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10 January,2002 Seminar of Master Thesis 1

Helsinki University of TechnologyDepartment of Electrical and Communication Engineering

WCDMA Simulator with Smart Antennas

Hong Zhang

Communication laboratory

Supervisor: Professor Seppo J. Halme

Instructor: M. Sc. Adrian Boukalov



Outline

1. Background2. Different approach in WCDMA system modelling 3. Spreading in WCDMA4. RAKE Receiver and Multiuser Detection5. Smart Antenna in WCDMA 6. Simulation Results7. Conclusion



The goal of 3Gto provide a wide variety of communication

services and high speed data access.

The increasing demand of high capacity

WCDMAradio access technology for 3G

To provide high capacity

Spreading Smart antenna RAKE receiver Multiuser detection

Simulation

1. Background

technique

tool



2. Different approach in WCDMA system modelling (1)

CDMA System Modelling

Synchronous CDMA

Asynchronous CDMA

Modeling with single path

Modeling with multipath

Modeling with smart antenna

Modeling with AWGN channel

Modeling with channel fading

With linear algebra knowledge

com

plex

ity



DOA

The tapped delay line model

T

β0

T

β 1

T

β N-1

Linear time-variant system β(τ ,t)vmax τmax<<1

Quasi-stationary βt(τ)Uncorrelated scatters

GWSSUS

Sampled

βi(t)δ( τ - τi )

Tapped delay lineWs τmax<<1

βj(t) δ( τ - jT)

Narrowband model β0(t)

�−

=

1

0

N

j

�i

Ray tracing model

where βj (t) is the complex amplitude, τj is path delay and θj is Direction Of Arrival, a( θ - θj) is the steering vectorGWSSUS: Gaussian Wide Sense Stationary Uncorrelated Scatters

DOA: Direction Of Arrival

h (t, τ, θ) = βj (t)δ( τ - τj ) δ( θ - θj)�−

=

1

0

N

j

2. Different approach in WCDMA system modelling (2):Mobile radio channel

h (t, τ, θ) = βj (t)δ( τ - τj ) a( θ - θj)�−

=

1

0

N

j

Multiple antennas in the receiver



xkdkbk

spreader

PN code

source of information

encoder/interleaver

transmitterfilter D/A

IF-RFupconverter

Block diagram of the mobile transmitter for user k

xk(t)

Block diagram of the base station receiver

receiver front � end

multiuserdetector

unit

sink K

sink 1Despreader unit 1

PN code

Despreader unit K

PN code

yMF

r (t)

b�

�

2. Different approach in WCDMA system modelling (3):the fundamental structure



Discrete time model base band uplink model for asynchronous CDMA system

over a mobile radio channel

n

r

d1(i)s1(i) u1 p c1,1(i) ... c1,M(i)

d2(i)s2(i) u1 p c2,1(i) ... c2,M(i)

dK(i)sK(i) u1 p cK,1(i) ... cK,M(i)

.

.

.

.

.

.

.

.

.

� The output after matched filtering and correlating

� The received signal

r = �−

=

1

0

L

i�

=

K

k 1�

=

M

m 1

)()(� , idic kmk ��

�

�

��

�

�

−− NQiL

mk

iNQ

Oi

O

)1(

, )(�s + n=SCd+n

y =C H SH S C d + C H SH n

Where )(� , imks = ��

�

�

��

�

�

− mkMOik

mkO

,�

)(�,

τ

τs

)(idk : the ith data symbol transmitted by user k

)(� iks : the zero-padded spreading sequence for symbols generated by user k

)(� , ic mk : the channel coefficients over the mth multipath for the ith symbol generated by user k.

L : the total amount of the data symbol sent by every active userK : the total amount of active users sending data to the BTSM� : the maximum delay spread normalised to sampling intervalM : the amount of resolvable multipath components per user data sequenceC: channel matrixS: the matrix of received spreading waveformn: Additive White Gaussian Noise

2. Different approach in WCDMA system modelling (4): Discrete time base band uplink model for asynchronous CDMA



ф = λ

θπ cos2 d

� The received signal

y = HC0 ΨHSH r = HC0 Ψ

HSH S ΨC0 d + HC0 ΨHSH n

� The output after matched filtering and correlating

� The phase difference of the received signal between adjacent antenna elements The ULA with the direction of arrival

(α, φ) indicated

d Bφ

θ

waveform

z

x

y

αB-1

1

D�

r = S Ψ C 0 d +n

where Ψ is the steering matrix

2. Different approach in WCDMA system modelling (5): Discrete time base band uplink model for asynchronous CDMA with smart antenna



3. Spreading in WCDMA (1)

an an-1 an-2 an-r

c1 c2 c3 cr

an = c1 an-1 + c2 an-1 + ... + cr an-

Linear shift register

� Pseudo Random (PN) sequence: a bit stream of �1�s and �0�s occurring randomly, or almost randomly, with some

unique properties.



