WiMax MIMO Circuit and System Design

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WiMax MIMO Circuit and System Design

Presenter: Eldon Staggs

Authors:Jim DeLap, John Borelli, Tony Donisi, Eldon StaggsAnsoft Corporation

FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

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FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

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FL=2.3GHzFU=2.7GHz

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SP SP

SP

SP SPSP

Pilot_Null_Insertion2

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti EncoderPreamble

Preamble_Insertion1

T/R SwitchPowerAmp

T/R Switch

LNA

Baseband Transmitter

Baseband Receiver

RF Transmitter

RF Receiver

Channel

h11h21h12h22

Preamble_Removal1

r1

r2

[~s2 ~s1]

Alamouti Decoder

h11h21h12h22

SP

OFDM_Tx

OFDM_Rx

SP

SP

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

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Fcutoff=10MHzAGC_Gain=100

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Mobile WiMax System• WiMax System Modeling

– Behavioral, Circuit and Physical

Agenda

Introduction to Mobile WiMax

System Architecture

MIMO Antennas

Receiver Circuit

Integration

Conclusion

WiMAX - Mid Range IEEE Communication Standard

< 1 m Body Area Networks

< 10 m Personal Area Networks

< 100 m Local Area Networks

< 10 Km Metro Area Networks

> 10 Km Wide Area Networks

Range Standard

Our focus today is Mobile WiMAX, a standard designed to enable high data rate applications such as the wireless Internet.Our focus today is Mobile WiMAX, a standard designed to enable high data rate applications such as the wireless Internet.

802.16

•Last mile broadband wireless access

• 40Mbps capacity up to 10km

•OFDM with QPSK/QAM16/QAM64

• Fixed, Portable (walking) and MobileMobile (in car) options

802.16e• 63Mbps peak capacity up to 3km at 2.3,2.5 or 3.5GHz

• No line-of-sight required

today

WiMAX Architecture Based on 2 Core Features: MIMO & OFDM

1. MIMO (Multiple Inputs Multiple Output = Many Antennas)– Advantage: More antennas means more data or reliability. For example,

if 2 TX and RX antennas are present, then data rate should double. Data rates will scale linearly.

– Challenge: How to design system so that interactions between multiple TX and RX are minimized.

Solutions, thus far, have emphasized 4 diversity schemes:

#1: #2: #3: #4: Space Time Coding

⎥⎦

⎤⎢⎣

⎡−

= *1

*2

21

SSSS

C

…Our examples today will illustrate how MIMO and OFDM can be simulated.Our examples today will illustrate how MIMO and OFDM can be simulated.

WiMAX Architecture Based on 2 Core Features: MIMO & OFDM

Our examples today will illustrate how MIMO and OFDM can be simulated.Our examples today will illustrate how MIMO and OFDM can be simulated.

2. OFDM (Orthogonal Frequency Division Multiplexing)

– Advantages:→ Relative immunity to multi-path effects→ Multiplexing schemes, using IFFT & FFT, are easily implemented→ Low sensitivity to time synchronization errors→ Tuned sub-channel receiver filters are not required (unlike

conventional FDM)

– Challenges:→ Sensitive to Doppler shift→ Sensitive to frequency synchronization→ High peak-to-average-power ratio (PAPR), requiring more

expensive transmitter circuitry, and possibly lowering power efficiency

Mobile WiMax Details• Flexibility

– All aspects can change dynamically to suit the channel

• WiMax MIMO 2x2 Configuration– Beamforming– Spatial Multiplexing

• Complicated algorithms for data rate increase• Data rate scales with min(Ntx,Nrx) antennas

– Space Time Coding• Diversity gain with easy implementation

• OFDM Implementation– Sub-carrier and Symbol times fixed– BW usage dictated by IFFT length– Downlink Data Rate

System Architecture

FL=2.3GHzFU=2.7GHz

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SP

SP SPSP

Pilot_Null_Insertion2

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti EncoderPreamble

Preamble_Insertion1

T/R SwitchPowerAmp

T/R Switch

LNA

Baseband Transmitter

Baseband Receiver

RF Transmitter

RF Receiver

Channel

h11h21h12h22

Preamble_Removal1

r1

r2

[~s2 ~s1]

