# A Generalized Spatial Modulation System Using Massive MIMO Space Time Coding Antenna Grouping
## 1 Introduction
Symbols are emitted through the active antennas through a conventional modulator. Therefore, the information is transferred not only by the amplitude/phase modulation techniques, but also by the antenna indices [17]. The SM and space shift key (SSK) modulation systems can eliminate ICI and IAI by using only one active antenna all over the transmission. This will limit the utilization of spatial dimension and design flexibility. Hence, a low complexity decoder is enabled for prominent performance. Another approach is performed in [18] for multiple active transmit antennas in SM (MA-SM) by adding a phase to each transmitted symbol to enhance the BER and achieve a high data rate. At the receiver, antenna detector used to detect the activated combination of the antenna group at transmitter. However, this system suffers from high BER when increasing the transmit antennas and suffers from complexity. Another approach is performed in [19] for multiple active transmit antennas in SM (MA-SM) by adding a phase for each transmitted symbol to enhance the BER and achieve a high data rate. At the receiver, an antenna detector is used to estimate the activated set of antenna combinations at the receiver. However, this system suffers from high BER when increasing the transmit antennas and suffers from complexity. Another way to determine the number of transmit antennas is proposed by [PERSON] in [20] to reduce system complexity. In the generalized spatial modulation (GSM), a set of transmit antennas are to be activated at the same time to simultaneously transmit a data symbol. In general, the transmitted information in GSM is conveyed over the active set of antennas at the transmitter and the transmitted symbol from a signal constellation. The number of antennas needed at the transmitter required to match a certain spectral efficiency in GSM is equal to half number of transmit antennas in SM, and a generalized space shift keying modulation (GSSK) is proposed in [21]. One of the key advantages of GSM is that it can transmit the same data symbol from more than one antenna at a time, which will overcome the effects of ICI at the receiver. GSM also achieves spatial diversity gains and increases the reliability of the wireless channel by providing replicas of the transmitted signal to the receiver. In order to avoid inter-symbol interference (ISI), the activated transmit antennas must be synchronized. The maximum likelihood (ML) detection algorithm is taken into consideration at the receiver in order to estimate the activated set of antenna combinations at the transmitter and the transmitted constellation symbol. To achieve a high transmit rate, GSM requires a large number of transmit antennas that increases the complexity of the system exponentially. Moreover, GSM decoders suffer from high complexity and the linear decoder also suffers from poor performance, so a new technique is to be proposed. In this paper, a new technique is proposed based on GSM modulation and space time encoding of the GSM-modulated symbols on different antenna subgroups. In the proposed technique, STC is performed for two successive GSM modulated symbols on two antenna subgroups. The STC is used to provide transmit diversity for the multiple antenna fading channels. Antenna grouping is utilized to increase the data rate and decrease the BER. The proposed technique (GSM-STC) uses the ML detection algorithm at the receiver to assess the set of activated combination of transmit antennas and the transmitted constellation symbols. The proposed technique is expected to offer a high data rate with low BER. The proposed technique is evaluated experimentally considering selective fading channels for different types of modulation. The simulation results show that the proposed technique achieves a higher data rate and lower BER compared to the conventional and the modified GSM techniques. The remainder of the paper is organized as follows.