Spreading: to multiply the input information bits by a PN code and get processing gain, the chip level signal�s bandwidth is much wider than that of input information bits. It maintains the orthogonality among different physical channels of each user.

Scrambling: to separate the signals from the different users. It doesn�t change the signal bandwidth. Each user has a unique scrambling code in the system.

� Uplink spreading and modulation

bit rate chip rate

P(t)

Channelization codes(Walsh/OVSF)

(Cd )DPDCH

j

Channelization codes(Walsh/OVSF) (Cc)

DPCCH

Scramblingcodes

(Csc)

P(t)

cos ( ωt)

sin ( ωt)

(Gold)

chip rate

WCDMAan interference limited system

Selecting codeshigh autocorrelation low cross correlation

Suppressing interference

3. Spreading in WCDMA (2) : Spreading and scrambling at the uplink



C 1,1 = ( 1 )

C 2,2 = ( 1 , 1 )

C 2,1 = ( 1 , 1 )

C 4, 2 = ( 1 , 1 , -1 , -1 )

C 4,1 = ( 1 , 1 , 1 , 1 )

C 4, 3 = ( 1 , -1 , 1 , -1 )

C 4,4 = ( 1 , -1, -1, 1 )

SF=1 SF=2 SF=4

� Walsh-Hadamard code� Purpose: spreading � Generation: code tree

� Gold code� Purpose: scrambling � Generation: modulo-2 sum 2 m-sequences

3. Spreading in WCDMA (3) : Walsh-Hadamard code and Gold code



4. RAKE Receiver and Multiuser Detection (1): RAKE receiver

r

ck,1(i)*

Correlator

sk(i)*

Finger 1

ck,M(i)*

Correlator

sk(i)*

Finger M

y

W1

W1

�T

o() �

T

o()

� Combining methods � Selection Combining � Maximal Ratio Combining (MRC) � Equal Gain Combining (EGC)

RAKE receiver:to collect the signal energy from different multipath componentsand coherently combine the signal

Output :

SNR

Optimalfor single user system

y = CH SH r



Optimal DetectorWCDMA

Multiple access

MAI

MUDdesign and analysis the

digital demodulation in the presence of

MAI

User 1 RAKE

User 2 RAKE

User K RAKE Vite

rbi A

lgor

ithm

r(t)

∧)(1 id

∧)(2 id

∧)(idK

��

Sub OptimalDetector

LMMSE: Linear Minimum Mean Square ErrorMUD: multiuser detectionMAI: multiple access interference

High complex

4. RAKE Receiver and Multiuser Detection (2): Multiuser Detection



Decorrelating Detector

SubOptimalDetector

Decorrelating detector for 2 synchronous users

r(t)s1(t)

s2(t)

y1

y2

+-

-+

�T

0

ρ

∧)(1 id

∧)(2 id

�T

0

�T

0

(synchronous)

(asynchronous)Decd� = [RT [1] z + R [0] + R [1] z-1 ]-1 y

Decd� = R-1y

LMMSE

LMMSE: Linear Minimum Mean Square ErrorMUD: multiuser detectionMAI: multiple access interference

(synchronous)

(asynchronous)

Decd� = (R+ σ2I)-1 y

Decd� = (RT [1] z + R [0] + R [1] z -1 + σ2I )-1 y

Noise

4. RAKE Receiver and Multiuser Detection (3): Multiuser Detection

Varying channel

Adaptive MMSE algorithm-RLS algorithm with adaptive memory

J(k) = �=

−n

i

in

1λ (| ζ(k)|2 )



5. Smart Antenna in WCDMA (1)

Desired signal

Interfering signal

� switched beam antenna array

Smart Antenna consists of antenna array, combined with signal processing in space (or time) domain

