Laboratory tests on the coexistence between 4G TDD and 3G/4G FDD in the 1900-1920 MHz spectrum band

The available radio spectrum has become scarce in recent years due to the rapid growth of wireless communications systems and the high demand for large bandwidth services. In this context, a large number of wireless networks will coexist and operate within the same frequency bands causing large co-channel and adjacent channel interference levels among them. The aim of this work is to evaluate the interference impact on both LTE-FDD and UMTS-FDD uplink transmissions operating in the 1920 MHz channel, caused by a LTE-TDD interfering signal (base station or mobile station) which operates in the adjacent band, by means of experimental results. The measurement results show that the interference effects caused by a LTE-TDD signal operating in the 5 MHz adjacent channel of the UMTS-FDD uplink signal are minimum and, therefore, the BEM values given by ECC report 39 are respected. Conversely, experimental results illustrate that the LTE-TDD interference is very harmful to the uplink LTE-FDD received signal, leading to the conclusion that new BEM definitions must be defined to protect LTE-FDD base stations.