Alamouti Decoder

h11h21h12h22

SP

OFDM_Tx

OFDM_Rx

SP

SP

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

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BehavioralBehavioral

Baseband Modeling• OFDM Modeling

– Guard Band– Cyclic Prefix

• Delay Spread & Multipath Immunity

• QAM Modulation– 4/16/64 Supported BSRC

RANDOM

CMUX

CMUX

CCONSTIFFT

SP

CCONST

CMUX

CYCLIC_PREFIX

BSRCRANDOM

SP

Sx

( ) f

x

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BSRCRANDOM

IFFT

CYCLIC_PREFIX

I

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RITOC

R

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CTORI

R

I

h11

h22

h21

h12

Tx Rx

U2Channel3

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti Encoder

IFFT

CYCLIC_PREFIX

SP

Null_Remover2

CYCLIC_REMOVE

CYCLIC_REMOVE

FFT

FFT

Pilot_Null_Insertion1Preamble

Preamble_Insertion2

h11h21h12h22

Preamble_Removal2

r1

r2

[~s2 ~s1]

Alamouti Decoder

h11h21h12h22

Baseband Modeling• Channel Detection

– Excite Transmit Antennas separately• Initial frequency estimation

– Pilots• Dynamic estimation

BSRCRANDOM

I

Q

RITOC

R

I

SP

SP

SP

SP

h11

h22

h21

h12

Tx Rx

U2Channel

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti Encoderr1

r2

[~s2 ~s1]

Alamouti DecoderI

Q

CTORI

R

I

SP

SP

BERP

ber_stc

SP

SP

Baseband Modeling

• Space Time Coding– Orthogonal Alamouti Codes

• SISO vs MIMO– Diversity gain

⎥⎦

⎤⎢⎣

⎡−

= *1

*2

21

SSSS

C

)]1[]0[(~

)]1[]0[(~

*1

1

*22

*2

1

*11

jjj

Mr

j

j

jjj

Mr

j

j

rhrhS

rhrhS

⋅+⋅=

⋅+⋅=

=

=

MIMO Antenna Design

FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

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FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

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FFT

FFT

SP SP

SP

SP SPSP

Pilot_Null_Insertion2

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti EncoderPreamble

Preamble_Insertion1

T/R SwitchPowerAmp

T/R Switch

LNA

Baseband Transmitter

Baseband Receiver

RF Transmitter

RF Receiver

Channel

h11h21h12h22

Preamble_Removal1

r1

r2

[~s2 ~s1]

Alamouti Decoder

h11h21h12h22

SP

OFDM_Tx

OFDM_Rx

SP

SP

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

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PhysicalPhysical

WiMax Physical Channel• Simplified Channel Model

– Path Loss with Friis Transmission equation – Non-Ideal effects often ignored

• Element coupling, Mismatch, Orientation– Single value for Antenna gains

• More Accurate Channel Model– Full-wave 3D EM modeling with HFSS– System Non-linearities

• Multi-path, Fading, etc.

2

4Pr

⎟⎠⎞

⎜⎝⎛=

RGtGr

Pt πλ

Rrtrtrtrrtt eaa

RGG

Ptα

πλφθφθ −

⋅Γ−Γ−⎟⎠⎞

⎜⎝⎛=

2*222

)1)(1(4

),(),(Pr

WiMax Physical Channel• Antenna Configurations

– SISO and full 2x2 MIMO– Designs centered at 2.5GHz

• Mobile Station– Laptop with WiMax Modem PC Card – Simple Radiating Mononpoles

• Base Station– Reflector backed Dipoles

Mobile Station Antenna• Tuned Monopole • Monopole Response

– Far Field– Return Loss

Base Station Antenna• Reflector Backed Dipole

– Optimized for Directivity• Dipole Response

– Far Field– Return Loss

Link Simulation

• Physical Channel– Antennas modeled– How to simulate link between?

• Utilize Ansoft HFSS Datalink– Fields from one drive another– Large separation without modeling air

HFSS Datalink

• Source Fields of Radiation Boundary– Imposed on target model with loss and phase

Source ModelSource Model Target ModelTarget Model

MIMO Datalink

Laptop Model with Dual Monopoles

BS Model with Dual Dipoles and reflector

Fields from Source model radiation BCMapped to target model using a Far FieldIncident Wave

MIMO Physical ChannelDatalink

MIMO Physical ChannelCircuit Model

• HFSS-HFSS Datalink maps fields from a source volume to the target volume

• Q: How does this translate to a working circuit model ?

