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七郎 / Seven Liu

科学与艺术,恰如人生中的红颜知己。 本博内容保留所有权利.

 
 
 

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4.19 BD coding and decoding BD的编码和解码  

2012-07-03 15:00:06|  分类: 读点英文 |  标签: |举报 |字号 订阅

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Once the channel bits steam is being read from the disc, the Physical Cluster can be assembled. The physical cluster is equivalent of 32 data frames, along with error correction, control data and the addressing system. The Physical Cluster is in the channel bit state and includes the synchronization pattern and the d.c. control bits used to control the d.c. level of the analogue HF-signal.

从盘片上读出的通道比特流被立即排列成"物理簇(Physical Cluster)"。一个物理簇等于32个"数据帧"(data frame)加上纠错码、控制数据和寻址系统。物理簇仍为包含同步模式的通道位状态,用直流控制位(d.c. control bits)来控制模拟高频信号的直流电平。

There are 45 channel bits in between each d.c. control bit. Each row of the Physical Cluster starts with a synchronization pattern of 30 channel bits, each containing a 9T-symbol in addition to regular symbols.

直流控制位之间是45个通道位。物理簇的以同步模式每行排列30个通道位,每行除了正常符号还包含一个9T符号用于同步。

After assembling the physical cluster the d.c. control bits are removed and the channel bit stream is sent through the 17PP-demodulation process. The demodulation process converts the channel bits to source bits at a 3-to-2 ratio (i.e. 12 channel bits results in 8 source bits). The special synchronization pattern, which includes the 9T-symbol, is used in the demodulation process. When the Physical Cluster is demodulated, the ECC-Cluster can be assembled.

排列好物理簇之后,直流控制位被移除,通道比特流被送去进行17PP解调制处理。解调制过程将通道位按3:2比例(即每12个通道位转换成8个源位)转换成源位(source bits)。解调制过程使用了包含9T符号的特殊同步模式。物理簇经解调后,被重新组装成EEC簇。

The ECC-Cluster consists of a matrix of 155 columns and 496 rows, where the last 64 rows are error correction for the main user data. Sandwiched between the user data columns (also though the error correction at the bottom of the ECC-Cluster) are three columns of Burst Indicating Subcode, BIS. Thus there are 38 bytes (columns) of user data (and error correction) between each column of BIS-code. The user data is protected by a strong Reed Solomon error correction code ("Long Distance Code" or LDC). The BIS-columns are also protected by a strong, separate, Reed Solomon code.

ECC簇是由155列496行构成的矩阵,其最后的64行用于对主用户数据进行纠错。(尽管纠错码在ECC的底部)还有夹在用户数据之间的是3列BIS(Burst indication Subcode,突发错误指示子码)。这样,每列BIS码之间就是38位(列)用户数据(和纠错码)。用户数据由强壮的里德·所罗门纠错码(即Long distance code,长程码,LDC)保护。而BIS列也由强壮的、单独的里德·所罗门码进行保护。

Correcting digital errors in the ECC-Cluster is down by first checking the BIS columns. As the name suggests, the BIS-columns indicates the presence of possible burst errors in the ECC-Cluster. This is done by checking for errors in at least two consecutive BIS-columns. A burst error is therefore defined as at least 40 bytes long (1 BIS-byte, then 38 user data bytes plus 1BIS byte). The synchronization is also used as a burst indicator and forms the first column of the ECC-cluster. Prior information about possible burst errors will assist in correcting the user data in the ECC-Cluster and thus increases the correction capabilities. Having a strong protection system against burst errors is critical for the Blu-ray Disc format, as the thin cover Layer and high NA lens makes the format much more sensitive to burst error (such as fingerprint and scratches) than, for instance, the DVD format.

ECC簇内的纠错过程是,首先检查BIS列。顾名思义,BIS列用以指示在ECC簇中是否出现了突发错误。这通过检查至少两个连续的BIS列来完成。因此突发错误的长度被定义成至少40字节(1个BIS字节,然后是38个用户数据字节再加一个BIS字节。同步字节也用于指示突发错误和构成ECC簇的第一列。先探测可能的突发错误信息有助于在ECC簇中纠正用户数据,因而提高了纠错能力。拥有针对突发误码的强壮数据保护系统对于BD来说是非常重要的,因为薄薄的一层覆盖层和高数值孔径光头使BD格式对突发误码(诸如指纹、划伤的影响)相对于DVD格式来说尤其敏感。

 

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Key Words:

·Physical Cluster 物理簇

·d.c. control bits 直流控制位

·data frame 数据帧

·addressing system 寻址系统

·channel bit stream 通道比特流、通道位流

·channel bit 通道位

·source bits 源位

·ECC-cluster ECC簇,纠错控制块

·BIS,Burst indication Subcode 突发错误指示子码

·Reed Solomon error correction code 里德和所罗门纠错码,一种编码方式,尤其适于对付突发误码。

·LDC,Long distance code,长程码,里德所罗门编码之一种

·assemble 组合,组装

·Burst 突发误码

·in addition to 除了……之外

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