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Technology TrainingDecember 4, 2012

saket.n@mail01.huawei.com

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Outline

LTE radio resources

Duplex techniquesFDD / TDD

Multiple antenna techniques

Reference signals

Throughput calculation Rank Index

PCI (Physical cell identity)

Cyclic prefix (CP)

Network architecture

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Resource Block

LTEradio resource = time-frequency chunk

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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 Bandwidth

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Parameter Value

Bandwidth (MHz) 1.4 3 5 10 15 20

Frame /subframe

duration10/1 ms

Subcarrier spacing 15KHz

Resource blocks 6 15 25 50 75 100

Number of used

subcarriers72 180 300 600 900 1200

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

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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

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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

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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 signals

1. Cell specific DL reference signals Every DL subframe Across entire DL bandwidth

2. UE specific DL reference signals Intended for individual UEs

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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.

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Cell specific reference signals

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UE Specific RS

UE specific RSused for beam forming

Provided in addition to cell specific RS

Sent over resource block allocated for DL-SCH (applicable only

for data transmission)

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Note: additional reference signals

increase overhead. One of the most

beneficial use of beam forming is at the

cell edgeimproves SNR

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Throughput calculation

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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 indoorsites i.e. (151167).

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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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