AIRCOM LTE Webinar 5 - LTE Capacity

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This is the 5th webinar in our LTE series focusing on LTE capacities and caperbilites

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  • Hi everyone, according to this presentation, Method 1 (from the TS36.213) Calculation Procedure for downlink(PDSCH) is as follows : i) refer to TS36.213 Table 7.1.7.1-1 ii) get I_TBS for using MCS value (Let’s assume MCS is 1. in this case, I_TBS is 1 ) iii) refer to TS36.213 Table7.1.7.2.1 iv) go to column header indicating the number of RB (Let’s assume that RB is 50) v) go to row header ‘1’ which is I_TBS vi) we would get 1800 (if the number of RB is 50 and I_TBS is 9) vii) (This is Transport Block Size per 1 ms for one Antenna). I wonder if this size comes from doing 3 OFDM symbols x 12 sucarriers x 50 RBs= 1800. the 3 OFDM symbols are the ones from the PDCCH channel, maybe?
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AIRCOM LTE Webinar 5 - LTE Capacity

  1. 1. © 2013 AIRCOM International Ltd AIRCOM LTE Webinar Series: What affects LTE Cell throughput
  2. 2. 2 © 2013 AIRCOM International Ltd About the Presenters Graham Whyley – Lead Technical Trainer  AIRCOM Technical Master Trainer since 2005  Currently responsible for all LTE training course creation and delivery  Over 20 years of training experience at companies including British Telecom and Fujitsu Contact us at training@aircominternational.com Adam Moore – Learning & Development Manager  With AIRCOM since 2006  Member of CIPD
  3. 3. 3 © 2013 AIRCOM International Ltd About AIRCOM  Founded in 1995  14 offices worldwide  Over 150 LTE customers  Acquired Symena in 2012  Products deployed in 159 countries  Comprehensive Tool and technology training portfolio Network Advise Audit PlanOptimise Manage AIRCOM is the leading provider of mobile network planning, optimisation and management software and consultancy services.  TEOCO offer very complimentary assurance an optimisation solutions as well as an excellent analytics portfolio.  Significantly stronger combined offering for customers  Find out more at www.aircominternational.com
  4. 4. 4 © 2013 AIRCOM International Ltd LTE PORTFOLIO ACCREDITATION COURSES A202 AIRCOM Accredited LTE Planning and Optimisation Engineer (5 days inc exam)
  5. 5. 5 © 2013 AIRCOM International Ltd Agenda-What affects LTE Cell throughput  Maximizing the data rate and spectral efficiency are the main targets in LTE cellular systems.  Transport Block Size  Codewords  LTE UE categories  What effects Cell throughput
  6. 6. 6 © 2013 AIRCOM International Ltd What affects Cell throughput L1/L2 IP UDP GTP-U eNode B L1 MAC RLC PDCP Relay L1 MAC RLC PDCP UE IP Application TCP/UDP DATA DATA DATA DATA DATA DATA
  7. 7. 7 © 2013 AIRCOM International Ltd User Plane Application ApplicationApplication Rate TCPoverhead UDP Real TimeNon Real Time TCPoverhead UDP Real TimeNon Real Time IPoverhead IPoverhead RLC layer will concatenate or segment the data coming from PDCP layer into correct block size RLC PDCP overhead RLC PDCP overhead
  8. 8. 8 © 2013 AIRCOM International Ltd WHAT IS A TRANSPORT BLOCK RLC HEADER RLC HEADER RLC MAC MAC HEADER TRANSPORT BLOCK RLC MAC IP TCP /UDP
