Abstract-In this paper, we review the requirements for forward error correction (FEC) decoding for next generation wireless modems -mobile Worldwide Interoperability for Microwave Access (WiMAX) and third generation partnership project long term evolution (3GPP LTE). FEC decoder consists of mainly three components: control channel decoder, data channel decoder, and hybrid automatic repeat query (HARQ) combining. Control channel decoder is constrained by latency budget which impacts buffering as well as power management of modem signal processing chains. For WiMAX, both Viterbi and Turbo decoders are required to receive control channel while for LTE, only Viterbi decoder is required. For data-channel, a highthroughput Turbo decoder is required to support high data rate. HARQ combining is mainly dominated by memory size and bandwidth requirements given the maximum data rate, maximum number of HARQ processes and re-transmission formats. We analyze the requirements and discuss possible candidate architectures for three components.

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The advantages of the Low Earth Orbit (LEO) satellite include low-latency communications, shorter positioning time, higher positioning accuracy, and lower launching, building, and maintenance costs. Thus, the introduction of LEO satellite constellation as a regional navigation augmentation system for the current navigation constellations is studied in this paper. To achieve the navigation performance requirement with the least system cost, a synthetic approach is presented to design and deploy a cost-efficient LEO navigation augmentation constellation over 108 key cities. To achieve lower construction costs, the constellation is designed to be deployed by constrained piggyback launches, which brings additional complexity to the constellation design. Two optimization models with discrete and continuous performance indices are established. They are solved by the genetic algorithm and differential evolution algorithm, and both Walker and Flower constellations are adopted. Results for 77 and 70 satellites are obtained. During the construction phase, a synthesis procedure containing five impulses is proposed by utilizing natural drift under J 2 perturbation. This work presents a method for designing the optimal LEO navigation constellation under a constraint deployment approach with the lowest construction cost and a strategy to deploy the constellation economically.

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