Abstract:
A system and method for partitioning a bandwidth of a single channel among plural multimedia streams in a time varying manner. The partitioning is undertaken by dynamically establishing first and second bit rates respectively associated with first and second multimedia streams.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to multimedia transmission. 
     BACKGROUND 
     Multimedia such as video and audio can be transmitted over a number of paths, including cable, the Internet, and broadcast. For instance, satellite or terrestrial broadcast stations can be used to transmit multimedia to mobile computing devices such as mobile telephones. 
     Typically, multimedia data is voluminous, which means that significant transmission path bandwidth, unfortunately a finite resource, must be used. This is particularly the case for high fidelity multimedia, e.g., high resolution video. That is, the higher the quality of service being provided, the more bandwidth must be used. 
     As recognized by the present invention, several multimedia streams can be pooled together in a single channel. The channel might have a constant overall bandwidth in terms of bit rate, i.e., the number of bits that can be transmitted in the channel per unit time cannot exceed the “bandwidth” of the channel. Typically, each stream in the channel will be accorded a fixed fraction of the bandwidth. Accordingly, the bit rate for each multimedia stream typically is fixed. 
     As further recognized by the present invention, however, a multimedia stream might require a higher bit rate for a given quality of service (QOS) some of the time and a lower bit rate for the same QOS at other times. As an example, in a video stream, when the video sequence makes a hard cut (i.e., a large amount of pixel changes are taking place), a higher bit rate is required to achieve the same QOS as could be achieved at other times with a lower bit rate when relatively little action is taking place. Or, in terms of audio streams, a higher bit rate might be required at the beginning of a speech or music segment than at other times during the stream to achieve the same QOS. 
     Having made the above critical recognitions, the present invention further understands that one multimedia stream in a channel might require a relatively low bit rate at the same time that another stream in the channel might require a relatively high bit rate, and that it consequently would be desirable to allocate the limited overall bandwidth of the channel in a way that can account for this. 
     SUMMARY OF THE INVENTION 
     The invention is a system and method for partitioning a bandwidth of a single channel among plural multimedia streams in a time varying manner. 
     Accordingly, a method for multimedia data transmission includes pooling at least first and second multimedia data streams together in a single channel. The method also includes dynamically establishing first and second bit rates respectively associated with the first and second streams, in light of channel bandwidth constraints. The channel may be a broadcast channel. For the purposes of the non-limiting embodiment below, a “base layer” may be defined as the most important part of the bits stream which, if successfully received, decoded, and presented to the user, would result in a baseline level of video, audio, or other multimedia stream acceptable to the user. On the other hand, an “enhancement layer” would, when combined with the base layer, enhance or improve the quality, frequency, signal-to-noise ratio, etc. of the multimedia stream when presented to the user, compared to that of the base layer alone. 
     In one non-limiting embodiment, each stream defines a respective sequence of frames and each frame includes a base layer and at least one enhancement layer. At least one of the enhancement layers is dynamically selected for omission from the channel for at least some frames. The selection can be based on a quality of service (QOS) metric such as signal-to-noise ratio, or by program stream importance. In an illustrative non-limiting example, the enhancement layer selected for omission in a frame is the layer providing the highest overall QOS to its respective stream among the enhancement layers of the other streams that are being simultaneously transmitted in that frame. This limits the total bandwidth of the combined frames so that it does not exceed the channel bandwidth, while providing a minimum QOS to each stream. 
     In another non-limiting embodiment, the streams can be quantized jointly. In this circumstance, during quantization, a benefit of adding bits to the stream for each stage of quantization is evaluated, and bits are added (or not) to the stream based thereon, in light of channel bandwidth constraints. 
     As another alternative, the bit rates can be established to establish surplus channel bandwidth that is useful for sending ancillary data. 
     In another aspect, a computer executes logic that includes partitioning a bandwidth of a single channel among plural multimedia streams in a time varying manner. 
