1. A method for estimating a bit error rate in a data transmission system comprising: detecting symbols by a maximum likelihood detector, that provides path metrics of a decoded path and a best competitor path at predetermined symbol positions; calculating quantized absolute path metric differences between the decoded path and the best competitor path at said predetermined symbol positions; and counting events when a quantized absolute path metric difference is equal to one of a set of difference values, thereby obtaining an event count for each difference value in the set of difference values; estimating the bit error rate based on a summation of partial bit error rates, wherein each partial bit error rate is based on a relationship of the event count for a first difference value from the set of difference values and a path probability corresponding to the first difference value.