AASeminarSeminar

onon

“MIMO OFDM ”“MIMO-OFDM ”Presented by

Mr Arjun NichalMr.Arjun Nichal

ContentsContentsContentsContentsRequirements of wireless world

FDM(Frequency Division Multiplexing)

OFDM(O th l F Di i i M lti l i )OFDM(Orthogonal Frequency Division Multiplexing)

MIMO(Multiple Input Multiple Output)

Combined model of MIMO-OFDM

ApplicationsApplications

Conclusion

Requirements of wireless worldRequirements of wireless worldRequirements of wireless worldRequirements of wireless worldData rate

100 Mb/s for moving client1 Gb/s for fixed client

Spectrally efficient

High quality of service

System implementation cost should be less

FDM(Frequency Division Multiplexing)FDM(Frequency Division Multiplexing)

Fig Frequency division multiplexing

Each signal is modulated to a different carrier frequency

Fig. Frequency division multiplexing

Carrier frequencies separated so signals do not overlap (guard bands)

Drawbacks of FDMDrawbacks of FDMDrawbacks of FDMDrawbacks of FDM

Guard band reduces the spectrum efficiency

Fig. FDM Spectrum

Guard band reduces the spectrum efficiency

Intersymbol Interference

Why Why OFDM(Orthogonal Frequency OFDM(Orthogonal Frequency

Division Multiplexing)?Division Multiplexing)?

Spectrally efficient & offers high data rate

Capable to remove the interference.

Filter used for separating the subcarrier conveniently implementedFilter used for separating the subcarrier conveniently implemented

Solves the multipath-propagation problem

OFDMOFDMOFDMOFDMMulti-carrier modulations that use orthogonal waveform f d l i h b i ll d h l for modulating the sub-carriers are called orthogonal frequency division multiplex (OFDM) schemes

A form of Multicarrier Modulation.

Different symbols are transmitted over different subcarriers

Spectra overlap, but signals are orthogonal.

OFDM SpectrumOFDM SpectrumOFDM SpectrumOFDM Spectrum

Fig. FDM Vs OFDM Spectrum

OFDM Transreceiver modelOFDM Transreceiver modelOFDM Transreceiver modelOFDM Transreceiver model

Fig. OFDM Transreceiver model

ICI(InterICI(Inter--Carrier Interference)Carrier Interference)ICI(InterICI(Inter Carrier Interference)Carrier Interference)

ICI caused due to loss in orthogonality

Fig. Cyclic prefix

Cyclic prefix is a copy of the last part of the OFDM symbol

Used to maintain the receiver carrier synchronization

Advantages of OFDMAdvantages of OFDMAdvantages of OFDMAdvantages of OFDMEfficiently Deals With Multi-path Fading

Solves the ISI problem

Enhanced Channel Capacity

Better synchronization at transmitter and receiver

Robustness to Narrowband Interference

Disadvantages of OFDMDisadvantages of OFDMDisadvantages of OFDMDisadvantages of OFDM

More complex than single-carrier modulationMore complex than single carrier modulation

High sensitivity inter-channel interference ICIHigh sensitivity inter channel interference, ICI

OFDM is sensitive to frequency clock and phase OFDM is sensitive to frequency, clock and phase offset

MIMOMIMOMIMOMIMO

Fig. Simple MIMO system

Use multiple transmit and multiple receive antennas for a

single user

Now this system promises enormous data rates!

MIMOMIMOMIMOMIMOSpatial multiplexing MIMO

R diDSP DR diRadio

Radio

DSP

DSP

DS

p

BitSplit

BitsBit

Merge

TX

Radio

Radio

Bits

RX

Multiple independent link between Transmitter & Receiver

Fig. Spatially multiplexing MIMO

p p

There are cross path between antenna

MIMO system model for two Transmit MIMO system model for two Transmit R R & Receive antenna& Receive antenna

User data stream User data stream

h11

h12

h21

h22

s1 y1s1

s2

y1

y2

Transmitted vector ‘s’ Received vector ‘y’

y = Hs + n

Where H =h11 h12

h22h21

Advantages of MIMOAdvantages of MIMOAdvantages of MIMOAdvantages of MIMOHigh data rate 1Gbps

At the same time, they provide reliable communications

High SNRs.

Higher data rate in fading zone

Provides high bandwidth.

MIMOMIMO--OFDM combined modelOFDM combined modelMIMOMIMO OFDM combined modelOFDM combined model

T1

T2

Wireless channel

T2

R1

R2

Fig. OFDM-MIMO combined model

MIMOMIMO--OFDM Block outputsOFDM Block outputsMIMOMIMO OFDM Block outputsOFDM Block outputs1. Input to Time Domain

( ) ( ){ }1,...,2,1,0 −=

=Nn

kXIDFTnx1,...,2,1,0 Nn

2. Guard Interval ( ) ( )( )⎩

⎨⎧

−=−+−−=+

=1,...,1,0,

1,...,1,,NnnxNNnnNx

nx ggf

3. Channel ( ) ( ) ( )nwnhnxy ff +⊗=

( ) ( )4. Guard Removal ( ) ( ) 1,...,1,0 −== Nnnyny f

5 Output to Frequency ( ) ( ){ }= nyDFTkY5. Output to FrequencyDomain

( ) ( ){ }1,...,2,1,0 −= Nk

y

6 Output( ) ( ) ( ) ( ) ( )++= kWkIkHkXkY

6. Output1,...,1,0 −= Nk

7. Channel Estimation ( ) ( )( ) 1,...,1,0 −== NkkHkYkX

ee

Applications of MIMOApplications of MIMO--OFDMOFDMApplications of MIMOApplications of MIMO OFDMOFDM

MIMO-OFDM radar for direction estimationMIMO-OFDM radar for direction estimation

Orthogonal waveforms

Fig. MIMO-OFDM Radar

Applications of MIMOApplications of MIMO--OFDMOFDMApplications of MIMOApplications of MIMO OFDMOFDM

Digital Audio and Video BroadcastingDigital Audio and Video Broadcasting

Less multipath distortion

R d d i fReduced interference

4G(Forth Generation)

Wireless LAN

ConclusionConclusionConclusionConclusion

MIMO-OFDM is a efficient wireless systemMIMO OFDM is a efficient wireless system

Efficient use of the available bandwidth since the

subchannels are overlapping

MIMO-OFDM used for highest data rate applications

It provides reliable communication

ReferencesReferencesReferencesReferencesA.A. Kishk & A.W. Glisson “MIMO-OFDM radar for direction estimation”

IET Radar Sonar Navig ,vol. 4, no.1, pp. 28–36,April 2009.

Chih-Hung Lin, Robert Chen-Hao Chang, “Implementation of Channel

Estimation for MIMO-OFDM Systems”, IEEE Transaction on broadcasting,

vol.9, no.1,pp.42-44, 2010.

Jian Xu Sang Jin Lee Woo Seok Kang & Jong Soo Seo “Adaptive Resource Jian Xu, Sang-Jin Lee, Woo - Seok Kang & Jong-Soo Seo, Adaptive Resource

Allocation for MIMO-OFDM Based Wireless Multicast Systems”, IEEE

Transactions on broadcasting, vol. 56, no. 1, march 2010.

Textbook by Mischa Schwartz, “Mobile Wireless Communications”, page

no.129-134.

http://www.wikipedia.com

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