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PRML stands for partial-response maximum likelihood sequence detection. It is an advanced method of determining the sequence of binary data that is stored on a disk or other medium or that is received via wire, optical or wireless transmission. Partial-response means controlled inter-symbol interference (ISI). That is, the data represented by the received waveform are packed so closely together that they overlap (interfere). The "controlled" part means that there is some identifiable structure to the overlapping. This structure is "taught" to a sophisticated sequence detector that looks only for the possible controlled patterns of ISI in the received waveform. This provides a much more robust detection method in the presence of noise. This type of detection is often used with trellis coding to futher improve detection. Trellis coding encodes the data such that the possible received sequences that are most similar are not used. This provides extra capability to distinguish between received waveforms in the presence of noise and distortion. PHY layer, short for physical layer, refers the portion ("layer") of a communications or networking specification that defines the physical characteristics of the signal and the tranmission and detection methods. These methods can be quite simple or very complex. As speeds and bandwidths increase in xDSL, cable modems, Gbit Ethernet, and in optical and wireless systems, more complex communications techniques continue to be employed. This is typically driven by the desire to keep the same physical medium (e.g., Cat 5 cable, coax, mixed mode fiber) while increasing the rate of the data that travels on that medium. The more complex communications techniques are chosen to provide reliable performance in the presence of the unique signal anomilies caused by using the current medium at higher and higher rates. The best
way to get started in PRML for data storage, or to advance your current
skill level, is to take the class PRML Lab. This hands-on lab class, which
features ChannelScience.com's PRMLpro™
software, is written by ChannelScience.com and presented through KnowledgeTek,
Inc. You can also find additional information at our storage
links page, at PRML
FAQs and at our book
review page. Please contact us for a free initial consultation. e-mail:
connect@ChannelScience.com |
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