The combination of the convolutional coding and modulation scheme,
known as Trellis-Coded Modulation (TCM), can achieve significant coding gain
without reducing the data rate or requiring more bandwidth.
The TCM can be found in many communication systems such as CCITT modems (V.17, V.32, etc), wireless,
xDSL or IEEE 802.3ab Gigabit Ethernet.
The general purpose TCM decoder IP core is using the 8-PSK & 16/32/64-QAM signal constellation
and an 8-state systematic encoder for subset selection. The information bits recovery method is the Viterbi algorithm.
The register-exchange method is implemented
and the survivor memory length is parameterizable, according with performance required.
Also the trace-back decoding method can be available.
In the Radix-4 Add-Select-Compare Unit, modulo-normalization or simple normalization
for the accumulated path metrics can be used.
The register-exchange/trace-back process is controlled by a finite state machine.
The TCM decoder IP core can be relatively easy to modify for the IEEE 802.3ab Gigabit Ethernet standard.
In this case a 4D PAM-5 modulation scheme is employed. The multi-dimensional modulation requires another approach for
the Branch Metrics Unit: 2D BMU diagram ,
4D BMU diagram .
Selectable modulation: 8-PSK or 16/32/64-QAM
8-states TCM encoder, rate R=2/3
Register Exchange decoding method for lower latencies