AIRCOM LTE Webinar 2 - Air Interface

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This second webinar discusses LTE Air Interface, the link between a mobile device and the network, and a fundamental driver of the quality of the network.

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AIRCOM LTE Webinar 2 - Air Interface

  1. 1. Graham Whyley Lead LTE Technical Trainer The webinar will start shortly. AIRCOM LTE Webinar Series: LTE Air-Interface (Part 1) 1 © 2013 AIRCOM International Ltd
  2. 2. Graham Whyley Lead LTE Technical Trainer www.aircominternational.com/Webinars AIRCOM LTE Webinar Series: LTE Air-Interface (Part 1) 2 © 2013 AIRCOM International Ltd
  3. 3. 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 Adam Moore – Learning & Development Manager  With AIRCOM since 2006  Member of CIPD Contact us at training@aircominternational.com 3 © 2013 AIRCOM International Ltd
  4. 4. About AIRCOM AIRCOM is the leading provider of mobile network planning, optimisation and management software and consultancy services.       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 Find out more at www.aircominternational.com 4 © 2013 AIRCOM International Ltd
  5. 5. Agenda- LTE Air-Interface (Part 1)  LTE Air-Interface        5 What is own cell Interference? What is other cell Interference? What is SINR? What is Physical Resource Block cyclic prefix Time Transmission Interval (TTI) Normal & Extended © 2013 AIRCOM International Ltd
  6. 6. PRACH PARAMETERS- LTE TROUBLE SHOOTING COURSE Unlikely to get own cell interference: Same time/Same Frequency However If you lose timing advance Frequency PRACH Different Time UE 2 Frequency UE 1 Timing Av RRC CONNECTED Time Slot Data Evolved Node B (eNB) Time Slot Packet Scheduling PS allocates frequency and Time to the UE 6 Data UE 1 UE 2 © 2012 AIRCOM International Ltd
  7. 7. PRACH PARAMETERS- LTE TROUBLE SHOOTING COURSE PRACH Parameters effect coverage UPLINK THROUGHPUT Unlikely to get own cell interference: Same time/Same Frequency PRACH Parameters affect coverage However If you lose timing advance Frequency PRACH Different Time UE 2 Frequency UE 1 Timing Av RRC CONNECTED An other reason for own Interference Inter-symbol This effects coverage/Capacity 7 Time Slot Data Timing Advance effect coverage Evolved Node B (eNB) Time Slot Packet Scheduling PS allocates frequency and Time to the UE Data UE 1 UE 2 © 2012 AIRCOM International Ltd
  8. 8. Function Evolved Node B (eNB) Evolved Node B SINR ave = S I+N I = Iown + Iother (eNB) RRC CONNECTED UE at cell edge Same time slot Same Frequency PS allocates frequency and Time to the UE Packet Scheduling Data Other Cell Interference Evolved Node B (eNB) Packet Scheduling Data PS allocates frequency and Time to the UE 8 © 2012 AIRCOM International Ltd
  9. 9. Traffic SINR SINR ave = S I+N I = Iown + Iother There are a number of ways of controlling other cell Interference 9 © 2013 AIRCOM International Ltd
  10. 10. Channel Quality Indicator CQI=15 The CQI indicates the downlink channel quality CQI=10 Evolved Node B RF conditions will change as the user moves CQI=1 (eNB) CQI=8 Packet Scheduling Downlink 16-QAM User reports CQI index8, it informs the eNB that, for the CQI bandwidth being reported, it can support a transport block using 16-QAM modulation and a coding rate of approximately 0.48 with a block error of less than 10%. 10 © 2013 AIRCOM International Ltd
