WO2001035671A1 - Method of transmission of image by cdma system - Google Patents

Method of transmission of image by cdma system Download PDF

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Publication number
WO2001035671A1
WO2001035671A1 PCT/CN2000/000336 CN0000336W WO0135671A1 WO 2001035671 A1 WO2001035671 A1 WO 2001035671A1 CN 0000336 W CN0000336 W CN 0000336W WO 0135671 A1 WO0135671 A1 WO 0135671A1
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Prior art keywords
image
coding
transmission
rate
transmission method
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PCT/CN2000/000336
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English (en)
French (fr)
Inventor
Yingtao Li
Shengxi Pan
Bingyu Qu
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Huawei Technologies Co., Ltd.
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Application filed by Huawei Technologies Co., Ltd. filed Critical Huawei Technologies Co., Ltd.
Priority to US09/857,853 priority Critical patent/US6407990B1/en
Priority to EP00967508A priority patent/EP1229737A4/en
Priority to AU77693/00A priority patent/AU7769300A/en
Priority to JP2001537286A priority patent/JP2003514465A/ja
Publication of WO2001035671A1 publication Critical patent/WO2001035671A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/136—Incoming video signal characteristics or properties
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters
    • H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
    • H04W52/265—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account the quality of service QoS
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/103—Selection of coding mode or of prediction mode
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
    • H04N19/63—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters
    • H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
    • H04W52/262—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account adaptive modulation and coding [AMC] scheme
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B2201/00—Indexing scheme relating to details of transmission systems not covered by a single group of H04B3/00 - H04B13/00
    • H04B2201/69—Orthogonal indexing scheme relating to spread spectrum techniques in general
    • H04B2201/707—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation
    • H04B2201/70703—Orthogonal indexing scheme relating to spread spectrum techniques in general relating to direct sequence modulation using multiple or variable rates
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/124—Quantisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC

Definitions

  • the present invention relates to the field of image compression coding technology and code division multiple access (CDMA) mobile communication technology, and in particular, to a method for implementing image compression coding and transmission that can adapt to the soft capacity characteristics of a CDMA system.
  • CDMA code division multiple access
  • a certain degree of compression can be performed on the image data under the condition that a certain degree of distortion is allowed.
  • the compression ratio is different due to the different image properties. For example, when the size of entropy is different, an image with large entropy should be compressed more, and an image with lower entropy should be compressed less. For another example, for a moving image, if the change is slow, the compression ratio should be higher than the normal value. Is to reduce the frame rate of image encoding and decoding. Therefore, for different image encoding frames, in order to ensure the quality of image transmission, different image compression ratios should be used, that is, the image encoding rate should be changed accordingly.
  • CDMA code division multiple access
  • system capacity is a concept of soft capacity.
  • the system operator can increase the frame error rate during peak traffic periods, thereby increasing the number of available channels.
  • CDMA is a self-interference system, when the load on its neighboring cell is light, the interference experienced by this cell is corresponding. If it is reduced, the capacity can be increased appropriately.
  • the features of soft capacity also include residential breathing function and so on.
  • the digital image coding algorithm uses a fixed rate algorithm controlled by an external command, such as the CCITT H.261 algorithm.
  • an external command control algorithm cannot consider the nature of the image itself.
  • the coding rate is a A fixed amount
  • the existing fixed-rate algorithm controlled by external commands cannot consider the nature of the image itself, so that the characteristics of the soft capacity of the CDMA system cannot be used well. Summary of the invention
  • the purpose of the present invention is to solve the problem that the fixed-rate coding algorithm cannot adapt to the characteristics of the system's soft capacity when the image transmission of the CDMA system is adopted, and proposes to change the image coding rate according to the specific characteristics of the image, so that the system capacity in the statistical sense is increased. Image transmission method.
  • the present invention provides an image transmission method for maintaining image transmission quality and increasing capacity of a code division multiple access (CDMA) mobile communication system.
  • the method includes at least the following steps:
  • the present invention provides an image transmission method for maintaining image transmission quality and increasing capacity of a code division multiple access (CDMA) mobile communication system.
