Discussion on 5G+4G wireless network collaboration and key networking technologies

Labs Guide

This article starts with analyzing the background and necessity of 5G+4G wireless network collaborative construction, and points out the natural advantages of 5G+4G collaborative construction in terms of frequency, equipment, and site. On this basis, the key technologies of 5G+4G wireless network coverage collaboration and capacity collaboration are analyzed, and a collaborative networking solution is proposed. Based on this solution, it can not only cope with the current 4G network capacity challenges, but also build a wireless network evolution infrastructure with 5G leading competitive advantages, and at the same time achieve the goal of building a 5G boutique network with reduced costs and increased efficiency.

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1. Favorable conditions for 5G+4G collaborative construction

The construction of 5G network is a national strategy for my country to become a powerful network country. 5G network is a key infrastructure for realizing industrial innovation and upgrading, and it is of great significance. After years of accumulation, my country's operators have the largest number of wireless base station sites in the world. At the same time, unlike the upgrade of 1G/2G/3G/4G wireless network technology, operators have inherent huge advantages in upgrading from 4G to 5G network. In addition to the abundant site resources that can be shared, it also includes the following sharing capabilities.

• Frequency sharing: 5G networks are allocated licenses for the use of multiple frequency bands, among which the 2.6GHz band is shared by 5G and 4G with a total of 160MHz spectrum resources from 2515 to 2675MHz. This not only gives operators the advantage of lower wireless link loss and thus saves network construction investment, but also allows them to fully utilize the existing 4G 2.6GHz band operating experience to manage 5G networks. At the same time, it can also give full play to the driving capacity of the industrial chain and maximize the common model of equipment capabilities and terminal capabilities.
• Equipment sharing: Based on spectrum resource bandwidth sharing, 5G+4G shared hardware equipment is developed to achieve the baseband's ability to convert between different standards (also known as mode conversion). While building a 5G network, the abundant network capabilities can be taken into account while meeting 4G business needs, maximizing equipment utilization efficiency.
• Business capabilities: The overall capacity of 4G networks is still growing, and the shortage of spectrum resources in some areas is becoming increasingly prominent, and the pressure on user service perception is growing. 5G eMBB and 4G eMBB are both mobile data services, which can achieve business synergy and sharing with 4G networks. At the same time, 5G networks can provide at least ten times the peak rate of 4G, millisecond-level transmission latency, and hundreds of billions of connections. Therefore, while the two share network capabilities synergistically, they can better meet the actual needs of the long-term joint development of converged services and differentiated services.

4G is in the ascendant, 5G has already arrived, and 5G+4G will coexist for a long time in terms of network and business support capabilities. This article will explore the key technologies for the coordinated development of 5G+4G wireless networks from the perspective of wireless network planning technology, which can fully tap the existing advantages of 4G networks and give full play to the new capabilities of 5G technology and networks, and achieve cost-saving and efficiency-enhancing network construction and operation with the maximum synergy of the two, which is also conducive to network evolution and development.

2. Analysis of key technologies for collaborative construction of 5G+4G network coverage

The main goal of wireless network coverage is to focus on the network construction value area and achieve the network coverage goal with the most reasonable network structure, the best equipment selection and the best investment cost performance. With the simultaneous development of user needs and technological evolution, wireless cellular networks are gradually evolving towards a new networking architecture. While maintaining the relative stability of the existing outdoor cellular network structure, in the early stage of 5G+4G collaborative development, there are the following key contents.

2.1 5G+4G site resource sharing technology

2.1.1 Make full use of existing 5G+4G site sharing

On the shared 2.6GHz frequency band, 5G network coverage and service capabilities are superior to 4G standards. Therefore, 4G and 5G have the ability to share sites. In terms of network planning technology, they can make full use of existing base station site rooms to carry out fast and low-cost network construction.

On this basis, unlike the previous network construction goals of standardized indicators for the entire network, 5G network construction can achieve flexible indicators based on "1:1" shared sites. This network construction idea is based on the fact that when the original 4G site is upgraded to 5G, the network coverage and service indicators will be better than 4G. At the same time, considering different scenarios, the spacing between 4G macro sites is different. Therefore, the spacing between macro sites planned for the 5G target network can be based on reality, based on the existing full physical site, with different planning indicators (such as setting challenge indicators, benchmark indicators and minimum indicators separately), to select ideal structure sites, adapt the most cost-effective solution to different regions, and ensure investment benefits.

2.1.2 Sky surface sharing

After years of development and technological iteration, the public mobile communication network has many 2G/3G/4G antenna points and limited space. Due to its technical characteristics, 5G AAU needs to occupy a separate antenna, so it is necessary to integrate and incorporate the 4G/5G antenna feed system. The best goal for antenna feed integration is 2~3 antennas per cell, that is, 1 antenna each for FDD, TDD, and 5G or 1 antenna each for 4G and 5G. Based on the principles of effective matching and moderate advancement, precise supporting construction is carried out, and the integration of existing resources and future development needs is achieved through the design of a reasonable antenna feed transformation plan, which can achieve precise construction and reduce rent and construction costs.

