Regularized Variable-Node LT Codes with Improved Erasure Floor Performance

We consider the use of extrinsic information transfercharts for the design of Luby Transform (LT) codes over thebinary erasure channel (BEC). In particular, we formulate anoptimization problem to determine asymptotically good check-node degree distributions in terms of decoder overhead. Wefurther propose a modified encoding scheme that maximizes theminimum variable-node degree, thus optimizing the erasure-floorperformance at the expense of decoder overhead, and resultingin a regularized variable-node degree distribution. The two ap-proaches are combined to jointly improve decoder overhead anddecoder erasure floor by incorporating the proposed encodingstrategy into the convex optimization problem. The performanceof the proposed schemes is investigated for transmission over theBEC through density evolution and numerical simulations. Theoptimized codes compare favorably to conventional LT codes,and are further extended to enable improved performance forunequal erasure protection.QC 20140519