Constructing QCLDPC codes based on dimension reduction for physical layer security As a recently proposed physical layer security scheme, the twodimensional transmission scheme prevents eavesdropping, but the bit error rate (BER) of the receiver becomes high. A new coding scheme for QuasiCyclic LowDensity ParityCheck (QCLDPC) codes to improve the performance of the receiver is proposed and named as dimension reduction coding. This new scheme constructs the base matrix, which is necessary to obtain the parity check matrix of QCLDPC codes, from the channel coefficient matrix of twodimensional transmission scheme. Then, by analyzing the relationship between the base matrix and the parity check matrix of QCLDPC codes, we find out the conditions that the base matrix must satisfy so that the corresponding parity check matrix has no shortest cycle in Tanner graph. Furthermore, a dimension reduction algorithm is presented to modify the base matrix and obtain parity check matrices with good performance. Finally, simulation results are given and validate the feasibility of this method.

Decoding Scheduling for Unequal Error Protection QuasiCyclic LowDensity ParityCheck Codes Algebraic constructions of quasicyclic (QC) lowdensity paritycheck (LDPC) codes with unequal error protection (UEP) capabilities have recently been proposed, which can provide different errorcorrecting capabilities for different parts of the coded bits. However, conventional decoding algorithms are not designed for LDPC codes with UEP. In this paper, we propose three decoding schemes for UEP QCLDPC codes extended from existing scheduling strategies, tailored to the special structures of the paritycheck matrices. Simulation results show that the proposed schemes can provide improved error rate performance especially for coded bits on low protection levels. The decoding convergence can also be accelerated, thereby reducing the computational complexity.