 (and/or associated PCIe bandwidth for save/restore operation). For large transport blocks, HARQ buffer is about 25KB per CB. Since this is a large amount of RAM, the 5G standard has a fea- ture that allows for reduced HARQ RAM usage. This feature is called LBRM and is defined in 3GPP TS 38.212 Section 5.4.2.1. Using LBRM the HARQ RAM usage goes down to about 12.5KB per CB. On code block versus transport block level CRC On the first transmission the forward error correction acceleration (FECA) engine verifies both the CB and TB level CRCs. However, in retransmit scenarios, the TB CRC is not explic- itly (re-)verified by the FECA engine. This opens the question of (error) performance rate-what is the chance that a corrupted TB is passed as correct to the MAC layer? To analyze this scenario, start by plotting Bit Error Rate (BER) (wrongly decoded bit) ver- sus both CB and TB error rates as shown in Fig. -13 below: HARQ operation assumes (in typical operation) a approximately 10% TB error rate. This is the target TB error rate to which transmit power, modulation and Forward Error Correction rates are tuned by the scheduler algorithm. Chapter 3 Hardware system dimensioning CB and TB Error Rate 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09 1.0E-10 TB Error Rate CB Error Rate FIGURE 3-13 Code block (CB) and transport block (TB) error rate as a function of bit error rate (BER). The above chart implies a BER of somewhere between 10 6 and 10-7 We assume 10-6 as the nominal operating point. In this scenario: The CB Error Rate (the probability that a CB has at least lbit error) is calculated as: CB_error_rate = 1-(1-BER)CB_size = 1-(1-10-6)8448 = 8.4 X 10-3. The TB Error Rate (the probability that a CB has at least lbit error) is approximated as: CB_error_rate X num_CBs_in_TB = 8.4 X 10-3 X 55 = 0.46. CRC24B = 0xC00031 is used for CB CRC which has a Hamming distance of 4 over Payload length up to 8M bits. Therefore, all combinations of 3-bit errors will be detected but some combinations of 4-bit errors may