5) Radio Procedures

8/14/2019 5) Radio Procedures

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MobileCommProfessionals, Inc.

Your Partner for Wireless Engineering Solutions


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Overview of LTE Measurements

CQI Measurements

Handover Measurements

Cell Search Procedure

PLMN SelectionCell Selection and Reselection

Random Access Procedure

Paging

Objective


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LTE Physical Layer - Introduction

It provides the basic bit transmission functionality over air

LTE physical layer based on OFDMA downlinkand SC-FDMA inuplinkdirection This is the same for both FDD and TDD mode of operation

There is no macro-diversityin use

System is reuse 1, single frequency network operation is feasible

No frequency planning required

There are no dedicated physical channelsanymore, as all resource mapping isdynamically driven by the scheduler

FDD

..

..

..

..

Downlink Uplink

Frequency band 1

Frequency band 2

.. ..Single frequencyband

TDD


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FDD -Frame Structure

FDD Frame structure ( also called Type 1 Frame) is

common to both uplink and downlink.

Divided into 20 x 0.5ms slots

10 ms frame

0.5 ms slot

s0 s1 s2 s3 s4 s5 s6 s7 s18 s19..

1 ms sub-frame

SF0 SF1 SF2

SF9..

sy4sy0 sy1 sy2 sy3 sy5 sy6

0.5 ms slot

SF3

Frame length =10 ms

FDD: 10 ms sub-frame for UL

- 10 ms sub-frame for DL1 Frame = 20 slots of 0.5ms each

1 slot = 7 ( NCP) or 6 (ECP)

SF: SubFrame

s: slot

Sy: symbol


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TDD has a single frame structure: same as FDD but with some

specific fields to enable also TD-SCDMA co-existence (China):DwPTS, GP, UpPTS

Subframe 0 and DwPTS are reserved for downlink;

subframe2 and UpPTS are reserved for UL.

Remaining fields are dynamically assigned between UL and DL

SF

#0

. . .f

time

UL/DL

carriersubframe 0

D

wPTS

GP

UpPTS SF

#2

SF

#4subframe 2

subframe 4

SF

#0

. . .

D

wPTS

GP

U

pPTS SF

#2

SF

#4subframe 0 subframe 2 Subframe 4

half frame

DwPTS: Downlink Pilot time Slot

UpPSS: Uplink Pilot Time Slot

GP: Guard Period to separate UL/DL

Downlink Subframe

Uplink Subframe

TDD -Frame Structure


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There are 7 frame configurations, according to different DL/UL

partition

1 frame = 10ms

1 subframe = 1ms

DL

DL

DL

DL

DL

DL

DL

DL

DLDL

DL DLDL

DL DL DL DL DL

DL

DLDL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DL

DLDL

UL

UL

UL

UL

UL

UL

UL UL UL UL UL

ULUL

UL

UL

UL

UL

UL

UL

UL

UL

UL

UL

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

SS

0

1

2

3

4

5

6

DL Downlink subframe

UL Uplink subframeSS Special Switching subframe

TDD -Frame Structure


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Cell Search

1.PSS Primary Synchronisation Signal

(Time-slot & Frequency synchronisation

+ Physical cell id (0,1,2) )

2. SSS Secondary Synchronisation Signal

(Frame synchronisation

+ Physical Cell id group (1..168) )

4.PBCHPhysical Broadcast Channel

(MIBDL system bandwidth, PHICHconfiguration)

3.DL Reference Signals

(Channel estimation & measurements

like CPICH in UMTS)

eNodeB

UE


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Physical layercell identity

(1 out of 504)

Find Cell

0 1 167

0 1 2 0 1 2 0 1 2

Possible planning of the 504sequences:

3 (orthogonal) X 168 (pseudo-random) = 504

Cells belonging to the same Node-B

get the 3 different cell IDs from thesame group

Cells belonging to different Node-Bsget the different cell IDs fromdifferent groups

Cell Groups

Cell IDs


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2 3 4 5 7 8 9 10

1 2 3 4 5 6 7

1 2 3 4 5 6

10ms Radio frame

1ms SubframeSSS

PSS0.5ms (One slot)

Normal CP

Extended CP

PSS and SSS frame and slot structure in time domain in theFDD case

Time Synchronization FDD


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1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7

1 2 3 4 5

10ms Radio frame

1ms SubframeSSS

PSS1 ms TTI (two slots = 20.5ms)

Normal CP

Extended CP

1 2 3 4 5 6 7

1 2 3 4 5 66

PSS and SSS frame and slot structure in time domain in theTDD case

Time Synchronization TDD


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Frequency Synchronization PSS

OFDM Modulator

0000Five zerosFive zeros

ZCM(0) ZCM(1) ZCM(62)

Length 63 Zadoff-ChuSequence

62 subcarriers (d.c. not included)


PSS structure in frequency domain -> only 62 subcarriers out of 72 used. Thisis because the length of the Zadoff-Chu Sequence is 63 (d.c. not included).

