Digital Communications Subcategories

Osi Model Security 1	Protocols
And Network Synchronization	Optical Switching Networks

Coherent modulation requires ____ level of synchronization.

A. One
B. Two
C. Three
D. None of the mentioned

Explanation: Coherent modulation requires three levels of synchronization – phase symbol and frame.

Non coherent system requires

A. Phase synchronization
B. Frequency synchronization
C. Phase & frequency synchronization
D. None of the mentioned

Explanation: Non coherent system requires frequency synchronization.

For block codes _____ is necessary.

A. Phase synchronization
B. Frequency synchronization
C. Frame synchronization
D. None of the mentioned

Explanation: Frame synchronization is necessary when the information is organized in blocks or messages of some uniform number of symbols. Thus block code needs frame synchronization.

The synchronization necessary for BPSK is

A. Frequency tracking
B. Bit timing
C. Phase tracking
D. All of the mentioned

Explanation: Non coherently detected BPSK is the simplest digital receiver and it requires frequency tracking, bit timing synchronizations and also phase synchronization.

Transmitter synchronization implies

A. One way communication
B. Two way communication
C. One & two way communication
D. None of the mentioned

Explanation: Transmitter plays a role in synchronization by varying the frequency and timing of its transmissions to correspond to expectation of receiver. This transmitter synchronization implies two way communication.

As the synchronization levels increases, cost

A. Decreases
B. Increases
C. Remains the same
D. None of the mentioned

Explanation: For each level increase in synchronization levels, cost increases.

Synchronization is used in system which has

A. Non coherent modulation techniques
B. Many users accessing
C. Non coherent modulation techniques & many users accessing
D. None of the mentioned

Explanation: For communication system using non coherent modulation techniques and many users accessing the central communication node, synchronization is necessary.

Which method has fast acquisition and can work without return link?

A. Open loop method
B. Closed loop method
C. Open & closed loop method
D. None of the mentioned

Explanation: The main advantage of open loop method is that acquisition is fast, the procedure can work without return link and the amount of real time computation that is required is small.

Which method has two way link?

A. Open loop method
B. Closed loop method
C. Open & closed loop method
D. None of the mentioned

Explanation: Closed loop method requires return link, large amount of real time processing and has two way link.

Which method requires external authority and is inflexible?

A. Open loop method
B. Closed loop method
C. Open & closed loop method
D. None of the mentioned

Explanation: Open loop method is inflexible, does not adjust quickly to unplanned changes and needs external authority that provides prior knowledge, where as closed loop method does not need all these.