Desired signal

Interfering signal

� adaptive antenna arrayType

Broad-band beam-former structure

Reference signal

Weight control

Error signal

y(t)

Tτ1 (φi,θi)r1 T

w11 w12 w1M

TτB (φi,θi)rB T

wB1 wB2 wBM

Steering Delay

-

+

�

y(t) = �=

B

n 1

wn rn (t)



ConventionalBeamforming

Statistically Optimum

Beamforming

Adaptive Beamforming

RLS algorithm with adaptive memory

wc = (1 /B ) s

MMSE w = R-1 pMax SNR Rn

-1Rs w = λmax wLCMV w = R-1c[cHR-1c]-1g

G(k) =)()1()(1

)()1(1

1

krkPkrkrkP

H −+−

−

−

λλ

ζ(k) = d(k) - w� H (k-1) r(k)

w(k)= w� (k-1) + G(k) ζ *(k) P(k) = λ-1 P(k-1) - λ-1 G(k) rH (k) P(k-1)

λ(k)= λ(k-1)+α Re[ )1(� −kHψ r(k) ζ *(k)]]−+

λλ

S(k) = λ-1[I - G(k) rH (k)] S(k-1) [I - r (k)GH(k)]+ λ-1 G(k) GH(k)- λ-1 P(k)

)(kψ = [I - G(k) rH (k)] )1(� −kHψ + S(k) r(k) ζ *(k)

MMSE: mimimize mean square errorLCMV: Linearly Constrained Minimum Variance RLS: recursive least squares

5. Smart Antenna in WCDMA (2): Beamforming schemes



6. Simulation (1)

� Simulation block diagram of transmitter in WCDMA uplink spreading scrambling

bit rate

chip rate

chip rate

Modulation(BPSK)

Pulse shaping filter

Channelh(1)(t)

dK(i)( user K)

MAI

d2(i) ( user 2) Modulation

(BPSK)


Channelh(2)(t)

Modulation(BPSK)


Channelh(K)(t)

d1(i) ( user 1)


6. Simulation (2)

� Simulation block diagram of 2- D RAKE receiver in uplink WCDMA

User K

User 1Spatial processing Temporal processing (RAKE)

Multiuser

Detection

W1,M

W1,2

n(t)

●

●

●●

●

●

●

●

W1,1●

●●

●*1(t-τM)

*1(t-τ2)

*1(t-τ1)

WK,M

WK,2●

●

●

●

●

WK,1●

●●

●*1(t-τM)

*1(t-τ2)

*K(t-τ1)

�T

o()

�T

o()

�T

o()

�T

o()

�T

o()

�T

o()

∧)(1 id

∧)(idK


c~

c~

�

� �

�

�

�



6. Simulation (3)

� Channel: ray tracing channel model The simulation area : the campus area of Dresden University of Technology.

Simulation area

BTS MS location



6. Simulation Results(4)

� Assume all the users randomly access the channel, and the PN code of each user is acquired and synchronized perfectly in the base station.

� Assume the number of fingers in RAKE receiver equal to the number of multipath components.

� The channel parameters are updated symbol by symbol, i.e. channel varies with time.

The system performance of 1-D RAKE and conventional

matched filter receiver for single user

System performance of 1- D RAKE receiver with Decorrelating Detector

and linear MMSE

DD: Decorrelating Detector LMMSESA: smart antenna for spatial processing PG: Processing GainMUD: Multiuser Detection


0 10 20 30 40 50 60 70 80

10-2

10-1

100

System performance

SNR (dB)

BER

ConventionalRakeSA RAKESA RAKE adaptive MUD(RLS)


6. Simulation Results(5)

3 antenna elements3 active users

2 antenna elements3 active users

The system performance of 1-D RAKE with different

Processing Gain

The system performance of 1-D RAKE withspreading by Walsh codes and scrambling by Gold codes

spreading and scrambling by random codes

The system performance of 2-RAKE receiver with RLS algorithm with adaptive memory for spatial processing and MUD

DD: Decorrelating Detector LMMSESA: smart antenna for spatial processing PG: Processing GainMUD: Multiuser Detection



7. Conclusion

� The simulation results have shown that spreading, RAKE receiver, multiuser detection and smart antenna are very important techniques to improve WCDMA system performance and increase system capacity.

wcdma simulator with smart antennas - · pdf filewcdma simulator with smart antennas ......

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