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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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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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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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
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Hinweis der Redaktion
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.