  • the method includes at least the following steps:
  • variable rate coding according to the nature of the image
  • the present invention provides an image transmission method for maintaining image transmission quality and increasing capacity of a code division multiple access (CDMA) mobile communication system.
  • the method includes at least the following steps:
  • variable rate coding according to the nature of the image
  • the above-mentioned variable rate coding may use a threshold subband coding or a differential prediction coding.
  • the thresholded subband coding method includes at least the following steps:
  • the compression coding can use conventional compression coding.
  • the decomposed image may be further subjected to threshold subband coding.
  • the rate of image coding may be reduced by increasing the set threshold to increase the capacity of the system.
  • the differential prediction encoding method includes at least the following steps:
  • the calculation time is the image difference between the two frames before and after
  • a high compression ratio algorithm is used. Since the CDMA system is a self-interference system, its capacity is a concept of soft capacity. There is a certain proportional relationship between the coding rate and the transmission power. When the coding rate is changed and the transmission power is changed, the system capacity can be obtained accordingly. increase. Therefore, under the condition of maintaining the image transmission quality, if the compression rate of the encoding rate is changed and the encoding rate is changed according to the specific properties of the image, the compression rate of the image encoding may be further increased. This makes it possible to increase the soft capacity of a CDMA transmission system in a statistical sense. However, the existing external command control algorithm does not consider the nature of the image itself, so that the soft capacity characteristics of the CDMA system cannot be used well.
  • variable-rate image compression coding transmission method of the present invention By adopting the variable-rate image compression coding transmission method of the present invention, the stability of image properties can be maintained, and the capacity of a CDMA system in a statistical sense can be increased.
  • FIG. 1 is a schematic diagram of a thresholded subband coding process according to the present invention.
  • FIG. 2 is a flowchart of increasing the system capacity by changing the spreading factor according to the present invention.
  • FIG. 3 is a flowchart of using the intermittent transmission method without changing the spreading factor of the present invention.
  • Mode for Carrying Out the Invention The present invention is described in detail below with reference to the drawings.
  • the present invention adopts an encoding method that uses the image's own properties to change the compression ratio of an image, and changes the encoding rate accordingly, thereby maintaining stable image quality.
  • the above-mentioned object is achieved by encoding an image by using a band-type subband coding image compression method, a differential prediction coding image compression method, and the like.
  • the process of subband coding using a thresholded subband coding class image compression algorithm is shown in Figure 1.
  • the specific process is as follows: (a) The original image A is decomposed into four parts: 1, 2, 3, and 4; each part has different properties. For example, after using a fast Fourier transform (FFT), the frequency characteristics of each part of the image are different. These transforms also include discrete cosine transform (DCT), wavelet transform, etc., each part of the transformed image has correspondingly different properties.
  • FFT fast Fourier transform
  • DCT discrete cosine transform
  • the part of 1 is basically a reduced image of image A, and the data is similar to that of image A; only a small part of the data of 2 and 3 is larger, and the other is close to zero; and the data of 4 is almost all close to zero.
  • a threshold X is set.
  • the threshold X can be set to 0.2.
  • the absolute value of the data in images 1, 2, 3, and 4 is less than This value makes them zero.
  • Subband coding can be continued for images 1 or 2, 3, and 4. In this way, they are broken down into 4 pieces each. Since the data of images 2, 3, and 4 are basically close to zero, generally only image 1 is sub-band encoded.
  • Differential prediction coding is particularly suitable for moving images.
  • the specific process is to set a moving image.
  • a and B are two frames before and after.
  • d distance (A, B), which represents the difference between A and B images. This distance function should satisfy the visual relationship of the images.
  • a threshold value X is set according to the visual characteristics of the human eye and a certain statistical algorithm.
  • the function of this threshold value is similar to the threshold of subband coding.
  • d> x it indicates that the difference between A and B images is large. If you ca n’t compress too much, use a low compression ratio algorithm and set the compression ratio to kl. When 0 ⁇ , it means that there is not much difference between A and B images. Increasing compression will not affect the image quality. Therefore, a high compression ratio algorithm is used. Let its compression ratio be k2. From the above, k] ⁇ k2.
