Abstract:
A wireless communication system for transmitting uncompressed video pixels from a transmitter to a receiver over a wireless channel is provided. The transmitter includes an interleaver that interleaves the video pixels into interleaved pixels, and an encoder that convolutionally encodes the interleaved pixels at the transmitter before transmission to the receiver. The receiver includes a decoder that decodes the encoded pixels, and a deinterleaver that deinterleaves the decoded pixels. When the video pixels include pixel errors, such interleaving and deinterleaving reduces pixel error clustering and improves video quality.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 60/785,773, filed on Mar. 24, 2006, incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to uncompressed video signal processing and, in particular, to pixel interleaving for improving video signal quality. 
       BACKGROUND OF THE INVENTION 
       [0003]    With the proliferation of wireless communication systems, it has become highly desirable to transmit video information among wireless stations. One application of wireless transmission of video is transmitting uncompressed video from a source station to a destination station wirelessly. 
         [0004]    To provide reliable wireless transmission, convolutional codes are often used to correct channel errors due to channel fading, shadowing, noise and interference. 
         [0005]    Although most channel errors are corrected using convolutional codes, residual pixel errors remain and tend to cluster together. Such error patterns are easily identified by human eyes and significantly degrade the perceived quality of the video. 
         [0006]    Residual pixel error clustering may also occur when pixel partitioning is used to take advantage of spatial correlations for improving uncompressed video transmission reliability. In such cases, neighboring pixels are divided into different partitions and different partitions are transmitted as different packets separately over lossy wireless channel. At a destination station, the packets are used for reconstructing a nearby erroneous packet. However, in certain areas of a packet where the spatial correlation is not high enough, a reconstructed version is not as accurate, thereby resulting in noticeable pixel errors that typically form clustered patterns. 
         [0007]    As such, residual pixel errors are often clustered together due to convolutional encoding or spatial reconstruction based on nearby partitions. Conventionally, to improve video quality, an additional outer code, or some stronger convolutional code, is required to correct such residual errors. Alternatively, a higher transmit power is required to provide stronger protection against hostile channel conditions. Such approaches for improving video quality add certain non-negligible operational and equipment complexity and cost. There is, therefore, a need for a method and system for improving transmission quality for uncompressed video, with reduced complexity. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a method and system for improving transmission of video pixels from a transmitter to a receiver over a wireless channel. In one embodiment, this is achieved by obtaining the video pixels from a video source, interleaving the video pixels into interleaved pixels, convolutionally encoding the interleaved pixels into encoded pixels and transmitting the encoded pixels to the receiver in units of packets (or sub packets). When the video packets/sub packets include pixel errors, interleaving reduces the pixel error clustering effect. 
         [0009]    In one example, interleaving the video pixels into interleaved pixels further includes block interleaving the video pixels into interleaved pixels. In another example, interleaving the video pixels into interleaved pixels further includes randomly interleaving the video pixels into interleaved pixels. Yet in another example, interleaving the video pixels into interleaved pixels further includes convolutionally interleaving the video pixels into interleaved pixels. 
         [0010]    The receiver decodes the transmitted pixels and deinterleaves the decoded pixels. Based on the interleaving process implemented at the transmitter, the deinterleaving process at the receiver can include deinterleaving the decoded pixels by block deinterleaving, random deinterleaving, convolutional deinterleaving, etc. 
         [0011]    These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a functional block diagram of a wireless communication system including a wireless transmitter and a wireless receiver that implements pixel interleaving for wireless video transmission, according to an embodiment of the present invention. 
           [0013]      FIG. 2A  shows an example of residual pixel errors that tend to cluster together as a result of convolutional decoding without pixel interleaving, or as a result of packet (sub packet) reconstruction based on pixel partitioning. 
           [0014]      FIG. 2B  illustrates an example of the effect of pixel interleaving, according to an embodiment of the present invention, wherein clustering of error pixels is substantially reduced. 
           [0015]      FIG. 3  shows an example of block pixel interleaving, according to an embodiment of the present invention. 
           [0016]      FIG. 4  shows an example of random pixel interleaving, according to an embodiment of the present invention. 
           [0017]      FIG. 5  shows an example of convolutional pixel interleaving, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The present invention provides a method and system for pixel interleaving for improving video signal transmission quality from a transmitter to a receiver over wireless communication channels. As noted, most wireless channel errors can be corrected at a receiver using convolutional codes, while certain residue pixel bit errors remain. It has been observed, however, that the residue bit errors typically form several clusters. When the erroneous bits are collected to reconstruct video pixels at the receiver, the pixel errors henceforth form clusters as well. 
         [0019]    Accordingly, in order to reduce such clustering of pixel errors, in one embodiment the present invention provides pixel interleaving at the transmitter, and corresponding pixel deinterleaving at the receiver. 
         [0020]      FIG. 1  shows a functional block diagram of an example wireless communication system (e.g., communication network)  100 , according to the present invention, including a video source  101 , a transmitter (sender) station  102 , a receiver (destination) station  104  and a video sink  105  (e.g., video display). Video signals from the video source  101  are transmitted from the transmitter  102  to the receiver  104  over a wireless communication channel, for consumption by the video sink  105 . 
