Scrambling

7/18/2019 Scrambling

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Dr. Stefan BrückQualcomm Corporate R&D Center Germany

3G/4G Mobile Communications Systems



Chapter V: Physical Layer of UMTS

2 Slide 2



Physical Layer of UMTS (R99/HSPA)

Basic CDMA Concept

Selected Physical Layer Aspects

UMTS (R99)

High-Speed Downlink Packet Access (HSDPA)

High-Speed Uplink Packet Access (HSUPA, E-DCH)

3 Slide 3



Basic CDMA Concept

4

Code Division Multiple Access (CDMA) is a method in which multiple usersoccupy the same time and frequency allocations

Slide 4



Orthogonal Spreading - Basics

5

Transmission using the entire bandwidth is achieved by spreading eachsymbol with a pre-defined sequence with fixed chip rate → Increase of theutilized bandwidth

The figure shows an example of a spreading sequence (-1, 1, 1, -1)

Slide 5



Despreading – Basics

6

The receiver despreads the chips by using the same orthogonal sequenceused at the transmitter

Note that under no noise conditions, the symbols are completely recoveredwithout any errors

Slide 6



OVSF Tree

7

Orthogonal Variable Spreading Factor (OVSF) codes are used to spread to the chiprate on both the UL and the DL

The chip rate in UMTS is 3.84 Mcps

On the UL, different OVSF codes separate dedicated Physical Channels (e.g. DPCCH,DPDCH) from a single terminal

On the DL, different OVSF codes separate UEs within a single cellSlide 7



Scrambling Codes

In DL (usually) one OVSF tree per cell, in UL one OVSF tree per terminal isused for spreading

The spreading codes are also called channelization codes

Strong interference would occur if a neighbor cell in DL or neighbor terminalis UL would use the same channelization code → additional protection isneeded

The solution is applying a scrambling sequence per cell (DL) and per

8

terminal (UE) The chip rate of the scrambling sequence is 3.84 Mcps as well

For the DL there are 512 so-called primary scrambling codes

Re-use of the scrambling codes is needed in the network

For the UL there are roughly 224 different scrambling codes

Slide 8



Physical Channels in UMTS

Primary common control physical channel, PCCPCH (DL)

Secondary common control physical channel, SCCPCH (DL)

Physical layer only channels

Synchronization channel, SCH (DL)

Common pilot channel, CPICH (DL)

Paging indicator channel, PICH (DL)

9

Acquisition indicator channel, AICH (DL)

Physical random access channel, PRACH (UL)

Dedicated physical channel, DPCH, DL

Dedicated physical channel DPCH,UL

Slide 9



Physical Layer Timing in UMTS (R99)

Frame Timing

Transmission Time Interval (TTI)

TTI: 10, 20, 40, 80 ms boundaries

10 ms radio frames, 15 slots perframe

38400 chips per frame

Slot Timing

10

c ps per s o , . ms

Symbol Timing

Symbol consists of a number ofchips

OVSF determines chips/symbol

OVSF ranges from 4 to 512chips/symbol (640 to 5 symbolsper slot)

Slide 10



Multiplexing and Coding Procedure

11

The transport channel data is broken into blocks and delivered everytransport time interval (TTI) for that particular transport channel.

The end result of the Physical Layer’s actions on the transport channel data

is a Coded Composite Transport Channel (CCTrCH)

Slide 11



Downlink Generic Physical Layer Procedure

Transport channel data delivered every TTI

CRC Attachment

Channel Coding

Rate Matching

Interleaving

12

Spreading using OVSF Channel codes

Scrambling

QPSK Modulation

Slide 12



Downlink Channel Coding

In UMTS, two types of forward error correction coding are applied

Convolutional codes

Used for common and dedicated transport channels

Applied for data rates ≤ 32 kbps (roughly)

Constraint length K = 9

Coding rate R = 1/2 and R = 1/3 depending on the transport channel

Turbo codes

13

se or e cate transport c anne s

Applied for data rates ≥ 64 kbps (roughly)

Based on parallel concatenated convolutional codes

Mother code rate is R = 1/3

Slide 13



Downlink Spreading and Scrambling

14

The symbols are spread using the same channelization code

Cch,SF,m is the mth OVSF code of spreading factor SF

Afterwards, the signal is scrambled using either a primary or secondaryscrambling code (PSC, SSC)

