Analysis of Direct Modulation Technique Employing FQPSK-B Signals
Rana, Md. Masud
Rahaman, D.M. Motiur
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The direct modulation architecture of recently standardized baseband filtered version of Feher-patented quadrature phase-shift keying (FQPSK-B) modulation is proposed. A continuous phase modulation (CPM) implementation alternative of a recently standardized class of FQPSK-B modulation is proposed. It is based on the fact that the FQPSK-B signal has quasiconstant amplitude and continuous phase characteristics, allowing CPM interpretation. Based on this, it derive the modulation index, premodulation filter and alternating change monitor differential encoder for the CPM generated FQPSK-B signal, to be fully compatible with the original I/Q-modulated one. Direct modulation architecture is simple and more cost efficient than the I/Q modulation architecture. With the proposed direct modulation architecture, FQPSK-B signals can be generated with existing FM modulation based transmitter system. The power spectral density of direct modulated FQPSK-B signals is practically the same with the I/Q modulated FQPSK-B signals and BER performance of coherent detection and noncoherent detection of direct modulated FQPSK-B signals are almost same with the I/Q modulated FQPSK-B.
- November 2007