1C00-20001204-014_LGE_CDSA

Title : CDSA : A Fast and Robust PN Code Acquisition Scheme for Cellular DS/CDMA Application

Abstract : This contribution discusses the key concepts, organization and operations of Correlation-Aided Distributed Sample Acquisition (CDSA) Based DS/CDMA Cellular System

Source : B.K Yi Y.J Song B.H Kim B.G Lee LGE Inc. LGE Inc. GCT SNU bkyi@lginfocomm.com yjsong@lginfocomm.com Date : December 04, 2000

Recommendation : Discussion for 1xEV-DV

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2C00-20001204-014_LGE_CDSA

Outline

I. Introduction

Serial Search (SSA)

Parallel Search (PSA)

Rapid Acquisition by Sequential Estimation (RASE)

Distributed Sample Acquisition (DSA)

II. Correlation-Aided Distributed Sample Acquisition (CDSA) Based DS/CDMA Cellular System

III. Application of CDSA to Inter-cell Asynchronous W-CDMA Cell Search

VI. Concluding Remarks

3C00-20001204-014_LGE_CDSA

I. Introduction

Issues on PN Code Acquisition Acquisition Time Speed-up Low Complexity (Hardware and Computation) Robustness

Low-SNR (Cell-boundary, Shadowing) Fading Frequency Offset

PN Code Acquisition Techniques

4C00-20001204-014_LGE_CDSA

Correlation - based Search (SSA, PSA)

Threshold Detector

| | 2 NI

( )

Search Control Clock

dL-1dL-2d0 d1d1 d2 d3 d4 d0 d2 d3 d4 dL-2 dL-1

Transmitter SRG Receiver SRG

sk sk

bk

bk+skbk+sk+sk

Scrambling Descrambling

(continued)

(User Channel)

(Pilot Channel)

5C00-20001204-014_LGE_CDSA

Rapid Acquisition by Sequential Estimation: State Loading

(AWGN, Moderate SNR, Coherent Acquisition)

Transmitter SRG Receiver SRG

Scrambling Descrambling

dL-1dL-2d0 d1 d2 d3 d4 dL-1dL-2d0 d1 d2 d3 d4

sk sk

bk+sk

bk+sk+skbk

(continued)

(User Channel)

(Pilot Channel)

6C00-20001204-014_LGE_CDSA

(continued)

Goal of the Work Design of Noncoherent (or Differentially-coherent), Rapid, and Ro

bust Acquisition / Cell-search Schemes with Minimal Complexity by employing Generalized State Loading Techniques

7C00-20001204-014_LGE_CDSA

Distributed Sample Acquisition (DSA)

User Data

State Correction

ComparisonState

SamplingState

Sampling

dL-1d0 d1 d2 d3 dL-1d0 d1 d2 d3

sm sm

zn zn

Main SRG (long)

Main SRG (long)

Scrambling DescramblingUser Data

MainSequence

Data Signal(User Channel)

MainSequence

dS-1d0 d1

Igniter SRG (short)

State Signal(Pilot Channel)

Transmitter Receiver

cm

IgniterSequence

(continued)

8C00-20001204-014_LGE_CDSA

II. Correlation-Aided DSA Based DS/CDMA Cellular System

BS (Tx) and MS (Rx) have two kinds of SRG's Igniter SRG with short period NI (=2S) Main SRG with long period NM (=2L): targeted scrambling sequence

BS samples a main SRG state sample in every NI chip interval, spread it with a short igniter code of length NI, and then transmit it as a state signal (or the common pilot signal) of the BS.

Several samples may be transmitted concurrently to speed up the synchronization in a moderate SIR environment

After igniter code acquisition applying a conventional search method, MS’s detect the main SRG state samples sequentially.

State sample comparison-correction based main SRG Synchronization L corrections and V verifications by a set of pertinent sampling-comparison-correc

tion circuits synchronize the MS main SRG to the BS main SRG. Asymptotically, 2L / (2S +L+V) times faster acquisition than Serial-search with

minimal complexity increase (IS95/cdma2000: L=15) (L=15, S=7): 256 times; (L=15, S=8): 128 times

State Symbol Correlation Process for Robust Acquisition in Worst-case Channel Environment

9C00-20001204-014_LGE_CDSA

CDSA-based DS/CDMA System (BS)

Data signal(1)

Sampling Timing

Data signal(2)

DSA - Spreader Sample - Spreader

Data signal(J)

Q-main SRG

I-main SRG Time-advanced Sampling

NITc

{sm}

{sm}

{sm}

ai [1]

{wm }[1]

Igniter SRG-2

Igniter SRG-1

{cm}

ai [2]

{wm }[2]

ai[J]

{wm }[J]

Spreading

Spreading State

signal (CPICH)

PSK SymbolMapping

{zi} xi fi

v0

10C00-20001204-014_LGE_CDSA

Common Pilot Channel Modulation Example for CDSA As I-channel PN state and Q-channel PN state have a one-to-one

correspondence in cdma2000, the BS has only to broadcast I-main SRG state samples to the MS’s.

