Performance analysis of clustered CDMA-OQAM- OFDM Networksnts.uni-duisburg-essen.de/downloads/nt-prakt12... · Filter Bank Multicarrier (FBMC): Enhancement in the physical layer of

Performance analysis of

clustered CDMA-OQAM-

OFDM Networks

Mohamed Rawash

Committee Members: Prof. Dr.-Ing. A. Czylwik

Prof. Dr.-Ing. Jan C. Balzer

Master Thesis Defense

Outline

Motivation and Objective

Technical background and Methodology

Concept and System Description

Simulation Results & Performance Analysis

Conclusion & Future Work

2

Mohamed Rawash Performance analysis of clustered SS 2018CDMA-OQAM-OFDM Networks


Motivation:

Challenges for wireless communication field

• Increasing transmission data rate

• Robust transmission against fading channel conditions

• Increasing bandwidth utilization

3



Objective:

Achieving reliable tranmission while keeping the data rate to an acceptable level

by:

• Building models for clustered CDMA-OFDM and CDMA-FBMC networks

• Applying different tranmission schemes and radio channel conditions

• Anaylzing the performance of the two networks and comparing them

4


Outline






5


Technical background

Legacy CP-OFDM:

Dominant modulation technology for broadband wireless transmission

• Robust transmission in frequency selective transmission media

• Simple implementation using IFFT/FFT

• Wideband transmission over radia channels

Basic principle

• Dividing the wide spectrum into large number of orthogonal narrowband subcarriers

• Using rectangular pulse shaping filters

• Attaching Cyclic-Prefix to avoid Inter-Block-Interference (IBI)

6



CP-OFDM realization:

Pulse shaping filter

• Rectangular pulse shaping filter

• Sharp edges of the impulse response in time domain

• Sinc function of the channel transfer function in frequency domain

• Long trails of side lobes

7

g(t)

t



CP-OFDM realization:

Cyclic Prefix

• Repeatition of the last symbols of each block

• Attaching the repeated packet at the begining of each OFDM block

• To overcome the multipath propagation phenomenon of radio channels

• Realization & impact of CP

Choice of time interval for guard band greater than the maximum channel delay

𝑇𝑔 > 𝜏𝑚𝑎𝑥

Regular estimation of channel conditions

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Decrease of the useful data rate



CP-OFDM modeling :

Composite transmit Signal

x t =

𝑛=1

𝑁

𝑘=−∞

∞

𝑆𝑛 𝑘 . 𝑔𝑃 𝑡 − 𝑘𝑇𝑆 . 𝑒𝑗2𝜋𝑓𝑛𝑡

Pulse shaping filter

𝑔 𝑡 = rect (𝑡 −

𝑁𝑇2

𝑁𝑇)

9



Filter Bank Multicarrier (FBMC):

Enhancement in the physical layer of broadband multicarrier modulation

• Filter bank of non-rectangular shape in time domain and fulfilling Nyquest criterion

• Orthognality only between the neighboring sub-channels

• Symbols Overlap in time domain

Basic principle

• Dividing the transmission channel associated with the available bandwidth into

subchannels

• Selecting a prtotype filter and designing a filter bank

• No cyclic-prefix needed

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FBMC realization:

Prototype Filter

• The first filter in the flter bank is called prototype filter

• All other filters are derived from the prototype filter by frequency shifts

• For better performance of the filter impulse response and to reduce the out of band ripples,

more filter coefficients are to be realized

• The impulse response in time domain exceeds the multicarrier sysmbol duration by a factor

of K (overlapping factor)

• The filter design satisfy the Nyquest criterion

Filter impulse response corsses the zero axis at multiple integers of the symbol period

Frequency coefficients are symmetrical around the cut-off frequency

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FBMC realization:

Prototype Filter

𝐻 𝑓 = ා

𝑘=−(𝐾−1)

𝐾−1

𝐻𝑘

sin(𝜋 𝑓 −𝑘𝑀𝐾

𝑀𝐾)

𝑀𝐾 sin(𝜋 𝑓 −𝑘𝑀𝐾

)

prototype filter frequency response for

different overlapping factors (PHYDYAS filter)

12

K H0 H1 H2 H3 𝜎2

2 1 2 / 2 - - -35

3 1 0.911438 0.411438 - -44

4 1 0.971960 2 / 2 0.235147 -65



FBMC realization:

Prototype Filter

• From the prototype filter frequency response we notice the following

Almost suppression of the out-of-band ripples compared to the corresponding one of

the FFT filter

Sub-channel interference is limited to the neighboring subchannels

No need for the Cyclic prefix

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Enhancement in bandwidth utilization & limited ISI



FBMC realization:

Offset-QAM modulation

• By filter bank design, the subchannels with either even indicies or

odd ones do not overlap

• This property affects the choice of the modulation scheme if high

data rate is needed

• OQAM overcomes the problem of frequency domain overlapping of

the neighboring sub-channels

• Transmitting the real parts of the subchannels with even indicies

while transmitting the imaginary part of the odd indices and

alternatively changing between real and imaginary parts.

