Differential Optical Spatial Modulation For Wireless Optical Communication

Optical spatial modulation(OSM),as a new wireless optical spatial multiplexing technology,has attracted wide attention since it was proposed.The basic principle of the OSM is that in addition to the traditional modulation technology of digital domain,the index of the laser also carries additional bits information,thus significantly increasing the transmission rate of the classical optical multiple input multiple output(MIMO)system.At the same time,OSM only has a small number of lasers to be activated in one symbol period,which avoids the inter-channel interference and inter-antennas synchronization.However,the current research of OSM assumes that the channel state information(CSI)is fully known at the transmitter and receiver.This assumption is true when the channel state changes slowly or is in a quasi-static environment.In high-speed moving scenarios or fast fading channels,channel estimation is particularly difficult.On actual communication systems,pilot signals are often used to achieve channel estimation.Inserting pilot signals into the traditional data frame structure not only takes up a certain amount of frequency resources,resulting in a reduction in transmission rate and spectrum efficiency,but also the error of the estimation results will seriously affect the error performance of the entire system.Therefore,to effectively avoid complicated channel estimation,this thesis researches the differential optical spatial modulation(DOSM)system.Combining intensity modulation technology to construct a coding matrix that satisfies the differential process,and the error performance,spectrum efficiency and transmission rate of the DOSM system are improved.Details as follows:(1)The DOSM system effectively avoids the problem of CSI estimation,and achieves higher spectral efficiency due to the use of pulse amplitude modulation(PAM),but its error performance is limited.For this reason,the thesis proposes a DOSM-PPM system using high energy efficient pulse position modulation(PPM).The system uses PPM orthogonality to design a space-time dispersion matrix that satisfies the differential process and realizes the optimization of the error performance of the differential system.At the same time,the union bound technology and Gaussian kernel density approximate estimation are used to analyze the theoretical average bit error rate performance bounds of the systems and compare with the existing DOSM and OSM systems.The results show that compared with traditional DOSM and differential optical space shift keying,when the spectral efficiency is 1 bits/s/Hz and the bit error rate is 1×10^-3,the signal to noise ratio of the system is improved by 1 dB and 3 dB.Different lasers load different PPM signals to significantly increase transmission rate.(2)Although the DOSM-PPM system improves the error performance and transmission rate,it sacrifices part of the spectrum efficiency.Based on this,for the space time dispersion matrix in DOSM-PPM,PAM signals are introduced again,and a high-dimensional differential optical spatial modulation(HD-DOSM)system is constructed by using the amplitude ratio.The bit error rate expression is deduced by the union bound technology,and the performance of DOSM-PPM is compared at the same time.The results show that the introduction of PAM improves the spectrum efficiency of DOSM-PPM,and achieves a compromise between the error performance and spectrum efficiency of the DOSM system.Under the same spectrum efficiency,the HD-DOSM system improves the error performance and reduces the number of emitting lasers.In addition,for the high-complexity maximum likelihood decoding algorithm,the space and symbol constellations are detected step by step,which effectively reduces the computational complexity of the system.