JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III SPREAD SPECTRUM COMMUNICATIONS Previous Question Paper (February - 2023 - R16)

A Hybrid Direct Sequence system is a spread spectrum technique that combines two or more different spreading methods, typically Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS), within a single communication link. This combination is employed to achieve a higher processing gain and improved resistance to interference or jamming compared to using either technique individually.

A Pseudo-Noise (PN) sequence is a periodic binary sequence that exhibits properties similar to random noise while being deterministic. Its primary properties are:

• Balance Property: In each period of the sequence, the number of ones exceeds the number of zeros by exactly one. For a sequence of length N = 2ⁿ - 1, there are (N+1)/2 ones and (N-1)/2 zeros.
• Run Property: The distribution of runs (consecutive identical symbols) follows a specific pattern where half the runs are of length 1, one-fourth are of length 2, one-eighth are of length 3, and so on, for both ones and zeros.
• Correlation Property: The autocorrelation function of the sequence is two-valued. It is periodic and takes a value of 1 when the shift is a multiple of the period N, and a constant value of -1/N for all other shifts within the period.