     In a further non-limiting embodiment, a tangible computer readable storage medium contains instructions to perform a method on a computer, with the method comprising partitioning a bandwidth of a single channel among plural multimedia streams in a time varying manner. In variations of this embodiment, the streams can be transmitted together in the single channel, and the partitioning act can be undertaken by dynamically establishing first and second bit rates respectively associated with first and second streams, the channel can be at least one of: a broadcast channel; a multicast channel; and a unicast channel. Optionally, each stream can define a respective sequence of frames and each frame can include at least a base layer and at least one enhancement layer, and the method can include dynamically selecting at least one of the enhancement layers for omission from the channel for at least some frames. In such an embodiment, the enhancement layer selected for omission can be the layer providing the highest overall QOS to its respective stream among the enhancement layers. Further options include those wherein: each stream is constituted using MPEG principles; the streams are quantized jointly, and the method includes, during quantization, for each stream evaluating a benefit of adding bits to the stream; the act of dynamically establishing first and second bit rates at least in part depends on the evaluating logic; the bit rates are established to provide surplus channel bandwidth useful for sending ancillary data; the method uses at least one relative importance metric; and the enhancement layer selected for omission is the layer used for enhancing a less important multimedia stream. 
     In still another aspect, a system for transmitting at least first and second multimedia streams in a single channel includes means for establishing a first bit rate for the first stream during a first frame of the first stream. The system also includes means for establishing a second bit rate for the first stream during a second frame of the first stream, with the first and second bit rates being different from each other. 
     The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of the present architecture; 
         FIG. 2  is a flow chart of the logic for dynamically establishing the bit rates of the streams during joint quantization of the streams; 
         FIG. 3  is a flow chart of the logic for dynamically establishing the bit rates of the streams when enhancement layers are used; and 
         FIG. 4  is a table schematically showing base layers and enhancement layers of two streams. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to  FIG. 1 , a system is shown, generally designated  10 , that dynamically establishes the bit rate of each of plural multimedia streams  12  that are combined by a stream combiner or stream combiner module  14  and broadcast together in a single channel by a transmitter or transimitter module  16 . More particularly, the bit rates of the streams  12  are dynamically established in accordance with the logic below by a bit rate establishing computer or module  18 , prior to being combined into a single channel and transmitted in accordance with principles known in the art. 
     The non-limiting preferred embodiment shown in  FIG. 1  shows a multimedia transmitter  16  that uses wireless means, and more particularly that uses code division multiple access (CDMA) principles. The streams can be broadcast to plural receivers if desired, or transmitted using point-to-point wireless transmission principles. It is to be understood that the present principles apply to other forms of wireless communication such as GSM, TDMA, wideband CDMA, OFDM, etc. as well as transmission of multimedia over cable systems, the Internet, etc. As used herein in the singular, “multimedia stream” means a single stream representing a single program, e.g., a single music piece or a single television show or movie potentially with accompanying text, images, etc. 
     As disclosed below, the dynamic allocation of bandwidth can depend on perceived levels of quality based on some objective measure. Quality of service (QOS) is one such measure. QOS can be measured in several ways, such as, for example, by signal to noise ratio as expressed in decibels. 
     Referring to  FIG. 2 , as indicated at block  20  the streams  12  may be quantized jointly with each other using, e.g., MPEG audio and video quantization principles known in the art. Under these circumstances the logic moves to block  22  which indicates that at each stage of quantization, e.g., for each frame to be quantized, blocks  24  and  26  are undertaken. 
     Moving to block  24 , the benefit of adding more bits to each stream for the stage under test than are currently allocated are evaluated. This evaluation can be done iteratively, starting with a default number of bits that represents a minimum QOS, for a predetermined number of iterations, or until a predetermined “benefit” threshold is reached, and always under the constraint that the total number of bits per unit time allocated to the plural streams remains within the channel bandwidth. As mentioned above, the evaluation can be based on a perceived level of quality based on some objective measure such as QOS as indicated by, for example, signal to noise ratios as expressed in decibels. 
     Once the evaluations for the stage under test are completed for each stream, the logic moves to block  26 . At block  26 , bits are added to the stream or streams that show the highest improvement in benefit from the addition of bits, within the constraint of the channel&#39;s bandwidth. Stated differently, the bit rates of the streams are dynamically optimized for each frame using a user-defined protocol. 
