In the context of direct sequence spread spectrum, the term 'processing gain' describes the relationship between which two quantities?

• A. Carrier frequency to data rate.
• B. Transmitter power to receiver sensitivity.
• C. Chipping rate to data rate.
• D. Modulation index to coding rate.

Answer: (C)

In direct-sequence spread spectrum, processing gain measures how much the signal is spread by the pseudorandom code. It is the ratio of the chipping rate (how fast the spreading code changes) to the data rate (how fast the actual information bits are sent). This means how many chips are used to represent each data bit. For example, if the chip rate is 4 Mbps and the data rate is 1 kbps, the processing gain is 4000 (about 72 dB), indicating a large improvement in resilience to noise after the signal is despread. The higher the chip rate relative to the data rate, the greater the processing gain and the better the system can suppress interference. The other options don’t describe this relationship between spreading and data rate.