An orbital angular momentum, OAM, multiplexing communication system in which a multi uniform circular array, hereinafter, M-UCA, formed of a plurality of uniform circular arrays, hereinafter, UCAs, that are concentrically disposed is provided in each of a transmitting station and a receiving station , each of the UCAs having a plurality of antenna elements disposed circularly at an equal interval; signals in a plurality of OAM modes are generated and transmitted from each of the UCAs of the transmitting station; signals in the plurality of OAM modes are received and demultiplexed by each of the UCAs of the receiving station ; and streams of the number of UCAs x the number of OAM modes are subjected to spatial multiplex transmission, wherein: the transmitting station includes a signal processing unit that generates the streams of the number of UCAs x the number of OAM modes to be transmitted in the plurality of OAM modes from each of the plurality of the UCAs of the M-UCA; and the receiving station includes a signal processing unit that receives the signals in the plurality of the OAM modes demultiplexed by each of the plurality of the UCAs of the M-UCA, and demultiplexes the received signals for each of the streams from signals in an identical OAM mode; characterised in that : the signal processing unit of the transmitting station is configured to perform spatial modulation A of two bits by selecting one of a pair of OAM modes in which a subsequent bit is transmitted according to 0 and 1 of a first bit, and to generate a stream in which the subsequent bit is transmitted in the selected OAM mode; and the signal processing unit of the receiving station is configured to demultiplex streams corresponding to the plurality of the UCAs from signals in the pair of OAM modes, and to add the first bit used in the spatial modulation A to the demultiplexed streams such that signals are demodulated for each of the streams. the transmitting station includes a signal processing unit that generates the streams of the number of UCAs x the number of OAM modes to be transmitted in the plurality of OAM modes from each of the plurality of the UCAs of the M-UCA; and the receiving station includes a signal processing unit that receives the signals in the plurality of the OAM modes demultiplexed by each of the plurality of the UCAs of the M-UCA, and demultiplexes the received signals for each of the streams from signals in an identical OAM mode; characterised in that : the signal processing unit of the transmitting station is configured to perform spatial modulation A of two bits by selecting one of a pair of OAM modes in which a subsequent bit is transmitted according to 0 and 1 of a first bit, and to generate a stream in which the subsequent bit is transmitted in the selected OAM mode; and the signal processing unit of the receiving station is configured to demultiplex streams corresponding to the plurality of the UCAs from signals in the pair of OAM modes, and to add the first bit used in the spatial modulation A to the demultiplexed streams such that signals are demodulated for each of the streams. the signal processing unit of the transmitting station is configured to perform spatial modulation A of two bits by selecting one of a pair of OAM modes in which a subsequent bit is transmitted according to 0 and 1 of a first bit, and to generate a stream in which the subsequent bit is transmitted in the selected OAM mode; and the signal processing unit of the receiving station is configured to demultiplex streams corresponding to the plurality of the UCAs from signals in the pair of OAM modes, and to add the first bit used in the spatial modulation A to the demultiplexed streams such that signals are demodulated for each of the streams. <EOS>