  9. 9. 9 © 2013 AIRCOM International Ltd User Plane Application ApplicationApplication Rate TCPoverhead UDP Real TimeNon Real Time TCPoverhead UDP Real TimeNon Real Time IPoverhead IPoverhead RLC PDCP overhead RLC PDCP overhead L1 MAC UE overhead overhead L1 MAC UE overhead overhead MAC layer selects the modulation and coding scheme configures the physical layer QPSK 2 bits 16QAM 4 bits 64QAM 6bits Different coding Rates
  10. 10. 10 © 2013 AIRCOM International Ltd LTE UE categories Normal Cyclic Prefix 7 symbols = 0.5 ms FrequencyDomain 12subcarriers=180kHz Time Domain Resource Element 2 bits 4 bits 6 bits
  11. 11. 11 © 2013 AIRCOM International Ltd Now how many bits are transferred in this 1ms transport block size? Modulation and coding scheme (MCS): The MCS index (0…31) is used by the base station to signal to the terminal the modulation and coding scheme to use for receiving or transmitting a certain transport block. Each MCS index stands for a certain modulation order and transport block size index
  12. 12. 12 © 2013 AIRCOM International Ltd RRC Connection Reconfiguration Message Since the size of transport block is not fixed MCS Index |UE ID/RNTI Type |C-RNTI | |Subframe Number |2 | |UE ID/RNTI Value |'8627'H || |Transport Block Indicator |single TB info | |Modulation Order DL 1 |QAM64 | |New Data Indicator DL 1 |new data | |Redundancy Version DL 1 |0 | |Reserved |0 | |Modulation Scheme Index DL |24 | RRC Connection Reconfiguration Message Modulation Scheme Index DL 24
  13. 13. 13 © 2013 AIRCOM International Ltd How much bits are transferred in this 1ms transport block size? It depends on: The MCS (modulation and coding scheme) The number of resource blocks assigned to the UE Normal Cyclic Prefix 7 symbols = 0.5 ms FrequencyDomain 12subcarriers=180kHz Time Domain Extended Cyclic Prefix 6 symbols = 0.5 ms 12subcarriers=180kHz Time Domain Resource Element 2 bits 4 bits 6 bits
  14. 14. 14 © 2013 AIRCOM International Ltd Transport Block Size Tables  Look-up table is referenced by the TBS Index and the number of allocated Resource Blocks RRC Connection Reconfiguration Message Modulation Scheme Index DL 24
  15. 15. 15 © 2013 AIRCOM International Ltd POLL eNB assigns MCS index 12 and 2 resource blocks (RBs). What is the transport block size? 1. 56 2. 144 3. 616 4. 376 5. 440
  16. 16. 16 © 2013 AIRCOM International Ltd POLL eNB assigns MCS index 12 and 2 resource blocks (RBs). What is the transport block size? 1. 56 2. 144 3. 616 4. 376 5. 440
  17. 17. 17 © 2013 AIRCOM International Ltd Table 7.1.7.2.1-1 Look-up table is referenced by the TBS Index and the number of allocated Resource Blocks
  18. 18. 18 © 2013 AIRCOM International Ltd What affects LTE Cell throughput
  19. 19. 19 © 2013 AIRCOM International Ltd Coding Rate
  20. 20. 20 © 2013 AIRCOM International Ltd Coding rate L1 MACoverhead overhead L1 MACoverhead overhead MAC layer selects the modulation and coding scheme configures the physical layer Code rate: The code rate is defined as the ratio between the transport block size and the total number of physical layer bits per subframe that are available for transmission of that transport block. The code rate is an indication for the redundancy that has been added due to the channel coding process