The Gs are the DL weight factors: G is for the Physical Channels, Gp, Gs for thePrimary and Secondary Synchronization Channels (not covered)

Slide 14



Downlink Physical Channel

15

The DPDCH and the DPCCH are time multiplexed into the DPCH

The DPCCH includes TPC, TFCI and Pilot bits TPC bits are power control commands for the uplink

TFCI bits include information of the transport format

Pilots bits are used for channel estimation

Slide 15



Uplink Generic Physical Layer Procedure

Transport channel data delivered every TTI

CRC Attachment

Channel Coding

Interleaving

Rate Matching

16

Spreading using OVSF Channel codes

PN Scrambling

QPSK Modulation

Slide 16



Uplink Spreading and Scrambling

17

The physical channels are spread to the chip rate with individualchannelization codes and then scrambled with the same scrambling code

In the UL, the DPCCH is always on the Q branch

The DPDCHs can be on both the I and Q branch

If there is only one DPDCH, it is on the I branch (BPSK modulation)

βs are the UL weight factors, βd is for data and βc is for control

Slide 17



Uplink Physical Channel

18

UL DPCH is consists of two Physical Channels, the DPDCH and the DPCCH

UL Dedicated Physical Data Channel (DPDCH) sent on I data branch

UL Dedicated Physical Control Channel (DPCCH) sent on Q data branch

Slide 18



Common Pilot Channel

19

The Common Pilot Channel (CPICH) provides an in-cell timing reference andis used for DL channel estimation

There are two types of Common Pilot Channels

Primary CPICH (P-CPICH)

Secondary CPICH (S-CPICH)

Slide 19



Primary and Secondary Common Pilot Channel

The properties of the P-CPICH are as follows:

The same channelization code is always used for the P-CPICH, Cch,256,0

The P-CPICH is scrambled by the PSC

There is one and only one P-CPICH per cell

The P-CPICH is broadcast over the entire cell Typically 10% of the DL power are allocated to the P-CPICH

The properties of the S-CPICH are as follows:

An arbitrar channelization code of SF 256 is used for the S-CPICH

20

An S-CPICH is scrambled by either the PSC or an SSC There may be zero, one, or several S-CPICH per cell

An S-CPICH may be transmitted over the entire cell or only over part of the cell

When a S-CPICH is used, it is scrambled with a PSC or SSC

Slide 20



HSDPA Background

Initial goals

Establish a more spectral efficient way of using DL resources providing data ratesbeyond 2 Mbit/s, (up to a maximum theoretical limit of 14.4 Mbps)

Optimize interactive & background packet data traffic, support streaming service Design for low mobility environment, but not restricted

Techniques compatible with advanced multi-antenna and receivers

Standardization started in June 2000

21

Broad forum of companies Major feature of Release 5

Enhancements in R7 HSPA+

Advanced transmission to increase data throughput

Signaling enhancements to save resources

Slide 21



HSDPA Basics

Evolution from R99/Rel. 4

5 MHz Bandwidth

Same spreading by OVSF and scrambling codes

Turbo coding

New concepts in Rel. 5

Adaptive modulation (QPSK vs. 16QAM), coding and multicodes

22

Fast scheduling in NodeB (TTI = 2ms)

Hybrid ARQ

Enhancements in Rel. 7 HSPA+

Signaling enhancements

64QAM

MIMO techniques, increase of the bandwidth (dual carrier)

Slide 22



Higher Order Modulation

Standard modulation scheme in UMTS networks

QPSK 2 bit per symbol

With HSDPA, modulation can be switched between two schemes

QPSK 2 bit per symbol 16-QAM 4 bit per symbol

23

Low bitrate → robust to High bitrate → Sensitive todisturbances disturbances

Slide 23



HS-DSCH Principle I

Channelization codes at a fixed spreading factor of SF = 16

Up to 15 codes in parallel

SF=8

SF=4

SF=2

CC

24

OVSF channelization code tree allocated by CRNC

HSDPA codes autonomously managed by Node B MAC-hs scheduler

Example: 12 consecutive codes reserved for HS-DSCH, starting at C16,4

Additionally, HS-SCCH codes with SF = 128 (number equal to simultaneousUEs)

SF=16

Physical channels (codes) to which HS-DSCH is mapped CPICH, etc.

