3GPP LTE Technical Overview

3GPP LTE TechnicalOverview

Sherlockgz3/1/2010

V3.0

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Content

• Highlight on following items– Technology evolution– 3GPP LTE requirement and releases– LTE Key Features– LTE network architecture

• Network elements and interfaces– LTE network functions– LTE Air Interface

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Wireless Technology Evolution• 1G (from early 1980 and commercialized in the middle of

80s)– Analog FDMA– AMPS (car phone)

• 2G (from early 1990s)– Digital wireless communication– TDMA and CDMA– GSM and IS-95

• 3G (late 1990s)– Wideband CDMA– WCDMA, CDMA2000, and TD-SCDMA

• 3.5G (early 2000s)– Wideband CDMA– Data only: EVDO Rev0/Rev A, HSDPA, HSUPA

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Wireless Technology Evolution

• 3.5G~4G (late 2000s)– OFDM, OFDMA, SC-FDMA– Mobile WiMAX (IEEE 802.16e), 3G LTE

(R8/R9)• 4G (from 2010)

– OFDMA and SC-FDMA– LTE-Advanced (R10 ->)

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Radio Technology EvolutionClic

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3GPP Release Concept

• Sprint requests R10

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Evolution of Mobile StandardsClic

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3GPP Requirement Input to LTE• Significantly increased DL bit

rates up to 1Gbps (100MHzbandwidth above R10)

• Significantly increased UL bitrates to up 500Mbps

• Increased cell edge bit rates• Low delay• Higher spectrum efficiency• Scalable bandwidth per cell

(operator option)• Acceptable UE complexity and

costs• Optimization for various UE

mobility speed up to 500km/h

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3G LTE Requirement (R8)• Spectrum efficiency

– DL: 3~4 times of HSDPA– UL: 2~3 times of HSUPA

• Frequency Spectrum:– Scalable bandwidth: 1.4,3,5,10,15,20MHz– To cover all frequencies of IMT-200:450MHz to 2.6GHz

• Peak Date rate: (R8)– DL: >100Mbps for 20MHz spectrum allocation– UL: > 50Mbps for 20MHz spectrum allocation

• Latency:– C-plane: < 100ms to establish U-plane– U-plane: < 10ms from UE to server

• Coverage:– Performance targets up to 5km, light degradation up to 30km

• Mobility:– LTE is optimized for low speeds 0~15km/h but– Connection maintained for speeds up to 350 or 500km/h– Handover between 3G and 3G LTE

• Real-time < 300ms• Non-real-time < 500ms

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Achievable & Supported Peak Data RatesClic

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LTE FDD and TDD ModesClic

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Bandwidth -> 100 MHz (R10)

• 3GPP also defined a potential bandwidthfor LTE-Advanced: Carrier Aggregation

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Key LTE FeaturesClic

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LTE End-to-End IP ApproachClic

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LTE Network ArchitectureClic

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LTE Network Architecture• eNodeB

– All radio interface-relatedfunctions

• MME– Manages mobility, UE, and

security parameters• S-GW

– Node that terminates theinterface towards E-UTRAN

• P-GW– Node that terminates the

interface towards PDN

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LTE Network Architecture

• Elements and Interfaces

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LTE Network Function Structure

EPC

S1

PDN

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4G Technical SpecificationSummary

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LTE Radio Air-InterfaceWhy OFDM?/Basic OFDMA/Basic SC-FDMA

Modulation/Constellation/Link AdaptionRadio frame structure

Radio channels/PSS/SSS/RSProtocol stack

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OFDM Technology

• Why does LTE accept OFDM technologyin broadband system (4G) Instead ofTDMA and CDMA?

• What is the major problem which blockTDMA/CDMA extend to 4G?

• What advantages and disadvantages withOFDM technology?

