NEC Corporation (NEC) has successfully demonstrated real-time digital wireless Orbital Angular Momentum (OAM) mode multiplexing transmission over 40 meters in the 80 GHz-band. This technology can help solve the ever-increasing demand for high-capacity wireless connections for 5G networks. NEC aims to use this technology for its iPASOLINK series of ultra-compact microwave and mmWave communication products, which are capable of extremely reliable, high-capacity mobile backhaul solutions for 5G networks.
In recent years, more and more base stations are required for proper transmission coverage, especially in hot spots and ultra-dense urban areas, where the cell grid becomes very dense. Additionally, datacenters will be moving to the edge in order to handle low latency requirements. However, it is difficult to connect these high-density cell sites with just optical fibers.
Moreover, traffic volume between 5G base stations can reach up to 100Gbps and it is extremely challenging to create sufficient transmission capacity with existing methods, such as using wider channels, multi-channels or increasing the modulation scheme. Therefore, high-capacity wireless backhaul is a key technology to cover the whole network and OAM mode multiplexing technology is attracting a great deal of attention.
OAM is one of the physical characteristics of electro-magnetic wave propagation. A feature of an OAM signal is that it has a spiral phase front. The number of spiral planes in a signal is called an OAM mode, and the shape of all modes is different. This means that all of the OAM modes are independent of each other. Therefore, multiple OAM modes transmitted on the same channel simultaneously can be separated and demodulated at receivers. This is an OAM mode multiplexing transmission.
NEC has developed a real-time digital signal processing circuit and successfully demonstrated, for the first time in the world, wireless transmission over a distance of 40 meters with a modulation of 256 QAM in the E-band (71 to 86 GHz) by multiplexing 8 OAM modes. In this demonstration, 7.4 Gbps (8 modes x 8 bit/symbol x 115 Mbaud) were transmitted using a symbol rate of 115 Mbaud.
The newly developed digital signal processing circuit superposes and separates the OAM modes with high precision, which improves the spectrum efficiency.
Going forward, NEC will work on research and development to realize 128 bps/Hz (8 modes x Dual polarization x 8 bit/symbol), as well as 100-meter transmission in the higher frequency D-band (130 to 174.8 GHz) by the end of in 2019. Transmission at 100 meters in the D-band will be one of the key technologies applicable to backhaul for 5G base stations and the fronthaul between CU (Central Unit: aggregation base station) and DU (Distributed Unit: remote station).
This research and development was conducted as part of "The Research and Development Project of OAM Mode Multiplexing Radio enabling Ultra High Capacity Transmission in Millimeter-wave bands" under a contract with the Ministry of Internal Affairs and Communications, Japan.
