International Business Machines Corporation

Huo-Bing Yin

John W Fennel, Jr

Robert J Hallett

Mukesh P Patel

In a TDMA satellite communication system, one of the stations is elected the primary station which transmits a reference burst to all other stations to synchronize the local clocks in each station. Each subsidiary station in turn responds by transmitting a local transmit reference burst to enable synchronization of the local transmit clocks. In order to assure that the synchronous operation of the network will continue when the reference station experiences a failure, an alternate reference station is designated in the network which will assume the role of the primary reference station in a baton passing operation in the event that the existing primary reference station must abdicate its reference role. An improved method and apparatus for carrying out the baton passing operation monitors the channel error rate at the reference station and the alternate station. The error rate is measured by detecting FEC from assessing the error syndromes in the reference bursts from the reference station as received at the reference and alternate stations. This refined monitoring technique is combined with the coarser technique of monitoring the number of negative acknowledgement signals from the subsidiary stations indicating that they have not correctly received reference bursts, to yield a more refined determination at the reference station of its effectiveness as a reference station. The alternate station uses a similar technique to determine if it is sufficiently healthy to play the role of alternate station.

Baton passing method and apparatus for maintaining synchronization in a

An adaptive delta modulation system is disclosed which features an improved digital compandor which may be used with a digital integrating network. The compandor executes a companding algorithm having a nonlinear characteristic to provide a rapid increase in step size to follow the fast rising start or fast decaying end of talkspurts in input signals so as to minimize any slope overload distortions and to provide a small increase or decrease in step size during the smooth portion of the talkspurts in input signals to reduce any granular noise effect. The step size generated by the compandor is directly related to the input signal level, providing a maximum companding range in which good signal-to-noise characteristics are preserved for the soft or low voiced speaker as well as for the loud voiced speaker and providing a fast transient response most suitable for telephone applications. The step size logic of the compandor has a built-in minimum step size circuit which insures that a well behaved idle pattern of alternating ones and zeros will appear at the digital output when the input signal is zero, and which provides a mechanism to rapidly build up the step size when an input signal appears. The step sizes can be integrated with an integrating network to reconstruct the input signal. The compandor may be used in conjunction with a digital integrating network which exhibits, for example, a system function, having either a single pole or a zero and a pair of poles which may be real or complex. The filter constants can be chosen to match any input spectrum to obtain optimum performance. A significantly high signal-to-noise ratio and a wide companding range have been obtained with the disclosed compandor. By providing storage elements in the compandor and in a digital integrating network and storing the calculated intermediate values, a plurality of input for output analog signals can be time division multiplexed and delta modulated with a single delta modulation system.

Adaptive delta modulation system

An improved bucket brigade circuit is disclosed having an improved transfer efficiency and dynamic range. Conventional bucket brigade circuits consist of a chain of storage capacitors and charge transfer circuits functioning as an analog shift register. Due to the nodal capacitance at the first load of prior art circuits, the charge thereon cannot be maintained at an optimum level because of voltage pull-back and charge redistribution during the fall time of the clock pulse. The invention disclosed herein provides an additional capacitor connecting the first node of the circuit to the inverse of the clock waveform, thereby eliminating the voltage pull-back and charge redistribution problem, resulting in an improved charge transfer efficiency and dynamic range for the circuit.

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Potomac, MD, United States of America

Huo-Bing Yin