DL-SCH/PDSCHAstrini Kusumawardhani

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Outline

• Introduction• DL-SCH and PDSCH Encoding• DL-SCH and PDSCH Decoding• Smoke Test PDSCH

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Introduction

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Introduction

Figure 1. The radio interface protocol architecture and the SAPs between different layers.

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Introduction

Figure 2. Mapping Transport Channel to Physical Channels

Figure 3. Mapping Control Information Channels to Physical Channels

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DL-SCH and PDSCHEncoding

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DL-SCH/PDSCH Encoding Scheme

Figure 4. DL-SCH/PDSCH Processing Scheme

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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])

3. Determine RBG bitmap availableN_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])

BW = 10 MHzNRB = 50So, RBG size = 3.

MCS = 1So, Qm = 2, I_TBS = 1

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Pre-processing before DL-SCH Encoding (2)

5. Determine N_PRB and TBS, from I_TBS and data.size

6. Determine allocated RBG RBG_allocated = N_PRB / RBG_size = 6 / 3 = 2.

7. Determine 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

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 )

I_TBS = 1Data.size = 100Find, TBS near 100 then get TBS = 208.For TBS =208, get N_PRB = 6.

RBG allocated

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Review Pre-processing• 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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DL-SCH Encoding (1)

1. Add CRC

CRC24A:

B = TBS + CRC = 208 + 24 = 232 bits.

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DL-SCH Encoding (2)2. Code Segmentation

B = 232; Z = 6144

if (B≤Z) { L = 0; C = 1; B’ = B}

if(C==1) {C+ = 1; K+ = B ; C- = 0; K- = 0 }

if (B>Z) { L = 24; ; B’ = B + C.L}

if(C>1) {C*K+ ≥ B’ ; K- < K+ ; ; C+ = C – (C-) }

For this example:B = 232

So,L=0C+ = 1; K+ = 232C- = 0; K- = 0

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DL-SCH Encoding (3)3. Channel Coding – Turbo Coding

= 1* 3 = 3 rows

= 0* 3 = 0 rows

Code Rate = input / output = 1/3

Turbo coding consists of:1. Constituent Encoders2. QPP Interleaver

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DL-SCH Encoding (4)4. Rate Matching – Turbo Rate Matching

Turbo rate matching steps:1. Sub-interleaver2. Bit-collection3. Bit-Selection

What is desired code-rate?Input : 3*colOutput :

lte_tch_param.G

Code-rate = input / outputlte_tch_param.G = ???

For this example:

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DL-SCH Encoding (5)5. Code Block Concatenation

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Review DL-SCH Encoding

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PDSCH Encoding (1)

1. ScramblingUsing pseudo-random sequence generation.Pattern: Scrambling initialization is performed in each frame, using :

Total output = 1284 bits.

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PDSCH Encoding (2)

2. ModulationQPSK, 16QAM, 64QAM based on Qm.MCS = 1 Qm = 2 QPSK

Total output = 642 symbols.

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PDSCH Encoding (3)3. Resource Element Mapping

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Review PDSCH Encoding

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DL-SCH and PDSCHDecoding

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DL-SCH/PDSCH Decoding Scheme

PDSCH

DL-SCH

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PDSCH Decoding

1. Resource Element Demapper

2. Demodulation MapperUsing Soft-Demodulation, which are bit 0 = negative and bit 1 = positive.

3. Descrambling

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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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DL-SCH Decoding

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Smoke Test PDSCH

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Smoke Test PDSCH

Result :

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References1. Standard 3GPP TS 36.211 V9.1.0 (2010-03) – Physical Channels and Modulation. 2. Standard 3GPP TS 36.212 V9.3.0 (2010-09) – Multiplexing and Channel Coding.3. Standard 3GPP TS 36.213 V9.3.0 (2010-09) – Physical Layer Procedures.4. 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.html6. http://www.sharetechnote.com/html/BasicProcedures_LTE.html