Abstract: The increasing requirements for higher data rates in cellular systems lead wireless communication companies to invent femtocell (FMC) which is a small cell size. FMC is a low power cellular home base station, low in cost, operating within a licensed spectrum and designed for use in residential or small business areas, both indoors and outdoors, and deployed to improve cellular system coverage. FMC has been deployed extensively and is included in the Long Term Evolution (LTE) and the Worldwide Interoperability Microwave Access (WiMAX) networks for indoors. This paper presents the interference, SINR and the probability of connection at the downlink for a varying number of FMCs based on the LTE and WiMAX OFDMA range. Moreover, the comparison of interference, SINR and probability of connection are studied for three different indoor areas. In addition, a comparison for the probability of connection with various threshold values and various number of FMCs is simulated and presented in 3-D. The downlink interference occurs from neighbouring FMCs to the target user equipment (UE), when the signal transmits from the serving FMC to the target UE and the signals which are transmitted from the neighbouring FMCs would have the same subchannels during the downlink transmission. Keywords: Femtocell, Home Base Station, Interference, SINR, UserEquipment, Indoors, OFDMA, Downlink