LTE Physical Downlink Shared Channel PT. Fusi GLobal Teknologi Indonesia

1. DL-SCH/PDSCH
Astrini Kusumawardhani
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2. Outline
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Introduction
DL-SCH and PDSCH Encoding
DL-SCH and PDSCH Decoding
Smoke Test PDSCH
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3. Introduction
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4. Introduction
Figure 1. The radio interface protocol architecture and the SAPs between different layers.
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5. Introduction
Figure 2. Mapping Transport Channel to Physical Channels
Figure 3. Mapping Control Information Channels to Physical Channels
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6. DL-SCH and PDSCH
Encoding
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7. DL-SCH/PDSCH Encoding Scheme
Figure 4. DL-SCH/PDSCH Processing Scheme
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8. Pre-processing before DL-SCH Encoding (1)
1. MAC sends MCS and data to DL-SCH.
Example:
MCS = 1, Data.data = random, Data.size = 100, BW = 10 Mhz.
2. Determine RBG size (based on Table 7.1.6.1-1 [36.213])
BW = 10 MHz
NRB = 50
So, RBG size = 3.
3. Determine RBG bitmap available
N_RBG = NRB / RBG_size = 50 / 3 = 17
4. Determine I_TBS and Qm from MCS (based on Table 7.1.7.1-1 [36.213])
MCS = 1
So, Qm = 2, I_TBS = 1
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9. Pre-processing before DL-SCH Encoding (2)
5. Determine N_PRB and TBS, from I_TBS and data.size
I_TBS = 1
Data.size = 100
Find, TBS near 100 then get TBS = 208.
For TBS =208, get N_PRB = 6.
6. Determine allocated RBG
RBG_allocated = N_PRB / RBG_size = 6 / 3 = 2.
7. Determine RBG Bitmap
1000000001000000000000000
RBG allocated
8. Encoding PCFICH (to inform UE about how many symbols the DCI spans in that
subframe) : CFI = 3
9. Encoding PDCCH (to encode DCI that carries information related to
downlink/uplink scheduling assignment )
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10. Review Pre-processing
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MCS = 1
Data.data = random; Data.size = 100
BW = 10 MHz; NRB = 50
RBG_size = 3
N_RBG = 17
I_TBS = 1; Qm = 2
TBS = 208; N_PRB = 6
RBG_allocated = 2
RBG_bitmap = 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Figure 5. Pre-processing Result
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11. DL-SCH Encoding (1)
1. Add CRC
CRC24A:
B = TBS + CRC = 208 + 24 = 232 bits.
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12. DL-SCH Encoding (2)
2. Code Segmentation
For this example:
B = 232
So,
L=0
C+ = 1; K+ = 232
C- = 0; K- = 0
B = 232; Z = 6144
if (B≤Z)
{ L = 0; C = 1; B’ = B}
if (B>Z)
{ L = 24;
if(C==1)
{C+ = 1; K+ = B ;
C- = 0; K- = 0 }
if(C>1)
{C*K+ ≥ B’ ; K- < K+ ;
; C+ = C – (C-) }
; B’ = B + C.L}
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13. DL-SCH Encoding (3)
3. Channel Coding – Turbo Coding
Code Rate = input / output = 1/3
Turbo coding consists of:
1. Constituent Encoders
2. QPP Interleaver
= 1* 3 = 3 rows
= 0* 3 = 0 rows
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14. DL-SCH Encoding (4)
4. Rate Matching – Turbo Rate Matching
Turbo rate matching steps:
1. Sub-interleaver
2. Bit-collection
3. Bit-Selection
What is desired code-rate?
Input
: 3*col
Output : lte_tch_param.G
Code-rate = input / output
lte_tch_param.G = ???
For this example:
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15. DL-SCH Encoding (5)
5. Code Block Concatenation
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16. Review DL-SCH Encoding
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17. PDSCH Encoding (1)
1. Scrambling
Using pseudo-random sequence generation.
Pattern:
Scrambling initialization is performed in each frame, using :
Total output = 1284 bits.
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18. PDSCH Encoding (2)
2. Modulation
QPSK, 16QAM, 64QAM
MCS = 1
Qm = 2
based on Qm.
QPSK
Total output = 642 symbols.
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19. PDSCH Encoding (3)
3. Resource Element Mapping
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20. Review PDSCH Encoding
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21. DL-SCH and PDSCH
Decoding
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22. DL-SCH/PDSCH Decoding Scheme
PDSCH
DL-SCH
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23. PDSCH Decoding
1.
Resource Element Demapper
2.
Demodulation Mapper
Using Soft-Demodulation, which are bit 0 = negative and bit 1 = positive.
3.
Descrambling
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24. Pre-Processing before DL-SCH Decoding
1. MAC sends MCS, RBG bitmap, RBG size, and BW.
MCS = 1; RBG bitmap = 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ;
RBG size = 3; BW = 10 MHz.
2. Calculate N_PRB = RBG_allocated * RBG_size = 2 * 3 = 6.
3. Determine I_TBS and Qm from MCS . Then, get TBS.
I_TBS = 1 and Qm = 2
TBS = 208
4. Determine code-block segmentation
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25. DL-SCH Decoding
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26. Smoke Test PDSCH
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27. Smoke Test PDSCH
Result :
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28. References
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Standard 3GPP TS 36.211 V9.1.0 (2010-03) – Physical Channels and Modulation.
Standard 3GPP TS 36.212 V9.3.0 (2010-09) – Multiplexing and Channel Coding.
Standard 3GPP TS 36.213 V9.3.0 (2010-09) – Physical Layer Procedures.
Jing Zhu, Haitao Li. (2011). “On The Performance of LTE Physical Downlink Shared Channel”.
International Conference on Computer Science and Network Technology.
5. http://www.steepestascent.com/content/mediaassets/html/LTE/Help/PDSCH.html
6. http://www.sharetechnote.com/html/BasicProcedures_LTE.html
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