Multiplex communications – Fault recovery
Reexamination Certificate
1997-10-24
2001-10-09
Chin, Wellington (Department: 2664)
Multiplex communications
Fault recovery
C382S252000
Reexamination Certificate
active
06301222
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the transmission of image data and other types of signal data, and more particularly to techniques for transmitting data over lossy packet networks such that the impact of packet loss on reconstructed signal quality is minimized.
BACKGROUND OF THE INVENTION
In many data transmission applications, it is common for data to “hop” over network links of different capacities. For example, a typical scenario might involve a high-capacity network link switching over to a wireless link. Networks in which such hopping occurs are generally referred to as heterogenous networks. In heterogenous networks, packets may have to be dropped to accommodate a hop to a lower-capacity link. Packets could also be lost in the network due to transmission errors or congestions. If packet retransmission is not a viable option, due to real-time transmission constraints or other limitations, it is still important to provide the receiver with the most meaningful information possible despite the packet loss.
For applications in which image data is transmitted, a conventional approach to alleviating the packet loss problem is to send the images in a layered, multiresolution manner. This approach separates the data into parts of unequal importance. Packets are then labeled with an indication of the priority of the data contained therein. Thus, in a scenario in which a packet needs to be dropped, a network control mechanism may be used to discard the lowest priority packets first. At the receiver, the image is reconstructed from the high-priority essential information carried in packets which were labeled as such and therefore not dropped. A similar technique used in video data transmission is described in G. Karlsson and M. Vetterli, “Three-Dimensional Subband Coding of Video,” Proc. IEEE Int. Conf. Acoust., Speech and Signal Proc., pp. 1100-1103, New York, N.Y., April 1988. Although this technique does not require the introduction of additional data, it does require the additional complexity of examining the contents of each packet to determine priority. In addition, it is generally not applicable to transmission over the Internet, which is based on the Internet Protocol (IP) and does not provide priority, levels, and transmission over broadband networks based on asynchronous transfer mode (ATM), which can accommodate only two priority levels. These and other important networks may therefore require packet retransmission, redundant packet transmission or other inefficient techniques in order to ensure a desired quality level for the image reconstructed at the receiver.
SUMMARY OF THE INVENTION
The invention provides improved techniques for transmitting data in the presence of packet loss, without substantially increasing the processing overhead or the amount of data that must be sent. The techniques are suitable for use in conjunction with data transmission over a wide variety of lossy packet networks, including the Internet and broadband ATM networks, and may be used with raw or compressed image data, as well as video, audio and other types of data. The invention generally represents signal data in such a way that, when separated into packets, all packets are of approximately the same importance. As a result, when packets are randomly lost in a lossy packet network, the resulting degradation in the reconstructed signal is substantially uniform regardless of which packets are lost.
In an illustrative embodiment of the invention, a signal transmission system assigns portions of an image signal to packets such that each of the packets has an approximately equal cumulative image signal energy, and then transmits the packets over the network. In one possible implementation, the image is separated into subbands using a cosine-modulated orthonormal filter bank. An energy equalization algorithm is then used to assign the subbands to the packets such that the cumulative image signal energies of the packets are approximately equal. A DC band of the image may be separated from the remainder of the image, and inserted into each of the packets. A given packet also includes labels identifying each of the subbands in that packet, such that a receiver can direct the appropriate subbands to corresponding channels of a synthesis filter bank.
Another possible implementation of the transmission system includes a scrambler for scrambling the image such that pixels in the image are mapped to different spatial positions. This produces a whitened image which is subsequently separated into subbands. The use of the whitened image allows the subbands to be assigned deterministically to the packets. Each packet therefore need only include one label identifying which portion of the scrambled image it contains. The packets may also include an overall brightness indicator derived from a DC band of the scrambled image. A receiver uses the overall brightness indicator to scale a pre-set scrambled low-pass image, and adds the scaled low-pass scrambled image to an output of a synthesis filter bank which recombines the subbands of the scrambled image. The recombined scrambled image is then unscrambled to reconstruct the original image. Both of the above-described illustrative implementations provide graceful degradation in reconstructed image quality in the presence of packet loss. Alternative embodiments may be configured to process video, audio, speech and other types of data.
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Kovacevic Jelena
Ng Francis Man Lung
Chin Wellington
Duong Frank
Lucent Technologies - Inc.
Ryan & Mason & Lewis, LLP
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