ZadoffChuSequences are

based on CAZAC =Constant Amplitude

Zero Auto-Correlation

sequences Cell ID Root index(M)

0 25

1 29

2 34

3 different PSSsequences

corresponding to 3different cell IDs.

They could begenerated by using a

different root sequenceM for the Zadoff-

Sequences

3GPP TS 36.211


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Time slot (0.5 ms) syncronization

PSS placed strategically at the beginning and middle of frame

Estimation is vendor specific (matched filtering)

Frame ambiguity of 0.5 ms

Find physical layer cell ID

1 out of 3 sequences sent on PSS

1 to 1 mapping with the physical cell ID (table specified by 3GPP*)

The cell ID group not known yet

PSS Primary Synchronisation Signal

eNod

eB

UE


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SSS0 in

subframe 0

SSS1 insubframe 5

OFDM Modulator

0000

a0 a1 a30

Length-31 binary sequence

b0 b1 b30


a , b = two different

cyclic shifts of a singlelength-31

binary sequence

Frequency Synchronization SSS

SSS structure in frequency domain

2 different SSS per cell:

SSS0 in subframe 0 and SSS1

in subframe 5.

SSS0 and SSS1 have the same

structure but are shifted infrequency domain

The cyclic shift is

Dependent on thePhysical layer cell

ID group (1..168)


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SSS Secondary Synchronisation Signal

Frame (10 ms) synchronization

2 different sequences depending on the cell group are sent: SSS0 and

SSS1

By observing the combination of pairs SSS0 and SSS1 the UE can identify

either the begining or the middle of the frame

Example: the sequence SSS0-PSS is indicating the begining of theframe, SSS1-PSS the middle of the frame

Find physical layer cell ID group

Sequences SSS0 and SSS1 are mapped with the cell id group 1..168 (tablespecified by 3GPP*)

The combination of SSS0 and SSS1 is giving the cell ID group


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PSS and SSS Frame in Frequency and Time Domain for FDD Case

10 ms Radio frame

5 ms repetition

period

One subframe (1 ms)

6R

Bs7

2subcarriers

=1.4

MHz

(minimumL

TEBan

dwidth)

Frequency

Time

SSS

PSS

Reference signals

Unused RE

PSS and SSS


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Cell Search







4.PBCH Physical Broadcast Channel

(MIB DL system bandwidth, PHICHconfiguration)



like CPICH in UMTS)

eNodeB

UE


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DL Reference Signals

Used for: DL channel quality measurements DL channel estimation for coherent demodulation at the UE Too many signals reduce the DL capacity Too less signals may be not be enough for channel estimation

Easy to be found by UEs

Like CPICH (Common Pilot Channel) in UMTS


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DL Reference Signals

Freque

ncy

Time

First slot Second slot

Reference signal

*Normal CP (cyclic prefix) assumed

In Frequency: 1 reference symbol toevery 6thsubcarrier

In one RB (resource block = 12subcarriers): every 3rdsubcarrier

In Time is fixed: 2 reference symbolsper Time slot (TS 0 & TS 4)

1 2 3 4 5 6 7 1 2 3 4 5 6 7

Diffe ent Refe ence Signals


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Reference signal

F

requency

Time

Shift = 0 Shift = 1 Shift = 5

Different Reference SignalsFrequency Shift

Cell specific Reference Signals in Case of


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Antenna port 0 Antenna port 1

Reference signal Unused symbol

Cell-specific Reference Signals in Case ofMulti-Antenna Transmission


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Cell Search







4.PBCH Physical Broadcast Channel

(MIB DL system bandwidth, PHICHconfiguration)



like CPICH in UMTS)

eNodeB

UE


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PBCH Design Criteria

Detectable without the knowledge of system Bandwidth mapped to the central 72 subcarriers

over 4 symbols

during second slot of each frame

Low system overhead & good coverage

Send minimum information only the MIB (Master InformationBlock)