2.2 5G+4G equipment sharing technology

2.2.1 Sharing of device capabilities

Unlike the evolution from 2G to 3G and from 3G to 4G network standards, the 5G network is based on the same spectrum resources as the existing mature 4G network. This can give full play to the advantages of the mature 4G D-band industry chain and achieve shared hardware for 5G+4G base stations based on existing equipment, thereby maximizing the advancement of new 5G technologies.

In order to give full play to the capabilities of 5G equipment and take into account the needs of 4G networks, the following capabilities are required for new 5G equipment: the ability to support 160MHz full spectrum bandwidth, the ability to support SA/NSA common mode, the ability to support 5G+4G common mode/mode conversion, and the ability to support dynamic power sharing. At present, domestic and foreign manufacturers have completed equipment research and development and can achieve large-scale supply.

In this case, newly built 5G base stations can share resources in the manner of "sharing sites, sharing frames, sharing boards, and sharing antennas", avoiding waste caused by independent construction, and giving full play to the advantages of single-bit construction costs and operating costs.

2.2.2 Coordination of equipment construction

When 5G+4G are co-located, a common mode construction method can be adopted in which the 5G base station reversely activates the 4G function to meet the business needs of both networks at the same time. In terms of equipment arrangement, the original 4G D-band narrowband equipment (60MHz) RRU supports frequency bands that overlap with 5G equipment. It can be considered to be relocated to the peripheral area to continue to exert its capacity and avoid equipment waste, and to migrate to new sites in the demand area to fill blind spots or existing sites to supplement capacity needs. For physical sectors with abundant bandwidth, the F-band can be removed at the same time. At this time, the entire set of 4G baseband and RF equipment can be reused to maximize investment savings. For platforms with fierce competition for antenna resources, there is a risk that the pole resources will be occupied after the narrowband RRU is removed, which needs to be avoided as much as possible.

If the 4G D-band equipment is not removed, the requirements for the coordination of its equipment frequency and NR need to be considered. Since these devices only support 60MHz bandwidth and partially overlap with the 5G initial planned frequency band (the overlapping part is 40MHz bandwidth), and the 4G equipment has poor frequency shifting capabilities, it is bound to have a short life cycle. In addition, it is also necessary to consider that in this case, it is difficult for non-common mode equipment to implement technical means such as joint transmission and resource sharing within the frequency band, and the performance of the 4G network will be affected to a certain extent.

Based on the above analysis, when we carry out construction, we usually dismantle old D-band equipment and at the same time use 5G to reversely activate 4G functions to make up for the needs of 4G network coverage and capacity.

2.3 5G+4G frequency sharing technology

In the early stage of 5G commercialization, the network carried fewer services. At this time, power sharing technology was used to achieve the allocation and adjustment of 160MHz spectrum resources between standards, taking into account the capacity requirements of 5G+4G dual-standard networks and improving the utilization of spectrum resources. As 5G network users and services gradually develop, a single-standard 100MHz+60MHz target solution will eventually be formed.

2.3.1 Static frequency allocation and sharing technology

In the early stage of 5G construction, while clearing the 4G D-band, it is also necessary to consider the sharing and allocation of 5G and 4G frequency resources. We can follow the principle of focusing on the present and giving priority to meeting business needs, allocate bandwidth on demand according to different business scenarios, and adopt different frequency usage strategies.

• Scenario 1: 4G hotspot and the initial stage of 5G services. At this time, the demand for 4G services is high and is given priority in frequency allocation. Consider reserving one more frequency point (4*20MHz) for 4G and only opening 80MHz bandwidth for 5G.
• Scenario 2: 5G experience priority service demonstration area and other 5G key scenarios. Considering giving priority to meeting 5G needs, 100MHz is opened continuously from bottom to top using 2515~2615MHz frequency. 4G services absorb business volume as much as possible through FDD1800MHz and A band re-cultivation, reducing the frequency use strategy for 4G D band bandwidth requirements.

2.3.2 Dynamic Frequency Allocation Technology

Taking into account the need for long-term coexistence and coordinated development of 5G and 4G networks, in addition to the above static frequency allocation and sharing mechanism, it is also necessary to promote the industry to realize the maturity and application of 5G equipment 2.6GHz frequency 5G+4G fully dynamic sharing technology, improve resource mobilization flexibility, and reduce network maintenance costs.

5G+4G dynamic spectrum sharing technology can flexibly adapt to the needs of cell services and realize random scheduling of two services on the same carrier, thereby more fully improving equipment utilization and 160MHz bandwidth frequency resource utilization efficiency. The dynamic carrier sharing implementation mechanism is as follows.

