What is the effect of increasing the order of QAM on BER at a fixed SNR?

• A. Higher order QAM reduces BER at fixed SNR.
• B. Higher order QAM requires a constant SNR.
• C. Higher order QAM increases bits per symbol; increases BER at fixed SNR.
• D. Higher order QAM uses fewer constellation points and reduces BER.

Answer: (C)

Increasing the order of QAM means packing more constellation points into the same signal space, so each symbol carries more bits. At a fixed SNR, the constellation points are closer together, and the channel noise makes it more likely that the received point is mistaken for a neighboring symbol. That higher probability of symbol error translates into more bit errors as well, especially since each symbol now represents more bits. So you get the benefit of more data per symbol (higher bits per symbol) but at the cost of higher BER for the same SNR. The other statements don’t fit because higher order QAM does not reduce BER or require a fixed SNR; it increases the necessary SNR to maintain the same BER, and it uses more, not fewer, constellation points.