  • the values of kl and k2 and the specific value of threshold X are related to the requirements of the application system.
  • the threshold subband coding mode and differential prediction coding mode By changing the threshold subband coding mode and differential prediction coding mode, it is possible to change the compression ratio and coding rate according to the nature of the image, thereby maintaining the stability of the image quality and making it possible to increase the statistical capacity of the CDMA system. Because, in a general image coding algorithm, if a certain image is compiled, the coding rate of a certain frame of image is kl, and the spreading gain is SF1. In the case of changing the rate coding, the coding rate becomes k2 If the spreading gain is SF2, the following relationship exists:
  • E b energy per bit at the source of the transmitted digital signal
  • N 0 noise power spectral density in the channel
  • E c In the spread spectrum communication, the energy of the spreading chip after spreading the digital signal is set to 101ogk2 / kl.
  • the spreading gain and transmission power of the system need to be changed.
  • the capacity of the channel can be increased. For example, when the rate of image coding is reduced by half, the transmission power is also reduced by half. From a statistical sense, it means that it can increase regular users by 50%.
  • the system can also use Intermittent sending technology. Intermittent transmission technology means that signals are sometimes transmitted over a small period of time, and sometimes signals are not transmitted. Since the image frame rate cannot be noticed as long as the frame rate is greater than 25 frames per second, as long as the discontinuity time is less than 1/25 of a second, people cannot notice it.
