Question E8C11:
What is the relationship between symbol rate and baud?  

Choices:  
A: They are the same  
B: Baud is twice the symbol rate  
C: Baud rate is half the symbol rate  
D: The relationship depends on the specific code used    

Correct Answer is  A: They are the same  

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Correct answer: A — They are the same.

1) Why this is correct:
- Baud is defined as the number of symbols (signal changes) per second.
- Symbol rate is the number of symbols transmitted per second.
- Therefore, by definition, baud = symbol rate.

2) Why the other choices are incorrect:
- B: “Baud is twice the symbol rate” — Incorrect. There is no general 2:1 relationship. This confusion often arises from mixing up bit rate with symbol rate in specific modulations.
- C: “Baud rate is half the symbol rate” — Incorrect for the same reason; there is no general 1:2 relationship.
- D: “Depends on the specific code used” — Incorrect. Coding and modulation affect how many bits each symbol carries, but they do not change the equality: baud = symbol rate.

3) Useful formulas and rules of thumb:
- Baud (symbol rate): $$R_s = \text{symbols per second}$$
- Bit rate and symbol rate: $$R_b = R_s \times \text{(bits per symbol)}$$
- For $M$-ary modulation (e.g., $M$-PSK, $M$-QAM): $$\text{bits per symbol} = \log_2(M), \quad \Rightarrow \quad R_b = R_s \log_2(M)$$
- Example: QPSK ($M=4$) carries 2 bits/symbol, so $R_b = 2 R_s$.

Key takeaway: baud measures symbols per second, not bits per second.