What is Spatial Modulation?

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Spatial  Modulation (SM) is a technique that can enhance the capacity of MIMO schemes by exploiting the index of transmit antenna to convey information bits. In this paper, we describe this technique, and present a new MIMO transmission scheme that combines SM and spatial multiplexing.

Having one (or few) active RF chains but still being able to exploit all transmit-antenna elements for multiplexing and transmit-diversity gains

 Offering Maximum-Likelihood (ML) optimum decoding performance with single-stream decoding complexity

 Working without the need of (power inefficient) linear modulation schemes (QAM) or allowing us to use constant envelope modulation (PSK) with negligible performance


Massive MIMO:

 Many (hundreds or more) transmit-antennas

 All transmit-antennas are simultaneously-active: multi-RF MIMO but antennas are less expensive and more EE than state-of-the-art

 EE: reduction of transmit (RF) power


 Many (hundreds or more) transmit-antennas

 One (or few) transmit-antennas are simultaneously-active: single- RF MIMO

 EE: reduction of transmit (RF) power and circuits power

Transmission Concepts Related to SM (5/5) In Millimeter–wave Mobile Broadband (MMB) system design, the cost of implementing one RF chain per transmit–antenna can be prohibitive. For this reason, analog baseband beamforming or RF beamforming with one or a few active RF chains can be promising low–complexity solutions. Proposal: low– complexity hybrid RF/baseband precoding schemes where large antenna– arrays are driven by a limited number of transmit/receive chains.

SPACE modulation  is a novel digital modulation conceptfor Multiple–Input–Multiple–Output (MIMO) wireless systems, which is receiving a growing attention due to the possibility of realizing low–complexity and spectrally– efficient MIMO implementations . The space modulation principle is known in the literature in various forms, such as Information–Guided Channel Hopping (IGCH) , Spatial Modulation (SM) , and Space Shift Keying (SSK) modulation . Although different from one another, all these transmission technologies share the same fundamental working principle, which makes them unique with respect to conventional modulation schemes: they encode part of the information bits into the spatial positions of the transmit–antennas in the antenna–array, which plays the role of a constellation diagram (the so–called “spatial–constellation diagram”) for data modulation. In particular, SSK modulation exploits only the spatial–constellation diagram for data modulation, which results in a very low–complexity modulation  concept for MIMO systems. Recently, improved space modulation schemes that can achieve a transmit–diversity gain have been proposed . Furthermore, a unified MIMO architecture based on the SSK modulation principle has been introduced .

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