  • the process of intermittent transmission is shown in FIG. 3, and the system is first initialized; then the variable rate coding is performed according to the nature of the image, and the variable rate coding here is the aforementioned subband coding with threshold and / or differential prediction coding; Then, the discontinuity point is calculated according to the image coding rate. Specifically, the starting point and the end point are calculated first, and then the free space between them is calculated, so that the discontinuity point can be known. Then the interleaving process is performed, that is, the interleaving algorithm is used for the bits that are sent intermittently. Randomize it in the frame and rearrange it; finally, add it to the spreading address code by spreading, and then transmit it to complete the encoding transmission process of one frame. After that, the number of frames is increased by 1, and the steps after the initialization are returned, and the next frame is encoded and transmitted.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Multimedia (AREA)
  • Quality & Reliability (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Mobile Radio Communication Systems (AREA)

Description

码分多址通信系统的图像传输方法
技术领域
本发明涉及图像压缩编码技术及码分多址 （CDMA )移动通信技术 领域， 特别涉及一种能适应 CDMA 系统软容量特点的图像压缩编码及 传输的实现方法。 发明背景
图像压缩编码技术中， 对于一般的图像， 在允许一定失真度的条件 下， 可对图像数据进行一定限度的压缩。 同时， 考虑每一个具体的图像 编码帧时， 由于其图像性质的不同， 压缩比也有所不同。 例如当熵的大 小不同时， 熵大的图像应该多压缩， 而熵小的图像应该少压缩； 又例如 对于移动图像， 如果其变化较慢， 则压缩比应该比正常值高， 具体的操 作可以是降低图像编译码的帧率。 因此， 对于不同的图像编码帧， 为了 保证图像传输的质量， 应该采用不同的图像压缩比， 亦即其图像编码速 率也应作相应的变化。
另一方面， 码分多址（CDMA )数字移动通信系统以其新颖的技术 显示了巨大的发展潜力。 在 CDMA 系统中， 系统容量是一个软容量的 概念。 例如： 系统经营者可在话务量高峰期将误帧率提高， 从而增加可 用信道数， 而且由于 CDMA 是一个自干扰系统， 当其相邻小区负荷较 轻时， 本小区所受的干扰相应减小， 容量就可适当增加。 体现软容量特 性的还有小区呼吸功能等等。
然而，在 CDMA系统的图像传输过程中，数字图像编码的算法采用 外部命令控制的固定速率算法， 如 CCITT H.261算法， 这样的外部命令 控制的算法无法考虑图像本身的性质， 编码速率是一个固定量， 这在保 持图像传输质量大于某一门限的前提下， 限制了统计意义上的 CDMA 系统容量的提高。 这是因为在保持图像传输质量的前提下， 即保持信道 传输质量不变的情况下， 图像编码速率与发射功率之间存在一定的比例 关系， 改变编码速率， 相应地调整发射功率， 就可以使增加统计意义上 的系统容量成为可能。 而现有的外部命令控制的固定速率算法无法考虑 图像本身的性质， 使得 CDMA 系统的软容量的特性未能得到很好的利 用。 发明内容
本发明的目的是为了解决 CDMA 系统的图像传输采用固定速率编 码算法不能适应系统软容量特点的问题， 提出一种才 据图像的具体性质 改变图像编码速率， 使统计意义上的系统容量得到增加的图像传输方 法。
