LTE Long Term Evolution

Présentation au sujet: "LTE Long Term Evolution"— Transcription de la présentation:

1 LTE Long Term Evolution

2 Mobile communication system evolution
AMPS GSM UMTS WCDMA LTE Advanced Global System for Mobile communications Advanced Mobile Telephone System CDMA One (IS-95) TD-SCDMA TACS Code Division Multiple Access Based on IS-95 Total Access Communications System UMB EV-DO Rev C CDMA2000 DAMPS（IS-136) ETACS Digital - Advanced Mobile Phone System Based on IS-136 The 1G (First Generation) mobile systems were not digital, i.e. they utilized analogue modulation techniques. The main systems included: AMPS (Advanced Mobile Telephone System) - This first appeared in 1976 in the United States. It was mainly implemented in the Americas, Russia and Asia. Various issues including weak security features made the system prone to hacking and handset cloning. TACS (Total Access Communications System) - This was the European version of AMPS with slight modifications, as well as operating in different frequency bands. It was mainly used in the United Kingdom, as well as parts of Asia. ETACS (Extended Total Access Communication System) - This provided an improved version of TACS. It enabled a greater number of channels and therefore facilitated more users. Extended Total Access Communication System WiMAX WiMAX 802.16m Other

3 3GPP Time Line and Evolution
Bit rate

4 IMT Advanced Requirements
Specific requirements of the IMT-Advanced report included: All-IP packet switched network and Interoperability with existing wireless standards. Share and use the network resources to support more simultaneous users per cell Scalable channel bandwidth 5–20 MHz, optionally up to 40 MHz Seamless connectivity and global roaming across multiple networks (smooth handovers). 1 Gbit/s in the downlink should be possible over less than 67 MHz bandwidth Data rate : 100 Mbit/s (high speeds) 1 Gbit/s (fixed positions). Peak link spectral efficiency : 15 bit/s/Hz (downlink) 6.75 bit/s/Hz (uplink) In the downlink spectral efficiency up to : 3 bit/s/Hz/cell (outdoor) 2.25 bit/s/Hz/cell (indoor)

5 LTE Background Introduction
What is LTE？ LTE (Long Term Evolution) is known as the evolution of radio access technology conducted by 3GPP. The radio access network will evolve to E-UTRAN (Evolved UMTS Terrestrial Radio Access Network), and the correlated core network will evolved to SAE (System Architecture Evolution). What can LTE do？ Flexible bandwidth configuration: supporting 1.4MHz, 3MHz, 5MHz, 10Mhz, 15Mhz and 20MHz Peak date rate (within 20MHz bandwidth): 100Mbps for downlink and 50Mbps for uplink Time delay: <100ms (control plane), <5ms (user plane) Provide 100kbps data rate for mobile user (up to 350kmph) Support eMBMS Circuit services is implemented in PS domain: VoIP Lower cost due to simple system structure

6 LTE Network Architecture
Main Network Element of LTE The E-UTRAN consists of e-NodeBs, providing the user plane and control plane. The EPC consists of MME, S-GW and P-GW. Network Interface of LTE The e-NodeBs are interconnected with each other by means of the X2 interface, which enabling direct transmission of data and signaling. S1 is the interface between e-NodeBs and the EPC, more specifically to the MME via the S1-MME and to the S-GW via the S1-U Compare with traditional 3G network, LTE architecture becomes much more simple and flat, which can lead to lower networking cost, higher networking flexibility and shorter time delay of user data and control signaling. UMTS LTE

