The 5G vision set forth by IMT-2020 is an amazing thing. It opens up so many possibilities for consumers, the environment, health and safety, humanity. Virtually every industry will be transformed, and new ones will emerge. The three defined use cases: enhanced mobile broadband (eMBB) to support extreme data rates, ultra-reliable low latency communications (URLLC) for near instant communications, and massive machine type communications (mMTC) for massive interconnects, are foundational to setting the 5G specifications.
The 3GPP is developing standards for radio interference technologies to be submitted to the ITU (International Mobile Telecommunications 2020) for compliance with the IMT-2020 requirements. While these standards are in some ways an extension to existing 4G standards, they really are radically different from what’s in use today. If the standards are radically different, then it’s not a stretch that the tests required to verify 5G product designs are also radically different.
The initial 5G New Radio (NR) release 15 was introduced in December 2017, and the full release is targeted for June 2018. Release 15 focuses on specifying standards for the eMBB and URLLC use cases. Standards for the mMTC will be addressed in future standards releases. New releases of the standard will continue to roll out over many years. No previous standard has attempted to cover such a broad range of bandwidths, data rates, coverage, and energy efficiency.
Some key differences in 5G NR release 15 include:
- Flexible numerology enables scalability – Where subcarrier spacing was fixed to 15 kHz in 4G LTE, it now scales to higher spacings. Wider spaced subcarriers shorten the symbol period, which enables higher data rates and lower latency for URLLC use cases. In contrast, with shorter subcarrier spacing, longer symbol periods allow for lower data rates and energy efficiency for IoT, or the mMTC use case.
- mmWave frequencies open up more bandwidth – LTE supports up to six channel bandwidths, from 1.4 MHz to 20 MHz. These can be combined through carrier aggregation for a maximum bandwidth of 100 MHz. The initial 5G NR release 15 specifies frequency up to 52.6 GHz with aggregated channel bandwidths up to 800 MHz. Initial target frequency bands are 28 GHz and 39 GHz. To put this in perspective, these mmWave bands alone can encompass the entire spectrum of the current 3G and 4G mobile communications system. This additional spectrum is essential to enabling eMBB extreme data rates.
- Massive MIMO to increase capacity – MIMO in LTE uses multiple antennas to send multiple, independent streams of data through the same frequency and time space. MIMO has been shown to increase data rates by making better utilization of the spectrum. With Massive MIMO, the number of antenna elements on the base station is considerably greater than the number on the device. Implementing multiple antennas on base stations and devices will be essential to increasing capacity and achieving the throughput envisioned in eMBB use cases.
New Test Challenges
These new standards will introduce new challenges in test.
Flexible numerology complicates the development of the 5G NR waveforms and introduces many new use cases that need to be tested. In addition, it also introduces a new levels of coexistence testing with 4G and potentially Wi-Fi.
mmWave frequencies with more bandwidth changes all assumptions about conducted tests. Due to the higher frequencies and use of highly integrated multi-antenna arrays, tests will now be performed over-the-air (OTA).
Massive MIMO increases the number of antennas, and subsequently the number of beams coming out of base stations and devices. These beam patterns, whether at sub-6 GHz or mmWave, need to be characterized and validated in an OTA test environment.
Viewing a 256 QAM waveform with antenna pattern
Radically different? Absolutely. Test solutions must be flexible and scalable so that they cover the
number of use cases, frequencies, and bandwidths, as well as OTA validation. The test solutions must also evolve as the standards evolve. Check out this article series by Moray Rumney to understand more about how test will change as we move into the next stage of 5G development: The Problems of Testing 5G Part 1.