Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
2000-10-18
2004-02-10
Baderman, Scott (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S799000, C375S233000
Reexamination Certificate
active
06691260
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an error propagation control method and device for performing error propagation control in multi-level decision feedback equalization (MDFE), and more particularly to an error propagation control method and device suitable for M3DFE.
2. Description of the Related Art
Recently the surface recording density of magnetic disk devices and magnetic tape devices is dramatically increasing. An increase in surface recording density means an increase in transfer speed. If the same signal processing method is used, an increase in transfer speed induces an increase in recording frequency, reaching the limit of recording because of [the limitation of] the write head. Therefore improving signal processing is in progress.
In signal processing, multi-level decision feedback equalization (MDFE) has been proposed. This method prevents a decrease in bit interval and code interference due to a decreased bit interval, therefore the signal-to-noise ratio can be improved.
Also, M3DFE, where a plurality of decision paths of MDFE are set, has been proposed (INTERMAG '99 Conference, AD-8). With this method, SNR can be improved even more so than MDFE.
FIG. 13
is a functional block diagram of a conventional M3DFE system, and FIG.
14
and
FIG. 15
are drawings depicting the path selection sequence thereof.
As
FIG. 13
shows, the M3DFE system
90
has a plurality of decision paths
80
and
81
of MDFE. One MDFE (multi-level decision feedback equalizer)
80
is basically comprised of a feedback filter
93
, an addition circuit
91
, a detector
92
and a buffer memory
94
.
The other MDFE (multi-level decision feedback equalizer)
81
has the same structure, comprising a feedback filter
97
, an addition circuit
95
, a detector
96
and a buffer memory
98
. The feedback filters
93
and
97
feedback the output of a decision by the detectors
92
and
96
to the addition circuit
91
and
95
. The output of the feedback filters
93
and
97
is changed so as to be the opposite polarity of the input pulse polarity. In other words, the feedback filters
93
and
97
assume that the polarity of the input reproducing signal pulse alternates.
The output polarity of the feedback filter is therefore normally in the opposite direction from the polarity to be input to the forward filter, which is not illustrated, in the previous stage. The addition circuits
91
and
95
determine the difference between the output of the forward filter and the output of the feedback filters
93
and
97
. As a result, the output of the addition circuits
91
and
95
become a waveform with the “0” level at the center.
Then the detectors
92
and
96
execute binary decision for the output of the addition circuits
91
and
95
by a predetermined threshold value (e.g. “0” level). The output of the detectors (decision units) is a binary code series, but is in a four value state because of one bit convolution by the M3DFE circuit.
This M3DFE selects either an MDFE operation for outputting the detection result of one MDFE path, or an M3DFE operation for selecting a detection signal of a path which error signal is smaller according to the detection results of the two MDFE paths when it is judged that error probability is high in the above path. For this a path controller
99
is disposed.
This operation will be described with reference to FIG.
14
. operation is different between inside the erasure area and outside the erasure area. At first, in the outside of the erasure area, the detection result of the MDFE path
80
is output via the buffer
94
. During this time, the path controller
99
monitors the output Yt (n) of the adder
91
, and when the absolute value abs (Yt(n)) becomes smaller than a predetermined level &agr;t, the erasure area starts with this point as the erasure point.
Erasure starts when detecting the input Yt (n) of the decision unit
92
deviates from the ideal sample for a predetermined distance, that is, when detecting the error probability is high. Outside the erasure area, the operation is the same as MDFE, but inside the erasure area, the paths have different decision results from the erasure start point. And error signals for an error path are increased by the feedback filters
93
and
97
.
Specifically, a bit flip
82
is set on the other MDFE path
81
so that the decision result of the decision unit
96
on the other MDFE path
81
is inverted by the bit flip
82
. Normally an erasure ends when several samples have passed after the erasure point (e.g. length of the buffer
94
). This erasure end point is called a “merge”.
Therefore different decision results are stored in the buffer memories
94
and
95
. The path controller
99
selects a path which has a smaller error signal at the merge point (best path). For example, if the error of the MDFE path
80
is smaller, the detection result of the buffer
94
is output. Whereas if the error of the MDFE path
81
is smaller, the detection result of the buffer
98
is copied to the buffer
94
, then the data of the buffer
94
is output.
If a sample which error probability is even higher exists inside the erasure area, as shown in
FIG. 15
, then the erasure area may be continued after selecting the best path. This continuous point is called a “resplit”.
The M3DFE method, which outputs a detection result with less error, has about a 2dB gain compared with the MDFE method.
However, with the conventional M3DFE method, which has no error propagation control function, the error propagates to other data if an error exists, which makes detection impossible. This makes it especially difficult [for M3DFE] to be applied to the magnetic recording field.
An error propagation control method which can be applied to the MDFE method is known, but this cannot be applied to a multi-level decision feedback equalizer having a plurality of paths, even if it can be applied to a single feedback equalizer.
SUMMARY OF THE INVENTION
With the foregoing in view, it is an object of the present invention to provide an error propagation control method and device to add the error propagation control function to a multi-level decision feedback equalizer having a plurality of paths.
It is another object of the present invention to provide an error propagation control method and device to implement an error propagation control sequence to apply error propagation control technology, which is applied to a single feedback equalizer, to a multi-level decision feedback equalizer having a plurality of paths.
In order to achieve the above objects, the present invention is an error propagation control method for a multi-level decision feedback equalizer having a plurality of multi-level decision feedback paths comprising: a first error propagation detection step for detecting error propagation of a first multi-level decision feedback path, a second error propagation detection step for detecting error propagation of a second multi-level decision feedback path, a step for performing error propagation control of the first multi-level decision feedback path according to the error propagation detection by the first error propagation detection step for outside the erasure area, and a step for performing error propagation control of a selected path based on the error propagation detection result of the selected path at the erasure end point.
An error propagation control device of the present invention comprises: a first error propagation detector for detecting an error propagation of a first multi-level decision feedback path, a second error propagation detector for detecting an error propagation of a second multi-level decision feedback path, and a control section for performing error propagation control of the first multi-level decision feedback path according to error propagation detection by the first error propagation detector for outside the erasure area and for performing error propagation control of a selected path based on the error propagation detection result of the selected path
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