7 Page 7 SAE SAE Brief Introduction
SAE（System Architecture Evolution）considers evolution for the whole system architecture, including： Flat Functionality. Take out the RNC entity and part of the functions are arranged on e-NodeB in order to reduce the latency and enhance the schedule ability, such as interference coordination, internal load balance, etc. Part of the functions are arranged on core network. To enhance the mobility management, all IP technology is applied, user-plane and control-plane are separated. The compatibility of other RAT is considered. S1-MME: Reference point for the control plane protocol between E-UTRAN and MME. S1-U: Reference point between E-UTRAN and Serving GW for the per bearer user plane tunnelling and inter eNodeB path switching during handover. S3: It enables user and bearer information exchange for inter 3GPP access network mobility in idle and/or active state. S4: It provides related control and mobility support between GPRS Core and the 3GPP Anchor function of Serving GW. In addition, if Direct Tunnel is not established, it provides the user plane tunnelling. S5: It provides user plane tunnelling and tunnel management between Serving GW and PDN GW. It is used for Serving GW relocation due to UE mobility and if the Serving GW needs to connect to a non-collocated PDN GW for the required PDN connectivity. S6a: It enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between MME and HSS. Gx: It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging Enforcement Function (PCEF) in the PDN GW. S8: Inter-PLMN reference point providing user and control plane between the Serving GW in the VPLMN and the PDN GW in the HPLMN. S8 is the inter PLMN variant of S5. S9: It provides transfer of (QoS) policy and charging control information between the Home PCRF and the Visited PCRF in order to support local breakout function. S10: Reference point between MMEs for MME relocation and MME to MME information transfer. S11: Reference point between MME and Serving GW. S12: Reference point between UTRAN and Serving GW for user plane tunneling when Direct Tunnel is established. It is based on the Iu-u/Gn-u reference point using the GTP-U protocol as defined between SGSN and UTRAN or respectively between SGSN and GGSN. Usage of S12 is an operator configuration option. S13: It enables UE identity check procedure between MME and EIR. SGi: It is the reference point between the PDN GW and the packet data network. Packet data network may be an operator external public or private packet data network or an intra operator packet data network, e.g. for provision of IMS services. This reference point corresponds to Gi for 3GPP accesses. Rx The Rx reference point resides between the AF and the PCRF in the TS 23.203 [6]. SBc Reference point between CBC and MME for warning message delivery and control functions. Page 7

8 FDMA TDMA CDMA and OFDMA

9

10 Page 10 OFDM Introduction OFDM
OFDM （Orthogonal Frequency Division Multiplexing） is a modulation multiplexing scheme. The system bandwidth is divided into a plurality of orthogonal. Orthogonality of different subcarriers is achieved by the baseband IFFT. OFDM OFDM has many advantages that can meet the needs of E-UTRAN, which is one of B3G and 4G key technology. OFDM is a modulation multiplexing scheme, and the corresponding multi-access techniques is OFDMA. OFDMA are used in LTE downlink. For LTE uplink the multiple access scheme is SC-FDMA . OFDM与OFDMA的比较 Page 10

11 OFDMA and SC-FDMA Block Diagram

12 ISI (Inter Symbol Interference)
Cyclic Prefix COPY and insert ISI (Inter Symbol Interference) CP Normal 5,2 µs first symbol 4,7 µs other symbol Extended 16,7 µs

13 Page 13 OFDMA & SC-FDMA OFDM & OFDMA DFT-S-OFDM & SC-FDMA
OFDM (Orthogonal Frequency Division Multiplexing) is a modulation multiplexing technology, divides the system bandwidth into orthogonal subcarriers. CP is inserted between the OFDM symbols to avoid the ISI. OFDMA is the multi-access technology related with OFDM, is used in the LTE downlink. OFDMA is the combination of TDMA and FDMA essentially. Advantage: High spectrum utilization efficiency due to orthogonal subcarriers need no protect bandwidth. Support frequency link auto adaptation and scheduling. Easy to combine with MIMO. Disadvantage: Strict requirement of time-frequency domain synchronization. High PAPR. DFT-S-OFDM & SC-FDMA DFT-S-OFDM (Discrete Fourier Transform Spread OFDM) is the modulation multiplexing technology used in the LTE uplink, which is similar with OFDM but can release the UE PA limitation caused by high PAPR. Each user is assigned part of the system bandwidth. SC-FDMA（Single Carrier Frequency Division Multiple Accessing）is the multi-access technology related with DFT-S-OFDM. Advantage: High spectrum utilization efficiency due to orthogonal user bandwidth need no protect bandwidth. Low PAPR. The subcarrier assignment scheme includes Localized mode and Distributed mode. Page 13

