261
coding required at decoding by the UE before mapping to the Physical Channel and sending.
Since error correction encoding can be added as the ratio (Code Rate) between the Information Bit count (number
of CRC bits added to TBS), which is the size of the user data, and the Physical Channel Bit count with PDSCH per
Subframe becomes smaller, the Rx data error correction performance increases.
The above described ratio (Code Rate) is defined below.
Code Rate = Information Bit count/Physical Channel Bit count
The 3GPP TS 36.213 7.1.7 Modulation order and transport block size determination notes that "The UE may skip
decoding a transport block in an initial transmission if the effective channel Code Rate is higher than 0.930, where
the effective channel code rate is defined as the number of downlink information bits (including CRC bits) divided
by the number of physical channel bits on PDSCH". As a result, when the DL-SCH Code Rate sent from the BTS
exceeds 0.93, the UE cannot decode DL-SCH and returns an error (NACK).
Example: When Channel Coding = RMC and Antenna Config. = 2x2 MIMO (OpenLoop)
Tables B.1.2-1 and B.1.2-2 below show the MCS Index value and Code Rate at Full RB Mapping for each bandwidth.
Table B.1.2-1 shows the value for Subframe #0 and Table 4 for Subframe #1-4, and #6-9.
Depending on the MCS Index setting, sometimes the UE may be unable to decode DL-SCH if the Code Rate exceeds
0.930. Subframe #0 can be decoded by a smaller MCS Index than other subframes.
As shown in Fig. B.1.2-1, there are non-PDSCH Physical Channels PBCH, PSS, and SSS in Subframe #0, so the PDSCH
region is smaller than other subframes.
Table B.1.2-1. Relationship between Subframe#0 MCS Index Value and Code Rate
The UE can decode DL-SCH at the MCS Index where the Code Rate is 0.930.
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