With the continuous development of wireless networks, multi-stream aggregation (MSA, MulTIple Stream AggregaTIon) can achieve 500% edge throughput improvement through deep integration of multi-standard, multi-carrier and multi-layer networks, realizing borderless networks. The concept enables users to enjoy high-speed and stable data access services regardless of their location on the network, and it will become the key technology for future network evolution.
The popularity of smart terminals and the rapid development of mobile broadband have led to explosive growth in mobile data services. The industry expects that global mobile data traffic will grow exponentially in the next decade, which will bring unprecedented impact to the current network.
Current network challenges
The current network is usually deployed in a single-layer network, that is, different radio access technologies (RATs, Radio Access Technology), such as GSM, UMTS, LTE, and Wi-Fi, which are independently deployed and managed, and through different core networks. The device accesses the network. At the same time, users can only transmit data with a single node in a RAT, resulting in insufficient utilization of radio resources, repeated investment in network infrastructure, and inability to further improve network capacity.
Although HetNet is a typical application scenario for improving network capacity, as the number of small stations increases, more and more “cell edges†will appear in the future, resulting in frequent handovers, increased handover failure rates, and edges. The phenomenon of lowering the throughput of users has become more and more prominent, and these have an impact on the user experience. Therefore, issues such as mobility, interference, and resource utilization are the main challenges facing the current network.
Mobility
With the intensive deployment of HetNet, the number of small stations is gradually increasing, frequent switching and ping-pong switching will continue to emerge. In general, the signal propagation characteristics of the small station and the macro station are different due to the low deployment position of the small station antenna. As the distance increases, the attenuation of the macro station signal is slower. After the small station is deployed, although the signal strength near the small station is obviously improved, as the distance from the small station increases, the signal will rapidly decay, and in serious cases, the user will drop the call.
In short, due to the fast-fading characteristics of the small-station channel and the interference caused by the introduction of the small station, the handover failure rate in the HetNet scenario is generally higher than that in the traditional isomorphic (only macro-deployment) scenario. The rate is especially noticeable when the user switches from a small station to a macro station.
If the small station is deployed within the coverage of the macro station, because of the co-channel interference of the macro station, the coverage of the small station will obviously shrink, that is, the closer the station is to the macro station, the smaller the coverage. . For example, if the small station is deployed at the edge of the macro station, its coverage can reach more than 100m; if the small station is deployed in the center of the macro station, its coverage can only reach tens of meters or even dozens of meters. In addition, because of the presence of co-channel interference, the throughput of users is also significantly reduced.
Resource utilization
In general, there are always differences in different business needs between macro stations and small stations at different times and geographical locations. In the traditional HetNet scenario, resources cannot be shared between different sites, resulting in insufficient resource utilization and different user experiences under different sites.
Because of its large coverage, macro stations can attract more users. Therefore, the load of the macro station may be heavier, which will result in lower throughput of users in the macro station, especially the edge users of the macro station. The macro station is far away, and at the same time it is interfered by the same frequency station, and its user throughput is lower. For small stations, because of the coverage constraints, the number of users that are attracted to them is small and the load is light, so the throughput of users in small stations is high. Therefore, the user experience under the macro station and the small station is obviously inconsistent.
The key technology for future wireless network evolution - MSA
With the continuous development of wireless networks, MSA can solve the problems of mobility support to be upgraded, outstanding interference problems and low resource utilization due to the deep integration of multi-standard, multi-carrier and multi-layer networks. , which greatly enhances the edge throughput and truly realizes the concept of a borderless network.
By adopting the perfect combination of network layering and MSA, the future wireless network can enable users to enjoy high-speed and stable data access services regardless of the location of the network, achieving ultra-wideband, zero-waiting and ubiquitous connectivity. Bring high-speed, high-quality, and simple, free-to-share business experiences. Among them, network layering refers to a multi-layer network architecture, including the Host Layer and the BoosTIng Layer, as shown in Figure 1. Host Layer is mainly used to ensure network coverage. By establishing a Host link, it provides signaling and data transmission for users, providing ubiquitous connectivity and ensuring a reliable basic user experience. BoosTIng Layer is mainly used to improve network capacity by establishing Boosting. Link to provide users with the transmission of data to achieve the best user experience. MSA is a key technology for organic aggregation of Host Layer and Boosting Layer. It provides multi-stream aggregation for users through multiple nodes, which further enhances user experience and network capacity. This technology has been widely recognized in the industry and has been gradually adopted from 3GPP R10 version. Support has become a hot topic in current standards discussions.
A network entity on the RAN side, such as a BBU pool or a SRC (Single Radio Controller), can be used as a centralized control node of the MSA to perform unified control functions to better implement network layering, data offload, and coordinated scheduling.
Host Layer: Guarantee a reliable basic user experience
Host Layer can effectively solve the mobility and interference problems facing the current network.
In the same-frequency scenario, the host layer can adopt the same cell ID network deployment mode, and the same physical cell identifier (PCI, Physical Cell Identifier) ​​is used by different nodes to avoid intra-frequency handover. In an inter-frequency scenario, such as multi-carrier. Or a multi-standard scenario, the Host Layer allows the user to always attach to the macro station, that is, no matter how the user moves within the coverage of the macro station, the host link between the user and the macro station is always maintained, thereby avoiding the inter-frequency handover.
