Abstract: Each node in a communication system transmits and receives state variable signals indicating internal node states or timings, generates transitions in its internal state or timing at a basic rate but at timings adjusted according to the received state variable signals, transmits data in time slots synchronized to the output state variable signals, receives data signals from the other nodes, detects collisions between the received data signals, and changes the timing of its time slots when a collision is detected, by shifting the phase of the transitions, or by inserting additional dummy transitions and transmitting corresponding dummy output state variable signals. The nodes can thereby assign their own time slots and avoid collisions autonomously.

Abstract: Each node in a communication system receives state variable signals from other nodes indicating the internal operating states or internal timing of the other nodes, and transmits a state variable signal indicating its own internal operating state or timing. Each node also determines whether each received state variable signal is valid. Transitions in the internal operating state or timing of a node take place at a basic transition rate but at times adjusted according to the valid state variable signals received from other nodes. A group of neighboring nodes transmitting data signals can thereby autonomously reach a steady state in which their data signals do not collide, without having their timing control disrupted by reflected state variable signals or other invalid state variable signals.

Abstract: Each node on a communication path receives state variable signals from other nodes indicating the internal operating states or internal timing of the other nodes, and transmits a state variable signal indicating its own internal operating state or timing. Transitions in the internal operating state or timing of a node take place at a basic transition rate but at times adjusted according to the state variable signals received from other nodes. The basic transition rate varies according to position on the communication path. The nodes can thereby establish transmitting time slots that follow each other in progression on the communication path, enabling data signals to be relayed from the starting node to the destination node with minimal delay at each intermediate node.

Abstract: A communication timing control apparatus for use in the nodes of a communication system includes a signal communication unit that transmits a state variable signal to neighboring nodes and receives state variable signals from those nodes. An external control signal, such as a beacon signal transmitted by a control node, is also received. The state variable signals indicate internal operating states or timings of the nodes; the control signal indicates a basic transition rate. A timing decision unit causes internal state or timing transitions to occur at timings responsive to the basic transition rate and the received state variable signals, adjusting the transition timings so as to avoid signal collisions and to adapt to changing system conditions, Use of the control signal enables a steady timing state to be reached quickly.

Abstract: Each node in a communication system transmits and receives state variable signals indicating internal node states or timings. A single node may transmit two or more differently phased series of state variable signals. Neighboring nodes interact by adjusting the timing phase at which they transmit each series of state variable signals according to the timing of state variable signals transmitted in other series, and state variable signals received from other nodes. The nodes can thereby establish time slots in which they can transmit data without collisions, and different nodes can receive different total amounts of time slot width by transmitting different numbers of series of state variable signals.

Abstract: Each node in a communication system transmits and receives state variable signals indicating internal node states or timings, generates transitions in its internal state or timing at a basic rate but at timings adjusted according to the received state variable signals, transmits data in time slots synchronized to the output state variable signals, receives data signals from the other nodes, detects collisions between the received data signals, and changes the timing of its time slots when a collision is detected, by shifting the phase of the transitions, or by inserting additional dummy transitions and transmitting corresponding dummy output state variable signals. The nodes can thereby assign their own time slots and avoid collisions autonomously.

Abstract: Each node on a communication path receives state variable signals from other nodes indicating the internal operating states or internal timing of the other nodes, and transmits a state variable signal indicating its own internal operating state or timing. Transitions in the internal operating state or timing of a node take place at a basic transition rate but at times adjusted according to the state variable signals received from other nodes. The basic transition rate varies according to position on the communication path. The nodes can thereby establish transmitting time slots that follow each other in progression on the communication path, enabling data signals to be relayed from the starting node to the destination node with minimal delay at each intermediate node.

Abstract: Each node in a communication system transmits and receives state variable signals indicating internal node states or timings. A single node may transmit two or more differently phased series of state variable signals. Neighboring nodes interact by adjusting the timing phase at which they transmit each series of state variable signals according to the timing of state variable signals transmitted in other series, and state variable signals received from other nodes. The nodes can thereby establish time slots in which they can transmit data without collisions, and different nodes can receive different total amounts of time slot width by transmitting different numbers of series of state variable signals.

Abstract: A communication timing control apparatus for use in the nodes of a communication system includes a signal communication unit that transmits a state variable signal to neighboring nodes and receives state variable signals from those nodes. An external control signal, such as a beacon signal transmitted by a control node, is also received. The state variable signals indicate internal operating sates or timings of the nodes; the control signal indicates a basic transition rate. A timing decision unit causes internal state or timing transitions to occur at timings responsive to the basic transition rate and the received state variable signals, adjusting the transition timings so as to avoid signal collisions and to adapt to changing system conditions. Use of the control signal enables a steady timing state to be reached quickly.

