Top Measurement Challenges for 5G New Radio Designers
2018-12-18 | 7 min read
5G New Radio (NR) has very aggressive goals to meet the IMT-2020 vision. 5G NR engineers are pushing their designs into new operating bands at higher frequencies with wider channel bandwidths. The air interface will need to have more flexibility than ever before so that the wireless communications system can respond and adapt very quickly to many different use scenarios. Meeting the needs of enhanced mobile broadband (eMBB), ultra-reliable low latency communications (URLLC), and massive machine type communications (mMTC) will challenge every designer in ways we probably still don’t understand. Some of the initial challenges are already being addressed by market leaders as they introduce their first 5G NR compliant devices and infrastructure products into the market next year.
Here are some of the biggest measurement challenges 5G NR designers are addressing today.
1. Signal quality at millimeter wave frequencies
One of the firsts areas addressed by 3GPP is enhanced mobile broadband where very high data rates are needed for applications like high-speed streaming of 4K or 8K UHD movies. In 5G NR, the key to enabling higher data rates will be the use of higher transmission bandwidths. Higher transmission bandwidths will be available between 3.5 GHz and 6 GHz and in mmWave frequency bands in frequency range 2 between 24.25 to 52.6 GHz. With peak data rate targets as high as 20 Gbps in the downlink (DL) and 10 Gbps in the uplink (UL), mmWave operating bands where more contiguous bandwidth is available will be critical for sending lots of data. Impairments that were not an issue at sub-6 GHz, now become more problematic at mmWave frequencies and extra consideration is needed to determine test approaches. Test solutions need to accommodate multiple higher frequency, wider bandwidth channels with greater resolution in order to accurately evaluate the performance of 5G components and devices. Due to the sensitivity with these higher frequency signals, extra care is needed around system cables and connectors, and system level calibration will be critical.
2. Multi-element active antenna over-the-air tests
5G will change from cell-based coverage to beam-based coverage. Multi-antenna techniques such as MIMO and beam steering will be used to increase capacity and coverage. With beam-based access techniques, there are many new challenges designers must overcome to ensure that a base station and user terminal can find each other, establish a quality communications link, and maintain the link while traveling through the network.
Going to beam-based communications means that 5G NR antennas need to be verified for the correct antenna gain, side lobes, and null depth for the full range of 5G frequencies and bandwidths. The side lobes and nulls must be in the proper location to tune system performance and maximize the radiated efficiency of the signal. This requires measuring the 3D antenna beam patterns in an OTA test environment.
5G NR initial access and attach procedures also need to be verified. Procedures are defined for beam acquisition and tracking, beam refinement, beam feedback, and beam switching. Designs must implement, validate, and optimize all these functions, or the user could experience dropped calls or poor performance. Testing the protocol early in the development cycle will ensure the device can establish and maintain a call. Measuring end-to-end throughput over-the-air will be necessary to understand the full performance. These throughput tests should also be performed with real-world impairments like excessive path loss, multi-path fading, and delay spread.
3. Testing many different user scenarios
5G NR needs to accommodate many different usage scenarios from very high throughput to low packet size, to very low latencies with high reliability. To support such a wide variety of use cases, the 5G NR physical layer was defined with high flexibility.
- The OFDM (orthogonal frequency division multiplexing) multi-carrier waveform with cyclic prefix can help with the higher data throughput and delay-sensitive application needs. While OFDM has been used in the past, it’s new for the uplink, adding complexity to device designs.
- Scalable numerology allows for subcarrier spacing to scale, enabling shorter slot duration as frequency increases to optimize for different service levels in throughput, latency, or reliability.
- Mini-slots enable shorter duration than a standard slot and can be located anywhere within the slot. Mini-slots can provide low latency payloads with an immediate start time without needing to wait for the start of a slot boundary.
- A flexible slot configuration allows for dynamic allocation of uplink/downlink for better efficiency based on the traffic. A slot can be structured as all downlink, all uplink, or a mix of uplink and downlink.
Multiple services can be supported simultaneously through the use of bandwidth parts. This high level of flexibility and scalability equates to many more test cases that need to be validated.
Still many unknowns
5G NR air interface changes everything. These are the most demanding challenges for 5G NR designers today. There are still many unknowns and additional challenges that we’ll see as 5G progresses. To find out more about the latest in 5G, be sure to check back on this blog and access our latest 5G resources.
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