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We are witnessing the global move towards 5G. Countries, mobile operators, and cell PCB phone manufacturers are all scrambling to provide a new generation of cellular connectivity, or at least take the lead. However, the global move towards 5G does not mean that there will be 5G mobile phones capable of global roaming. Unlike the case of LTE, it may not be feasible to produce 5G mobile phones that support roaming on global 5G networks, or it may not be economical. On the contrary, 5G may push the mobile phone market in the opposite direction-more regional.
5G frequency bands are not global
First, the new "global" FR1 bands (n77, n78, and n79) are not actually global at all; in many cases, countries are allocating different subsets of these bands (see Figure 1 and Figure 2). Secondly, the allocation of the FR2 millimeter wave frequency band is similar, which multiplies the problem. Third, many operators will initially deploy non-standalone (NSA) 5G, which will introduce complex and difficult-to-control interaction issues between 5G and regional LTE frequency bands
Some people may remember the dawn of the LTE era, when frequency bands 1 and 7 were regarded as global frequency bands. Unfortunately, these two frequency bands are only used in some areas. Other frequency bands that are regarded as global frequency bands (such as frequency band 41) have also produced regional distribution differences when they are deployed. For example, the United States has allocated all available frequency bands, while China has only selected a part. Until now, a more uniform allocation of frequency band 41 was considered, with the purpose of deploying 5G NR in the re-allocated frequency band n41.
For the same reason, the new "global" bands n77, n78, and n79 also have the same fragmentation problem. The ways in which countries and regions allocate spectrum to mobile operators or auction spectrum have hardly changed.
Phone problem
The resulting regional distribution differences have had a significant impact on mobile phone manufacturers, and they must figure out how to support conflicting needs. Operators usually want mobile phones to be optimized for the frequency bands they use. However, mobile phone manufacturers want to sell globally, or at least in a large area, to support the different frequency bands and carrier aggregation (CA) combinations used by all their target markets.
In addition, leading manufacturers have chosen to participate in the Global Certification Forum (GCF) interoperability certification, which provides the advantage of roaming using LTE mobile phones. The common practice of GCF is to verify interoperability in the entire frequency range of the designated frequency band. This begs the question: What happens when an operator or a group of operators deploys only a subset of the allocated frequency bands?
Consider the case of n77, which covers 3.3 to 4.2 GHz. In theory, a single n77 solution will support the use of mobile phones using this frequency band in all regions of the world. In reality, operators need solutions that are optimized for a subset of the spectrum allocated in their respective regions-in some cases, as narrow as 100MHz. If n77 cannot be used as a global solution, what about the n78 from 3.3 to 3.8 GHz? Please think twice. So far, only a few operators plan to deploy the 3.3 to 3.4 GHz part of n77 or n78. Do mobile phone manufacturers need to achieve interoperability in a frequency range that has not even been deployed? Of course, the operator does not need to do this.
Implementing more regional solutions can provide performance advantages, mainly because mobile phone manufacturers can customize filtering and optimize power and low-noise amplifiers tuned for a subset of frequency bands. For example, at the initial launch, most if not all of the n77 front-end modules will use non-acoustic filters, which provide good performance for the very wide 900MHz spectrum (much wider than any current LTE band). When using a subset of n78, such as 400MHz, bulk acoustic wave (BAW) filters with steep filter skirts provide better performance, thereby improving out-of-band frequency rejection and reducing insertion loss at the edge of the band. This is an example of a trade-off scheme for a mobile phone manufacturer. Focusing on regional solutions will improve the network performance of mobile operators, but will lose global roaming capabilities.
Frequency band n79 (4.4 to 5GHz) also has the same dilemma. China prefers the 4.8 to 4.9 GHz part of this frequency band, while Japan considers 4.5 to 4.6 GHz. Solutions that support the entire frequency band will work in these two countries, but will not be optimized for any narrower subset. If you are an operator in these two countries, would you choose the global n79 solution or provide a higher-performance solution for users in your country? On the other hand, as a manufacturer, do you want to provide different phones for China and Japan or launch the same phone in both countries?
The regional allocation of the FR2 spectrum makes the fragmentation problem more challenging, and there are differences between regions and between operators in each region (see Figure 3). Considering the antenna, the RF implementation of millimeter-wave mobile phones may be more frequency-dependent than below 6GHz. If the mobile phone must support multiple widely spaced millimeter wave frequency ranges, it may require multiple antenna arrays, or at least more complex, lossy antennas. The bigger challenge is that the millimeter wave front end may be implemented in multiple configurations of the mobile phone, each configuration will take up valuable space, and the mobile phone itself faces size limitations. Considering that the size of mobile phones is approaching the limit of portability, this is a problem.
The use of millimeter wave 5G frequency bands will also vary from country to country.
NSA, SA and LTE
The initial approach to 5G is different in each region. In many regions of the world, operators plan to accelerate 5G deployment by adopting NSA 5G. The NSA uses the LTE anchor band for control and uses a wider 5G band to provide faster data rates. Using this method, operators only need to use their existing LTE network to quickly implement 5G, without the need to build a new 5G core network. However, some Chinese operators plan to quickly transition from NSA to standalone (SA) 5G, or in some areas, directly transition from LTE to SA 5G. SA does not require an LTE anchor point and requires the construction of a full 5G network, but it simplifies the implementation of multi-band CA combinations, especially on the uplink (UL).
