d continues with fresh transmission of the same code block. A number of parallel channels for HARQ can help improve the throughput as one process is awaiting an acknowledgment; another process can utilize the channel and transmit subpackets. Fig. 4.54 illustrates the operation of chase combining HARQ (HARQ-CC) scheme and how the retransmission of the same coded bits changes the combined energy per bit Eb while maintaining the effective code rate intact. 2. HARQ with incremental redundancy: In this HARQ scheme, additional parity bits are sent in subsequent retransmissions. Therefore, after each retransmission, a richer set of parity bits is available at the receiver, improving the probability of reliable decoding. In incremental redundancy schemes, however, information cannot be recovered from parity New Radio Access Physical Layer Aspects (Part 2) 541 Information bits CRC insertion Information bits Minimum 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 Minimum 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 4.54 Illustration of the chase combining and incremental redundancy HARQ schemes 15]. bits alone. In incremental redundancy HARQ (HARQ-IR) scheme, a number of coded bits with increasing redundancy are generated and transmitted to the receiver when a retransmission is requested to assist the receiver with the decoding of the information bits. The receiver combines each retransmission with the previously received bits belonging to the same packet. Since each retransmission carries additional parity b