Abstract: Each node in a communication system receives state variable signals from other nodes indicating the internal operating states or internal timing of the other nodes, and transmits a state variable signal indicating its own internal operating state or timing. Each node also determines whether each received state variable signal is valid. Transitions in the internal operating state or timing of a node take place at a basic transition rate but at times adjusted according to the valid state variable signals received from other nodes. A group of neighboring nodes transmitting data signals can thereby autonomously reach a steady state in which their data signals do not collide, without having their timing control disrupted by reflected state variable signals or other invalid state variable signals.

Abstract: A picture coder divides a frame of coded picture data into a critical segment including information needed for decoding other segments in the frame, and at least one non-critical segment including only information needed for its own decoding. The critical segment is made smaller than the non-critical segments, by controlling the segment size directly, for example, or by controlling a quantization step size or a forced intra-coding rate. The small size reduces the probability of the loss of critical information during packet transmission of the coded data, when each segment is transmitted as a separate packet. Alternatively, the size of all segments is reduced when conditions on the communication path indicate a high probability of transmission errors.

Abstract: In a picture transmission system that transmits a series of pictures from a coding apparatus to a decoding apparatus, each picture being coded and decoded with reference to a preceding picture, when a transmission error occurs, the decoding apparatus detects a decoding error caused by the transmission error and sends an error signal to the coding apparatus. The coding apparatus and decoding apparatus then both modify part of a reference picture affected by the decoding error, making identical modifications. A subsequent picture is coded and decoded with reference to the modified reference picture, thereby recovering from the transmission error with minimum loss of coding efficiency and picture quality.

Abstract: A picture decoding apparatus decodes a series of coded frames, each including a temporal reference. Past temporal references are used to estimate the temporal reference of the-current frame. If the temporal reference differs greatly from the estimated value, it is modified according to the estimated value. A coded frame may be divided into segments, each segment having its own temporal reference. In this case, the temporal references received in one coded frame are stored and compared, and a single temporal reference is selected for the coded frame. As a result, temporal-reference errors do not seriously disrupt the timing of the decoded picture.

Abstract: In a system that divides data frames into blocks and codes at least some of the blocks by intra-frame coding, errors in decoding these blocks are concealed by two methods: replacement of the erroneous block by its DC component, and replacement of the erroneous block with data from the preceding frame. The selection between these two methods is made according to one or more of the following criteria: reliability of the DC value; motion-vector size; motion-vector change from the preceding frame; and whether intra-frame coding was selected or forced. These selection criteria improve the probability of successful error concealment.

Abstract: Transmission units such as packets of coded data are received in a transmission layer, converted to coding units, supplied to a coding layer, and decoded in the coding layer. Errors in arriving transmission units are detected in the transmission layer. The results of error detection in the transmission layer are used when the coding units are decoded in the coding layer, preferably by having the transmission layer provide the coding layer with error information explicitly indicating which of the coding units are free of errors and which are not.

Abstract: A moving picture coded by inter-frame coding, with motion compensation, is decoded by an apparatus that stores at least two previously decoded frames, together with information identifying any erroneous parts of the previously decoded frames. The current frame is decoded with reference to a predicted frame assembled from decodable parts of the previous frames. When a motion vector points to a non-decodable part of a previous frame, it is extended farther back to a decodable part of an earlier frame. The extension can be made linearly, or by using previous motion vectors. Picture distortion caused by error propagation is thereby reduced.

Abstract: A transmission system transmits a series of coded frames from a transmitting device to a receiving device, using both intra-frame coding and inter-frame coding. The receiving device decodes the frames and sends acknowledgment signals to the transmitting device. The transmitting device selects the reference frame employed in inter-frame coding according to these acknowledgment signals. The method of reference frame selection can be varied according to an assessment of transmission channel quality. The assessment criteria, or the reference frame selection method itself, can be varied in response to input from a human user.

Abstract: Each of consecutively transmitted frames representing motion images is composed of a given number of blocks. A SAD cumulative value representing an image variation history is derived per block. Blocks to be refreshed, i.e. to be intraframe-coded, are selected based on the SAD cumulative values. Specifically, a given number of the blocks whose corresponding SAD cumulative values are larger among all the SAD cumulative values are selected, or those blocks whose corresponding SAD cumulative values are greater than a threshold value are selected. Thus, the blocks which actually require “refresh” can be preferentially refreshed.

Abstract: Each of consecutively transmitted frames representing motion images is composed of a given number of blocks. A SAD cumulative value representing an image variation history is derived per block. Blocks to be refreshed, i.e. to be intraframe-coded, are selected based on the SAD cumulative values. Specifically, a given number of the blocks whose corresponding SAD cumulative values are larger among all the SAD cumulative values are selected, or those blocks whose corresponding SAD cumulative values are greater than a threshold value are selected. Thus, the blocks which actually require “refresh” can be preferentially refreshed.

Abstract: A coder receives from a decoder the reception result of coded data, estimates the reception capability of the decoder and, based on the estimate result, updates accordingly the reference data on which prediction coding is to be based. This enables the reference data to be updated according to the reception capability of each decoder.