Spread Spectrum Questions And Answers

Spread Spectrum Questions And Answers

1. What is spread spectrum communication, and how does it work?

If a system meets all of the above criteria, it is classified as a spread spectrum communication system.

1. The signal takes up far more bandwidth than is required to transmit the information.

2. Spreading is performed via a data-independent spreading signal, also known as a code signal.

3. The original data is recovered by comparing the received spread signal to a synchronized copy of the spreading signal that was used to spread the data at the receiver.

2. Describe the advantages of spread spectrum systems?

Both military and civilian uses benefit from spread spectrum systems. The advantages of using a spread spectrum system are stated below.

1) Suppression of interference

2) Multiple entry points

3) Lowering the energy density

4) High-resolution time and

 5) Message privacy

3. What does Pseudonoise Sequence mean?

A coded sequence of 1s and 0s with specific autocorrelation qualities is known as a pseudo-noise (PN) sequence.

Both the transmitter and receiver are aware of the PN sequence, which is a deterministic, periodic signal. It appears to have captured white noise's statistical features. As a result, to an unauthorized listener, it looks to be a random signal.

4. What are the qualities of randomness?

A random binary sequence is one in which the existence of either the binary sign 1 or the binary symbol 0 is equally likely. Many of the qualities of a genuinely random binary sequence are shared by PN sequences. As a test for the appearance of randomness, every periodic binary sequence can be subjected to three fundamental features. They are 1) The attribute of balance 2) Correlation property and 3) Run property

5. Identify the property of balance.

The number of 1s is always one more than the number of 0s throughout each period of the sequence. The Balance property is what it is called.

6. Identify the Run Property.

One-half of the runs of 1s and 0s in each period of the sequence is one length, one-fourth are two lengths, one-eighth are three lengths, and so on. The property is called 'Run Property'.

7. Describe the property of correlation.

A sequence's autocorrelation function is binary-valued and periodic. The correlation property is the name for this property.

8. How do you make a pseudo-noise (PN) sequence?

In spread spectrum communications, the class of sequences utilized is frequently periodic, meaning that a series of 1s and 0s repeats itself perfectly with a defined time. A frequently used periodic PN sequence is represented by the maximum length sequence, a form of cyclic coding.

Maximum length sequences, also known as PN sequences, may be easily constructed using shift register circuits with feedback from one or more stages. N = 2m–1, where m is the number of shift register stages, is the length of the PN sequence.

9. What are some of the drawbacks of using a spread spectrum system?

1. Increased bandwidth for transmission

2. The complexity of the system

3. Delay in processing

10. Explain how spread spectrum modulation methods are classified.

I. Types of averaging systems

2. Avoidance type systems 1. Direct Sequence Spread Spectrum (DS-SS) System

1. Time hopping system 2. Frequency-hopping Spread Spectrum (DS-SS) system 3. Chirp

4. Hybrid Techniques

11. Define the DS-SS (Direct Sequence Spread Spectrum) technique.

The employment of a PN sequence to modulate a phase shift keyed signal allows immediate spreading of the transmission bandwidth in Direct sequence spread spectrum (DS-SS) systems.

12. What are the Direct Sequence Spread Spectrum (DS-SS) system's performance parameters?

1) Processing gain is an essential performance parameter of the Direct Sequence Spread Spectrum (DS-SS) technology. 2) Error Probability, and 3) Jamming Margin

13. Specify the amount of processing gain.

The gain produced by processing a spread spectrum signal over an unspread signal is the processing gain of a DS-SS system. It's also known as the ratio of the spread-spectrum signal's bandwidth to the bandwidth of the unspread signal.

Processing Gain (PG) = Spread Signal Bandwidth Unspread Signal Bandwidth

Also, PG = ๐‘‡๐‘๐‘‡๐‘, where Tb is the bit duration, Tc is the Chip duration

14. Calculate the DS-SS BPSK system's likelihood of error.

The DS-SS BPSK system's probability of error is

Pe = 1/2๐‘’๐‘Ÿ๐‘“๐‘√(๐ธ๐‘/๐ฝ๐‘‡๐‘)

where Eb - energy per bit

J - Average interference power

Tc - Chip duration

15. Define a Jamming Margin

The average interference power J divided by the average signal power Ps is known as the jamming margin.