     “Quantization” is discussed below. It should be noted that quantization could be fixed but may also be variable in addition to the number of layers used, and that in some embodiments bandwidth allocation consequently can be fully independent of quantization. 
     Some schemes such as MPEG4 allow for so-called “enhancement layers” of bits during quantization. As mentioned above, a “base layer” is provided for each frame for each stream that represents a minimum amount of data necessary to render the frame, with enhancement layers for the frame being available to add fidelity to the image or sound provided by the base layer. The benefit provided by the increased bit rate resulting from the addition of the enhancement layers can be indicated along with the enhancement layers themselves. 
     Recognizing this, block  28  of  FIG. 3  shows that the base layer of each frame of each stream, along with the associated enhancement layer or layers, are received at block  28 . Also, a QOS measure is provided along with each layer that indicates the amount of “benefit” associated with the layer. At block  30 , to conserve overall channel bandwidth the enhancement layer(s) that add the least benefit for the particular set of stream frames (for “n” streams, there will be “n” frames in the set) are discarded. Other metrics of bandwidth allocation can be used, such as the relative importances of the competing streams, number of subscribers for competing streams, presence of commercials in the streams, and number of users in a particular zone of coverage who desire a particular stream. Indeed, in some circumstances it may be desirable to remove a particular stream altogether, i.e., base layer and enhancement layer. 
       FIG. 4  illustrates one preferred, non-limiting logic for undertaking this. For illustration purposes,  FIG. 4  assumes that two streams are to be transmitted in a single channel, with each stream having a base layer for each frame and potentially two enhancements layers per frame. The numbers in the table of  FIG. 4  represent QOS and specifically cumulative signal-to-noise (SNR) ratios as represented in decibels. 
       FIG. 4  also assumes that the dynamic bit rate protocol being used essentially seeks to establish a minimum QOS for each stream for each frame, and that the channel has a bandwidth that is sufficient only to carry five of the six layers at a time, i.e., FIG.  4  assumes that the channel can carry only five layers per transmission period. Accordingly, the enhancement layer providing the highest SNR for a period is omitted in the exemplary non-limiting protocol represented by  FIG. 4 . That is, the second enhancement layer of the first stream provides a cumulative db level of “17” for periods 1, 2, 4, and 5, which is higher than the cumulative db level provided by any other layer for those periods, and so is discarded for periods 1, 2, 4, and 5. On the other hand, the second enhancement layer of the second stream provides a cumulative db level of “16” for period 3, which is higher than the cumulative db level provided by any other layer for period 3, and so is discarded for the third period. 
     It is to be understood that other protocols and other measures of QOS can be used without departing from the scope of the present invention. For example, any enhancement layer providing a cumulative SNR for any particular frame or period that is higher than a predetermined threshold can be omitted. 
     Or, as another example, if stream A has a base layer quality of four (4) db and, with an enhancement layer, a quality of eight (8) db, and stream B has a base layer quality of ten (10) db and, with an enhancement layer, a quality of thirty (30) db, one of two heuristics can be applied to determine which enhancement layer to omit. If the enhancement providing the greatest overall benefit of any enhancement layer is to be maintained, the enhancement layer of stream A would be omitted. However, if it is desired to provide the best quality for the worst stream, the enhancement layer for stream B can be omitted. 
     Alternatively to allocating the entire channel bandwidth to the multimedia streams, the principles above can be used to reduce the bandwidth needed by each stream so that surplus channel bandwidth is obtained. The surplus bandwidth can be used to send real-time ancillary data to augment one or more of the streams (e.g., character overlays, graphics, etc.) or to send non-real time ancillary data such as a picture display during a song or ordering information, to augment a stream. Yet again, the surplus bandwidth can be used to send other broadcast data, system control data, programming data, encryption keys, subscription or programming information, etc. 
     While the particular JOINT TRANSMISSION OF MULTIPLE MULITMEDIA STREAMS as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. ′112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited as a “step” instead of an “act”.