Introduction to Mobile Cellular Networks Part II: RAN / UTRAN

1. Introduction to Mobile Cellular NetworksPart II: RAN / UTRAN VU 389.134 Video and Multimedia Transmissions over Cellular Networks 10.10.2011 (http://www.nt.tuwien.ac.at/teaching/courses/winter-term/389134)

2. Repetition of the last lecture • Fill out the missing bits ;) X X X X

3. Repetition of the last lecture • Fill out the missing bits ;) X X X X X X X X

4. Repetition of the last lecture X 2G X X X 3G

5. Outline of this lecture • LTE Basics • Radio Link GPRS • TDMA • Slot format • Channels • Radio Link UMTS • WCDMA • Slot format • Channels • Upgrade to HSDPA (high level point of view)

6. LTE Core Network Basics

7. Introduction to Long Term Evolution (LTE) • 3GPP started 2004 the project “long-term evolution” • First final version was included in Release 8 of 3GPP • Commercial deployment started in 2009 in Sweden Stockholm • Real deployment not expected till end of 2010 • Motivation: data-rates growing exponentially

8. Targets of LTE • High data-rates • Download:100Mbps • Upload: 50Mbps • 1G for LTE Advance • Low delay • Sub 10ms delay • Short setup time & Short transfer delay • Core network “clean-up” • Reduced cost per bit • Backwards compatible • Co-Exist with GSM/UMTS • Re-farming of 2G and 3G spectrum • Hand-over • Relay topology for LTE Advanced (not finalized yet)

9. Evolution of UMTS

10. Architecture of LTE

11. Architecture of LTE 1 • Main changes in LTE • UTRAN  E-UTRAN (new radio access) • Only one node left: eNodeB • Smaller number of RAN interfaces • GPRS core network (CN)  System Architecture Evolution (SAE) • SAE = EPC (Evolved Packet Core) + eUTRAN • Differences to GPRS-CN • Simplified architecture • All IP Network (AIPN) • Support for, multiple heterogeneous RANs, including legacy systems as GPRS, but also non-3GPP systems (say WiMAX) • Core network (EPC) is now responsible for control of UE and the linked bearers • Bearer: IP packet flow with a defined QoS (between gateway and UE)

12. Architecture of LTE 2 Core Network Radio Access Network Operator, IMS, … S5 Serving SAE Gateway PDN SAE Gateway eNode B S7 PCRF SGSN, UMTS, … eNode B S4 MME EPS Evolved Packet System EPC Evolved Packet Core P-GW Packet Data Net GW S-GW Serving Gateway eNBevolvedNodeB PCRF PolicyandCharging Rules Functions HSS Home Subscriber Server S1-MME S11 SGi S1-U S1-U X2 X2 X2 S6a eNode B HSS (HLR) S3 NodeB RNC SGSN GGSN RNC SGSN

13. Architecture of LTE 3 • Main logical nodes in EPC are: • Serving Gateway (S-GW) = SGSN • Data gateway • Mobility Management Entity (MME) = SGSN-GW • Setup bearer path, … • PDN Gateway (P-GW) = GGSN or HomeAgent • IP anchor • Further EPC nodes are: • Home Subscriber Server (HSS) = HLR • Subscriber Database • Policy Control and Charging Rules Function (PCRF) • Charging and user related QoS settings • Evolved UTRAN (E-UTRAN) • Single logical node: eNodeB or eNB • eNodeB combines all functions found in Rel99 RNC and NodeB

14. The LTE Network Architecture eNB EPS Evolved Packet System EPC Evolved Packet Core P-GW Packet Data Network GW S-GW Serving Gateway eNBevolvedNodeB MME Mobility Management Ent. RB Radio Bearer NAS Non Access Stratum MME Inter Cell RRM NAS Security Radio AdmCont Idle State Mobility Handling Con Mob Cont RB Control EPS BearerControl RRC PDCP P-GW S-GW RLC UE IP addrallocation S1 Mobility Anchor MAC Packet Filtering PHY IP Anchor

15. Link Layer Design

16. Protocol Stack User-Plane • Packet Data Convergence Protocol (PDCP) • IP header compression based on Robust Header Compression (ROHC) • In-sequence delivery of upper layers PDUs • Duplicate elimination of lower layer SDUs • Timer based discard • Ciphering and integrity protection of transmitted data • Radio Link Control (RLC) • AM / UM / TM • ARQ • Segmentation/concatenation • Retransmission handling • In-sequence delivery to higher layers • Re-establishment • Medium Access Control (MAC) • Hybrid-ARQ retransmissions • Uplink and downlink scheduling at the eNB • Priority Handling • Mapping between logical and transport CHs UE eNB PDCP PDCP RLC RLC MAC MAC PHY PHY