  11. 11. Channel Quality Indicator The CQI indicates the downlink channel quality Coding Rate PS takes the decision to OPSK 16QAM assign a particular MCS 64QAM 2bits/Hz 4bits/Hz 6bits/Hz (modulation and coding scheme) for a particular modulation and coding scheme Evolved UE. Node B CQI CQI (eNB) CQI QPSK for noisy channels Physical Uplink Control Channel (PUCCH) Packet Scheduling CQI Physical Uplink Shared Channel(PUSCH) The CQI mainly depends on the received signal to interference plus noise ratio, because a high data rate can only be received successfully at a high SINR. Periodic Reporting Normally on PUCCH, PUSCH used when multiplexed with data 11 Aperiodic Reporting When requested by eNodeB (DCI format 0 on PDCCH) Always on PUSCH © 2013 AIRCOM International Ltd
  12. 12. SINR - Signal to Interference & Noise Ratio S: indicates the power of measured usable signals. SINR ave = S I+N I = Iown + Iother Path Loss 12 © 2013 AIRCOM International Ltd
  13. 13. SINR - Signal to Interference & Noise Ratio CQI Modulation Actual coding rate Required SINR I: interference signals from other cells in the current system plus own cell N: indicates background noise, which is related to measurement bandwidths and receiver noise coefficients UEs typically use SINR to calculate the CQI (Channel Quality Indicator) they report to the network 13 QPSK 0.11719 -3.75 QPSK 0.18848 -2.55 4 QPSK 308/1024 -1.15 QPSK 449/1024 1.75 6 QPSK 602/1024 3.65 7 16QAM 378/1024 5.2 8 16QAM Quality Indicator 6.1 Channel 490/1024 9 16QAM 616/1024 7.55 10 64QAM 466/1024 10.85 11 64QAM 567/1024 11.55 12 S: indicates the power of measured usable signals. -4.46 5 The components of the SINR calculation can be defined as: SINR ave = S QPSK I + N 0.07618 I = Iown + Iother 64QAM 666/1024 12.75 13 64QAM 772/1024 14.55 14 64QAM 873/1024 18.15 15 64QAM 948/1024 19.25 1 2 3 not defined in the 3GPP specs but defined by the UE vendor. © 2013 AIRCOM International Ltd
  14. 14. Function Evolved Node B (eNB) SINR SINR = 19db SINR=-4.46dB SINR ave = S I+N I = Iown + Iother QPSK 2bits/Hz Evolved Node B 16QAM 4bits/Hz 64QAM 6bits/Hz (eNB) Data Packet Scheduling By improving SINR you will increase coverage and throughput SINR SINR = 19db SINR=-4.46dB QPSK 2bits/Hz 14 Evolved Node B 16QAM 4bits/Hz 64QAM 6bits/Hz (eNB) Packet Scheduling Data © 2012 AIRCOM International Ltd
  15. 15. Traffic SINR Point of interest 15 © 2013 AIRCOM International Ltd
  16. 16. Poll What is meant by adaptive modulation and coding (AMC)? 16 © 2013 AIRCOM International Ltd
  17. 17. Poll Link adaptation, or adaptive modulation and coding (AMC), is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link If the base station receives the data correctly Sends the mobile a positive acknowledgement on the physical hybrid ARQ indicator channel (PHICH). 17 © 2013 AIRCOM International Ltd
  18. 18. Poll 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. Scheduling grant Change parameters like uplink modulation scheme QPSK for noisy channels 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 uplink modulation scheme. 18 © 2013 AIRCOM International Ltd
  19. 19. What is a time slot? Physical Resource Block time slot 0 You need allot of frequencies Block of Frequencies 19 Same Time-Different Frequency Own cell interference zero time slot 1 Same Frequency -Different time Own cell interference zero Block of Frequencies Block of Frequencies Block of Frequencies SINR ave = S I+N I = Iown + Iother Block of Frequencies © 2013 AIRCOM International Ltd
  20. 20. What is a time slot? 10ms 0.5ms time slot 0 time slot 1 You need allot of frequencies Block of Frequencies Block of Frequencies Block of Frequencies Block of Frequencies Block of Frequencies 20 time slot 2 time slot 19 UE1 TTI = 1ms 10 sub channels in 10mS Physical Downlink Control Channel (PDCCH) TTI = 1mS UE3 © 2013 AIRCOM International Ltd
