GDMT Features:
· G.DMT has the option to allow for data transmission using bit serial synchronous transfer mode (STM) as an
alternative to ATM cell transport. ATM, and its associated ATM adaptation layers (AAL0, AAL1, AAL2,
AAL3/4, and AAL5), allows all types of traffic to be carried. The different AAL mechanisms permit the
delivery of real-time and non-real-time video, and the transport of Internet Protocol (IP) traffic, using the
point-to-point protocol (PPP) over ATM over ADSL protocol stacks. Designating ATM as the transport
mechanism ensures the robustness of G.DMT.
· ATU-R transmission of timing, synchronized to the ATU-C, is the classic method of timing a network.
· GDMT supports four framing structures. The ATU-C negotiates which framing structure to use with the ATUR
during activation, and sets itself to the reported framing structure accordingly.
· Transport of Network timing Reference (NTR). G.DMT has the capability of transport the NTR from the CO
side to the CPE side.
· G.DMT can transport two latency paths, allowing different applications, performance and robustness
services.
· Optional TCM as a combination of convolutional coding and QAM. The redundancy of convolutional coding requires more states in the TCM QAM constellation than with QAM alone. TCM uses an encoding scheme similar to the one used for QAM, but adds extra bits for its error correction work. If trellis coding had been selected on the transmit side, the data would pass through the Viterbi decoder on the receive side. The Viterbi algorithm for decoding uses the structure of the trellis (the allowable transitions) and the input data to determine the most likely path through the trellis. VOCAL G.DMT support Trellis and Viterbi.Implementations: · Full Software Implementation. Figure 2 shows the task partition for the receiver (RX) and the Transmitter
(TX) for the case of all software implementation.
Figure 2. GDMT task partition for full software implementation· Software with hardware acceleration Implementation. The hardware implementation of the TEQ needs
32 taps for the scalar transversal filter in 16 points fixed point arithmetic in a 2.208 MHz clock frequency.
This implementation is easy using serial multipliers with a low cost and low risk.
· Full hardware Implementation. Hardware implementation of the TEQ needs 32 taps for the
scalar transversal filter in 16 points fixed point arithmetic in a 2.208 MHz clock frequency. This
implementation is easy using serial multipliers with a low cost and low risk. Hardware
implementation of the 512 points real, 64 points complex FFTs is in 16 points fixed point
arithmetic with a 2.208 MHz clock frequency using efficient Radix 8 with serial multipliers with a
low cost and is available as a core from many vendors. Hardware implementation of the Reed-
Solomon decoder uses the Berlekamp-Massey decoder with a standalone syndrome calculation. the
algorithm uses a log domain table look-ups to implement the GF(256) multiplies with a low cost and is
available as a core from many vendors