17. Protocol Stack Control-Plane • Radio Resource Control (RRC) • RRC Connection Setup • Paging • Broadcast • Radio Bearer Control • UE Measurements • NAS • EPS bearer mgnt • Authentication • Paging in IDLE • Security Control UE eNB MME NAS NAS RRC RRC PDCP PDCP RLC RLC MAC MAC PHY PHY

18. Introducing Bearers • Bearer: IP packet flow with a defined QoS setting established between a gateway and the UE (very similar to a PDP Context) • No PDP Context in LTE • Default / Dedicated Bearers • GTPv1 –C (29.060) only supports PDP-Context • GTPv2 –C supports bearers (29.274) • Not radical different, • LTE GTP setup • Userplane: GTPv1 –U • Controlplane: GTPv2 -C Serving SAE Gateway GTPv2-C MME S11 GTPv1-C S3 SGSN SGSN

19. Mapping between Logical and Transport CHs Downlink logicalchannels PCCH BCCH CCCH DCCH DTCH MAC Layer Downlink transportchannels PCH BCH DL-SCH PHY Layer PCCH PagingControl Channel BCCH Broadcast Control Channel CCCH Common Control Channel DCCH DedicatedControl Channel DTCH Dedicated Traffic Channel PCH Paging Channel BCH Broadcast Channel DL-SCH DownlinkShared Channel

20. Mapping between Logical and Transport CHs Uplink logicalchannels CCCH DCCH DTCH MAC Layer Uplink transportchannels RACH UL-SCH PHY Layer CCCH Common Control Channel DCCH DedicatedControl Channel DTCH Dedicated Traffic Channel RACH Random Access Channel UL-SCH DownlinkShared Channel

21. Radio Interfaces

22. Outline of this part • Reading the standard: • Site: http://www.3gpp.org • GSM: • 00 – 11 • GSM (GPRS) • 41 – 55 • UMTS R99 • 21 – 37 • Today: • TS 25.401 "UTRAN overall description", • TS 25.301 "Radio Interface Protocol Architecture“ • Lecture slides • http://www.nt.tuwien.ac.at/teaching/courses/winter-term/389134

23. Accessing a Share Media • Physical access to the media • How to share the media between different users • Discrimination on: Time, Frequency, Codes, Space • GPRS: Time (TDMA) • UMTS: Codes ((W)CDMA) TDMA Time Division Multiple Access CDMA Code Division Multiple Access

24. Physical and Logical Channels – The Difference • Physical channels • Provide bearers for different logical channels • Each channel is identified through its physical parameters • Transport channels • Provide bearers for information exchange MAC/physical • Transport channels are unidirectional • Logical channels • Provide bearers for information exchange between MAC and RLC • Logical channels can be bi-directional • Two types: traffic channels, control channels RLC Radio Link Control MAC Media Access Contr.

25. GSM Radio Link: TDMA • Time Division Multiple Access • Random Access: ALOHA + collision detection • Signaled Access: fixed time slots • Each user is assigned one or more time slots • Signaling overhead • How to … full–duplex? • Orthogonal frequency bands (GSM 900: 880-915/ 925-960 MHz) • 124 Channels with 200kHz each Down Up

26. GSM Radio Link: Physical Channels • Time Division Multiple Access • Random Access: ALOHA + collision detection • With Signaling: fixed time slots • Each user is assigned one or more time slots • Frame structure of GSM • The basic TDMA frame TDMA Time Division Multiple Access GSM Global System for Mobile Communications 1 2 3 4 5 6 7 8 4,615ms Data S Train Data S Guard Guard Tail Tail 577s

27. GSM Radio Link: Logical Channels • Traffic Channels (TCHs) • Full/Half rate channels (TCH/F or H) • 13kbit/s of audio information (map to 22.8kbit/s encoded bit rate) • Broadcast Channels (BCHs) • Downlink only, beacon signals • Frequency Correction Channel (FCCH) • MS frequency tuning (frequency only – frame timing is missing!) • Synchronization Channel (SCH) • Frame timing + BSIC • Broadcast Control Channel (BCCH) • Cell specific information (LAI, permitted power, neighboring cells …) • Common Control Channels (CCCHs) LAI Local Area Information BSIC Base Station Info Code

