A comparative study on the modified Max-Log-MAP turbodecoding by extrinsic information scaling

A simple but effective technique to improve the performance of the Max-Log-MAP algorithm is to scale the extrinsic information exchanged between two MAP decoders. A comprehensive analysis of the selection of the scaling factors according to channel conditions and decoding iterations is presented in this paper. Choosing a constant scaling factor for all SNRs and iterations is compared with the best scaling factor selection for changing channel conditions and decoding iterations. It is observed that a constant scaling factor for all channel conditions and decoding iterations is the best solution and provides a 0.2-0.4 dB gain over the standard Max- Log-MAP algorithm. Therefore, a constant scaling factor should be chosen for the best compromise.

The modified Max-Log-MAP turbo decoding algorithm by extrinsic information scaling for wireless applications

The iterative nature of turbo-decoding algorithms increases their complexity compare to conventional FEC decoding algorithms. Two iterative decoding algorithms, Soft-Output-Viterbi Algorithm (SOVA) and Maximum A posteriori Probability (MAP) Algorithm require complex decoding operations over several iteration cycles. So, for real-time implementation of turbo codes, reducing the decoder complexity while preserving bit-error-rate (BER) performance is an important design consideration. In this chapter, a modification to the Max-Log-MAP algorithm is presented. This modification is to scale the extrinsic information exchange between the constituent decoders. The remainder of this chapter is organized as follows: An overview of the turbo encoding and decoding processes, the MAP algorithm and its simplified versions the Log-MAP and Max-Log-MAP algorithms are presented in section 1. The extrinsic information scaling is introduced, simulation results are presented, and the performance of different methods to choose the best scaling factor is discussed in Section 2. Section 3 discusses trends and applications of turbo coding from the perspective of wireless applications.

Magna Charta and Parliament 1900-1914

In 1915 plans for the celebration of the 700th anniversary of Magna Carta had to be dropped following the outbreak of the First World War. Such celebrations marked a sense of Magna Carta as an event in the history of these islands. The usage of the term Magna Carta in Parliament in the run-up to the First World War, however, shows that its granting was not seen only as a significant historical event to be memorialised. During the period from 1900, opening with war in South Africa and ending in 1914 with war throughout Europe, the Great Charter was mentioned 85 times in Parliament. As a period marked by a lengthy constitutional crisis in 1909-11 and beset with problems in Ireland and the Empire, this seems like a good case study period to choose. This short paper attempts to analyse how and why it was invoked in Parliament in the years and what these various usages tell us about how Magna Carta was understood at the time.