(a) Define and distinguish between binary phase shift keying BPSK and Quadriphase shift keying (QPSK) as means of digital modulation of a carrier. [20%]
(b) A digital signalling system sends data at 10 bit/sec on a radio carrier. For both BPSK and QPSK sketch the power spectra, indicating all important features in the two different cases:
(i) natural or unfiltered transmission
(ii) maximally filtered according to the Nyquist signalling criterion. [30%]
(c) Explain clearly why the output signal to noise for a given carrier power and same bit rate in presence of additive white noise may be exactly the same for QPSK and BPSK. [20%]
(d) A Low Earth Orbiting (LEO) micro-satellite using either BPSK or QPSK modulation on its down link. The power available to receiver on the ground is P = 15 × 10-16 W in presence of white noise of density kT = 4 × 10-21 W/Hz. Noise factor in the receiver is 6 dB. Data rate is fb = 4800 bits/sec Determine:
(i) the Eb/N0 ratio
(ii) output signal to noise ratio γ2
(iii) estimate the (BER) from the approximate formula