SIBs (System Information Blocks) are sent on PDSCH

MIB (Master Information Block) content: DL system Bandwidth

PHICH configuration (PHICH group number)

System frame number SFN


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PBCH Mapping

6R

Bs7

2subcarriers=1.4

MHz

(minimumL

TEBan

dwidth)

First subframe (1 ms)

Slot0

Slot1

SSS

PSS

Reference signals

Unused RE

PBCH

Freque

ncy

Time

C


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PBCH Repetition Pattern

72subcarriers

Repetition Pattern of PBCH = 40 ms

one radio frame = 10 ms


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Initial Access

8.PRACH Preamble

11. PDSCH Physical Downlink Shared Channel

12.PUSCH Physical Uplink Shared Channel

(Random Access response, ID of the receivedpreamble, UL resources for TX,

C-RNTI)

(RRC: RRC Connection Request,

C-RNTI,

TMSI or random number)


(Contention Resolution,

C-RNTI & TMSI)

eNodeB

UE

d l


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Random Access-Initial Access

Random access procedure handled by MAC and PHY Layer through PRACH (in UL)

and PDCCH ( in DL)RACH only carries the preambles and occupies 6 resource blocks in a subframe

Multiplexing of PRACH with PUSCH and


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Multiplexing of PRACH with PUSCH andPUCCH

PUCCH

PUCCH

PRACH PRACH

PUSCH

PRACH slot

Duration( e.g. 1ms)

PRACH slot period

TotalUL

Ban

dwidth

Time

PRACHbandwidth

(1.08MHz)

UL PRACH is orthogonal with the data in PUCCH and PUSCH (reserved resources)

Reserve resources for PRACH preambles

Frequency: 6 Resource Blocks x 180 KHz = 1,08 MHz

Time: 1 ms

PRACH P bl R i d t th N d B


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PreambleCP

PreambleCP

Other users

Other users

Otherusers

Otherusers

PRACH slot duration

GT = Guard Time

Observation interval

UE close

to the

eNodeB

UE at the

Cell edge

PRACH Preamble Received at the eNodeB

CP = Cyclic Prefix It can be seen that the UE at celledge is using almost all Guard Time


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PRACH Formats and Cell Ranges

PreambleCP

CP

CP

CP

GT

GT

GT

GT

Preamble

Preamble

Preamble

Preamble

Preamble

100 s800 s

684 s 800 s 520 s

203 s 1600 s 200s

684 s 1600 s 720 s

2 ms

2 ms

3 ms

Format 0

Format 1

Format 2

Format 3

1 ms

100 Km

CELL RANGE

29 Km

77 Km

14 Km


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Intra-Cell Interference

64 different orthogonal Preambles availablein each cell obtained by cyclic shift of a

Zadoff-Chu sequenceIf however collision is happening (2 UEsusing the same preamble) -> contentionresolution process

How can multiple terminals performrandom access attempt at the same time

without collision?

Solution ?eNodeB

UE3

UE2

UE1


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Initial Access

8.PRACH Preamble


12.PUSCH Physical Uplink Shared Channel

(Random Access response, ID of the receivedpreamble, UL resources for TX,

C-RNTI)

(RRC: RRC Connection Request,

C-RNTI,

TMSI or random number)


(Contention Resolution,

C-RNTI & TMSI)

eNodeB

UE

DL Transmission


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DL Transmission

2. PUCCH Physical Uplink Control Channel(CQI based on DL reference signals measurements)

3. PCFICH Physical Control Format Indicator Channel

(How many symbols (1,2,3) in thebeginning of the sub-frame are forPDCCH)

4. PDCCH Physical Downlink Control Channel

(Downlink assignment for PDSCH:

Modulation & coding, resource blocks)


(user data initial transmission)

6. PUCCH Physical Uplink Control Channel (or PUSCH)

(ACK/ NACK for HARQ)


(user data eventual re-transmission)

1. DL Reference signals

eNodeB

UE

DL Transmission


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DL Transmission

Process description:The eNodeB is broadcasting the Reference Signals (like CPICH in UMTS)

