Channel hardening in massive Multiple-Input Multiple-Output (MIMO) systems is a hot research field that needs investigation. As the number of antennas increases, channel starts to behave deterministically and small-scale fading decreases. This is called hardening phenomenon. Since there is a lack of real world study of the hardening effect in massive MIMO channels, this paper aims at investigating channel hardening in an outdoor real-world scenario by using a linear double polarized transmitting antenna array and a cylindrical dual polarized receiving array. Measurements are performed in two different routes and hardening is analyzed in terms of different polarization combinations and different antenna subsets by fixing the transmitter or receiver and using coefficient of variation (CV2) as a metric. The results show that in terms of getting more pronounced hardening, it is more beneficial to fix the position of the transmitting antenna along the array. Selecting a certain subset of antennas, it can be observed that channel does not soften. This gives rise to the possibility of using antenna selection algorithms. For achieving the same hardening level, more antennas are needed in the Line of Sight (LoS) scenario since the channel is shown to experience more hardening in Non-Line of Sight (NLoS) scenario. Furthermore, it is shown that polarization has little impact in the channel hardening of a NLoS scenario. These results are very important from the point of view of network operators.
Measurement-based characterization for polarimetric channel hardening in outdoor environments
2022-06-01
3722342 byte
Conference paper
Electronic Resource
English
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