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# Channel code with embedded pilot tracking tones for DVCR

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## Abstract

The proper functioning of a digital video recorder is largely governed by the selection of a suitable channel code in conjunction with both the detection method and the tracking system. The channel code for the digital video cassette recorder (DVCR) satisfies a variety of design requirements. The paper provides an overview of those requirements. A detailed description is given of the constriction of the new channel code, called 24→25 code, that complies with the given constraints and involves only a minor drawback in terms of the overhead needed. The servo position information is recorded as low-frequency components, pilot tracking tones, which are embedded in the recorded stream of binary digits

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... Let E[a(x)] denote the expected value of the variable a(x) of all possible x ∈ Q n . For symmetry reasons, it is immediate that, see (2), that E[ρ x,i ] = 0, 1 ≤ i ≤ n − 1. Using (3) and (6), we infer that E[H x (f )] = 1, which is the well-known result that the mean of the spectral content is independent of the frequency f (white noise). ...
... The (unnormalized) auto-correlation coefficient, nρ x,i , is the sum of the n − i bipolar variables x 1 x i+1 , x 2 x i+2 , . . ., x n−i x n , see (2), so that nρ x,i ∈ {−n+i, −n+i+2, . . . , n−i}. ...
... Spectral null codes have been applied in a myriad practical communication [15] and data storage systems [2,3,4,5,6]. In this section, we analyze the difference in spectral performance and redundancy of the newly developed spectral shaping codes and prior art dc-balanced codes having a null at dc, f = 0. ...
Article
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We investigate a new approach for designing spectral shaping block codes with a target spectrum, H_t(f), that has been specified at a plurality of frequencies. We analyze the probability density function of the spectral power density function of uncoded n-symbol bipolar code words. We present estimates of the redundancy and the spectrum of spectral shaping codes with specified target spectral densities H_t(f_i) at frequencies f_i. Constructions of low-redundancy codes with suppressed low-frequency content are presented that compare favorably with conventional dc-balanced codes currently used in data transmission and data storage devices with applications in consumer electronics.
... Spectrum shaping codes, also known as spectrum null codes, are channel codes that have spectrum nulls at specific frequencies. They have been applied extensively in the magnetic tape as well as the optical recording systems [1], [2], which are key constituents of consumer electronics products. They are also expected to bring significant performance gain for the recently proposed dedicated servo recording system [3], which is a promising technology for the ultra mobile hard-disk drive for tablets. ...
... A k constraint which specifies the maximum number of consecutive '0's between two '1's in the channel coded sequences is also required for the above magnetic recording systems. Spectrum shaping codes that generate non-zero spectrum nulls have been applied in digital video consumer electronics products such as (mini)DV, where the code rate is 24/25 [1]. The code is designed by using a polarity bit switching method but the k constraint is not guaranteed. ...
... The spectrum was computed on the basis of 10 million channel bits. Note that with p = 1 and a scrambler polynomial of g(x) = 1 + x, the GS scheme is equivalent to the polarity bit switching method used by [1]. Observe that with the increase of p, both the width and depth of the spectrum nulls at the dual servo frequencies increase. ...
Conference Paper
We propose a systematic code design method for constructing efficient spectrum shaping constrained codes for high-density data storage systems. Simulation results demonstrate that the designed codes can achieve significant spectrum shaping effect with only around 1% code rate loss and reasonable computational complexity.
... pectrum shaping codes, also known as spectrum null codes, are channel codes that have spectrum nulls at specific frequencies. They have been applied extensively in the magnetic tape as well as the optical recording systems [1], [2], which are key constituents of consumer electronics products. They are also expected to bring significant performance gain for the recently proposed dedicated servo recording system [3], [4], which is a promising technology for the ultra-mobile hard-disk drive (HDD) for tablets. ...
... Codes with a spectrum null at 0 f  , also called dc-free codes [5], [6], are typically used to facilitate filtering of lowfrequency noise such as finger marks on the optical disc surface. Codes with spectrum nulls at non-zero frequencies are Manuscript effective in eliminating the interference of narrow band signals to the data signal [1], [7], [8]. For example, in the magnetic tape or the dedicated servo recording system with dual-frequency servo signals, on even tracks the servo signal has a frequency f 1 and on odd tracks the servo signal frequency is f 2 . ...
