Nowadays, broadband satellite systems are requested to provide high bit rates to the end user in order to support new multimedia services with QoS capabilities.
If the rate estimate is too low, more bits are requested.
If the decoded bitplane CRC corresponds to the original data CRC, then the decoding process is considered successful; otherwise, more parity bits are requested.
In this way, when more syndrome bits are requested by the decoder, the already received bits can be reused in the next decoding attempt, see Figure 1.
The success of the channel decoding algorithm is determined by module 8b; if the decoding algorithm does not converge, more parity bits are requested using the feedback channel.
Further bits are requested until the estimated bit error rate drops below a given threshold, then each coefficient value is reconstructed using a minimum mean square error estimator, and the IDCT returns the decoded Wyner-Ziv frame.
Syndromes (blocks of syndrome bits) are requested one by one through the feedback channel, and the requests are stopped when a sufficiently reliable decoded result is reached, see Figure 1.
In [12], adaptive validation is also introduced: for a small subset of the WZ frames, the parity bits are requested for correct inter-view and temporal SIs, introducing an overhead.
Indeed, more accurate SI at the decoder implies that fewer bits are requested from the encoder through a feedback channel, so that the bitrate is reduced for the same quality.
For the performance's comparison, we define the throughput of the traditional ACK/NACK ARQ scheme as B c o r r e c t B T. And the throughput of our relay-assisted IDMA partial retransmission scheme as B c o r r e c t B T + B f e e d b a c k, where B feedback includes all information describing which set of bits are requested for retransmission.
