In digital data transmission, a line code should have the following properties (A) Transmission bandwidth should be as small as possible (B) Transmitted power should be as high as possible (C) Transmission bandwidth should be as high as possible (D) Transmitted power should be as low as possible Choose the correct answer from the options given below:
(A) and (D) only
Understanding Line Code Properties in Digital Transmission
In digital data transmission, line coding is the process of converting digital data (a sequence of bits) into a digital signal that can be transmitted over a communication medium. The properties of the chosen line code significantly impact the performance and efficiency of the transmission system.
Let's analyze the given properties:
- (A) Transmission bandwidth should be as small as possible: Bandwidth is the range of frequencies occupied by the signal. In communication systems, bandwidth is a valuable and often limited resource. Using less bandwidth for transmitting data allows for more efficient use of the frequency spectrum, potentially allowing more signals to be transmitted simultaneously or reducing the complexity of filtering required. Therefore, minimizing transmission bandwidth is a desirable property for a line code.
- (B) Transmitted power should be as high as possible: Transmitted power relates to the energy used to send the signal. High power consumption is generally inefficient and costly. Also, high power signals can cause interference to other communication systems. For efficient and environmentally friendly communication, keeping the transmitted power low while ensuring reliable reception is preferred. So, high transmitted power is not a desirable property.
- (C) Transmission bandwidth should be as high as possible: As discussed in point (A), high bandwidth usage is inefficient. A line code that requires high bandwidth is less desirable compared to one that uses less bandwidth for the same data rate.
- (D) Transmitted power should be as low as possible: As explained in point (B), minimizing transmitted power is beneficial for efficiency, cost, and reducing interference. This is a desirable property for a line code.
Based on this analysis, the desirable properties for a line code in digital data transmission are having a transmission bandwidth that is as small as possible and transmitted power that is as low as possible.
Comparing this with the options, the correct combination of desirable properties is (A) and (D).
| Property | Description | Desirable? |
|---|---|---|
| (A) Small Bandwidth | Efficient use of frequency spectrum | Yes |
| (B) High Power | High energy consumption, potential interference | No |
| (C) High Bandwidth | Inefficient use of frequency spectrum | No |
| (D) Low Power | Low energy consumption, reduced interference | Yes |
Key Properties of Line Codes
Beyond low bandwidth and low power, other important properties of a good line code include:
- DC component: Ideally, the line code should have a zero DC component to avoid power waste and allow transmission through transformers.
- Clock recovery: The signal should contain enough transitions to enable the receiver to easily recover the timing clock.
- Error detection capability: Some line codes incorporate mechanisms for detecting errors.
- Spectral characteristics: The power spectral density should be concentrated at frequencies suitable for the transmission medium.
- Cost and complexity: The coding and decoding process should be relatively simple and inexpensive to implement.
Revision Table: Digital Transmission Concepts
| Term | Meaning | Relevance to Line Codes |
|---|---|---|
| Line Code | Mapping of digital data bits to a digital signal waveform. | Determines the signal properties like bandwidth, power, DC component. |
| Bandwidth | Range of frequencies the signal occupies. | Lower bandwidth is generally preferred for efficiency. |
| Transmitted Power | Energy used to send the signal. | Lower power is preferred for efficiency and less interference. |
| DC Component | Average value of the signal over time. | Zero DC component is desirable to avoid power loss and allow AC coupling. |
| Clock Recovery | Ability to extract the timing information from the received signal. | Transitions in the signal are needed for effective clock recovery. |
Additional Information on Line Codes
Various line coding schemes exist, each with different properties. Examples include Unipolar, Polar (NRZ, RZ), Bipolar (AMI, Pseudoternary), Manchester, and Multilevel schemes (like MLT-3, 2B1Q). The choice of a specific line code depends on the requirements of the transmission system, such as the desired data rate, available bandwidth, noise levels, and the type of transmission medium (e.g., twisted pair, coaxial cable, fiber optic). Modern communication systems often use complex line coding schemes optimized for specific performance metrics like spectral efficiency, power efficiency, and error resilience.
Important Questions from Introduction To Digital Modulation
If the in‐phase and quadrature components in an M‐ary PSK system are permitted to be independent, then this scheme becomes a:
Which of the following statements are correct?
A. M‐ary modulation scheme is preferable where the bandwidth requirement is important.
B. M‐ary PSK system considers 'M' different phases in the range 'π/2'.
C. In M‐ary modulation scheme, only coherent detection is possible.
D. M‐ary QAM scheme uses 'm 2' carrier signals having the same frequency.
Choose the correct answer from the options given below:
In digital communication, Inter Symbol Interference (ISI) is a form of distortion where one symbol interferes with subsequent symbols. An eye diagram is used to study the extent of ISI in a communication channel. Which of the following is FALSE?
The data rate of QPSK is ______ as that of BPSK for the same symbol rate.
In ASK modulation:
