Research Of Adaptive Spatial Modulation And Antenna Selection For MIMO Systems

Recently, wireless communication has been one of the hottest issues in the communication field as it breaks the physical constraint of wired communication and allows the users to communicate wherever the radio waves can reach. As the wireless communication technologies develop, people’s need for high communication and capacity has been developing. However, the resources to increase the transmit rate and capacity are on the verge of saturation. Then, a new technique which can increase the transmit rate without sacrificing the bandwidth and power of transmission begins to rise, that is MIMO (Multiple-Input Multiple-Output). Multi-input-multi-output (MIMO) technologies have received wide attention because it can make full use of space to increase the data rate and improve the spectrum efficiency.Spatial modulation (SM) has emerged as a very famous technique by using antenna indices to convey information. In SM scheme, only one antenna at the transmitter is active at one time slot so that the inter-channel interference (ICI) and inter-antenna synchronization (IAS) are completely avoided. However, the main disadvantage of conventional SM is that the number of transmit antenna must be a power of two, which means a lot of transmit antennas are needed when the spectral efficiency is high. Then, an extended spatial modulation (ESM) scheme was proposed in which allows all transmit antennas at a time slot to convey information even those not activated enhancing the spectral efficiency linearly with the number of transmit antennas.In this paper, we propose a new adaptive spatial modulation called hybrid spatial modulation (HSM) to improve the performance of the system. In HSM, the transmission scheme switches between SM and ESM based on the value of the Euclidean distance. However, the probability of occurrence of ESM is low. Hence, an EDAS scheme is jointly used in ESM to decrease the difference of probability between SM and ESM because this difference determines the performance of the system. Then, to reduce the high complexity of EDAS scheme occurred in exhaust searching, a COAS scheme is utilized. Finally, we combine the two improved ESM schemes with the conventional SM scheme based on the value of the Euclidean distance, namely, EDAS-HSM and COAS-HSM, respectively. We demonstrate that EDAS-HSM achieves a better performance whereas COAS-HSM balances the tradeoff between capacity and performance. The simulation result shows that the HSM system outperforms SM and ESM by 2 dB and 4 dB signal-to-noise (SNR) gain respectively. Additionally, EDAS-HSM and COAS-HSM performs better than HSM by 3 dB and 2 dB SNR gain respectively and EDAS-HSM scheme outperforms COAS-HSM scheme about 1 dB SNR gain.