INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK

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INTERPOLATION BASEDMULTIMODE PRECODING FOR

MIMO OFDM WITH LIMITEDFEEDBACK

PRESENTED BY:

DISHANT KHOSLAM.TECH(1`st Year)ECE

ROLL NO.11092025



INTRODUCTION

� MIMO-OFDM is used to achieve high spectral efficiency and high link reliability over space and frequency selective wireless channels.

� MIMO-OFDM capitalizes on the reduced-complexity per sub-carrier processing of OFDM to enable an easier fulfillment of the highcapacity and/or diversity promises of MIMO systems.

� In spatial multiplexing, multiple independent parallel data streams are

transmitted on the MIMO channel, in an attempt to approach theMIMO capacity.

� Linear precoding improves the robustness of spatial multiplexing torank deficiencies of the MIMO channel.

� Spatial multiplexing with linear precoding simply multiplies the spatialdata streams, prior to transmission, by a precoding matrix that isdesigned according to some form of transmit CSI.

� The optimization criteria for designing the precoding matrix includeminimizing the mean squared error , maximizing the minimum distance

between two received data vectors, maximizing the minimum SNR andmaximizing the mutual information.



OFDM PRINCIPLE

Frequency

Frequency

Channels

Channels

50% Bandwidth saved

b) Orthogonal Frequency DivisionMultiplexing

a)F

requency DivisionMultiplexing



ORTHOGONAL FREQUENCY DIVISION

MULTIPLEXING



OFDM TRANSMITTER AND RECEIVER

Modulation(QPSK, QAM etc.) IFFT D/A

Modulation(QPSK, QAM etc.) FFT A/D

Transmitter

Receiver

DataIn

Data

Out

BasebandOFDMSignal

BasebandOFDMSignal



CYCLIC PREFIX EXTENSION

TTg

Original OFDMSymbol

Cyclically Extended OFDMSymbol

Multipath Component - A

Multipath Component - B

Multipath Component - C

max



INTERPOLATION

� Interpolation is a method of constructing new data points within

the range of a discrete set of known data points.

� Often a number of data points are obtained by sampling or

experimentation, and Interpolation tries to construct a function

which closely fits those data points.

� Spatial interpolation allows an estimation of data to be made at a

particular point given that surrounding values are known.

� Temporal interpolation would be able to approximate the value

of a given point at a particular instance in time, even if the device

is not sensing at that exact moment. This would require that at

least one previous and one subsequent device values are available

for that particular device.



MIMO Techniques

� Precoding Technique

� Spatial Multiplexing Technique

� Diversity Coding Technique



PRECODING TECHNIQUE

Radio

D

S

PBits

Radio

RX

BitsTX

BitsRXRadio

D

S

PBits

Radio

TX

Radio

Radio

� Precoding is multi-stream beamforming. In single beamforming,

the same signal is emitted from each of the transmit antennas

with appropriate phase such that the signal power is maximized

at the receiver input.

� The benefits of beamforming are to increase the received signal

gain, by making signals emitted from different antennas add upconstructively, and to reduce the multipath fading effect.



SPATIAL MULTIPLEXING TECHNIQUE

Radio

Radio

DSP

DSP

Bit

SplitBits

Bit

Merge

TX

Radio

RadioRX

Bits

DSP

DSP

� In spatial multiplexing, a high rate signal is split into multiple

lower rate streams and each stream is transmitted from a different

transmit antenna in the same frequency channel.

� Spatial multiplexing is a very powerful technique for increasing

channel capacity at higher signal-to-noise ratios (SNR). Themaximum number of spatial streams is limited by the lesser in

the number of antennas at the transmitter or receiver.



DIVERSITY CODING TECHNIQUE

� In diversity methods, a single stream is transmitted, but the signal

is coded using techniques called space-time coding.

� The signal is emitted from each of the transmit antennas with full

or near orthogonal coding.



MIMO-OFDM SYSTEM



OFDM ADVANTAGES

� Makes efficient use of the spectrum by allowing overlap.

� OFDM is more resistant to frequency selective fading than singlecarrier systems are.

� Eliminates ISI and IFI through use of a cyclic prefix.

� Using adequate channel coding and interleaving one can recover

symbols lost due to the frequency selectivity of the channel.

� Channel equalization becomes simpler than by using adaptiveequalization techniques with single carrier systems.

� It is possible to use maximum likelihood decoding with reasonable

complexity, as OFDM is computationally efficient by using FFTtechniques to implement the modulation and demodulation functions.

� In conjunction with differential modulation there is no need toimplement a channel estimator.

� Provides good protection against cochannel interference.



OFDM LIMITATIONS

� Sensitive to Doppler shift.

� Sensitive to frequency synchronization problems.

� High peak-to-average-power ratio (PAPR), requiring linear transmitter circuitry, which suffers from poor power efficiency.

� Loss of efficiency caused by Cyclic prefix/Guard interval.



APPLICATIONS

� Digital Audio and Video Broadcasting

� Asymmetric Digital Subscriber Line (ADSL)

� Wireless Networking

� Power-line Technology



CONCLUSION AND FUTURE WORK

OFDM has become one of the most popular air-link technologies for future broadband wirelesscommunications. To further improve its bandwidthefficiency and system performance, adaptive resourceallocation and smart antenna techniques have been widely.

OFDM for wireless communication has intensively been anactive research area in the past 10 years due toimplementation of DSP based algorithm using VLSI.However there are many unsolved issues OFDM basedradio networks, such as spectrum sensing , interferenceidentification and transceiver design. Still some of the open

issues and remaining hurdles on the way to a full-scalecommercialization of MIMO systems are antenna issues ,receiver complexity , system integration and signaling andCSI at transmitter.



REFERENCES

� William Stallings, ³Wireless Communications and Networking´,

Prentice Hall, 2003.

� Theodore S. Rappaport, ³Wireless Communications: Principles

& Practice´, Prentice Hall, 2002.� www.wikipedia.com



THANKS

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INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK