Research On Relay And CoMP Technologies For Intercell Interference Suppression In4G Wireless System

In4G and4G Beyond mobile communication systems, the required data ratesincrease exponentially with the expanding number of user terminals and the emergenceof new multimedia applications. The limited spectrum resources lead to more frequentspectrum reuse, accompanied by the sever inter-cell interference problem. Despite theuse of OFDMA technology can effectively eliminate the intra-cell interference, thereis still not a mature solution for inter-cell interference suppression. In this paper, twosolutions are proposed from different angles against the characteristics of4G wirelesssystems: from the system architecture perspective, we introduce relay nodes to expandthe cell coverage area and improve the channel quality of the cell edge users; fromthe signal processing perspective, adjacent cells jointly design beamforming vector inorder to reduce inter-cell interference.For the relay studies, this thesis mainly focuses on the performance analysis of atwo-hop fixed gain AF MIMO relay system in the presence of co-channel interference.Depending whether the noise or the interfernce are at the relay node, two scenarios areconsidered. In addition, both the base station and the mobile station are equipped withmultiple antennas while the relay is single antenna. Since the users at the cell edge aresubjected to more severer interference, we specifically focus on this kind of users, i.e.,there are multiple interferers at the mobile station. For these scenarios above, basedon the derived outage probability expressions, accurate ergodic capacity estimationis acquired with the help of general moments in the former case. As for the secondcase, in order to quantify the effect of multi-antenna and co-channel interference onthe system performance, asymptotic analysis is carried out to get the diversity orderexpression. It is validated that our analyses are agreed with the corresponding MonteCarlo simulations. For the multicell beamforming design, this thesis focuses on how to apply the ideain an actual system properly. There are mainly two difficulties: the imperfect of theCSI and distributed implementation. Based on the primal decomposition, a distribut-ed robust downlink beamforming algorithm is proposed for the sum transmit powerminimization problem. The algorithm is simple and only limited backhaul informa-tion exchange is needed. Standard cellular network parameters are used to simulatethe practical system. Numerical results show that the performance is very close to thecentral algorithm and also the convergence rate is very fast.