same time over multiple channels.
- 15. DIGITAL-TO-ANALOG CONVERSION We need to convert analog to digital and digital to analog signal because most of the devices operate with digital signals. Concerning them, data in analog form needs to be modified in a digital signal. Besides, we cannot send a digital signal by air because most of the communication channels use air as a communication medium. Therefore, we need to change digital signals to an analog to make it travel by air.
- 16. Carrier Wave A carrier signal or carrier wave is a sine wave that is modulated with an input signal to carry information because the carrier signal contains a higher frequency than the given input signal.
- 17. Digital-to-Analog conversion techniques Amplitude- Shift Keying (ASK) Frequency- Shift Keying (FSK) and Phase- Shift Keying (PSK)
- 18. ASK VS FSK VS PSK In Amplitude-Shift Keying (ASK), carrier signals amplitude modifies proportionally with the information signal and produces a digitally modulated signal. And if frequency modifies proportionally with an information signal, then frequency shift keying (FSK) is produced. Alike, the phase of the carrier signals modifies proportionally with the information signal than phase-shift keying (PSK) is produced.
- 19. Pros and Cons of ASK Both modulation and de- modulation processes are easy. It has a simple receiver design. Error probability is high. Performance in the presence of noise is poor.
- 20. Pros and Cons of FSK It has a lower probability of error. Performance in the presence of noise is better than ASK. FSK modulation and de-modulation both processes are moderately complex. It uses larger bandwidth compared to other modulations.
- 21. Pros and Cons of PSK Performance in presence of noise better than FSK Error probability is low. It has lower bandwidth efficiency. Detection and recovery algorithms are complex.
- 22. Baseband Baseband is the original frequency range of a transmission signal before it is modulated. It modulates carrier signals to generate a broadband analog signal.
- 23. Bandpass Bandpass is a range of frequencies that are transmitted through a bandpass filter to remove unwanted frequencies. If the available channel is a bandpass channel, analog data must be converted to an analog signal by Analog-to-analog conversion before transmission.
- 25. Amplitude Modulation (AM) The power level of the information signal changes the amplitude of the carrier signal in proportion to generate the modulated signal
- 26. Frequency Modulation (FM) The power level of the information signal changes the frequency of the carrier in proportion to generating the modulated signal. The bandwidth of frequency modulation is high, 10-times higher than signal frequency.
- 27. Phase Modulation (PM) The power level of the information signal only changes the phase of the carrier signal to generate the modulated signal.
- 28. Two Station Broadcasts In One Station • Sometimes we receive one radio broadcast on another station because we know radio-wave has three parts, frequency, amplitude, and wavelength. • Each radio station produces a specific set of frequencies that radio device antenna collects and radio tuners lockdown them to present the information. If the turner failed to lockdown or frequencies are collided with unwanted noise, we can hear two station broadcasts in one station
- 29. The bandwidth utilization The bandwidth utilization is the amount of bandwidth utilized from the total bandwidth available. Multiplexing helps to reach maximum efficiency of bandwidth utilization. It is a set of techniques that combined multiple signals into one signal over a shared medium.
- 30. Analog to Digital and Digital to Analog We need to convert analog to digital and digital to analog signal because most of the devices operate with digital signals. Concerning them, data in analog form needs to be modified in a digital signal. Besides, we cannot send a digital signal by air because most of the communication channels use air as a communication medium. Therefore, we need to change digital signals to an analog to make it travel by air.
- 31. Types of Multiplexers • Frequency Division Multiplexing (FDM) • Wavelength Division Multiplexing (WDM) • Time Division Multiplexing (TDM) FDM and WDM are analog multiplexing and TDM is digital multiplexing.
- 32. Frequency Division Multiplexing (FDM) The communication channel is divided by frequency. It requires complex connections to the transmitter and receiver. FDM uses analog signals.
- 33. Guard Band A guard band is an additional part of FDM that prevents Signals from overlapping and helps each signal to remain separate.
- 34. Wavelength Division Multiplexing The communication channel is divided by wavelength. It requires complex connections to the transmitter and receiver. WDM uses optical signals.
- 35. Time Division Multiplexing (TDM) The communication channel is divided by time. It does not require complex connections to the transmitter and receiver. TDM uses digital and analog signals.
- 36. Transmission Media In network communications, a Transmission Media is a physical connection or an interface between the transmitter and the receiver.
- 37. Transmission Media Types Guided Transmission Medium Unguided Transmission Medium
- 38. Guided Transmission Medium Guided Transmission Medium refers to a physical path for transmission.
- 39. Guided Transmission Medium Twisted pair cable Coaxial cable Fiber optics
- 40. Twisted Pair Cable • The purpose of twisting the wire in a twisted pair cable because it eliminates Electromagnetic Interference (EMI). • Electromagnetic Interference generates noise or interference that corrupts data. • The Shielded Twisted Pair uses a metallic shield that prevents external resistance for better performance.
- 41. Unshielded Twisted Pair Cable • Unshielded Twisted Pair Cable does not use an external layer as shields or jackets. • Unshielded twisted pair cable costs cheaper and does not require much maintenance. • Unshielded twisted pair cable data rates slow comparatively shielded twisted pair cable. • Noise and error are comparatively high.
- 42. Shielded Twisted Pair Cable • Shielded twisted pair cable uses an external layer as shields or jacket. • Shielded twisted pair cable costs moderately expensive. • Shielded twisted pair cable provides high data rates. • Less noise and error
- 43. Coaxial Cables • We use coaxial cables when the distances are high, otherwise fiber optics. Coaxial cables performance is comparatively low, and its setup is easier than fiber optic. • The design of coaxial cable consists of a copper wire that is surrounded by additional layers that shielding as an outer protective jacket to prevent damage to the signal. As a result, it transmits high-frequency signals at low loss.
- 44. Fiber optics To pass data through the optical fiber, we use modulation of data into an analog signal and transmit it as light, so it reflects frequently until the data reached the receiver. Registered Jack 45 or RJ45 is the most common twisted- pair connector.
- 45. Thanks