On rate performance of M‐ary amplitude shift keying compact ultra massive array systems for massive connectivity

Abstract Compact ultra massive array (CUMA) is a new form of the emerging fluid antenna system where a huge number of flexible‐position antennas are selected to produce the output signal. By making sure that the in‐phase channels (similarly for the quadrature channels) of the desired signal at the selected antenna ports align, it builds an advantage of the desired signal over the interference. It is known that CUMA as a multiple access scheme is able to deal with hundreds of users on the same channel use, in the case of rich scattering, if binary phase shift keying is considered. It is nevertheless unclear if higher‐level modulation can bring even greater network rate in this extreme massive connectivity scenario. This letter investigated this situation by presenting the average data rate expression of CUMA when M‐ary amplitude shift keying is used, assuming a binary symmetric channel. Numerical results reveal that M‐ary amplitude shift keying can indeed raise the rate performance considerably.