联合LDPC码与clipping降OFDM系统峰均比的方法*

针对正交频分复用(OFDM)系统中存在的高峰均比问题，提出了一种简单而有效的降低峰均比(PAPR)的联合方法，即将低密度奇偶校验码（LDPC）与传统的限幅(clipping)技术相结合的方法。该方法通过clipping技术降低OFDM信号的PAPR，同时结合LDPC码改善clipping技术带来的系统误比特率（BER）恶化与频域滤波降低带外功率辐射。MATLAB仿真结果表明，该方案能够简单而有效地降低PAPR并提高系统的BER性能，以及抑制带外功率辐射，证明了该联合方法的有效性。

Method of reducing PAPR with LDPC coding and clipping in OFDM system

The definition of information flow security properties are based on different semantic model, which is difficult to make comparison between them. This paper used Petri net as unified model to describe the security system, defined four security properties on Petri net and analyzed the logic relationship between them. The traditional algorithmic verification method for information flow was known as unwinding method, which was not sufficient and could be just used in deterministic system. The second work of this paper was giving a sufficient algorithmic verification method for the security properties had been defined and programming to implement the method. Finally, it shows the application of this method in covert channel.