Session 5 T ch c nica c l a Aspect c s t of o f L T L E

Transcription

1 Session 5 Technical Aspects of LTE Part III: Uplink and Downlink Channels ITU ASP COE Training on Technology, Standardization and Deployment of Long Term Evolution (IMT) Sami TABBANE 9-11 December 2013 Islamic Republic of Iran 1

2 Agenda 1. LTE Radio Interface 2. Downlink Features 3. Downlink Radio Resources 4. DL Reference Signals 5. Uplink Features 6. Radio Channels 2

3 LTE/SAE 1. LTE Radio Interface 3

4 LTE physical layer DL: adaptive OFDM Scheduling channel and link adaptation dependent in the time and frequency domain User #1 scheduled Δf=15kHz User #2 scheduled User #3 scheduled UL: SC-FDMA with a dynamic bandwidth (pre-coded OFDM) PAPR Better spectrum efficiency Reduced UL interference (allows intra-cell orthogonality) frequency 180 khz Flexible bandwidth (with resolution of 180 khz) Possibility to deploy in bandwidth of <5 MHz to 20 MHz Multiple antennas, RBS and terminal MIMO, antennas lobes, TX- and RX diversity, interference rejection High bitrates and higher capacity TX frequency RX Harmonised FDD and TDD concept FDD and TDD maximum spectrum sharing Maximum UE capacity: BW = 20 MHz f DL < 5 5 FDD-only MHz Half-duplex TDD-only FDDf DL/UL f DL f UL f UL 4

5 Temporal structure of LTE Temporal Structure of High Level Transmission LTE A radio frame duration T frame = 10 ms, consists of 10 sub-frames, duration T subframe = 1 ms Provide consistent time intervals LTE radio access delays expressed as multiples of the unit time T s = 1/ T frame = T s, T subframe = T s 5

6 Temporal structure of LTE In FDD mode (Operation in paired spectrum) all subframes of a carrier either used for uplink or in downlink Downlink / Uplink subframes Allocation for the FDD 6

7 Temporal structure of LTE For the 5 MHz, there are 512 sub-carriers of 15 khz. The total band is 7.68 MHz. Larger than the 5 MHz band 7

8 Temporal structure of LTE Advantages of using LTE TDD: it is possible to dynamically change the up and downlink balance and characteristics to meet the load conditions. 7 up / downlink configurations have been defined. D/U is a subframe for downlink/ Uplink transmission and S is a "special" subframe used as a guard time. 8

9 Temporal structure of LTE In TDD mode (Operation in non-paired spectrum): The first and sixth subframes (subframes 0 and 5) are always allocated to the DL The other sub-frames can be allocated to UL or DL The 1 st and 6 th subframes contain synchronization signals: Transmitted in each cell Allows the current and neighboring cells scan. 9

10 Temporal structure of LTE TDD Downlink / Uplink Allocation of subframes 10

11 Temporal structure of LTE 5/5 TDD mode subframes allocation flexibility allows several asymmetries in terms of radio resources (sub-frames) allocated on uplink and downlink The allocation of sub-frames must be the same for neighboring cells to avoid severe interference between uplink and downlink asymmetry Uplink / Downlink cannot change dynamically (the frame rate) There are two types of frame structure in LTE: Generic type 1: used in FDD and TDD Generic type 2: used in TDD for coexistence with systems based on the 3GPP TD-SCDMA 11

12 LTE/SAE 2. Downlink Features 12

13 Downlink physical resources Downlink Physical resource 13

14 DL physical resource One frame (10 ms) 1 resource block (12 7 = 84 resource elements) One sub-frame (1 ms) One resource element 12 sub-carriers One slot (0.5 ms) Temporal structure: T CP T u 10 ms frame = 10 sub-frames of 1 ms 1 sub-frame = 2 slots of 0.5 ms 1 slot = 7 symbolsofdm (6 symbols if extended CP) Resource blocks: 12 sub-carriers during 1 slot Allocation by pair of 2 consecutive resource blocks DC carrier not used 14

