ilar changes in coding schemes CS-2, CS-3 and CS-4. These changes are to provide incremental redundancy support, as will now be explained. Table 6.1 Modulation and Coding Scheme in EDGE Modulation User rate (kbps) 8-PSK 8-PSK 8-PSK 8-PSK 8-PSK EDGE: NETWORK PLANNING AND OPTIMISATION Link Adaptation and Incremental Redundancy As the propagation conditions change with time and region, the quality of the signal changes. Because of this, the modulation and coding schemes change all the time. Link adaptation is used for maximising the throughput per channel and changing the coding scheme depending upon the channel conditions. Basically, this leads to provision of the highest throughput pos- sible with the lowest amount of delay. This gives better link quality and makes EDGE a more efficient system. Link adaptation (LA) algorithms are responsible for link adaptation. These algorithms activate the LA feature based on bit-error probability (BEP) measurements. Incremental redundancy (IR) improves the throughput and is done by automatically adapting the total amount of transmitted redundancy to the radio channel conditions. This is achieved using two techniques: ARQ (automatic repeat request) and FEC (forward error cor- rection). In the GPRS system, when errors are detected in the RLC blocks, re-transmission is requested and provided until the correct information reaches the destination. FEC provides the redundant user information that is used by the receiver to correct errors caused by radio channel disturbances. However, in an EDGE system, not all the redundant information is sent immediately. Only a small amount is send at first. If decoding is then successful, this saves a lot of capacity; if decoding is unsuccessful, then the normal ARQ process takes place. Because the LA algorithm selects the amount of redundancy for each individual transmission, this process basically reduces the number of re-transmissions and subsequent delays. The re-transmission mechanism in EDGE is more efficient (than in GPRS networks) by virtu