• Real and imaginary parts sent with time offset of half the multicarrier

symbol duration

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Spreading Schemes:

Allocation of spread data to radio resources

Frequency Spreading

• Allocate spread data to parallel subcarriers at the

same time frame

Time Spreading

• Allocate spread data to different time frames/slots

over the same subcarrier

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Outline






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Concept & System Description

CDMA-OFDM:

Concept & principles

• Multicarrier spread spectrum system

• Wide spectrum transmission, while using lare number of narrowband subcarriers

• Exploits the success of the spread spectrum technique in transmission robustness against

radio channels‘ impairments

• Avoids the frequency selectivity of the fading channels using the multicarrier CP-OFDM

modulation

• Suitable for multiuser applications where different users share the radio resources

simultaneously

• user’s data separation achieved via different user-specific orthogonal spread codes

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CDMA-OFDM:

Block Diagram

• Transmitter

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Spread code

1

Spread code

2

Spread code

Nu/K

∑ S/P

QAM

Mod.

IFFT

+

CPSpread code

1

Spread code

2

Spread code

Nu/K

∑ S/P

di

dNu

s1

s2

sNu

SK-1

S0ML/K

ML/K

Base Station



CDMA-OFDM:

Block Diagram

• Receiver

19

ML

D

Channel S/P FFT

Mobile Station

ML/K

QA

M D

emo

d.

Rk



Previous Work:

• S. Kaiser, "OFDM-CDMA versus DS-CDMA Performance Evaluation for Fading Channels," IEEE, 1995.

• Clustered CDMA-OFDM outperforms DS-CDMA

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CDMA-FBMC:

Concept & principles

• Multicarrier spread spectrum system

• Wide spectrum transmission, while dividing the assocciated channel into sub-channels

• Exploits the success of the spread spectrum technique in transmission robustness against

radio channels‘ impairments

• Avoids the frequency selectivity of the fading channels using the multicarrier FBMC

modulation without a need for cyclic prefix

• Suitable for multiuser applications where different users share the radio resources

simultaneously

• user’s data separation achieved via different user-specific orthogonal spread codes

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CDMA-FBMC:

Block Diagram

• Transmitter

22

Spread code

1

Spread code

2

Spread code

Nu/K

∑ S/P

OQAM

Mod.IFFT

Spread code

1

Spread code

2

Spread code

Nu/K

∑ S/P

di

dNu

s1

s2

sNu

SK-1

S0ML/K

ML/K

Base Station


Filter

Bank


CDMA-FBMC:

Block Diagram

• Receiver

23

3-t

ap

Equal

izer

Channel S/P

Mobile Station

ML/K

OQ

AM

Dem

od

FFT


Outline






24


Simulation results & performance analysis

System Parameters:

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Parameter CDMA-OFDM CDMA-FBMC

No. subcarriers 64

Time frames 64

Modulation scheme QAM OQAM

Modulation order 4

CP length 1/4 -

Filter type - PHYDYAS, K= 4

No. of users 16

Cluster size 1,2,4,8 &16

Sampling rate 10 MHz

Channel Bandwidth 10 MHz

Spreading types Frequency spreading and time spreading

Spreading code Walsh-Hadamard



Performance of an unclustered network & AWGN :

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Performance of an unclustered network & ETU300 :

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Performance of a 4-cluster network & AWGN :

28



Performance of a 4-cluster network & ETU300 :

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Performance of single cluster network & AWGN:

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Performance of single cluster network & ETU300:

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Comparative figures of frequency clustering for different cluster sizes & AWGN

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Comparative figures of frequency clustering for different cluster sizes & ETU300

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Comparative figures of time clustering for different cluster sizes & AWGN

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Comparative figures of time clustering for different cluster sizes & ETU300

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Outline






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Summary & conclusive remarks:

Two different multicarrier modulation networks based on CDMA spread spectrum

technique were developed and simulated using the scientific development platform

MATLAB, namely CDMA-OFDM and CDMA-FBMC

CDMA-FBMC usually outperforms CDMA-OFDM in terms of BER

CDMA-FBMC always outperforms CDMA-OFDM in terms of achievable throughput

CDMA-FBMC transmission system is an interesting scheme and promising candidate for

multiuser communication especially over fading channels and low SNR environments

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Future Directions:

Applying interleaving in time and frequency before sending the data over the channel that

will make the transmission robust against burst errors

Considering combined clustering scheme in both time domain and frequency domain

simultaneously

Applying other detection techniques at the receiver (MMSE, ZF, MRC)

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Thank You for your attention!

Questions?

39

Key References

I. Blel and R. Bouallegue, "REAL CDMA-OFDM/OQAM TRANSMISSION SYSTEM BASED ON

WALSH HADAMARD SPREADING CODE OVER RAYLEIGH FADING CHANNEL," IEEE

L. Chrislin, P. Siohan, R. Legouable and M. Bellanger, "CDMA Transmission with Complex

OFDM/OQAM," EURASIP Journal onWireless Communications and Networking, 2008.

R. GHARSALLAH and R. BOUALLEGUE, "Comparison between MC-CDMA and CDMA-

OFDM/OQAM systems in presence of MIMO channel," IJCSI International Journal of Computer

Science Issues, vol. 9, 2012

M.Bellanger, "FBMC physical layer: a primer," June 2010. [Online]. Available: http://www.ict-

phydyas.org/teamspace/internal-folder/FBMC-Primer_06-2010.pdf

L. Häring, "OFDM Transmission Technique," Nachrichtentechnische Systeme - Univerität Duisburg-

Essen, Duisburg, 2015

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http://www.ict-phydyas.org/teamspace/internal-folder/FBMC-Primer_06-2010.pdf

Performance analysis of clustered CDMA-OQAM- OFDM Networksnts.uni-duisburg-essen.de/downloads/nt-prakt12... · Filter Bank Multicarrier (FBMC): Enhancement in the physical layer of

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