15 Downlink physical resources Cyclic prefixes of different lengths can be used in different subframes Each Resource Block is composed of 12 subcarriers in a slot of 0.5 ms Each Resource Block is composed of: 12 * 7 = 84 Resource Elements for normal cyclic prefix 12 * 6 = 72 Resource Elements for extended cyclic prefix Resource Block for a Normal Cyclic Prefix 15

16 Signaling A DL resource contains signaling bits: Specific reference signals (RS) of the Cell (channel estimation and CQI measurements) L1/L2 signaling (for DL HARQ and scheduling info, UL scheduling, power commands) Primary and secondary synchronization signals (Cell selection) Broadcast and paging channel One frame (10 ms) One sub-frame (1 ms) One resource element 12 sub-carriers One slot (0.5 ms) T CP T u 16

17 Downlink physical layer 3. Downlink Radio Resources 17

18 Radio resources (1) 18

19 Radio resources (2) 19

20 Frame structure 20

21 Downlink physical layer 4. DL Reference Signals 21

22 Overview Signals on the DL PHY layer P-SS (Primary Synchronization Signal): used for initial sync S-SS (Secondary Synchronization Signal): frame boundary determination RS (reference signals): pilots for channel estimation and tracking Signals on the UL PHY layer Demodulation Reference Signal: sync and channel estimation SRS (Sounding reference signals): transmitted on the uplink to allow the network estimate the quality of the channel on different frequencies. 22

23 Downlink reference signals To perform coherent demodulation, the terminal needs to estimate the channel Insert known reference symbols in the OFDM time-frequency grid LTE Downlink Reference Signals The reference symbols are inserted: In the first OFDM symbol and the third symbol from the end of slot With a frequency spacing of 6 subcarriers With 3 sub-carriers spacing between the first and second reference symbols 4 reference Resource Block symbols 23

24 Downlink reference signals To reduce noise channel estimation on the time-frequency grid, the terminal must perform interpolations on symbols of multiple reference To estimate the channel of a Resource Block, the terminal can use the symbols of Resource Blocks references neighbors and slots / subframe previous For a frequency selective channel, the ability to interpolate in the frequency domain is limited The ability to interpolate in the time domain is limited in cases of: High mobility of the terminal TDD (The previous sub-frames cannot be allocated to the downlink) 24

25 Downlink reference signals Structure of the reference signals in case of downlink transmission with 2 antennas 25

26 Downlink reference signals Structure of the reference signals in case of downlink transmission with 4 antennas 26

27 Downlink transport channel processing Downlink Transport Channel Processing 27

28 Uplink physical layer 5. Uplink Features 28

29 UL frame structure Sub-frame = 2 slots 1 slot = 6 blocks for the data (each block consists in one DFTS-OFDM symbol) 1 block for the reference signals (used for UL channel estimation for the coherent demodulation) Transmission bandwidth and frequency location are controlled by Node B scheduler If a single frequency transmitter is used, resources can be treated the same as in OFDMA User #1 User #2 Data Reference signal 29

30 Uplink physical resources Structure of DFTS-OFDM Transmission Base A DFT of size M is applied to a block of M symbols The output of DFT is applied to a subset of the inputs of IFFT of size N. 30

31 Uplink physical resources The basic parameters of the uplink in LTE are as far as possible aligned with the downlink: Spacing between subcarriers f = 15 khz Resource Blocks consisting of 12 subcarriers Unlike the downlink, the DC subcarrier is used in the uplink because: The presence of a DC subcarrier in the middle of the spectrum makes possible the allocation of the entire band to a single mobile while maintaining the low PAPR property DFT pre-coding spreads the effect of DC interference for M symbols of a block making it less critical than for a normal OFDM transmission 31

32 Uplink physical resources The total number of subcarriers in the uplink is N sc = 12*N RB The physical layer in the uplink allows much flexibility in terms of frequencies band system: Any number of Resource Blocks from 6 The time structure is very similar to the downlink: Each sub-frame consists of two slots of duration T slot = 0.5 ms Each slot consists of a number of DFT blocks including a cyclic prefix Two periods of cyclic prefix: Normal and extended 32

