Pilot contamination reduction based on improved power control in M-MIMO systems

In multi-user Massive MIMO (M-MIMO) TDD systems, the performance of achievable rates in UL/DL is limited by pilot contamination with the number of BS antennas grows. On the basis of a simplified channel model which allows us to obtain the achievable rates easily, the intercell interference factor is defined as “orthogonality factor” for the first time in this paper. The orthogonality factor is denoted by the orthogonality of pilots from interference cells to the target cell. We propose an improved pilot power control scheme. We consider the partial pilot power control scheme with dividing the time slot of pilots into two parts and making the pilots staggered only from interference cells, while pilots from the target cell are still transmitted in the whole time slots. As a consequence, the inter-cell interference factor is always reduced to half with the proposed scheme. In addition, we also obtain an additional conclusion that the inter-cell interference factor decreases with the increase of the number of UTs. Ultimately, the pilot contamination is mitigated and the achievable sum rates are improved significantly with the proposed scheme. The numerical results demonstrate the proposed scheme is effective obviously.