14 Frequency Band of LTE From LTE Protocol: Duplex mode: FDD and TDD
Support frequency band form 700MHz to 2.6GHz Support various bandwidth: 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz, 20MHz Protocol is being updated, frequency information could be changed. FDD Frequency Band E-UTRA Band Uplink (UL) Downlink (DL) Duplex Mode FUL_low – FUL_high FDL_low – FDL_high 1 1920 MHz – 1980 MHz 2110 MHz 2170 MHz FDD 2 1850 MHz 1910 MHz 1930 MHz 1990 MHz 3 1710 MHz 1785 MHz 1805 MHz 1880 MHz 4 1755 MHz 2155 MHz 5 824 MHz 849 MHz 869 MHz 894MHz 6 830 MHz 840 MHz 875 MHz 885 MHz 7 2500 MHz 2570 MHz 2620 MHz 2690 MHz 8 880 MHz 915 MHz 925 MHz 960 MHz 9 MHz MHz MHz MHz 10 1770 MHz 11 MHz MHz MHz MHz 12 698 MHz 716 MHz 728 MHz 746 MHz 13 777 MHz 787 MHz 756 MHz 14 788 MHz 798 MHz 758 MHz 768 MHz … 17 704 MHz 734 MHz ... TDD Frequency Band E-UTRA Band Uplink (UL) Downlink (DL) Duplex Mode FUL_low – FUL_high FDL_low – FDL_high 33 1900 MHz – 1920 MHz TDD 34 2010 MHz 2025 MHz 2010 MHz 35 1850 MHz 1910 MHz 36 1930 MHz 1990 MHz 37 38 2570 MHz 2620 MHz 39 1880 MHz 40 2300 MHz 2400 MHz

15

16 Carrier Frequency EARFCN Calculation
The values of FDL_low，NDL，NOffs-DL can be found from 3GPP , as below：

17 Radio Frame Structure (1)
Radio Frame Structures Supported by LTE: Type 1, applicable to FDD Type 2, applicable to TDD FDD Radio Frame Structure: LTE applies OFDM technology, with subcarrier spacing f=15kHz and 2048-order IFFT. The time unit in frame structure is Ts=1/(2048* 15000) second FDD radio frame is 10ms shown as below, divided into 20 slots which are 0.5ms. One slot consists of 7 consecutive OFDM Symbols under Normal CP configuration FDD Radio Frame Structure Concept of Resource Block: LTE consists of time domain and frequency domain resources. The minimum unit for schedule is RB (Resource Block), which compose of RE (Resource Element) RE has 2-dimension structure: symbol of time domain and subcarrier of frequency domain One RB consists of 1 slot and 12 consecutive subcarriers under Normal CP configuration Page 17

18 Resource Block

19 Radio Frame Structure (2)
TDD Radio Frame Structure: Applies OFDM, same subcarriers spacing and time unit with FDD. Similar frame structure with FDD. radio frame is 10ms shown as below, divided into 20 slots which are 0.5ms. The uplink-downlink configuration of 10ms frame are shown in the right table. Uplink-downlink Configurations Uplink-downlink configuration Downlink-to-Uplink Switch-point periodicity Subframe number 1 2 3 4 5 6 7 8 9 5 ms D S U 10 ms D: Downlink subframe U: Uplink subframe S: Special subframe Huawei supports UL-DL Configuration type 0,1,2 and 5 (type 5 is only for demonstration) DwPTS: Downlink Pilot Time Slot GP: Guard Period UpPTS: Uplink Pilot Time Slot TDD Radio Frame Structure Page 19

20 Special Subframe Structure
Special Subrame Structure: Special Subframe consists of DwPTS, GP and UpPTS . 9 types of Special subframe configuration. Guard Period size determines the maximal cell radius. (100km) DwPTS consists of at least 3 OFDM symbols, carrying RS, control message and data. UpPTS consists of at least 1 OFDM symbol, carrying sounding RS or short RACH. Configuration of special subframe Special subframe configuration Normal cyclic prefix DwPTS GP UpPTS 3 10 1 9 4 2 11 12 5 6 7 8 Page 20

21 Radio Frame Structure (3)
CP Length Configuration: Cyclic Prefix is applied to eliminate ISI of OFDM. CP length is related with coverage radius. Normal CP can fulfill the requirement of common scenarios. Extended CP is for wide coverage scenario. Longer CP, higher overheading. CP Configuration Configuration DL OFDM CP Length UL SC-FDMA CP Length Sub-carrier of each RB Symbol of each slot Normal CP f=15kHz 160 for slot #0 144 for slot #1~#6 12 7 Extended CP 512 for slot #0~#5 6 f=7.5kHz 1024 for slot #0~#2 NULL 24 (DL only) 3 (DL only) Slot structure under Normal CP configuration (△f=15kHz) Slot structure under Extended CP configuration (△f=15kHz) Slot structure under Extended CP configuration (△f=7.5kHz) Page 21

