Thursday, November 27, 2014

LTE FDD DL code rate calculation

1. Formula to calculate DL code rate for a non-special subframe (No PSS, SSS, PBCH is transmitted) is as follows:

Code Rate = (input bits+ CRC bits)/(numOfRes * Q')

In above equation,

input bits = tbs + parity bits (3GPP 36.212 5.1)
tbs is mapped to tables in 3GPP 36.213 7.1.7.2, depending on transmission configuration. I.E. number of layers.
parity bits = CRC overhead = 24 bits (For LTE PDSCH)
CRC bits = CRC overhead * numberOfCodeblock (3GPP 36.212 5.1)
numberOfCodeBlock = ceilt[input bits/(Z - L)] where Z = 6144, L = CRC overhead = 24
numOfRes (in 1ms) = [( NRBsc  * NDLsymb * 2 ) - NRBsc - numberOfResOccupiedByAntennaPortsPerPRB ] * NPRB
Q' = 6 bits for PDSCH (64QAM)


2. For PCFICH = 01 (CFI = 1), TM3, NPRB = 50 (10MHz), NRBsc = 12, NDLsymb = 7:
numberOfResOccupiedByAntennaPortsPerPRB = 12
MCS28 -> tbs = 36696 bits
CRC bits = 24 * ceil[(36696+24)/6120] = 144 bits
Q' = 6 bits (64QAM)

numOfRes (in 1ms) = [(12 * 7 * 2) - 12  - 12 ] * 50
                                 = 144 * 50 = 7200

=> DL code rate = (36696 +24 + 144)/(7200 * 6) = 0.853 < 0.931 (3GPP.36.213 7.1.7)


2. For PCFICH = 01(CFI = 1), TM7, NPRB = 50 (10MHz), NRBsc = 12, NDLsymb = 7:
numberOfResOccupiedByAntennaPortsPerPRB = 12 (antenna ports 0, 1) + 12 (antenna ports 5 or 7 and 8)

MCS28 -> tbs = 36696 bits
CRC bits = 24 * ceil[(36696+24)/6120] = 144 bits
Q' = 6 bits (64QAM)

numOfRes (in 1ms) = [(12 * 7 * 2) - 12  - 24 ] * 50
                                 = 132 * 50 = 6600

=> DL code rate = (36696 +24 + 144)/(6600 * 6) = 0.9309 < 0.931 (3GPP.36.213 7.1.7)
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10 comments:

  1. UnknownMarch 3, 2016 at 11:05 AM

    Dear River He,

    thanks for your post. I wonder how the 36696 bits in your example, from table 7.1.7.2.2-1-1 in document 3GPP TS 36.213 are calculated. How many OFDM symbols do they consider per RB?

    Thank you. Best regards,

    Natalia.

    ReplyDelete
    Replies
    1. UnknownJune 25, 2016 at 6:09 AM

      Hi.

      I am confused about how the Transport Block Size Table is generated, and I guess it has an assumption of the REs in an RB.

      Are you get the answer? If you get one, please help me.

      Thank you, best regards/

      Delete
    2. UnknownJune 26, 2016 at 1:54 PM

      please can you send the reference material '7.1.7.2.2-1-1 in document 3GPP TS 36.213' to my email magajisuleiman1203@gmail.com

      thanks

      Delete
  2. River HeMarch 8, 2016 at 6:05 AM

    This comment has been removed by the author.

    ReplyDelete
  3. River HeMarch 8, 2016 at 6:06 AM

    Hi Natalia,

    Thanks for reading my post. Unfortunately, I don't have a clear answer to your question. To the best of my knowledge, the maximum tbs is reverse calculated based on pre-defined coderate (which is chipset decoding capability limited) and available REs for PDSCH in LTE resource grids. Perhaps a standard specialist could help you on this topic.


    Regards

    River He

    ReplyDelete
    Replies
    1. UnknownJune 26, 2016 at 1:58 PM

      please can you send the reference material '7.1.7.2.2-1-1 in document 3GPP TS 36.213' to my email magajisuleiman1203@gmail.com

      thanks

      Delete
  4. UnknownOctober 5, 2016 at 6:37 PM

    Dear River He,

    Thanks for your post. I wonder how to get NumOfREs in more detail.
    numOfRes (in 1ms) = [( NRBsc * NDLsymb * 2 ) - NRBsc - numberOfResOccupiedByAntennaPortsPerPRB ] * NPRB

    You took NRBsc from that. Is it due to CFI? And what is numberOfResOccupiedByAntennaPortsPerPRB? How can I get the value?

    Thanks,
    Richard.

    ReplyDelete
  5. River HeOctober 11, 2016 at 6:22 AM

    Hi Richard,

    The NRBsc is from 3GPP definition. It is 12 subcarriers in this article.
    The numberOfResOccupiedByAntennaPortsPerPRB is calculated based o n the antenna ports number. Minimum is 2. Please refer to following link for graphical view.
    http://dhagle.in/LTE

    Regards

    River He

    ReplyDelete
  6. UnknownJuly 10, 2019 at 1:08 AM

    very good example. wonder to know how is your calculation method evolve to cover NR.

    ReplyDelete
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