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In a direct-sequence CDMA system, the chip rate is \(1.2288\times 10^6\) chips per second. If the processing gain is desired to be at least 100, the data rate

1. must be less than or equal to 12.288 × 10³ bits per sec
2. must be greater than 12.288 × 10³ bits per sec
3. must be exactly equal to 12.288 × 10³ bits per sec
4. can take any value less than 122.88 × 10³ bits per sec

Correct answer: must be less than or equal to 12.288 × 10³ bits per sec

Solution

In DS-CDMA, processing gain is \(G_p=R_c/R_b\). With chip rate \(R_c=1.2288\times10^6\) chips/s and \(G_p\ge100\), the data rate must satisfy \(R_b\le1.2288\times10^6/100=12.288\times10^3\) bits/s.

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