Technology TrainingJanuary 24, 2013

saket.n@mail01.huawei.com

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Outline• LTE radio resources• Duplex techniques – FDD / TDD• Multiple antenna techniques• Reference signals• Throughput calculation• Rank Index• PCI (Physical cell identity)• Cyclic prefix (CP)• Network architecture• Attach/Detach• Important DT parameters

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Resource Block

• LTE – radio resource = “time-frequency chunk”

• Time domain 1 frame = 10 ms = 10 sub-frames 1 subframe = 1 ms = 2 time slots 1 slot = 0.5 ms = 7 (or 6) OFDM

symbols • Frequency domain

1 OFDM carrier = 15KHz

Resource Block (RB) = 12 carriers in one TS (12*15KHz x 0.5ms)

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Scalable BandwidthParameter Value

Bandwidth (MHz) 1.4 3 5 10 15 20Frame /subframe

duration 10/1 ms

Subcarrier spacing 15KHz

Resource blocks 6 15 25 50 75 100Number of used

subcarriers 72 180 300 600 900 1200

OFDM symbols /slot 7 (normal CP), 6 (extended CP)

LTE frequency bands

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TDD & FDD

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TDD frame configurations

• Different configurations allow balancing between DL and UL capacity

• Adjacent cells have same allocation

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TDD Special Subframe Configurations

Special Subframe Formats

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Multi antenna techniques• LTE uses of multiple antennas at

both communication ends• MIMO Techniques

– Spatial multiplexing– TX diversity – SDMA (Space division multiple access)– Beam forming

Downlink MIMO

Uplink MIMO

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Reference signals• Reference signals :

– Cell search & initial acquisition – DL channel quality estimation

• Mainly there are two type of reference signals1. Cell specific DL reference signals

– Every DL subframe– Across entire DL bandwidth

2. UE specific DL reference signals– Intended for individual UE’s

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• There are 504 different Reference Sequences (RS)• They are linked to PHY-layer cell identities • Shifts are introduced to avoid collision between RS of adjacent cells• For a given PHY Cell ID - sequence is the same regardless of the bandwidth used.

Cell specific reference signals

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UE Specific RS

• UE specific RS – used for beam forming• Provided in addition to cell specific RS• Sent over resource block allocated for DL-SCH (applicable only

for data transmission)

Note: additional reference signals increase overhead. One of the most beneficial use of beam forming is at the cell edge – improves SNR

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Throughput calculation• An exercise to calculate throughput for different configurations.

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Rank Index

• Represents the number of layers to be used in downlink transmission.

• Rank Index values are proposed by the UE based on the radio conditions.

• eNodeB may or may not follow UE proposal.• 2x2 MIMO

– Spatial multiplexing : RI = 2– Transmit diversity : RI = 1– SDMA: RI = 1– Beam forming : RI = 1

• 4x4 MIMO– Spatial Multiplexing : RI = 2, 3, 4.– Transmit Diversity : RI = 1.– SDMA: RI = 1– Beam forming : RI = 1

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Physical cell identity (PCI)• PCI = PSS + 3* SSS• Primary synchronization signal :

– Frequency synchronization.– Time slot synchronization.– 3 PSS values (0,1,2)

• Secondary synchronization signal :– Radio frame synchronization.– TDD/FDD duplex information.– CP length.– 168 SSS values, (0 to 167).

• 3*168 = 504 different PCI values.

• Planning guidelines:• Co PCI scenario must never happen.• All 3 cells of a site should have same SSS.• PSS should be defined 0 for first sector, 1

for second sector, 2 for third sector.• Some SSS should be reserved for indoor

sites i.e. (151 – 167).

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Cyclic prefix• Multipath propagation degrades orthogonality between carriers, to regain the orthogonality –

cyclic prefix is used.• Copying the last part of a symbol shape for a duration of guard-time and attaching it in front of

the symbol.• A receiver typically uses the last part of the following symbol to locate the start of the symbol and

begin then with decoding.• Normal CP : Length is 4.7 us. With normal CP, 7 symbols per time slot.• Extended CP : Length is16.7 us. 6 symbols per time slot.

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LTE Architecture

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Evolved packet core (EPC)• MME (Mobility Management Entity)

– Control plane function.– Idle mode tracking.– Allocation of temporary identities to UE.– Paging.– Choosing the SGW for UE during initial attach.– User authentication & interaction with HSS (home subscriber server). – Roaming.

• SGW (Serving Gateway)– User plane function.– Carry data packets.

• PGW (PDN Gateway)– Connects to the external data network.

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LTE Call flowAttach time :

• A general range for Attach time is 150 ms +/- 25 ms.

• Control plane latency includes attach & detach time.

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LTE Call flow - Detach

Detach time :A general range for Detach time is 50 ms +/- 10 ms .

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QCI – QoS class identifier

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Attach – Moving to new MME

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GUTI, GUMMEI, TAI & ECGI• PLMN ID = MCC + MNC

• MMEI (MME ID)• MMEI = MMEGI (MME group ID) + MMEC (MME code)

• GUMMEI (Globally unique MME ID):• GUMMEI = MCC + MNC + MMEI (MME ID)

• GUTI ( Globally unique temporary ID)• GUTI = TMSI + GUMMEI

• TAI (Tracking area ID) = MCC + MNC + TAC (Tracking area code)

• ECGI (EUTRAN cell global ID) = MCC + MNC + eNB ID + Cell ID

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RSRP• Reference signal received power:

Clutter Type Average Clutter Loss for 2300 MHz

Acceptable Outdoor RSRP Level

dBm

Indoor RSRP level as per definition of cell edge: -UL> 512

kbps

Dense Urban 24 -91 -115

Urban 20 -95 -115

Suburban 16 -99 -115

Rural 10 -105 -115

RSRP values:• Near : > -75 dBm, SINR > 25.• Middle : - 85 dBm to -95 dBm, SINR 17 to 20.• Edge : -100 to -110 dBm, SINR 8 to 12.

