Practical issues with TCM

TCM is now used extensively in modern high-speed telephone and radio modems. For example, a 28.8 kbps dial-up modem (V.34 standard) can use up to 1408-QAM, with a 16-state, rate 2/3 code.
There are some practical issues to note with TCM:
  • Increasing the number of symbol states may incur an implementation penalty as well as the theoretical Eb/N0 penalty, requiring greater amplitude and phase accuracy in the TX/RX system.
  • More symbol states may result in an increased peak to mean ratio for the transmit hardware to cope with.
  • When TCM systems are operated in very poor signal conditions, they 'fall over' much more rapidly than the uncoded equivalent throughput system.