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Fading In Wireless System

• Multi-path makes the channel responsetime dispersive– Received signals with different attenuation,

delay, phase shift -> Cause Inter SymbolInterference (ISI)

• Dip fading Introduces errors in the decision deviceat the receiver output

– Radio signal distortion -> Noise -> systemless reliable

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ISIClic

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ISI

• Longer delay spreads result in frequency selective fading• Higher data rate, symbol time become shorter and

receiver sample clocks must become correspondinglyfaster so that ISI becomes much more severe – possiblyspanning several symbol periods

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Solution for ISI• Equalizers (GSM system)• Rake Receivers

(CDMA/WCDMA system)– Sub-receivers (fingers)

which are correlated eachassigned to a differentmultipath component

– Each finger independentlydecodes a single multipathcomponent

– The contribution of allfingers are combined toresult in higher C/N (Eb/No)

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TDMA/CDMA -> Broadband System?

TDMA/CDMA– Practical implementation issues and

complexities limit their acceptance• More Equalizers/Rake receivers must be

used for the received symbols spreadingover 20MHz and it will request:– Higher chip rate to process more Equalizers

and Rake receivers– More energy on the receiver

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Alternative Solution Minimize ISI

• Methods to reduce ISI interference:– Reduce the symbol rate, but data rate goes down too– Add more Equalizers/Rake receivers, but more

complexities and expensive• Solution:

– Use multicarrier to reduce ISI effect– Transmit data over multiple carriers in parallel– Narrow, slower channels are much less vulnerable ISI– Cycle Prefix

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FDM Becomes OFDM

Each carrier has an orthogonal relationshipWith each other

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OFDM• OFDM has a susceptibility to signal dispersion

under multipath conditions– Multi-carrier narrowband system where the whole

system bandwidth is split into multiple smallersubcarriers and transmit the data in parallel streamssimultaneously/independently

– Each subcarrier is modulated using varyingmodulation orders, such as QPSK, 16QAM, 64QAMdepending on signal quality.

– OFDM symbols is generally much longer thansymbols on single carrier system of equivalent datarate

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Orthogonality

The channel bandwidth is divided into multiple carriers to reduce ISI• each symbol occupies the whole bandwidth•Very short symbol duration to ensure high rate

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Add CP -> Reduce ISI

• Add a prefix to absorb channel effect and avoid ISI• Cycle Prefix (CP) permits to assist demodulation

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Using CP Reduce ISI

f = 15KHz = 1/Tu after adding CP, the total symbol length Ts = Tu + Tg

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Effect of Cyclic Prefix (CP)• CP increases the symbol time by copying part of the back of the

symbol in front of it• The effect is to add a guard period at the beginning of each symbol• When there is multipath, the delay component falls within the guard

period of the next symbol• Since the guard period contains information that is thrown away, the

original symbol is left intact• As long as the multipath components fall within the CP window, ISI

is avoidedNote: CP is a overhead adding the system so it impacts the overall throughput• CP is too small, not overcome ISI• CP is too large, it add significant overhead to the transmission

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Frame Type 1 with Normal CPClic

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LTE Subcarrier

Only one DC subcarrier in the Bandwidth from 1.4 to 20 MHz

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LTE Modulation - QPSKClic

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LTE Modulation - 16QAMClic

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LTE Modulation - 64QAMClic

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Link Adaption and RobustnessClic

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Link Adaption and RobustnessClic

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OFDM Advantages/Disadvantages

• There are two truly remarkable OFDMcharacters:– Each OFDM is preceded by a Cyclic Prefix

(CP), which is used to effectively eliminate ISI– The subcarriers are very tightly spaced to

make efficient use of available bandwidth,without Inter-carrier Interference

• Two principle weaknesses relative to singlecarrier system:– Susceptibility to carrier frequency errors

• Local oscillator offset or Doppler shifts– A larger signal-to-average power ratio (PAPR)

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Difference Between OFDM and OFDMA

• OFDM: users are assigned fractions of the totalsubcarriers available for fractions of the available time

• OFDMA: users are allocated a specific # of subcarriers(as PRB) for a predetermined amount of time. Allocationof PRBs is handled by a scheduling function at eNodeB.

