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I'm trying to understand QAM transmission and I'm struggling to understand this sentence, 'The advantage of using QAM is that it is a higher order form of modulation and as a result it is able to carry more bits of information per symbol. By selecting a higher order format of QAM, the data rate of a link can be increased. Article here'
Could someone explain what the term 'higher order form of modulation' means. Does it mean that the carrier frequency is higher?
Higher order modulation means with each use of the channel, you transmit more bits. For example, in $8-$ary QAM, 3 bits are transmitted in each channel use. In other words, each 3 bits are mapped to one of the 8 available waveforms to be transmitted over the channel. If you use $16-$ary QAM, then 4 bits are transmitted with each channel use. In general, for $M-$ary QAM, $\log_2(M)$ bits are transmitted with channel use. The larger $M$, the more bits are transmitted per channel use. However, as $M$ increases, the distance between the constellation points decreases, and this means that the probability of error increases. So, there should be a trade-off between the constellation size, and the probability of error.
