Suppose that electrical pulses having random amplitudes arrive at an electronic counter in
accordance with a Poisson process with rate . The amplitude of a pulse is assumed to decrease
with time at an exponential rate. That is, if a pulse has amplitude A upon arrival, then its amplitude
at a time t units later will be Ae -t , with being a constant. We further suppose that the initial
amplitude of the pulses are independent and have a common distribution F.
Let S1 , S2 , ..., be the arrival times of the pulses and let A1 , A2 , ..., be their respective amplitudes.
Then,
N (t )
B(t ) = Ae i
- (t -S i )
i =1
represents the total amplitude of the electric counter at time t. Compute the expected value E[B(t)]
of B(t). [Hint: B(t) contains two types of randomness: one due to N(t) and one due to A. It might
help to condition on N(t).]
