JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III SPREAD SPECTRUM COMMUNICATIONS Previous Question Paper (August/September - 2024 - R16)

Spread spectrum is a communication technique in which the transmitted signal occupies a bandwidth much larger than the minimum bandwidth required to transmit the information. This is achieved by spreading the signal over a wide frequency band using a spreading code, which improves resistance to interference, jamming, and multi-path fading.

A spreading code (or pseudo-noise code) is a deterministic, high-bit-rate sequence of 1s and 0s that appears random but is known to both the transmitter and receiver. It is used to modulate the information signal, thereby increasing its bandwidth and allowing for secure, multiple-access communication.

Gold codes offer several distinct advantages in spread spectrum communication systems, primarily due to their correlation properties:

• Large Set Size: Unlike m-sequences, which have a limited number of sequences for a given shift register length, Gold codes provide a much larger set of sequences. This allows for a greater number of unique codes, which is essential for supporting multiple users in Code Division Multiple Access (CDMA) systems.
• Bounded Cross-Correlation: Gold codes exhibit a well-defined and bounded cross-correlation property. This ensures that interference between different users is kept at a predictable, low level, which significantly improves the signal-to-interference ratio and system capacity.
• Ease of Generation: They are generated by the modulo-2 addition of two preferred m-sequences with the same length. This structure allows for efficient hardware implementation using simple shift registers and XOR gates, making them highly practical for real-time communication hardware.