本发明提供一种保持图像传输质量、 增加码分多址 （CDMA )移动 通信系统容量的图像传输方法， 该方法至少包括以下步骤：
( a )根据图像的性质进行变速率编码；
( b )保持信道传输质量不变， 通过改变扩频因子， 调节发射功率或 保持扩频因子不变， 采用间断发射方式增加系统的容量。
本发明提供一种保持图像传输质量、 增加码分多址（CDMA )移动 通信系统容量的图像传输方法， 该方法至少包括以下步骤：
( 1 )依据图像性质进行变速率编码；
( 2 )根据图像编码率计算扩频因子；
( 3 )根据扩频因子改变发射功率；
( 4 )通过扩频发射出去；
( 5 ) 重复步骤（ 1 ) 至（ 5 )， 进行后续帧的编码发射。 本发明提供一种保持图像传输质量、 增加码分多址 （CDMA)移动 通信系统容量的图像传输方法， 该方法至少包括以下步骤：
( 1 )依据图像性质进行变速率编码；
(2)根据图像编码率计算间断点；
(3)对间断发送的信号， 采用交织算法在帧内将其随机化， 并重新 排列；
(4)通过扩频发射出去；
( 5 ) 重复步骤（ 1 ) 至 （ 5 ), 进行后续帧的编码发射。
上述的变速率编码可以采用带阈值的子带编码或差分预测编码。 所述的带阈值的子带编码方法， 至少包括以下步骤：
( 1 )将原始图像分解为性质不同的图像；
( 2 )根据人眼的视觉特性及统计结果设定阈值；
(3)对图像进行编码， 小于所述阈值的数据为零；
( 4 )对非零量进行量化和压缩编码，该压缩编码可以采用常规的压 缩编码。
进一步可对分解后的图像继续进行带阈值的子带编码。
在所述的带阈值的子带编码方法中， 可以通过增大所设定的阈值来 降低图像编码的速率， 以增加系统的容量。
所述的差分预测编码方法， 至少包括以下步骤：
( 1 )计算时间上是前后两帧的图像差异；
( 2 )根据人眼的视觉特性及统计结果设定门限值；
(3) 当 （1 ) 中计算所得的图像差异大于所述门限值时， 则采用低 压缩比算法；
(4) 当 （1 ) 中计算所得的图像差异小于所述门限值时， 则采用高 压缩比算法。 由于 CDMA系统是一个自干扰系统， 其容量是一个软容量的概念， 其编码速率与发射功率间存在一定的比例关系， 在改变编码速率， 并改 变发射功率的情况下， 系统的容量可以相应得到增加。 因此， 在保持图 像传输质量的条件下， 如果根据图像的具体的性质改变编码速率的压缩 比， 并改变编码速率， 则图像编码的压缩率有进一步增加的可能。 可以 由此使增加统计意义上的 CDMA传输系统的软容量成为可能。 而现有 的外部命令控制的算法因未考虑图像本身的性质， 使得 CDMA 系统的 软容量的特性未能得到很好的利用。
通过采用本发明的变速率的图像压缩编码传输方式， 可以保持图像 性质的稳定， 并使统计意义上的 CDMA系统容量得到增加。 附图简要说明
图 1是本发明的带阈值子带编码过程的示意图。
图 2是本发明的改变扩频因子增加系统容量的流程图。
图 3是本发明的不改变扩频因子采用间断发射方式的流程图。 实施本发明的方式 下面结合附图对本发明进行详细描述。 本发明采用利用图像自身性质改变图像的压缩比的编码方法， 并使 编码速率也相应改变， 从而保持图像质量稳定。 具体来说， 是通过带阔 值的子带编码类图像压缩方法和差分预测编码的图像压缩方法等对图 像进行编码， 来达到上述目的。
采用带阈值的子带编码类图像压缩算法子带编码的过程如图 1 所 示， 其具体过程为： ( a )将原始图像 A分解为 1、 2、 3、 4四部分图像， 每一部分的性 质不同， 例如采用快速傅立叶变换（FFT )后， 每部分图像的频率特性 不同。 这些变换还包括离散余弦变换（DCT )、 小波变换等， 变换后的 每部分图像具有相应不同的性质。其中假设 1的部分基本上是图像 A的 缩小像， 其数据和图像 A的数据很类似； 2和 3的数据只有一小部分比 较大， 其它接近于零； 而 4中数据几乎全接近零。
( b )根据人眼的视觉特性及统计结果， 设定一个阈值 X , 例如可 以设定阈值 X为 0.2， 当经过子带编码后， 图像 1、 2、 3、 4中的数据的 绝对值小于这个值时， 则令它们为零。
对经过 )和（b )二个步骤的数据进行一些通常的编码， 当 1、 2、 3、 4中的零数据越多， 编码后的数据越少。 由于图像的性质不同， 例如 其熵值不同， 对所设定的同一个阔值， 其压缩比也不同。 例如图像 2、 3 中接近零的数据多， 因此其压缩比也大， 而图像 4由于几乎全接近零， 因此根据设定的阈值使其为零。
