  In 1995, Best et al. published a formula for the exact bit error probability
for Viterbi decoding of the rate R=1/2, memory m=1 (2-state) convolutional
encoder with generator matrix G(D)=(1 1+D) when used to communicate over the
binary symmetric channel. Their formula was later extended to the rate R=1/2,
memory m=2 (4-state) convolutional encoder with generator matrix G(D)=(1+D^2
1+D+D^2) by Lentmaier et al.
  In this paper, a different approach to derive the exact bit error probability
is described. A general recurrent matrix equation, connecting the average
information weight at the current and previous states of a trellis section of
the Viterbi decoder, is derived and solved. The general solution of this matrix
equation yields a closed form expression for the exact bit error probability.
As special cases, the expressions obtained by Best et al. for the 2-state
encoder and by Lentmaier et al. for a 4-state encoder are obtained. The closed
form expression derived in this paper is evaluated for various realizations of
encoders, including rate R=1/2 and R=2/3 encoders, of as many as 16 states.
  Moreover, it is shown that it is straightforward to extend the approach to
communication over the quantized additive white Gaussian noise channel.
