Design of Joint Source/Channel Codes for Rayleigh Fading Channels

9314221 Vaishampayan我们解决了衰落信道的源信道联合编码问题。众所周知，信道编码和交织技术可以提高分集的阶数。然而，这些代码传统上为所有传输的比特提供统一的错误保护。实际上，对于许多源，量化器中的一些比特比其他比特更重要。研究表明，在给定系统分集水平的情况下，非等错保护方案可以大大提高衰落信道的性能。我们还提供了一种设计不相等错误保护方案的方法，以最小化失真判据，服从整体系统的分集水平。此外，我们注意到，与代码提供的分集顺序相比，交错系统所需的交错延迟非常大。在语音编码应用中，整个通信系统的设计必须满足延迟预算。因此，交错延迟限制了可以分配给源编码器/解码器的延迟。我们证明了对交织延迟有约束的信道编码的构造可以看作是为有限数量的独立慢衰落信道设计编码的问题，其中任何一个慢衰落信道都不允许交织。代码可以实现的分集顺序受可用的独立信道数量的限制。然而，码的速率被限制为分集阶的倒数。为了绕过这个约束，我们使用这样一个事实，即对于连续字母源，并非源编码器/解码器所看到的有效信道的每个转移概率都需要表现出最大的分集顺序。这允许提高代码的速率。我们将研究为瑞利衰落信道构建组合源码和信道码的结构化技术。＊＊＊

9314221 Vaishampayan We address the issue of combined source and channel coding for fading channels. It is well-known that channel coding, together with interleaving, can be used to achieve an improvement n diversity order. However, these codes have traditionally offered uniform error protection for all bits transmitted. In reality, for many sources, some bits from the quantizer are more important than others. We show that unequal error protection schemes can offer greatly improved performance on the fading channel given a fixed diversity level in the system. We also provide a method for designing unequal error protection schemes in order to minimize a distortion criterion, subject to an overall system diversity level. Additionally, we note that the interleaving delay required in interleaved systems is very large compared to the diversity orders that the code provides. In speech coding applications the entire communications system must be designed to meet a delay budget. The interleaving delay thus restricts the delay that can be allocated to the source coder/decoder. We show that the construction of a channel code with a constraint on the interleaving delay can be treated as a problem of designing a code for a restricted number of independently slow fading channels in which interleaving is not allowed on any of the slow fading channels. The diversity order that the code can achieve is restricted to the number of independent channels available. However, the rate of the code is then restricted to the reciprocal of the diversity order. In order to get around this constraint, we use the fact that for continuous alphabet sources, not every transition probability for the effective channel as seen by the source coder/decoder need exhibit the maximum order of diversity. This allows the rate to the code to be increased. We will examine structured techniques for constructing combined source and channel codes for the Rayleigh fading channel. ***