这样， 通过设定使小于该阈值的数据为零， 而只利用余下的非零数 据表示图像， 用来表示图像的数据量就被压缩。
可以对图像 1或者 2、 3、 4继续进行子带编码。 这样它们每个又分 解为 4块。 由于图像 2、 3、 4的数据基本接近于零， 因此一般只对图像 1进行子带编码。
由于图像的性质， 熵小的图像接近于零的数据较多， 而熵大的图像 接近于零的数据较少。 因此， 当设定同一个阈值时， 对不同的图像来说， 熵小的图像的压缩比要高， 其相应的编码速率较低； 而熵大的图像压缩 比要低， 其相应的编码速率较高。
当设定较大的阈值时， 可以舍弃更多的细节信息， 在图像质量下降 不大的条件下， 使图像压缩比更高， 而编码速率更低。 由于图像的压缩比和编码速率有一定的比例关系， 因此， 通过对性 质不同例如熵的大小不同的图像， 采用固定阈值的子带编码， 使不同性 质的图像其图像压缩比也不同， 编码速率也随着变化。 可以由此达到改 变编码速率的目的， 并使解码后的图像质量基本恒定。
差分预测编码特别适用于移动图像， 其具体过程为， 设定移动图像
A和 B在时间上是前后两帧， 令 d = distance ( A， B ), 表示 A、 B图像 的差异， 此距离函数应满足图像视觉关系。
根据人眼的视觉特性和某种统计算法设定一门限值 X , 此门限值的 作用类似于子带编码的阔值， 当 d〉x时，表明 A、 B图像间的差异较大， 不能压缩太多， 则采用低压缩比算法， 设压缩比为 kl , 当 0 < 时， 表 明 A、 B图像间差异不大， 加大压缩不会影响图像质量， 因此采用高压 缩比算法， 设其压缩比为 k2。 从上述可知， k】 < k2。 这里， kl、 k2 的 值及门限 X的具体值和应用系统的要求有关。
根据 kl、 k2的值， 又有很多方法压缩图像， 如根据量化的比特数的 多少等来进行压缩。 一般地， 当移动图像运动较慢时， 编码之后接近零 的数据较多， 压缩比要高。
通过改变阈值的子带编码方式和差分预测编码方式， 能够实现根据 图像的性质改变压缩比及编码速率， 从而保持图像质量的稳定， 并使 CDMA系统统计上的容量的增加成为可能。 因为， 在一般的图像编码算 法中， 如果对某一图像进行编译的过程中， 某帧图像的编码码率为 kl， 扩频增益为 SF1 , 在改变速率编码的情况下， 编码速率变为 k2, 扩频增 益为 SF2, 则有下列关系存在：
kl *SFl = k2*SF2 ( 1 )
因此， 当编码速率 k2下降， 即 k2 < kl时， 扩频增益 SF2会增加。 为保持信道的传输质量不变， 即保持 信噪比 Eb/No = Ec/N。+ lOlogSF ( dB ) 的值不变， 其中，
Eb: 发射的数字信号的源头处每比特能量
N0: 信道中噪声功率频谱密度
Ec: 在扩频通信中， 对数字信号扩频后的扩频码片的能量 设 = 101ogk2/kl,则当设定码速率改变前后的 Ec分别为 Eel和 Ec2 时， 有：
Ec2/N0 = Ecl / N0 + lOlogSFl / SF2
= Ecl / N0 + 101ogk2/kl
= Ecl/N0 + C (dB) (2)
由此可以看出， 若 C (dB)小于 0, 即 K2<K1时， Ec2应小于 Ecl, 亦即当编码速率改变时， 发射功率应作相应改变。 特别当编码速率降低 时， 发射功率也应相应降低。
也可以将上式中的对数运算转为普通的代数运算， 得到：
Ec2 = k2/kl*Ecl
因此， 为使信道的传输质量不变， 需要改变系统的扩频增益和发射 功率。 而通过将降低发射功率的部分用于对新增用户的发射， 能够增加 信道的容量。 例如， 当图像编码的速率下降一半时， 发射功率也下降一 半， 从统计意义上看， 意味着可以增加 50%的常规用户。
改变扩频因子增加系统容量的具体过程如图 2所示， 首先将系统初 始化； 然后依据图像性质进行变速率编码， 这里的变速率编码即上述的 带阈值的子带编码和 /或差分预测编码； 接着根据图像编码率计算扩频 因子， 计算的方法利用了公式（ 1); 然后根据公式（2) 中发射功率和 扩频因子的关系， 改变发射功率， 在扩频后发射出去， 完成一帧的编码 发射过程。 其后， 程序返回初始化以后的步骤， 进行下一帧的编码发射。
保持信道的传输质量不变， 除了降低发射功率外， 系统还可以采用 间断发送技术。 间断发射技术是指， 在细微的时间段上有时发射信号， 有时不发射信号。 由于图像帧率只要每秒大于 25 帧人就不能察觉到， 故只要间断的时间小于 1 / 25秒， 人就察觉不到。
在发射过程中， 当扩频增益不变时， 对于编码比特率下降的部分， 在相应的时间没有数据， 由此实现间断发射。
