Even before the COVID-19 virus emerged to challenge global supply chains, the RF and microwave semiconductor industry was facing significant headwinds. The cellular market, particularly mobile handsets, enables more than 50 percent of compound semiconductor revenue. This application has been a strong driver for the industry for more than a decade, but the engine is running out of steam. RF GaAs device revenue declined in 2019 and the culprit was a reduction in smartphone shipments. Despite this stumble, the future looks brighter for the compound semiconductor industry. The reason for this optimism is 5G networks and devices and this new standard is poised to become the growth engine for the entire semiconductor industry.
Wireless operators have been deploying 5G networks and devices since 2019, so the three pillars of the 5G vision should be familiar. Figure 1 shows a simple representation of the main tenets of the 5G vision, along with the features promised by these pillars. The challenge for operators and equipment manufacturers will be the timing and extent of the implementation of these pillars.
5G is an imprecise term in general usage. 5G can refer to the standalone or non-standalone version that makes use of the existing LTE core and signaling network. There are also the mmWave frequencies (also known as “FR2” or “high band”) or sub-6 GHz frequencies (also known as “FR1” and comprised of “low band” and “mid-band”). The 3GPP industry standards body is working to codify 5G with ongoing work on Release 15 with Releases 16 and 17 scheduled for approval by the end of 2022 to address other aspects of 5G.
In addition to the ongoing development of technical standards, fundamental questions for the industry concern the business model for 5G. How will operators differentiate 5G networks from LTE networks? Will the 5G network address all or just a subset of the pillars and goals of the 5G vision?
SUB-6 GHz 5G NETWORKS
Deploying a new generation of wireless networks is an expensive proposition and operators are working to identify and monetize 5G applications. While there is a substantial development effort aimed at addressing all three pillars of the 5G vision, the early 5G marketing messages focus more on the enhanced mobile broadband (eMBB) feature of 5G. Operators are competing based on network coverage and speed and this has implications for the sub-6 GHz network architectures and technologies.
If the criterion is speed, or capacity, sub-6 GHz 5G networks are at an immediate disadvantage. This is a byproduct of the Shannon-Hartley theorem, which describes the theoretical maximum data rate transmitted in a specific channel bandwidth:
C = B*log2 (1+SNR)
where: C = channel capacity limit (bits/s), B = channel bandwidth (Hz) and SNR = signal to noise ratio.
Even as new sub-6 GHz frequency bands are being assigned globally, bandwidth is measured in the tens or hundreds of MHz in these bands. At mmWave frequencies, bandwidth is easily in the GHz range. This is a fundamental disadvantage for the sub-6 GHz networks compared to mmWave. Figure 2 shows Ericsson’s view of how to evolve an existing LTE network to 5G with best-in-class coverage, capacity and performance. This hybrid network incorporates existing 2G/3G/4G standards and bands, along with 5G sub-6 GHz and mmWave bands. The evolution starts with carrier aggregation (CA) at different LTE bands. The evolved network incorporates dual connectivity, where the downlink operates in a 5G sub-6 GHz band containing more channel bandwidth, while the uplink signal remains on the LTE network. Ultimately, the network evolves to incorporate various combinations of CA and dual connectivity in the sub-6 GHz and mmWave bands.
Figure 2 shows a migration vision for an operator to upgrade their LTE networks to a full feature 5G network. This evolution involves multiple bands and standards, CA and dual connectivity, making implementation complex and costly. The sub-6 GHz portion of the network has channel bandwidth deficiencies and it increases the complexity of the hybrid network, but it provides many benefits for the 5G network.