22 Brief Introduction of Physical Channels
Downlink Channels： Physical Broadcast Channel (PBCH): Carries system information for cell search, such as cell ID. Physical Downlink Control Channel (PDCCH) : Carries the resource allocation of PCH and DL-SCH, and Hybrid ARQ information. Physical Downlink Shared Channel (PDSCH) : Carries the downlink user data. Physical Control Format Indicator Channel (PCFICH) : Carriers information of the OFDM symbols number used for the PDCCH. Physical Hybrid ARQ Indicator Channel (PHICH) : Carries Hybrid ARQ ACK/NACK in response to uplink transmissions. Physical Multicast Channel (PMCH) : Carries the multicast information. Uplink Channels： Physical Random Access Channel (PRACH) : Carries the random access preamble. Physical Uplink Shared Channel (PUSCH) : Carries the uplink user data. Physical Uplink Control Channel (PUCCH) : Carries the HARQ ACK/NACK, Scheduling Request (SR) and Channel Quality Indicator (CQI), etc. MAC Layer Physical Layer Mapping between downlink transport channels and downlink physical channels MAC Layer Physical Layer Physical broadcast channel (PBCH) - The coded BCH transport block is mapped to four subframes within a 40 ms interval; - 40 ms timing is blindly detected, i.e. there is no explicit signalling indicating 40 ms timing; - Each subframe is assumed to be self-decodable, i.e. the BCH can be decoded from a single reception, assuming sufficiently good channel conditions. Physical control format indicator channel (PCFICH) - Informs the UE about the number of OFDM symbols used for the PDCCHs; - Transmitted in every subframe. Physical downlink control channel (PDCCH) - Informs the UE about the resource allocation of PCH and DL-SCH, and Hybrid ARQ information related to DL-SCH; - Carries the uplink scheduling grant. Physical Hybrid ARQ Indicator Channel (PHICH) - Carries Hybrid ARQ ACK/NAKs in response to uplink transmissions. Physical downlink shared channel (PDSCH) - Carries the DL-SCH and PCH. Physical multicast channel (PMCH) - Carries the MCH. Physical uplink control channel (PUCCH) - Carries Hybrid ARQ ACK/NAKs in response to downlink transmission; - Carries Scheduling Request (SR); - Carries CQI reports. Physical uplink shared channel (PUSCH) - Carries the UL-SCH. Physical random access channel (PRACH) - Carries the random access preamble. Mapping between uplink transport channels and downlink physical channels Page 22

23 Downlink Physical Channel
Downlink Physical Channel Processing scrambling of coded bits in each of the code words to be transmitted on a physical channel modulation of scrambled bits to generate complex-valued modulation symbols mapping of the complex-valued modulation symbols onto one or several transmission layers precoding of the complex-valued modulation symbols on each layer for transmission on the antenna ports mapping of complex-valued modulation symbols for each antenna port to resource elements generation of complex-valued time-domain OFDM signal for each antenna port Modulation Scheme of Downlink Channel Shown at the right table Phy Ch Modulation Scheme PBCH QPSK PCFICH PDCCH PHICH BPSK PDSCH QPSK, 16QAM, 64QAM PMCH Page 23

24 Uplink Physical Channel
Uplink Physical Channel Processing scrambling modulation of scrambled bits to generate complex-valued symbols transform precoding to generate complex-valued symbols mapping of complex-valued symbols to resource elements generation of complex-valued time-domain SC-FDMA signal for each antenna port Modulation Scheme of Downlink Channel Shown at the right table Phy Ch Modulation Scheme PUCCH BPSK, QPSK PUSCH QPSK, 16QAM, 64QAM PRACH Zadoff-Chu Page 24

25 Downlink Physical Signals (1)
Downlink RS (Reference Signal): Similar with Pilot signal of CDMA. Used for downlink physical channel demodulation and channel quality measurement (CQI) Three types of RS in protocol. Cell-Specific Reference Signal is essential and the other two types RS (MBSFN Specific RS & UE-Specific RS) are optional. One Antenna Port Cell-Specific RS Mapping in Time-Frequency Domain Characteristics: Cell-Specific Reference Signals are generated from cell-specific RS sequence and frequency shift mapping. RS is the pseudo-random sequence transmits in the time-frequency domain. The frequency interval of RS is 6 subcarriers. RS distributes discretely in the time-frequency domain, sampling the channel situation which is the reference of DL demodulation. Serried RS distribution leads to accurate channel estimation, also high overhead that impacting the system capacity. Two Antenna Ports RE Not used for RS transmission on this antenna port RS symbols on this antenna port Four Antenna Ports R1: RS transmitted in 1st ant port R2: RS transmitted in 2nd ant port R3: RS transmitted in 3rd ant port R4: RS transmitted in 4th ant port MBSFN: Multicast/Broadcast over a Single Frequency Network Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3 Page 25

