The Great Potential of Optical Spatial Modulation Technology
As a potential alternative, wireless optical communications (WOCs) have the advantages of broadband, security and easy deployment. The application scenarios widely involved in military, emergency communications and next generation access networks. Unfortunately, when the laser signal is transmitting in the atmosphere, it is affected by factors like atmospheric attenuation, atmospheric turbulence, inter-channel interference and pointing errors. Optical multiple input multiple output (OMIMO) is one of the promising technologies to improve WOCs performance. It can improve system capacity without additional transmitting power and has an excellent performance in improving data transmission rate and resisting atmospheric fading. However, simultaneous activation of multiple lasers leads to increasing system complexity and the actual power consumption. In addition, inter-channel interference (ICI), inter-antenna synchronization (IAS) and antenna correlation have become the application hindering of OMIMO systems. Based on the idea of OMIMO technology, optical spatial modulation (OSM) extends the modulation scheme from the traditional digital domain to the digital-spatial domain. Both digital modulation and laser index are utilized to transmit data, which greatly improves the channel capacity and data transmission rate. Since only a small amount of lasers are activated at per symbol duration, the inadequacy of OMIMO is compensated. OSM technology has the advantages of low complexity, high power efficiency, less ICI and more accurate synchronization of antennas. As a result, OSM is considered to have the application potential in the next generation access networks.
The research team of wireless optical communication and sensor technology in Lanzhou University of Technology, which led by Prof. Huiqin Wang, has recently been devoted to the research of high speed optical wireless optics in modulation technologies and low-complexity decoding and detection algorithms. In the review paper, they introduce the background and basic concept of OSM in detail. Moreover, the principle and the research status of several basic OSM schemes are analyzed systematically. Furthermore, the technical problems and countermeasures enroll in practical applications are discussed. In addition, the technical problems need to be further studied and the technology trends in recent OSM research are listed. To the issue of rapidly growing of data bandwidth requirement, the generalized principle of OSM/OSSK communications and enhanced optical spatial modulation (EOSM) scheme with a variable number of activated lasers is proposed by the team. The EOSM scheme increases spatial domain mapping by activating different index combinations of one or two lasers at a time slot duration. Moreover, different PPM constellations are mapped onto the different composite indexes. This scheme improves the data transmission rate and laser power utilization, and breaks the restrictions that laser number must be an integer power of 2 at the transmitter side. When the data transmission rate is 6 bpcu, the BER performance of EOSM scheme is close to that of spatial pulse position modulation (SPPM) scheme, and much better than that of spatial pulse amplitude modulation (SPAM) scheme and generalized spatial pulse position modulation (GSPPM) scheme. Compared with SPPM, SPAM and GSPPM systems, the proposed EOSM system uses 12, 12 and 3 fewer lasers, respectively, which greatly reduces the system cost. The proposal provides a valid approach to realize high capacity wireless optical communications.
Figure 1 Comparison of BER performance of different systems at the same data rate
Figure 2 Comparison of spectrum efficiency and computational complexity at the same data rate
This research is supported by the National Natural Science Foundation of China (Nos.61861026, 61875080, and 61465007).
About The Group
Wireless optical communication and sensor technology research team, led by Prof. Huiqin Wang, is affiliated with theSchool of Computer and Communication, Lanzhou University of Technology. The team has long been committed to research and technology development of wireless optical communication technologies in the fields of atmospheric channel transmission characteristics, channel coding schemes, modulation techniques, channel estimation methods and signal detection algorithms. The team has 2 professors, 1 associate professor, 2 lecturers, and more than 20 doctoral and postgraduate candidates at present. In recent years, the team has presided over more than 20 scientific research projects, such as National Natural Science Foundation of China, provincial and ministerial research projects. The team members applied for 23 national invention patents of China, among which 8 have been authorized. Moreover, the team has 5 authorized utility model patents, and 6 authorized software copyright and awarded 6 prizes at the department level or above. In addition, more than 60 peer reviewed academic papers and 3 textbooks were published. The team members also serve as reviewers of several famous academic journals.
Mao Yicong, Wang Huiqin, Zhang Yue, et al. Research status and development of optical spatial modulation technology[J]. Opto-Electronic Engineering, 2020, 47(3): 190712.