5G manufacturing: Overcoming gNB test challenges

Article By : Jessy Cavazos

Before operators start capturing the new revenue streams from 5G, the industry must tackle what is perhaps the greatest challenge of all for the technology: manufacturing test.

5G is moving fast.  In 2018, we saw the emergence of the first chipsets. This year, we will see the first commercial deployments of next generation Node B 5G base stations (gNBs) and devices. The technology is progressing across the mobile ecosystem from chipset and device manufacturers to network equipment manufacturers (NEMs) and service providers. Before operators start capturing the new revenue streams from 5G, the industry must tackle what is perhaps the greatest challenge of all for the technology: manufacturing test.

Don’t get me wrong.  5G is disrupting the entire wireless ecosystem from research and development (R&D) to the field with an exponential increase in complexity notably due to the use of massive multiple input multiple output (MIMO), the extension to millimeter-wave (mmWave) frequencies, and beamforming. However, manufacturing is the phase in the product lifecycle where the rubber meets the road. For 5G to be successful, NEMs must find ways to test infrastructure equipment cost-effectively, provide high quality in accelerating timelines, and remain flexible to address spikes in volume, channel requirements, and more frequency bands. These three factors – increased device complexity, finding breakthroughs to lower the cost of test, and faster time to market, are entirely at odds. NEMs’ greatest challenge in manufacturing is to address them simultaneously to win the 5G race.

With massive MIMO, the number of channels increases to 16, 32, 64, and even 128, impacting test times significantly which has a corresponding increase in the cost of test.  NEMs must increase their test speed substantially while controlling the footprint of test equipment on their manufacturing floor and ensuring the scalability of their manufacturing test operations.

In parallel, mmWave frequencies provide link budget issues due to higher power loss at these frequencies as well as the need to test over the air since the antennas are bonded directly on the radio chip providing no access to a cable. These factors reduce the dynamic range. Making an accurate measurement becomes even more challenging.  NEMs are under tremendous pressure to reduce the cost of manufacturing base stations, yet these challenges require more material, such as over-the-air (OTA) chambers and high performing instruments.

Practical OTA testing solution for gNB manufacturing
With 5G and the quest for wider bandwidths, NEMs have had to leave the familiar, yet very crowded frequency spectrum below 6 GHz, to operate at uncrowded frequencies in the more difficult mmWave spectrum.  Referred to as frequency range 1 (FR1) in the 5G New Radio (5G NR) standard specification, frequencies below 6 GHz are drastically different from the infamous mmWave frequencies of 5G NR’s frequency range 2 (FR2), which go from 24.25 GHz to 52.6 GHz.

Less used than sub-6GHz frequencies, the mmWave spectrum is giving users the data rates they want by allowing wider bandwidths since many other applications do not use this space.  While this aspect is attractive, the propagation characteristics of mmWaves are not.  Because of higher diffraction, penetration, and atmospheric loss, there is high path loss at these frequencies, which limits the range of wireless signals.  This has prompted the use of phased arrays and eliminated the space previously used to place probes. 5G results in a disruptive shift for test operations from conducted tests to radiated tests (also known as OTA testing).

In an OTA measurement setup, excess path loss between the instruments and the device under test (DUT) reduces the signal-to-noise ratio (SNR) causing poor error vector magnitude (EVM) and adjacent channel power ratio (ACPR).  Superior ACPR instrument performance is critical to minimize interference by ensuring that the instrument is only transmitting within its assigned channel.

R&D engineers can use high-performance microwave instruments to overcome the mmWave path loss challenge.  In manufacturing, using such instruments can be overkill and cause the cost of test to increase significantly.  Instead, you may want to consider a banded solution that combines instruments of lower frequency range with an external mmWave transceiver to provide the right balance between performance and price.  This solution has the up and down conversion at the measurement plane, which reduces insertion loss providing the needed performance at a much wider power range. This approach provides you a much more affordable and flexible 5G manufacturing test solution for high frequencies.

Figure 1 highlights how a remote mmWave transceiver head reduces insertion loss in an OTA test setup.

