RFID readers, RFID tags, software, and methods decode a signal received in an RFID system. From received data, a decoder determines a number of possible test series for the output. In one embodiment, the decoder uses a memory of a previous sample to derive a subsequent sample in the test series, so as to ensure that all the test series are valid. A metric is then computed for how well each test series fits the received data. The metrics are compared to select for output the test series with the best fit. In a further embodiment, at least one of the metrics is further used to determine if a collision were present.