  21. 21. 21 © 2013 AIRCOM International Ltd CQI Modulation Efficiency Actual coding rate Required SINR 1 QPSK 0.1523 0.07618 -4.46 2 QPSK 0.2344 0.11719 -3.75 3 QPSK 0.3770 0.18848 -2.55 4 QPSK 0.6016 308/1024 -1.15 5 QPSK 0.8770 449/1024 1.75 6 QPSK 1.1758 602/1024 3.65 7 16QAM 1.4766 378/1024 5.2 8 16QAM 1.9141 490/1024 6.1 9 16QAM 2.4063 616/1024 7.55 10 64QAM 2.7305 466/1024 10.85 11 64QAM 3.3223 567/1024 11.55 12 64QAM 3.9023 666/1024 12.75 13 64QAM 4.5234 772/1024 14.55 14 64QAM 5.1152 873/1024 18.15 15 64QAM 5.5547 948/1024 19.25 The coding rate indicates how many real data bits are present out of 1024 while the efficiency provides the number of information bits per modulation symbol. 602/1024 = 0.5879 QPSK = 2bits Efficiency= 2x0.5879=1.1758 data bits per symbol Coding Rate
  22. 22. 22 © 2013 AIRCOM International Ltd Coding Rate 602/1024 = 0.5879 QPSK = 2bits Efficiency= 2x0.5879=1.1758 data bits per symbol DL BEARER – 64QAM, Efficiency 5.5 SINR +19,25 High cell throughput DL BEARER – QPSK Efficiency 0.1523 SINR -4.46 Low cell throughput
  23. 23. 23 © 2013 AIRCOM International Ltd Coding Rate
  24. 24. 24 © 2013 AIRCOM International Ltd CQI Modulation Efficiency Actual coding rate Required SINR 1 QPSK 0.1523 0.07618 -4.46 2 QPSK 0.2344 0.11719 -3.75 3 QPSK 0.3770 0.18848 -2.55 4 QPSK 0.6016 308/1024 -1.15 5 QPSK 0.8770 449/1024 1.75 6 QPSK 1.1758 602/1024 3.65 7 16QAM 1.4766 378/1024 5.2 8 16QAM 1.9141 490/1024 6.1 9 16QAM 2.4063 616/1024 7.55 10 64QAM 2.7305 466/1024 10.85 11 64QAM 3.3223 567/1024 11.55 12 64QAM 3.9023 666/1024 12.75 13 64QAM 4.5234 772/1024 14.55 14 64QAM 5.1152 873/1024 18.15 15 64QAM 5.5547 948/1024 19.25 Coding Rate CQI = 15 Terminal Density High throughput
  25. 25. 25 © 2013 AIRCOM International Ltd Code word L1 MACoverhead overhead TRANSPORT BLOCK • 24 bit checksum (CRC) to the transport block This CRC is used to determine whether the transmission was successful or not, and triggers Hybrid ARQ to send an ACK or NACK codeword Transmitter Transport Block Transport Block CRC Compute CRC Modulation Receiver Error detection Demodulation Transport Block CRC NACK Transport Block CRC NACK L1 converts the transport block into a code-word Re-transmissions will reduce throughput
  26. 26. 26 © 2013 AIRCOM International Ltd Adaptive re-transmission If the base station receives the data with errors Two ways for it to respond 1. The base station can trigger a non adaptive re-transmission by sending the mobile a negative acknowledgement on the PHICH. The mobile then re-transmits the data with the same parameters that it used first time around. 2. Alternatively, the base station can trigger an adaptive re-transmission by explicitly sending the mobile another scheduling grant. It can do this to change the parameters that the mobile uses for the re-transmission, such as the resource block allocation or the modulation scheme. Scheduling grant maximum number of re-transmissions without receiving a positive response Change parameters like uplink modulation scheme QPSK for noisy channels
  27. 27. 27 © 2013 AIRCOM International Ltd Code word If the transport block is too small, it is padded up to 40 bits If the Transport Block is too big, it is divided into smaller pieces, each of which gets an additional 24 bit CRC A codeword, then, is essentially a transport block with error protection. Note that a UE may be configured to receive one or two transport blocks (and hence one or two codewords) in a single transmission interval Maximum of 2 codewords used to limit signalling requirement (CQI reporting, HARQ acknowledgements, resource allocations) L1 MAC TRANSPORT BLOCK codeword L1 MAC TRANSPORT BLOCK codeword
