Bit Error Rate Testing of Advanced Channels

The performance goal of channel engineering is the minimization of received errors. A measure of this performance is the bit error rate (BER), or the ratio of received errors to received samples. Computer channel models are used to generate simulate readback samples, which are processed by the receiver of interest.

In addition to computer simulations, we have developed a BER Tester (right) for use with our spinstands. This tester can emulate a digital detector that uses up to three samples along with a feedback filter. Such an arrangement would typically be used to evaluate DFE or FDTS/DF detectors, but the detector can also implement nonlinear detection schemes such as RAM-DFE or neural network detectors. The hardware is flexible with respect to the modulation code and can accept RLL(0,k), RLL(1,k), and MTR(2;k) codes. Because the test hardware was built with off-the-shelf components, its speed is limited to about 25 MHz. However, this is adequate for most magnetic tape recording applications. Although the system cannot perform realtime detection at higher data rates, we have the equipment to sample a block of data at any practical rate and then feed the samples to the detector hardware at a rate it can handle.