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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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FL=2.3GHzFU=2.7GHz
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BSRCRANDOM
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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
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
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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
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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
SP
BSRCRANDOM
IFFT
CYCLIC_PREFIX
I
Q
I
Q
RITOC
R
I
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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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
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
0.5
FL=2.3GHzFU=2.7GHz
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FL=2.3GHzFU=2.7GHz
0.5
BSRCRANDOM
IFFT
SPCYCLIC_PREFIX
SP Sx ( )fx
SP
I
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CTORIR
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
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
IFFT
SPCYCLIC_PREFIX
SP Sx ( )fx
SP
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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
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
SP
CYCLIC_PREFIX
SP Sx ( )fx
SP
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RITOCR
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CTORIR
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
