Research On Interference Alignment In Distributed Antenna Systems

There is a great development occurs in the study of wireless communication in recent years due to the higher demand people have for information communication. As a key factor affecting the performance of the wireless communication systems, interference has long been a hot issue. Interference alignment is a transmission strategy that design precoder and zero-forcing combiner to achieve the maximum degrees of freedom.Prior works prove that interference alignment is a cooperative transmission strategy that improves spectral efficiency in high signal-to-noise ratio region (SNR), yet performs poorly in low-SNR scenarios. This limits interference alignment’s utility in cellular systems to some extent as it is ineffective in improving cell-edge data rates. Distributed antenna system, however, can boost cell-edge SNR, creating the environment for interference alignment.This thesis first introduces the basic interference alignment system model and studies the theory of interference alignment in MIMO system with interference channels. Followed by introduction to the distributed interference alignment and alternating minimization algorithm, as well as validates the bit error rate (BER) performance of the two algorithms. We prove that a system can be considered to be proper and feasible when the numbers of equations does not exceed the number of variables.Secondly, as the existing interference solutions neglect the per-remote-radio power constrains imposed on distributed antenna system, this thesis considers two types of interference alignment systems:one with maximum power constraints, and the other with strict power constraint. The analysis shows that because of the simple power back-off, the sum-rate of the first kind of system suffer a loss and the other kind of system negatively affect the feasibility of the system because of the strict power constraints put on it. In this thesis, the distribution of the factor that causes the rate-loss is characterized analytically and the condition for proper and feasible system with strict power constraints is given, the algorithm of alternating minimization in this power constraint system is extended as follow.Finally, this thesis analyze the performance of a more practical system with channel estimation error.Then find the cumulative distribution function (CDF) of each stream’s SNR and set up simulation of sum-rate and SER of DAS IA system.