Overview and Basics of LTE


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Overview of LTE, its an old one @ 2009.

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Overview and Basics of LTE

  1. 1. Presenting the Future: LTE 3GPP Release 8 By Chaitanya T K Email:tkchaitanya@tataelxsi.Co.In
  2. 2. Discontent is the first step in the progress of a man or a nation.        -Oscar Wilde
  3. 3. Why LTE ?         Less number of components so less cost,low latency and complexity. End user perspective: Support for high end multimedia services High data rates fast downloading capabilities Support for multicast and broadcast services Low latency and high reliability Global roaming between different radio access technologies Support for DVB-H
  4. 4.       Network provider perspective: Scalable bandwidth results in high flexibility (1.4 –20mhz) Easy upgrade from existing technologies High spectral efficiency (3-4 times HSPA) High ARPU(average revenue per user) ALL IP network
  5. 5. Requirements         Simple architecture in terms of number of components, low cost ,latency and complexity. Down->OFDMA (384 kbps), UP->SC-FDMA (86 kbps) 2 operating modes: FDD and TDD User plane latency (UE->BS) < 5ms and control plane <100ms (idle->active) Seamless mobility (prepared handoff’s) QOS directly evolved from HSPA+ ALL IP network Spectrum utilization: 1.4 Mhz to 20 Mhz
  6. 6. Requirements
  7. 7. Frequency Bands
  8. 8. BW Comparison:
  9. 9. Block Diagram
  10. 10. Functionality of All the Components in LTE eNobeB:    Radio resource management: Radio bearer control,Radio admission control,Scheduling, radio resource allocation (UL and DL),paging message forwarding , ROHC (user plane encryption) and Ciphering (PDCP) EPC and enB have a many-many mapping to support redundancy,load sharing and avoiding congestion.
  11. 11. MME: Mobility management Entity       Tracking and maintenance of UE position Inter MME handovers pre-ordained Inter 3GPP handovers AS (UE-enB) and NAS(UE-MME) security Controls NAS signaling Consults HSS on 6a then chooses SGW and PDNGW accordingly (establishes a bearer between UE and PDNGW)
  12. 12. S-GW:      Routing and forwarding user data to PGW through S5 (GTP/PMIP based) Provides user plane tunneling and inter eNB handovers through s1u Inter 3GPP mobility through s1a (SGWSGSN) Lawful interception and accounting Provides local mobility
  13. 13. PDN GW:         It is UE’s default router Provides user plane mobility and inter 3GPP handoff by acting as HA Allocates IP address during default EPS bearer setup QOS is here in the DL Enforces DL data rate ensuring that user is not crossing the subscription levels S7 to PCRF S5 to SWGW(GTP/PMIP/Both) Provides global mobility
  14. 14. HSS:Home Subscriber Service    Stores subscription info (User info,Authentication and authorization ) S6a interface to MME for ciphering and auth (Mutual auth and integrity check) 1 or more HSS as per the number of subscribers
  15. 15. PCRF    Policy control decision and flow based charging Contacts IMS for dynamic QOS and charging related service through “rx reference point” Controls service data flows and IP bearer
  16. 16. Redundancy     When the UE powers up and attaches to the network eNB performs a load balancing algorithm to choose MME from MME pool Then similarly MME selects SGW from SGW pool By the we can achieve high fault tolerance and low congestion This can be implemented using MME identifiers (MMEC,MMEGI,MMEI and GUMMEI)
  17. 17. Layer 3 Layer 2 Layer 1 Control / Measurements Protocol Stack Radio Resource Control (RRC) Logical channels Medium (MAC) Access Physical layer Control Transport channels
  18. 18. Layers Functionality:    PDCP sublayer (terminated in eNB on the network side) performs ROHC, ciphering and integrity protection; MAC- Mapping between logical channels and transport channels; Multiplexing/demultiplexing of RLC PDUs belonging to one or different radio bearers into/from transport blocks (TB) delivered to/from the physical layer on transport channels;
  19. 19. MAC (Contd…):  MAC: - Traffic volume measurement reporting; - Error correction through HARQ; - Priority handling between logical channels of one UE; - Priority handling between UEs by means of dynamic scheduling; - Transport format selection; - Padding.
  20. 20. RLC sub layer:     Transfer of upper layer PDUs supporting AM or UM; TM data transfer; Error Correction through ARQ (CRC check provided by the physical layer, in other words no CRC needed at RLC level); Segmentation according to the size of the TB: only if an RLC SDU does not fit entirely into the TB then the RLC SDU is segmented into variable sized RLC PDUs, which do not include any padding;
  21. 21. RLC (Contd…..)    Re-segmentation of PDUs that need to be retransmitted: if a retransmitted PDU does not fit entirely into the new TB used for retransmission then the RLC PDU is re-segmented; The number of re-segmentations is not limited; Concatenation of SDUs for the same radio bearer;