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OFDMAClic

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OFDMA and SC-FDMAClic

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OFDMA and SC-FDMAClic

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OFDMA TransmitterClic

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OFDMA ReceiverClic

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Difference Between DL and UPClic

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Benefit from SC-FDMAClic

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OFDMA Specific Data for LTEClic

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LTE Parameters

5.2 for 1st symbol/4.7 for other 6 following symbolsCP Length ( s)

7 Normal/6 (short/long CP)OFDM Symbols/Subframe

1536076803840Sample per Slot

30.7215.367.68Sample Rate (MHz)

90%90%90%DL bandwidth Efficiency

18.0159.0154.515Occupied Channel Bandwidth (MHz)

847423211Guard Subcarriers

1201601301Number of Occupied Subcarriers (IncludeDC subcarrier)

20481024512IFFT/FFT Size

1005025Number of Resource Blocks

15KHz15KHz15KHzSubcarrier spacing

20MHz10MHz5 MHzSpectrum Allocation

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OFDMA Specific Data for LTEClic

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LTE FDD Frame StructureClic

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LTE FDD Frame StructureClic

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Resource BlockClic

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Physical Resource BlockClic

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Resource Element Group (REG)Clic

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REGClic

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LTE Radio Channels Structure

Radio C

hannels

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Radio ChannelsClic

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Logical ChannelType of information it carries

• Control Channels– Broadcast Control Channel (BCCH)

• Transmission of System information to all UEs in a cell– Paging Control Channel (PCCH)– Common Control Channel (CCCH)

• Transmission of control information in conjunction with randomaccess, ic. UE has no RRC connection

– Dedicated Control Channel (DCCH)• For a specific UE which has RRC connection

– Multicast Control Channel (MCCH)• Traffic Channels

– Dedicated Traffic Channel (DTCH)• User data transmission to/from a specific UE

– Multicast Traffic Channel (MTCH)

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Transport ChannelsClic

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Transport Channels

• Downlink– Broadcast Channel (BCH)

• A fixed TF and used for transmission of MIB– Paging Channel (PCH)

• Support discontinuous reception (DRX)– Downlink Shared Channel (DL-SCH)

• Transmission of DL data• Transmission of SIB, parts of BCCH• Supports DRX

– Multicast Channel (MCH)• Uplink

– Uplink Shared Channel (UP-SCH)– Random Access Channels (RACH)

• Support PRACH

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Transport Channel MappingClic

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From Transport to PhysicalChannel

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From Transport to PhysicalChannel

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Physical Channel

• Primary synchronization signal (pss)• Secondary synchronization signal (sss)• Reference signaling (RS)

• DM RS• Sounding RS

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LTE Channel MappingClic

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DL Physical Channels• Transport Channels:

– Physical Downlink Shared Channel (PDSCH)– Physical Broadcast Channel (PBCH)– Physical Multicast Channel (PMCH)

• Control Channels:– Physical Control Format Indicator Channel (PCFICH)– Physical HARQ Indicator Channel (PHICH)– Physical Downlink Control Channel (PDCCH)

• DL L1/L2 control signaling

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PDSCH• Main data bearing channel• PDSCH carriers data: Transport Blocks which

are MAC PDU passed from MAC layer to PHYlayer once per 1ms.

• QPSK, 16QAM and 64QAM• Minimum Physical Resource Block (PRB =

7x12x2 = 168 REs) is transmitted on PHY Layer• PDSCH is also used to transmit broadcast

information not transmitted on the PBCH. Called(SIBs and Paging messages)

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PBCHPhysical Broadcast Channel (PBCH):• Only for Master Information Block (MIB)

• DL system bandwidth• PHICH structure• PBCH transmission is spread over four 10sm frames (0~3 subframesIn 40ms)

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PBCHClic

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D-BCH SchedulingClic

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SIB 1 SchedulingClic

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SIB2,…SIB8 SchedulingClic

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SI-Messages SchedulingClic

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SI-Messages SchedulingClic

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Control Channels

Control Channels occupy the first 1,2,or 3 OFDMSymbols in the first subframe and extendOver the entire bandwidth

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PDCCH

• Function of PDCCH:– Carriers the resource assignment for UEs– Downlink Control Information (DCI)– Multiple PDCCHs can be transmitted on the

same sub-frame using Control ChannelElements (CCE)

– QPSK modulation is used for the PDCCH

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REGClic

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PDCCH Blind Detection• How a UE search for the DCI?

