Research On Adaptive Spatial Modulation For Mm Wave Communication System

With the requirement of higher communication rates,sub-6G frequency bands are increasingly scarce,while millimeter wave(mm Wave)bands can provide abundant bandwidth,which therefore can offer higher transmission rates.Hence,mm Wave communication technology arises great attention in academy and industry.Due to shorter wavelength of mm Wave,massive antenna arrays are often exploited in mm Wave communication systems to overcome the high path-loss and to expand the coverage area.However,with the increase of transmitted antennas,both the communication cost of full digital link and the complexity of detection increase.Spatial modulation is considered as one of effective technologies to deal with those problems.Only one radio frequency chain is needed in spatial modulation,which reduces the transmission cost to some extend.Though it activates one transmitted antenna and one radio frequency chain at each time slot,spatial modulation maintains a relative high transmission rates in that it makes an exploitation of antenna index to carry information bits.A fixed modulation order is taken into consideration in the conventional spatial modulation technology during the symbol mapper process,not taking the channel state information into account,which degrades the performance of communication systems.Thus researchers proposed adaptive spatial modulation(ASM)technology based on the fixed transmission rates and the fixed bit error rates,respectively.For ASM technologies based on the fixed transmission rates,the optimal modulation order combination is selected from all modulation order combination subjected to the fixed transmission rates through the exhaustive search,which is of high computational complexity.Furthermore,most of researches on ASM technologies based on the fixed bit error rates focuses on the uniform linear array(ULA),not exploiting the vertical dimension of channel to improve the spectral efficiency,while the uniform planar arrays(UPA)are more common in the mm Wave communication.To deal with problems discussed above,we propose three spatial modulation schemes as follows,(1)To reduce the computational complexity of the ASM technology based on the fixed transmission rates,we propose a low-complexity ASM(LR-ASM)technology,which shrinks the search scope of antennas by cosine similarity at first and then exploits the rotational symmetry of QAM to further shrink the search scope of modulated symbols.The simulation results show that the LR-ASM technology can reduce computational complexity on finding the optimal modulation order combination with little increase of bit error rates.(2)To make full use of the vertical dimension of channel,we propose the ASM technology with UPA.Simulation results depict that the proposed ASM technology can obtain higher spectral efficiency than that of the ASM technology with ULA at the same signal to noise ratio.(3)To reduce the probability of error detection on antenna index brought by the increase of transmitted antennas,we introduce the antenna selection algorithm to the ASM technology using UPA.Simulation results show that the bit error rates of the proposed ASM technology is lower than that of the ASM technology with ULA,while spectral efficiency of the proposed ASM technology is higher than that of the ASM technology with ULA.