Question

A direct sequence spread spectrum technique uses 10 flip-flop linear feedback shift register as PN code generator. The jamming margin produced by the system will be

• A. 10 dB
• B. 20 dB
• C. 30 dB
• D. 40 dB

Hint:

In a DSSS system, jamming margin is directly proportional to processing gain. If the length of the register is n, the processing gain is equal to \(2^n - 1\), approximately equal to \(2^n\).

Answer 1

The Correct Option is C

In a direct sequence spread spectrum (DSSS) system, the processing gain of the system is calculated as the length of the PN sequence or the number of chips. If n flip-flops are used, the length of the PN sequence is \( 2^n - 1\). The jamming margin, is equal to the processing gain in dB, and is equal to the 10 times log10 of the processing gain. For 10 flip flops, the processing gain (approximately equal to the jamming margin) will be: \[ Processing \, Gain = 2^{10} - 1 = 1023 \] \[ Jamming \, Margin = 10 log_{10} 1023 \approx 10 \times 3 = 30 dB \] Therefore the jamming margin is approximately equal to 30 dB.