This paper presents novel results for Massive MIMO time division duplex (TDD) system where the beam- forming vector in the down-link makes use of MMSE channel estimates with quasi-orthogonal pilot sequences as opposed to orthogonal pilot sequences used in the prior art. The proposed method tackles the issue of pilot contamination by adapting the length of quasi-orthogonal pilot sequences according to the channel conditions or coherence time, leading to maximization of the total throughput. We compute the optimal length of the pilot sequences, for both orthogonal and quasi- orthogonal pilot sequences, that maximizes the achievable rates. We formulate the design criteria of the proposed scheme by using a classical theorem of estimation theory for multi- variate Gaussian distribution. Then we solve the criteria using heuristic algorithms and carry out simulations for different coherence times in a multi-cell system. It is shown that our proposed scheme requires 17\% less pilot resources as compared to schemes that employ orthogonal pilots. Furthermore, an interesting trade-off between the choice of pilots and the sum rate is observed for variable length of coherence interval.


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    Title :

    Massive MIMO with Quasi Orthogonal Pilots: A Flexible Solution for TDD Systems


    Contributors:


    Publication date :

    2017-09-01


    Size :

    287620 byte




    Type of media :

    Conference paper


    Type of material :

    Electronic Resource


    Language :

    English