3G/4G Mobile Communications Systems. Dr. Stefan Brück Qualcomm Corporate R&D Center Germany

Transcription

1 3G/4G Mobile Communications Systems Dr. Stefan Brück Qualcomm Corporate R&D Center Germany

2 Chapter IV: Radio Interface and Application Protocols 2 Slide 2

3 Radio Interface and Application Protocols Logical, Transport and Physical Channels Channel Mapping in UMTS and LTE Layer 3 Control Plane Protocol Radio Resource Control (RRC) Layer 2 Protocols Radio Link Control (RLC) Medium Access Control (MAC) MAC Architecture in HSPA and LTE PDU Formats for MAC-hs, MAC-ehs, LTE MAC (DL-SCH) Stop and Wait Hybrid Automatic Repeat Request Protocol Example of an Application Protocol: X2 Application Protocol 3 Slide 3

4 UMTS and LTE Channels Downlink transmitted by UTRAN, received by UE Uplink transmitted by UE, received by UTRAN Common carriers information to/from multiple UEs Dedicated carries information to/from a single UE using dedicated resources Shared carries information to/from a single UE using shared resources Logical defined by what type of information is transferred, e.g., signaling or user data Transport defined by how data is transferred over the air interface, e.g., multiplexing of logical channels Physical defined by physical mapping and attributes used to transfer data over the air interface, e.g. spreading rate 4 Slide 4

5 Channel Mapping UMTS Release 99 Channels 5 Slide 5

6 Channel Mapping UMTS Dedicated Channels These channels carry user and signaling data between UTRAN and an individual UE DCCH carries RRC and NAS signaling The number of DTCH assigned is determined by the application, e.g. for voice three DTCHs are assigned to one UE DCCHs and DTCHs are mapped to a single DCH or may be assigned an individual DCH In R99 deployments all DCHs are mapped to a single DPDCH The DPCCH carries information generated at PHY such as pilot, power control bits. There is always exactly one DPCCH 6 Slide 6

7 Typical UMTS R99 Service Combinations Service Combination Uplink 3.4kbps signalling + PS I&B 64kbps + AMR Voice 12.2kbps 3.4kbps signalling + PS I&B 128kbps 3.4kbps signalling + PS I&B 8kbps + PS Strm 64kbps+ AMR Voice 12.2kbps 3.4kbps signalling + AMR Voice 12.2kbps 3.4kbps signalling + CS 64kbps Service Combination Downlink 3.4kbps signalling + PS I&B 64kbps + AMR Voice 12.2kbps 3.4kbps signalling + PS I&B 384kbps 3.4kbps signalling + PS I&B 8kbps + PS Strm 16kbps+ AMR Voice12.2kbps 3.4kbps signalling + AMR Voice 12.2kbps 3.4kbps signalling + CS 64kbps I&B Strm Interactive & Background Streaming 7 Slide 7

8 HSDPA and HSUPA Channel Mapping 8 Slide 8

9 Typical UMTS HSPA Service Combinations Service Combination Uplink 3.4kbps signalling + PS I&B 64kbps 3.4kbps signalling + PS I&B 64kbps + CS 64kbps 3.4kbps signalling + PS I&B 384kbps 3.4kbps signalling + PS I&B 8kbps + AMR Voice 12.2kbps 3.4kbps signalling + PS Strm 32kbps + PS I&B 8kbps+ AMR Voice 12.2kbps 3.4kbps signalling + PS I&B EDCH EDCH signalling + PS I&B EDCH Service Combination Downlink 3.4kbps signalling + PS I&B HSDSCH 3.4kbps signalling + PS I&B HSDSCH + CS 64kbps 3.4kbps signalling + PS I&B HSDSCH 3.4kbps signalling + PS I&B HSDSCH + AMR Voice 12.2kbps 3.4kbps signalling + PS Strm HSDSCH 32kbps + PS I&B HSDSCH + AMR Voice 12.2kbps 3.4kbps signalling + PS I&B HSDSCH 3.4kbps signalling + PS I&B HSDSCH 9 Slide 9

10 Channel Mapping LTE Downlink Most DL data is carried on the DL-SCH and its corresponding PDSCH In contrast to UMTS, there are no dedicated transport channels in LTE 10 Slide 10

