In this paper, we propose a predictive method to construct regular column-weight-three LDPC codes with girth g = 8 so that their Tanner graphs contain a minimum number of small trapping sets. Our construction is based on improvements of the Progressive Edge-Growth (PEG) algorithm. We first show how to detect the smallest trapping sets (5, 3) and (6, 4) in the computation tree spread from variable nodes during the edge assignment. A precise and rigorous characterization of trapping sets (5, 3) and (6, 4) are given, and we then derive a modification of the Randomized Progressive Edge-Growth (RandPEG) algorithm [1] to take into account a new cost function that allows to build regular column-weight dv = 3, girth 8 LDPC codes free of (5,3) and with a minimization of (6,4). We present the construction and the performance results in the context of quasi-cyclic LDPC (QC-LDPC) codes.
This paper proposes a collaborative system based on WebRTC technology to improve digital universities eLearning environment. It allows teachers and students, through a web browser, to communicate via chat, audio and camera. It also supports file transfer and screen sharing for computer connected lab equipment. All these features are functional in an IP environment without need for Internet access. For its design and realization, we had to implement a WebRTC signalisation server to manage real-time applications, using the three WebRTC APIs: MediaStream for the acquisition and synchronization of audio and video, Peer Connection for communication between user's browsers and RTCDataChannel for file transfer, Chat and Screen Sharing.
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