  21. 21. Physical downlink control channel (PDCCH) 10ms 0.5ms sub channel time slot 0 Block of I need to read the PDCCHFrequencies Is it QPSK, 64 QAM, 16QAM What is the size of the transport Block? Do I do hopping? What about Power control What is my uplink/Down link resources? time slot 1 time slot 2 time slot 3 time slot 19 UE1 Physical Downlink Shared Channels Physical downlink control channel (PDCCH) I cannot change my MCS till I see another PDCCH Scheduling grant I need to change MCS At the start of each subframe, a few symbols are reserved for the control information that the base station transmits on the PCFICH, PDCCH and PHICH. The number of control symbols can vary from one subframe to the next, depending on how much control information the base station needs to send. 21 © 2013 AIRCOM International Ltd
  22. 22. What is Physical Resource Block? 100 Physical Resource Blocks 0.5ms time slot 0 Frequencies 1200 12 subcarriers 12 subcarriers Block of Frequencies 12 subcarriers Block of Frequencies 12 subcarriers Block of Frequencies 12 subcarriers 22 Block of Frequencies Block of Frequencies In LTE the Physical Resource Block is made up of 12 subcarriers If there are 100 Physical Resource Blocks you would require 1200 frequencies © 2013 AIRCOM International Ltd
  23. 23. Master Information Block Bandwidth 1.4 (MHz) # of RBs 6 3 5 10 15 20 LTE-Uu Air-Interface 15 25 50 75 100 MIB Evolved Node B (eNB) 20MHz 15MHz 10MHz 5MHz 3MHz Subcarriers 72 180 300 600 900 1200 1.4MHz Channel Bandwidth in Resource Blocks 6 x 12 = 72 Subcarriers 50 x 12 = 600 Subcarriers 23 © 2013 AIRCOM International Ltd
  24. 24. Master Information Block Logical BCCH Transport PCCH CCCH DCCH DTCH MCCH MTCH BCH PCH DL-SCH MCH PHYS. PBCH PDSCH PMCH REFERENCE SIGNALS R R R R R 0 24 © 2013 AIRCOM International Ltd
  25. 25. Physical Resource Block 12 subcarriers 0.5ms Physical Resource Block time slot 0 Normal Frame 84 OFDM symbols (12x7) cyclic prefix In the time domain, a guard interval may be added to each symbol to combat inter-OFDM-symbol-interference due to channel delay spread Normal 7 Extended 6 12 subcarriers Resource Element(RE) : The smallest unit made up of 1 symbol x 1 subcarrier QPSK = 2bits 16 QAM = 4bits 64 QAM = 6bits Extended 72 OFDM symbols(12x6) 25 7 symbols © 2013 AIRCOM International Ltd
  26. 26. Channel Bandwidth Carrier spacing 15 kHz 12 subcarriers in the frequency domain x Carrier spacing 15 kHz = 180 kHz 100 x 180khz= 18Mhz 12 subcarriers = 180 kHz Frequency Domain Normal Cyclic Prefix Normal Frame 84 OFDM symbols (12x7 ) 7 symbols = 0.5 ms Time Domain Channel Bandwidth in Resource Blocks 50 x 180khz= 9Mhz 26 © 2013 AIRCOM International Ltd
  27. 27. Channel Bandwidth Channel Bandwidth (MHz) 1.4 3 5 10 15 20 Transmission Bandwidth Config. (RB) 6 15 25 50 75 100 Number of Subcarriers 72 180 300 600 900 1200 Occupied Bandwidth (MHz) 1.08 2.7 4.5 9.0 13.5 18.0 20 MHz Channel Bandwidth (20MHz) Transmission Bandwidth Configuration (RB) 100 x 180khz= 18Mhz 27 12 subcarriers in the frequency domain x Carrier spacing 15 kHz = 180 kHz © 2013 AIRCOM International Ltd
  28. 28. Any questions? 28 © 2013 AIRCOM International Ltd
  29. 29. Delay spread Greater the Delay spread Greater the Guard period Extended Evolved Node B (eNB) 2 1 3 If we sample here Direct signal If we sample here Reflection 1 Last Reflection Guard Period 29 Sampling Window © 2013 AIRCOM International Ltd
  30. 30. Delay spread radio waves travel at speed of light = 300 000000m/s For LTE, the normal CP length has been set at 4.69 μs, enabling the system to cope with path delay variations up to about 1.4 km. 300m× 4.69 =1.4km Extended cyclic prefix of 16.7 μs for highly dispersive environments. variations up to about 5km 300mx 16.7 =5km 30 © 2013 AIRCOM International Ltd