,,

Slide 24



HS-DSCH Principle II

Resource sharing in code as well as time domain:

Multi-code transmission, UE is assigned to multiple codes in the same TTI

Multiple UEs may be assigned channelization codes in the same TTI

Code

25

Example: 5 codes are reserved for HSDPA, 1 or 2 UEs are active within oneTTI

Data to UE #1 Data to UE #2 Data to UE #3

Time (per TTI)

not used

Slide 25



UMTS Channels with HSDPA

26

e

UEUE

Cell 2

R99 DCH (in SHO) UL/DL signalling (DCCH) UL PS service UL/DL CS voice/ data

Rel-5 HS-DSCH

DL PS service

(Rel-6: DL DCCH)

= ServingHS-DSCH cell

Slide 26



HSDPA Channels

HS-PDSCH

Carries the data traffic

Fixed SF = 16; up to 15 parallel channels

QPSK: 480 kbps/code, 16QAM: 960 kbps/code

HS-SCCH

Signals the configuration to be used in this TTI

HS-PDSCH codes modulation format TB information

27

Fixed SF = 128 Sent two slots (~1.3msec) in advance of HS-PDSCH

HS-DPCCH

Feedbacks ACK/NACK and channel quality information (CQI)

Fixed SF = 256, code multiplexed to UL DPCCH Feedback sent ~5msec after received data

Slide 27



Timing Relations (DL)

TB size & HAR Info

Downlink DPCH

HS-SCCH

3 × Tslot (2 msec)

Tslot (2560 chips)

ch. code & mod

28

NodeB Tx view

Fixed time offset between the HS-SCCH information and the start of thecorresponding HS-DSCH TTI: τHS-DSCH-control (2 × Tslot= 1.33msec)

HS-DSCH and associated DL DPCH not time-aligned

DATAHS-PDSCH

- = × slot msec

τHS-DSCH-control= 2 × Tslot

Slide 28



Timing Relations (UL)

DATA

plink DPCCH

HS-PDSCH

3 × Tslot (2ms)

-

Tslot (0.67 ms)

29

UE Rx view

Alignment to m × 256 to preserve orthogonality to UL DPCCH

HS-PDSCH and associated UL DPCH not time-aligned (but “quasi synch”)

S-DPCCH

m × 256 chips

τUEP = 7.5 × Tslot (5ms)-

C IA/NC IA/NC IA/NCQI A/N

Slide 29



Hybrid Automatic Repeat Request

HARQ is a stop-and-wait ARQ

Up to 8 HARQ processes per UE

In HSDPA the HARQ is asynchronous and adaptive

Retransmissions are done at MAC-hs layer, i.e. in the Node B

Triggered by NACKs sent on the HS-DPCCH

The mother code is a R = 1/3 Turbo code

Code rate adaptation done via rate matching, i.e. by puncturing and repeating

30

bits of the encoded data

Two types of retransmission

Incremental Redundancy

Additional parity bits are sent when decoding errors occured

Gain due to reducing the code rate

Chase Combining

The same bits are retransmitted when decoding errors occured

Gain due to maximum ratio combining

HSDPA uses a mixture of both types

Slide 30



HARQ Processes

1 2 23 4 5 31

RTTHARQ

DataHS-PDSCH

31

HARQ is a simple stop-and-wait ARQ

Example

RTTmin = 5 TTI Synchronous retransmissions (MAC-hs decides on transmission)

UE support up to 8 HARQ processes (configured by Node B) Min. number: to support continuous reception

Max. number: limit of HARQ soft buffer

Number of HARQ processes configured specifically for each UE category

1 2 3 4 5ACK/NACKHS-DPCCH

Slide 31



Adaptive Modulation and Coding

In HSDPA adaptive Modulation and Coding is applied

The data rate can be changed per TTI by changing the transport block size as wellas the number of codes being used in parallel