33 Uplink physical resources Sub-frame and Slot Structures: each sub-frame consists of 2 Slots Each slot consists of 6 or 7 DFTS-OFDM blocks 33

34 Uplink physical resources Unlike the uplink, the resource blocks assigned to the terminal in the uplink must be consecutive in the frequency domain Same as in the downlink, a resource block in the uplink is composed of 12 DFTS-OFDM subcarriers in a slot of 0.5 ms RB: Resource Block Resource allocation in the uplink 34

35 Uplink physical resources Inter-slot frequency hopping can be used in the uplink Physical resources used on the 2 slots do not occupy the same subcarriers RF transmission band completely covers the spectrum in the uplink The frequency hopping changes the DFT-IFFT mapping Frequency hopping two benefits: Diversity and frequency diversity interference Frequency hopping in the uplink 35

36 Uplink Transport Channel Processing 1/3 Transport Channel Processing in the uplink 36

37 Downlink physical layer 6. Radio Channels 37

38 Radio channels To be flexible, the E-UTRAN offers several types of channels: Logical channels (What is transmitted) Transport channels (How is it transmitted) Physical channels The logical channels correspond to data transfer services offered by the protocols of the radio interface to higher layers There are two types of logical channels: Control channels: Transfer of Control Plane Information Traffic channels: Transfer user plane information 38

39 Radio channels E-UTRAN mapping between channel types (as in the network). 39

40 Radio channels The E-UTRAN channel model was inherited from the UTRAN channel model Logical Channels / Transport Channels Association in the MAC Layer of RNC UTRAN / FDD 40

41 Radio channels UTRAN and E-UTRAN models: Share almost the same logical channels Completely different scale of transport channels: DCH channel present in the UTRAN has disappeared from the E-UTRAN Point-to-point E-UTRAN Data services are packet oriented and use a single transport channel: SCH (Shared Channel) The radio interface follows the same operating mode as the network all-ip packet core E-UTRAN channels are simpler The SCH is an evolution of the HS-DSCH (HSDPA) and E-DCH (HSUPA) 41

42 Channels(4) 42

43 Channels(3) Logical Channels Control channels: Broadcast Control Channel (BCCH) Paging Control Channel (PCCH) Common Control Channel (CCCH) Multicast Control Channel (MCCH) Dedicated Control Channel (DCCH) Traffic channels: Dedicated Traffic Channel (DTCH) Multicast Traffic Channel (MTCH) Mapping between the logical and transport channels DL 43

44 Radio channels Logical control channels: BCCH (Broadcast Control Channel): Systems information broadcasting; Broadcast information used by the terminal operator to know the configuration of common channels and how to access the network The PCCH (Paging Control Channel): paging information to terminals 44

45 Radio channels CCCH (Common Control Channel): Used to connect terminal and E-UTRAN in the absence of RRC connection Used in the initial communication establishment phase MCCH (Multicast Control Channel): used to transmit MBMS (Multimedia Broadcast and Multicast Services) information to one or more terminals DCCH (Dedicated Control Channel): Point-to-point bidirectional channel carrying control information (RRC and NAS) between a terminal and the network 45

46 Radio channels Logical traffic channels: DTCH (Dedicated Traffic Channel): point-to-point bidirectional, between a terminal and the network for user data MTCH (Traffic Multicast Channel): point-to-multipoint channel transfer network data to one or more terminals (associate the MBMS service) Transport channels describe how and with what characteristics data is transferred over the radio interface: Channel coding, CRC protection, interleaving, packet size transmitted Transport Format 46

47 LTE Downlink Logical Channels 47

48 LTE Downlink Logical Channels 48

49 Channels 49

50 Channels Transport Channels Onlysharedchannels. Downlink transport channels: Broadcast Channel (BCH) Downlink Shared Channel (DL-SCH) Paging Channel (PCH) Multicast Channel (MCH) 50

