Fusi PDSCH

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LTE Physical Downlink Shared Channel

PT. Fusi GLobal Teknologi
Indonesia

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  • LTE (long-term evolution) was designed primarily for high-speed data services.LTE radio interface is designed based on a layered protocol stack, divided into 4 layer shown in figure 1:Packet Data Convergence Protocol (PDCP)Radio Link Control (RLC)Medium Access Control (MAC)Physical Layer (PHY) = the actual transmission and reception of data in forms of transport blocks.To efficiently support various Quality of Services classes of services, LTE adopts a hierarchical channel structure. There are three different channel types defined in LTE—logical channels (what to transmit), transport channels (how to transmit), and physical channels (actual transmission).Three type of channels:Logical channels : used by the MAC to provide services to the RLCTransport channels :used by the PHY to offer services to the MACPhysical channels : The main function of PHY is the actual transmission and reception of data in forms of transport blocks.
  • Control Information Channels: DCI, CFI, HI, UCI (uplink).DCI is scheduler. A scheduler is a key element in BS and it assigns the time and frequency resources to different users in the cell. CFI indicates how many symbols DCI spans.Today, we’ll discuss about DL-SCH and PDSCH.DL-SCH used for transmitting the downlink data.PDSCH used to transmit the downlink shared channel (DL-SCH).
  • Encoding is performed in Base Station (BS).
  • In SISO (single input single output), layer mapper and precoding steps do almost nothing.
  • DL-SCH used for transmitting the downlink data.CRC is used for error detection in transport blocks.Transport block is divided by cyclic generator polynomial G-CRC24A to generate 24 parity bits.
  • Minimum code block size = 40. if less than minimum, add filler bits in the beginning to achieve total 40.Maximum code block size = 6144. if greater than maximum, segment the code block.
  • Turbo coding = forward error correction and improves channel capacity by adding redundant information.Encoder using Parallel Concatenated Convolutional Code (PDCCC), consist of 1st and 2nd constituent encoder, also Quadratic Permutation Polynomial (QPP).
  • Rate-matching block creates an output bitstream with a desired code-rate.
  • Used to transmit the downlink shared channel (DL-SCH).Scrambling created using a length-31 Gold sequence generator and initialized using radio network temporary identifier (n-RNTI), cell ID (n-cellID), slot number (n-s), and codeword index (q = {0,1}). Because of SISO, q = 0.
  • The modulation mapper takes binary digits, 0 or 1, as input and produces complex-valued modulation symbols, x=I+jQ, as output.QPSK = pair of bits are mapped to one complex-valued modulation symbols.
  • Decoding is performed in User Equipment (UE).
  • Demodulation : hard-decision (make firm decision whether one or zero is transmitted) and soft-decision (provides with some side information together with the decision).We use soft-decision demodulation, called viterbi. Tahanterhadap noise.
  • Integration test to verify the data received in UE based by comparing with data transmitted in BS.
  • Fusi PDSCH

    1. 1. DL-SCH/PDSCH Astrini Kusumawardhani 1
    2. 2. Outline • • • • Introduction DL-SCH and PDSCH Encoding DL-SCH and PDSCH Decoding Smoke Test PDSCH 2
    3. 3. Introduction 3
    4. 4. Introduction Figure 1. The radio interface protocol architecture and the SAPs between different layers. 4
    5. 5. Introduction Figure 2. Mapping Transport Channel to Physical Channels Figure 3. Mapping Control Information Channels to Physical Channels 5
    6. 6. DL-SCH and PDSCH Encoding 6
    7. 7. DL-SCH/PDSCH Encoding Scheme Figure 4. DL-SCH/PDSCH Processing Scheme 7
    8. 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 8
    9. 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 ) 9
    10. 10. 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 10
    11. 11. DL-SCH Encoding (1) 1. Add CRC CRC24A: B = TBS + CRC = 208 + 24 = 232 bits. 11
    12. 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} 12
    13. 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 13
    14. 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: 14
    15. 15. DL-SCH Encoding (5) 5. Code Block Concatenation 15
    16. 16. Review DL-SCH Encoding 16
    17. 17. PDSCH Encoding (1) 1. Scrambling Using pseudo-random sequence generation. Pattern: Scrambling initialization is performed in each frame, using : Total output = 1284 bits. 17
    18. 18. PDSCH Encoding (2) 2. Modulation QPSK, 16QAM, 64QAM MCS = 1 Qm = 2 based on Qm. QPSK Total output = 642 symbols. 18
    19. 19. PDSCH Encoding (3) 3. Resource Element Mapping 19
    20. 20. Review PDSCH Encoding 20
    21. 21. DL-SCH and PDSCH Decoding 21
    22. 22. DL-SCH/PDSCH Decoding Scheme PDSCH DL-SCH 22
    23. 23. PDSCH Decoding 1. Resource Element Demapper 2. Demodulation Mapper Using Soft-Demodulation, which are bit 0 = negative and bit 1 = positive. 3. Descrambling 23
    24. 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 24
    25. 25. DL-SCH Decoding 25
    26. 26. Smoke Test PDSCH 26
    27. 27. Smoke Test PDSCH Result : 27
    28. 28. References 1. 2. 3. 4. 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 28

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