在 CDMA系统中，间断发射的过程如图 3所示，首先将系统初始化； 然后依据图像性质进行变速率编码， 这里的变速率编码即上述的带阈值 的子带编码和 /或差分预测编码； 接着根据图像编码速率计算间断点， 具体来说， 是先计算出起点和终点， 然后计算其间的空余空间， 由此可 知其间断点； 然后进行交织过程， 即对间断发送的比特， 采用交织算法 在帧内将其随机化， 并重新排列； 最后通过扩频加到扩频地址码上， 再 发射出去， 完成一帧的编码发射过程。 其后， 对帧数加 1， 返回初始化 以后的步骤， 进行下一帧的编码发射。
虽然单个比特的发射功率不变， 但由于是间断发射， 降低了对整个 CDMA系统的统计意义上的千^ ί尤， 如整个空间的电磁波减少， 从而达到 了增加系统容量的目的， 同时对系统性能 （人的感知） 没有影响。 以上所述仅为本发明的较佳实施例而已， 并不用以限制本发明， 凡 在本发明的精神和原则之内， 所作的任何修改、 等同替换、 改进等， 均 应包含在本发明的权利要求范围之内。

Claims

权利要求书
1、 一种增加码分多址 （CDMA) 移动通信系统容量的图像传输 方法， 其特征在于该方法至少包括以下步骤：
(a)根据图像的性质进行变速率编码；
(b)保持信道传输质量不变， 通过改变扩频因子， 调节发射功率或 保持扩频因子不变， 采用间断发射方式增加系统的容量。
2、 根据权利要求 1所述的图像传输方法， 其特征在于， 步骤（a) 中所述的变速率编码采用带阈值的子带编码方法， 步骤为：
( 1 )将原始图像分解为性质不同的图像；
( 2 )根据人眼的视觉特性及统计结果设定阈值；
(3)对图像进行编码， 小于所述阈值的数据为零；
(4)对非零量进行量化和压缩编码。
3、 根据权利要求 2所述的图像传输方法， 其特征在于， 进一步 可对分解后的图像继续进行带阔值的子带编码。
4、 根据权利要求 2或 3所述的图像传输方法， 其特征在于， 在 所述的带阈值的子带编码方法中， 通过增大所设定的阈值来降低图像编 码的速率， 以增加系统的容量。
5、 根据权利要求 1所述的图像传输方法， 其特征在于， 步骤（ a ) 中所述的变速率编码也可以采用差分预测编码方法， 步骤为：
( 1 )计算时间上是前后两帧的图像差异；
( 2 )根据人眼的视觉特性及统计结果设定门限值；
(3) 当 （1 ) 中计算所得的图像差异大于所述门限值时， 则采用低 压缩比算法；
(4) 当 （1 ) 中计算所得的图像差异小于所述门限值时， 则采用高 压缩比算法。
6、 根据权利要求 1 所述的图像传输方法， 其特征在于， 所述步 骤 （b) 中通过改变扩频因子， 调节发射功率增加系统容量的方法包括 以下步骤：
( 1 )依据图像性质进行变速率编码；
(2)根据图像编码率计算扩频因子；
(3)根据扩频因子改变发射功率；
(4)通过扩频发射出去；
( 5 ) 重复步骤（ 1 ) 至 （ 5 ), 进行后续帧的编码发射。
7、 根据权利要求 1 所述的图像传输方法， 其特征在于， 所述步 骤 （b) 中采用间断发射方式增加系统容量的方法包括以下步骤：
( 1 )依据图像性质进行变速率编码；
(2)根据图像编码率计算间断点；
(3)对间断发送的信号， 采用交织算法在帧内将其随机化， 并重新 排列；
(4)通过扩频发射出去；
(5) 重复步骤（1 )至 （5), 进行后续帧的编码发射。
8、 一种增加码分多址 （CDMA)移动通信系统容量的图像传输 方法， 其特征在于该方法至少包括以下步骤：
( 1 )依据图像性质进行变速率编码；
(2)根据图像编码率计算扩频因子；
(3) 居扩频因子改变发射功率；
(4)通过扩频发射出去；
( 5 ) 重复步骤（ 1 )至（ 5 ), 进行后续帧的编码发射。
9、 根据权利要求 8 所述的图像传输方法， 其特征在于， 所述步 骤（1 ) 中的变速率编码采用带阈值的子带编码或差分预测编码。
10、 一种增加码分多址 （CDMA)移动通信系统容量的图像传输 方法， 其特征在于该方法至少包括以下步骤：
( 1 )依据图像性质进行变速率编码；
(2)根据图像编码率计算间断点；
(3)对间断发送的信号， 采用交织算法在帧内将其随机化， 并重新 排列；
(4)通过扩频发射出去；
( 5 ) 重复步骤（ 1 ) 至（ 5 )， 进行后续帧的编码发射。
11、 根据权利要求 10所述的图像传输方法， 其特征在于， 所述步 骤（1 ) 中的变速率编码采用带阈值的子带编码或差分预测编码。
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