Introduction[1] Three techniques are used independently or in tandem to improve receiver signal...

Introduction[1]bullThree techniques are used independently or in tandem to

improvereceiver signal qualitybullEqualization compensates for ISI created by multipath with

timedispersive channels (WgtBC)1048766Linear equalization nonlinear equalizationbullDiversity also compensates for fading channel impairments

and isusually implemented by using two or more receiving

antennas1048766Spatial diversity antenna polarization diversity frequencydiversity time diversity

bull The former counters the effects of time dispersion (ISI) while thebull latter reduces the depth and duration of the fades experiencedbull by a receiver in a flat fading (narrowband) channelbull bull Channel Coding improves mobile communication linkbull performance by adding redundant data bits in the transmittedbull messagebull bullChannel coding is used by the Rx to detect or correct some (or all)bull of the errors introduced by the channel (Post detectionbull technique)bull 1048766Block code and convolutional code

bull Equalization Techniquesbull bull The term equalization can be used to describe any signalbull processing operation that minimizes ISI [2]bull bull Two operation modes for an adaptive equalizer trainingbull and trackingbull bullThree factors affect the time spanning over which anbull equalizer converges equalizer algorithm equalizerbull structure and time rate of change of the multipath radiobull channelbull bullTDMA wireless systems are particularly well suited forbull equalizers

bull Nonlinear Equalization

bull bullUsed in applications where the channel distrotion is too severe

bull bullThree effective methods [6]

bull 1048766Decision Feedback Equalization (DFE)

bull 1048766Maximum Likelihood Symbol Detection

bull 1048766Maximum Likelihood Sequence Estimator (MLSE)

bull Diversity Techniquesbull bullRequires no training overheadbull bullCan provides significant link improvement with little added costbull bullDiversity decisions are made by the Rx and are unknown to the Txbull bullDiversity conceptbull 1048766If one radio path undergoes a deep fade another independent

path maybull have a strong signalbull 1048766By having more than one path to select from both the

instantaneousbull and average SNRs at the receiver may be improved often by as

muchbull as 20 dB to 30 dB

bull Diversity Techniques

bull bullMicroscopic diversity and Macroscopic diversity

bull 1048766The former is used for small-scale fading while the latter for large-scale

bull fading

bull 1048766Antenna diversity (or space diversity)

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bull The former counters the effects of time dispersion (ISI) while thebull latter reduces the depth and duration of the fades experiencedbull by a receiver in a flat fading (narrowband) channelbull bull Channel Coding improves mobile communication linkbull performance by adding redundant data bits in the transmittedbull messagebull bullChannel coding is used by the Rx to detect or correct some (or all)bull of the errors introduced by the channel (Post detectionbull technique)bull 1048766Block code and convolutional code















bull fading


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bull fading


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Introduction[1] Three techniques are used independently or in tandem to improve receiver signal...

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