OTA TESTING
Verifying 5G with OTA testing ADNAN KHAN | ANRITSU CO.
The 5G realm puts a new emphasis on making measurements without hardwired connections.
5G SYSTEMS are being rolled out globally, bringing with them throughput speeds of up to 10 Gbps, higher frequencies that extend into the millimeter wave (mmWave) spectrum, and devices operating in multiple radio access technologies (RATs). Engineers are faced with considerable design challenges in 5G. Among these challenges is the stringent testing associated with chipsets, devices, and systems. Over-the-air (OTA) testing approaches are becoming the norm for testing 5G New Radio (5G NR) user equipment (UE) and base stations, especially in mmWave. The move to higher frequencies, including sub-6 GHz Frequency Range 1 (FR1) and mmWave Frequency Range 2 (FR2), arises in large part to the crowding of the RF spectrum. For these reasons, 5G NR networks and UE devices require advanced technologies and OTA measurements to characterize performance accurately. For a given transmit power level, mmWave signals do not travel as far as lower-frequency RF/microwave signals. The free space propagation loss is a square function of the frequency and distance. For maximum signal propagation distances, 5G NR systems must direct signal energy between network nodes and UE devices, using active antenna systems (AAS), beamforming, and high-speed signaling techniques. 4G LTE and earlier wireless generations transmitted signal energy in all directions, for a 360° signal around a base station at relatively high transmit power levels compared to 5G NR systems. Operating at mmWave frequencies with lower transmit power levels, 5G networks have considerably more base stations for proper coverage.
ANTENNA ARRAYS Directional signal beams in 5G NR systems are transmitted and received using antenna arrays. Rather than the omnidirectional signal energy transmitted in a 4G LTE system, a 5G NR device will locate a 5G NR base station within range by receiving an identifying signal from the base station. Signaling between the base eeworldonline.com
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station and UE will establish the An example of test equipment for coordinates for directed energy 5G UE device testing that provides beams formed by antenna performance levels exceeding those arrays in the base station and expected of DUTs in terms of frequency device. As such, there can be range, frequency accuracy, signal a communication beam in the sensitivity, and dynamic range. Uplink (UL) and a separate one in the Downlink (DL). A 5G base station is two subsystems – a baseband controller unit and a remote radio head (RRH) – that are connected by a fiber-optic cable. The RRH contains a highly integrated transceiver (TRX) and AAS. 5G NR base stations are smaller and have lower power compared to 4G LTE towers. The size of the antenna is also inversely proportional to the operation frequency. As such, at 28 GHz or 39 GHz, an 8x8 patch antenna array may be 5 cm or smaller. It’s physically not possible to have a connectivity port on the antenna in mmWave. Also, the loss if a cable is connected will be significant. Neither the Base Transceiver Station (BTS) or UE can have a test connectivity port at mmWave. Hence, testing in an OTA environment becomes a necessity for proper RF characterization and performance analysis. Advanced AAS circuits in 5G radio equipment try to maximize propagation distances at mmWave frequencies where signal energy is limited (and more expensive than at lower frequencies). 4G LTE leverages multiple-input, multiple-output (MIMO) antenna approaches to overcome signal path losses and enhance throughput and capacity. 5G NR networks use multiple AAS units in massive MIMO configurations to direct mmWave energy through space as efficiently as possible. 6 • 2020
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