The UE is performing measurements on Reference Signals

Based on the measurements the UE is generating the CQI

The CQI is transmitted to the eNodeB

UE Proposes eNB an optimum MCS so BLER is on target

4-bit CQI Table


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DL T i i


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DL Transmission


(CQI based on DL reference signals measurements)


(How many symbols (1,2,3) in the beginning ofthe sub-frame are for PDCCH)





(user data -> initial transmission)






eNodeB

UE

PCFICH


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CFI = control format indicators

Indicates how many OFDM symbols per subframe are for PDCCH: 1, 2 or 3symbols

The CFI is carried by 32 bits of information

16 RE Resource Elements distributed in frequency

Sent in the first 3 symbols of the subframe

PCFICH

PCFICH Structure


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72subcarriers

Time

PCFICH resource elements

Resource elements reserved forreference symbols

Rate 1/16block code

ScramblingQPSK

modulation

2 bits 32 bits 32 bits 16

symbols

4

4

4

4

One ResourceElement Group

(REG) = 4 RE

D.C.

2 input bits are enough to signal the PDCCH size:1, 2 or 3 symbols

PCFICH Structure

PDCCH Resource Adjustment from


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PDCCH Resource Adjustment fromPCFICH

First subframe (1ms) Second subframe(1ms)

12subcarriers

Frequency

Time

Control region -1 OFDM symbol

Control region 3 OFDM symbols

Indicated by

PCFICH

DL T i i


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DL Transmission


(CQI based on DL reference signals measurements)


(How many symbols (1,2,3) in the beginning ofthe sub-frame are for PDCCH)





(user data -> initial transmission)






eNodeB

UE

PDCCH D i


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Several PDCCHs could be transmitted in one subframe

One PDCCH contains DCI = DL control information DCI could indicate:

Uplink scheduling grants for PUSCH

Downlink scheduling assignments for PDSCH

TPC command for PUSCH and PUCCH

The DCI may have different size (depending on the information e.g. scheduling orpower control command different formats possible)

The number of bits for one PDCCH may change based on channel conditions:

UE at cell edge more bits per PDCCH

UE close to BTS less bits per PDCCH

PDCCH Design

Size of the PDCCH Region


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Frequency

Time

Slot No. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

PDCCH region

1,2,3 OFDM symbolsin the beginning

of the subframe

not allocated byPCFICH, PHICH

Subframe 0 Subframe 1Subframe 2Subframe 3Subframe 4Subframe 5Subframe 6

Size of the PDCCH Region

PDCCH Size


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PDCCH Size

REG = Resource Elements Groups

RE = Resource Elements

UE 1

UE 2

Allocation for UE 1

Allocation for UE 2

Frequency

Time

PCFICH

PHICH

PDCCH

PDSCH Physical Downlink


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Contain the actual user data from DL-SCH

Use the available Resource Elements

Allocation is signalled by PDCCH

Also used for:

SIBs (System Information Block) of the system information

Paging

PDCCH acting like a Paging Indicator Channel in UMTS

PDSCH Physical DownlinkShared Channel

eNodeB

UE

Physical Downlink Shared Channel


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Frequency

Time

Slot No. 0 1 2 3 4 5 6 7 8 9

Subframe 0 Subframe 1 Subframe 2 Subframe 3 Subframe 4 ..

SSS

PSS

PBCH

PCFICH

PHICH

PDCCH

Reference signals

PDSCH UE1

PDSCH UE2

Physical Downlink Shared Channel

System Information


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System Information ( )

SIB 2 SIB 3 SIB 4 SIB 11

Fixed repetion 80 msFirst transmission in subframe #5for which SFN mod 8 = 0Indicates the allocation of theother SIBs 2...11

SIB 1

System Information

MIB: Master Information Block

SIB: System Information Block

SFN: System Frame Number

UE

eNodeB

MIBSent on PBCH!

40 ms repetition

System Information


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SIB 1

- Cell access related information (PLMN, cell identity, Tracking Area code etc.)

- Information for cell selection

-TDD configuration

- Information about time-domain scheduling of the remaining SIBs

SIB 2 - Access barring information

-Radio resource configuration of common channels (e.g. PCCH)

-Frequency information (UL UARFCN, uplink bandwidth)

SIB 3 -Cell-reselection information that is common for intra-frequency, inter-frequency

and/or inter-RAT cell re-selection.

SIB 4 -Neighbor cell related information only for intra-frequency cell re-selection.