26 Downlink Physical Signals (2)
Synchronization Signal: synchronization signals are used for time-frequency synchronization between UE and E-UTRAN during cell search. synchronization signal comprise two parts: Primary Synchronization Signal, used for symbol timing, frequency synchronization and part of the cell ID detection. Secondary Synchronization Signal, used for detection of radio frame timing, CP length and cell group ID. Characteristics: The bandwidth of the synchronization signal is 62 subcarrier, locating in the central part of system bandwidth, regardless of system bandwidth size. Synchronization signals are transmitted only in the 1st and 11rd slots of every 10ms frame. The primary synchronization signal is located in the last symbol of the transmit slot. The secondary synchronization signal is located in the 2nd last symbol of the transmit slot. Caution: Synchronization signals are sometimes named as Synchronization Channel (P-SCH & S-SCH) in some documents. The meaning should be the same, which represents the signals transmitted in the specified time-frequency locations. Please don’t be confused with Share Channel (SCH). Synchronization Signals Structure Page 26

27 Uplink Physical Signals
Uplink RS (Reference Signal): The uplink pilot signal, used for synchronization between E-UTRAN and UE, as well as uplink channel estimation. Two types of UL reference signals: DM RS (Demodulation Reference Signal), associated with PUSCH and PUCCH transmission. SRS (Sounding Reference Signal), without associated with PUSCH and PUCCH transmission. Time Freq Allocated UL bandwidth of one UE DM RS associated with PUSCH is mapped to the 4th symbol each slot Time Freq Characteristics: Each UE occupies parts of the system bandwidth since SC-FDMA is applied in uplink. DM RS only transmits in the bandwidth allocated to PUSCH and PUCCH. The slot location of DM RS differs with associated PUSCH and PUCCH format. Sounding RS’s bandwidth is larger than that allocated to UE, in order to provide the reference to e-NodeB for channel estimation in the whole bandwidth. Sounding RS is mapped to the last symbol of sub-frame. The transmitted bandwidth and period can be configured. SRS transmission scheduling of multi UE can achieve time/frequency/code diversity. DM RS associated with PUCCH (transmits UL ACK signaling) is mapped to the central 3 symbols each slot Time Freq DM RS associated with PUCCH (transmits UL CQI signaling) is mapped to the 2 symbols each slot Caution：The SRS mapping will be difference in many documents, since the protocol are still under discussion when these document been compiled. The mapping shown in this slide is the result from the latest protocol version. System bandwidth PUCCH is mapped to up & down ends of the system bandwidth, hopping between two slots. Page 27

28 Downlink Resource Structure
Type I frame, single antenna, ΔF = 15 kHz Standard RB: One of center 6 RBs: Legend: Downlink Reference Signals PBCH (Physical Broadcast Channel) PSS (Primary Synchronisation Signal) SSS (Secondary Synchronisation Signal) PDCCH / PHICH / PCFICH (Physical - Downlink Control / HARQ Indicator / Control Format Indicator - Channels) PDSCH (Physical Downlink Shared Data Channel) © Forsk 2010

29 Downlink Resource Structure
7 OFDM symbols at normal CP per slot (0.5 ms) OFDM Symbol 0 CP OFDM Symbol 1 CP OFDM Symbol 2 CP CP OFDM Symbol 3 CP OFDM Symbol 4 OFDM Symbol 5 CP CP OFDM Symbol 6 1 2 3 4 5 6 1 2 3 4 5 6 Legend: Downlink Reference signals PBCH PSS SSS PDCCH / PHICH / PCFICH PDSCH Centre 6 RBs 1 subframe = 2 slot (1 ms) SF 0 SF 1 SF 2 SF 3 SF 4 SF 5 SF 6 SF 7 SF 8 SF 9 1 frame = 10 subframe (10 ms) © Forsk 2010

