Bob,
In GPRS/EGPRS, there are different coding schemes, such as CS1 to CS4 in GPRS and MCS1 to MCS9 in EGPRS.
Each scheme provides a different useful throughput and a different protection ratio.
High tput with low protection or low tput with high protection.
As soon as the BLER becomes bad, the retransmissions rate increase… But then the link adaptation mechanism kicks in and the coding scheme is decreased, in order to provide more protection. The system choses to decreae the useful tput in order to give more protection.
As a direct consequence, the impact of bad BLER decreases. Retransmission rates are reduced, the receiver is able to decode the useful signal even under bad BLER conditions.
So you see, each coding scheme can accept a certain BLER. And this value for each CS can be found in 3GPP-something 🙂 (radio aspects I think)
Pan, our 3GPP master, what’s the ref number? 45 something? :))