Normally, a 5G carrier is configured with 4 UE working bandwidths (BWPs), and the terminal is configured with 1 or 4 BWPs depending on its capabilities. When the UE accesses from BWP0, it accesses the corresponding BWP depending on the initial network configuration. When the 5G carrier and 4G are co-covered, the 5G+4G dynamic spectrum sharing technology enables the 5G carrier to dynamically adjust the support for multiple BWPs, thereby enabling the carrier to change between the two states of dormancy and activation according to demand. This process is the spectrum "reallocation" process. The 5G+4G dynamic spectrum sharing technology can achieve dynamic spectrum allocation at a level of more than minutes based on the judgment conditions that trigger "reallocation".

2.4 5G+4G Power Sharing

2.4.1 Analysis of the impact of power coordination configuration

Currently, 5G base station equipment can reach a nominal power of 240W (long-term demand is 320W). Considering that the D band allocates 100MHz bandwidth to 5G and 20MHz bandwidth to 4G, 5G can meet the full power configuration of 200W. If 4G requires more carrier configuration, power limitation will occur. At this time, 5G+4G power allocation needs to be considered to maximize network performance.

First, the impact of different power configurations on capacity is analyzed: when 4G opens 2~3 new D-band carriers (and 3D-MIMO capability is available after 4G is reversely opened through 5G), and each carrier is fully powered according to the power spectrum density of 2W/Hz, then 5G has a remaining power of 160W. The 5G network will suffer a capacity loss of about 10% due to the power reduction, while the 4G network can obtain a 42% capacity increase higher than the low power configuration due to sufficient power. The calculation results of the capacity loss ratio of different power configurations are shown in Table 1.

Table 1 Impact of different power configurations on 4G and 5G network capacity

Next, we analyze the impact of different power configurations on coverage. As shown in Figure 1, from the test network test data results, we can see that under the same station spacing conditions, even if the 5G power is reduced to 120W, the downlink coverage performance is still better than the 3.5GHz 5G standard capability when the power is fully configured.

2.4.2 Scenario-based Power Coordination Configuration Solution

From the above analysis, we can see that the performance loss caused by 5G power reduction is small, but it can bring obvious 4G performance gain. At the same time, considering the early stage of 5G, the coverage and capacity requirements of 4G networks are still the top priority. Therefore, under the condition of 240W transmission power equipment, we should follow the principle of facing the present and giving priority to meeting business needs. The 5G+4G power allocation recommendations for different bandwidths are shown in Figure 2.

• Scenario 1: Considering that the coverage and capacity of 4G networks are still the top priority in the early stages of 5G, the frequency and power requirements of 4G should be met first. It is recommended to allocate 2W/MHz power resources to 4G first, and then allocate the remaining power resources to the 5G network.
• Scenario 2: In scenarios with demonstration significance or other important areas, in order to provide a service experience close to the theoretical rate, 5G should be configured with a total of 100MHz bandwidth resources from 2515 to 2615MHz, and 5G power should be allocated according to the power spectrum density of 2W/MHz. At the same time, 4G 3D-MIMO can be reversely opened at the D3 frequency point to absorb the existing 4G capacity.

3. Collaborative construction of 5G+4G network capacity

3.1 Environmental changes lead to uncertainty in the development of 4G services

The 5G power strategy will lead to profound changes in the industry and industrial chain. At the same time, the implementation of new control policies will also lead to uncertainties in the future development of 4G business.

First, the 5G power strategy and possible new businesses will stimulate the growth of total mobile traffic, and are expected to drive the simultaneous development of 4G businesses.

Secondly, the rapid development of 5G terminals will promote the 5G consumer industry, thereby promoting the 5G network to effectively divert traffic from 4G. First, the form of 5G terminals is developing rapidly and the variety is rich. Second, the price of 5G terminals is not higher than that of 4G. Starting from the second quarter of 2020, manufacturers will gradually launch low-end and mid-range 5G mobile phones, and it is expected that the price of mobile phones will drop to 1,000 to 2,000 yuan by the end of 2020.

Thirdly, policy factors have brought about changes in the competitive environment. From a long-term perspective, this will have a certain inhibitory effect on the growth of 4G network traffic. On September 1, 2019, the sale of unlimited data packages was completely discontinued. Starting from October, the competent authorities have added new control requirements for the three major operators, which is expected to improve the competitive environment and further improve quality and efficiency.

After 4G business experienced a peak in traffic driven by the development of mobile business demand and unlimited packages, the above factors have now emerged, which will profoundly affect the development of 4G business and bring uncertainty to it. The turning point of 4G business development is at a critical stage, and overly cautious or overly bold expansion strategies will bring losses. During this period, in order to ensure user perception and avoid investment waste, the expansion of 4G networks needs to be planned more accurately, and the newly added 5G resources should be fully utilized to provide them to the existing 4G to achieve cost reduction and efficiency improvement.

