The initial 5G New Radio (NR) specification was released by the Third-Generation Partnership Project (3GPP) standards committee in December 2017. 5G chipsets have started to appear, so as a result, the race to trial infrastructure and devices will accelerate. What does this mean for those designing 5G devices? 5G NR will support limited use cases in the beginning. This article focuses on 5G NR release 15, uncovers some misconceptions, and describes the boundaries and implications for device designs.

5G NR holds many promises for consumers—extreme download rates to view ultra, high-definition videos, low-latency applications like mission-critical drones, and devices talking to other devices without going through the network. These are well defined in the IMT for 2020 and beyond vision. According to the November 2017 Ericsson Mobility Report, total mobile data traffic is expected to raise at a compounded annual growth rate of 42 percent. This will put huge demands on the wireless network, and new technologies are needed to achieve these goals.

Like building a house, the first step is a solid foundation to support the structure. New capabilities in the initial release will support enhanced mobile broadband (eMBB) and ultra-reliable, low-latency (URLLC) use cases, while support for other use cases in massive machine-type communications (mMTC), which is primarily for IoT applications, will be defined later in 2019. 5G NR standards are still under development, and will be rolled out over the next several years. How much of the 5G vision can be made real by what’s been released so far? Let’s explore what can be realized with initial R15 and implications for your designs.

Fact or Fiction?

5G NR is a replacement for 4G networks.

False: 4G LTE is continuing to evolve and, in fact, will play a major role in the success of 5G. When devices are connected to the network, 4G and 5G will coexist to provide broader coverage and to facilitate the use of new technologies on the network. Developments in 4G LTE-Advanced Pro are already seeing gigabit throughput rates by using higher order modulation, more MIMO (multiple-input, multiple-output) streams, and aggregating both licensed and unlicensed spectrum using techniques like LTE-LAA (Licensed Assisted Access). There will be integration between 4G and 5G, and the initial release of 5G NR will be in non-standalone mode (NSA) where the 5G network will rely on the 4G network for scheduling and control of the signal. The final state of R15 will support standalone (SA) mode, but the expectation is that 4G, 5G, and even the convergence of WiFi will all continue to work in conjunction to deliver a diverse set of services. What it comes down to is that 4G is not disappearing anytime soon. Device designers will need to consider coexistence of 5G NR, 4G LTE, and WiFi on the same carrier with the possibility of RF interference, as well as network collisions when scheduling three different protocols.

5G will utilize flexible numerology to address diverse spectrum and services.

True: 5G NR introduces a flexible numerology to enable a wide range of frequencies, and the scheduling of diverse services that can be high throughput, low latency, or even high latency for IoT type of applications. The subcarrier spacing is no longer fixed to 15 kHz. Instead, the carrier spacing scales by 2µ x 15 kHz as the frequency increases. This enables scalable slot duration so that some slots can run in less time. To support future low-latency, mission-critical applications, a mini-slot is shorter in duration than a standard slot and can start at any time without waiting for the start of a slot boundary.

With the introduction of flexible numerology in 5G NR, the number of test cases has exploded and device designers will need to create and analyze waveforms in the frequency-, time-, and modulation-domain[DJ1] , along with verifying the device’s performance on the network with different numerologies.

With the multiplexing of different numerologies, only subcarriers within the same numerology are orthogonal to each other. Mixing of different numerologies on a carrier can cause interference with subcarriers of another numerology. RF coexistence testing will be needed to ensure there is no in-band or out-of-band emissions causing interference with other signals on the carrier.

5G NR is all about mmWave spectrum.

False: While the use of mmWave spectrum will be critical to meeting the extreme data throughput expected in 5G mobile broadband, frequency bands below 6 GHz will also be used for all three use cases: eMBB, ULLRC, and mMTC. Sub-6 GHz spectrum is well-understood, and many countries are freeing up spectrum for sub-6 GHz initial releases. 3.4 GHz to 3.8 GHz is being considered by about 20 countries, where more contiguous spectrum can be found. Sub-6 GHz has some challenges, but using wider carrier bandwidths at mmWave frequencies are where we will see a new set of issues not previously experienced in commercial mobile communications. 5G NR has specified frequency use up to 52.6 GHz, and there are several countries conducting trials in the 26, 28, and 39 GHz bands.

