Coded data generation or conversion – Digital code to digital code converters – To or from 'n' out of 'm' codes
Reexamination Certificate
1999-12-21
2001-05-15
Young, Brian (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from 'n' out of 'm' codes
C341S095000, C340S398100, C375S213000
Reexamination Certificate
active
06232896
ABSTRACT:
Device for encoding n-bit source words into corresponding m-bit channel words and decoding m-bit channel words into corresponding n-bit source words.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, wherein the stream of databits of the source signal is divided into n-bit source words, which device comprises converting means conceived to convert said n-bit source words into corresponding m-bit channel words in accordance with a conversion of the parity preserve type, where m and n are integers, with m>n.
The invention also relates to a method of encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, wherein the stream of databits of the source signal is divided into n-bit source words, said source words being converted into corresponding m-bit channel words in accordance with a conversion of the parity preserve type, where m and n are integers, with m>n.
The invention further relates to a binary channel signal comprising a stream of databits, converted from a binary source signal comprising a stream of databits, wherein the stream of databits of the source signal comprises n-bit source words, the channel signal comprising m-bit channel words, each one of said m-bit channel words corresponding to one of said n-bit source words in accordance with a conversion of the parity preserve type, where m and n are integers, with m>n.
The invention further relates to a record carrier comprising a binary channel signal comprising a stream of databits, converted from a binary source signal comprising a stream of databits, wherein the stream of databits of the source signal comprises n-bit source words, the channel signal comprising m-bit channel words, each one of said m-bit channel words corresponding to one of said n-bit source words in accordance with a conversion of the parity preserve type, where m and n are integers, with m>n.
The invention further relates to a device for decoding a stream of databits of a binary channel signal into a stream of databits of a binary source signal, wherein the stream of databits of the channel signal is divided into m-bit channel words, which device comprises deconverting means conceived to deconvert said m-bit channel words into corresponding n-bit source words in accordance with a deconversion of the parity preserve type, where m and n are integers, with m>n.
2. Description of the Relate Art
An encoding device and a decoding device mentioned in the foregoing are known from U.S. Pat. No. 5,477,222 (PHN 14448). The document discloses a device for encoding a stream of databits of a binary source signal into a stream of databits of a binary channel signal, satisfying a (1,7) runlength constraint. This means that, in a serial datastream of the channel signal, minimally one ‘zero’ and maximally seven ‘zeroes’ are present between two consecutive ‘ones’ in the channel signal. The device further realizes a minimization of the repeated minimum transition runlength.
In this respect it should be noted that, normally, an additional precoding step, such as a
1
T precoding, is applied to the (1,7) constrained sequence, resulting in a runlength-limited sequence with a minimum runlength of 2 and a maximum runlength of 8.
The known conversion is parity preserving (PP). ‘Parity preserving’ means that the parity of the n-bit source words to be converted equals the parity, after modulo-2-addition, of the corresponding m-bit channel words in which they are converted. As a result, the encoding device as claimed does not influence the polarity of the signal.
As the conversion is parity preserving, DC-control can be applied by inserting DC-control bits in the datastream of the source words, which is more efficient than the insertion of extra bits in the channel bitstream, the so-called merging bits. DC-control implies the reduction of the power of the channel bit stream near zero frequency. The spectral notch at DC allows retrieval of the threshold level from the detected waveform, which is essential for detection and timing-recovery with the PLL.
In this PP channel code, no additional DC-control is present in order to further reduce the power of the channel bit stream near zero frequency, or to reduce the overhead for DC-control by reduction of the number of parity preserve DC-control bits.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved device for encoding n-bit source words into corresponding m-bit channel words, in which extra DC-control is possible.
The device in accordance with the invention is characterized in that the device further comprises control means for carrying out DC-control on said binary channel signal by introducing a freedom of choice in the source-to-channel conversion.
The invention is based on the recognition that DC-control will be made possible by introducing an appropriate freedom of choice in the source-to-channel mapping. Therefore, two options in the choice for some particular source-to-channel conversions are created. Both options are different in one extra ‘1’ in the channel bitstream in NRZI-notation, i.e. the difference is one extra transition in the channel bitstream. Due to this extra transition, the so-called running-digital sum (RDS) value can be kept within certain bounds. This kind of DC-control will be referred to as stochastic DC-control.
In the parity preserve channel code, already mentioned in U.S. Pat. No. 5,477,222, DC-control is also performed by limiting the RDS within certain bounds. The main difference with the known parity preserve channel code is that this code needs extra bits, the so-called parity preserve bits, before the channel encoding operation in order to control the RDS value. In this invention, the RDS value can also be controlled be introducing a freedom of choice in the source-to-channel mapping with double options. In order to maintain the same amount of DC-control, fewer extra bits can be used, allowing a higher capacity of the record carrier with signals encoded in accordance with the presented code stored on it.
The device in accordance with the invention is also characterized in that the device further comprises control means conceived to minimize the repeated minimum transition runlength on said binary channel signal by introducing a freedom of choice in the source-to-channel conversion.
The invention is based on the recognition that in encoding in accordance with the known encoding device, relatively long sequences comprising only the minimum transition runlength may occur, leading to a deterioration of the bit detection in a receiver, followed by transmission and subsequent decoding of the channel signal in the receiver. In a channel signal satisfying a specific runlength constraint, such as (1,7) or (1,8), this means that relatively long sequences ‘ . . . 0101010101. . .’ occur, resulting in relatively long sequences ‘ . . . 001100110011. . . .’ in the sequence after
1
T preceding. The devices in accordance with the invention restrict the lengths of these sequences, so that an improved bit-detection in a receiver can be realized. Such a restriction is known as R epeated
M
inimum
R
unlength
L
imitation (RML).
The method in accordance with the invention is characterized in that the method further carries out DC-control on the binary channel signal by introducing a freedom of choice in the source-to-channel conversion.
The signal in accordance with the invention is characterized in that in said binary channel signal, a pair of blocks of p consecutive m-bit channel words, being converted from the same block of p consecutive n-bit source words, is present, the blocks of the pair differing from each other in the bit value at one bit position only in said blocks, p being an integer which is larger than 1.
The record carrier in accordance with the invention is characterized in that, in said binary channel signal, a pair of blocks of p consecutive m-bit ch
Coene Willem M. J.
Kahlman Josephus A. H. M.
Belk Michael E.
Nguyen John
U.S. Philips Corporation
Young Brian
LandOfFree
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