Picture coder, picture decoder, and picture transmission system in which acknowledgment signals are sent in packed form

An improved decoder of the type having an input means for receiving coded data representing a series of frames from a coder through a first channel, and a decoding means for decoding the coded data by intra-frame decoding and inter-frame decoding, wherein said decoding means decodes each frame in the series of frames as a certain number of blocks, the certain number being an arbitrary positive integer, and performs inter-frame decoding by decoding a block in one frame with reference to a corresponding block in preceding frame specified as a reference frame in the coding data, the reference frame being changed when a decoding error occurs, said improved coder comprising:

• a decoding-error memory means for storing decoding-error information about the blocks:
• an acknowledgment signal packing mean, coupled to said decoding-error memory means, for constructing an acknowledgment signal by packing the decoding-error information of a plurality of the blocks into the acknowledgment signal, the acknowledgment signal identifying the blocks in the plurality of blocks individually;
• and
• an acknowledgment signal transmitting means, coupled to said acknowledgment signal packing means, fro transmitting the acknowledgment signal to said coder through a second channel.

An improved method of transmitting a series of frames from a transmitting device, of the type in which each frame in the series of frames includes a certain number of blocks, the certain number being a positive integer, and at least some of the blocks in at least some of the frames are coded by inter-frame coding in the transmitting device, transmitted to the receiving device, then decoded by inter-frame decoding in the receiving device, the inter-frame coding and inter-frame decoding being performed with reference to corresponding blocks in a preceding frame designated as a reference frame, said improved method comprising:

• packing decoding-error information about a plurality of the blocks into an acknowledgment signal at the receiving device, the decoding-error information indicating whether decoding errors occurred in respective blocks;
• transmitting the acknowledgment signal from the receiving device to the transmitting device;
• unpacking the acknowledgment signal at the transmitting device, thereby obtaining decoding-error information about individual blocks in the plurality of blocks;
• and
• selecting reference frames at the transmitting device according to the decoding-error information.