Abstract
Massive MIMO is a key technique in the fifth generation (5G) of wireless networks. This technique, by increasing base station (BS) antennas and exploiting spatial diversity, improves system performance in terms of common criteria such as spectral efficiency. Cell free massive MIMO is considered for 6G mobile communications to overcome the shortcomings associated with the cellular design. In this system, BS antennas are distributed across the system environment and provide uniform service to all users. Also, space time block codes (STBCs) can be used to improve the diversity gain and reliability of the system. In this paper, a cell free massive MIMO system is investigated in the uplink considering effects of channel estimation errors. Users are equipped with two antennas and employ STBC. Lower bound of spectral efficiency is derived for the zero forcing (ZF) and maximal ratio combining (MRC) decoders. Furthermore, spectral efficiency is compared for dual and single antenna users. Moreover, two power control problems are defined based on minimizing the total transmit power and maximizing the minimum rate of the users. Also, an algorithm is proposed for removing the inefficient BSs in the network. The proposed theoretical ideas are evaluated via numerical simulations.
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