... It specifies the maximum number of consecutive '0's between two '1's in the channel coded sequences, and hence facilitates timing recovery of the channel readback signal. Spectrum shaping codes that generate non-zero spectrum nulls have been applied in digital video consumer electronics products such as (mini)DV, where the code rate is R=24/25 [1]. The code is designed by using a polarity bit switching method but the k constraint is not guaranteed. ...
Article
This paper proposes systematic code design methods for constructing efficient spectrum shaping codes with the maximum runlength limited constraint k, which are widely used in data storage systems for digital consumer electronics products. Through shaping the spectrum of the input user data sequence, the codes can effectively circumvent the interaction between the data signal and servo signal in high-density data storage systems. In particular, we first propose novel methods to design high-rate k constrained codes in the non-return-to-zero (NRZ) format, which can not only facilitate timing recovery of the storage system, but also avoid error propagation during decoding and reduce the system complexity. We further propose to combine the Guided Scrambling (GS) technique with the k constrained code design methods to construct highly efficient spectrum shaping k constrained codes. Simulation results demonstrate that the designed codes can achieve significant spectrum shaping effect with only around 1% code rate loss and reasonable computational complexity.
... The classes of runlengthlimited constraints and spectral-null constraints have already been introduced. In addition, there are constraints that generate spectral lines at specified frequencies, called pilot tracking tones, which can be used for servo tracking systems in videotape recorders [118], [115]. Certain channels require a combination of time and frequency constraints [128], [157], [160]; specifically DC-balanced RLL sequences have found widespread usage in recording practice. ...
... The classes of runlengthlimited constraints and spectral-null constraints have already been introduced. In addition, there are constraints that generate spectral lines at specified frequencies, called pilot tracking tones, which can be used for servo tracking systems in videotape recorders [118], [115]. Certain channels require a combination of time and frequency constraints [128], [157], [160]; specifically DC-balanced RLL sequences have found widespread usage in recording practice. ...
Article
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Constrained codes are a key component in digital recording devices that have become ubiquitous in computer data storage and electronic entertainment applications. This paper surveys the theory and practice of constrained coding, tracing the evolution of the subject from its origins in Shannon's classic 1948 paper to present-day applications in high-density digital recorders. Open problems and future research directions are also addressed
Chapter
Digital transmission and recording systems invariably transport information across a band of restricted width. The center frequency of this band may be high with respect to the band width, as it is in radio transmission. It may also be of the same order of magnitude or even zero, as in cable transmission and digital recording. In the first case the information must be modulated on to a carrier in order to convert it into the passband. In the second case this step is, in principle, not needed. The adjective ‘baseband’ serves to indicate that no carrier modulation is used. Instead, baseband transmission systems typically use a modulation code to match the characteristics of the data to those of the channel. At the receiving end of the system, equalization, detection, timing recovery and adaptation techniques are combined to recover the data. In the forthcoming chapters we discuss all these subjects. By way of introduction and motivation, the. present chapter gives a survey of three important application areas of digital baseband transmission, namely digital subscriber lines, digital magnetic recording and digital optical recording. The aim is to convey a flavor of the origin, nature and importance of the various transmission impairments that arise, to exemplify some of the techniques that exist to prevent and/or counteract them, and to show that the principal types of impairment are common to all systems. For future reference we also model some of the impairments analytically. We should stress that the present survey is only meant as an introduction to the various application areas. As such it is restricted both in scope and in depth. Section 2.5 lists several references that provide much more complete treatments.
Chapter
Baseband modulation codes are widely applied in such diverse fields as digital line transmission [21, 28, 18, 116], digital optical transmission [111, 16], and digital magnetic and optical storage [ 105, 100, 106]. They act to translate the source data sequence d n into a sequence a k that is transmitted across the channel (Fig. 4.1; see also Chapter 3). The principal goal is to enable the receiver to produce reliable decisions $${\hat d_n}$$ about d n . Code design should, therefore, account for the characteristics of both channel and receiver. (Because modulation coding is the only type of coding that we consider in this chapter, we shall usually say ‘coding’ where we mean ‘modulation coding’.)