30 Uplink Resource Structure
7 OFDM symbols at normal CP per slot (0.5 ms) OFDM Symbol 0 CP OFDM Symbol 1 CP OFDM Symbol 2 CP CP OFDM Symbol 3 CP OFDM Symbol 4 OFDM Symbol 5 CP CP OFDM Symbol 6 1 2 3 4 5 6 1 2 3 4 5 6 Legend: UL DMRS (Uplink Demodulation Reference Signal) UL SRS (Uplink Sounding Reference Signal) PUCCH (Physical Uplink Control Channel) (incl.HARQ feedback and CQI reporting) Demodulation Reference Signal for PUCC PUSCH (Physical Uplink Shared Data Channel) 1 subframe = 2 slot (1 ms) SF 0 SF 1 SF 2 SF 3 SF 4 SF 5 SF 6 SF 7 SF 8 SF 9 1 frame = 10 subframe (10 ms) © Forsk 2010

31 Physical Layer Procedure — Cell Search
Basic Principle of Cell Search: Cell search is the procedure of UE synchronizes with E-UTRAN in time-freq domain, and acquires the serving cell ID. Two steps in cell search: Step 1: Symbol synchronization and acquirement of ID within Cell Group by demodulating the Primary Synchronization Signal; Step 2: Frame synchronization, acquirement of CP length and Cell Group ID by demodulating the Secondary Synchronization Signal. Initial Cell Search: The initial cell search is carried on after the UE power on. Usually, UE doesn’t know the network bandwidth and carrier frequency at the first time switch on. UE repeats the basic cell search, tries all the carrier frequency in the spectrum to demodulate the synchronization signals. This procedure takes time, but the time requirement are typically relatively relaxed. Some methods can reduce time, such as recording the former available network information as the prior search target. Once finish the cell search, which achieve synchronization of time-freq domain and acquirement of Cell ID, UE demodulates the PBCH and acquires for system information, such as bandwidth and Tx antenna number. After the procedure above, UE demodulates the PDCCH for its paging period that allocated by system. UE wakes up from the IDLE state in the specified paging period, demodulates PDCCH for monitoring paging. If paging is detected, PDSCH resources will be demodulated to receive paging message. About Cell ID： In LTE protocol, the physical layer Cell ID comprises two parts: Cell Group ID and ID within Cell Group. The latest version defines that there are 168 Cell Group IDs, 3 IDs within each group. So totally 168*3=504 Cell IDs exist. represents Cell Group ID, value from 0 to 167; represents ID within Cell Group, value from 0 to 2. Search Freq Sync Signals PBCH PDCCH PDSCH Caution: 170 Cell ID groups are defined in the earlier protocol version. So totally 170*3=510 Cell IDs exists, which is mentioned in some early-written documents. Please be noticed this differences. Page 31

32 Physical Layer Procedure — Radom Access
Basic Principle of Random Access : Random access is the procedure of uplink synchronization between UE and E-UTRAN. Prior to random access, physical layer shall receive the following information from the higher layers: Random access channel parameters: PRACH configuration, frequency position and preamble format, etc. Parameters for determining the preamble root sequences and their cyclic shifts in the sequence set for the cell, in order to demodulate the random access preamble. Two steps in physical layer random access: UE transmission of random access preamble Random access response from E-UTRAN Detail Procedure of Random Access: Physical Layer procedure is triggered upon request of a preamble transmission by higher layers. The higher layers request indicates a preamble index, a target preamble received power, a corresponding RA-RNTI and a PRACH resource . UE determines the preamble transmission power is preamble target received power + Path Loss. The transmission shall not higher than the maximum transmission power of UE. Path Loss is the downlink path loss estimate calculated in the UE. A preamble sequence is selected from the preamble sequence set using the preamble index. A single preamble is transmitted using the selected preamble sequence with calculated transmission power on the indicated PRACH resource. UE Detection of a PDCCH with the indicated RA-RNTI is attempted during a window controlled by higher layers. If detected, the corresponding PDSCH transport block is passed to higher layers. The higher layers parse the transport block and indicate the 20-bit grant. RA Preamble PRACH RA Response PDCCH RA-RNTI: Random Access Radio Network Temporary Identifier Page 32