11 Channel Mapping LTE Uplink Most UL data is carried on the UL- SCH and its corresponding PDSCH In contrast to R99 UMTS, there are no dedicated transport channels in LTE 11 Slide 11

12 Layer 2 Overview 12 The Layer 2 consists of the following sublayers Packet Data Convergence Protocol (PDCP) performs header compression and decompression of IP streams Broadcast/Multicast (BMC) supports cell broadcast functions Radio Link Control (RLC) performs segmentation, reassembly, concatenation and provides various data transfer mode Medium Access Control maps logical channels onto transport channels, performs traffic volume reporting, scheduling Slide 12

13 Layer 2 Overview SDUs and PDUs Protocol Data Unit Unit of data exchanged between peer layers in a network May contain information, addressing, and data Service Data Unit Set of data sent by a user of the services of a given layer Transmitted to the peer service semantically unchanged 13 Slide 13

14 Layer 2 Overview Data Flow Example (UMTS) 14 Slide 14

15 UMTS Protocol Stack Control Plane Radio Resource Control (RRC) Access stratum control System information processing Paging and notification RRC connection management NAS layer message routing Ciphering and integrity protection control Radio Bearer management RRC mobility Measurement control and reporting 15 Slide 15

16 UMTS Protocol Stack User Plane Physical Layer (PHY) Error detection on transport channels Forward error correction encoding/decoding Interleaving/deinterleaving of transport channels Multiplexing/demultiplexing of transport channels Rate matching Modulation/demodulation Spreading/despreading Measurements (e.g., FER, transmit power) Radio Link Control (RLC) Segmentation, reassembly, concatenation, padding Retransmission control, flow control Duplicate detection, in-sequence delivery Error correction Ciphering acknowledged and unacknowledged mode Medium Access Control (MAC) Mapping and multiplexing of logical to transport channels Priority handling of data flows UE identification on common channels Traffic volume measurements Random Access Channel procedure Scheduling Ciphering transparent mode 16 Slide 16

17 RLC Overview Functions (TS , TS ) Radio Link Control Functions Transfer of user data and signaling Segmentation and reassembly Concatenation Padding Error correction In-sequence delivery of upper layers PDUs Duplicate detection Flow control Sequence number check Protocol error detection and recovery Ciphering (UM and AM only) SDU discard 17 Slide 17

18 RLC Overview Architecture The primary function of the RLC is to transfer user data and signaling Data flow to and from upper layers are carried by Radio Bearers and may carry either signaling data (Signaling Radio Bearer) or user data (Radio Access Bearer) Each Radio Bearer is mapped to a RLC entity, which operates in of the three data transfer modes: transparent mode (TM), unacknowledged mode UM, or acknowledge mode (AM) 18 Slide 18

19 RLC Overview Data Transfer Modes Transparent Mode (TM) Unreliable service Separate receive and transmit entities Supports a set of fixed SDU sizes configured by RRC Unacknowledged Mode (UM) Unreliable service Separate receive and transmit entities Supports arbitrary SDU sizes Acknowledged Mode (AM) Reliable service Bidirectional entity Supports arbitrary SDU sizes 19 Slide 19

20 RLC Overview Data Transfer Modes (cntd.) Radio Bearers using RLC TM: BCCH, PCCH, CS Voice DTCH Radio Bearers using RLC UM: one DCCH, PS DTCH used for error tolerant and delay sensitive applications 20 Radio Bearers using RLC AM: one DCCH, PS DTCH used for error sensitive and delay tolerant applications Slide 20

21 RLC Transparent Mode In TM Mode, PDUs are transferred with little interaction by RLC No header is added Segmentation and reassembly If the SDU size is too large to fit into a single PDU, it may segmented at Tx and reassembled at Rx side Ciphering for logical channels is performed by the MAC 21 Slide 21

22 RLC Unacknowledged Mode A small header containing information about segmentation, concatenation and sequence number is added Segmentation and reassembly Sequence number check Used during reassembly to detect corrupted SDUs 22 Slide 22

23 RLC Acknowledged Mode AM Mode provides reliable service based on ACKs and NACKs Segmentation and reassembly Error correction PDUs received in error are retransmitted In-sequence delivery PDUs are delivered to upper layers in the same order as they were submitted to the transmitted RLC Flow control Configurable transmit and receive window sizes Ciphering of logical channels is performed by RLC 23 Slide 23