• A: Utilize the [Z] matrix in Nexxim1. Excite each antenna in system with a 1 A current source2. Using Datalink, measure O.C. voltage at all the other antennas3. Construct [Z] matrix from Voltages

MIMO Physical ChannelCircuit Model

• Voltage values extracted as real/imaginary pairs

• Assembled into [Z] matrixjkIj

iij

kIVZ

≠=

=,0

WiMax Circuit Design

FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

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FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

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FL=2.3GHzFU=2.7GHz

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FL=2.3GHzFU=2.7GHz

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SP

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CYCLIC_PREFIX

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Null_Remover1

CYCLIC_REMOVE

CYCLIC_REMOVE

FFT

FFT

SP SP

SP

SP SPSP

Pilot_Null_Insertion2

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti EncoderPreamble

Preamble_Insertion1

T/R SwitchPowerAmp

T/R Switch

LNA

Baseband Transmitter

Baseband Receiver

RF Transmitter

RF Receiver

Channel

h11h21h12h22

Preamble_Removal1

r1

r2

[~s2 ~s1]

Alamouti Decoder

h11h21h12h22

SP

OFDM_Tx

OFDM_Rx

SP

SP

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

Sx ( )fx

CircuitCircuit

Antenna/Circuit Test Bench

• 2x2 MIMO Channel• Dual Receiver

– 2.5GHz to Baseband

WiMax Single RX Block Diagram

• Receiver per Antenna– Variable Gain LNA– Active Balun– IQ Mixer– Baseband Filter– AGC

• UMC 0.13um CMOS

WiMax Receiver• Variable-Gain LNA

– 2-stage, inductively-loaded cascode topology– output follower stage gain control.

12mA 12mA

2mA

RFin

RFou

GC

AVD

D

AGN

D

AGND1

PD

Ibias

AGND1

IbiasPDAVDD

AGND1

U31Nexxim8

l=25uw=25u

mimcaps_rf

M=1

c_tot_m=0.669p

l_cr

20k_

rfdo=1

50u

w=5

.7u

s=2.

