This paper presents a method of the reverse recognition of the check matrix coded by low density parity check code (LDPC), which is based on the posterior probability log likelihood ration (LLR). The posterior probability LLR was obtained by estimating the channel amplification and the variance of the noise in the received code. A reverse recognition of LDPC code check matrix was achieved following the LLR mean value maximization principle. Simulation results show that the receiver can precisely retrieve the LDPC check code used by the sender under different channel circumstances through the LDPC reverse recognition method.

Admission control is required to determine whether new connections should be admitted to network to guarantee the quality of service (QoS) for data transmission. This paper proposes a new active measurement-based admission control (AMBAC) method to guarantee the QoS in IP network. The basic idea of this method is: the ingress router actively sends probe packets to egress router and the egress router makes the admission control by monitoring the received probe packets. The proposed method is fully scalable and has less response time. The simulation results show that AMBAC can strictly guarantee the QoS of data transmission and effectively improve the utilization of network resource.