Figure 1 Classic test set up at FR2 frequencies

Figure 2 An OTA test set up with remote mmWave transceiver head for lower insertion loss

Scalable instruments for more frequency bands and wider channel bandwidths

5G NR frequency ranges operate across multiple bands numbered from 1 to 255 for FR1 and 257 to 511 for FR2.  Maximum channel bandwidth increases to 100 MHz for sub-6 GHz frequencies and 400 MHz for mmWave frequencies.  This channel bandwidth is 5 to 20 times that of LTE standards since LTE, LTE-A, and LTE-A Pro all had a maximum channel bandwidth of 20 MHz. Maximum aggregated channel bandwidth is also much higher in 5G NR (almost twice that of LTE variations) reaching 400 MHz for FR1 and up to 1.6 GHz for FR2 compared to 100 MHz in LTE-A and 640 MHz in LTE-A Pro.

Equipping their manufacturing operations with test instruments that can flexibly handle the greater number of frequencies (including mmWaves) and the wider channel bandwidths of 5G NR is essential for NEMs to minimize the increase in the cost of test from 5G. Instrument scalability helps contain test equipment footprint and therefore saves manufacturing floor space for which contract manufacturers typically charge by the square foot.

Wider channel bandwidths also make the performance requirements for error vector magnitude (EVM), flatness, and dynamic range more difficult to achieve. NEMs need instruments that provide superior radio frequency (RF) performance with low frequency response for amplitude and phase to reduce signal-to-ratio (SNR) degradation from corrections. In addition, beware of other factors that can lead to lower measurement accuracy such as the components, switches, and cables in the measurement system and measure the frequency response at test fixtures, cables, connectors and mixers.  Using a remote extender head helps eliminate these issues.

Modular-based instrumentation for fast multi-antenna systems test

To improve spectral efficiency and coverage, 5G uses MIMO and beamforming concepts. In design verification, multi-antenna radio frequency (RF) systems increase the complexity of the test setup and make achieving proper synchronization time-consuming. In the manufacturing stage, the focus is on making sure that each channel works properly.  Therefore, all channels are tested single-handedly.

NEMs needs test solutions that perform fast testing of DUTs and can scale as they transition from 4 to 8-port 4G devices to 5G with 16, 32. 64 or 128 channels. They need solutions that support multi-channel and multi-site testing and deliver high throughput. With the Keysight vector transceiver (VXT), for example, the vector signal generator (VSG) and vector signal analyzer (VSA) are integrated into a two-slot PXIe module. An 18-slot PXI chassis can support up to eight VXT modules in a 4U size.  Software and hardware accelerated measurements also maximize test speed across power and frequency ranges for multiple channels and radio formats.

While considering test solutions for your 5G manufacturing test operations, be cautious about their effectiveness for this environment by reviewing signal generation and analysis bandwidth capacity, output power, phase noise, amplitude accuracy, EVM and ACLR performance, automation features, calibration aspects, and the solution’s footprint.

Figure 3 5G NR test setup for a multi-band DUT with multi-antenna configuration

Bridging the gap between verification and manufacturing for faster time to market

Engineers face significant technical challenges in manufacturing for 5G that translate into higher costs and longer time to market. The scalability, small footprint, and RF performance of their test solutions are critical to cover both FR1 and FR2 frequencies, expand to higher-order MIMO, and reduce false positives.

However, an overarching strategy that bridges the gap between integration and verification and volume manufacturing could give you the edge over your competition by accelerating this transition.  A common application programming interface (API) works wonders, by facilitating integration into manufacturing systems and common software, and helps reduce development efforts dramatically accelerating your time to market.  Also, consistent measurement algorithms and common hardware can provide correlation of data across the product lifecycle aiding in shorter transition times and faster troubleshooting.

“He who fears being conquered is sure of defeat”

The cost of test challenge with 5G is no joke. More frequency bands, wider channel bandwidths, and complex multi-antenna configurations can be significant drivers for costs requiring higher-performance instruments and increasing test times. But NEMs can effectively address these challenges by partnering with test and measurement experts that provide innovative solutions that address the technical complexity brought by 5G while controlling its impact on costs and time. As Napoleon Bonaparte famously said, “He who fears being conquered is sure of defeat”. Don’t let the complexity of 5G slow you down on your way to market leadership.  

Visit Keysight for more on 5G manufacturing test challenges and solutions and high-volume test for gNBs.

Jessy Cavazos is part of Keysight’s Industry Solutions Marketing team.

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