– UE searches for possible resource allocations in the related searchspace

• Search space:– Indicate the set of CCE locations where the UE may find its PDCCH– Each PDCCH carrier one DCI and is identified by a RNTI, which is

implicitly encoded in CRC attachment of the DCI– Two search space: UE is required to monitor both spaces

• Common search space– DCIs for system information (SI-RNTI), Paging (P-RNTI), PRACH response (RA-

RNTI)– Using aggregation level 4 and 8

• UE-specific search space– DCI for UE-specific allocation using the UE’s assigned C-RNTI, semi-persistent

scheduling (SPS C-RNTI) or temporary C-RNTI– Using all aggregation level (1,2,4,and 8)

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PDCCH Blind Detection Steps• Receive DL subframe• Decode PCFICH• Decode PHICH• Calculate REs for PDCCH = total REs in the first n(1,2,or 3) OFDM symbols

-> DL RS REs– PDFICH REs– PHICH REs

• De-interleaves PDCCH REs into CCEs and arrange the CCEs sequentially• Controlled by RRC about which types of DCI messages to monitor

– Blindly search common search space first– Blindly search UE-specific search space

• After each blind detection, UE checks the CRC with the correspondingRNTI:– If CRC succeeds, UE can derive the exact DCI format of the detected PDCCH

from the payload size and RNTI.– Knowing the DCI format, UE can go ahead and put the payload

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PCFICH/PHICH• PCFICH Functions:

– Carrier the Control Frame Indicator (CFI)• How many OFDM symbols used for control channel

transmission in each sub-frame (typically 1,2, or 3)– QPSK– 32 bits CFI is mapped to 16 Resource Elements– Located at first OFDM symbol on DL frame

• PHICH Functions:– Carrier HARQ ACK/NAK

• Indicate UE whether the eNB correctly received uplink userdata carried on PUSCH

• BPSK

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DL Physical Signals

• DL Physical Signals:– Synchronization Signal (SS)

• Primary Synchronization Signal (PSS)• Second Synchronization Signal (SSS)

– Reference Signal (or Symbol)

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Synchronization• Access LTE service

– Cell search procedure to determine:• LTE Network Timing – Synchronization

– Symbol timing acquisition• Frequency parameters to demodulate downlink signals

– Carrier frequency synchronization» Mitigate the effect of frequency errors resulting form Doppler shift

• Sampling clock synchronization

• Synchronization Signals:– Primary Synchronization Signal (PSS)– Secondary Synchronization Signal (SSS)

• UEs use PSS and SSS for– Initial synchronization and– Detecting neighbor cells in preparation for HO

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PSS and SSS• UE can obtain following information:

– Cell identity– Cyclic prefix length– FDD or TDD

• SS are transmitted twice per 10ms frame– PSS/SSS is located in the last FDMA symbol of 1st and 11th slot

of each frame.– PSS/SSS is the same for any given cell in every sub-frame– PSS uses a sequence as Zadoff-Chu– SSS uses a sequence as M-Sequences

• LTE defines PSS/SSS occupy the center 6 RBs– 62 subcarriers in total, with 31 sub-carriers mapped on each side

of the DC subcarrier (unused RE: 72 (6x12) – 62 = 10) so thisleaves 5 unused subcarriers at each extremity of the 6 center RB

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PSS/SSS in FrameClic

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PSS/SSS LocationClic

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Downlink Reference Signals (RS)

• The DL reference signals consist of referencesymbols which are known symbols insertedwithin the Resource Block (RB)

• RS can be used by UE for DL channelestimation to enable coherent detection

• Three types of Reference Signals:– Cell specific RSs (Up to 4)– MBSFN RSs– UE-specific RSs

• It is sent every sub-frame

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location of RSCell-specific reference signals• Reference signal in a PRB• In case of a single antenna

port (a single transmit antenna)• Physical Cell Identity (PCI) 3 x

168 = 504 different PCIs

Used for• Coherent demodulation in the

UE• Channel-quality measurement

for scheduling• Measurement for mobility

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RS Location for 2 Antenna Ports -DL

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DL Control and User Symbolslocation

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location of RS with MultipleAntenna Ports

RS Configuration for 4 antenna ports Separately transfer to avoid ISI

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RSs in Frame GridClic

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Measurement Qualities on RSClic