24 U-Plane Protocol Stack (System Simulator) 24 Slide 24

25 Example: Parameters for DL 384 kbps / PS RAB RLC SDU Size Table taken from 3GPP TS , v Slide 25

26 MAC Overview Functions (TS , TS ) Medium Access Control (MAC) Functions Logical and transport channel mapping Identification of UEs on common transport channels Prioritizing logical channels Multiplexing/de-multiplexing of logical channels Transport format combination selection (Scheduling) Ciphering (for RLC TM only) (Segmentation) (Reordering) (HARQ) 26 Slide 26

27 UTRAN MAC Overview Architecture I/III The MAC in R99 consists of three parts MAC-c/sh: controls access to the common transport channels MAC-b: controls access to the broadcast channel MAC-d: controls access to the dedicated channels 27 Slide 27

28 UTRAN MAC Overview Architecture II/III The MAC in R5 was extended to support HSDPA MAC-hs: This part of the MAC resides in the Node B to allow fast Hybrid ARQ. It is also responsible for scheduling of the HS-DSCH 28 Slide 28

29 UTRAN MAC Overview Architecture III/III The MAC in R6 was extended to support HSUPA MAC-e: provides fast retransmissions by HARQ MAC-es: provides reordering functionalities 29 On the UTRAN the MAC is split between the Node B (MAC-e) and the RNC (MAC-es) Slide 29

30 MAC Entity and HARQ Entity in 3GPP Common definitions in LTE and HSDPA There is one MAC entity per cell There is one HARQ entity per supported UE The HARQ entity handles the hybrid ARQ functionality for one user A number of parallel HARQ processes are used to support the HARQ entity The HARQ processes are of stop and wait type The HARQ process can be re-used if the associated ACK/NACK is received again Definitions in HSDPA There is one HARQ process per TTI for single stream transmission There two HARQ processes per TTI for dual stream transmission This definition applies for MAC-ehs only Definitions in LTE A HARQ process is associated with one or two MAC PDUs 30 Slide 30

31 MAC-hs Entity in the UTRAN (Rel5, Rel6) MAC-d flows MAC-hs Priority Queue Priority Queue distribution Priority Queue Scheduling/Priority handling Priority Queue distribution Priority Queue HARQ entity TFRC selection Priority Queue MAC Control The queues store MAC-d PDUs which are also called MAC-hs SDUs In the MAC-hs only entire MAC-d PDUs from one priority queue can be mapped into one MAC-hs PDU Multiplexing and segmentation of MAC-d PDUs is not offered in the MAC-hs The MAC-hs header indicates the queue ID, the TSN and the MAC-d PDU sizes. The smallest size 21 bits Associated Uplink Signalling HS-DSCH Associated Downlink Signalling 31 Slide 31

32 MAC-ehs Entity in the UTRAN (Rel7) MAC-d flows MAC-ehs LCH-ID MUX Scheduling/Priority handling LCH-ID MUX The queues store MAC-d PDUs which are also called MAC-ehs SDUs A reordering SDU is a complete or a segment of a MAC-ehs SDU Priority Queue Priority Queue MAC Control A reordering PDU consists of several reordering SDUs of the same priority queue Segment ation Segment ation Finally, a MAC-ehs PDU consists of one or several reordering PDUs from up to three priority queues Associated Uplink Signalling HARQ entity TFRC selection HS-DSCH Associated Downlink Signalling The MAC-ehs offers multiplexing and segmentation The MAC-ehs header indicates the logical channel ID, the TSN, segmentation and SDU sizes. The smallest size is 24 bits 32 Slide 32

