Abstract—Spatial modulation (SM) is a new transmission technique for multi-antenna systems in which the transmit antennas are used to modulate the signal. In this paper, the symbol error rate (SER) performance of SM is investigated. In SM, a signal domain modulation (i.e. amplitude-phase modulation) and an antenna domain modulation (i.e. space shift keying) are combined together to achieve a certain transmission rate while exploiting the properties of two independent modulation domains. A key question is the fine balance between the constellation sizes in the two domains when a constant rate is targeted. For a fixed rate, there are many ways to assign constellation vectors to the spatial and signal domains. In this paper, < Final Year Projects > we investigate optimal constellation breakdown between space and signal domains. The analysis is based on the union bound of the error probability of SM with two typical APM schemes, i.e. phase-shift keying (PSK) and square quadrature amplitude modulation (S-QAM). It is shown that, at any transmission rate, there exists an optimal APM dimension in which the SER is minimized. Furthermore, a trade-off between the number of transmit antennas and the transmit power is introduced.
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