Numerous software reliability growth models have been proposed. The authors present three metrics which have been helpful in assessing the applicability and predictive validity of these models. These metrics are the relative fitting error metric, the short term predictive validity metric and the long term predictive validity metric. The application of these three metrics is illustrated on estimation of field reliability of telecommunication switching systems.>

A reference code, with an associated bound on the code rate, for the encoding of correlated digital sources is introduced. The reference code is adaptive and simple to implement. Image coding results obtained using concatenated trellis and reference encoding are presented. For the images studied, the reference code attains an average code rate of approximately 0.64 bits/bit, or a reduction in information rate of approximately 36%.

An analog-digital hybrid decoder which combines amplitude and duration threshold detection and bipolar violation sensing capabilities for decoding bipolar signals is described. The main features of the decoder are: 1) a preamplifier with automatic gain control (AGC), 2) amplitude and duration threshold detectors, 3) a bipolar violation sensor, and 4) a unipolar pulse generator. The decoder is extremely robust and is self-synchronizing. If, during operation, burst errors occur, introducing bipolar violations in the received signal, the decoder decides that, where a violation has occurred, a binary "0" was transmitted. If, for some reason, the decoder is perturbed from its synchronous condition, it requires at most 1-b duration to reacquire synchronization. That is, the decoded message contains at most one erroneous bit.

Bipolar signal waveforms for digital communication are normally accomplished by coding the message sequence first and then pulse shaping the bipolar signal. The coding is relatively simple to mechanize; the pulse shaping may present some difficulty and approximation techniques may have to be used. A hybrid digital-analog mechanization of a bipolar signal waveform generator in which the bipolar encoding and pulse-shaping operations are combined is described.