Difficulties to be solved for commercial acceleration of carrier Aggregation

Difficulties to be solved for commercial acceleration of carrier Aggregation

The increase in network coverage and the popularity of wireless applications bring a good user experience, and the willingness of users to use 4G services is also increasing. According to statistics, LTE users consume GB of data traffic per month on average, almost twice the usage of non-LTE users. Various novel wireless applications have gradually become part of people's daily life in the 4G era, and LTE Networks are becoming increasingly mature in this process. With the increase of users and traffic, the LTE network load of a single carrier continues to rise. When users get used to high-speed and high-quality services, they are willing to pay for it, we also look forward to a faster and better application experience. In this context, the evolution of LTE Networks has been put on the agenda.

Carrier aggregation has received much attention

As the evolution version of LTE, LTE-A has higher speed and spectrum utilization, lower communication latency, can improve the performance of mobile communication network, and thus bring a better service experience for users. The LTE-A system has introduced many enhancement technologies to greatly improve the performance indicators such as network peak rate and cell average spectrum efficiency. The most important technology is carrier aggregation.

In the LTE system, the transmission bandwidth supports a maximum of 20 MHz, such bandwidth can no longer meet the technical specifications of the LTE-A. To meet the requirements of a single user's peak rate and system capacity improvement, the most direct way is to increase the system transmission bandwidth. In order to be compatible with LTE and make full use of fragmented spectrum, carrier aggregation is proposed as a technical solution to increase transmission bandwidth. The core idea of carrier aggregation technology is to aggregate multiple consecutive or discrete carriers with narrow bandwidth to form a wider spectrum. This technology not only satisfies the LTE-A system's demand for large bandwidth, but also can effectively use the fragmented spectrum resources.

In 2013, the carrier aggregation technology began to be applied to commercial networks. The earliest Network adopted the 10 MHz + 10 MHz aggregation method, and the peak download rate was 150 Mbit/s. By the end of 2014, a total of 49 Commercial LTE-A networks were deployed with carrier aggregation, of which 19 had a downlink peak rate of 300 Mbit/s (FDD, 20 MHz + 20 MHz ), 10 networks can reach 225 Mbit/s (FDD, 20 MHz + 10 MHz or 15 MHz + 15 MHz ). After the TD-LTE network uses two 20 MHz carrier aggregation, the downstream peak rate also reached 220 Mbit/s. In 2015, commercial networks are expected to introduce more tri-carrier aggregation, with a downstream peak rate of up to 450 Mbit/s.

Introduction and planning of carrier Aggregation

1. Deployment of carrier Aggregation

At present, carrier aggregation is mainly used in macro base stations or indoor distribution systems that are jointly covered by multiple carriers. Carrier aggregation implemented by macro-micro collaboration and heterogeneous networks will be discussed in the next phase. The method of carrier aggregation includes intra-band carrier aggregation and cross-band carrier aggregation, which can be implemented through the hardware and software upgrade of the base station equipment.

In the hardware part, the baseband Resource Board of the secondary carrier needs to be added. In the case of cross-band aggregation, the remote RF unit (RRU) needs to be added ). When the aggregation within the frequency band or the interval between different frequency bands is small (for example, convergence between the 1.8G band and the 2.1G band), we recommend that you share the antenna to avoid additional antenna installation. Before the implementation of the project, it is necessary to conduct scanning tests on the frequency band of the secondary carrier to ensure that there is no external interference. The software department should pay attention to version upgrades, aggregation relationship configurations of different frequency carrier cells, and inter-cell same frequency Neighbor Relationship and switching settings.

2. Impact on network coverage and capacity

At present, the mainstream method of carrier aggregation is downlink dual-carrier aggregation enhancement. The uplink does not support aggregation enhancement, which will also affect network planning. If the network uses the same-band aggregation mode, which has little impact on network coverage, you can follow the single-carrier LTE network planning method. If the convergence of different frequencies is adopted, the coverage difference needs to be considered. Because LTE Networks are generally uplinked, uplink coverage is usually used to determine the coverage of base stations during single-carrier planning. To optimize the effective coverage of base stations during aggregation of high and low frequencies, we recommend that the low frequency segments be used as the main carrier and the uplink frequency of the low frequency segments and the downlink frequency of the high frequency bands be used for aggregation, the base station coverage scope is jointly determined by the uplink coverage of the low frequency segment and the downlink coverage of the high frequency segment.

The main purpose of carrier aggregation deployment is to increase the user's peak rate and network capacity. According to the reports of commercial networks outside China and the results of domestic test network Driving Test (DT) and fixed point test (CQT, the average rate and peak rate of users in the dual-carrier aggregation mode are two times that in the single-carrier mode, and the effect is obvious, basically meeting the design requirements.

Problems to be resolved

Although carrier aggregation has been commercially available internationally for some time, due to the large number of commercial LTE frequencies, the combined spectrum mode after aggregation is very complex, in addition, there are some differences between the carrier combinations used in China and the international market. Therefore, basic preparations must be made before large-scale commercial deployment, with the focus on the following aspects.

1. Terminal Equipment commercialization

Terminals are a key factor restricting the commercial use of carrier aggregation. To give full play to the advantages of LTE-A Network Carrier aggregation, the need for terminal cooperation. Currently, mainstream Cat4 commercial terminals support a maximum download rate of only 150 Mbit/s. We need to take full advantage of the high-speed carrier aggregation rate, we recommend that you use the Cat6 terminal (the maximum download speed is 300 Mbit/s ). Currently, Cat6 terminals are deployed in 22 commercial LTE-A carrier aggregation networks around the world, but they use different frequencies (for example, at present, there are no commercial terminals supporting LTE FDD1.8GHz/2.1GHz carrier aggregation ). It is an important task to promote the commercialization of carrier aggregation terminals suitable for 4G frequencies in China.

2. Standardization of base station functions

R10-based LTE Base Station Equipment supports carrier aggregation, but there are some differences in technology implementation between base station equipment manufacturers. For example, manufacturers use different methods to add and delete sub-carriers. The addition, deletion, and decision algorithms of sub-carriers are also different. To promote the commercialization of carrier aggregation, a unified function standard for base station equipment should be formulated to promote base station equipment providers to further improve the functions of the equipment.

3. optimal network performance

In the process of introducing the carrier aggregation function, although the hardware and software upgrades of the equipment are designed to avoid the major impact on the existing commercial network, some technical problems will inevitably be introduced, you need to adjust the network to optimize the network performance. This includes switching between single and dual carriers, load balancing of the main carrier, priority policies for scheduling of different terminals, etc. Further research, verification, and optimization are required through the test network.