51 Radio channels The transport channels are classified into two categories: Downlink Transport Channels Uplink Transport Channels Downlink transport channels: BCH (Broadcast Channel): Associated with the BCCH Has a predefined transport format PCH (Paging Channel): Associated to the PCCH DL-SCH (Downlink Shared Channel): control and user data MCH (Multicast Channel): Associated to MBMS 51

52 Radio channels Uplink transport channels: UL-SCH (Uplink Shared Channel): Equivalent to DL-SCH RACH (Random Access Channel): Limited transfer of control information Used at the beginning of the establishment of a communication and in case of RRC state change Physical channels: represent the implementation of the transport channels on the radio interface Structure related to the characteristics of the OFDM physical interface 52

53 LTE Downlink Transport Channel 53

54 LTE Downlink Transport Channel 54

55 Radio channels Downlink physical channels: Physical Downlink Shared Channel (PDSCH): user data and signaling of higher layers, Physical Downlink Control Channel (PDCCH): scheduling decisions to individual UEs, i.e. scheduling assignments for uplink and downlink, Physical Multicast Channel (PMCH): Multicast / Broadcast information, Physical Broadcast Channel (PBCH): System Information, Physical Control Channel Format Indicator (PCFICH): Number symbols for the PDCCH (1, 2, 3, or 4 symbols are possible). PCFICH is needed because the load on PDCCH can vary, depending on the number of users in a cell and the signaling formats conveyed on PDCCH, Physical Hybrid ARQ Indicator Channel (PHICH): ACK and NACK. 55

56 Radio channels Uplink physical channels: Physical Uplink Shared Channel (PUSCH): user data and signaling high layers Physical Uplink Control Channel (PUCCH): control information, including ACK and NACK. Physical Random Access Channel (PRACH): random access The physical layer uses the physical signals: Reference signals (signal through the antenna port on the DL) Timing signals (primary and secondary signals) 56

57 Radio channels System Information is composed of: Critical information systems: Fixed format, Updated frequently, with the PBCH Dynamic and less critical information systems: Association with a transport channel with more flexibility in terms of band and repetition period DL-SCH 57

58 Radio channels Multicast channels MCCH and associated MTCH: Transport channel for the MCH service offering multi-cell MBMS DL-SCH channel in case the MBMS service is available in a single cell Physical channels PUCCH, PDCCH, PCFICH and PHICH: Do not carry higher layers information. Carry information related to coding and HARQ RACH is a transport channel: Carries a preamble (All first bits are sent by the terminal to the network to request access) 58

59 PBCH channel Physical Broadcast Channel (PBCH): Carries system information necessary for network access (RACH parameters,...) Occupies 1.08 MHz (6 Resource Blocks) band independent of the carrier bandwidth Uses a convolutional coding. Information partially carried by the PBCH: The Master Information Block is carried by PBCH The System Information Blocks are carried by the PDSCH 59

60 LTE Downlink Physical Channels 60

61 LTE Downlink Physical Channels 61

62 LTE Uplink Logical Channels 62

63 LTE Uplink Transport Channel 63

64 LTE Uplink Physical Channels 64

65 PBCH channel Center of the PBCH band Locating (600 subcarriers = 9 MHz) 65

66 Physical channels synthesis: subframe structure on the carrier DL PBCH: Broadcast channel PCFICH: PDCCH symbol PDCCH: Assigns PDSCH/PUSCH PHICH: Indicates HARQ- ACK for UL PDSCH: Transmits Data PMCH: Transmits Multicast channel Synchronization Signal: UE synchronization UL PUCCH: Transmits ACK/NACK, CQI, SR PUSCH: Transmits Data PRACH: Transmits Random Access Preamble SRS: For UL CQI measurement 66

67 Physical channels synthesis 67

68 Physical channels synthesis 68

69 Radio Architecture 69

70 LTE downlink frame 70

71 Thank you 71