RAKE DEMODULATOR

BY

AJAL.A.J

NOMENCLATURE

• RAKE DEMODULATOR

IT HAS BEEN COINED FOR THIS DEMODULATOR STRUCTURE BY

PRICE AND GREEN (1958 )

RAKE DEMODULATOR

OPTIMUMDEMODULATOR

REALIZATION

ALTERNATEDEMODULATOR

REALIZATION

ANOTHER NAME

• TAPPED DELAY LINE DEMODULATOR

• TAPPED DELAY LINE DEMODULATOR ATTEMPTS TO COLLECT THE SIGNAL ENERGY FROM ALL THE RECEIVED SIGNAL PATHS THAT FALL WITHIN THE SPAN OF THE DELAY LINE AND CARRY THE SAME INFORMATION

• IN ITS ACTION IS SOME WHAT ANALOGU8S TO AN ORDINARY GARDEN RAKE .

WE CALL THIS AS AN OPTIMUM DEMODULATOR ALSO WHY

BECAUSE …………

• CAN ALTERNATIVE REALIZATION OF THE OPTIMUM DEMODULATOR EMPLOYS A SINGLE DELAY LINE THROUGH WHICH IS PASSED THE RECEIVED SIGNAL R (t)

TAP WEIGHTS ……

• TAP WEIGHTS PROVIDES US WITH

L REPLICAS OF SAME TRANSMITTED SIGNAL AT THE RECEIVER

HENCE IN A RECEIVER THAT PROCESS THE RECEIVED SIGNAL IN AN OPTIMUM MANNER WILL ACHIEVE THE PERFORMANCE OF AN

EQUILAENT L TH ORDER DIVERSITY COMMUNICATION SYSTEM

CONSIDER ……………• CONSIDER BINARY SIGNALLING OVER

THE CHANNEL .

• WE HAVE 2 EQUAL ENERGY SIGNALS ,

WHICH ARE

EITHER

ANTIPODAL OR ORTHOGONAL

ASSUMPTION

WHAT IS TO BE NEGLECTED ?• NEGLECT ISI DUE TO THE MULTIPATH

NOTE

ISI IS INTER SYMBOL INTERFERENCE

SINCE

BAND WIDTH OF THE SIGNAL EXCEEDS THE COHERENT BAND WIDTH OF THE CHANNEL

• ASSUME THAT THE CHANNEL TAP WEIGHTS ARE KNOWN

• HERE THE 2 FILTERS ARE MATCHED TO V1 (t) & V2 (t)

• AlsoThe samples are passed toa decision

circuit that selects the signal corresponding to largest output

ASSUMPTION