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Constrained codes are a kev component in the digital recording devices that have become ubiquitous in computer data storage and electronic entertainment applications. This paper surveys the theory and practice of constrained coding, tracing the evolution of the subject from its origins in Shannon's classic 1948 paper to present-day applications in high-density digital recorders. Open problems and future research directions are also addressed.
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In multimode constrained coding, in each encoding interval a source word is mapped to multiple channel representatives, one of which is selected to generate sequences with the required constraint(s). In general, multimode codes have been designed to meet single sequence constraints. In this paper, we propose a cascade selection method in multimode coding for generation of sequences that satisfy multiple constraints. Our simulation results demonstrate that it is straight-forward to meet multiple constraints with our selection technique.
Conference Paper
Pilot tracking tones are used to derive head position reference information in camcorders and DVCRs. A simple pilot tone encoder has been designed by using a new approach, called ''calculate-and-correct'' method, in which encoding is preformed by assuming that all the control bits are 0's and the results are corrected if necessary. Owing to this method, the hardware size can be significantly reduced while low clock rate of 41.85 MHz is used. The correctness of the method has been verified by theoretical analysis and by extensive simulation.
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Coding techniques for improving the reliability of information storage on noisy magnetic recording channels are considered. It is assumed that the Lorentzian channel model applies and that the retrieved signal is perturbed with additive white Gaussian noise. The immunity against additive noise of state-of-the-art codes such as DC-free, runlength-limited, and trellis codes are assessed
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The signal-to-noise ratio of pilot tracking tones embedded in binary coded formats has been assessed. It has been found that the signal-to-noise ratio can be improved when the redundancy of the code is increased. Since the signal-to-noise ratio of the pilot tracking tone limits the maximum attainable bandwidth of the servo system, a compromise has to be found between the redundancy of the code and the performance of the servo system. The signal-to-noise ratio of pilot tones based on the polarity switch technique, which is attractive as no lookup tables are required for encoding and decoding, is substantially smaller than that of codes based on the fixed disparity format.
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The CTL tracking method is usually employed in VTRs etc.. in order to make the CTL tracking possible, the CTL signal synchronizing with reference signal is recorded on the tape and, during playback, the tracking servo works to maintain a constant phase between the drum revolution and the CTL signal. The CTL therefore, requires a stationary head to record or read the CTL signal, which opposes to simplify the mechanism. Furthermore, the manual tracking control is necessary, as the mechanical factors (for example, X-value, head mounting accuracy, and so on) introduce tracking error.
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The concept and real-time implementation of an experimental home-use digital HDTV recorder is presented. An advanced motion-compensated DCT bit-rate reduction system is used to realize high-quality images at 50 Mbit/s only, thereby enabling small recording mechanics for portable applications and featuring a new high-efficiency channel code with embedded tracking information
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An experimental digital video recording system based on small recording mechanics is described. High picture quality at moderate recording bit rates is obtained with component coded video and application of an advanced bit-rate reduction technique based on the discrete cosine transform (DCT). A single actuator allows for high tracking accuracy and multispeed playback. Reasonable picture quality has been obtained at 10 Mb/s. High picture quality, with hardly noticeable coding noise, was obtained at 19 Mb/s. For scenes with critical motion, the use of motion-adaptive processing is required.
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In digital data transmission (respectively, storage systems), line codes (respectively, recording codes) are used to tailor the spectrum of the encoded sequences to satisfy constraints imposed by the channel transfer characteristics or other system requirements. For instance, pilot tone insertion requires codes with zero mean and zero spectral density at tone frequencies. Embedded tracking/focus servo signals produce similar needs. Codes are studied with spectral nulls at frequencies f=kf_{s}/n , where f , is the symbol frequency and k, n are relatively prime integers with k leq n; in other words, nulls at rational submultiples of the symbol frequency. A necessary and sufficient condition is given for a null at f in the form of a finite discrete Fourier transform (DFT) running sum condition. A corollary of the result is the algebraic characterization of spectral nulls which can be simultaneously realized. Specializing to binary sequences, we describe canonical Mealy-type state diagrams (directed graphs with edges labeled by binary symbols) for each set of realizable spectral nulls. Using the canonical diagrams, we obtain a frequency domain characterization of the spectral null systems obtained by the technique of time domain interleaving.