S5-1.5 Digital Modulation Techniques

Work through these

• Optimum receiver for binary digital modulation schemes

  The receiver that makes the best decision it can, and the reference every scheme below is measured against. Understanding it as a distance comparison in signal space makes the rest of the topic fall out rather than needing memorising.

• Binary ASK: signalling and BER

  The simplest scheme and the worst performer. It is here mainly as the baseline the other two beat, and knowing why it loses is more useful than its formula.

• Binary PSK: signalling and BER

  The best of the binary schemes at a given energy per bit. If you can say why in terms of distance between the two signals, you have understood the unit rather than memorised it.

• DPSK: signalling and BER

  Encoding the change instead of the absolute phase, so the receiver needs no coherent reference. A small penalty in error rate for a large simplification, which is an engineering bargain you will meet again and again.

• Binary FSK: signalling and BER

  The middle performer, and the one that survives amplitude disturbances best. Comparing it against the other two on the same energy per bit is the point of the exercise.

• Comparison of digital modulation schemes

  The item the whole topic exists for. Put the three error rate curves on one axis and the ordering stops being a fact to recall and becomes something you can reason out.

• Introduction to M-ary signalling; QPSK

  Sending two bits per symbol in the same bandwidth, which is the doorway to every higher order scheme in modern radio. Once you see why the constellation can be read this way, the jump to larger ones is small.

• Lab: ASK, FSK, BPSK and QPSK generation and detection

  The bench version of the topic, ending on the four-point scheme. Watching the constellation rather than the waveform is the habit worth picking up here.

• Lab: data formats and line coding techniques

  How bits become voltages before any of the above happens. Line coding decides the spectrum and whether a receiver can recover timing at all, which is overlooked often and expensive to get wrong.