NEC
NEC develops optical fiber wireless system that realizes smaller millimeter-wave distributed antennas and lower power consumption for Beyond5G/6G
~ Contributing to stabilizing millimeter wave communications in environments with many obstacles ~
……
NEC has developed and successfully demonstrated a 1-bit fiber transmission optical fiber wireless system that enables the
construction of stable millimeter-wave communication networks at low cost for Beyond 5G/6G. By using this method, it is possible to transmit high-frequency analog signals using inexpensive
general-purpose electric-to-optical converters for digital
communications, and a small distributed antenna unit can be realized at low cost.
This makes it possible to create a stable millimeter-wave
communication environment at a low cost in environments with many obstructions, such as high-rise buildings, underground malls, factories, railways, and indoors.
This result will be presented at the international conference “IEEE MTT-S International Microwave Symposium (IMS2024)” to be held in Washington, DC, USA from June 16th (local time).
●Development background
High-speed wireless communication using millimeter wave technology is expected to be a key technology for Beyond 5G/6G. In particular, since approximately 80% of mobile communication traffic occurs indoors, millimeter waves are being considered as an indoor countermeasure. However, because the millimeter wave band has large propagation loss and high straightness, it is necessary to ensure line-of-sight between base stations and terminals in order to achieve sufficient QoS (quality of service). Installing distributed antenna units
(hereinafter referred to as Distributed Antenna) that directly transmit and receive data to and from terminals at a high density and avoiding obstructions is an effective way to solve this problem, but the size and power consumption of DA , the cost of installing the required amount is a major issue.
Therefore, NEC has developed an optical fiber radio system
(hereinafter referred to as RoF) and its transmission method that can make DAs smaller, lower power consumption, and lower costs.
[Image 1: https://prtimes.jp/i/78149/616/resize/d78149-616-e8d8cf0de8ee4c771235-0.png&s3=78149-616-6f9635158e32ad65b334f2b37814a894-3543×976.png ]
Figure 1 Millimeter wave mobile network using optical fiber wireless system ●Challenges of conventional wireless fiber optics (RoF) and approaches to solving them
Conventional RoF is classified into digital RoF systems (hereinafter referred to as digital RoF) and analog RoF systems (hereinafter referred to as analog RoF), as shown in Figure 2. Digital RoF transmits digital signals generated by a radio unit (RU) to a DA via fiber. DA used in digital RoF needs to be equipped with a digital signal processing device (DSP) and a digital-to-analog converter (DAC), resulting in high power consumption and high cost. Analog RoF uses a method that generates high-frequency analog signals in the RU and transmits them to the DA via fiber. In analog RoF, the DA requires no DSP or DAC, simplifying the configuration, while the
electrical-to-optical converter requires a dedicated converter that requires high linearity for analog signals. This is a factor that drives up device costs.
Therefore, NEC has developed a 1-bit fiber transmission method and a 1-bit RoF system (hereinafter referred to as 1-bit RoF) using it. The 1-bit fiber transmission method converts a high-frequency analog signal into a 1-bit pulse signal and transmits it through fiber.The desired analog signal can be regenerated by passing it through a filter. 1-bit RoF using this method makes it possible to use inexpensive general-purpose electrical-to-optical converters for digital communications, just like digital RoF, and at the same time, unlike analog RoF, it does not require DSP or DAC in the DA. plug. In other words, 1-bit RoF is a system that can combine the advantages of digital RoF and analog RoF.
[Image 2: https://prtimes.jp/i/78149/616/resize/d78149-616-c07a959d403ec4198f63-1.png&s3=78149-616-5ea256f47b495f0f8c84362bb46ac403-3461×2150.png ]
Figure 2 Types of optical fiber wireless systems
●Efforts to realize 1-bit RoF system
In order to put 1-bit RoF into practical use, there was an issue with the low signal-to-noise and distortion characteristics of the 1-bit modulator that converts it into a 1-bit pulse signal. Now, we have developed a vector decomposition method (Note 1) with excellent noise and distortion characteristics as a 1-bit fiber transmission method for downlink. Additionally, for the uplink, we have developed a digital reproduction method that cancels the signal distortion that occurs in 1-bit fiber transmission and reproduces the original signal. As a result, we succeeded in suppressing deterioration of
signal-to-noise and distortion characteristics during 1-bit fiber transmission in both downlink and uplink directions.
[Image 3: https://prtimes.jp/i/78149/616/resize/d78149-616-d8c35b062bca69591c10-2.png&s3=78149-616-c2de09016234554a54745bd2f4ce214e-3210×997.png ]
Figure 3 Proposed 1-bit optical fiber wireless system
Additionally, in order to confirm that the newly developed 1-bit RoF system complies with mobile communication standards, we have developed a new optical fiber wireless prototype device (Note 2) for the 40 GHz band consisting of a wireless unit and a small DA. did. As a result of the demonstration, compliance was confirmed (Note 3).
[Image 4: https://prtimes.jp/i/78149/616/resize/d78149-616-ae8132d54d8e9c9f7641-3.png&s3=78149-616-315ff59c1938253663858d3c3fe56616-3090×1391.png ]
Figure 4 40GHz band distributed antenna unit
This makes it possible to install small, low-cost DAs at high density. Additionally, line-of-sight between DA and terminals can be ensured, which is expected to improve the millimeter wave communication environment.
●Next development
We have developed a 1-bit fiber transmission method that enables smaller millimeter-wave dispersion antennas, lower power consumption, and lower costs. Optical fiber wireless systems that apply this method will be able to construct stable millimeter-wave communication networks at low cost, even in environments with many shields, such as high-rise buildings, underground malls, factories, railways, and indoors, and beyond5G/6G. This will help promote the spread of high-speed, high-capacity communications using millimeter waves. We will continue to develop high-speed, large-capacity technologies for beyond 5G/6G.
●Announcement schedule
This research result will be presented at the Photonic-Enabled Systems and Solutions session of the IEEE MTT-S International Microwave Symposium (IMS2024), which will be held in Washington, DC, USA from June 16th (local time). The presentation will be titled “over-Fiber System with Hybrid Architecture for 40-GHz Band”.
Lecture time: June 18th 8:40 a.m. (local time)
Lecture title: 1-Bit Digital Radio-over-Fiber System with Hybrid Architecture for 40-GHz Band
Conference website: https://ims-ieee.org/
[Acknowledgment]
This research is part of the results of the Ministry of Internal Affairs and Communications commissioned research, “Research and Development for Expansion of Radio Wave Resources (JPJ000254).” (Note 1) Vector decomposition method: A method that decomposes a wireless signal into two signals with constant amplitude. Another name is outphasing method.
https://jpn.nec.com/techrep/journal/g23/n01/230110.html
(Note 2) To achieve miniaturization of DA, we developed a ΔΣ modulator IC that can operate at 5Gbps as a 1-bit modulator for uplink using a general-purpose CMOS process. The IC size is 2×1.5mm.
(Note 3) Confirmed compliance with 3GPP standardization in OTA measurement.
This article has been partially generated with the assistance of AI.