Design of Joint Source/Channel Codes for Rayleigh Fading Channels

9314221 Vaishampayan我们解决了针对衰落信道的组合源和信道编码的问题。众所周知，信道编码与交织一起可用于实现N个分集阶数的改善。然而，这些码传统上为传输的所有比特提供统一的差错保护。实际上，对于许多信源来说，量化器中的某些比特比其他比特更重要。我们证明了当系统中的分集电平固定时，不等差错保护方案可以在衰落信道中提供极大的性能改善。我们还提供了一种设计不等差错保护方案的方法，以便在总体系统分集水平的约束下最小化失真准则。此外，我们注意到，与码提供的分集阶数相比，交织系统中所需的交织延迟非常大。在语音编码应用中，整个通信系统必须设计成满足延迟预算。因此，交织延迟限制了可以分配给信源编码器/解码器的延迟。我们证明了具有交织延迟约束的信道码的构造可以看作是为有限数量的独立慢衰落信道设计码的问题，其中在任何慢衰落信道上都不允许交织。码可以实现的分集顺序受限于可用独立信道的数量。然而，码率随后被限制为分集阶数的倒数。为了绕过这一限制，我们利用这样的事实，对于连续的字母表信源，不是信源编码器/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阶数的分集。这允许增加对代码的速率。我们将研究为瑞利衰落信道构造组合信源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. ***