JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III SPREAD SPECTRUM COMMUNICATIONS Previous Question Paper (March - 2024 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
(25 Marks)
What are pseudo noise sequences in spread spectrum systems?
Answer
A Pseudo Noise (PN) sequence is a deterministic, periodic binary sequence that exhibits statistical properties similar to those of true random noise, despite being generated by a predictable algorithm. In spread spectrum systems, these sequences are used to spread the signal bandwidth and provide secure communication by ensuring that only receivers with the identical synchronized code can recover the original information.
Define key terms such as feedback polynomial, tap positions, and shift register length in relation to binary shift register sequences.
Answer
In the context of linear feedback shift registers (LFSR) used for generating binary sequences, the key terms are defined as follows:
- Shift Register Length (n): This refers to the total number of memory stages (flip-flops) in the register. It determines the maximum possible period of the generated sequence, which is 2n - 1 for a maximal-length sequence.
- Feedback Polynomial: This is a characteristic polynomial, typically denoted as f(x), that defines the feedback logic of the register. It represents the linear combination of register stages that are XORed together to produce the input bit for the first stage.
- Tap Positions: These are the specific indices of the shift register stages that are selected to be fed back into the XOR gate network. The tap positions correspond to the non-zero coefficients of the feedback polynomial.
What is the objective of optimum tracking of wideband signals?
Answer
Sign in to view the complete answer paper.
How does a double dither non-coherent tracking loop differ from a traditional coherent tracking loop?
Answer
Sign in to view the complete answer paper.
How does synchronization using a matched filter work for initial synchronization of the receiver spreading code?
Answer
Sign in to view the complete answer paper.
What are the main challenges associated with synchronization by estimating the received spreading code?
Answer
Sign in to view the complete answer paper.
What is the purpose of Cellular Code Division Multiple Access (CDMA) in cellular communication systems?
Answer
Sign in to view the complete answer paper.
How does CDMA impact network architecture and infrastructure, including cell planning and handoff procedures?
Answer
Sign in to view the complete answer paper.
What is the performance of Spread Spectrum Systems without coding?
Answer
Sign in to view the complete answer paper.
What is the use of Viterbi Algorithm?
Answer
Sign in to view the complete answer paper.
Part B
(50 Marks)
Explain the fundamental concepts of spread spectrum systems. How do they differ from traditional communication systems?
Answer
Sign in to view the complete answer paper.
Describe the principles and operation of Direct Sequence Spread Spectrum (DSSS). How does DSSS achieve signal spreading and interference rejection?
Answer
Sign in to view the complete answer paper.
Introduce Gold codes as a specific type of binary shift register sequences. Explain their construction using two M-sequences and the use of different time offsets to generate a family of unique sequences. Discuss the benefits of Gold codes in spread spectrum applications.
Answer
Sign in to view the complete answer paper.
Explain the principle behind the tau-dither non-coherent tracking loop and how it estimates the timing phase of the spreading code.
Answer
Sign in to view the complete answer paper.
Design an innovative tracking algorithm that combines multiple techniques to achieve optimum tracking of wideband signals in spread spectrum systems.
Answer
Sign in to view the complete answer paper.
Evaluate the effectiveness of a double dither non-coherent tracking loop in mitigating the effects of noise, interference, and other impairments in spread spectrum systems, considering its ability to maintain accurate code synchronization under challenging conditions.
Answer
Sign in to view the complete answer paper.
Develop a comprehensive evaluation framework to compare the performance of different base band delay-lock tracking loop designs, considering metrics such as tracking accuracy, acquisition time, and robustness to impairments.
Answer
Sign in to view the complete answer paper.
Describe the concept of an optimum synchronizer for initial synchronization of the receiver spreading code, including its working principle and advantages.
Answer
Sign in to view the complete answer paper.
Explain the maximum likelihood estimation approach for synchronization by estimating the received spreading code and discuss its advantages and potential limitations.
Answer
Sign in to view the complete answer paper.
Discuss the components and operation of a Cellular CDMA system, including base stations, mobile stations, spreading codes, and the role of the control channel.
Answer
Sign in to view the complete answer paper.
Discuss interference cancellation techniques in multi-user detection, such as Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) cancellation, and their impact on reducing interference and improving system performance.
Answer
Sign in to view the complete answer paper.
Discuss the challenges and considerations involved in designing and implementing spread spectrum systems without coding, including synchronization, interference mitigation, and receiver design.
Answer
Sign in to view the complete answer paper.
Discuss the Bit-Error Rate (BER) calculation in convolutional coding, considering factors such as the channel model, code rate, and modulation scheme.
Answer
Sign in to view the complete answer paper.
Describe the optimum decoding rule in block coding and its importance in error detection and correction.
Answer
Sign in to view the complete answer paper.