28. GSM Radio Link: Logical Channels • Common Control Channels (CCCHs) • Start up phase of information exchange between MS and BS • Paging Channel (PCH) • Paging a MS due to a call from landline • Downlink only, may be (miss) used for traffic and commercials • Random Access Channel (RACH) • Allows the MS to request for resources in the cell • Uplink only • Access Grant Channel (AGCH) • Grants access to a stand alone Control Channel in the cell (after RACH) • Dedicated Control Channels (DCCHs) • Dedicated to one MS, bi-directional • Standalone Dedicated Control Channel (SDCCH) • Slow Associated Control Channel (SACCH) • Fast Associated Control Channel (FACCH)

29. GSM Radio Link: The frame structure • How to map low data rate logical channels? • Avoid excessive signaling • GSM introduces a given frame structure • Allow low data rate bearers on the logical link layer • Frames of GSM • Hyper frame • Encryption (3h) • Super frame • Cell broadcast • Multi frame • Signalling • TDMA frame • 8 Timeslots (users) • Timeslot • Data channel

30. GSM Radio Link: Physical Channels • Slow Associated Contr CH (SACCH) • Permanent on connection • Takes 2 slots from a multi frame • Slot 13 and 26 over up to 4 multi frames • 950bit/s (in bursts!) • Fast Associated Contr CH (FACCH) • Only if heavy signaling is needed (HO) • No normal TCH channel • Steals bit between Midamble and Data • 456 bit in 8 consecutive TDMA frames • Random Access CH (RACH) • Uplink slot for access burst • Only present if cell not fully loaded

31. A real example: KPI analysis • Error causes for mobile terminals attach requests • What mobile generate the most signals (faulty terminals) • Analysis on IuPS show 10 top users generating 100 requests per second • Why? • More detailed analysis show • Same mobile has different patterns throughout the day • Why? • Any Ideas…. • Consider the picture! • Mobility is the key • Different cells have different mappings

32. A real example: KPI analysis II • Signaling load in a cell • A certain cell shows periodic massive register rejects? • Certain neighbors show similar behavior • Cell was not loaded • Ideas? • Hints: • GMM • Train • Physical layer • LAC at a train line • Handover of all idle terminals cause overload in the BCCH! • Next cells impacted by the mobiles rejected to change LAC All mobiles in IDLE get active to register in LAC-B BCCH Resources depleted!

33. GSM Radio Link: Summary • TDMA based transmission • Slot based physical channels • One physical channel – mapping needed • 8 users per cell • One power amplifier • Signaling hidden in super-frames • Data transfer in bursts • Allows for different data rate channels • Cells may be signaling limited • Information of the physical layer is important to understand measurements at the link layer!

34. From GSM to GPRS • PS domain • Core network elements • PCU unit • More than one slot per user and TDMA multi frame • Up to 8 slots (classes of mobiles) • Allows higher data rate • Up / Down link not symmetric • Packet oriented traffic • Different coding sets (data protection) • CS 1 - 4 • Mobility management • Allow physical idle and logical active at the same time • Different to audio data CS Code Set

35. Repetition of the last lecture 2G 3G

36. UMTS Radio Link: Welcome to the UTRAN • UTRAN: UMTS RAN • Contains: RNC, NodeB, MS • Supports softhandover (SH) • RNC fully meshed • Protocols, Interfaces • Iub, Iur, Uu • RANAP • Operation modes RNC Radio Network Controller SRNC Serving RNC DRNC Drift RNC

37. UMTS RAN: The Protocol Architecture RRC Radio Resource Control PDCP Packet Data Conv. Proto. BMC Broadcast Message Contr. RLC Radio Link Control MAC Media Access Control

38. UMTS RAN: The Protocol Architecture • Packet Data Convergence Protocol (PDCP) • PS data header compression • Protocol abstraction layer (support for IPv4 and IPv6 • Optional implementation (not used) • Radio Link Control Protocol • Two modes of operation • Transparent, Non-Transparent • Ack / NonAck • Functions • Mapping • Ciphering • Error correction • Flow control, segmentation

39. UMTS RAN: The Protocol Architecture • Broadcast Multicast Control Protocol (BMC) • Cell broadcast messages • Storage and planning of messages • Radio Resource Control Protocol (RRC) • Routing Function Entity • Route CM and MM to/from RNC • Broadcast Control Function Entity • Paging / Notification Ctrl FuncEnt • Dedicated Control Function Entity • Transfer Mode Entity • All UTRAN to UE control functions

