A new type of digital echo canceler for two-wire digital transmission is presented. The new principle involves very simple signal processing and is thus an interesting alternative for digital transmission on subscriber lines. The principle is compared with other echo cancellation techniques, and it is shown how choice of line code, equalization, and carrier recovery are affected by the new echo canceler. A theoretical analysis of the principle is given, taking into account finite accuracy, jitter, noise, and correlated data streams. The echo canceler can be used for line attenuation up to 40 dB. At 80 kbits/s this corresponds to at least 7 km 0.6 mm cable and is sufficient to cover more than 99 percent of the existing Norwegian subscriber lines.

A New Digital Echo Canceler for Two-Wire Subscriber Lines

A user-orientated telephone instrument including high-fidelity speech encoding, encryption capability and many function presently provided by centralized call processing is described. Utilizing an ADPCM encoding process including forward error correction, a high quality relatively noise immune signal is provided. To the user, the instrument appears as a unique electronic telephone which offers many special services to facilitate communications with other people and with computers. Advanced features such as optional hands-off voice on/off-hook control, personal identification by voice print and remote chart presentation are provided.

High fidelity speech encoding for telecommunications systems

In this paper the main characteristics and the performance of two systems implemented for two wire digital transmission on subscriber lines are presented. Both systems utilize different time intervals to transmit bursts of bits in the two directions with an information bit rate of 80 kbits/s and a line bit rate in the bursts of 256 kbits/s. One system employing WAL2 as the line code exhibits extreme circuitry simplicity and low power consumption. The other system, which employs CMI as the line code, shows better performance in the presence of line disturbances.

A Comparison of Digital Subscriber Line Transmission Systems Employing Different Line Codes

Adopting digital techniques in the local network area will enhance the possibility of extending digital operation capability to the subscriber's equipment. The problem is to convey digital signals at a bit rate of at least 64 kbits/s in both directions over existing two-wire subscriber loops. This paper describes a time-shared two-wire digital subscriber transmission system in which the directional separation of two signals (GO and RETURN) is accomplished by the time division bidirectional transmission method in burst-mode, and also reports results of investigations on the feasibility of an all digital telephone subscriber loop system.

Time-Shared Two-Wire Digital Subscriber Transmission System and Its Application to the Digital Telephone Set

In a multi-level transmission system, a binary digital signal is converted into a multi-level signal by generating successive multi-level symbols each having a polarity opposite the polarity of the average DC level of preceding symbols, with the first symbol having a first polarity when the first binary bit is a logical "0" and having a second polarity when the first bit is a logical "1". If desired, the logical values of all bits after the first bit can be complemented prior to generating the appropriate multi-level symbols.

Burst signal transmission system

The Electronics Research Laboratory at the Norwegian Institute of Technology has since 1974 studied PCM-transmission in the local subscriber plant. A short discussion of this work is presented together with choice of design parameters and concept for a digital subscriber set. Construction and laboratory testing of the digital subscriber set are described. The paper concludes with a discussion on future development.

R. Torbergsen

Papers

A Digital Subscriber Set