33 MAC-hs and MAC-ehs Entities in the UE To MAC-d M AC-hs Disassembly Disassembly Reordering Reordering Re-ordering queue distribution HARQ HS-DSCH Associated Downlink Signalling To M AC-d M AC-ehs LCH-ID D em ux Reasse mbly Reo rdering Associated Uplink Signalling LCH-ID D em ux Reassembly Reordering Re-o rdering queue distributio n Disassembly HARQ HS-DSC H Associated Downlink Signalling Associated Uplink Signalling MAC Control M AC Contro l The disassembly unit removes the MAChs/MAC-ehs header and potential padding bits Padding is introduced since a finite set of MAC-hs/MAC-ehs PDUs is allowed New octed-aligned PDU sizes have been introduced together with MAC-ehs, i.e. the PDU sizes are multiples of one byte The reordering queue distribution routes the received MAC-hs PDUs or the reordering PDUs to the correct reordering queues based on the queue ID or received logical channel identifier The reordering entity reorders received MAC-hs PDUs/reordering PDUs according to the received TSN The reassembly entity reassembles segmented MAC-ehs SDUs 33 Slide 33

34 Why MAC-ehs Segmentation in HSDPA In Rel. 5 6 the RLC PDU sizes was either fixed to 336 bits or 656 bits The RLC protocol applies a window based ARQ mechanism with a window size W of up to 4095 PDUs The RLC protocol can send at most 4095 PDUs before a status report is received from the UE. Some UEs only support a window size of 2047 PDUs In the RLC protocol the maximal throughput T is limited to T W PDU Size [bits] T RLC + T RTT Timer Status Prohibit The RLC round trip time is typically in the order of 80ms 120ms in real world The timer status prohibit should be set to similar values as the RLC RTT Therefore it is very difficult to achieve 14.4 Mbps in HSDPA with realistic parameter settings and window sizes of 2047 PDUs The flexible RLC PDU size (up to 1500 bytes) introduced in Rel. 7 together with MAC-ehs segmentation overcomes this bottleneck 34 Slide 34

35 Differences of MAC-hs/ehs and LTE MAC MAC-hs does not support segmentation MAC-ehs segmentation needed in HSDPA The RLC protocol resides in the RNC The RLC does not have fast information about required MAC-ehs SDU sizes in the Node B In LTE both RLC and MAC reside in the Node B The MAC can inform the RLC about required MAC SDU sizes per TTI. Segmentation is done in the RLC Additionally, no re-ordering is supported in the LTE MAC Reordering to higher layers is done in the RLC 35 Slide 35

36 MAC PDU Formats VF Queue ID TSN SID 1 N 1 F 1 SID 2 N 2 F 2 SID k N k F k MAC-hs PDU MAC-hs header MAC-hs SDU MAC-hs SDU Padding (opt) Mac-hs payload LCH-ID 1 L 1 TSN 1 SI 1 F 1 LCH-ID k L k TSN k SI k F k MAC-ehs PDU MAC-ehs header Reordering PDU Reordering PDU Mac-ehs payload Padding (opt) LTE MAC PDU (DL-SCH) 36 Slide 36

37 Stop and Wait HARQ Protocol in HSDPA and LTE 2 ms DL transmission at NodeB... HARQ process #1 HARQ process #2 HARQ process #3 HARQ process #4 HARQ process #5 HARQ process #6 HARQ process #1 HARQ process #2... DL reception at UE... HARQ process #1 HARQ process #2 HARQ process #3 HARQ process #4... ACK/NACK feedback to NodeB DL processing at UE HARQ process #1 HARQ process #2 A HARQ process is in charge of the transmission (and possible subsequent re-transmission) of one MAC PDUs Once the MAC PDU is sent the HARQ process waits for the ACK/NACK from the UE to decide whether to schedule a re-transmission or a new MAC-hs PDU transmission. The round trip time delay is typically 6 TTI = 12 ms in HSDPA In LTE the round trip time is 8 TTI = 8 ms 37 Slide 37

38 Horizontal Layers Vertical Planes The protocol structure consists of two main layers, Radio Network Layer and Transport Network Layer Vertically, the protocols are separated in control and user plane All (E)-UTRAN related issues are visible only in the Radio Network Layer The Transport Network Layer applies standard transport technology that is selected for (E)-UTRAN without any (E)-UTRAN specific requirements Application protocols (AP) are control plane protocols in the Radio Network Layer of entities They control the signaling to other entities Examples of Applications Protocols in UTRAN NBAP: Node B RNC RANAP: RNC SGSN/MSC RNSAP: RNC RNC Examples for Applications Protocols in E-UTRAN X2AP: enb enb S1AP: enb MME 38 Slide 38