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RSRQ & SINR• Reference signal received quality (RSRQ) :

– Similar to Ec/Io in 3G.– 95% samples should be better than -12.

• Signal to noise ratio (SINR) :– Excellent : > 25.– Good : Between 15 to 25.– Average : Between 5 to 15.– Poor : Less than 5.

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BLER & UE Tx power• BLER :

– LTE works on 10% BLER.– 95% samples should be less than 10.

• UE Tx power :• Class 3 UE has max Tx power as 23 dBm +/- 2.• 95% samples should be less than 15.

– Poor : > 15.– Average : Between 5 to 15.– Good : Less than 5.

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CQI• Channel quality indicator (CQI) :

– UE request for the specific modulation & coding scheme.– Range is 0 to 15.– For a cluster 95% samples should be greater than 10.

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UE states in LTE

LTE UE States:

1- Idle2- Active3- Detached

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UE states in LTE• Idle

• Exact location is not known. Only TAC is known.• Bearer information is not known, only default bearer is available.• RRC connection is released.• UE monitors paging channels for incoming calls.• UE does not inform network about the cell change.• Performs neighboring cell measurements and cell selection/reselection.• Idle mode is UE power conservation state.• Reduces signaling overheads as compared to Active state.

• Active• Network knows the serving Cell ID.• UE transmits & receives data.

• Detached • UE disconnected or powered off.

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Layer 3 states

Layer 3 Protocols :1- RRC (Radio resource control)2- NAS (Non access stratum)

• RRC States : • Idle • Connected

• NAS States :• EMM (EPS Mobility Management)

• Deregistered• Registered

• ECM (EPS Connection Management)• Idle• Connected

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Channel structure

• Logical channels – Formed by RLC

• Transport channels– Formed by MAC

• Physical channels– Formed by PHY– Consist of a group of assignable radio

resource elements

Uu interface

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PHY DL Channels• PDSCH – Physical DL Shared CH

– Downlink data traffic.– Paging.– RACH response.

• PDCCH – Physical Downlink Control CH– Carries mainly scheduling information– Resource allocation on DL.– UL scheduling grants.– Power control .

• PHICH – Physical Hybrid ARQ Indicator – Reports status of Hybrid ARQ.– Ack / nack response.

• PCIFIC – Physical Control Format Indicator– Number of OFDB symbols for PDCCH up to 3 symbols per

subframe.

• PBCH – Physical Broadcast CH– Broadcast information necessary for accessing the network.– System bandwidth, MIMO etc.– SIBs (system information block).– MIB (master information block).

• PMCH – Physical Multicast Channel– Data and signaling for multicast LTE Channels

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Layer 1 & Layer 2 Throughput

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PHY UL Channels• PUSCH – Physical Uplink Shared Channel

– Uplink user data .

• PUCCH – Physical Uplink Control Channel– Reports Hybrid ARQ acknowledgements.– CQI.– RI.– PMI.– Buffer status report.

• PRACH – Physical Random Access Channel– Used for random access.– Scheduling requests.

LTE Channels

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Transport channels

• BCH – Broadcast CH– Transport for BCCH

• PCH – Paging CH– Transport for PCH

• DL-SCH – Downlink Shared CH– Transport of user data and signaling.

• MCH – Multicast channel– Used for multicast transmission

• UL-SCH – Uplink Shared CH– Transport for user data and signaling

• RACH – Random Access CH– Used for UE’s accessing the network

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Logical channels

• BCCH – Broadcast Control CH– System information sent to all UEs

• PCCH – Paging Control CH– Paging information when addressing UE

• CCCH – Common Control CH– Access information during call establishment

• DCCH – Dedicated Control CH– User specific signaling and control

• DTCH – Dedicated Traffic CH– User data

• MCCH – Multicast Control CH– Signaling for multi-cast

• MTCH – Multicast Traffic CH– Multicast data

LTE Channels

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Handover Optimization• Basic optimization parameters:

– Offset– Hysteresis– Time to trigger– Thresholds

• LTE Handover events:– A1– A2– A3– A4– A5iRAT HO:– B1– B2

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Event A3

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A3 optimization

• The smaller the value of a3offset+hysteresisa3 the faster we release the calls to neighboring cells.

• The higher the value of a3offset+hysteresisa3 the more difficult we make it for calls do handover to other cells.

• Time to trigger:

• If a3offset+ hysteresisa3 is relatively large (i.e.: 6dB or stronger), then a value of timetotriggera3 under 100 ms is acceptable.

• If a3offset+ hysteresisa3 is relatively small (i.e.: 2dB), then a value of timetotriggera3 should be around 320 to 640 ms.

• The value allocated to timetotriggera3, hence, depends on:– Parameter setting of a3offset and hysteresisa3,– Morphology (dense urban, urban, suburban, rural)– Speed of UE in the cells (freeways and or suburban roads).

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A3 examples

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Event A2

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Event A2 examples

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Event A1

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Event A4

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Event A5

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Event B1

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Event B2