What happens to the data throughput when transitioning from quadrature phase shift keying (QPSK) to 16-QAM (quadrature amplitude modulation) in a channel of the same bandwidth?

When transitioning from quadrature phase shift keying (QPSK) to 16-QAM in a channel of the same bandwidth, the data throughput effectively doubles. This occurs because QPSK encodes data by varying the phase of the signal to represent two bits of information per symbol, while 16-QAM uses both phase and amplitude variations to encode four bits of information per symbol.

In practical terms, 16-QAM allows for more data to be transmitted in the same amount of time because it increases the number of distinct symbols that can be sent within the same bandwidth. By going from a system that can send two bits per symbol to one that can send four bits per symbol, the overall capacity of the channel is improved, leading to a doubling of data throughput without increasing the required bandwidth.

Thus, the advantage of using 16-QAM over QPSK enables more efficient utilization of the available bandwidth, which is why the correct answer reflects this increase in throughput.