33 Physical Layer Procedure — Power Control
Basic Principle of Power Control: Downlink power control determines the EPRE (Energy per Resource Element); Uplink power control determines the energy per DFT-SOFDM (also called SC-FDMA) symbol. Downlink Power Control: The transmission power of downlink RS is usually constant. The transmission power of PDSCH is proportional with RS transmission power. Downlink transmission power will be adjusted by the comparison of UE report CQI and target CQI during the power control. Uplink Power Control: Uplink power control consists of opened loop power and closed loop power control. A cell wide overload indicator (OI) is exchanged over X2 interface for integrated inter-cell power control, possible to enhance the system performance through power control. PUSCH, PUCCH, PRACH and Sounding RS can be controlled respectively by uplink power control. Take PUSCH power control for example: PUSCH power control is the slow power control, to compensate the path loss and shadow fading and control inter-cell interference. The control principle is shown in above equation. The following factors impact PUSCH transmission power PPUSCH: UE maximum transmission power PMAX, UE allocated resource MPUSCH, initial transmission power PO_PUSCH, estimated path loss PL, modulation coding factor △TF and system adjustment factor f (not working during opened loop PC) UE report CQI DL Tx Power X2 UL Tx Power System adjust parameters EPRE: Energy per Resource Element DFT-SOFDM: Discrete Fourier Transform Spread OFDM Page 33

34 Page 34 Adaptive Modulation and Coding
2 bits per symbol in each carrier. 4 bits per symbol in each carrier. 6 bits per symbol in each carrier. The most appropriate modulation and coding scheme can be adaptively selected according to the channel propagation conduction, then the maximum throughput can be obtained for different channel situation. Page 34 Page 34 34

35 LTE Feature MIMO ICIC SON CSFB ANR
Automatic Detection and Collision PCI Mobility Load Balancing CSFB

36 Page 36 MIMO Downlink MIMO Uplink MIMO
MIMO is supported in LTE downlink to achieve spatial multiplexing, including single user mode SU-MIMO and multi user mode MU-MIMO. In order to improve MIMO performance, pre-coding is used in both SU-MIMO and MU-MIMO to control/reduce the interference among spatial multiplexing data flows. The spatial multiplexing data flows are scheduled to one single user In SU-MIMO, to enhance the transmission rate and spectrum efficiency. In MU-MIMO, the data flows are scheduled to multi users and the resources are shared within users. Multi user gain can be achieved by user scheduling in the spatial domain. Uplink MIMO Due to UE cost and power consumption, it is difficult to implement the UL multi transmission and relative power supply. Virtual-MIMO, in which multi single antenna UEs are associated to transmit in the MIMO mode. Virtual-MIMO is still under study. Scheduler assigns the same resource to multi users. Each user transmits data by single antenna. System separates the data by the specific MIMO demodulation scheme. MIMO gain and power gain (higher Tx power in the same time-freq resource) can be achieved by Virtual-MIMO. Interference of the multi user data can be controlled by the scheduler, which also bring multi user gain. DL-MIMO Virtual-MIMO Page 36

37 SFBC (Transmit Diversity) MCW (Spatial Multiplexing)
DL MIMO SFBC (Transmit Diversity) MCW (Spatial Multiplexing) codeword UE1 User1 SFBC Mod UE1 Layer 1, CW1, AMC1 UE2 Layer 2, CW2, AMC2 MIMO encoder and layer mapping Same stream transmitted simultaneously in certain form of MIMO coding at the same time-frequency resource from both antenna ports (Rank = 1) Depending on the environment & number of antennas, SFBC can reduce fading margin by 2~8 dB, to extend coverage, and enhance system capacity Multiple data streams transmitted at the same time-frequency resource from different antenna ports The terminal must have at least 2 Rx antennas for spatial multiplexing (SM) Page 37 Page 37

38 Page 38 ICIC（Inter-Cell Interference Coordination）
ICIC is one solution for the cell interference control, is essentially a schedule strategy. In LTE, some coordination schemes( ICIC ) can control the interference in cell edges to enhance the frequency reuse factor and performance in the cell edges. The edge band is assigned to the users in cell edge. The eNB transmit power of the edge band can be high. Center Band Center Band Center Band Cell 2,4,6 Primary Band Cell 1 Edge Band Center Band The center band is assigned to the users in cell center. The eNB transmit power of the center band should be reduced in order to avoid the interference to the edge band of neighbor cells. Cell 3,5,7P Edge Band Page 38

39 SON（ Self-Organising Networks ）
SON Brief Introduction SON (Self Organization Network) is the functions of LTE that required by the NGMN (Next Generation Mobile Network) operators. From the point of view of the operator’s benefit and experiences, the early communication systems had bad O&M compatibility and high cost. New requirements of LTE are brought forward, mainly focus on FCAPSI (Fault, Configuration, Alarm, Performance, Security, Inventory) management: Self-planning and Self-configuration, support plug and play Self-Optimization and Self-healing Self-Maintenance