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UE Measurement ReportClic

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UE Measurement Report

Channel State Information: CQI, PMI, RI

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Location of UE-Specific RSUE-specific reference

signals• Reference signal length

=BW of PDSCH (RBs)• Used as a reference

demodulation in the UE• Only transmitted on RBs

where the correspondingPDSCH is mapped

• Antenna port 5

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UL Physical Channels

• Physical Uplink Shared Channel (PUSCH)– User bearers and control signals

• Physical Uplink Control Channel (PUCCH)– UL L1/L2 Signaling

• Physical Random Access Channels(PRACH)– UL transmission of the random access

preamble as given by the RACH

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Uplink Physical Signals (RS)• Reference Signals (RS)

– Demodulation Reference Signals (DM-RS) which are used toenable coherent signal demodulation at the eNB

• DM-RS are time multiplexed with uplink data and are transmitted onthe fourth or third symbol in the slot for normal CP

– Sounding Reference Signal (SRS)• Estimate the channel quality of the uplink channel for different UEs

in order to be able to apply uplink proper scheduling• Estimate the timing of UE transmissions and to derive timing-control

commands for uplink time alignment– SRS is introduced as a wider band reference signal typically

transmitted in the last symbol of a 1ms sub-frame– User data transmission is not allowed in this block, which results in

about 7% reduction in up link capacity– SRS can be turned off at eNB

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UL Control SignalsUplink L1/L2 control signaling consists of one or

more following pieces of information:– HARQ ACK/NACK

• Response DL transmission– CQI (Channel Quality Indicator)

• UE generates based on estimated DL reference signals andSINR (like EVDO DRC)

– Scheduling Requests• Use to request UL-SCH resources due not to have a valid

scheduling grant– If UE doesn’t have a scheduled PUSCH grant (like Idle mode),

only PUCCH can be used for all control signals– If UE does have a scheduled PUSCH grant (like RRC_CONN

mode), only PUSCH can be used for most of UL control signals

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PRACH

• UE sends random access preamble toeNB in non-synchronization mode evenDL is synchronized through PBCCH

• Synchronize UE with eNB– UL timing alignment or timing re-alignment for

UE in idle mode• PRACH consists of 72 subcarriers (6 RBs)• Four different Random Access (RA)

preamble formats

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Random Access Procedure

• Since the initial access attempt can’t bescheduled by the eNB, RA procedure is bydefinition contention based

• User data on the contention-based uplinkmay be impacted due to retransmission

• Contention-solution is to separate thetransmission of the RA preamble. Souplink synchronization must be obtainedfrom the transmission of user data

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Random Access Procedure• Once RA preamble is transmitted, UE will

monitor the PDCCH for RA-RNTI (UE identity) inthe RA response window time (40ms?)– If UE finds a its RA-RNTI, it monitors PDSCH for a RA

response message, containing (RAPID. Timing ).After this, UE can transmit the RA message 3

– If no response has been received, UE will do• Increases the transmitted power and tries again until it gets a

response• Stop RA until it reaches the maximum allowed

retransmissions– RA procedure failure will be indicated to the upper layers

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Non-Synchronization RA

UE obtains UL synchronization and is assigned resources for uplinkTransmission after 5 step

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RA Signaling Flow

6ms

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RA Physical Resource

• PRACH location in 10ms frame– 2nd sub-frame– 72 subcarriers (1.08MHz)

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RA preamble FormatClic

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PUCCH• Independently transmission of UL control

signaling:– HARQ ACK/NACK

• PUCCH format 1A for no spatial multiplexing (1TB per TTI)• PUCCH formant 1B for spatial multiplexing with two

transport blocks (2TB) per TTI– Channel Quality Indicators (CQI)

• PUCCH format 2– Scheduling request for UL transmission

• PUCCH format 1• This channel transmits in a frequency region at

the edge of the system bandwidth

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PUCCH Format 1A/1B• Format 1A supports a single ACK bit to be used for no

DL spatial multiplexing• Format 1B supports two ACK bits for the case of DL-

SCH spatial multiplexing with 2TB per TTI• BPSK or QPSK• Cyclic shift of the length-12 CAZAC sequence for 1A and