  22. 22. RLC (Contd…..)      In-sequence delivery of upper layer PDUs except at HO; Duplicate Detection; Protocol error detection and recovery; SDU discard; Reset.
  23. 23. RRC and NAS:   RRC (terminated in eNB on the network side) performs the functions listed below: - Broadcast; - Paging; - RRC connection management; - RB control; - Mobility functions; - UE measurement reporting & control. NAS control protocol (terminated at MME) - EPS bearer management; - Authentication; - ECM-IDLE mobility handling; - Paging origination in ECM-IDLE; - Security control.
  24. 24. RRC in detail:       Broadcast of System Information related to the non-access stratum (NAS); Broadcast of System Information related to the access stratum (AS); Paging; Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN including: Allocation of temporary identifiers between UE and E-UTRAN; Configuration of signalling radio bearer(s) for RRC connection: Low priority SRB and high priority SRB.
  25. 25. RRC in detail(Contd…):    Security functions including key management; Establishment, configuration, maintenance and release of point to point Radio Bearers; Mobility functions including:  UE measurement reporting and control of the reporting for intercell and inter-RAT mobility;  Handover;  UE cell selection and reselection and control of cell selection and reselection;  Context transfer at handover.
  26. 26. RRC in detail(Contd…):      Notification for MBMS services; Establishment, configuration, maintenance and release of Radio Bearers for MBMS services; QoS management functions; UE measurement reporting and control of the reporting; NAS direct message transfer to/from NAS from/to UE.
  27. 27. LTE Access Network Architecture
  28. 28. Functional Split between EUTRAN and EPC
  29. 29. RLC Layer
  30. 30. PDCP Functional Overview
  31. 31. PDCP Sub layer
  32. 32. ARQ and HARQ ARQ:  ACK/NACK based scheme  RLC mechanism HARQ:  ACK/NACK based scheme  MAC layer mechanism  Buffers the corrupted packets and waits for the next packet, based on that 2 packets it decodes the original packet.  Implicit Link adaptation technique (Coarse Data rate selection)
  33. 33. ARQ and HARQ (Contd...)      Tx an encoded packet incrementally which saves BW It reduces the amount of redundancy Synchronous in UL but Asynchronous in DL Parallel Processes of HARQ are allowed in MAC layer These 2 techniques along with the TCP retransmissions provide robust and reliable medium.
  34. 34. L2 Structure for Down Link The PDCP, RLC and MAC layers together constitute L2.
  35. 35. L2 Structure for UP Link
  36. 36. ROHC (RFC 3095 and 5225)  Modes:  Unidirectional Mode Bi-directional optimistic mode Bi-directional reliable mode    States:  Initialization & Refresh, First-Order Second-Order States  
  37. 37. QOS:      There are 9 QOS classes categorized into BR and GBR with different priorities. DSCP is also used here. Each class is represented by a Qos Class Identifier (QCI) Classes are configured based on the latency, packet loss and data rate. Applications requiring similar QOS are clubbed together as an SDF aggregate allocating a single EPS bearer for those 2 flows.
  38. 38. QOS Bearers
  39. 39. Mobility States of a UE in LTE
  40. 40. A Typical Uninterrupted Hand Off
  41. 41. Idle Mobility Management using Traffic Areas
  42. 42. Comparison b/w Release7and8:
  43. 43. PHY Layer Concepts: OFDMA Vs. SCFDMA
  44. 44. Time Domain Comparison:
  45. 45. Comparison Contd……
  46. 46. Channel Dependent Scheduling:
  47. 47. General Block Diagram:
  48. 48. Comparison b/w different schemes:
  49. 49. Framing:
  50. 50. Type 1 Frame Structure:
  51. 51. Type 2 Frame Structure:
  52. 52. Resource Grid:
  53. 53. BW/Resource Configuration:
  54. 54. Logical Channels in LTE
  55. 55. Transport Channels in LTE
  56. 56. Mapping of Logical to Transport Channels Note: The mappings shown in dotted lines are still being studied by 3GPP.
  57. 57. LTE Vs WiMax: 2 Sibling Rivalries     2 different technologies so cannot compare.They do not compete in same market Wimax is ready for deployment whereas LTE will be deployed mass in 2013. LTE is superior to 802.16e when compared to speed, but 802.16m will achieve almost the same speeds as LTE. For fixed and low roaming Wimax but for High Roaming-LTE.Alternatively LTE can be used for macro cellular coverage and Wimax for Micro cell coverage
  58. 58. Contd….     LTE release 8 supports interop between LTE and Wimax. Also HSPA+ is highly used and also for most of the users it provides sufficient BW and data rate @ 14 Mbps So the three technologies may co exist For Wimax we require new equipment but for LTE service providers can upgrade.
  59. 59. 3 Current Hot Technologies:
  60. 60. Comparing all the Contemporary Technologies
  61. 61. Future    Release-9 (LTE advanced) is on the way, draft initialization will start in Dec2008 and Dec-2009 1st draft release is expected. LTE-advanced supports data rates of 1 gig/s It also aims on improvising the predefined global roaming.
  62. 62. Its not that I am so smart , its just that I stay with problems longer - Albert Einstein
  63. 63. Thank You 