3.2 5G reverse activation of 4G function is an important technical means for 5G+4G capacity coordination

In this case, making full use of the common mode/conversion mode capabilities of the equipment and reversely opening the 4G function in the 5G base station is an important technical means for 5G+4G capacity coordination.

3.2.1 Engineering implementation method of 5G reverse activation of 4G function

When using 5G macro base station equipment to reversely activate the 4G function, it is necessary to purchase another set of BBU baseband board hardware and hardware license for the 4G function, AAU to share 5G equipment through feeding, and RRU software license to reuse the software license of the original 4G base station frequency clearance and withdrawal.

3.2.2 Carrier bandwidth equivalent capacity of 5G reverse activation of 4G function

According to the test data of the experimental network, for different 5G base station channel capabilities, after reverse activation, the 20MHz carrier bandwidth throughput capacity can be equivalent to a 4G carrier multiple, see Table 2.

Table 2 Comparison of network performance of 5G base stations with different channel types in reverse activation of 4G

3.3 5G+4G Collaboration to Ensure 4G Network Capacity Planning Method

According to the above analysis of business development and 5G+4G collaborative implementation methods, accurate planning of 4G network expansion needs to be closely integrated with the pace of 5G network construction. Therefore, the 4G expansion strategy is divided into the following scenarios for consideration.

• Scenario 1: In the 5G planning area, the 5G reverse activation of 4G function is used to compensate for the 4G performance loss caused by the 4G D-band frequency clearance, while taking into account some capacity growth needs.
• Scenario 2: In non-5G planning areas, make full use of the software and hardware resources removed from the 5G planning area to achieve capacity expansion and capacity sharing through equipment reuse.

3.3.1 Reverse activation of 4G through 5G to compensate for 4G performance loss caused by 4G D-band frequency clearance

The D band plays an important role in the 4G network, and good comprehensive coverage is formed by D band and F band sites. In particular, the D band sites are more abundant, and the impact on the continuous coverage basic underlying network after frequency clearance needs to be fully considered.

The initial construction of 5G projects will be concentrated in densely populated urban areas, which are precisely where 4G D-band sites are concentrated, with a higher proportion of D-band carriers and capacity absorption. While building the 5G network, the synergy of 5G+4G will be fully utilized, and the technical characteristics of 5G reverse activation of 4G functions will be used to supplement the capacity and coverage requirements of the 4G network after the D-band is cleared.

3.3.2 Analysis of path selection strategy for cell-level 4G capacity guarantee

After multiple phases of construction, the 4G network has a very complex station type. Taking the antenna surface of the outdoor cell as the statistical granularity, the 4G physical sector covering a physical area includes multiple logical cell types, such as single D sector (1D/2D/3D cell), F/D sector (1F1D/1F2D, etc.), single F sector, D/F/FDD mixed sector, etc. In addition, there are 6 frequency band resources available for 4G network expansion: F band, A band, and D band of TD-L standard, D band for 5G reverse activation of 4G function, and 1800MHz and 900MHz bands of FDD standard. Considering that the implementation of the project will also involve specific implementation methods such as additional hardware and software expansion, more expansion methods can be selected. This existing station type structure and optional implementation methods are physically complex, which will inevitably bring complexity in selecting expansion standards and using frequency bands when expanding different sectors.

Since the reverse activation of 5G to 4G function still requires some additional investment, here, taking the method of maximizing investment benefits as an example, when considering the 4G expansion strategy, priority is given to the scheduling of FDD 1800MHz/F/A carrier capacity of other cells in the network. When it cannot meet the demand, consider using 5G to reversely activate 4G function to supplement it. The expansion strategy for each physical sector is shown in Figure 3.

When considering different construction strategies, such as optimizing 4G network performance or simplifying engineering implementation difficulty, there are different path choices. It can also be seen that the complexity of the 5G+4G capacity coordination solution has doubled the difficulty of planning. If the above coordination requirements and algorithms are tooled to achieve automatic selection of cell-level capacity coordination, it will greatly reduce the difficulty of planning and flexibly complete multiple strategy selections and comparisons.

4. Conclusion

my country has proposed to promote the construction of a strong manufacturing and network power through 5G from the national strategic level. The demand for 5G network construction has become the key infrastructure for the comprehensive digital transformation of the economy and society. If the concept of 5G+4G coordinated development can be fully implemented and deeply considered during engineering planning, and the synergistic advantages of 5G and 4G networks in technical standards and engineering construction can be integrated, the service quality for a large number of existing 4G users can be maintained, and the quality of 5G network construction can be improved.

[This article is an original article by 51CTO columnist "Mobile Labs". Please contact the original author for reprinting.]

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