L. Botha

New multilevel line codes

Values of channel capacity for multilevel sequences with the number of signal levels ranging from 4 to 7, subject to three classes of channel input restrictions, are presented. Seven line codes that are suitable for use in baseband digital communication systems are also presented, together with their error propagation properties. The codes are shown to satisfy tight channel input restrictions, making them suitable for use in digital communications systems.<<ETX>>

A new runlength limited code for binary asymmetric channels

Abstract - In write-once optical data storage, one is faced with an (d, k, e, I)-parameters is to avoid confusion when making asymmetry between marlcs and non-marks. This means that a code comparisons to NRZI (d, k) sequences [4]. is required of which the minimum runlength of zeros and ones differ. Such a new runlength limited code with rate 3/4 is III. THE NEW RATE CODE presented. For this new code the minimum runlength of zeros is one and the minimum runlength of ones is two. The maximum runlengtbs of both zeros and ones are restricted to seven. The encoder, decoder, power spectrum and error propagation properties of this new code are given. I. INTRODUCTION In write-once optical data storage, one is faced with an asymmetry between marks and non-marks due to the practical lower limit of the mark size [1]. This is due to fact that with increasing information density, the lengths of the non-marks diminish, but the marks cannot be made arbitrarily small. Van Uijen

Band pass line codes

This paper considers block codes and finite state machine codes with higher-order spectral zeros at DC for use where a speech channel and data are transmitted on the same twisted pair. The use of these codes is proposed for the asymmetrical digital subscriber line and the South African Diginet system.<<ETX>>

A new runlength limited code for binary asymmetric channels (optical storage)

A novel runlength limited code with code rate 3/4 suitable for write-once optical storage is presented complying with the ( alpha , beta , gamma , delta )=(1, 2, 7, 7) constraint. For this code, the minimum runlength of zeros is one and the minimum runlength of ones is two. The maximum runlengths of both zeros and ones are restricted to seven. If the (d, k)=(1, 7) code was to be used on the same channel the code rate would be 2/3. thus, an increase of 12% in the data rate and a 12% increase in the detection window have been obtained. The encoder, decoder, power spectrum, and error propagation properties of this code are presented. >

New multilevel line codes for baseband communication-an experimental study

Codes considered for the North American ISDN and similar new multilevel line codes that comply with strict transmission channel input restrictions are discussed briefly. A short description of the experimental set up, used to evaluate the new multilevel line codes, is given. Measured eye patterns and spectra of some multilevel line codes are presented and compared with the line code 2B1Q, which was proposed for North American applications.<<ETX>>

The transformation of line codes

Abstract Theorems relating characteristic equations and values of channel capacity of some classes of constrained sequences to other classes are presented. These results provide new characteristic equations which can be used for the calculation of channel capacity, and enable existing tables containing values of channel capacity for constrained sequences to be used to find previously unknown values of capacity for other classes of sequences. Algorithms for transforming DC-free line codes and their decoders to minimum bandwidth line codes, and vice-versa, are presented. These algorithms are then used to obtain two new minimum bandwidth line codes.

The adaptation of constrained codes to new channel input restrictions

The authors present several theorems and corollaries relating characteristic equations and values of channel capacity of some constrained sequences with different sets of input restrictions. These results provide with new characteristic equations for some classes of constrained sequences which can be used for enumeration of these sequences. It also becomes possible to find previously unknown values of channel capacity for some sequences by using tables which were calculated for other sequences. Code transformation algorithms which are systematic and easy to apply are presented with which a code, designed for use on a previously studied constrained channel, can be transformed to a new code with different constraints. This precludes the necessity of applying complex code synthesis algorithms to the new class of constraints.<<ETX>>

Higher order DC-constrained line codes

The authors consider the use of multilevel line codes which generate sequences with higher-order spectral nulls at DC for the suppression of low-frequency spectral contents of the digital signal so that a baseband speech signal can be inserted at low frequencies. The use of these line codes is proposed for the asymmetrical digital subscriber line (ADSL). The new line codes exhibit a large dead band at DC, and can thus be considered for use on the control channel of the ADSL. A further advantage of using the block codes is that the additional spectral nulls in the pass band of each of these block codes make it possible to insert pilot tones at these frequencies, to aid with functions such as clock recovery at the receiver.<<ETX>>

Low frequency suppression of baseband coded sequences

Two classes of sequences with favourable low frequency spectral suppression are considered. They are sequences with higher order zeroes at zero frequency and sequences which comply to restrictions on the time between crossings of the average RDS value. It is shown how these sequences can be used to transmit a conventional analog speech channel on the same channel as a digital signal, but totally independent from it. An optimization problem regarding the choice of a code sequence for a specific application is then considered, and finally a new code with suppressed low frequencies is presented.<<ETX>>