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FMT Modulation for Wireless Communication. Santosh V Jadhav (Advisor: Prof V M Gadre). Multicarrier System:. Spectral partitioning: -s inc(f) overlapping (OFDM) -Non-overlapping (FMT) OFDM: FMT :. Spectral characteristics:OFDM. Spectral characteristics:FMT.

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FMT Modulation for Wireless Communication

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Fmt modulation for wireless communication
FMT Modulation for Wireless Communication

Santosh V Jadhav

(Advisor: Prof V M Gadre)


Multicarrier system
Multicarrier System:

Spectral partitioning:

-sinc(f) overlapping (OFDM)

-Non-overlapping (FMT)

OFDM:

FMT :





Ofdm v s fmt
OFDM v/s FMT:

OFDM: -perfect detection(zero ISI, zero ICI) under ideal

channel and absence of noise.

-simple equalization scheme with cyclic prefix

-high spectral overlap.

FMT: -nearly rectangular frequency-domain amplitude

characteristic

-High spectral containment, negligible ICI

-The absence of the cyclic prefix, together with the

reduced no of virtual carriers

-Equalizer is required even under ideal channel

condition and absence of noise


Why to prefer fmt over ofdm
Why to prefer FMT over OFDM?

-Cyclic Extension in OFDM

-> Loss of transmission efficiency

-High spectral overlap in OFDM

-> Frequency offset sensitivity

-In OFDM side lobes are just 13dB lower than the main lobe

-> Significant power leakage into adjacent band



Efficient implementation dft based fmt system
Efficient implementation: DFT based FMT system -

FMT Transmitter-


Contd fmt receiver
Contd…FMT Receiver-


Prototype design
Prototype Design:

Prototype filter h(n) completely defines the system. Allows tradeoff between-

- No. of subcarriers

- Level of spectral containment

- Complexity of implementation and latency

Can be designed by any standard FIR filter design method. Typical design parameters are-

- fcutoff : determines the ISI per subchannel

- Stopband energy : determines ICI introduced by adjacent subchannels, so should as low as possible


Contd e g
Contd…e.g. -

Blackman Window

=14, fcutoff = 0.3/T

Hamming Window

=14, fcutoff = 0.38/T


Equalization in fmt system
Equalization in FMT System:

Due to negligible ICI, each subchannel will be independent of adjacent channel(s) as shown -

Simplified subchannel model is –


Contd
Contd…

Subchannel impulse response ( = 14):

So, ISI and per subchannel equalization is must.


Conventional schemes and fmt specific equalizer design
Conventional Schemes and FMT specific equalizer design

-Channel is equalized by one-tap equalizer

-ISI due to transmit and receive filter need to be compensated.

Linear equalizer

DFE equalizer


Contd1
Contd…

Here estimated error –

Optimality criterias –

- Zero forcing(ZF)

- MMSE


Simulation results with mmse
Simulation results with MMSE

QPSK, M=64, =14:


Contd2
Contd…

8-PSK, TCM encoder, M=64, =14


Problems with conventional method and solution
Problems with conventional method and solution

Problems-

The process of making hard decisions on the channel symbols actually destroys information pertaining to how likely each of the possible channel symbols might have been.

Solution-

1. Additional soft information can be converted into probabilities that each of the received symbol takes on and can be exploited by a BER optimal decoding algorithm.

2. Let decoder generate its own soft information based on the soft information received from equalizer and use it in the process of equalization. So let soft information flow in both direction between decoder and equalizer for no of iteration -> Turbo Equalizer.



Contd3
Contd…

Turbo Equalizer-

-Channel equalized by 1-tap filter

-SISI equalizer neutralizes the effect of transmit and

receive filters.


Performance of turbo equalization based schemes
Performance of Turbo equalization based schemes

MMSE-DFE(BPSK, Hamming, =10):


Contd4
Contd…

MMSE-LE(BPSK, Hamming, =10):


Future scope
Future Scope:

-Turbo equalization based scheme to be extended to other higher order constellations (like QPSK, QAM)

-Turbo equalizer for STBC-FMT

-Multi-user detection in FMT Systems

-Adapting the System if flat fading assumption fails


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