1B is further specified by an orthogonal cover sequencewhich is applied to 3 reference symbols per slot

• Cyclic shift hopping and orthogonal cover hopping areused in order to reduce ICI between PUCCH RBs

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PUCCH Format 1

• Scheduling Request (SR) Only– UE requests to be scheduled

• No reference signals are transmitted• Multiplexing of SR with CQI and/or ACK/NAK on

PUCCH– CQI: Drop CQI when SR is transmitted– When SR is positive, the ACK/NACK is transmitted

using the SR resource– When SR is negative, the ACK/NACK is transmitted

using the ACK/NACK resource

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PUCCH Format 2

• Use for CQI reports– QPSK– Each QPSK symbol is multiplexed by a cyclically

shifted length-12 CAZAC sequence and transmitted inone SC-FDMA symbol

• CQI from different UEs can be transmitted onthe same resource region by assigning differentcyclic shifts

• One cyclically shifted sequence carriers a singleCQI report

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PUCCH Control Region• PUCCH consists of one RB per transmission at one end of the

system bandwidth following by a RB in the following slot at theopposite end of the channel spectrum, like frequency hopping toobtain frequency diversity gain, estimated about 2 dB

• A PUCCH control region comprises every two such RBs• BPSK/QPSK

322416842Number of Resource Blocks

16128421PUCCH Control Regions

20151052.51.4System Bandwidth (MHz)

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PUCCH Allocation

PUCCH (UE # 2)PUCCH (UE #1)


PUCCH (UE #6)PUCCH (UE #5)


::

::

::

::





5 MHz with 8 RBs

10 MHz with 16 RBs

50 RB

s

10MH

z/180KH

z = 55 RBs

GB

GB

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PUSCH

– Carrier user data– QPSK/16QAM/64QAM– Adjacent data symbols are mapped to adjacent SC-

FDMA symbols in the time domain before beingmapped across subcarriers

– Possible to ‘bundle’ a group of 4 TTIs to improveperformance at cell edge and reduce higher layerprotocol overhead

• MAC PDU is segmented for transmission over multiple TTIs.• Transmissions are allocated based on multiple RBs.

– Inter-slot frequency hopping is a option• Frequency diversity gain

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Control Signals on PUSCH• When UE is transmitting data on PUSCH, control

signaling can’t be simultaneously sent on PUCCH as thiswould violate the single-carrier properties.

• Only HARQ and CQI are transmitted on PUSCH whenUE already is scheduled

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Control Signals on PUSCHNormal CP:

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UE Measurement Report

Channel State Information: CQI, PMI, RI

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CQI Report• Two types of CQI report in LTE:

– Periodic CQI report is carried by PUCCH– Aperiodic CQI report is carried by PUSCH

• When UE needs to send UL data in the same subframe as the scheduledperiodic CQI report, the periodic CQI report will used the PUCCH, togetherwith UL data transmission.

• At this moment, PUCCH resource will be in idle• eNB can trigger aperiodic report

• Three type of CQI report:– Wideband CQI:

• CQI value for the entire downlink system bandwidth– UE selected subband CQI:

• CQI report divides the system bandwidth into multiple subbands, selects aset of preferred subbands (like best M subbands), then report one CQI valuefor the wideband and one differential CQI value for the set of M subbands

– Higher layer configured subband CQI:• Divide the entire system bandwidth into multiple subbands,then reports one

wideband CQI and multiple differential CQI values, one for each subband

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Sub-Band Index with 5&10 MHZClic

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PMI and RI• Precoding Matrix Indicator (PMI)

– Indicate the codebook, eNB should use for datatransmission over multiple antennas based on theevaluation of received reference signal

• Rank Indicator (RI)– Indicates the number of transmission layers that the

UE can distinguish– Spatial multiplexing can be supported only when RI>1

• If closed loop MIMO is used, PMI and RI arealso reported

• For spatial multiplexing, CQI is reported basedon per codeword (Max = 2)

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PUSCH and PUCCH ReportingModes

• Three reporting modes on PUSCH– No spatial multiplexing mode

• Only CQI– On PUCCH with format 2 if no PUSCH resource are scheduled– On PUSCH if PUSCH resources are scheduled

