5G Test: Issues and Implications
The fifth-generation of cellular technology, known as 5G, promises to enable a sea change in telecommunications, automation, and computing. Some analysts and futurists have suggested it has the potential to revolutionize society in ways even greater than the internet itself. However, the performance requirements of 5G creates a series of unique challenges for IC/SOC test, PCB assembly test, finished device test, and network equipment conformance test.
5G is the common name for the IMT-2020 performance requirement, defined by the International Telecommunication Union (ITU-R). Technologies that meet the IMT-2020 requirements may market their technologies as 5G, in the same way that technologies meeting the 4G requirements – including Long Term Evolution (LTE) governed by the 3rd Generation Partnership Project (3GPP) family of standards, and WiMAX governed by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 family of standards – were commonly called 4G. 3GPP’s technology for 5G wireless equipment is known as New Radio or “NR”.
Like previous cellular generations that focused on improvement of connectivity for portable computing devices, 5G improves user-experienced data rates by orders of magnitude and reduces latency to nearly real time levels. Additionally, 5G adds support for timing-critical applications like accurate positioning (without need for GPS satellites) for intelligent/autonomous vehicles and virtual or augmented reality, and expands support for Internet of Things (IoT) applications and robotic systems. 5G radios will make use of beamforming and multiple-input, multiple-output (Massive MIMO) antennas that leverage spatial multiplexing and multipath to improve channel performance and spectral efficiency. To reach the performance levels required by 5G, designers will push computing, memory, digital and analog/RF circuitry, and semiconductors to their limits.
Additionally, the complexity of conformance testing required is growing exponentially with each generation of cellular technology; 3GPP Release 14 (which contained some pre-5G elements) specified approximately 15,000 tests in the full conformance suite. 3GPP Release 15 (early 5G) specifies approximately 300,000 tests – a 20-fold increase in test complexity. We should expect that 3GPP Release 16 (pure 5G) will specify additional tests. It is worth noting that these numbers do not include coexistence testing intended to show that 5G devices and equipment will not interfere with non-5G devices in shared spectrum. As the number of tests increases, the cost of test goes up – and the need for higher test speed and test flexibility will increase.
Testing the RF Front Ends (RFFEs) of 5G equipment and devices is challenging, as the air interface frequencies range from 450 MHz to 6 GHz (in the FR1 bands) and 24.25 GHz to 52.6 GHz (in the FR2 bands) and include both licensed and unlicensed bands. Power consumption of the 5G RFFE (especially in user devices) will be a consideration, as power amplifier efficiencies tend to fall as output frequencies rise. Additionally, power management architectures on both the 5G receiver and transmitter will need to be very responsive to variations in signal level, which can change rapidly when the 5G link is using higher frequencies that are heavily influenced by line-of-sight impairments.
In 5G use profiles where high throughput is needed, the 5G baseband integrated circuit and system-on-chip devices will use extremely fast data rates – on the order of 32 gigabits per second for some SERDES interfaces in 5G NR base station equipment. Nyquist-Shannon sampling theorem requires clock rates at least twice the data rate, which implies that sampling clocks in test systems will run at speeds equal to or greater than the higher 5G air interface frequencies – this has significant implications for the design of signal integrity test fixtures and circuits. Likewise, latency requirements for 5G are at or below 1 millisecond end-to-end, which implies that test fixtures and circuits must be able to measure and manage transitions at high speed.
Given the above, it becomes obvious that digital circuits in 5G NR equipment and devices (and the testers used to analyze them) must be designed with RF techniques, with attention paid to transmission line effects, terminating impedances, and reflection of signals from mismatched terminations. In some cases, frequencies will be so high that only radiated tests will be possible, as transmission line effects and RF calibration requirements will make conducted tests impossible. For integrated circuit and system-on-chip devices at low-nanometer geometries, it will be important to analyze cross-coupling between on-chip circuit blocks.
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