Uncertainty in Field-Level Measurements of LTE Signals Associated With User Load

Recent modulation schemes in mobile communications, as Long Term Evolution (LTE), give rise to the question of how to properly assess the exposure to the electromagnetic fields generated by base station signals. This letter examines the changes in the field strength associated with the user load variations in the LTE signals. First, we have generated a set of signals, with the same configuration parameters, modifying only the percentage of user load and simulating how it alters the field level. Then, a setup for measurements is defined, and two electric field probes are exposed to the previous analyzed signals in a controlled environment. Field strength meter readings are recorded as in a real case of exposure evaluation. Uncertainties concerning probes performance and environmental conditions are also calculated to have an overall budget. Due to the user load changes, field-level variations up to 11 dB have been found. The measurement uncertainty of the exposure level may be dramatically increased by these field fluctuations.