QPSK,QAM.ppt - QUADRATURE PHASE SHIFT KEYING INTRODUCTION In BPSK each symbol contains only one bit Therefore symbol rate is same as bit rate The

# QPSK,QAM.ppt - QUADRATURE PHASE SHIFT KEYING INTRODUCTION...

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INTRODUCTION In BPSK, each symbol contains only one bit. Therefore symbol rate is same as bit rate The bandwidth of BPSK signal is therefore If two or more bits are combined in one symbol then the bit rate will be reduced. This reduces the transmission bandwidth. In QPSK, two successive bits are combined. This forms four distinct symbols. When the symbol is changed to next symbol the phase of carrier signal is changed by 45° i.e. π/4 radians.
SYMBOLS AND THEIR PHASE SHIFTS
OQPSK TRANSMITTER
The b e (t) waveform represents even bit stream and b o (t) waveform represents odd bit stream. b e (t) modulates the carrier b o (t) modulates the carrier These carriers are also called as quadrature carriers. The resultant modulated signals are
Where and are basically BPSK signals. The only difference is that T S = 2T b . The adder adds these two signals and gives the output as
PHASOR DIAGRAM OF QPSK Since the even bit stream and odd bit stream cannot change at a time, the maximum phase change in QPSK signal will be π/2.

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• Spring '18
• Prof. S. S. Bhatlawande

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