With 5G NR release 15 in June 2018, how soon can you expect to see 5G devices operating at mmWave frequencies? The current buzz is sooner than you expect.
At the recent IMS 5G Summit, I learned about some timelines. Initial mmWave releases are expected to be point-to-point, or point-to-multi-point, but not fully 5G NR compliant. But soon after, in the first half of 2019, operators and equipment makers are planning to introduce 5G devices with mmWave radios in select cities. This poses some pretty significant challenges for designers to produce a mmWave mobile device that meets expected quality of service while traveling through the network.
mmWave isn’t new for wireless communications, but it is new for cellular communications. 5G NR specifies frequency up to 52.6 GHz and new operating bands that open up almost 10 GHz of new spectrum.
- Frequency Range 1 (FR1): 400 MHz to 6 GHz adds 1.5 GHz of new spectrum in frequency bands: 3.3-4.2 GHz, 3.3–3.8 GHz, 4.4–5 GHz.
- Frequency Range 2 (FR2):25 to 52.6 GHz adds 8.25 GHz of new spectrum in frequency bands: 26.5–29.5 GHz, 24.25–27.5 GHz, 37–40 GHz. Initial mmWave targets are 28 GHz and 39 GHz in Japan and the US.
mmWave, where there is greater modulation bandwidth, is essential to meeting the extreme data throughput envisioned in 5G mobile broadband. However, establishing a mmWave communication link and tracking a mmWave device through the mobile network will be a challenge. mmWave signals just don’t behave the same as signals under 6 GHz.
5G NR will use technologies like beam steering and new initial access procedures to enable a mmWave communication link, but transmitters and receivers must also be able to produce and demodulate high-quality signals in the device and base station. IQ impairments, phase noise, linear compression (AM to AM) and nonlinear compression (AM to PM), and frequency error can all cause distortion in the modulated signal. Phase noise is one of the most challenging factors in mmWave OFDM systems. Too much phase noise in designs can result in each subcarrier interfering with other subcarriers, leading to impaired demodulation performance. These issues are even more problematic at mmWave frequencies with wider bandwidths.
Evaluating a signal’s modulation properties provides one of the most useful indicators of signal quality. Viewing the IQ constellation helps to determine and troubleshoot distortion errors. A key indicator of a signal’s modulation quality is a numeric error vector magnitude (EVM) measurement that provides an overall indication of waveform distortion. As modulation density increases, so too does the requirement for better EVM. Shown here is the 3GPP (Third Generation Partnership Project) TS 38.101-1 EVM requirement for 5G UE (user equipment).
Modulation scheme for PDSCH
Measurements of the overall spectrum are also used to validate the signal’s RF performance.
Test solutions don’t just migrate from sub 6 GHz. The test equipment needs to operate at the higher mmWave frequencies with wider modulation bandwidths and have better specifications than the device under test (DUT). When designing test solutions, you now need to be even more concerned about issues like adapters and cables, switching, over-the-air test, and system-level calibration. The measurement system needs to perform better than the DUT’s design goals, and a proper system level calibration helps to eliminate uncertainties due to test fixtures and is valuable for very wide bandwidth signals.
To find out more about overcoming the challenges of mmWave device design and test, check out this white paper series that looks at many of the challenges you can expect with 5G NR including, the new flexible numerology, mmWave design considerations, MIMO and beamforming, and over-the-air testing challenges at www.keysight.com/find/5GNR.