Over-the-air testing of 5G millimeter-wave radios
After years of hype, the world is quickly being introduced to 5G.
Country by country and provider by provider, this can mean different things. Much of the world is focusing initial 5G rollouts on the 3GPP defined FR1 bands (those carriers with frequencies below 6 GHz). The widest allotment of spectrum for FR1 5G is 100 MHz or less.
While this amount of bandwidth will provide much higher performance over legacy wireless standards, it isn’t the best 5G can do. FR2 — or millimeter-wave (mmWave) — frequencies typically operate around 24, 28 or 39 GHz and can support single carriers up to 400 or 800 MHz channels made up of side-by-side aggregated carriers.
In addition to the practical differences between FR1 and FR2 signals, there are also technological differences that will impact performance and testing. Per the 3GPP standard, mmWave 5G NR signals have subcarrier spacing of either 120 or 240 kHz, compared to only 30 or 60 kHz for FR1. FR2 signals also have more SSB beams.
All 5G NR base stations transmit SSB beams through the antenna’s transmission sector, but mmWave radios use between 12 and 64 beams, whereas FR1 radios are limited to 4 or 8 beams. With 64 beams, the radio can transmit narrower beams with more power, which improves the efficiency of the radio and helps avoid interference.
However, more beams requires decoding more bits from the PBCH in order to read out all 64 beam indexes in their correct position. It also requires a greater number of antenna elements in the antenna array used for beam forming. This makes it impossible to do connected testing and verification of the radios, forcing users to do all testing OTA.
Finally, mmWave signals have shorter wavelengths (as hinted in the name), which will cause greater propagation loss through both air and most physical objects — including windows, which are often coated with UV protective films, which strongly attenuate mmWave RF. This means 5G mmWave service will require greater radio density and strategic placement/alignment. It will also make signals more vulnerable to interference, and requires test equipment with lower noise floors and faster sweep speeds in the mmWave bands.
The Field Master Pro MS2090A handheld real-time spectrum analyser provides several valuable solutions for spectrum clearing at mmWave. To begin, users can use the instrument in conjunction with Anritsu’s Mobile InterferenceHunter to map out their coverage area and identify any hot spots with potential RF energy. They can then pinpoint the location of the potential interference and work to clear it out.
The instrument also offers 110 MHz of real-time spectrum analyser (RTSA) bandwidth and power density display to watch out for difficult-to-find, intermittent interference. With an omni-directional antenna, the instrument can be set up in an infinite persistence and left to run for minutes or hours to ensure no signals are present.
Once spectrum is clear and radios are going up, it will be key to ensure the radios are configured correctly and performing per standard. The Field Master Pro MS2090A offers a full 5G NR demodulation suite, which decodes the SSB beams to provide the following information:
- Cell ID, Sector ID, and Cell Group — important for verifying the configuration of the radios
- Frequency error — where less error promotes greater signal quality and faster throughputs
- Time offset — all 5G NR signals should be tightly synchronized to GPS to avoid interference between cells
- Individual beam RSRP, RSRQ, and SINR — key indicators of radio performance and signal quality
- EVM of the individual SSB parts
- Multi cell measurements — a measurement of multiple radios in the same to identify radio handoff points and possible gaps in coverage
- Channel power / occupied bandwidth.
Anritsu’s Field Master Pro MS2090A is specially designed to handle the challenges of mmWave installation and maintenance. The Field Master Pro MS2090A gives users the most accurate, robust measurements possible and is the first solution to provide full, uninterrupted frequency coverage from 9 kHz up to 54 GHz, allowing allows users to test any 5G NR signal — from FR1 to FR2 and anything in between.
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