Novel spatial modulation based system designs for multi-user multiple-input multiple-output systems

A new and promising transmission technique that is applicable to multiple-input multiple-output (MIMO) systems, is proposed when entering 2010s: spatial modulation (SM). In addition to transmission over conventional modulated symbol, antenna indices are also used in SM transmission technique. Thus, a new perspective has been given to communication. The SM technique, which has advantages over classical MIMO and single-input single-output (SISO) systems is popular in recent in terms of spectral efficiency, energy efficiency and error performance. In 2015, a new transmission technique was proposed to increase the spectral efficiency and error performance of SM: quadrature spatial modulation (QSM). In this new technique has been shown in leading papers in the literature where higher error performance is achieved and spectral efficiency is improved compared to SM. While point-to-point (P2P) SM and QSM studies are frequently encountered in the literature, SM and QSM-based multi-user (MU) applications have gained importance in recent years. In this study, designs of SM and QSM based novel systems for multi-user MIMO systems is evaluated and analyzed. Firstly, based on the MU-MIMO SM study which is available in the literature, QSM is applied to the related system and the MU-MIMO QSM system is proposed in order to improve both spectral efficiency and error performance. It has been shown that the proposed system is superior to the MU-MIMO SM system proposed in the literature in terms of both total spectral efficiency and spectral efficiency per user. It has also been shown via the computer simulations the MU-MIMO QSM system has higher error performance than the MU-MIMO SM system. Studies have been carried out by considering the disadvantaged aspects of the proposed MU-MIMO QSM scheme and the MU-MIMO SM scheme that available in the literature. New unique systems have been proposed to improve the current MU-MIMO SM system in the literature and proposed MU-MIMO QSM system in this study, in terms of cost and power consumption, especially since it has only one radio frequency (RF) chain per user: MU-MIMO SM / QSM systems with reduced number of RF chains. These proposed systems allow different users to communicate over the same RF chain and the same SM / QSM transmission vector. Thus, the same number of users as MU-MIMO SM and MU-MU QSM systems has been proposed as a unique system that can serve with fewer RF chains. Also, error performance analysis for the proposed system is done with a new approach. This approach is based on the average bit error probability (ABEP) calculation approach through antenna indices and modulated symbols separately. Although there is one article in the literature where the similar approach is used with a different calculation method, the approach that we propose for QSM and the related mathematical derivations are not found in the literature yet. Thus, multi-user systems and the QSM literature have been gained a new perspective. Thirdly, a common information-transmitted MU-MIMO QSM system has been proposed, considering that there is a common information transmission from a base station (BS) to all users. Common-information is known as "multicast" in the literature. Multicast and user-specific datas were obtained by loading to the antenna indices and modulated symbols in different combinations. Therefore, different scenarios for the common information-transmitted MU-MIMO QSM scheme are evaluated and individual ABEP derivations are proposed for each scenario. It has been shown that theoretically derived error probability calcu1ations and computer simulations give compatible results. It also been compared the error performance over both multicast data and user-specific data. Fourth and finally, as a result of literature search for multi-user MIMO systems, it has been observed that a fixed number of transmit antenna assignments are made to each user in the transmitter BS. For this reason, a variable number of transmitter antenna assignment algorithms have been proposed to provide both a more flexible transmitter antenna selection and transmission in different spectral efficiencies for higher priority users in the communication system. Thus, a more flexible antenna allocation method was developed and all possible antenna combinations were obtained in BS. It has been shown that transmission can be achieved by selecting the most appropriate antenna assignment combination for the relevant users in the system and it has been shown that it can be adapted to SM and QSM based MU-MIMO systems. Thus, feasibility is provided for these systems. Thus, by the proposed novel studies have been contributed to the multi-user MIMO systems literature. Different novel schemes have been developed for each of the spectral efficiency, error performance and cost, which are the parameters to be improved.