39 LTE X2 Protocol Structure (TS ) Radio Network Layer Control Plane X2-AP User Plane User Plane PDUs Transport Network Layer Transport Network User Plane Signaling Transport Transport Network User Plane SCTP IP Data link layer Physical layer Data Transport GTP-U UDP IP Data link layer Physical layer Clear separation between radio network and transport network layers The radio network layers defines interaction between enbs The transport network layer provides services for user plane and signaling transport 39 Slide 39

40 X2 Application Protocol (X2AP) The X2AP is responsible for providing signaling between enbs X2AP functions are executed by so called Elementary Procedures Rel. 8 defines eleven EPs related to different X2AP functions In Rel. 9 four additional EPs have been defined Class 1: EPs with response (success or failure) Class 2: EPs without response In LTE Rel. 8/9 limited load management functionality is supported Its functionality is extended in Rel. 10 Function Mobility Management Load Management Reporting of General Error Situations Resetting the X2 Setting up the X2 enb Configuration Update Mobility Parameters Management Mobility Robustness Optimisation Energy Saving Elementary Procedure(s) a) Handover Preparation b) SN Status Transfer c) UE Context Release d) Handover Cancel a) Load Indication b) Resource Status Reporting Initiation c) Resource Status Reporting Error Indication Reset X2 Setup enb Configuration Update Mobility Settings Change a) Radio Link Failure Indication b) Handover Report Cell Activation Release 8 Release 9 40 Slide 40

41 X2 AP Load Management The X2AP load management function is used by the enbs to indicate resource status, overload and traffic load to each other The load management function consists of the EPs Load Indication (class 2) Purpose: Transfer load and interference coordination information between enbs An enb initiates the procedure by sending LOAD INFORMATION message to another enb Resource Status Reporting Initiation (class 1) Purpose: Request the reporting of load measurements to another enb The procedure is initiated with a RESOURCE STATUS REQUEST message sent from enb 1 to enb 2 and enb 2 answers with RESOURCE STAUS RESPONSE message Resource Status Reporting (class 2) Purpose: Report the result of measurements admitted by enb 2 following a successful Resource Status Reporting Initiation procedure The enb 2 reports the results of the measurements in RESOURCE STATUS UPDATE message enb1 enb2 LOAD INFORMATION enb 1 enb 2 RESOURCE STATUS REQUEST RESOURCE STATUS RESPONSE enb 1 enb 2 RESOURCE STATUS UPDATE 41 Slide 41

42 Information Elements of LOAD INFORMATION UL Interference Overload Indication IE: Indicates the interference level experienced by the indicated cell on all resource blocks, per PRB. Values: High Interference, Medium Interference, Low Interference UL High Interference Indication IE: Indicates, per PRB, the occurrence of high interference sensitivity, as seen from the sending enb. The receiving enb should try to avoid scheduling cell edge UEs in its cells for the concerned PRBs Values: High Interference Sensitivity, Low Interference Sensitivity Relative Narrowband Tx Power (RNTP) IE: Indicates, per PRB, whether downlink transmission power is lower than the value indicated by the RNTP Threshold IE Values: Tx power exceeding RNTP threshold, Tx power not exceeding RNTP threshold Detailed definition of interference, interference sensitivity are implementation specific 42 Slide 42

43 RESOURCE STATUS REQUEST Message The reporting can be periodic or event based In case of periodic reporting request, the RESOURCE STATUS UPDATE message is used Periodicity is either 1s, 2s, 5s, 10s Supported measurements Radio Resource Status IE indicates the usage of the PRBs in Downlink and Uplink DL GBR PRB usage, UL GBR PRB usage, DL non-gbr PRB usage, UL non-gbr PRB usage, DL Total PRB usage, UL Total PRB usage The report is an integer value ranging from 0 to 100 S1 TNL Load Indicator IE indicates the status of the S1 Transport Network Load experienced by the cell Low Load, Medium Load, High Load, Overload Hardware Load Indicator IE indicates the status of the Hardware Load experienced by the cell Low Load, Medium Load, High Load, Overload Composite Available Capacity Group IE indicates the overall available resource level in the cell in Downlink and Uplink. Detailed definition of measurements are implementation specific 43 Slide 43