The mother code rate is R = 1/3

Codes rates up to R = 1 are achieved by puncturing

Users in favorable channel conditions (based on Channel Quality indication)are assigned higher code rates and higher order modulation (16QAM, 64

32

It is the task of the scheduler to decide on the instantaneous data rate

Slide 32



Supported Transport Block Sizes (Rel. 5)

Index TB Size Index TB Size Index TB Size1 137 86 1380 171 6324

2 149 87 1405 172 6438

3 161 88 1430 173 6554

4 173 89 1456 174 6673

5 185 90 1483 175 6793

6 197 91 1509 176 6916

7 209 92 1537 177 7041

8 221 93 1564 178 7168

9 233 94 1593 179 7298

10 245 95 1621 180 7430

11 257 96 1651 181 7564

12 269 97 1681 182 7700

13 281 98 1711 183 7840

14 293 99 1742 184 7981

15 305 100 1773 185 8125

16 317 101 1805 186 8272

17 329 102 1838 187 8422

18 341 103 1871 188 8574

19 353 104 1905 189 8729

20 365 105 1939 190 8886

46 674 131 3090 216 14155

47 686 132 3145 217 14411

48 699 133 3202 218 14671

49 711 134 3260 219 14936

50 724 135 3319 220 15206

51 737 136 3379 221 15481

52 751 137 3440 222 15761

53 764 138 3502 223 16045

54 778 139 3565 224 16335

55 792 140 3630 225 1663056 806 141 3695 226 16931

57 821 142 3762 227 17237

58 836 143 3830 228 17548

59 851 144 3899 229 17865

60 866 145 3970 230 18188

61 882 146 4042 231 18517

62 898 147 4115 232 18851

33

21 377 106 1974 191 9047

22 389 107 2010 192 9210

23 401 108 2046 193 9377

24 413 109 2083 194 9546

25 425 110 2121 195 9719

26 437 111 2159 196 9894

27 449 112 2198 197 10073

28 461 113 2238 198 10255

29 473 114 2279 199 10440

30 485 115 2320 200 10629

31 497 116 2362 201 10821

32 509 117 2404 202 11017

33 521 118 2448 203 11216

34 533 119 2492 204 11418

35 545 120 2537 205 11625

36 557 121 2583 206 11835

37 569 122 2630 207 12048

38 581 123 2677 208 12266

39 593 124 2726 209 12488

40 605 125 2775 210 12713

41 616 126 2825 211 12943

42 627 127 2876 212 13177

43 639 128 2928 213 13415

44 650 129 2981 214 13657

45 662 130 3035 215 13904

64 931 149 4265 234 19538

65 947 150 4342 235 1989166 964 151 4420 236 20251

67 982 152 4500 237 20617

68 1000 153 4581 238 20989

69 1018 154 4664 239 21368

70 1036 155 4748 240 21754

71 1055 156 4834 241 22147

72 1074 157 4921 242 22548

73 1093 158 5010 243 22955

74 1113 159 5101 244 23370

75 1133 160 5193 245 2379276 1154 161 5287 246 24222

77 1175 162 5382 247 24659

78 1196 163 5480 248 25105

79 1217 164 5579 249 25558

80 1239 165 5680 250 26020

81 1262 166 5782 251 26490

82 1285 167 5887 252 26969

83 1308 168 5993 253 27456

84 1331 169 6101 254 27952

85 1356 170 6211

Slide 33



HSDPA UE Categories

The specification allows some freedom to the UE vendors

12 different UE categories for HSDPA with different capabilities (Rel.5)

The UE capabilities differ in

Max. transport block size (data rate)

Max. number of codes per HS-DSCH

Modulation alphabet (QPSK only)

-

34

Soft buffer size

The MAC-hs scheduler needs to take these restrictions into account

Slide 34



HSDPA – UE Physical Layer Capabilities (Rel. 5)

HS-DSCHCategory

Maximumnumber ofHS-DSCH

multi-codes

Minimum inter-TTI interval

MaximumMAC-hs TB size

Total number ofsoft channel

bits

Theoreticalmaximum datarate (Mbit/s)

