Interference Between Management Based On Cooperative Beam Forming Technology

As the development of wireless communication and rapid growth of the amount ofuser’s business, along with the reuse of frequency resource, future wireless cellularnetworks face many challenges, the interference between cells is one of the majorproblems. In order to improve the spectrum efficiency of the system, futurecommunication system tends to use the same frequency in the whole network, but thisintroduces co-channel interference to the system. This effects service quality of userswhich especially in the cell edge between cells.OFDM technology which is the key technology of physical layer of the nextgeneration mobile communication can effectively fight intra-interference between users,but it still can not mitigate intel-cell interference. MIMO technology is developed in thisbackground. It can improve the system throughput, expand coverage area and improveusers’ performance in the edge area of the cell. MIMO technology has been employed inthe3GPP LTE criterion, it’s main application is Transmit Diversity, SpatialMultiplexing, Beamforming and Multi-User MIMO (MU-MIMO).What this dissertationdiscussed is the beamforming technology of MIMO. The beamforming technology inthe case of Non-CoMP bases on per-cell can make local cell’s users obtain a bettersignal power and Signal-to-Noise Ratio, but this method also produces seriousinterference to users in adjacent cells. In the multi-cell scenarios with BSs’ collaboration,effective beamforming technology, in which condition of ensuring the user’ servicequality, can effectively reduce the inter-cell interference, and minimize the transmissionpower to improve power efficiency, so as to improve the overall system performance.This dissertation is divided into two major parts, and they studied differentbeamforming algorithm with BSs’ collaboration respect to different perspective.In the first part, it briefly introduces the convex optimization programming theorywhich we often meet with in the engineering problem and its simple application. Then itintroduces the solution to downlink beamforming problem for mitigating the inter-cellinterference in multi-cell scenarios. The kenel criterion is to minimize the total weightedtransmitted power across the base-stations subject to Signal-to-Interference-and-Noise-Ratio (SINR) constraints at the remote users. Throughthe deduction and transformation, the problem can be expressed as the SOCP or SDPproblem. It is not difficult to solve such standardizing problems through the existingsolver tools. This part also proved downlink-uplink duality for the multi-cell settingusing the Lagrangian duality theory. As a basis, it derived a simplified algorithm whichis called iterative function evaluation algorithm, it can find the optimal beamformingvector. It can reduce computational complexity and naturally leads to a distributedimplementation in Time-Division Duplex (TDD) system. The simulation results showthat it has better performance than some traditional algorithm.In the second part, it solves the coordinated beamforming problem from anotherperspective. It considered how to improve the users’ service quality at a fixedtransmitting power, that is to maximize users’ SINRs. This dissertation points out that,the problem is a coupling problem, its computational complexity is relatively high, so itsettled for second, explored a suboptimum but with less computation solution. Thisalgorithm is similar to the solution using SLNR criteria, and its practical significance isto decouple the problem and lead a distributed implementation for the system. Insimulation we compared other corresponding algorithm and its performance. Also, thisdissertation compared the performance of the algorithm proposed in the first part.