Building 5G Fronthaul Networks for IoT

5G cellular mobile communications are coming and bringing with them a host of new applications. The higher bandwidth and lower latency of 5G wireless technology will allow for more and faster data, but also forces you to rethink transport networks.

5G requires a smaller radio footprint than in 4G to support massive 5G traffic within the licensed spectrum bands. Part of the 5G spectrum is offloading to the millimeter-wave (mmWave) band. However, mmWave has a shorter reach, and this also shrinks the cell size. The ever-increasing number of 5G cell sites requires a shift in the way mobile transport networks operate. This is when the fronthaul, the way that a baseband processor interacts with antenna signals, comes into focus.

The closer proximity and higher bandwidth of 5G cells will alter the way you use near-field communications and the Internet of Things (IoT). Several small cells in a store or shopping mall will provide real-time cloud-based augmented reality (AR) to customers. Deploying home internet services will change. Instead of cabling an entire building, fiber will run to rooftop cells that will provide high-speed and low-latency access to all its occupants. While all of this is already possible with existing wireless networks, 5G will significantly enhance the delivery of such services.

The Customer: NICT

The National Institute of Information and Communications Technology (NICT) promotes a full spectrum of research and development (R&D) activities in Japan. It aims to make Japan a world leader in information communications technology through close ties with academic and business communities domestically and abroad. The findings of its R&D activities impact society in a broad range of fields beyond academia and commerce.

NICT serves as a technical advisory body that helps the Japanese government with radio spectrum planning and bandwidth allocation. The institute also performs research on advanced fiber optic and photonic network technology. Fiber is reaching the limits of its capacity, and the institute is trying to push those limits. Recently, NICT developed a photonics and electronics convergence device that converts data transmitted as light across fiber-optic networks to highly efficient mmWave radio signals for wireless transmission.

The Challenge: Testing Network Latency in Real Time

In collaboration with the Graduate School for the Creation of New Photonics Industries (GPI), NICT researchers are working on the optimization of low-latency data compression for the fronthaul of 5G transport networks.

Efficient fronthauling requires high-throughput, low-latency, and space-and-time compression techniques for 5G radio frequency signals. Compressing merged radio channels reduces the amount of data being transported from the multiple antennas at a cell site to the cloud quickly. Extracting only the data in channels in use and compressing them saves overhead by not compressing the data streams of antennas that are not actively transmitting.

Algorithms called subspace tracking allows data extraction blindly and adaptively. Low latency audio compression techniques reduce the size of these signals. Using these tools, NICT researchers were able to route 256-antenna long term evolution (LTE) signals, which require a 260-gigabaud optical interface in the conventional fronthauling technique like the common public radio interface (CPRI), over a 10-gigabaud optical interface. It was one of the institute’s most significant engineering achievements of 2018.

The compression side of the equation is easy, but latency is a significant challenge because it is affected by many factors. The number of channels and antennas; the distance between cells; the type of digital signal processing (DSP) circuits, digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) in use; and the network infrastructure all play a part in determining latency. A computer model can also simulate compression, but the same is not true for latency.

The Solution: The M3300A Test Platform

NICT needed to test different configurations of its fronthaul architecture and its compression solution for latency. The only way to do this was in real time. NICT could have purchased FPGA chips from Xilinx and peripherals from other vendors, hooked them up to a test environment by integrating with high-speed DAC and ADC interface boards, and then asked a technician to program them. However, this would have taken too much time, and cost far too much money. This testing would have amounted to $100,000 per trial, making it challenging to keep up with the rapid pace of 5G/IoT R&D.

NICT needed a simpler hardware implementation solution to support its researchers during the testing phase. Keysight’s FPGA-based multiple-channel arbitrary waveform generator (AWG) and digitizer combination solution (M3300A) was the best fit for analyzing its space-time fronthaul compression solution in real time.

The Results: Accelerating R&D with Keysight

With the ready-to-go FPGA programming environment and prompt support by Keysight’s engineers, NICT attained almost the same level of expertise as a dedicated programmer and was able to use the Keysight M3300A test platform to verify and then demonstrate various iterations of its design within a year. It saved NICT months of extra effort and approximately $50,000 by doing the FPGA programming itself, with guidance from Keysight’s engineers. The Keysight solution and support helped NICT focus on the R&D process and freed its researchers to direct all their resources into redesigning, upgrading, and updating algorithms as it moved toward a definitive version of its fronthaul technology.