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Introduction to MIMO Systems
Published in Brijesh Kumbhani, Rakhesh Singh Kshetrimayum, MIMO Wireless Communications over Generalized Fading Channels, 2017
Brijesh Kumbhani, Rakhesh Singh Kshetrimayum
Moreover, in SM, all the information bits are not transmitted physically. A part of information bit sequence is mapped to transmit antenna indices (spatial constellation) and the antenna corresponding to mapped index is used to transmit information bits mapped to signal constellation. A system model for SM MIMO is given in Figure 1.6. This SM MIMO system model considers an Nt × Nr MIMO system having Nt antennas at transmitter side and Nr antennas at the receiver side. For M-ary modulation scheme, each block of log2(Nt) + log2(M) bits of information is mapped by the SM mapper to signal constellation and spatial constellations. log2(Nt) bits of each block are mapped to points in spatial constellations which select the antenna and log2(M) bits are mapped in the signal constellation and modulated by symbol modulator using a suitable digital modulation scheme. The digitally modulated signal constellation point is then transmitted from the antenna to which the spatial constellation point is mapped. Thus, using SM, we effectively get spectral efficiency gain of log2(Nt)bits/s/Hz without costing any extra bandwidth or power. Only one antenna depending on the incoming data bits is active at a time overcoming the problems of inter channel interference and the requirement of inter antenna synchronization. These are advantages of SM over (Vertical-Bell Laboratories Layered Space-Time) V-BLAST and MIMO orthogonal frequency division multiplexing (OFDM) systems. At the receiver, transmit antenna index and transmitted symbol are estimated separately in suboptimal scheme [76, 77]. SM de-mapper appends the estimated transmit antenna and detected symbol accordingly to regenerate the transmitted information bits. Table 1.1 shows how the bits are mapped in spatial domain and the signal domain for spectral efficiency of 3 bits/s/Hz using BPSK and 4QAM schemes with 4 and 2 transmitter antennas respectively. The transmitted vector will have all zero elements except the one which will transmit the digitally modulated data bits as shown below.
Adaptive Quadrature Spatial Modulation
Published in IETE Technical Review, 2020
S. Oladoyinbo, N. Pillay, H. Xu
SM [2,3], is an example of a new form of MIMO that employs transmit antennas in an innovative manner, alleviating the major limitations of conventional MIMO systems [2,3]. SM based schemes have been well investigated in the context of multipath channels [1] and are sparsely populated in contrast to the conventional MIMO schemes, due to the fact that only a single transmit antenna is employed at every transmission instant [1,2]. However, SM has a criticism of its data rate enhancement being proportional to logarithm base-two of the total number of transmit antennas, unlike other spatial multiplexing techniques, such as vertical Bell Laboratories layered space-time architecture (V-BLAST) [4], which has a linear relationship.