hile the standard GSM forward error correction mechanisms (e.g. bit interleaving across TDMA bursts) are already applied in EGPRS, the focus here will be on the additional LA capability of EGPRS that significantly improves link performance and dynamically compensates for changing fading environments. Given a typical fading environment (as illustrated in Figure 2.87), EGPRS throughput and latency will be affected based on the forward error correction (FEC) of its current MCS. As the fading changes, a different MCS may be more appropriate either to increase the throughput due to less bit errors or to increase the FEC to compensate for additional bit errors. The link adaptation of EGPRS allows a full range of nine modulation coding schemes to adjust to changing channel conditions. However, one of the most critical aspects in link adaptation is the change from GMSK to 8-PSK. As discussed previously, Radio Network Planning and Optimisation Table 2.26 GPRS/EGPRS coding schmes, modulation, FEC and bit rate Coding Modulation RLC blocks/ Bit rate scheme radio block code rate User bits/20 ms [bps] 12 000 14400 20 000 EGPRS MCS-1 MCS-2 11 200 MCS-3 14 800 MCS-4 17600 MCS-5 8-PSK 22 400 MCS-6 29 600 MCS-7 448 + 448 44800 MCS-8 544 + 544 54400 MCS-9 592 + 592 59200 there is a decrease in average power (assuming the initial GMSK link is at full power) with this change in modulation and this directly leads to increased TBF failures in threshold link level areas. Specifically, setting up the TBF in GMSK and then changing to 8-PSK could cause a link loss for each attempt at establishing a TBF. Table 2.26 outlines the modulation, forward error correction and channel bit rate for all GPRS and EGPRS modulation coding schemes. Considering the objective of maximising the bit rate and minimising latency, the following key considerations must be made when optimizing link adaptation settings to compensate for channel performance (focusing on the MCS-4 and MCS-5 boundary): LLC Frames (FER) RLC Blocks (BLER) Coding TDMA Bursts (FEC, Bit In