Among the new challenges from the introduction of mmWave are those due to increased path loss, blockage, and other propagation issues that will limit the cell coverage. Beamforming will be used to help overcome the signal propagation issues but has its own challenges that are described later in this article. There will be additional difficulties in efficiently generating and receiving high-quality signals in the much wider bandwidths. Having sufficient test capability to measure the signal’s RF performance with tests like EVM, ACPR, and SEM will be important.

5G mmWave tests need to be conducted over-the-air (OTA).

It depends: Most sub-6 GHz tests are performed by physically connecting a coaxial cable from the device to the test system. At mmWave frequencies, components are smaller and have higher levels of integration that can limit the connection points, making it difficult, if not impossible, to make a cabled connection. Without a cabled connection, designers will need to rely on OTA test. The mmWave OTA test will introduce new uncertainties with the ‘air interface’ as the connection. There are different tests performed on a UE verses a base station, and performed at different stages of the product lifecycle. For example, 3GPP technical specification for radio transmission and reception lists the following tests:

UE Base Station Documents TS 38.101 User Equipment (UE) radio transmission and reception TS 38.104 Base Station radio transmission and reception TS 38.141 Base Station conformance testing Radiated transmitter tests Transmitted power Output power dynamics Transmit signal quality Output RF spectrum emissions Spurious emissions Radiated transmit power Base station output power Output power dynamics Transmit ON/OFF power Minimum output power Transmitted signal quality Occupied bandwidth Adjacent channel leakage ratio (ACLR) Operating band unwanted emissions Transmitter spurious emissions Transmitter intermodulation Radiated receiver tests Diversity characteristics Reference sensitivity power level Maximum input level Adjacent channel selectivity Blocking characteristics Spurious response Intermodulation characteristics Spurious emissions Sensitivity Reference sensitivity level Dynamic range In-band selectivity and blocking Out-of-band blocking Receiver spurious emissions Receiver intermodulation In-channel selectivity

One of the biggest challenges in design is antenna position and blockage, or phantom signals. OTA measurements in R&D should include beam-pattern measurements, cross-polar measurements, and beam- or null-steering to understand performance, while conformance tests are still to be defined. 3GPP recently added a compact antenna test range (CATR) test method that uses a parabolic reflector system to make the waveform look like it’s coming from a greater distance. This method can provide an accurate, lower cost, compact alternative to the typical far-field test chambers.

5G NR massive MIMO and beamforming will use antenna arrays with hundreds of antenna elements.

False: While massive MIMO implies hundreds of antennas on the base station, 5G NR R15 only supports up to 8×8 MIMO—that’s 64 antenna elements, the same currently supported in 4G LTE. Massive MIMO is loosely defined as having a much greater number of antennas on the base station than on the device, and is implemented as multi-user MIMO (MU-MIMO). For initial release, up to 8×8 MIMO is being installed on the base station and 2×2 on devices. Future releases of the specification will likely add support for higher order MIMO implementations. Massive MIMO will be implemented at sub-6 GHz and mmWave spectrums with first commercial deployments below 6 GHz. MIMO can be implemented in several ways, and beamforming is a special case used to combine multiple antenna elements to focus the power in a specific direction. This technique will help improve the signal to noise plus interference ratio (SNIR) ratio for a specific user. 5G NR specifies new initial access techniques for beamforming that will utilize beam sweeping so that the base station can identify the strongest beam and establish a connection as shown below.

MIMO and beamforming have many challenges both at sub-6 GHz and mmWave. In addition to the challenge of finding a beam through initial access, the overall beam management, handover efficiency, and throughput all need to be verified.

Summary

Many companies are in a heated battle to be first to market with 5G products. With the many trials underway and 5G modem chipsets on the market, infrastructure and devices are soon to follow. New challenges with 5G NR, 4G, and WiFi coexistence, flexible numerology, signal quality at mmWave spectrum, testing OTA, and beam management will require you to think differently about how you test. You will need to consider the waveform performance with different numerologies and at higher mmWave frequencies. In addition, since networks and base stations are not built out yet, network emulators, channel emulators, and OTA test solutions will help verify the device’s real-world performance.