  28. 28. 28 © 2013 AIRCOM International Ltd Codeword • Maximum of 2 codewords used to limit signalling requirement (CQI reporting, HARQ acknowledgements, resource allocations) • Transmit diversity provides the fallback when only a codeword is transferred The number of layers is always less than or equal to the number of antenna ports (transmit antennas). Layer 1 Layer 2 Codeword 1
  29. 29. 29 © 2013 AIRCOM International Ltd Transmit Diversity  Transmit diversity requires multiple antenna elements at the transmitter, and one or more antenna elements at the receiver  3GPP has specified transmit diversity schemes based upon using either 2 or 4 antenna elements at the transmitter  Transmit diversity transfers a single code word during each 1 ms subframe Modulated Codeword Layer 1 Layer 2 Layer mapping for 2 layers Modulated Codeword Layer 3 Layer 4 Layer mapping for 4 layers Layer 1 Layer 2
  30. 30. 30 © 2013 AIRCOM International Ltd 4 Layers Codewords Layers Mapping 2 4 The first codeword is split (odd/even) between the first two layers , the second codeword is split between the second two layers. Each codeword same length Layer 1 Layer 2 Layer 3 Layer 4 4 layers – 2 codewords Codeword 1 Codeword 2 Note that the number of layers is always less than or equal to the number of antenna ports (transmit antennas). The number of layers used in any particular transmission depends (at least in part) on the Rank Indication (RI) feedback from the UE
  31. 31. 31 © 2013 AIRCOM International Ltd MIMO  MIMO can transfer either 1 or 2 code words during each 1 ms sub-frame  CQI reporting, link adaptation and HARQ run independently for each code word Resource Allocation Type (0 or 1) Resource Block Assignment TPC Command for PUCCH HARQ Process Number Modulation and Coding Scheme New Data Indicator Redundancy Version Modulation and Coding Scheme New Data Indicator Redundancy Version Precoding Information Transport Block 1 information Transport Block 2 information DCI Format 2 The scheduling commands for downlink transmissions are more complicated, and are handled in Release 8 by DCI formats 1 to 1D and 2 to 2A
  32. 32. 32 © 2013 AIRCOM International Ltd Cell throughput CQI = 1 CQI = 15 10Mhz Maximizing the data rate and spectral efficiency are the main targets in LTE cellular systems. CQI Modulation Efficiency Actual coding rate Required SINR 1 QPSK 0.1523 0.07618 -4.46 2 QPSK 0.2344 0.11719 -3.75 3 QPSK 0.3770 0.18848 -2.55 4 QPSK 0.6016 308/1024 -1.15 5 QPSK 0.8770 449/1024 1.75 6 QPSK 1.1758 602/1024 3.65 7 16QAM 1.4766 378/1024 5.2 8 16QAM 1.9141 490/1024 6.1 9 16QAM 2.4063 616/1024 7.55 10 64QAM 2.7305 466/1024 10.85 11 64QAM 3.3223 567/1024 11.55 12 64QAM 3.9023 666/1024 12.75 13 64QAM 4.5234 772/1024 14.55 14 64QAM 5.1152 873/1024 18.15 15 64QAM 5.5547 948/1024 19.25