40 SON_ANR (Automatic Neighbor Relation)
Add new Sites New site configured site Description: Auto configure and optimize Neighbor relations, intra-LTE and inter-RAT X2 automatic setup Operator defined rules and monitoring supported Benefits: Fast definition of Neighbor Relations up to 95% lower cost of neighbor relation planning and optimization Improve customer experience by reducing HO failure caused by missing neighbor relations ANR management is implemented through the following functions: Automatic detection of missing neighboring cells Automatic evaluation of neighbor relations Automatic detection of PCI collisions Automatic detection of abnormal neighboring cell coverage Page 40

41 Page 41 ANR functionality
ANR management is implemented through the following functions: Automatic detection of missing neighboring cells Automatic evaluation of neighbor relations Automatic detection of Physical Cell Identifier (PCI) collisions Automatic detection of abnormal neighboring cell coverage Automatic Neighbor Relation (ANR) can automatically add and maintain neighbor relations. The initial network construction, however, should not fully depend on ANR for the following considerations: ANR is closely related to traffic in the entire network ANR is based on UE measurements but the delay is introduced in the measurements. After initial neighbor relations configured and the number of UEs increasing, some neighboring relations may be missing. In this case, ANR can be used to detect missing neighboring cells and add neighbor relations. Page 41

42 Page 42 ANR functionality Two main type of ANR: Event triggered
Periodical reporting – fast ANR Both Event triggered and Fast ANR are applicable for same system or different systems Page 42

43 SON_Automatic Detection of PCI Collisions
A PCI collision means the serving cell and a neighboring cell have the same PCI but different ECGIs. PCI collisions may be caused by improper network planning or abnormal neighboring cell coverage (also known as cross-cell coverage). If two neighboring cells have the same PCI, interference will be generated. When a PCI collision occurs, the eNodeB cannot determine the target cell for a handover. In this situation, the handover performance deteriorates and the handover success rate is reduced. After a PCI collision is removed, the following conditions are met: The PCI is unique in the coverage area of a cell. The PCI is unique in the neighbor relations of a cell. Page 43

44 SON_Automatic Detection of PCI Collisions Cont.
After a neighbor relation is added to the NRT, the eNodeB compares the PCI of the new neighboring cell with the PCIs of existing neighboring cells in the case of IntraRatEventAnrSwitch is set to ON. If the new neighboring cell and an existing neighboring cell have the same ECGI but different PCIs, the eNodeB reports a PCI collision to the M2000. The M2000 collects statistics about PCI collisions and generates a list of PCI collisions. Reallocating PCIs PCI reallocation is a process of reallocating a new PCI to a cell whose PCI collides with the PCI of another cell. The purpose is to remove PCI collisions. The M2000 triggers the PCI reallocation algorithm to provide suggestions on PCI reallocation. Note: After the PCI of a cell is changed, the cell needs to be reestablished and the services carried on the cell are disrupted. Therefore, the PCI reallocation algorithm only provides reallocation suggestions. A PCI can be reallocated manually or automatically through a scheduled task configured on the M2000. Page 44

45 Page 45 SON_MLB( Mobility Load Balancing) Description: Benefits:
Exchange cell load information over X2 Offload congested cells Optimize cell reselection / handover parameters Cell A Cell B Cell C Benefits: Increase 10% system capacity and 10%-20% access success rate in unbalance scenario Improve customer experience by reducing call drop rate, handover failure rate, and unnecessary redirection caused by unbalanced load Page 45

46 How to solve Mobility Problems?
SON_MRO( Mobility Robust Optimization ) How to solve Mobility Problems? Value unnecessary HO Rate HO successful rate PONG PING Before adopt MRO After adopt MRO Description: HO parameters are optimized based upon long term UE mobility behavior Avoid Ping-Pong handover, handover too early, handover too late, etc Benefits: Reduce cost of mobility optimization Improve customer experience by reducing call drop rate and handover failure rate MRO is a feature that is applicable to the SON. It enables automatic optimization of handover-related parameter settings. Through handover scenario identification and handover counting in the scenarios, the MRO feature optimizes the handover-related parameter settings based on the counting results. MRO is aimed at minimizing handover failures, service drops, and undesirable handovers such as premature handovers, delayed handovers, and ping-pong handovers. It helps to avoid a waste of network resources caused by improper parameter settings.

47 THANK YOU

48 PAPR Cyclic Prefix