25-08-2017, 09:32 PM
Quadrature Phase Shift Keying Modulator and Demodulator for Wireless Modem
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Abstract
Digital modulation is a process that impresses a
digital symbol on to a signal suitable for transmission on a
wired or wireless medium in order to receive that signal at
receiving end correctly with out any loss of information.
Quadratic phase shift keying (QPSK) modulation technique
is the most widely used modulation scheme in modern digital
communication system; it provides high performance on
bandwidth efficiency and bit error rate. In this paper the
complete model of Quadrature Phase Shift Keying (QPSK)
modulator and demodulator has been developed. The model
has been simulated in Matlab using Simulink. Complete
results are tested and verified. In final hardware design and
implementation of QPSK for Wireless Modem has been
proposed. QPSK modulation has various applications
particularly in the design of wireless modem, cellular CDMA
communication.
INTRODUCTION
Internet has converted this world into global village. Now
people want to communicate while on move. Wireless is the
technology that makes it possible. In last few years, the mobile
radio communication industry has grown exponentially. By the
fabrication of high density low power, low noise, small size
and reliable digital and RF chips make radio equipment
smaller, cheaper and more reliable. Due to this explosive
growth of mobile and wireless users there are so many
problems created, the most critical problem is frequency
spectrum, Bit Error Rate (BER) and Bandwidth. In this paper
the Quadrature Phase Shift Keying is addressed as modulator
and demodulator for the wireless modem.
MODEL BLOCK DIAGRAM
A. QPSK Modulator
QPSK modulator consists of two binary phase shift keying
(BPSK) modulators, serial to parallel converter shift register,
oscillator and 900 phase shifter [5]. The binary serial bit
sequence with bit rate Rb applied to modulator is converted
into two bit parallel sequence I-bit and Q-bit each of having bit
rate Rb/2 [8]. These I and Q bits are applied to BPSK
modulators, whose carrier frequency is orthogonal to each
other. This orthogonal signal is achieved through phase shifter;
which shift the applied signal to 90 degrees. The out put from
both BPSK modulators is added by summing amplifier; which
results QPSK modulated signal.
CONCLUSION
At first stage the digital modulation has been reviewed
followed by Quadrature Phase Shift Modulation (QPSK). In
second stage the QPSK Modulator & Demodulator block
diagrams are discussed & Matlab Simulink simulation of both
(modulator & demodulator) has been presented. In final stage
the complete hardware implementation of QPSK Modulator-
Demodulator using MC1496 has been proposed.
In this paper the complete software model of QPSK
Modulator- Demodulator has been designed, simulated, and
tested using Simulink MATLAB. Hardware of QPSK
Modulator-Demodulator has been proposed using MC1496
(balanced Modulator-Demodulator).