SIB 5 -Inter-frequency cell re-selection like E-UTRAN related information

-Inter-frequency neighboring cell related information

SIB 6 -UTRA FDD and TDD frequency information for cell reselection

SIB 7 - Information relevant only for cell re-selection to the GERAN

SIB 8 - Information relevant only for cell re-selection to the cdma2000 system.

SIB 9 - Home eNodeB identifier

SIB 10 - Earthquake and Tsunami Warning System (ETWS) primary notification

SIB 11 - Earthquake and Tsunami Warning System (ETWS) secondary notification

System Information

UL Transmission


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UL Transmission


(UL scheduling request)

2. UL Sounding Reference Signal

(used by Node-B for channel dependent scheduling)

3. UL Demodulation Signal

(UL channel estimation, demodulation,

Like DPCCH in UMTS)4. PDCCH Physical Downlink Control Channel

(UL grantcapacity allocation)

5. PUSCH Physical Uplink Shared Channel

(user data initial transmission)

6. PHlCH Physical HARQ Indicator Channel


7. PUSCH Physical Uplink Shared Channel


eNodeB

UE

PUCCH and PUSCH Multiplexing


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PUCCH and PUSCH Multiplexing

Time

TotalULBandwith

PUCCH

PUCCH

PUSCH

1 subframe = 1ms

Frequency

12sub

carriers

PUCCH contains UCI = UL Control InformationUCI could indicate:

Scheduling requests HARQ ACK/NACK for DL transmission CQI = Channel Quality Indicator

PUCCH F t


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PUCCH Formats

PUCCHformat Modulation scheme Number of bits persubframe Type of information

1 N/A N/A Scheduling Request

(SR)

1a BPSK 1 ACK/ NACK

1b QPSK 2 ACK/ NACK

2 QPSK 20 CQI

2a QPSK+BPSK 21 CQI + 1 bit ACK/ NACK

2b QPSK+BPSK 22 CQI + 2 bits ACK/

NACK

eNodeB

UE

Uplink Reference Signals


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Uplink Reference Signals

Associated with transmissionof uplink data on PUSCH orPUCCH

Used for channel estimationfor coherent detection anddemodulation (both PUCCHand PUSCH)

DemodulationReference

Signals

Not associated with UL datatransmissions

Used for estimation of the ULchannel quality to enable thechannel dependent scheduling

Sounding

ReferenceSignals

UE

eNodeB

Design of Demodulation Reference Signals DRS


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Position of DRS

Time domain:

For PUCCH: the number and the exact position of the DRS is dependent on the format (1/1a/1b

or 2/2a/2b) used

For PUSCH: every 4thsymbol in every time

slot (the 3rdsymbol for the extended cyclic

prefix)

Frequency domain:

DRS has the same bandwidth like

the UL transmission of the terminal

Design of Demodulation Reference Signals DRS

Uplink DRS Multiplexed with PUCCH


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Uplink DRS Multiplexed with PUCCH

Time

TotalULBandwith

PUCCH

PUCCH

PUSCH

1 subframe = 1ms

F

requency

12subcarriers

ACK ACK DRS DRS DRS ACK ACKACK ACK DRS DRS DRS ACK ACK

CQI DRS CQI CQI CQI DRS CQI CQI DRS CQI CQI CQI DRS CQI

0

Simbol number (normal CP)

1 2 3 4 5 6 63210 54

ACK = AcknowledgmentCQI = Channel Quality IndicatorDRS = Demodulation Reference Signals

Sounding Reference Signals SRS


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The SRS can be used for:

initial Modulation and Coding Scheme (MCS) selection

initial power control for data transmissions

timing advance

Frequency dependent scheduling for the UL


eNodeB

UE



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Why Demodulation References Signals cannot be

used instead of SRS?

The demodulation reference signals are only

sent on the transmitted bandwidth!

We need an estimation of the whole

spectrum so the SRS may cover a different,often larger, frequency span than for example

PUSCH (if they are transmitted together).

The SRS is not necessarily transmitted

together with any physical channel


36Subcarriers

0 1 2 3 4 5 6 0 1 2 3 4 56

Slot 1 Slot 2

Normal CP

PUSCH DM RS

SRS

Subframe 0


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HAPPY LEARNING

MobileCommProfessionals, Inc.www.mcpsinc.com

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5) Radio Procedures