52u

nt=7

.5

p_ls

=3.8

2n

l=35uw=35u

mimcaps_rf

M=1

c_tot_m=1.286p

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l_cr20k_rf

do=150uw=2.5us=2.5u

nt=7.5

p_ls=7.42n

n_bpw_12_rf

nf=16

lf=0.12uwf=3u

M=4wt=48u

n_bpw_12_rf

nf=16

lf=0.12uwf=3u

M=4wt=48u

l_cr20k_rf

do=75uw

=6.3us=1.79unt=3

p_ls=0.43nl_cr20k_rf

do=149uw

=5.2us=1.8unt=5

p_ls=3.42n

l=26.6uw=26.6u

mimcaps_rf

M=1

c_tot_m=0.754p

l=100uw=100u

mimcaps_rf

M=1

c_tot_m=10.174p

n_bpw_12_rf

nf=16

lf=0.12uwf=3u

M=4wt=48u

n_bpw_12_rf

nf=16

lf=0.12uwf=3u

M=4wt=48u

l_cr20k_rf

do=75uw

=5.6us=2.5unt=2.5 p_ls=0.38n

l_cr20k_rf

do=150uw=2.7us=2.5u

nt=7.5

p_ls=7.13n

l_cr20k_rf

do=149uw

=5.2us=1.8unt=7

p_ls=4.57n

l=20uw

=2um

=1rnhr_rfr_zbt_m

=9.96k

l=26.6uw=26.6u

mimcaps_rf

M=1

c_tot_m=0.754p

n_bpw_12_rf

nf=16

lf=0.12uwf=1.8u

M=1wt=28.8u

n_bpw_12_rf

nf=16

lf=0.12uwf=1.8u

M=1wt=28.8u

n_bpw_12_rf

nf=16

lf=0.12uwf=1.8u

M=1wt=28.8u

l=20uw

=2um

=1rnhr_rfr_zbt_m

=9.96k

l=99.77uw=99.77u

mimcaps_rf

M=1

c_tot_m=10.128p

varmis_12_rf

w=10unf=8l=2u

m=1

cox_m=1710.5f

AVDDM

IFp

IFn

RFp

RFn

PD

Ibias

n_bpw_12_rf

nf=16

lf=0.12uwf=5u

M=1wt=80u

n_bpw_12_rf

nf=16

lf=0.12uwf=5u

M=1wt=80u

n_bpw_12_rf

nf=16

lf=0.12uwf=5u

M=1wt=80u

n_bpw_12_rf

nf=16

lf=0.12uwf=5u

M=1wt=80u

l=20uw

=2um

=8.5 rnhr_rfr_zbt_m

=1.172k

l=20uw

=2um

=8.5 rnhr_rfr_zbt_m

=1.172k

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

n_bpw_12_rf

nf=16

lf=0.12uwf=5u

M=4wt=80u

n_bpw_12_rf

nf=16

lf=0.12uwf=5u

M=4wt=80u

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l=20uw

=2um

=1

rnhr_rfr_zbt_m

=9.96k

l=35

.7u

w=5

0u

mim

caps

_rf

M=1

c_to

t_m

=1.8

51p

varmis_12_rf

w=10u

nf=8l=2u

m=1 cox_m

=1710.5f

varmis_12_rf

w=10u

nf=8l=2u

m=1 cox_m

=1710.5f

l=100uw=100u

mimcaps_rf

M=1

c_tot_m=10.174pl=100u

w=100u

mimcaps_rf

M=1

c_tot_m=10.174p

IbiasPDAVDD

AGND1

U98Nexxim15

WiMax Receiver• I-Q Mixer

– Dual, resistively-loaded Gilbert Cell cores– Folded RF feeds

0

LPF_Vtun

AVDD

BBIp

BBIn

IOutp

IOutn

VDDVtunOutp

Outn

Inp

InnGND

U155LPF10

VDD

Vctrl

p

Vctrl

n

Vin

Vinn Voutn

Vout

GN

Ddu

mp

GND

I350u

U156

Stg20

V1560 V1563 V1564 V1565 V1566 V1567

VDD

GND

Iinp

VoutnIinn

Voutp

I300uI500u_tia

PD

U163

OpStg14Inp

Inn

VDD

GND

Outp

Outn

I250u

PD

U154HPF18

VDD

Vctrl

pVc

trln

Vin

Vinn Ioutn

GN

Ddu

mp

GND

Ioutp

CM

ref

I350uI50u_cm

U161

Stg21

Bias

Inp

Inn

VDD

Outn

Outp

U158

HPF19

I50u_cm1I350u_stg2i

WiMax Receiver• Baseband Filter & AGC

– Buffered active (gm-C)/passive bandpass– Integrated Automatic Gain Control.

