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8/7/2019 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
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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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.
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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OFDM PRINCIPLE
Frequency
Frequency
Channels
Channels
50% Bandwidth saved
b) Orthogonal Frequency DivisionMultiplexing
a)F
requency DivisionMultiplexing
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ORTHOGONAL FREQUENCY DIVISION
MULTIPLEXING
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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
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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CYCLIC PREFIX EXTENSION
TTg
Original OFDMSymbol
Cyclically Extended OFDMSymbol
Multipath Component - A
Multipath Component - B
Multipath Component - C
max
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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.
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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MIMO Techniques
� Precoding Technique
� Spatial Multiplexing Technique
� Diversity Coding Technique
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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.
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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.
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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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.
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MIMO-OFDM SYSTEM
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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.
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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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.
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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APPLICATIONS
� Digital Audio and Video Broadcasting
� Asymmetric Digital Subscriber Line (ADSL)
� Wireless Networking
� Power-line Technology
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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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.
8/7/2019 INTERPOLATION BASED MULTIMODE PRECODING FOR MIMO OFDM WITH LIMITED FEEDBACK
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REFERENCES
� William Stallings, ³Wireless Communications and Networking´,
Prentice Hall, 2003.
� Theodore S. Rappaport, ³Wireless Communications: Principles
& Practice´, Prentice Hall, 2002.� www.wikipedia.com