LDPC-based Superposition Coding For Two-user Interference Channels

Users in Wire Communication are corresponding to each other through pint-to-point link, different from which, Wireless users are corresponding in air. In recent years, there is a large increase in the density of users, with the rapid development of wireless communication. Thus, how to solve the problem of interference among users effectively is the key to the current research.Firstly, this paper discusses some different types of two-user Interference Channel from the viewpoint of information theory. The two-user Strong Interference Channel can avoid the affect form interference and achieve its capacity limit, by treating interference as noise. However, the capacity region of two-user Weak Interference Channel hasn't been ensured. In 1981, Han and Kobayashi proposed a new capacity upper bound, derived by the best known achievability strategy, which divides the transmitted messages into two parts: a common part decodable by both receivers, and a private part decodable only by the intended receiver. There are four power-splitting schemes: symmetrical-splitting scheme, adaptive-splitting scheme, orthogonal-splitting scheme and ETW-splitting scheme, according to power-splitting coefficient. Simulation results indicates that under lower SNR, the optimal sum-rate of orthogonal-splitting scheme keeps invariant, and the optimal sum-rate of other schemes appear different change trends along with interference coefficient a; under higher SNR, if 0<a<0.08, symmetrical-splitting scheme and ETW-splitting scheme appear the best performance, and if 0.08<a<1, orthogonal-splitting scheme appears the best performance.Secondly, we use several optimal LDPC codes as component codes, to realize simulation about two-user Interference Channel based on BICM system, with successive interference cancellation iterative decoding algorithm. And according to formulas of rates and power splitting, we constantly improve related parameters to make the simulation system achieve the best performance, in case that every part of message includes single layer.Thirdly, we apply multilayer superposition coding modulation technology to this system, and propose a transmission scheme for two-user interference channel based on the superposition coding modulation. The transmitter divide each single-layer LDPC code into double-layer LDPC code. The overall system still uses successive interference cancellation iterative decoding algorithm, and the inner parts use multilevel decoding algorithm. Simulation results indicate that the improved scheme outperforms the previous scheme based on BICM system. Finally, we further make several improvement of the improved scheme stated before, and use non-binary LDPC decoding algorithm for inner parts to realize simulation. Simulation results indicate that the further improved scheme outperforms the previous scheme.