This document discusses various equalization techniques used in mobile communication systems. It describes that equalization is used to compensate for inter-symbol interference caused when the modulation bandwidth exceeds the coherence bandwidth of the radio channel. There are three main techniques discussed: equalization, diversity, and channel coding. Equalization counters inter-symbol interference, diversity reduces fading, and channel coding improves link performance by adding redundant data bits. Linear transversal equalizers and lattice equalizers are described as common equalizer structures.

1. Equalization Techniques
AANCHAL KUMARI
17001UEL01
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2. INTRODUCTION:
 The Mobile communication system requires signal processing techniques
which improves the link performance in mobile radio environments.
 There are three most popular techniques:
1) Equalization
2) Diversity
3) Channel coding
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Equalization:
 If the modulation bandwidth exceeds the coherence bandwidth of the
radio channel, ISI occurs and modulation pulses are spread in time.
 It is used for compensating Inter Symbol Interference.
 Equalizers must be adaptive as the channel is unknown and time varying.

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Diversity:
 Diversity technique used to compensate for fading channel impairments.
 Types of Diversity Techniques:
 Antenna Diversity
 Frequency Diversity
 Time Diversity
 Polarization Diversity
 Angle Diversity
 Code Diversity
 Antenna Diversity is implemented by using two or more receiving antennas.

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 While Equalization is used to counter the effects of ISI, diversity is
usually employed to reduce the depth and duration of the fades
experienced by a receiver in flat fading channel.
 These techniques can be employed at both base station and
mobile receivers.
 Spatial Diversity is the most widely used diversity technique.

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Channel coding:
 Used to Improve mobile communication link performance by adding
redundant data bits in the transmitted message.
 The coded message is then modulated for transmission in the wireless channel.
 coding can be considered to be a post detection technique.
 Types of channel codes:
 block codes
 convolutional codes.
 Channel coding is generally treated independently from the type of modulation
used.

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Classification of Equalizers:

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Linear Transversal Equalizer:
 LTE is the most common Equalizer structure.
 LTE is made up of tapped delay lines, with the taps spaced a symbol period
(Ts) .
 The transfer function can be written as a function of the delay
operator −𝑗𝜔𝑇𝑠 𝑜𝑟 𝑍^-1 .

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Two Types of LTE:
Finite impulse response (FIR) filter:
 Transfer function is a polynomial in Z^-1.
 Has many zeroes but poles only at z = 0.
Infinite impulse response (IIR) filter:
 Has both feedforward and feedback taps.
 Transfer function is a rational function of Z^-1 with poles and zeros.
 Tend to be unstable when used in channels where the strongest pulse arrives
after an echo pulse.

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Advantages of Lattice Equalizer:
 Numerical stability
 Faster coverage time
 Its unique structure allows dynamic assignment of the most effective length
of the lattice equalizer.
 When the channel becomes more dispersive, the length of the equalizer
can be increased by the algorithm without stopping the operation of the
equalizer.
 Only a fractions of stages is used if the channel is not very time dispersive.
 The main disadvantage of the lattice equalizer is its complex structure.

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