f a chase combining HARQ scheme and how the re-transmission of the same coded bits change the combined energy per bit (Eb) while maintaining the effective code rate intact. 2. Type II HARQ: in the original type II HARQ scheme, an alternate parity/user data re-transmission scheme is used. With the proper choice of channel encoder, the user information may also be recovered by parity bits. However, most type II algorithms adopt an incremental parity re- transmission scheme, in which only additional parity bits are sent in subsequent re- transmissions. Therefore, after each re-transmission, a richer set of parity bits is available at the receiver, improving the probability of reliable decoding. In incremental schemes; however, information cannot be recovered from parity bits alone. In an Incremental Redundancy (IR) HARQ scheme, a number of coded bits with increasing redundancy, where each represents the same set of input bits, are generated and transmitted to the receiver when a re-transmission is requested, to assist the receiver with the decoding of the information bits. The receiver combines each re-transmission with the previously received bits 7.2 Hybrid automatic repeat request functions Information Bits CRC Insertion Information Bits Mother Code Rate = R Channel Coded Bits Transmitted Bits Transmitted Bits Transmitted Bits Transmitted Bits Initial Transmission 1st Retransmission 2nd Retransmission Nth Retransmission Input Bits to Decoder Combined Energy Effective Coding Rate Chase Combining HARQ Information Bits CRC Insertion Information Bits Mother Code Rate = R Channel Coded Bits Puncturing to Generate Different Redundancy Versions Initial Transmission 1st Retransmission 2nd Retransmission Redundancy Version 1 Redundancy Version 2 Redundancy Version 3 Input Bits to Decoder Combined Energy Effective Coding Rate 3/2 R Incremental Redundancy HARQ FIGURE 7-6 An example illustration of the operation of chase combining and incremental redundancy HARQ schemes [12] belonging to the same packet. Since each re-transm