components of the received signal. These frequency
components are estimates of the transmitted DQPSK
symbols. A rectangular to polar conversion transforms
the I and Q signals into phase and magnitude form. A
block phase difference is then performed, and the symbols
deinterleaved to produce a stream of QPSK symbol
estimates, from which a Viterbi decoder recovers the final
bit stream.
2.1.2 Computational Complexity
The demodulator has a computational complexity of
about 200 DSP operations per sample, or 109
DSP operations per second for 30MHz operation. A DSP
operation is here taken to be an 8-bit addition, multiplyaccumulate
or load-store. Because much of the
arithmetic in the demodulator requires only 8-bit words,
it is not apparent that significant advantage could be
gained by using a DSP chip with much wider wordwidths.
Even assuming a DSP clock that is five times the
sample speed (i.e. 150 MHz), a DSP-based
implementation would require some 40 DSP chips, with
corresponding difficulties resulting from the partitioning