Category 1 5 3 7298 19200 1.2

Category 2 5 3 7298 28800 1.2

Category 3 5 2 7298 28800 1.8

Category 4 5 2 7298 38400 1.8

Category 5 5 1 7298 57600 3.6

35

Category 6 5 1 7298 67200 3.6

Category 7 10 1 14411 115200 7.2

Category 8 10 1 14411 134400 7.2

Category 9 15 1 20251 172800 10.1

Category 10 15 1 27952 172800 14.0

Category 11* 5 2 3630 14400 0.9

Category 12* 5 1 3630 28800 1.8

cf. TS 25.306Note: UEs of Categories 11 and 12 support QPSK only

Slide 35



Channel Quality Information (CQI)

Signalled to the Node B in UL each 2ms on HS-DPCCH

Integer number from 0 to 30 corresponds to a Transport Format ResourceCombination (TFRC) given by

Modulation Number of channelisation codes

Transport block size

36

Mapping defined in TS 25.213 for each UE category

Slide 36



CQI – Mapping Table (Rel. 5)

Tables specified in TS

25.214 For each UE category Condition: BLER ≤ 10%

Example for UE category 10

CQI value TransportBlock Size

Number ofHS-PDSCH

Modulation Reference poweradjustment ∆∆∆∆

NIR XRV

0 N/A Out of range

1 137 1 QPSK 0

…

6 461 1 QPSK 0

7 650 2 QPSK 0

…

15 3319 5 QPSK 0

28800 0

37 Slide 37

-

…

23 9719 7 16-QAM 0

24 11418 8 16-QAM 0

25 14411 10 16-QAM 0

26 17237 12 16-QAM 0

27 21754 15 16-QAM 0

28 23370 15 16-QAM 0

29 24222 15 16-QAM 0

30 25558 15 16-QAM 0



Background

E-DCH is a Rel. 6 feature with following targets

Improve coverage and throughput, and reduce delay of the uplink dedicatedtransport channels

Priority given to services such as streaming, interactive and background services,

conversational (e.g. VoIP) also to be considered Full mobility support with optimizing for low/ medium speed

Simple implementation

S ecial focus on co-workin with HSDPA

38

Standardization started in September 2002 Study item completed in February 2004

Stage II/ III started in September/ December 2004

Release 6 frozen in December 2005/ March 2006

Various improvements have been introduced in Rel. 7 & Rel. 8

Slide 38



E-DCH Basics

E-DCH is a modification of DCH – It is not a shared channel, such asHSDPA in the downlink !!

PHY taken from R99

Turbo coding and QPSK modulation

In Rel. 7 also 16QAM modulation is supported

Power Control

10 msec/2 msec TTI

Spreading on separate OVSF code, i.e. code multiplexing with existing PHY

39

c anne s

MAC similarities to HSDPA

Fast scheduling

Stop and Wait HARQ: but synchronous

New principles

Intra Node B “softer” and Inter Node B “soft” HO should be supported for the E-DCH with HARQ

Scheduling distributed between UE and Node B

Slide 39

UMTS Ch l i h E DCH



UMTS Channels with E-DCH

40

e

UEUE

Cell 2

R99 DCH (in SHO)

UL/DL signalling (DCCH) UL/DL CS voice/ data

Rel-5 HS-DSCH (not shown) DL PS service (DTCH) DL signalling (Rel-6, DCCH)

Rel-6 E-DCH (in SHO)

UL PS service (DTCH)

UL Signalling (DCCH)

= ServingE-DCH cell

Slide 40

E DCH Ch l



E-DCH Channels

E-DPDCH

Carries the data traffic

Variable SF = 256 … 2

UE supports up to 4 E-DPDCH in parallel

E-DPCCH

Contains the configuration as used on E-DPDCH

Fixed SF = 256

41

E-RGCH/ E-HICH

E-HICH carries the HARQ acknowledgements

E-RGCH carries the relative scheduling grants

Fixed SF = 128

Up to 40 users multiplexed onto the same channel by using specific signatures

E-AGCH

Carries the absolute scheduling grants

Fixed SF = 256

E-RGCH and E-AGCH are used for providing scheduled grants to the UE

Slide 41

E DPDCH d E DPCCH Ph i l L St t



E-DPDCH and E-DPCCH Physical Layer Structure Data, Ndata bits

Slot #1 Slot #14Slot #2 Slot #iSlot #0

Tslot = 2560 chips, Ndata = M*10*2 bits (k=0…7)

