Convolutional double accumulate codes (or double turbo DPSK)

We consider the serial concatenation of a convolutional code with two differential encoders (or accumulate codes). Simulations of such a concatenated scheme using a rate 1/2 outer convolutional code (sometimes punctured to increase the overall rate) show that, at high rates, the bit error rate (BER) and frame error rate (FER) performance of these codes is significantly better than a concatenation with only one accumulate code and a parallel concatenated convolutional code (PCCC) of similar complexity. An intuitive explanation for the performance of these codes is also given     

Scalable Web server clustering technologies

The exponential growth of the Internet, coupled with the increasing popularity of dynamically generated content on the World Wide Web, has created the need for more and faster Web servers capable of serving the over 100 million Internet users. Server clustering has emerged as a promising technique to build scalable Web servers. We examine the seminal work, early products, and a sample of contemporary commercial offerings in the field of transparent Web server clustering. We broadly classify transparent server clustering into three categories