As we enter the early stages of the “5G era,” new technologies are deploying to cover use cases around Enhanced Mobile Broadband (eMMB), Ultra-Reliable Low Latency Communications (URLLC), and Massive Machine Type Communication (mMTC). These use cases are not served by a single discrete technology, but rather a combination of multiple heterogeneous networks. 2018 is shaping up to be the onslaught of the “5G marketing wars,” with eMMB as the consumer focus for 5G. Mobile data traffic is continuing to rise at double digit rates as people consume more video on the go. In the context of 5G communications, this will drive deployment of higher capacity wireless networks in both connectivity and cellular technologies.
In cellular communications, we are seeing deployments of multiple 5G technologies, including millimeter-wave 5G, sub-6GHz 5G, as well as continued extensions to carrier aggregation in 4G LTE. Gigabit connectivity for the “last mile” (or few meters) into homes is currently rolling out in select deployment cities through fixed wireless access solutions that use millimeter-wave (mmWave) frequencies.
Fixed wireless access enables a fatter data pipe into the home or office, where it then gets translated into other technologies with which our existing mobile devices can communicate. This technology translation through a Home Gateway or Customer Premises Equipment (CPE) increases both the data capacity as well as the effective data rate that each user sees. Additionally, this enables the wireless carrier companies to deliver superior user experiences without the need to change existing mobile user equipment.
The unique properties of mmWave frequencies, compared to traditional 4G cellular communication frequencies, offer unique qualities that are advantageous to the fixed wireless eMMB use-case. In particular, these frequencies enable significantly smaller antenna geometries, where many antennas can be used in a phased array to “steer” the transmitted beam-formed signal directly to a particular end-user, rather than broadcasting in all directions. Economic production testing of this mmWave technology requires new measurement methodologies to address some of the challenges. Of particular note, this requires measuring the transmitted beam from the antenna arrays with no direct connection between the tester and the device to be tested.
In principle, measuring wireless signals over-the-air is nothing new for the industry… in the lab. Directly transferring this methodology from the lab to the manufacturing floor is difficult, as the size of the required chamber environment is much larger than what is used for existing 4G cellular equipment. This over-the-air setup represents a challenge for the industry, and efficient test techniques focused on antenna array measurements will be a key requirement for millimeter wave testing.
Another form of 5G, in the sub-6GHz spectrum, will also have early deployments toward the end of the year. This uses underutilized 3.5-4.9 GHz spectrum. From a measurement point of view, key test challenges entail higher antenna counts for massive MIMO and 5x to 10x wider bandwidths than today’s LTE technology.
Comparing to existing mobile devices using 4G LTE communication, there are typically two to four antennas used in the mobile device. For this new 5G technology in the sub-6GHz spectrum, it is expected that up to eight additional antennas will be used for MIMO, potentially bringing the total number of antennas in the compact form factor of a mobile device to ten or more! Not only does this represent a challenge in the potential for dramatically longer test times (i.e., more cost), there is also a requirement to measure antenna performance in a MIMO mode to ensure that within the device, there are no issues with antenna-to-antenna interference due to coupling or de-sensitivity in the system.
Additionally, 5G in the sub-6GHz spectrum will employ signals that use 100 MHz or 200 MHz of spectrum, compared to only 20 MHz in 4G LTE systems. 10x wider bandwidth represents a challenge to calibrate (or “flatten out”) the signals transmitted from the device, and requires new calibration techniques to do so. Additionally, with wider transmitted signals comes the challenge to ensure that the device is not emitting energy where it is not supposed to in the neighboring spectrum.
In all of the marketing of new 5G technologies, let’s not forget about 4G as it continues to evolve. Not only does 5G need to coexist with 4G, it is dependent on 4G. 5G may be getting the dramatic press release headlines, but these first waves of 5G products are operated in non-standalone mode. This means that establishing communication will start on the 4G network, then transfer data transmission to the 5G radios.
These improvements to cellular networks will ripple into local area Wi-Fi networks, as well. As the network capacity increases, Wi-Fi is evolving to efficiently manage data traffic on the local network. The big change in Wi-Fi in 2018 will be availability of 802.11ax products on the market. This technology brings 10x more capacity, mainly through shared-access techniques in the unlicensed bands. Access points will support more antennas (up to twelve), more radios (two or more), and higher bandwidths (up to 160 MHz). There will be a significant focus on validating product performance. Unlike previous versions of Wi-Fi, if a client device does not adhere to a minimum set of performance metrics, it will get “kicked off the network,” relegated to operate on a legacy network. In other words, if you don’t play by the rules, you won’t get any performance benefit. Emphasis in test will be in accurate power calibration and timing validation.
The macro trend in test for 2018 is focused on addressing new spectrum, wider bandwidths, and significantly more radios and antennas. For 5G cellular technologies, more bands are opening up not only in the sub-6GHz space, but also in the mmWave spectrum. For mmWave, test economics must improve in order to scale mmWave technology from exotic (small volume) applications to mainstream (high volume) consumer applications. No longer can you just slap some IC chips on a board and deliver a functional Wi-Fi product. 802.11ax introduces power and timing requirements to help bring organization to the chaotic unlicensed spectrum – if a product does not adhere to these requirements, the user will see no benefit. Test must tame these new technologies to enable fast product ramps with high quality.