Jamming Margin = ๐ฝ/๐‘ƒ๐‘  = ๐‘ƒ๐บ/๐ธ๐‘/๐‘0

where PG - Processing gain

๐ธ๐‘/๐‘0 - bit energy to noise density ratio

16. Define the FH-SS (frequency hopping spread spectrum) system.

The spectrum of the transmitted signal is spread sequentially in frequency hopping spread spectrum (FH-SS) systems by randomly hopping the data modulated carrier from one frequency to the next.

17. Identify and describe the different forms of frequency hopping.

Frequency hopping may be described in two ways, both of which are independent of technology.

1. Slow frequency hopping

We have a slow hopped signal in a frequency hopping (FH) system if the hopping is done at the symbol rate. The chip rate is identical to the symbol rate in this case.

2. Fast Frequency hopping

If there are numerous hops per symbol in a frequency hopping (FH) system, we get a quickly hopped signal. The chip rate is higher than the symbol rate in this case.

18. Define diversity in frequency hopping.

Multiple broadcasts of the same signal at various frequencies that are spaced apart in time are referred to as diversity. A signal is built with several duplicate copies, each broadcast on a different frequency, in frequency hopping with diversity. This signal has a better chance of surviving than a single similar signal.

19. Compare and contrast slow and fast hopping systems.

20. Define the term "synchronization."

Synchronization is the process of ensuring that the locally produced carrier at the receiver is in frequency and phase synchronism with the carrier at the transmitter. For successful functioning in spread spectrum communication systems, the broadcast and received PN codes must be perfectly aligned.

21. Identify and define the steps in the synchronization process.

Two methods are commonly used to synchronize the locally generated spreading signal with the incoming spread spectrum signal, They are namely:

1) Acquisition

The acquisition is the initial stage, which entails aligning the two propagating signals imperfectly.

2) Tracking

The second stage, tracking, takes over once the received spread-spectrum signal has been captured for fine alignment.

22. List the acquisition and tracking schemes

There are three distinct sorts of acquisition schemes. They are:

1. Serial Search Acquisition

2. Parallel Search Acquisition

3. Sequential Search Acquisition

Tracking comprises precision chip synchronization as well as carrier phase tracking for coherent demodulation. The most popular tracking loops are:

1. Delay-locked loop (DLL)

2. Tau-dither loop (TDL)

23. What is the definition of jamming?

Intentional disturbance in a communication system is referred to as jamming. The signaling waveform should be built in such a way that the jammer cannot obtain a significant jamming advantage by selecting a waveform and approach.

24. Create a design for an Anti-Jam (AJ) communication system.

1. The employment of direct sequence and frequency hopping spread spectrum methods to create frequency diversity.

2. Using time hoping to create variety in time.

3. The utilization of a narrow beam antenna for spatial discrimination.

25. Define ๐‘ฑ/๐‘บ Ratio

The (๐ฝ/๐‘†)๐‘Ÿ๐‘’๐‘ž๐‘‘ ratio is a merit metric that indicates how resistant a system is to interference. It is provided by:

 (๐ฝ/๐‘†)๐‘Ÿ๐‘’๐‘ž๐‘‘ = ๐‘ƒ๐บ/(๐ธ๐‘/๐ฝ๐‘œ)๐‘Ÿ๐‘’๐‘ž๐‘‘

where J - Average Received Jammer Power

S - Received Signal Power

PG - Processing Gain

(๐ธ๐‘/๐ฝ๐‘œ)๐‘Ÿ๐‘’๐‘ž๐‘‘ - bit energy per jammer noise power spectral density required for maintaining the link at a specified error probability.

26. Define Antijam margin.

The safety buffer against a certain hazard is known as the anti-jam (AJ) margin. It's described as

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.

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