Each cell employ one of 16 Complex Igniter Codes (Group Codes)

16 igniter codes (group codes) of length 256

512 modulated common pilot codes of length 32768

(DBPSK encoding of state samples: fj)

208 usec

co c1 c255

fo Ci f1 Ci f2 Ci f3 Ci f4 Ci f127 Ci fj Ci

26.67 ms 1 Sync Frame

Ci , i=0,1,…15

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Global Timing Relations and Cell Group Plan

Neighboring cells shall employ different igniter codes Trade-off relation between the number of igniter sequences in a cellul

ar system and the amount of co-channel (co-igniter) cell interference: complexity and performance trade-off

Multiple main sequences and igniter sequences can be obtained by phase shifts in the inter-cell synchronous systems such as IS95 and cdma2000.

Ex: 512 main and 7 [or 16] igniter sequences can be derived from an extended m-sequence of length 32768 and 2 [or 4] Gold sequences of length 256 through the cyclic shifts by 64*n chips

12C00-20001204-014_LGE_CDSA

26

NI = 2 8

26

NM = 2 15

Main Sequences

Igniter Sequences

0: {sm[0]}

1: {sm[1]}

2: {sm[2]}

3: {sm[3]}

510: {sm[510]}

511: {sm[511]}

0: {cm[0]}

1: {cm+64[0]}

2: {cm+128[0]}

3: {cm+192[0]}

4: {cm[1]}

5: {cm+64[1]}

6: {cm+128[1]}

Timing relations among igniter/main sequences (Ex: 7 groups and 512 cells)

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Cell group (igniter code) plan (Ex: 7 groups and 48 cells)

6,6

1,1

0,0

2,2

0,42

5,19

3,3

5,12

6,13

0,35

0,7

1,8

1,36

6,20

6,12

0,14

1,15

5,5

4,18

3,17

2,16

4,4

5,26

6,27

0,21

1,22

2,23

3,24

5,33

6,34

4,11

3,10

1,43

4,32

0,28

1,29

4,25

2,9

2,30

3,31

2,37

3,38

4,39

5,40

6,41

2,44

3,45

4,46

5,47

14C00-20001204-014_LGE_CDSA

State signal

Despreading

Data signal(u)

Correction Timing

Sampling Timing

Sample - Despreader

Sampling

Correction

Despreading

DSA - Despreader

NITc

iNITc

(i-1)NITc

dtNITc

1

( )*

PSK Symbol Detection

gi

{sm} {wm }[u]

+ Noise

+ NoiseiNITc

(i-1)NITc

dtNITc

1

Q-main SRG

I-main SRG Igniter SRG-2

Igniter SRG-1

Comparison

{cm}

ai [u]

yi

Store State Symbols for B Symbol Periods

State Symbol Correlation Based Frame Boundary Search

{zi}

h0

c0{zi}

CDSA-based DS/CDMA System (MS)

15C00-20001204-014_LGE_CDSA

System Timing Diagram

Igniter seq.

Igniter seq.

Tx

Main seq.

DBPSK symbol

State signal

Rx

Detected sample

Main seq.

Comparison

Sampling

resultCorrection

sampling

NI

NI -advanced

Dc (=1)

16C00-20001204-014_LGE_CDSA

• IS-95 I-Phase PN (x) = 1 + x5 + x7+ x8 + x9 + x13 + x15

T= A(x)t , h= [1 0 0 0]t , NI= 128

(a) DSA-Spreader

(b) DSA-Despreader

Sampling pulse

ComparisonCorrection pulse{zi}

{zi}

{sm}

c0

{bm+ sm} + sm+ sm}{bm

{zi}

Sampling pulsev0

{sm}

{bm} {bm+ sm}

Design Example

17C00-20001204-014_LGE_CDSA

III. Mean Acquisition Time Performance

512 Cells / System 100 Hz Classical Rayleigh Fading Igniter Seq. Period (Dwell Time), NI = 256

Main Seq. Period NM = 32768

False Acquisition Penalty Time = 1280NI (10 Frames) False Alarm Prob. = 0.05 (Acq. Detection), 0.001 (Verification) Verification Time = 10NI

Igniter Seq. Reuse Factor = 16 (4 Seq.’s, 4 Phase Offsets) Symbol Sequence Length for State Symbol Correlation Process

B = 128 Symbols Conventional PSA : 4 Correlators Operate in Parallel : Comparable co

mplexity

18C00-20001204-014_LGE_CDSA

(sec)

Ove

rall

Mea

n A

cqui

siti

on T

ime

SNR( c)

-25 -20 -15 -10 -510

-1

100

101

102

DSA

CDSA

PSA

(continued)

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IV.Concluding Remarks

CDSA scheme for rapid and robust acquisition of long-period PN sequences: Igniter Sequence + Comparison-correction Process : DSA

+ State Symbol Correlation Process : CDSA Revisit the goal of the work !

Acquisition / Cell Search Time Reduction Minimal Complexity Robustness: Shadowing, fading, frequency offset, etc.