– Close Loop multiplexing mode• CQI, PMI, and RI with wideband report on PUSCH

– Open Loop multiplexing mode• Only CQI and RI

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Uplink Reference Signals (RS)Clic

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Sounding Reference Signal• SRS can be used for uplink demodulation reference

– SRS can be configured:• A certain bandwidth (RBs)• 1 symbol in subframe used for SRS• A certain period in time between SRS transmissions (such as 2, 5, 10, 20,

40, 80, and 160 subframes)• A certain duration (eNB supports different SRS periods for different UEs)• Can be turn off (SRS is not sent when SR or CQI is sent on PUCCH)

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UL Resource Block (SRS Off)Clic

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SRS related ParametersClic

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3GPP LTE Channel MappingClic

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LTE Transmit Power

• Full Power transmission on DL– PDCCH Power Control

• Power transmission with power control onUL– Open Loop Power Control– Close Loop Power Control

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ALU DL Transmit Power

Default value RS setting

Cell coverage

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Synchronization Signals PowerSetting

Per RE and Per transmit antenna

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PBCH Power Setting• Transmit power per RE

and per transmit antenna• The higher the setting,

the more robust thePBCH reception with thecell coverage area, butthis reduces the poweravailable for otherdownlink signals andchannels

Default value setting

Key RF optimization parameter

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PCFICH/PHICH Power SettingClic

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PDCCH Power Setting

• Two PDCCH powersetting paramets:– PDCCHPowerOffsetS

ymbol1– PDCCHPowerOffsetS

ymbol2&3• dB as related to the RS

pwer

• Per RE and Pertransmit antenna

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PDCCH Power SettingClic

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PDCCH Power ControlClic

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PDCCH Power Control• The power is increased when Estimated SINR < target

SINR. The max increasing value is 6.7dB as default• The power is decreased when Estimated SINR >target

SINR. The max decreasing value is 12.8dB as default

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Total DL Transmit PowerClic

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PUCCH Power ControlClic

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DCI Format (DL)Clic

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PUCCH Power Control

Key RF Optimization Parameter

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PUSCH Power ControlClic

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PUSCH Power ControlClic

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SINR TargetClic

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CQI to SINR Lookup Table for DLClic

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BLER Loop ControlClic

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SINR-MCS Look Up Table for ULClic

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MCS Table for DL and ULClic

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Radio Protocol Stack OverviewClic

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Protocol Functions• C-plane (Control Plane)

– NAS function (L3)• Network attachment• Authentication• Setting up bearer• Mobility management• All NAS messages are ciphered and integrity protected by

the MME and UE

• U-plane (User Plane)• PDCP for RoHC• RLC for format and transport user traffic between UE and

eNB

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Radio Protocol Stack OverviewClic

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LTE Layer 2 Function StructureClic

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RRC Functions

– Setting and maintenanceradio bearers

– Handover decision control– Perform paging– Broadcasting system

information– Control UE measurement:

CSI (CQI, PMI, and RI)– Assign C-RNTI– Protection NAS messages

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RRC StatesClic

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PDCP Functions

• IP packet header is 20 octets• PDCP packet header is 1 or 2 octets after ROHC

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RLC FunctionsClic

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MAC FunctionsClic

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MAC - Scheduler• The scheduler in eNB determines dynamically

which UEs are supposed to receive data on theDL-SCH and sent data on the UL-SCH based onwhat resources it has

• Resources are composed of PRB andModulation Coding Scheme (MCS) whichdetermines the bit rate, the capacity of PRBs

• To select the adapted modulation and codingrate, the scheduler needs measurement reporton DL and UL

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DL Scheduler• Information needed

for the scheduler:– Amount of data– Radio resource

available– Radio condition on DL– CSI:

• CQI (channel qualityindicator)

• PMI (precoding matrixindicator)

• RI (ranking indicator)

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UL Scheduler

• The mechanism issimilar as DL but:– Measurements are

made by the eNB– The eNB scheduler

controls the UEtransmission

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Protocol States and MobilityClic

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End Section

Q/A

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3GPP LTE Technical Overview

Documents