After network layering, interference can be further divided into intra-layer interference and inter-layer interference. Coordinated scheduling can be used to resolve intra-layer interference. For example, for interference-sensitive users, the Host Layer can reduce the interference it can by coordinating the scheduling of neighbors. Separation of time-frequency resources can be used to resolve inter-layer interference. For example, a part of time-frequency resources are reserved for SFN (Single Frequency Network) transmission between different nodes of the Host Layer to achieve optimal coverage, while other time-frequency resources are in the node. Spatial multiplexing is used to achieve optimal efficiency. In other words, the layers are separated by ensuring that resources are independent of each other.
The Host Layer ensures the continuity of user services by avoiding handovers; it improves user throughput by reducing interference, thus ensuring a reliable basic user experience.
Boosting Layer: Delivering the best user experience
MSA is a key technology for organic aggregation of Host Layer and Boosting Layer. It further includes: Intra-frequency MSA, Inter-frequency MSA and Inter-RAT MSA for different application scenarios.
Intra-frequency MSA: Provides multi-stream aggregation for users by using multiple co-frequency nodes
In the traditional HetNet scenario, users can only transmit data with their single attached node, and system resources cannot be fully utilized. In the future, the network can adopt Intra-frequency MSA technology, so that users can dynamically realize data transmission with one or more optimal nodes, complete multi-stream aggregation between the same-frequency nodes, and achieve the best user experience. In the same-frequency MSA, the data transmission node is transparent to the user. Even in the scenario of different cell IDs, no signaling overhead is required, thereby maximizing the utilization of system resources and better solving the resources existing in the current network. Use incomplete problems to achieve consistency in user experience.
In addition, the Intra-frequency MSA also uses some advanced algorithms to achieve 200% edge throughput improvement, including: CS-PC (Coordination Scheduling Power Control), to achieve interference management through coordinated scheduling power control; CLB (Coordination Load Balance), which improves spectrum efficiency by adaptively coordinating load balancing; CoMP (Coordinated Multi-Point), which performs dynamic node selection or joint transmission based on real-time channel changes, thereby implementing load balancing of services.
Inter-frequency MSA: Provides multi-stream aggregation for users with multiple inter-frequency nodes
In the traditional HetNet scenario, when the user moves between the macro station and the small station, the inter-frequency handover will be triggered, which may affect the user experience. In the future, the network can use the Inter-frequency MSA technology to make the user always attach to the macro station, that is, always keep the Host link between the user and the macro station, and dynamically select the best small station, through the user and the best small station. The Boosting link between the data is used to offload the macro station. For the user, multi-stream aggregation between different carriers is formed, which further improves the user experience and network capacity.
According to the delay characteristics of the backhaul link between the macro station and the small station, the Inter-frequency MSA is divided into two scenarios: ideal backhaul and non-ideal backhaul. The ideal backhaul refers to the transmission of the backhaul link between the macro station and the small station. The delay can be neglected. The non-ideal backhaul refers to the transmission delay of the backhaul link between the macro station and the small station cannot be ignored. It is worth mentioning that in the non-ideal backhaul scenario, the data stream on different carriers of different nodes is flexibly aggregated, which is one of the core hotspots of the 3GPP Rel-12 standard, and has received extensive attention in the industry.
Inter-RAT MSA: Provides multi-stream aggregation for users with multiple nodes of different standards
Heterogeneous multi-stream aggregation (Inter-RAT MSA) is the key technology to achieve different integration schemes. The Host Layer can be UMTS or LTE, and the Booting Layer can be LTE or Wi-Fi.
Take the LTE and Wi-Fi convergence scenarios as an example. LTE is used as a Host Layer to provide coverage, to keep the host link between the user and the macro station always exist, to ensure reliable basic user connection; Wi-Fi as a Boosting Layer for capacity improvement, between the user and Wi-Fi Boosting links increase the transfer rate for the best user experience.
In the network deployment, the downlink traffic of most data services far exceeds the uplink. However, the transmission resources of the cellular network are basically symmetrical on the uplink and downlink, so the downlink data transmission of the cellular network needs to be more urgently enhanced. In addition, there are more serious access collisions, hidden terminals, and QoS issues due to the uplink of the Wi-Fi network, and these problems are rapidly deteriorating as the number of users increases. Based on the above considerations, Huawei believes that the most efficient transmission scheme is to use Wi-Fi mainly for downlink data transmission, that is, according to factors such as channel, network load and interference status, through the newly defined control entity SRC on the RAN side, flexibly The downlink data on the host link of the cell is offloaded to the Boosting link of the Wi-Fi, so that the peak experience of the user is doubled, and the network capacity can be greatly improved.
At present, based on the above solutions and technologies, Huawei has implemented MSA technology using existing product platforms, and successfully verified the user experience enhancement brought by network layering and MSA technology integration in the field, and truly realized the future borderless network. Concept.
Figure 1 Network layering and MSA convergence in future wireless networks
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