40. UMTS Radio Link: WCDMA • Separating radio resources in UMTS • TDD + TDMA + CMDA (UTRA TDD) • FDD + CDMA (UTRA FDD) – called WCDMA • Wideband compared to cdmaOne • Problem: Qualcom owns key patents in UTRA FDD (and pushed them to the standard ;) ) • WCDMA key numbers • Signal is spread using orthogonal codes • Higher bit rate – less spreading • Frequency reuse one (different cell planning) • Near-far effect - power control is important • Courses on modulation and spreading: • 389.063: Mobile Communications • 389.051: Introduction to Telecommunications

41. UMTS Radio Link: Logical Channels • Broadcast Control Channel (BCCH) • distributes information that allows UEs to attach to network • information about radio environment: power levels, network identity.. • Common Control Channel (CCCH) • for exchange of first messages with attaching UE • no specific (dedicated) control channel has been assigned yet • Dedicated Control Channel (DCCH) • for exchange of control information with attached UE • e.g. power control • Paging Control Channel (PCCH) • for paging UEs • Common Transport Channel (CTCH) • unidirectional downlink channel • for broadcasting information to all, or a group of UEs • Dedicated Transport Channel (DTCH) • exchange of user data

42. UMTS Radio Link: Transport Channels • Specify to how information is transferred • Provide specific service quality, e.g. • Bit rate, error protection, power level, access method • Data packets that are transmitted over Transport Channels are called „Transport Blocks“ • Several are transmitted simultaneously in „Transport Block Sets“ • Each Transport Channel is described by a set of „Transport Formats“ it can provide, i.e. • Transport Block Size, Transport Block Set Size, Transmission time interval • How long does it take to transmit a Transport Block Set • Type of error protection (Channel Coding and Cyclic Redundancy Check) • Channel Coding: redundant transmission of information • Efficiency of Channel Coding • For each Transport Block Set transmission, a suitable Transport Format is chosen from the Transport Format Set

43. UMTS Radio Link: Transport Channels (some) • Broadcast Channel (BCH) • downlink, fixed bit rate, high power level (needs to be audible to all) • used for BCCH • Random Access Channel (RACH) • uplink, random access • mostly used by CCCH and DCCH (also DTCH) • Dedicated Channel (DCH) • uplink and downlink, dedicated to a particular UE • one DCH may carry several DCCH and DTCH • Downlink Shared Channel (DSCH) • dedicated user traffic but shared by several users • very important for data traffic (no dedicated bandwidth for one user) • optional to implement • Note there is no Uplink Shared Channel • At the time of standardization no use was anticipated

44. UMTS Radio Link: Physical Channels • Common Pilot Channel (CPICH) • a signaling sequence known to network and UE is spread with the code used in the P-CCPCH, in which further information is available • Primary Common Control Physical Channel (P-CCPCH) • used by BCCH / BCH • uses a code broadcasted on CPICH • Every UE can listen • Dedicated Physical Data Channel (DPDCH) • physical channel dedicated to a user • Primary Synchronization Channel (for FDD) (P-SCH) • P-SCH sends known, invariant signaling sequence of 256 chips • allows UE to synchronize

45. UMTS Radio Link: Mapping of the Channels • GSM has one physical channel • UMTS has several physical channels • Mapping is more complex

46. UMTS Radio Link: Packetization on the Link • Dedicated channel for every transmission • We need packetization for • Error control • Synchronization • Start/End of Transmission • UMTS R99 packetization example

47. UMTS Radio Link: Transmission on DPDCH • Data flow in the UTRAN physical layer (64kbit/s)

48. UMTS Radio Link: Summary • WCDMA link • Max data rate DCH: 384kbit/s • Different data rate channels available • Higher complexity in the RAN • Meshed RNC • Soft Handover • Dedicated channels use packetization! • Errors will show time patterns • RLC • Two different operation modes • Used codes will introduce patterns (Turbo Code!) • Again – understand physical layer to understand measurements on Gn

49. From UMTS R99 to HSDPA • The goals • Reduce RTT • Introduce real PS-oriented bearers • New elements • The MAC-hs • Hybrid – ARQ • Adaptive Modulation and Coding (AMC) • MAC-hs RTT Round Trip Time AMC Adaptive Modulation and Coding

50. From UMTS R99 to HSDPA • Hybrid ARQ (HARQ) • Error correction methods: • Forward Error Correction (FEC) • Add information to protect payload, e.g. CRC • Automatic Repeat reQuest (ARQ) • TCP like acknowledgement • Hybrid ARQ combines FEC and ARQ • Adaptive Modulation and Coding (AMC) • UMTS R99 • Fixed modulation • Variable Spreading Factor (SF) • HSDPA • Fixed SF (16) • Adaptive modulation and coding (AMC)