DC 6 Flashcards
What is signal encoding in digital communications?
Signal encoding is the process of converting digital data into a form suitable for transmission over a communication medium, involving techniques like amplitude, frequency, or phase modulation.
What are the primary types of digital encoding?
The primary types of digital encoding include:
Non-Return to Zero (NRZ): No change in signal between bits.
Manchester Encoding: Combines clock and data in the same signal.
Differential Manchester Encoding: Signal transitions represent data changes, not absolute values.
What is NRZ encoding and its variations?
NRZ encoding keeps the signal level constant during the bit period. Variations:
NRZ-L (Level): Logic 1 is represented by one voltage level, and logic 0 by another.
NRZ-I (Inversion): Logic 1 causes a change in voltage level, logic 0 causes no change.
What is Manchester encoding?
Manchester encoding combines clock and data. A transition in the middle of each bit period represents a bit, with a high-to-low transition for logic 1 and low-to-high for logic 0.
What is Differential Manchester encoding?
In Differential Manchester encoding, a transition at the start of each bit period represents a clock signal. A transition in the middle indicates data: a high-to-low transition for logic 0, and a low-to-high transition for logic 1.
What is Biphase encoding, and its significance in networking?
Biphase encoding involves using two transitions per bit, ensuring synchronization. It’s used in environments like LANs for reliable data transmission.
What is scrambling in signal encoding?
Scrambling replaces sequences that would cause constant voltage (such as long zeros) with filling sequences, ensuring synchronization without increasing the data rate.
What is B8ZS encoding used for?
B8ZS is used in North America for digital signal transmission, replacing long strings of zeros with specific patterns, ensuring synchronization and preventing loss of signal.
What is HDB3 encoding used for?
HDB3 encoding is used in Europe and Japan for bipolar AMI (Alternate Mark Inversion) encoding, replacing four consecutive zeros with specific patterns to avoid synchronization issues.
What factors impact the performance of digital-to-analog modulation schemes?
The key performance factor is bandwidth. ASK and PSK have bandwidth directly related to the bit rate, while MPSK (Multilevel PSK) can improve bandwidth efficiency.
How does digital data get converted to analog signals?
Digital data is converted to analog signals using modulation techniques such as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK).
What is QPSK and how does it improve bandwidth usage?
QPSK uses phase shifts separated by 90°, allowing two bits to be transmitted per symbol, effectively doubling the data rate compared to BPSK.
How is analog data converted to digital signals for transmission?
Analog data is digitized using codecs, specifically via Pulse Code Modulation (PCM) or Delta Modulation (DM), converting the data into a digital format for transmission.
What is Pulse Code Modulation (PCM)?
PCM involves sampling analog data and quantizing the samples into binary codes. It provides a clear digital representation of analog signals.
What is Delta Modulation (DM)?
DM is a method where an analog signal is approximated by a staircase function, with each step representing a binary value, tracking changes in the signal.
