This paper proposes an echo cancellation algorithm that can be used for full-duplex digital data transmission over existing twisted-pair cables. The proposed algorithm is a form of the "sign algorithm." A new adaptation method is introduced to change the canceller step size according to the residual echo level by using the correlation between the echo and the error signal. The adaptation method can increase the echo canceller convergence speed by an order of magnitude over the conventional sign algorithm. An echo canceller utilizing the proposed algorithm is suitable for VLSI implementation, because it requires no multibits analog-to-digital converter. Theoretical analysis and parameter optimization are carried out. The rapid convergence property of the algorithm is verified by computer simulation as well as experiments.

Digital transmission techniques are expected to spread throughout the fixed-satellite service in the near future. The introduction of digital satellite systems will lead to a new requirement regarding how to connect the satellite link with terrestrial digital networks. This paper presents a satellite/terrestrial digital interface that has been developed to interconnect 2.048 Mbit/s PCM terrestrial and INTELSAT TDMA links which are in the plesiochronous relationship. Major functions of the interface include frame slip control, compensation for path length variation, and rate and format conversions. This paper also describes the design and implementation of the developed equipment, and experimental results for signal impairment due to the frame slips and PCM multiplex standard conversion. The experimental results demonstrate that a large humber of bit errors are induced by frame slips for voiceband data transmission above 4800 bits/s.

Performance improvement of the nearly instantaneous companding PCM (or block companding PCM) is discussed. A simplified algorithm is proposed. The design and performance of a channel bank adopting the proposed algorithm is described. The channel bank can transmit 44 voiceband signals on a standard T1 line. It provides commercially acceptable speech quality as well as sufficient transparency for voiceband data up to 4800 bits/s.

A discretely variable slope delta modulation (DVSD) codec is described, which is suitable for integrated circuit realization. The step size is varied by a pulse number modulation method that does not require a precision digital-to-analog conversion circuit. An adaptation algorithm is discussed, taking into consideration the effect of transmission errors. The quantizer and integrator portion has been fabricated on a monolithic chip using MOS technology. Results obtained from an experimental 32 kbit/s codec demonstrate its excellent performance.