In Data recovery( Due to some reason any data lost, LTE allows HARQ procedure to recover that data) procedure follows Soft combing.
Softcombing means, If any data received with erroors instead of discard we have to store that error data in buffers and combine this data with next re-transmitted data. so that fast recovery of original data is possible.
There are 2 types of soft combining
1) Chase Combing ::: This type of technique uses same type of information bits and parity bits for every retransmission. By combining same type of bits receiver can recover original data.
2) Incremental Redendancy ::: In this type for every retransmission some set of different bits are transmitted. In LTE, RV values we have 2,3,4,1 . These are like different set of bits. Lets assume we have 100 bits in circular buffer. RV1 ==>1-25bits, RV2=26-50, RV3=51-75,RV4=76-100. Hence for each retransmission different set of bits transmitted .