VDD

Vct

rlpVc

trln

Vin Vinn

Ioutn

GNDdump GNDdump

GND

Ioutp

CMref

I350u

I50u_cm

n_12_rf

nf=16

lf=0.2uwf=7.2u

M=2wt=115.2u

n_12_rf

nf=16

lf=0.2uwf=7.2u

M=2wt=115.2u

p_12_rf

nf=12

lf=0.15uwf=9.6u

M=1wt=115.2u

p_12_rf

nf=12

lf=0.15uwf=9.6u

M=1wt=115.2u

p_12_rf

nf=12

lf=0.15uwf=9.6u

M=7wt=115.2u

p_12_rf

nf=12

lf=0.15uwf=9.6u

M=7wt=115.2u

p_12_rf

nf=12

lf=0.3uwf=9.6u

M=14wt=115.2u

p_12_rf

nf=12

lf=0.3uwf=9.6u

M=14wt=115.2u

p_12_rf

nf=12

lf=0.2uwf=9.6u

M=10wt=115.2u

p_12_rf

nf=12

lf=0.2uwf=9.6u

M=10wt=115.2u

n_12_rf

nf=10

lf=0.2uwf=7.2u

M=2wt=72u

n_12_rf

nf=10

lf=0.2uwf=7.2u

M=2wt=72u

n_12_rf

nf=10

lf=0.2uwf=7.2u

M=1wt=72u

n_12_rf

nf=8

lf=0.2uwf=7.2u

M=2wt=57.6u

n_12_rf

nf=16

lf=0.3uwf=7.2u

M=4wt=115.2u

n_12_rf

nf=16

lf=0.3uwf=7.2u

M=4wt=115.2u

l=5.3uw=2um=20

rnhr_rfr_zbt_m=0.124k

Vsense

Vref

GND

Vout

VDD

I50u_s

U386

CMamp11

l=10uw=1um=1 rnhr_rf

r_zbt_m=10.089k

l=10uw=1um=1

rnhr_rfr_zbt_m=10.089k

l=10uw=1um=1

rnhr_rfr_zbt_m=10.089k

l=10uw=1um=1

rnhr_rfr_zbt_m=10.089k

Bias

BiasVfb Vfb

net_cmnet_cm

WiMax RX Linearity Metrics

• Compression– Single RF & LO to baseband

• Third Order Intercept– Two RF & Single LO– Swept & Spectral Response

Integration

FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

0.5

FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

0.5

FL=2.3GHzFU=2.7GHz

0.5

FL=2.3GHzFU=2.7GHz

0.5

BSRCRANDOM

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SP Sx ( )fx

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CYCLIC_PREFIX

SP

Null_Remover1

CYCLIC_REMOVE

CYCLIC_REMOVE

FFT

FFT

SP SP

SP

SP SPSP

Pilot_Null_Insertion2

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti EncoderPreamble

Preamble_Insertion1

T/R SwitchPowerAmp

T/R Switch

LNA

Baseband Transmitter

Baseband Receiver

RF Transmitter

RF Receiver

Channel

h11h21h12h22

Preamble_Removal1

r1

r2

[~s2 ~s1]

Alamouti Decoder

h11h21h12h22

SP

OFDM_Tx

OFDM_Rx

SP

SP

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

Sx ( )fx

CircuitCircuit

PhysicalPhysicalBehavioralBehavioral

Complete WiMax System• Baseband Tx/Rx

– QAM, STC Encoder/Decoder, OFDM

• RF Tx/Rx– Quadrature Mixing, Amplification, Filtering

• Channel– SISO & MIMO, Link, Noise

FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

0.5

FL=2.3GHzFU=2.7GHz

FL=2.3GHzFU=2.7GHz

0.5

FL=2.3GHzFU=2.7GHz

0.5

FL=2.3GHzFU=2.7GHz

0.5

BSRCRANDOM

IFFT

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CYCLIC_PREFIX

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SP

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RITOCR

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I

IFFT

CYCLIC_PREFIX

SP

Null_Remover1

CYCLIC_REMOVE

CYCLIC_REMOVE

FFT

FFT

SP SP

SP

SP SPSP

Pilot_Null_Insertion2

[s2 s1]

[-s2* s1]

[s1* s2]

Alamouti EncoderPreamble

Preamble_Insertion1

T/R SwitchPowerAmp

T/R Switch

LNA

Baseband Transmitter

Baseband Receiver

RF Transmitter

RF Receiver

Channel

h11h21h12h22

Preamble_Removal1

r1

r2

[~s2 ~s1]

Alamouti Decoder

h11h21h12h22

SP

OFDM_Tx

OFDM_Rx

SP

SP

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHz

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

45-45

Fcarrier=2.5GHz

Fcutoff=10MHzAGC_Gain=100

Sx ( )fx

BehavioralBehavioral

Circuit + BehavioralCircuit + Behavioral

PhysicalPhysical

Complete WiMax System• Behavioral and Physical

– SISO vs MIMO (Diversity gain)– EVM Distortion

• Circuit and Physical– Nonlinear interactions– Loading effects

• Behavioral, Physical and Circuit– BER distortion– Multipath degradation

Conclusion• WiMax System Modeling

– HFSS dynamic link for Channel– Nexxim for NL circuit impact– Unique Integration of Physical, Circuit & Behavioral

• HFSS, Nexxim & Designer together help you pave the way for:

First Pass System SuccessFirst Pass System Success

References• [1] IEEE Std 802.16-14 Air Interface for Fixed Broadband Wireless Access

Systems• [2] IEEE Std 802.16e-2005 Air Interface for Fixed Broadband Wireless

Access Systems• [3] Mobile WiMax – Part I: A Technical Overview and Performance

Evaluation– WiMax Forum

• [4]MIMO System Technology for Wireless Communications– By George Tsoulos

• [5] Digital Communications by Bernard Sklar• [6] OFDM for Wireless Multimedia Communications

– by Richard van Nee and Ramjee Prasad, Artech House Publishers• [7] The suitability of OFDM as a modulation technique for wireless

telecommunications, with a CDMA comparison– by Eric Lawrey, October 1997

• [8] Modeling an Advance Communication System based on OFDM– By Eldon Staggs, September 2000

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