Signal Interference—A New Problem in the Age of Wireless Communication That Can Suddenly Disconnect Your Smartphone

Main visual : Signal Interference—A New Problem in the Age of Wireless Communication That Can Suddenly Disconnect Your Smartphone

With the implementation of the fifth generation mobile communications system (5G), the next-generation communications standard planned for 2020, expectations are high for smoother, improved communications services. However, with the increase in traffic, the possibility of worsened communication quality due to signal interference is gaining attention. To address this issue, Fujitsu developed the world's first technological solution for removing signal interference that is thought to be unpredictable.

Signal Interference Lowers Communication Quality

Many people have experienced problems like having sudden difficulties connecting with their smartphones, or long upload times when trying to upload an image or a video taken at sporting or other events to social media. There are numerous potential causes for these problems, one of which is signal interference. The emergence of these problems is related to the rapid changes in the environment surrounding wireless communication.

Why Does Signal Interference Occur?

In Japan, the communication traffic volume has been increasing at an annual rate of 140 percent during the 10-year transition period from third generation wireless (3G) to fourth-generation wireless (4G/LTE). In order to secure communication capacity, more multiband operation stations that can increase the available bandwidth are being built, tripling the frequency assigned to wireless communication and doubling the number of bands. As we move into the future, in addition to the implementation of 5G, the increase in IoT devices is expected to further contribute to the increase in wireless traffic.

Signal interference is caused by these multiple-frequency signals and rusted metal. When multiple-frequency signals hit rusted metal objects like bolts, wire netting and chains in and around the wireless base stations, distorted waves are deflected, generating unexpected frequency elements. This generates interfering waves called passive intermodulation (PIM), which prevents normal communications. For example, when using a smartphone for communication, these unexpected frequency elements are received by the antennas at the base stations, adding unwanted noise and reducing communication quality. This can cause delays in upload and download speeds.

How Does the Technology Developed by Fujitsu for Removing Signal Interference Work?

In order to solve these problems, Fujitsu developed technology that can accurately predict the PIM that brings down communication quality, and cancels out the power of just those signal elements. The technology to compensate for distortions has already been implemented for things that send specific forms of electric power by commands, such as transistors, integrated circuits and diodes. An idea was raised for controlling PIM by applying the same technology to the receiving end of distorted interference waves on devices other than itself. This led to the first-ever attempt to develop this technology.

Effects of Fujitsu's signal interference removal technology

A vital component of this technology is the generation of non-linear replica signals. By accurately predicting the interference waves generated by distorted reflections, a replica is generated with digital signals. By subtracting these signals from the reception signals, the PIM interference signals are canceled, and only the intended reception signals are extracted.

Vital component: Non-linear replica signal generation

It is generally more common to process PIM based on polynomials where electric power and wave phases are represented by functions. However, because the terms of polynomials increase exponentially as the number of signal-sending carriers and the degree of modulation increase, it becomes impractical to implement the formulas on an electric circuit due to the unrealistic scale. Furthermore, many multiplication operations become necessary, causing problems for commercialization by making the downsizing of circuits difficult.

To address this issue, Fujitsu implemented the method for Digital Pre Distortion (DPD) technology designed for their high-output amplifiers in order to generate accurate waveforms using few multipliers, and made it possible to generate replicas that are more precise. As a result, this technology was able to fully recover the communication area lost to PIM, while the conventional method using polynomials could only recover from 1/30 to 1/5. Moreover, by downsizing the circuit volume Fujitsu was able to achieve both high functionality and compact design, which have been on-going challenges.

This technology utilizes the FPGA method, a semiconductor integrated circuit that can change the electronic control function of devices. This makes the technology very flexible, and can be deployed in existing equipment regardless of the manufacturer, giving it the benefit of easy deployment.

Implemented in 2017 as the World's First Signal Interference Removal Technology

This is the only technology of its kind in the world. Operation started in 2017, and the cancellation effects have been verified in sites where signal interference was actually occurring.

Signal interference caused by PIM can occur in any market where frequencies are expanding, meaning all places that have built mobile networks are areas of potential application. Developments are underway with a focus on developed countries and urban areas with high traffic, with plans to roll out sales promotion activities in the U.S. starting in 2019. In the future, the goal is to spread the use of this technology to mobile networks all around the world.

In addition, Fujitsu plans to provide this technology to companies that manage and operate indoor wireless broadcasting systems and cable TV, in addition to existing communications operators.

Fujitsu received the 2018 (66th) Electrical Science and Engineering Promotion Award* for this technology. This award is given to the creation of new technologies that help enrich people's lives. In this case, one of the factors that contributed to this award being given was the process of steadily engaging in activities to improve its feasibility and accuracy of the technology, while continuing to collect and analyze data when there is not much literature on PIM.

Preparing for the 5G + IoT Society

In addition to the implementation of 5G, IoT, the technology that connects various devices to the internet, is undergoing further advancements. As the volume of transmission data is expected to increase dramatically, in order to aim for more stable communications, it is necessary to achieve higher power and improved broadband communication. Meanwhile, as the frequencies in use increase, the potential impact toward reduced communication quality due to signal interference becomes more severe. Under these circumstances, the signal interference problem is not limited only to partial networks as it currently is, but in the future the entire mobile infrastructure may be impacted, meaning this could potentially become a major societal problem that affects corporate activities and people's social lives.

Fujitsu provides many solutions based on innovative technologies such as the signal interference removal technology to help create safe, secure and convenient mobile communications as we approach the era of the 5G + IoT society.

*: The Electrical Science and Engineering Promotion Award has a history that goes back to 1952, and is awarded by the Promotion Foundation for Electrical Science and Engineering for inventions, research, real-world implementation, software development and educational programs that achieve excellence in the field of electrical science and technology. The award is presented to people who have contributed to developing Japanese industries and improving people's lives, as well as to those who have a high potential for future contributions.