  31. 31. Summary so far 12 subcarriers = 180 kHz Frequency Domain Normal Cyclic Prefix Normal Frame 84 OFDM symbols (12x7) Resource Element 7 symbols = 0.5 ms 2 bits Time Domain 4 bits Extended Cyclic Prefix 6 bits Resource Block represents the basic unit of resource for LTE Resource Block is a grid: 12 subcarriers in the frequency domain (180 kHz) 6 or 7 symbols in the time domain (0.5 s) 72 or 84 Resource Elements per Resource Block Each Resource Element can accommodate 1 modulation symbol, e.g. QPSK, 16QAM, 64QAM Bandwidth 1.4 (MHz) 3 5 10 15 20 12 subcarriers = 180 kHz # of RBs 31 Extended 72 OFDM symbols(12x6) 6 symbols = 0.5 ms 6 15 25 50 75 100 Subcarriers 72 180 300 600 900 1200 © 2013 AIRCOM International Ltd
  32. 32. LTE is about 300Mbps 25% (4x4) Overhead about 20 Mhz-100PRB 12 subcarriers = 180 kHz Normal Cyclic Prefix 12 subcarriers x 7 OFDMA symbols= 84 How do we get 300Mbps? PDCCH Assume 20 MHz channel bandwidth, normal CP, 4x4 MIMO. 64 QAM modulation and no coding. 25% overhead 64 QAM 20 MHz reference signal Calculate the number of resource elements (RE) in a sub-frame with 20 MHz channel bandwidth: 7 symbols = 0.5 ms 84x100= 8400 Time Domain 12 subcarriers = 180 kHz Each RE can carry a modulation symbol: 2bits/4bits/6bits 8400x2=16800RE’s per subframe 32 12 subcarriers x 7 OFDMA symbols x 100 resource blocks x 2 slots= 16800 REs per sub-frame. 7 symbols = 0.5 ms 16800REs per sub-frame x 6 = 100800bits per ms 100800 x 1000 = 100800000 bits per second About 100 Mbits per transmitter (1x1) 4x4 MIMO about 400Mbits/s © 2013 AIRCOM International Ltd
  33. 33. Time-Division Duplexing (TDD) Normal / Extended Multicast-broadcast singlefrequency network (MBSFN) is a communication channel defined in Long Term Evolution (LTE). It can deliver services such as mobile TV using the LTE infrastructure 33 Normal Cyclic Prefix 7 symbols = 0.5 ms 12 subcarriers = 180 kHz Frequency-division duplexing(FDD) Normal / Extended 12 subcarriers = 180 kHz Frame Structures Extended Cyclic Prefix 6 symbols = 0.5 ms Time Domain © 2013 AIRCOM International Ltd
  34. 34. Multicast Traffic Channel (MTCH) Physical Downlink Shared Channels is shared Dedicated Traffic Channel (DTCH) Dedicated Control CHannel Logical BCCH PCCH DCCH DTCH MCCH MTCH SIB’s MIB Transport CCCH BCH PCH Physical Downlink Control Channel DL-SCH MCH SIB’s PDCCH PHYS. PBCH PDSCH PMCH REFERENCE SIGNALS Physical Downlink Shared Channels 7 symbols = 0.5 ms 7 symbols = 0.5 ms DCCH SIB’s 7 symbols = 0.5 ms 34 7 symbols = 0.5 ms © 2013 AIRCOM International Ltd
  35. 35. 12 subcarriers = 180 kHz Frame Structures 7 symbols = 0.5 ms For LTE, the normal CP length has been set at 4.69 μs, enabling the system to cope with path delay variations up to about 1.4 km. 35 © 2013 AIRCOM International Ltd
  36. 36. Frame Structures 12 subcarriers = 180 kHz Extended Cyclic Prefix Extended cyclic prefix of 16.7 μs for highly dispersive environments. variations up to about 5km 6 symbols = 0.5 ms Time Domain 36 © 2013 AIRCOM International Ltd
  37. 37. Next Topic LTE Carriers • • • • • RSRP, RSSI, RSRQ Frequency-division duplexing(FDD) Re-Farming Time-Division Duplexing (TDD) TDD- Standard sub-frames & Special sub-frames. • CQI reports 37 © 2013 AIRCOM International Ltd
  38. 38. LTE RAN Portfolio Contact us on training@aircominternational.com 38 © 2013 AIRCOM International Ltd
  39. 39. 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/Webinars.aspx 39 © 2013 AIRCOM International Ltd
  40. 40. Questions? © 2013 AIRCOM International Ltd

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