         [0021]    The transmitter  102  includes a pixel interleaver  108 , a convolutional encoder  110 , a channel interleaver  112  and a constellation mapper  114 . The receiver  104  includes a constellation demapper  116 , a channel deinterleaver  118 , a convolutional decoder  120  and a pixel deinterleaver  122 . The pixel interleaver  108  can be implemented in either a physical layer (PHY layer) or in an upper video processing layer of the transmitter  102 . Similarly, the pixel deinterleaver  122  can be implemented in either a physical layer or in an upper video processing layer of the receiver  104 . 
         [0022]    By placing the pixel interleaver  108  between the video source  101  and the convolutional encoder  110  in the transmitter  102 , the pixel interleaver  108  scrambles the pixel errors such that when the transmitted pixels are deinterleaved by the pixel deinterleaver  122  at the receiver  104  and displayed on the display  105 , the pixel errors are, e.g., randomly positioned, and are located far from each other. This makes the displayed pixel errors less identifiable by human eyes. This is illustrated by example in  FIGS. 2A-B . 
         [0023]      FIG. 2A  shows an example of residual pixel errors that tend to form a cluster  200  as a result of convolutional decoding or as a result of spatial reconstruction, and are therefore, easily identified by human eyes. In this example, the cluster  200  includes 3×3=9 residue pixel errors. Without pixel interleaving according to the present invention, the pixel errors that form the cluster  200  are visible to the human eyes when displayed. 
         [0024]      FIG. 2B  illustrates an example of the effect of pixel interleaving according to the present invention, wherein clustering of error pixels is substantially reduced. By the action of the pixel interleaver  108  and the corresponding action of the pixel deinterleaver  122 , the displayed error pixels  200  are positioned, e.g., randomly and essentially far apart from each other (spatially spread out) as pixels  204  when displayed. 
         [0025]    Accordingly, the error pixels no longer form a cluster, and are therefore, considerably less noticeable by human eyes. This is because human eyes detect pixel errors when the error area is large enough, and the error magnitude is over a certain threshold. This is especially true when the video signal has a high resolution (hence each pixel is of a very small size) and when the video is viewed from several meters away. 
         [0026]    The pixel interleaver  108  can be implemented in different ways. Example implementations include a block interleaver, a random interleaver and a convolutional interleaver. The pixel deinterleaver  122  in the receiver  104  is selected accordingly to perform a corresponding reverse function of the pixel interleaver  108 . 
         [0027]      FIG. 3  shows an example block-interleaving process  300  implemented by the pixel interleaver  108 , for interleaving a set of input pixels  302  in a frame that is input from the source  101 . The pixels  302  are read in (input) sequentially into a buffer (memory array)  304  in a column-by-column manner (top-bottom) for interleaving, and the interleaved pixels are then written out (output) of the buffer  304  sequentially in a row-by-row manner (left-right), as shown. 
         [0028]    A corresponding block-deinterleaving process in the pixel deinterleaver  122  of the receiver  104  restores the pixels. 
         [0029]      FIG. 4  shows an example random-interleaving process  350  implemented by the pixel interleaver  108 , for interleaving a set of input pixels  352  in a frame that is input from the source  101 . In random interleaving, there is no specific order in reading in, and writing out, the pixels. 
         [0030]    For example, in  FIG. 4 , the pixels  350  can be read in sequentially into a buffer  354  but written out of the buffer  354  randomly. It is also possible to read in the pixels randomly, but write them out sequentially. It is also possible to read in pixels randomly and write out the pixels randomly. All of the operations in  FIGS. 3-4  are carried out on a pixel level (not on a bit level). 
         [0031]    A corresponding random-deinterleaving process in the pixel deinterleaver  122  of the receiver  104  restores the pixels. 
         [0032]    In another example, a convolutional interleaving process is implemented by the pixel interleaver  108 . The convolutional interleaving process rearranges the pixels in a frame such that pixels are spatially dispersed before transmission. 
         [0033]      FIG. 5  shows an example convolutional interleaving process  400 , wherein pixels in an input pixel stream are parsed by a parsing function  402  into multiple paths for spatial dispersion. In the example of  FIG. 5 , four paths  404 A-D are shown, wherein the pixel on the first path  404 A is not delayed, while the pixels on the subsequent paths  404 B-D are delayed by D time units, 2D time units and 3D time units, respectively, where D is a positive integer. 
         [0034]    The pixels from the different paths  404 A-D are then processed by an output multiplexing function  408  that multiplexes the pixels from different paths into a pixel stream before transmission. 
         [0035]    A corresponding convolutional deinterleaving process in the pixel deinterleaver  122  of the receiver  104  restores the spatial positions of the dispersed pixels. 
         [0036]    Accordingly, the present invention provides a process for wireless transmission of video information, (such as uncompressed video) which reduces the clustering of pixel errors by using pixel interleaving at the transmitter, and corresponding pixel deinterleaving at the receiver. 
         [0037]    As is known to those skilled in the art, the aforementioned example architectures described above, according to the present invention, can be implemented in many ways, such as program instructions for execution by a processor, as logic circuits, as an application specific integrated circuit, as firmware, etc. The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.