Tslot = 2560 chips

E-DPDCHE-DPDCH

E-DPCCH 10 bits

Slot #3

42 Slide 42

1 subframe = 2 ms

1 radio frame, Tf = 10 ms

Subframe #0 Subframe #1 Subframe #2 Subframe #3 Subframe #4

Slot Format #i Channel Bit Rate(kbps)

Bits/SymbolM

SF Bits/Frame

Bits/Subframe

Bits/SlotNdata

0 15 1 256 150 30 101 30 1 128 300 60 20

2 60 1 64 600 120 403 120 1 32 1200 240 804 240 1 16 2400 480 1605 480 1 8 4800 960 3206 960 1 4 9600 1920 6407 1920 1 2 19200 3840 12808 1920 2 4 19200 3840 12809 3840 2 2 38400 7680 2560

S di f E DPDCH d E DPCCH



Spreading for E-DPDCH and E-DPCCH

43

ced,1 – ced,K are the channelization codes for the E-DPDCH’s, cec is the

channelisation code for the E-DPCCH βed,1 – βed,K are the gain factors for the E-DPDCH’s, βec is the gain factor for

the E-DPCCH

Slide 43

Timing Relation (UL)



Uplink DPCCH

10 msec

CFN

15 × Tslot (10 msec)

CFN+1

0.4 × Tslot (1024 chips)

±148chips

Downlink DPCH CFN

Timing Relation (UL)

44

E-DPDCH/ E-DPCCH time-aligned to UL DPCCH

Subframe #0

E-DPDCH/

E-DPCCH

3 × Tslot (2 msec)

Subframe #1 Subframe #2 Subframe #3 Subframe #4 2msec TTI

Slide 44

E AGCH Physical Layer Structure



E-AGCH Physical Layer Structure

45

The E-AGCH carries the absolute scheduling grant, which represents themaximum E-DPDCH / DPCCH power ratio (5 bits)

It is convolutional encoded with a R = 1/3 code

The spreading factor is SF = 256

Slide 45

E RGCH/E HICH Physical Layer Structure



E-RGCH/E-HICH Physical Layer Structure

46

For E-RGCH and E-HICH the same channel structure is applied

The E-RGCH is a dedicated or common downlink physical channel, whichcarries the relative scheduling grants from the Node B

In each slot a sequence of 40 ternary values is transmitted → Up to 40 userscan be multiplexed on the same channel

In each cell EHICH and E-RGCH for the same user are on the same code

Slide 46

HSUPA UE Categories



E-DCHCategory

Max. num.Codes

Min SF EDCH TTI Maximum MAC-eTB size

Theoretical maximum PHYdata rate (Mbit/s)

Category 1 1 SF4 10 msec 7110 0.71

Category 2 2 SF4 10 msec/

2 msec

14484/

2798

1.45/

1.4


HSUPA UE Categories

47

When 4 codes are transmitted, 2 codes are transmitted with SF2 and 2 with SF4

UE Category 7 supports 16QAM modulation

2 msec 5772.

2.89


Category 6 4 SF2 10 msec/2 msec

20000/11484

2.0/5.74

Category 7(Rel. 7)

4 SF2 10 msec/2 msec

20000/22996

2.0/11.5

Slide 47

Hybrid ARQ Operation



Hybrid ARQ Operation

N-channel parallel HARQ with stop-and-wait protocol

Number of HARQ processes N to allow uninterrupted E-DCH transmission

10 msec TTI: 4

2 msec TTI: 8

Synchronous retransmissions

Retransmission of a MAC-e PDU follows its previous HARQ (re)transmissionafter N TTI = 1 RTT

Incremental Redundanc via rate matchin

48

Max. # HARQ retransmissions specified in HARQ profile

New Tx 2 New Tx 3 New Tx 4 Re-Tx 1 New Tx 2 Re-Tx 3 New Tx 4 Re-Tx 1 Re-Tx 2New Tx 1

ACK

ACK

NACK

NACK

NACK

NACK

Slide 48

Transport Block Size Table for 10ms TTI



Transport Block Size Table for 10ms TTI

49 Slide 49

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