  33. 33. 33 © 2013 AIRCOM International Ltd Spectral efficiency Evolved Node B (eNB) modulation and coding scheme 64QAM 6bits/Hz 64QAM 6bits/Hz 64QAM 6bits/Hz 64QAM 6bits/Hz A 64 QAM the spectral efficiency cannot exceed N = 6 (bit/s)/Hz If a forward error correction (FEC) code with code rate 1/2 is added, meaning that the encoder input bit rate is one half the encoder output rate, the spectral efficiency is 50% of the modulation efficiency Different Coding Rates (Bit/s)/Hz per cell It is a measure of the quantity of users or services that can be simultaneously supported by a limited radio frequency bandwidth Efficiency 5.5547 Efficiency 5.1152 Efficiency 4.5234 Efficiency 3.9023
  34. 34. 34 © 2013 AIRCOM International Ltd Maximum data rate for CQI bearer 1 Assumptions: 10 Mz Bandwidth Normal Prefix Coding rate 0.07618 MIMO 1x1 Bandwidth (MHz) 1.4 3 5 10 15 20 # of RBs 6 15 25 50 75 100 Subcarriers 72 180 300 600 900 1200Normal Cyclic Prefix 7 symbols = 0.5 ms FrequencyDomain 12subcarriers=180kHz Time Domain CQI bearer 1 All 50 PRB MIMO 1x1
  35. 35. 35 © 2013 AIRCOM International Ltd 0 1 2 3 19 One Sub-frame = 1 mS 10 ms Number of Traffic symbols bits in a TTI = (4 x12) + (7x12)-6 =126 If QPSK bearer =126 x 2 =252 bits in 1ms Maximum data rate for CQI bearer 1 4 x12 7x12 Normal Cyclic Prefix 7 symbols = 0.5 ms FrequencyDomain 12subcarriers=180kHz Time Domain
  36. 36. 36 © 2013 AIRCOM International Ltd 0 1 2 3 19 One Sub-frame = 1 mS 10 ms Number of Traffic symbols bits in a TTI = (4 x12) + (7x12)-6 =126 If QPSK bearer =126 x 2 =252 bits in 1ms In10Mhzyouhave50PRBin1mS Maximum data rate for CQI bearer 1 In one TTI (1mS)you have 50 x 252 bits = 12600 bits per 1mS
  37. 37. 37 © 2013 AIRCOM International Ltd 0 1 2 3 19 One Sub-frame = 1 mS 10 ms Number of Traffic symbols bits in a TTI = (4 x12) + (7x12)-6 =126 If QPSK bearer =126 x 2 =252 bits in 1ms In10Mhzyouhave50PRBin1mS Maximum data rate for CQI bearer 1 In one TTI (1mS)you have 50 x 252 bits = 12600 bits per 1mS Coding Rate 12600 bits x 0.07618=959.104 bits in 1ms Bits per second =959.104 x 1000= 959104 kb/s =0.975 Mb/s in 10Mhz
  38. 38. 38 © 2013 AIRCOM International Ltd What have we not taken into account?
  39. 39. 39 © 2013 AIRCOM International Ltd Each Bearer has a maximum data rate Antenna 1 1 ms 12sub-carriersBits per second =959.104 x 1000= 959104 kb/s =0.975 Mb/s in 10Mhz WithoutMIMO CQI 15 CQI 1 Low throughput High throughput WithoutMIMO
  40. 40. 40 © 2013 AIRCOM International Ltd BearersWithoutMIMO
  41. 41. 41 © 2013 AIRCOM International Ltd Physical OverheadWithoutMIMO Antenna 1 Antenna 2
  42. 42. 42 © 2013 AIRCOM International Ltd Coverage/Capacity CQI 1 CQI 15 CQI 14 CQI 13 CQI 12 CQI 11 CQI 10 CQI 9 CQI 8 CQI 7 CQI 6 CQI 5 CQI 4 CQI 1CQI 3 CQI 2
  43. 43. 43 © 2013 AIRCOM International Ltd Summary Cell throughput is dependant on: • Modulation and coding scheme (MCS) (0…31) and Transport block size • Bandwidth • Normal / Extended Prefix • Transmission modes TX diversity, Su-MIMO etc. • LTE UE categories CQI (MCS) (0…31) Normal Cyclic Prefix 7 symbols = 0.5 ms FrequencyDomain 12subcarriers=180kHz Time Domain
  44. 44. 44 © 2013 AIRCOM International Ltd Next Topic Comparison between GSM, UMTS & LTE
  45. 45. 45 © 2013 AIRCOM International Ltd In Closing  Thank you for attending  Webinars webpage – keep up to date and register to receive email alerts on new webinars http://www.aircominternational.com/Web inars.aspx

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